History of prodrug
Objective of prodrug
Properties of ideal prodrug
Classification of prodrug
Limitation of prodrug
The concept of prodrug is first introduced by Adrian albert in 1958 to describe
the compound undergo biotransformation prior to eliciting their pharmacological
Prodrug is defined as therapeutic agent that are inactive but predictable
transformed into active metabolites.
Most of the drug available presently have some undesirable side effect that
hamper their therapeutic efficacy.
A therapeutically active drug may have limited utilization in clinical practices
because of various shortcomings like poor organoleptic properties, poor
bioavailability, short duration of action, non-specificity, incomplete absorption,
poor aqueous solubility, high first-pass metabolism or other adverse effect.
4. History of Prodrugs
• The first compound fulfilling the classical criteria of a prodrug was acetanilide,
introduced into the medical practice by Cahn and Hepp in 1867 as an antipyretic
agent. Acetanilide is hydroxylated to biologically active acetaminophen.
• Another historical prodrug is Aspirin (acetylsalicylic acid), synthesized in 1897 by
Felix Hoffman (Bayer, Germany), and introduced into medicine by Dreser in 1899.
• The prodrug concept was intentionally used for the first time by the Parke-Davis
company for modification of chloramphenicol structure in order to improve the
antibiotic’s bitter taste and poor solubility in water. Twoprodrug forms of
chloramphenicol were synthesized: chloramphenicol sodium succinate with a
good water solubility, and chloramphenicol palmitate used in the form of
suspension in children.
6. Objective of prodrug
• Prodrug design aims at overcoming a number of barriers to a drug’s usefulness.
- insufficient chemical stability
- poor solubility
- offensive taste or odour
- improved formulation
- improved chemical stability
- low oral absorption
- marked presystemic metabolism
- short duration of action
- improved bioavaliblity
- prolonged duration of action
- improve organ selectivity
- decreased side effect
7. Properties of ideal prodrug
• Pharmacological Inertness
• Rapid transformation, chemically or enzymatically,
into the active form at the target site
• Non-toxic metabolic fragments followed by
their rapid elimination
8. CLASSIFICATION OF PRODRUG
Prodrug based on structural association of molecules
• Carrier linked prodrugs
• Tripartite prodrug
• Mutual prodrugs
• Double prodrug
• Bio precursor
- Prodrug for amide, imides and acidic compounds
classification on the basis of sites of conversion into the active drug foam
• Type 1
• Type 2
9. Active Drug
Carrier linked prodrug
Chemical Prodrug Formation
• Carrier linked prodrug consists of the attachment of a carrier group
to the active drug to alter its physicochemical properties.
• The subsequent enzymatic or non-enzymatic mechanism releases the
active drug moiety.
10. Tripartite prodrug
Structure of most prodrug is bipartite (having two parts) in nature in which parent
drug is attached directly to promoiety bond.
In some cases bipartite prodrug may be unstable, the problem can be overcome by
designing a tripartite prodrug ( having three parts).
11. Mutual Prodrugs
• A mutual prodrug consists of two pharmacologically active agents coupled together so
that each acts as a promoiety for the other agent and vice versa.
• A mutual prodrug is a bipartite or tripartite prodrug in which the carrier is a synergistic
drug with the drug to which it is linked.
• Benorylate is a mutual prodrug aspirin and paracetamol.
• Sultamicillin, which on hydrolysis by an esterase produces ampicillin &
13. Polymeric prodrug
It is also known as macromolecular prodrugs.
The drug is dispersed or incorporated in the polymer without formation of covalent bond
between the polymer and drug.
Ex:- p-phenylene diamine mustard is covalently attached with polyamino
polymer backbone of polyglutamic acid .
In double prodrug concept, prodrug is further derivatized in a fashion such that enzymatic
conversion to prodrug is possible before prodrug can cleave to release active drug, for
example diesters of pilocarpic acid.
• Bio- precursor prodrugs produce
modification of their inactive form.
their effects after in vivo chemical
• Bio-precursor prodrugs rely on oxidative or reductive activation reactions
unlike the hydrolytic activation of carrier-linked prodrugs.
• They metabolized into a new compound that may itself be active or
further metabolized to an active metabolite
15. Classification based on the site of conversion
Prodrug also classified into two types on their site of conversion into a active drug
Type 1:- which are converted intracellularly (e.g. anti viral nucleoside analogs, lipid-
lowering statins, antibody directed enzyme prodrug, gene- directed enzyme prodrug))
Type 2:- which are converted extracellularly (e.g. etoposide phosphate,
16. Type Converting
Type I Intracellular Type IA Therapeutic
Type II Intracellular Type IB Metabolic
Type II Extracellular Type IIA GI fluid sulfasalazine
Type II Extracellular Type IIB Systemic
17. Limitation of prodrug
Formation of an unexpected metabolism from the total prodrug that may be toxic.
The inert carrier generated metabolic cleavage may also transform into toxic metabolite.
Duration its activation stage, the prodrug might consume a vital cell constituent such as
glutathione leading to its depletion.
Improvement of taste
Change in physical from of drug
Improvement the odour
Reduction in GI irritation
Reduction in pain on injection
Enhancement of drug solubility and dissolution rate
Enhancement of chemical stability
Enhancement of bioavailablity
Prevention presystemic metabolism
Prolongation duration of action
Reduction in toxicity
Site- specific delivery
19. Improvement of taste
• The undesirable taste arises due to adequate solubility and interaction of drug with taste
receptors, which can be solved by lowering the solubility of drug or prodrug in saliva.
• Chloramphenicol, an extremely bitter drug has been derivatized to chloramphenicol
palmitate, a sparingly soluble ester.
• It possesses low aqueous solubility which makes it tasteless and later undergoes in vivo
hydrolysis to active chloramphenicol by the action of pancreatic lipase.
Change in physical form of drug
• Some drugs in liquid foam are not formulation of solid dosage form especially if their dose
• The method of converting such liquid drugs into solid prodrug involves formation of
symmetrical molecules having a higher tendency to crystallize, for example, esters of
20. Imrovement of odor
• The ethyl mercaptan (tuberculostatic agent) has a boiling point of 25ºC and a strong
• Diethyl dithio isophthalate, a prodrug of ethyl mercaptan has a higher boiling point and is
Reduction in GI irritation
• Several drugs cause irritation and damage to the gastric mucosa through direct
contact, increased stimulation of acid secretion or through interference with
protective mucosal layer.
Salicylic acid Salsalate, Aspirin
Phenylbutazone N-methyl piperazine salt
Nicotinic acid Nicotinic acid hydrazide
21. Reduction in pain on injection
Pain caused by intramuscular injection is mainly due to the weakly acidic nature or poor
aqueous solubility of drugs.
Ex: IM injection of antibiotics like clindamycin and anti convulsant like phenytoin was
found to be painful due to poor solubility. So, prodrugs are produced like 2’phosphate
ester of clindamycin and hydantoic ester prodrug of phenytoin (fosphenytoin) an
aqueous soluble form of phenytoin respectively.
Inhancement of drug solubility
• The prodrug approach can be used to increase or decrease the solubility of a drug,
depending on its ultimate use.
Example-The solubility of betamethasone in water is 58 μg/ml at 25⁰C. The
solubility of its disodium phosphate ester (a charged ester promoeity) is more than
100 mg/ml, an increase in water solubility greater than 1500-fold.
Acetylated sulfonamide moiety enhanced the aqueous solubility of the poorly water-
soluble sodium salt of the COX-2 inhibitor Parecoxib ~300-fold.
22. Enhancement of chemical stability
• Chemical stability is an utmost necessary parameter for every therapeutic agent.
• The prodrug approach is based on the modification of the functional group responsible for the
instability or by changing the physical properties of the drug resulting in the reduction of
contact between the drug and the media in which it is unstable.
• Ex: Inhibiting the auto aminolysis, which occur due to capability of NH2 group of side chain to
attach β lactam ring of other molecule, in ampicillin molecule in concentrated solution it
generates polymeric species of ampicillin. By making hetacillin, a prodrug of ampicillin
formed by the reaction of acetone and ampicillin „ties up‟ the amine group and thus inhibits
Enhancement of bioavailablity
Various therapeutic agents such as water soluble vitamins, structural analogues of natural
purine and pyrimidine nucleoside, dopamine, antibiotics like ampicillin and carbenicillin,
phenytoin and cardiac glycoside such as gitoxin suffers with poor gastrointestinal absorption.
The prime cause of the poor absorption of these agents is their highly polar nature, poor
lipophilicity and/or metabolism during the absorption process.
On contrary gitoxin, a cardiac glycoside has very poor oral bioavailability due to limited
23. • Absorption of water soluble vitamin was enhanced by derivatization of thiolate ion to
form lipid soluble prodrugs .
• Dopamine was made useful by making its precursor L-Dopa. Though L- Dopa is highly
polar, it is actively transported through specific L–amino acid active transport
mechanism and regenerates dopamine by decarboxylation.
• Penta acetyl prodrug of gitoxin has four to five times more aqueous solubility.
• To increase aqueous solubility esterification with amino acids is done. Examples of such
prodrugs are valacyclovir and valgancyclovir, which are valine esters of the antiviral
drugs acyclovir and gancyclovir, respectively.
24. Prevention presystemic metabolism
Following oral administration, a drug must pass through two metabolizing organs i.e.,
liver and gastrointestinal mucosa, before reaching the general circulation.
Phenolic moiety, oxidative N– and O– dealkylation, ester cleavage and peptide
degradation are responsible for the pre-systemic metabolism of various drugs.
Two types of drugs fall into this category.
The first are drugs rapidly degraded by the acid condition of the stomach.
Drugs of second category degrade due to enzymes present in the gastrointestinal
mucosa and liver.
25. The first pass metabolism of a drug can be prevented if the functional group
susceptible to metabolism is protected temporarily by derivatization.
• Alternatively manipulation of the drug to alter its physicochemical properties may
also alter the drug – enzyme complex formation.
• Naltrexone (treatment of opioid addiction) and is readily absorbed from GIT and
hence undergoes Pre-systemic metabolism. Ester prodrugs such as O-
nitrobenzoate and acetylsalicylate increased bioavailablity 45 and 28 fold
Propranolol Propranolol hemisuccinate
26. Prolongation of duration of action
• Drugs with short half life require frequent dosing with conventional dosage
forms to maintain adequate plasma concentration of the particular drug.
• In plasma level time profile and consequently patient compliance is often poor.
• Prolongation of duration of action of a drug can be accomplished by the prodrug .
Prodrug can be formed by two approaches-
To control the release of prodrug
Drug Ester Prodrug
Testosterone Testosterone propionate
Estradiol Estradiol propionate
Fluphenazine Fluphenazine deaconate
27. Reduction of toxicity
• An important objective of drug design is to develop a moiety with high activity and low
• NSAIDs local side effects like gastric distress with various, which can be overcome by
• Another example is the bioprecursor Sulindac, as it is a sulphoxide, it doesn’t cause any
gastric irritation and also better absorbed.
• The prodrug Ibuterol is diisobutyrate ester of Terbutaline (a selective β-agonist
useful) in glaucoma. This prodrug, is 100 times more potent, has longer duration of
action and is free from both local and systemic toxicity.
28. Site specific drug delivery
• After its absorption into the systemic circulation, the drug is distributed to the various
parts of the body including the target site as well as the non-target tissue.
• These problems can be overcome by targeting the drug specifically to its site of
action by prodrug design
• The prodrug is converted into its active form only in the target organ/tissue by utilizing
either specific enzymes or a pH value different from the normal pH for activation e.g. 5-
amino salicylic acid.
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