Causes of reduced bioavailability of a drug includes
When the metabolism of a drug is high during its passage from the site of absorption into the systemic circulation, the rate, and extent of absorption of that drug decreases. absorption- amount of drug reaching the systemic circulation from the site of administration (Ref.Essentials of medical pharmacology TD Tripathi 7th edition page no.16,27)
High first pass metabolism
Increased absorption
IV drug administration
High lipid solubility
Endocrinology