The liver is the primary organ responsible for drug metabolism, where various enzymes and transporters facilitate the biotransformation of drugs into more polar and excretable forms.

Cytochrome P450 enzymes are a superfamily of enzymes involved in Phase I drug metabolism, responsible for oxidation, reduction, and other reactions that introduce functional groups onto drug molecules.

Glucuronidation is the primary mechanism of Phase II drug metabolism, where glucuronic acid is transferred to drug molecules, increasing their water solubility and facilitating their excretion.

Renal excretion is the primary pathway for drug excretion, where drugs and their metabolites are filtered by the kidneys and eliminated in urine.

Secretion is the process by which drugs are actively transported from the renal tubules back into the bloodstream, influencing the extent of drug elimination.

All of the factors mentioned, including age, gender, genetic variations, and drug interactions, can influence the rate and extent of drug metabolism and excretion.

First-pass metabolism refers to the process by which drugs are metabolized by enzymes in the intestinal mucosa before reaching systemic circulation, affecting their bioavailability.

Enalapril is an example of a prodrug, which is a pharmacologically inactive compound that is converted into an active form through metabolism.

Excretion refers to the process by which drugs are eliminated from the body unchanged, primarily through renal excretion or biliary excretion.

Digoxin is an example of a drug that undergoes significant enterohepatic recirculation, where it is excreted in bile, reabsorbed in the intestine, and returned to the liver, leading to prolonged elimination.

Distribution refers to the process by which drugs are distributed throughout the body after absorption, involving their movement into various tissues and compartments.

All of the factors mentioned, including protein binding, tissue perfusion, and the blood-brain barrier, can influence the distribution of drugs in the body.

Pulmonary excretion refers to the process by which drugs are eliminated from the body through the lungs, primarily involving volatile compounds or drugs that are metabolized to volatile products.

Ethanol is an example of a drug that undergoes significant pulmonary excretion, where it is eliminated from the body through the lungs after being metabolized to acetaldehyde.

Integumentary excretion refers to the process by which drugs are eliminated from the body through sweat, saliva, or tears, although it is a minor route of elimination compared to renal and biliary excretion.