First-Pass Metabolism

First-pass metabolism refers to the process by which the body metabolizes a drug before it enters the bloodstream fully. When a medication is taken orally, it travels to the liver after digestion, where enzymes break it down. This initial processing can significantly reduce the drug's effectiveness, as a portion of it may be transformed into inactive metabolites or eliminated from circulation. Consequently, the dosage needs to account for this loss to ensure that enough active substance reaches the systemic circulation to achieve the desired therapeutic effect.