Cimetidine, sold under the brand name Tagamet among others, is a

histamine Histamine is an organic nitrogenous compound involved in local immune responses communication, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Discovered in 19 ...

H₂ receptor antagonist that inhibits

stomach acid Gastric acid or stomach acid is the acidic component – hydrochloric acid – of gastric juice, produced by parietal cells in the gastric glands of the stomach lining. In humans, the pH is between one and three, much lower than most other an ...

production. It is mainly used in the treatment of

heartburn Heartburn is a burning sensation felt behind the breastbone. It is a symptom that is commonly linked to acid reflux and is often triggered by food, particularly fatty, sugary, spicy, chocolate, citrus, onion-based and tomato-based products. Ly ...

and

peptic ulcer Peptic ulcer disease is when the inner part of the stomach's gastric mucosa (lining of the stomach), the first part of the small intestine, or sometimes the lower esophagus, gets damaged. An ulcer in the stomach is called a gastric ulcer, while ...

s. With the development of proton pump inhibitors, such as omeprazole, approved for the same indications, cimetidine is available as an over-the-counter formulation to prevent heartburn or acid indigestion, along with the other H2-receptor antagonists. Cimetidine was developed in 1971 and came into commercial use in 1977. Cimetidine was approved in the United Kingdom in 1976, and was approved in the United States by the

Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respo ...

in 1979.

Medical uses

Cimetidine is indicated for the treatment of duodenal ulcers, gastric ulcers,

gastroesophageal reflux disease Gastroesophageal reflux disease (GERD) or gastro-oesophageal reflux disease (GORD) is a chronic upper gastrointestinal disease in which stomach content persistently and regularly flows up into the esophagus, resulting in symptoms and/or ...

, and pathological hypersecretory conditions. Cimetidine is also used to relieve or prevent heartburn.

Side effects

Reported

side effect In medicine, a side effect is an effect of the use of a medicinal drug or other treatment, usually adverse but sometimes beneficial, that is unintended. Herbal and traditional medicines also have side effects. A drug or procedure usually use ...

s of cimetidine include

diarrhea Diarrhea (American English), also spelled diarrhoea or diarrhœa (British English), is the condition of having at least three loose, liquid, or watery bowel movements in a day. It often lasts for a few days and can result in dehydration d ...

rash A rash is a change of the skin that affects its color, appearance, or texture. A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch, become warm, bumpy, chapped, dry, cracke ...

es,

dizziness Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to Balance disorder, disequilibrium or a non-specific feeling, such as giddiness or foolishness. Dizziness is a ...

fatigue Fatigue is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. It is a signs and symptoms, symptom of any of various diseases; it is not a disease in itself. Fatigue (in the medical sense) is sometimes associated wit ...

constipation Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The Human feces, stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the ...

, and muscle pain, all of which are usually mild and transient. It has been reported that mental confusion may occur in the elderly. Because of its hormonal effects, cimetidine rarely may cause

sexual dysfunction Sexual dysfunction is difficulty experienced by an individual or partners during any stage of normal sexual activity, including physical pleasure, desire, preference, arousal, or orgasm. The World Health Organization defines sexual dysfunction ...

including loss of libido and

erectile dysfunction Erectile dysfunction (ED), also referred to as impotence, is a form of sexual dysfunction in males characterized by the persistent or recurring inability to achieve or maintain a Human penis, penile erection with sufficient rigidity and durat ...

and gynecomastia (0.1–0.2%) in males during long-term treatment. Rarely, interstitial nephritis, urticaria, and angioedema have been reported with cimetidine treatment. Cimetidine is also commonly associated with transient raised aminotransferase activity; hepatotoxicity is rare.

Overdose

Cimetidine appears to be very safe in

overdose A drug overdose (overdose or OD) is the ingestion or application of a drug or other substance in quantities much greater than are recommended. Retrieved on September 20, 2014.

, producing no

symptom Signs and symptoms are diagnostic indications of an illness, injury, or condition. Signs are objective and externally observable; symptoms are a person's reported subjective experiences. A sign for example may be a higher or lower temperature ...

s even with massive overdoses (e.g., 20 g).

Interactions

Due to its non-selective inhibition of

cytochrome P450 Cytochromes P450 (P450s or CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that mostly, but not exclusively, function as monooxygenases. However, they are not omnipresent; for examp ...

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s, cimetidine has numerous

drug interaction In pharmaceutical sciences, drug interactions occur when a drug's mechanism of action is affected by the concomitant administration of substances such as foods, beverages, or other drugs. A popular example of drug–food interaction is the effect ...

s. Examples of specific interactions include, but are not limited to, the following: * Cimetidine affects the metabolism of methadone, sometimes resulting in higher blood levels and a higher incidence of side effects, and may interact with the antimalarial medication hydroxychloroquine. * Cimetidine can also interact with a number of psychoactive medications, including tricyclic antidepressants and

selective serotonin reuptake inhibitor Selective serotonin reuptake inhibitors (SSRIs) are a class of drugs that are typically used as antidepressants in the treatment of major depressive disorder, anxiety disorders, and other psychological conditions. SSRIs primarily work by blo ...

s, causing increased blood levels of these drugs and the potential of subsequent toxicity. * Following administration of cimetidine, the elimination half-life and area-under-curve of zolmitriptan and its active metabolites were roughly doubled. * Cimetidine is a potent inhibitor of tubular

creatinine Creatinine (; ) is a breakdown product of creatine phosphate from muscle and protein metabolism. It is released at a constant rate by the body (depending on muscle mass). Biological relevance Serum creatinine (a blood measurement) is an impor ...

secretion. Creatinine is a metabolic byproduct of

creatine Creatine ( or ) is an organic compound with the nominal formula . It exists in various tautomers in solutions (among which are neutral form and various zwitterionic forms). Creatine is found in vertebrates, where it facilitates recycling of ...

breakdown. Accumulation of creatinine is associated with uremia, but the symptoms of creatinine accumulation are unknown, as they are hard to separate from other nitrogenous waste buildups. * Like several other medications (e.g., erythromycin), cimetidine interferes with the body's metabolization of

sildenafil Sildenafil, sold under the brand name Viagra among others, is a medication used to treat erectile dysfunction and pulmonary hypertension, pulmonary arterial hypertension. It is also sometimes used off-label for the treatment of certain sym ...

, causing its strength and duration to increase and making its side effects more likely and prominent. * Clinically significant drug interactions with the CYP1A2 substrate theophylline, the CYP2C9 substrate tolbutamide, the CYP2D6 substrate desipramine, and the CYP3A4 substrate

triazolam Triazolam, sold under the brand name Halcion among others, is a central nervous system (CNS) depressant tranquilizer of the triazolobenzodiazepine (TBZD) class, which are benzodiazepine (BZD) derivatives. It possesses pharmacological properti ...

have all been demonstrated with cimetidine, and interactions with other substrates of these enzymes are likely as well. * Cimetidine has been shown clinically to reduce the clearance of

mirtazapine Mirtazapine, sold under the brand name Remeron among others, is an atypical antidepressant, atypical tetracyclic antidepressant, and as such is used primarily to treat Depression (mood), depression. Its effects may take up to four weeks but ca ...

imipramine Imipramine, sold under the brand name Tofranil, among others, is a tricyclic antidepressant (TCA) mainly used in the treatment of depression. It is also effective in treating anxiety and panic disorder. Imipramine is taken by mouth. Common s ...

timolol Timolol is a beta blocker medication used either by mouth or as eye drops. As eye drops it is used to treat increased pressure inside the eye such as in ocular hypertension and glaucoma. By mouth it is used for high blood pressure, chest ...

, nebivolol, sparteine,

loratadine Loratadine, sold under the brand name Claritin among others, is a medication used to treat allergies. This includes allergic rhinitis (hay fever) and hives. It is also available in drug combinations such as loratadine/pseudoephedrine, in whic ...

, nortriptyline, gabapentin, and desipramine in humans. * Cimetidine inhibits the renal

excretion Excretion is elimination of metabolic waste, which is an essential process in all organisms. In vertebrates, this is primarily carried out by the lungs, Kidney (vertebrates), kidneys, and skin. This is in contrast with secretion, where the substa ...

of metformin and procainamide, resulting in increased circulating levels of these drugs. * Interactions of potential clinical importance with cimetidine include

warfarin Warfarin, sold under the brand name Coumadin among others. It is used as an anticoagulant, anticoagulant medication. It is commonly used to prevent deep vein thrombosis and pulmonary embolism, and to protect against stroke in people who ha ...

, theophylline,

phenytoin Phenytoin (PHT), sold under the brand name Dilantin among others, is an anticonvulsant, anti-seizure medication. It is useful for the prevention of tonic-clonic seizures (also known as grand mal seizures) and focal seizures, but not absence se ...

carbamazepine Carbamazepine, sold under the brand name Tegretol among others, is an anticonvulsant medication used in the treatment of epilepsy and neuropathic pain. It is used as an adjunctive treatment in schizophrenia along with other medications and as ...

pethidine Pethidine, also known as meperidine and sold under the brand name Demerol among others, is a fully synthetic opioid pain medication of the phenylpiperidine class. Synthesized in 1938 as a potential anticholinergic agent by the German chemist Ot ...

and other

opioid Opioids are a class of Drug, drugs that derive from, or mimic, natural substances found in the Papaver somniferum, opium poppy plant. Opioids work on opioid receptors in the brain and other organs to produce a variety of morphine-like effects, ...

analgesic An analgesic drug, also called simply an analgesic, antalgic, pain reliever, or painkiller, is any member of the group of drugs used for pain management. Analgesics are conceptually distinct from anesthetics, which temporarily reduce, and in s ...

s, tricyclic antidepressants,

lidocaine Lidocaine, also known as lignocaine and sold under the brand name Xylocaine among others, is a local anesthetic of the amino amide type. It is also used to treat ventricular tachycardia and ventricular fibrillation. When used for local anae ...

terfenadine Terfenadine is an antihistamine formerly used for the treatment of allergic conditions. It was brought to market by Hoechst Marion Roussel (now Sanofi) and was marketed under various brand names, including Seldane in the United States, Triluda ...

amiodarone Amiodarone is an antiarrhythmic medication used to treat and prevent a number of types of cardiac dysrhythmias. This includes ventricular tachycardia, ventricular fibrillation, and wide complex tachycardia, atrial fibrillation, and paroxys ...

, flecainide,

quinidine Quinidine is a class I antiarrhythmic agent, class IA antiarrhythmic agent used to treat heart rhythm disturbances. It is a diastereomer of Antimalarial medication, antimalarial agent quinine, originally derived from the bark of the cinchona tre ...

fluorouracil Fluorouracil (5-FU, 5-fluorouracil), sold under the brand name Adrucil among others, is a cytotoxic chemotherapy medication used to treat cancer. By intravenous injection it is used for treatment of colorectal cancer, oesophageal cancer, stoma ...

, and

benzodiazepine Benzodiazepines (BZD, BDZ, BZs), colloquially known as "benzos", are a class of central nervous system (CNS) depressant, depressant drugs whose core chemical structure is the fusion of a benzene ring and a diazepine ring. They are prescribed t ...

s. * Cimetidine may decrease the effects of CYP2D6 substrates that are

prodrug A prodrug is a pharmacologically inactive medication or compound that, after intake, is metabolized (i.e., converted within the body) into a pharmacologically active drug. Instead of administering a drug directly, a corresponding prodrug can be ...

s, such as

codeine Codeine is an opiate and prodrug of morphine mainly used to treat pain, coughing, and diarrhea. It is also commonly used as a recreational drug. It is found naturally in the sap of the opium poppy, ''Papaver somniferum''. It is typically use ...

tramadol Tramadol, sold under the brand name Tramal among others, is an opioid analgesic, pain medication and a serotonin–norepinephrine reuptake inhibitor (SNRI) used to treat moderately severe pain. When taken by mouth in an immediate-release form ...

, and

tamoxifen Tamoxifen, sold under the brand name Nolvadex among others, is a selective estrogen receptor modulator used to prevent breast cancer in women and men. It is also being studied for other types of cancer. It has been used for Albright syndrome ...

. * Cimetidine reduces the

absorption Absorption may refer to: Chemistry and biology *Absorption (biology), digestion **Absorption (small intestine) *Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials *Absorption (skin), a route by which su ...

ketoconazole Ketoconazole, sold under the brand name Nizoral, among others, is an antiandrogen, antifungal drug, antifungal, and antiglucocorticoid medication used to treat a number of fungal infections. Applied to the skin it is used for fungal skin inf ...

and

itraconazole Itraconazole, sometimes abbreviated ITZ, is an antifungal medication used to treat a number of fungal infections. This includes aspergillosis, blastomycosis, coccidioidomycosis, histoplasmosis, and paracoccidioidomycosis. It may be given ...

(which require a low pH). * Cimetidine has a theoretical but unproven benefit in

paracetamol toxicity Paracetamol poisoning, also known as acetaminophen poisoning, is caused by excessive use of the medication paracetamol (acetaminophen). Most people have few or non-specific symptoms in the first 24 hours following overdose. These symptom ...

. This is because N-acetyl-p-benzoquinone imine (NAPQI), a

metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...

paracetamol Paracetamol, or acetaminophen, is a non-opioid analgesic and antipyretic agent used to treat fever and mild to moderate pain. It is a widely available over-the-counter drug sold under various brand names, including Tylenol and Panadol. Parac ...

(acetaminophen) that is responsible for its hepatotoxicity, is formed from it by the cytochrome P450 system (specifically, CYP1A2, CYP2E1, and CYP3A4). * Cimetidine is used in cancer metastasis research as a blocker of E-selectin.

Pharmacology

Pharmacodynamics

Histamine H₂ receptor antagonism

The

mechanism of action In pharmacology, the term mechanism of action (MOA) refers to the specific biochemical Drug interaction, interaction through which a Medication, drug substance produces its pharmacological effect. A mechanism of action usually includes mention o ...

of cimetidine as an

antacid An antacid is a substance which neutralization (chemistry), neutralizes gastric acid, stomach acidity and is used to relieve heartburn, indigestion, or an upset stomach. Some antacids have been used in the treatment of constipation and diarrhe ...

is as a

H₂ receptor

antagonist An antagonist is a character in a story who is presented as the main enemy or rival of the protagonist and is often depicted as a villain. It has been found to bind to the H₂ receptor with a K_d of 42 nM.

Cytochrome P450 inhibition

Cimetidine is a potent

inhibitor Inhibitor or inhibition may refer to: Biology * Enzyme inhibitor, a substance that binds to an enzyme and decreases the enzyme's activity * Reuptake inhibitor, a substance that increases neurotransmission by blocking the reuptake of a neurotransmi ...

of certain

(CYP)

s, including

CYP1A2 Cytochrome P450 1A2 (abbreviated CYP1A2), a member of the cytochrome P450 mixed-function oxidase system, is involved in the metabolism of xenobiotics in the human body. In humans, the CYP1A2 enzyme is encoded by the ''CYP1A2'' gene. Function ...

CYP2C9 Cytochrome P450 family 2 subfamily C member 9 (abbreviated CYP2C9) is an enzyme protein. The enzyme is involved in the metabolism, by oxidation, of both xenobiotics, including drugs, and endogenous compounds, including fatty acids. In humans, t ...

CYP2C19 Cytochrome P450 2C19 (abbreviated CYP2C19) is an enzyme protein. It is a member of the CYP2C subfamily of the cytochrome P450 mixed-function oxidase system. This subfamily includes enzymes that catalyze metabolism of xenobiotics, including some ...

CYP2D6 Cytochrome P450 2D6 (CYP2D6) is an enzyme that in humans is encoded by the ''CYP2D6'' gene. ''CYP2D6'' is primarily expressed in the liver. It is also highly expressed in areas of the central nervous system, including the substantia nigra. CYP2 ...

CYP2E1 Cytochrome P450 2E1 (abbreviated CYP2E1, ) is a member of the cytochrome P450 mixed-function oxidase system, which is involved in the metabolism of xenobiotics in the body. This class of enzymes is divided up into a number of subcategories, inclu ...

, and

CYP3A4 Cytochrome P450 3A4 (abbreviated CYP3A4) () is an important enzyme in the body, mainly found in the liver and in the intestine, which in humans is encoded by ''CYP3A4'' gene. It organic redox reaction, oxidizes small foreign organic molecules ( ...

. The drug appears to primarily inhibit CYP1A2, CYP2D6, and CYP3A4, of which it is described as a moderate inhibitor. This is notable since these three CYP

isoenzyme In biochemistry, isozymes (also known as isoenzymes or more generally as multiple forms of enzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. Isozymes usually have different kinetic parameters (e.g. di ...

s are involved in CYP-mediated drug

biotransformation Biotransformation is the biochemical modification of one chemical compound or a mixture of chemical compounds. Biotransformations can be conducted with whole cells, their lysates, or purified enzymes. Increasingly, biotransformations are effected ...

s; however, CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 are also involved in the oxidative

metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...

of many commonly used drugs. As a result, cimetidine has the potential for a large number of pharmacokinetic interactions. Cimetidine is reported to be a

competitive Competition is a rivalry where two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition can arise between entities such as organisms, indi ...

and reversible inhibitor of several CYP enzymes, although mechanism-based (suicide) irreversible inhibition has also been identified for cimetidine's inhibition of CYP2D6. It reversibly inhibits CYP enzymes by binding directly with the complexed

heme Heme (American English), or haem (Commonwealth English, both pronounced /Help:IPA/English, hi:m/ ), is a ring-shaped iron-containing molecule that commonly serves as a Ligand (biochemistry), ligand of various proteins, more notably as a Prostheti ...

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

of the

active site In biology and biochemistry, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical reaction. The active site consists of amino acid residues that form temporary bonds with the substrate, the ''binding s ...

via one of its

imidazole Imidazole (ImH) is an organic compound with the formula . It is a white or colourless solid that is soluble in water, producing a mildly alkaline solution. It can be classified as a heterocycle, specifically as a diazole. Many natural products, ...

ring (The) Ring(s) may refer to: * Ring (jewellery), a round band, usually made of metal, worn as ornamental jewelry * To make a sound with a bell, and the sound made by a bell Arts, entertainment, and media Film and TV * ''The Ring'' (franchise), a ...

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

atom Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...

s, thereby blocking the oxidation of other drugs.

Antiandrogenic and estrogenic effects

Cimetidine has been found to possess weak

antiandrogen Antiandrogens, also known as androgen antagonists or testosterone blockers, are a class of drugs that prevent androgens like testosterone and dihydrotestosterone (DHT) from mediating their biological effects in the body. They act by blocking t ...

ic activity at high doses. It directly and competitively antagonizes the

androgen receptor The androgen receptor (AR), also known as NR3C4 (nuclear receptor subfamily 3, group C, member 4), is a type of nuclear receptor that is activated by binding any of the androgenic hormones, including testosterone and dihydrotestosterone, in th ...

(AR), the

biological target A biological target is anything within a living organism to which some other entity (like an endogenous ligand or a drug) is directed and/or binds, resulting in a change in its behavior or function. Examples of common classes of biological targets ...

androgen An androgen (from Greek ''andr-'', the stem of the word meaning ) is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This includes ...

s like

testosterone Testosterone is the primary male sex hormone and androgen in Male, males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testicles and prostate, as well as promoting se ...

and

dihydrotestosterone Dihydrotestosterone (DHT, 5α-dihydrotestosterone, 5α-DHT, androstanolone or stanolone) is an endogenous androgen sex steroid and hormone primarily involved in the growth and repair of the prostate and the penis, as well as the production o ...

(DHT). However, the

affinity Affinity may refer to: Commerce, finance and law * Affinity (law), kinship by marriage * Affinity analysis, a market research and business management technique * Affinity Credit Union, a Saskatchewan-based credit union * Affinity Equity Pa ...

of cimetidine for the AR is very weak; in one study, it showed only 0.00084% of the

of the

anabolic steroid Anabolic steroids, also known as anabolic-androgenic steroids (AAS), are a class of drugs that are structurally related to testosterone, the main male sex hormone, and produce effects by binding to the androgen receptor (AR). Anabolism, Anaboli ...

metribolone (100%) for the human AR (K_i = 140 μM and 1.18 nM, respectively). In any case, at sufficiently high doses, cimetidine has demonstrated weak but significant antiandrogenic effects in animals, including antiandrogenic effects in the rat ventral prostate and mouse

kidney In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...

, reductions in the weights of the

male accessory gland Male accessory glands (MAG) are the seminal vesicles, prostate gland, and the bulbourethral glands. These glands are found only in mammals. In insects, male accessory glands produce products that mix with the sperm to protect and preserve them, ...

s like the

prostate gland The prostate is an male accessory gland, accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found in all male mammals. It differs between species anatomically, chemica ...

and

seminal vesicle The seminal vesicles (also called vesicular glands or seminal glands) are a pair of convoluted tubular accessory glands that lie behind the urinary bladder of male mammals. They secrete fluid that largely composes the semen. The vesicles are 5 ...

s in rats, and elevated

gonadotropin Gonadotropins are glycoprotein hormones secreted by gonadotropic cells of the anterior pituitary of vertebrates. They are central to the complex endocrine system that regulates normal growth, sexual development, and reproductive function. T ...

levels in male rats (due to reduced

negative feedback Negative feedback (or balancing feedback) occurs when some function (Mathematics), function of the output of a system, process, or mechanism is feedback, fed back in a manner that tends to reduce the fluctuations in the output, whether caused ...

on the axis by androgens). In addition to AR antagonism, cimetidine has been found to inhibit the 2-

hydroxylation In chemistry, hydroxylation refers to the installation of a hydroxyl group () into an organic compound. Hydroxylations generate alcohols and phenols, which are very common functional groups. Hydroxylation confers some degree of water-solubility ...

estradiol Estradiol (E2), also called oestrogen, oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of female reproductive cycles such as estrous and menstrual cycles. Estradiol is responsible ...

(via inhibition of CYP450 enzymes, which are involved in the metabolic inactivation of estradiol), resulting in increased

estrogen Estrogen (also spelled oestrogen in British English; see spelling differences) is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three ...

levels. The medication has also been reported to reduce testosterone

biosynthesis Biosynthesis, i.e., chemical synthesis occurring in biological contexts, is a term most often referring to multi-step, enzyme-Catalysis, catalyzed processes where chemical substances absorbed as nutrients (or previously converted through biosynthe ...

and increase

prolactin Prolactin (PRL), also known as lactotropin and mammotropin, is a protein best known for its role in enabling mammals to produce milk. It is influential in over 300 separate processes in various vertebrates, including humans. Prolactin is secr ...

levels in individual

case report In medicine, a case report is a detailed report of the symptoms, signs, diagnosis, treatment, and follow-up of an individual patient. Case reports may contain a demographic profile of the patient, but usually describe an unusual or novel occurrenc ...

s, effects which might be secondary to increased estrogen levels. At typical therapeutic levels, cimetidine has either no effect on or causes small increases in circulating testosterone concentrations in men. Any increases in testosterone levels with cimetidine have been attributed to the loss of negative feedback on the HPG axis that results due to AR antagonism. At typical clinical dosages, such as those used to treat peptic ulcer disease, the incidence of gynecomastia (breast development) with cimetidine is very low at less than 1%. In one survey of over 9,000 patients taking cimetidine, gynecomastia was the most frequent

endocrine The endocrine system is a messenger system in an organism comprising feedback loops of hormones that are released by internal glands directly into the circulatory system and that target and regulate distant organs. In vertebrates, the hypotha ...

-related complaint but was reported in only 0.2% of patients. At high doses however, such as those used to treat

Zollinger–Ellison syndrome Zollinger–Ellison syndrome (Z-E syndrome) is a disease in which tumors cause the stomach to produce too much acid, resulting in peptic ulcers. Symptoms include abdominal pain and diarrhea. The syndrome is caused by the formation of a gastrinoma ...

, there may be a higher incidence of gynecomastia with cimetidine. In one small study, a 20% incidence of gynecomastia was observed in 25 male patients with duodenal ulcers who were treated with 1,600 mg/day cimetidine. The symptoms appeared after 4 months of treatment and regressed within a month following discontinuation of cimetidine. In another small study, cimetidine was reported to have induced

breast The breasts are two prominences located on the upper ventral region of the torso among humans and other primates. Both sexes develop breasts from the same embryology, embryological tissues. The relative size and development of the breasts is ...

changes and

in 60% of 22 men treated with it. These adverse effects completely resolved in all cases when the men were switched from cimetidine to

ranitidine Ranitidine, previously sold under the brand name Zantac among others, is a medication used to decrease stomach acid production. It was commonly used in treatment of peptic ulcer disease, gastroesophageal reflux disease, and Zollinger–Ellis ...

. A study of the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

General Practice Research Database, which contains over 80,000 men, found that the

relative risk The relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group. Together with risk difference and odds ratio, relative risk measures the association bet ...

of gynecomastia in cimetidine users was 7.2 relative to non-users. People taking a dosage of cimetidine of greater than or equal to 1,000 mg showed more than 40 times the risk of gynecomastia than non-users. The risk was highest during the period of time of 7 to 12 months after starting cimetidine. The gynecomastia associated with cimetidine is thought to be due to blockade of ARs in the breasts, which results in estrogen action unopposed by androgens in this tissue, although increased levels of estrogens due to inhibition of estrogen metabolism is another possible mechanism. Cimetidine has also been associated with oligospermia (decreased sperm count) and

(e.g., decreased libido, erectile dysfunction) in men in some research, which are hormonally related similarly. In accordance with the very weak nature of its AR antagonistic activity, cimetidine has shown minimal effectiveness in the treatment of

androgen-dependent condition An androgen-dependent condition, disease, disorder, or syndrome, is a medical condition that is, in part or full, dependent on, or is sensitive to, the presence of androgenic activity in the body. Known androgen-dependent conditions include acne ...

s such as

acne Acne ( ), also known as ''acne vulgaris'', is a long-term Cutaneous condition, skin condition that occurs when Keratinocyte, dead skin cells and Sebum, oil from the skin clog hair follicles. Typical features of the condition include comedo, ...

hirsutism Hirsutism is excessive body hair on parts of the body where hair is normally absent or minimal. The word is from early 17th century: from Latin ''hirsutus'' meaning "hairy". It usually refers to a male pattern of hair growth in a female that ma ...

(excessive hair growth), and

hyperandrogenism Hyperandrogenism is a medical condition characterized by high levels of androgens. It is more common in women than men. Symptoms of hyperandrogenism may include acne, seborrhea, hair loss on the scalp, increased body or facial hair, and infre ...

(high androgen levels) in women. As such, its use for such indications is not recommended.

Pharmacokinetics

Cimetidine is rapidly absorbed regardless of

route of administration In pharmacology and toxicology, a route of administration is the way by which a medication, drug, fluid, poison, or other substance is taken into the body. Routes of administration are generally classified by the location at which the substance ...

. The

oral The word oral may refer to: Relating to the mouth * Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid **Oral administration of medicines ** Oral examination (also known as an oral exam or ora ...

bioavailability In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation. By definition, when a medication is administered intravenously, its bioavailability is 100%. H ...

of cimetidine is 60 to 70%. The

onset of action Onset of action is the duration of time it takes for a drug's effects to come to prominence upon administration. With oral administration, it typically ranges anywhere from 20 minutes to over an hour, depending on the drug in question. Other meth ...

of cimetidine when taken orally is 30 minutes, and peak levels occur within 1 to 3 hours. Cimetidine is widely

distributed Distribution may refer to: Mathematics *Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations *Probability distribution, the probability of a particular value or value range of a varia ...

throughout all tissues. It is able to cross the

blood–brain barrier The blood–brain barrier (BBB) is a highly selective semipermeable membrane, semipermeable border of endothelium, endothelial cells that regulates the transfer of solutes and chemicals between the circulatory system and the central nervous system ...

and can produce effects in the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

(e.g.,

headache A headache, also known as cephalalgia, is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of Depression (mood), depression in those with severe ...

somnolence Somnolence (alternatively sleepiness or drowsiness) is a state of strong desire for sleep, or sleeping for unusually long periods (compare hypersomnia). It has distinct meanings and causes. It can refer to the usual state preceding falling aslee ...

). The

volume of distribution In pharmacology, the volume of distribution (VD, also known as apparent volume of distribution, literally, ''volume of dilution'') is the theoretical volume that would be necessary to contain the total amount of an administered drug at the same c ...

of cimetidine is 0.8 L/kg in adults and 1.2 to 2.1 L/kg in children. Its

plasma protein binding Plasma protein binding refers to the degree to which medications attach to blood proteins within the blood plasma. A drug's efficacy may be affected by the degree to which it binds. The less bound a drug is, the more efficiently it can traverse o ...

is 13 to 25% and is said to be without pharmacological significance. Cimetidine undergoes relatively little

, with 56 to 85% excreted unchanged. It is metabolized in the

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

into cimetidine sulfoxide, hydroxycimetidine, and guanyl urea cimetidine. The major

of cimetidine is the

sulfoxide In organic chemistry, a sulfoxide, also called a sulphoxide, is an organosulfur compound containing a sulfinyl () functional group attached to two carbon atoms. It is a polar functional group. Sulfoxides are oxidized derivatives of sulfides. E ...

, which accounts for about 30% of excreted material. Cimetidine is rapidly eliminated, with an

elimination half-life Biological half-life (elimination half-life, pharmacological half-life) is the time taken for concentration of a biological substance (such as a medication) to decrease from its maximum concentration ( Cmax) to half of Cmax in the blood plasma. ...

of 123 minutes, or about 2 hours. It has been said to have a

duration of action Pharmacodynamics (PD) is the study of the biochemical and physiologic effects of drugs (especially pharmaceutical drugs). The effects can include those manifested within animals (including humans), microorganisms, or combinations of organisms (fo ...

of 4 to 8 hours. The medication is mainly eliminated in

urine Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...

History

Cimetidine, approved by the FDA for inhibition of gastric acid secretion, has been advocated for a number of dermatological diseases. Cimetidine was the prototypical histamine H₂ receptor antagonist from which the later members of the class were developed. Cimetidine was the culmination of a project at Smith, Kline and French (SK&F) Laboratories in Welwyn Garden City (now part of

GlaxoSmithKline GSK plc (an acronym from its former name GlaxoSmithKline plc) is a British Multinational corporation, multinational Pharmaceutics, pharmaceutical and biotechnology company with headquarters in London. It was established in 2000 by a Mergers an ...

) by James W. Black, C. Robin Ganellin, and others to develop a

histamine receptor The histamine receptors are a class of G protein–coupled receptors which bind histamine as their primary endogenous ligand. Histamine is a neurotransmitter involved in various physiological processes. There are four main types of histamine recep ...

antagonist An antagonist is a character in a story who is presented as the main enemy or rival of the protagonist and is often depicted as a villain. This was one of the first drugs discovered using a

rational drug design Drug design, often referred to as rational drug design or simply rational design, is the invention, inventive process of finding new medications based on the knowledge of a biological target. The drug is most commonly an organic compound, organi ...

approach. Sir James W. Black shared the 1988 Nobel Prize in Physiology or Medicine for the discovery of

propranolol Propranolol is a medication of the beta blocker class. It is used to treat hypertension, high blood pressure, some types of cardiac dysrhythmia, irregular heart rate, thyrotoxicosis, capillary hemangiomas, akathisia, performance anxiety, and ...

and also is credited for the discovery of cimetidine. At the time (1964),

was known to stimulate the secretion of stomach acid, but also that traditional

antihistamine Antihistamines are drugs which treat allergic rhinitis, common cold, influenza, and other allergies. Typically, people take antihistamines as an inexpensive, generic (not patented) drug that can be bought without a prescription and provides ...

s had no effect on acid production. In the process, the SK&F scientists also proved the existence of histamine H₂ receptors. The SK&F team used a rational drug-design structure starting from the structure of histamine — the only design lead, since nothing was known of the then hypothetical H₂ receptor. Hundreds of modified compounds were synthesized in an effort to develop a model of the receptor. The first breakthrough was ''N^α''-guanylhistamine, a partial H₂ receptor antagonist. From this lead, the receptor model was further refined and eventually led to the development of burimamide, the first H₂ receptor antagonist. Burimamide, a specific

competitive antagonist A receptor antagonist is a type of receptor ligand or drug that blocks or dampens a biological response by binding to and blocking a receptor rather than activating it like an agonist. Antagonist drugs interfere in the natural operation of recep ...

at the H₂ receptor, 100 times more potent than ''N^α''-guanylhistamine, proved the existence of the H₂ receptor. Burimamide was still insufficiently potent for oral administration, and further modification of the structure, based on modifying the

pKa In chemistry, an acid dissociation constant (also known as acidity constant, or acid-ionization constant; denoted ) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction :H ...

of the compound, led to the development of metiamide. Metiamide was an effective agent; it was associated, however, with unacceptable

nephrotoxicity Nephrotoxicity is toxicity in the kidneys. It is a poisonous effect of some substances, both toxic chemicals and medications, on kidney function. There are various forms, and some drugs may affect kidney function in more than one way. Nephrotoxin ...

and

agranulocytosis Agranulocytosis, also known as agranulosis or granulopenia, is an acute condition involving a severe and dangerous lowered white blood cell count (leukopenia, most commonly of neutrophils) and thus causing neutropenia in the circulating blood. I ...

. The toxicity was proposed to arise from the

thiourea Thiourea () is an organosulfur compound with the formula and the structure . It is structurally similar to urea (), with the oxygen atom replaced by sulfur atom (as implied by the '' thio-'' prefix). The properties of urea and thiourea differ s ...

group, and similar

guanidine Guanidine is the compound with the formula HNC(NH2)2. It is a colourless solid that dissolves in polar solvents. It is a strong base that is used in the production of plastics and explosives. It is found in urine predominantly in patients experi ...

analogues were investigated until the ultimate discovery of cimetidine. The compound was synthesized in 1972 and evaluated for toxicology by 1973. It passed all trials. Cimetidine was first marketed in the United Kingdom in 1976, and in the U.S. in August 1977; therefore, it took 12 years from initiation of the H₂ receptor antagonist program to commercialization. By 1979, Tagamet was being sold in more than 100 countries and became the top-selling prescription product in the U.S., Canada, and several other countries. In November 1997, the American Chemical Society and the Royal Society of Chemistry in the U.K. jointly recognized the work as a milestone in drug discovery by designating it an International Historic Chemical Landmark during a ceremony at SmithKline Beecham's New Frontiers Science Park research facilities in Harlow, England. The commercial name "Tagamet" was decided upon by fusing the two words "antagonist" and "cimetidine". Subsequent to the introduction onto the U.S. drug market, two other H₂ receptor antagonists were approved,

(Zantac, Glaxo Labs) and

famotidine Famotidine, sold under the brand name Pepcid among others, is a histamine H2 receptor antagonist medication that decreases stomach acid production. It is used to treat peptic ulcer disease, gastroesophageal reflux disease, and Zollinger–E ...

(Pepcid, Yamanouchi, Ltd.) Cimetidine became the first drug ever to reach more than $1 billion a year in sales, thus making it the first

blockbuster drug Medication (also called medicament, medicine, pharmaceutical drug, medicinal product, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy (pharmacotherapy) is an important part of the ...

. Tagamet has been largely replaced by proton pump inhibitors for treating peptic ulcers, but is available as an over-the-counter medicine for heartburn in many countries.

Research

Some evidence suggests cimetidine could be effective in the treatment of common warts, but more rigorous double-blind clinical trials found it to be no more effective than a placebo. Tentative evidence supports a beneficial role as add-on therapy in colorectal cancer. Cimetidine inhibits

ALA synthase Aminolevulinic acid synthase (ALA synthase, ALAS, or delta-aminolevulinic acid synthase) is an enzyme () that catalyzes the synthesis of δ-aminolevulinic acid (ALA) the first common precursor in the biosynthesis of all tetrapyrroles such as hemes ...

activity and hence may have some therapeutic value in preventing and treating acute porphyria attacks. There is some evidence supporting the use of cimetidine in the treatment of PFAPA.

Veterinary use

In dogs, cimetidine is used as an antiemetic when treating chronic gastritis.

References

External links

* {{Authority control CYP1A2 inhibitors CYP2D6 inhibitors CYP3A4 inhibitors Cytochrome P450 inhibitors Equine medications Guanidines H2 receptor antagonists Hepatotoxins Imidazoles Nitriles Nonsteroidal antiandrogens Thioethers Nephrotoxins Drugs developed by GSK plc

Medical uses

Side effects

Overdose

Interactions

Pharmacology

Pharmacodynamics

Histamine H2 receptor antagonism

Cytochrome P450 inhibition

Antiandrogenic and estrogenic effects

Pharmacokinetics

History

Research

Veterinary use

References

External links

Histamine H₂ receptor antagonism