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A prodrug is a pharmacologically inactive
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 ...
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 used to improve how the drug is absorbed, distributed, metabolized, and excreted (
ADME ADME is the four-letter abbreviation (acronym) for absorption (pharmacokinetics), ''absorption'', distribution (pharmacology), ''distribution'', ''metabolism'', and ''excretion'', and is mainly used in fields such as pharmacokinetics and pharmacol ...
). Prodrugs are often designed to improve bioavailability when a drug itself is poorly absorbed from the
gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...
. A prodrug may be used to improve how selectively the drug interacts with cells or processes that are not its intended target. This reduces adverse or unintended effects of a drug, especially important in treatments like
chemotherapy Chemotherapy (often abbreviated chemo, sometimes CTX and CTx) is the type of cancer treatment that uses one or more anti-cancer drugs (list of chemotherapeutic agents, chemotherapeutic agents or alkylating agents) in a standard chemotherapy re ...
, which can have severe unintended and undesirable side effects.


History

Many herbal extracts historically used in medicine contain
glycosides In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. ...
(sugar derivatives) of the active agent, which are hydrolyzed in the intestines to release the active and more bioavailable
aglycone An aglycone (aglycon or genin) is the chemical compound remaining after the glycosyl group on a glycoside is replaced by a hydrogen atom. For example, the aglycone of a cardiac glycoside would be a steroid A steroid is an organic compoun ...
. For example,
salicin Salicin is an alcoholic β-glucoside. Salicin is produced in (and named after) willow (''Salix'') bark. It is a biosynthetic precursor to salicylaldehyde. Salicin hydrolyses into Glucose, β-d-glucose and salicyl alcohol (saligenin). Salicyl al ...
is a β-D-glucopyranoside that is cleaved by esterases to release
salicylic acid Salicylic acid is an organic compound with the formula HOC6H4COOH. A colorless (or white), bitter-tasting solid, it is a precursor to and a active metabolite, metabolite of acetylsalicylic acid (aspirin). It is a plant hormone, and has been lis ...
.
Aspirin Aspirin () is the genericized trademark for acetylsalicylic acid (ASA), a nonsteroidal anti-inflammatory drug (NSAID) used to reduce pain, fever, and inflammation, and as an antithrombotic. Specific inflammatory conditions that aspirin is ...
, acetylsalicylic acid, first made by Felix Hoffmann at
Bayer Bayer AG (English: , commonly pronounced ; ) is a German multinational pharmaceutical and biotechnology company and is one of the largest pharmaceutical companies and biomedical companies in the world. Headquartered in Leverkusen, Bayer' ...
in 1897, is a synthetic prodrug of salicylic acid. However, in other cases, such as codeine and
morphine Morphine, formerly also called morphia, is an opiate that is found naturally in opium, a dark brown resin produced by drying the latex of opium poppies (''Papaver somniferum''). It is mainly used as an analgesic (pain medication). There are ...
, the administered drug is enzymatically activated to form sugar derivatives (morphine- glucuronides) that are more active than the parent compound. The first synthetic antimicrobial drug, arsphenamine, discovered in 1909 by Sahachiro Hata in the laboratory of
Paul Ehrlich Paul Ehrlich (; 14 March 1854 – 20 August 1915) was a Nobel Prize-winning German physician and scientist who worked in the fields of hematology, immunology and antimicrobial chemotherapy. Among his foremost achievements were finding a cure fo ...
, is not toxic to bacteria until it has been converted to an active form by the body. Likewise,
prontosil Prontosil is an antibacterial drug of the sulfonamide group. It has a relatively broad effect against gram-positive cocci but not against enterobacteria. One of the earliest antimicrobial drugs, it was widely used in the mid-20th century but is ...
, the first sulfa drug (discovered by
Gerhard Domagk Gerhard Johannes Paul Domagk (; 30 October 1895 – 24 April 1964) was a German pathologist and bacteriologist. He is credited with the discovery of Sulfonamide (medicine), sulfonamidochrysoidine (KL730) as an antibiotic for which he received th ...
in 1932), must be cleaved in the body to release the active molecule,
sulfanilamide Sulfanilamide (also spelled sulphanilamide) is a sulfonamide antibacterial drug. Chemically, it is an organic compound consisting of an aniline derivatized with a sulfonamide group. Powdered sulfanilamide was used by the Allies in World War ...
. Since that time, many other examples have been identified.
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 ...
, the first non-sedating
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 ...
, had to be withdrawn from the market because of the small risk of a serious side effect. However, terfenadine was discovered to be the prodrug of the active molecule, fexofenadine, which does not carry the same risks as the parent compound. Therefore, fexofenadine could be placed on the market as a safe replacement for the original drug.
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 ...
, another non-sedating antihistamine, is the prodrug of desloratadine, which is largely responsible for the antihistaminergic effects of the parent compound. However, in this case the parent compound does not have the side effects associated with terfenadine, and so both loratadine and its active metabolite, desloratadine, are currently marketed.UK Medicines Information Pharmacists Group
New Medicines on the Market: Desloratadine.
June 2001.


Recent prodrugs

Approximately 10% of all marketed drugs worldwide can be considered prodrugs. Since 2008, at least 30 prodrugs have been approved by the FDA. Seven prodrugs were approved in 2015 and six in 2017. Examples of recently approved prodrugs are such as dabigatran etexilate (approved in 2010), gabapentin enacarbil (2011), sofosbuvir (2013), tedizolid phosphate (2014), isavuconazonium (2015), aripiprazole lauroxil (2015), selexipag (2015), latanoprostene bunod (2017), benzhydrocodone (2018), tozinameran (2020) and serdexmethylphenidate (2021).


Classification

Prodrugs can be classified into two major types, based on how the body converts the prodrug into the final active drug form: * Type I prodrugs are bioactivated inside the cells (intracellularly). Examples of these are anti-viral nucleoside analogs that must be phosphorylated and the lipid-lowering statins. * Type II prodrugs are bioactivated outside cells (extracellularly), especially in digestive fluids or in the body's
circulatory system In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart ...
, particularly in the
blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood is com ...
. Examples of Type II prodrugs are salicin (described above) and certain antibody-, gene- or virus-directed enzyme prodrugs used in
chemotherapy Chemotherapy (often abbreviated chemo, sometimes CTX and CTx) is the type of cancer treatment that uses one or more anti-cancer drugs (list of chemotherapeutic agents, chemotherapeutic agents or alkylating agents) in a standard chemotherapy re ...
or immunotherapy. Both major types can be further categorized into subtypes, based on factors such as (Type I) whether the intracellular bioactivation location is also the site of therapeutic action, or (Type 2) whether or not bioactivation occurs in the gastrointestinal fluids or in the circulation system.


Subtypes

Type IA prodrugs include many antimicrobial and chemotherapy agents (e.g., 5-flurouracil). Type IB agents rely on metabolic enzymes, especially in hepatic cells, to bioactivate the prodrugs intracellularly to active drugs. Type II prodrugs are bioactivated extracellularly, either in the milieu of GI fluids (Type IIA), within the systemic circulation and/or other extracellular fluid compartments (Type IIB), or near therapeutic target tissues/cells (Type IIC), relying on common enzymes such as esterases and phosphatases or target directed enzymes. Importantly, prodrugs can belong to multiple subtypes (i.e., Mixed-Type). A Mixed-Type prodrug is one that is bioactivated at multiple sites, either in parallel or sequential steps. For example, a prodrug, which is bioactivated concurrently in both target cells and metabolic tissues, could be designated as a "Type IA/IB" prodrug (e.g., HMG Co-A reductase inhibitors and some chemotherapy agents; note the symbol " / " applied here). When a prodrug is bioactivated sequentially, for example initially in GI fluids then systemically within the target cells, it is designated as a "Type IIA-IA" prodrug (e.g., tenofovir disoproxil; note the symbol " - " applied here). Many antibody- virus- and gene-directed enzyme prodrug therapies ( ADEPTs, VDEPTs, GDEPTs) and proposed
nanoparticle A nanoparticle or ultrafine particle is a particle of matter 1 to 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. At ...
- or nanocarrier-linked drugs can understandably be Sequential Mixed-Type prodrugs. To differentiate these two Subtypes, the symbol dash " - " is used to designate and to indicate sequential steps of bioactivation, and is meant to distinguish from the symbol slash " / " used for the Parallel Mixed-Type prodrugs.; Table 1; Table 1


See also

* Hypoxia-activated prodrugs * Neurotransmitter prodrug *
Precursor (chemistry) In chemistry, a precursor is a compound that participates in a chemical reaction that produces another compound. In biochemistry Biochemistry, or biological chemistry, is the study of chemical processes within and relating to living organism ...
* Toxication


References


External links


Special Issue on Prodrugs: from Design to Applications
Pharmacokinetics * {{Combined substance use and adulteration