Modes of drug elimination and bioactive metabolites

Drug elimination is the removal of active drug from the body. Metabolism takes place largely in the liver and produces water soluble metabolites which can be excreted in the bile or urine. Metabolism may also produce active or toxic metabolites or a pharmacologically active drug from an inactive prodrug. Most volatile anaesthetics are excreted unchanged via the lungs. Drug elimination can be affected by factors such as first-pass metabolism, genetic variants and various disease processes. Knowledge of these processes will allow better prediction of pharmacokinetics in practice.