[Biologic availability and "1st pass" effect of drugs]

Bioavailability and "first pass"-effect are of increasing importance in Clinical Pharmacology. Bioavailability is the rate and above all the extent to which a drug reaches the systemic circulation. Reduced bioavailability may result from the physico-chemical properties of the drug, its solubility in the intestinal tract and its ability to permeate the gut wall. Reduced bioavailability may also result from a "first pass"-effect if the drug is metabolized during absorption by the enteral mucosa or during its first liver passage. Some conclusions may be drawn which are of importance for the clinic and pharmacy from the presented empirical and theoretical examples.