Phenazopyridine is a

medication Medication (also called medicament, medicine, pharmaceutical drug, medicinal product, medicinal drug or simply drug) is a drug used to medical diagnosis, diagnose, cure, treat, or preventive medicine, prevent disease. Drug therapy (pharmaco ...

which, when excreted by the kidneys into the

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 ...

, has a local

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 ...

effect on the

urinary tract The human urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressu ...

. It is often used to help with the

pain Pain is a distressing feeling often caused by intense or damaging Stimulus (physiology), stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sense, sensory and emotional experience associated with, or res ...

irritation Irritation, in biology and physiology, is a state of inflammation or painful reaction to allergy or cell-lining damage. A stimulus or agent which induces the state of irritation is an irritant. Irritants are typically thought of as chemical age ...

, or urgency caused by

urinary tract infections A urinary tract infection (UTI) is an infection that affects a part of the urinary tract. Lower urinary tract infections may involve the bladder (cystitis) or urethra ( urethritis) while upper urinary tract infections affect the kidney (pye ...

surgery Surgery is a medical specialty that uses manual and instrumental techniques to diagnose or treat pathological conditions (e.g., trauma, disease, injury, malignancy), to alter bodily functions (e.g., malabsorption created by bariatric surgery s ...

, or injury to the urinary tract. In 2021, it was the 285th most commonly prescribed medication in the United States, with more than 700,000 prescriptions.

Medical uses

Phenazopyridine is prescribed for its local analgesic effects on the

. It is sometimes used in conjunction with an

antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy ...

or other anti-infective medication at the beginning of treatment to help provide immediate

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 ...

atic relief. Phenazopyridine does not treat infections or injury; it is only used for symptom relief during a UTI, following surgery, or injury to the urinary tract. It is recommended that it be used for no longer than the first two days of antibacterial treatment, as longer treatment cannot kill bacteria and may mask symptoms. UTI therapy should be limited to one to two days. Phenazopyridine is prescribed for other cases requiring relief from irritation or discomfort during urination; for example, after the use of an in-dwelling

Foley catheter In urology, a Foley catheter is one of many types of urinary catheters (UC). The Foley UC was named after Frederic Foley, who produced the original design in 1929. Foleys are indwelling UC, often referred to as an IDCs (sometimes IDUCs). This dif ...

, endoscopic (

cystoscopy Cystoscopy is endoscopy of the urinary bladder via the urethra. It is carried out with a cystoscope. The urethra is the tube that carries urine from the bladder to the outside of the body. The cystoscope has lenses like a telescope or microscop ...

) procedures, or after

urethra The urethra (: urethras or urethrae) is the tube that connects the urinary bladder to the urinary meatus, through which Placentalia, placental mammals Urination, urinate and Ejaculation, ejaculate. The external urethral sphincter is a striated ...

prostate 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 ...

, or

urinary bladder The bladder () is a hollow organ in humans and other vertebrates that stores urine from the Kidney (vertebrates), kidneys. In placental mammals, urine enters the bladder via the ureters and exits via the urethra during urination. In humans, the ...

surgeries that may result in irritation of the

epithelial Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

lining of the urinary tract.

Side effects

Phenazopyridine produces a vivid color change in urine, typically to a dark orange to reddish color. This effect is common and harmless and indeed a key indicator of the presence of the medication in the body. Users of phenazopyridine are warned not to wear

contact lens Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic ...

es, as phenazopyridine has been known to permanently discolor them. Furthermore, it tends to leave an orange-yellow stain on surfaces (including fabrics) it comes in contact with. These color changes can be concerning for patients, who may mistake them for the presence of

blood in the urine Hematuria or haematuria is defined as the presence of blood or red blood cells in the urine. "Gross hematuria" occurs when urine appears red, brown, or tea-colored due to the presence of blood. Hematuria may also be subtle and only detectable with ...

. Phenazopyridine can cause

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 ...

upset stomach Abdominal pain, also known as a stomach ache, is a symptom associated with both non-serious and serious medical issues. Since the abdomen contains most of the body's vital organs, it can be an indicator of a wide variety of diseases. Given th ...

(especially when not taken with food), or

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 ...

. Less frequently it can cause a noticeable yellowish pigment change in the skin or eyes. This is due to a depressed excretion via the kidneys causing a buildup of the medication in the skin, and normally indicates a need to discontinue usage. Other such side effects include

fever Fever or pyrexia in humans is a symptom of an anti-infection defense mechanism that appears with Human body temperature, body temperature exceeding the normal range caused by an increase in the body's temperature Human body temperature#Fever, s ...

confusion In psychology, confusion is the quality or emotional state of being bewildered or unclear. The term "acute mental confusion"

shortness of breath Shortness of breath (SOB), known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing discomfort that con ...

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

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 ...

, and swelling of the face, fingers, feet, or legs. Long-term use may cause yellowing of nails. Phenazopyridine should be avoided by people with

glucose-6-phosphate dehydrogenase deficiency Glucose-6-phosphate dehydrogenase deficiency (G6PDD), also known as favism, is the most common enzyme deficiency anemia worldwide. It is an inborn error of metabolism that predisposes to red blood cell breakdown. Most of the time, those who ar ...

, because it can cause

hemolysis Hemolysis or haemolysis (), also known by #Nomenclature, several other names, is the rupturing (lysis) of red blood cells (erythrocytes) and the release of their contents (cytoplasm) into surrounding fluid (e.g. blood plasma). Hemolysis may ...

(destruction of

red blood cell Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood cel ...

s) due to

oxidative stress Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal ...

. It has been reported to cause

methemoglobinemia Methemoglobinemia, or methaemoglobinaemia, is a condition of elevated methemoglobin in the blood. Symptoms may include headache, dizziness, shortness of breath, nausea, poor muscle coordination, and blue-colored skin (cyanosis). Complications ma ...

after overdose and even normal doses. In at least one case, the patient had pre-existing low levels of

methemoglobin reductase Cytochrome-''b''5 reductase is a NADH-dependent enzyme that converts ferricytochrome from a Fe3+ form to a Fe2+ form. It contains FAD and catalyzes the reaction: In its b5-reducing capacity, this enzyme is involved in desaturation and elongati ...

, which likely predisposed her to the condition. It has also been reported to cause

sulfhemoglobinemia Sulfhemoglobinemia is a rare condition in which there is excess sulfhemoglobin (SulfHb) in the blood. The pigment is a greenish derivative of hemoglobin which cannot be converted back to normal, functional hemoglobin. It causes cyanosis even at ...

. Phenazopyridine is an

azo dye Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl and substituted aryl groups. They are a commercially important family of azo compounds, i.e. compounds containing the C−N=N−C l ...

. Other azo dyes, which were previously used in

textile Textile is an Hyponymy and hypernymy, umbrella term that includes various Fiber, fiber-based materials, including fibers, yarns, Staple (textiles)#Filament fiber, filaments, Thread (yarn), threads, and different types of #Fabric, fabric. ...

s, printing, and plastic manufacturing, have been implicated as

carcinogen A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and biologic agents such as viruse ...

s that can cause

bladder cancer Bladder cancer is the abnormal growth of cells in the bladder. These cells can grow to form a tumor, which eventually spreads, damaging the bladder and other organs. Most people with bladder cancer are diagnosed after noticing blood in thei ...

. While phenazopyridine has never been shown to cause cancer in humans, evidence from animal models suggests that it is potentially carcinogenic.

Pregnancy

This medication has shown no adverse events in animal models, but no human trials have been conducted. It is not known if phenazopyridine is excreted in

breast milk Breast milk (sometimes spelled as breastmilk) or mother's milk is milk produced by the mammary glands in the breasts of women. Breast milk is the primary source of nutrition for newborn infants, comprising fats, proteins, carbohydrates, and a var ...

Pharmacokinetics

The full

pharmacokinetic Pharmacokinetics (from Ancient Greek ''pharmakon'' "drug" and ''kinetikos'' "moving, putting in motion"; see chemical kinetics), sometimes abbreviated as PK, is a branch of pharmacology dedicated to describing how the body affects a specific subs ...

properties of phenazopyridine have not been determined. It has mostly been studied in

animal model An animal model (short for animal disease model) is a living, non-human, often genetic-engineered animal used during the research and investigation of human disease, for the purpose of better understanding the disease process without the risk of ha ...

s, but they may not be very representative of humans. Rat models have shown its half-life to be 7.35 hours, and 40% is metabolized hepatically (by the liver).

Mechanism of action

Phenazopyridine's

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 ...

is not well known, and only basic information on its interaction with the body is available. It is known that the chemical has a direct topical analgesic effect on the

mucosa A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It ...

lining of the urinary tract. It is rapidly excreted by the kidneys directly into the urine.

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 ...

is the major form of metabolism in humans, and the azo bond is usually not cleaved. On the order of 65% of an oral dose will be secreted directly into the urine chemically unchanged.

Brand names

In addition to its generic form, phenazopyridine is distributed under the following brand names:

References

{{Urologicals Azo compounds Drugs with unknown mechanisms of action 2-Aminopyridines Analgesics IARC Group 2B carcinogens Anilines