Lecture 3. III. Drug Metabolism. The aim of drug metabolism is to convert lipid soluble (non polar) drugs to polar metabolites easily excreted in urine. The liver is the principle organ of drug metabolism. The drug metabolite may be:
The aim of drug metabolism is to convert lipid soluble (non polar) drugs to polar metabolites easily excreted in urine.
The liver is the principle organ of drug metabolism.
Inactive: metabolism results in termination of drug action e.g. most drugs.
Active like the parent drug: e.g. diazepam (sedative and hypnotic).
Active and the parent drug is inactive: (prodrug)
Kidney is the major rout of excretion of drugs or their metabolites.
Other channels of excretion include the lungs, intestine, skin and milk.
Drugs are eliminated from the body either unchanged as the parent drug or as metabolites (a changed form of the drug).
Since drugs are small particles dissolved in the blood, they are usually filtered into the kidneys and then reabsorbed back into the bloodstream.
The dosage form that contains the therapeutically active agent (s), generally but not necessarily in association with inactive ingredients (e.g. tablet, capsule, suspension, ….. ).
Drug product selection:
The process of selecting dosage form in which the drug product will be manufactured.
The duration of drug therapy:
The time necessary for the treatment of a disease with a drug.
It reflects the drug concentration at which a toxic effect will appear.
Therapeutic drug Toxic
When a medication is administered intravenously, its bioavailability is 100%.
e.g.1Betamethasone Acetate and BetamethasoneValerate
e.g.2Tetracyclin Hydrochloride and Tetracyclin Phosphate
Also, different dosage forms containing the same active ingredients and produced by a single manufacturer are pharmaceutic alternatives.
e.g.1 Sustained-release dosage form (Olfen SR)R versus a standard immediate-release drug product of the same ingredient (Olfen)R.
e.g.2Diclofenac Sodium (Declophen)R ampoule and Diclofenac Sodium (Declophen)R tablet.