You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is The poor bioavailability of drugs, when given orally is due to: and explain in detail?
Ans: a (1st pass metabolism) Ref: KDT, 6th ed, p. 291st pass metabolism refers to metabolism of a drug during its passage from site of absorption into systemic circulation. All orally administered drugs are exposed to drug metabolizing enzymes in the intestinal wall and liver (through the portal vein).The poor bioavailability of some drugs are due to high 1st pass metabolism.Transdermal or inhalational drugs have limited magnitude of lst pass metabolism (pie systemic metabolism).Feature of drugs with high 1st pass metabolism1) Oral dose higher than sublingual or parenteral route2) Bioavailability increased in patients with liver disease4) Bioavailability of a drug is increased if another drug competing with it in 1st pass metabolism is given concurrently e.g., chlorpromazine and propranolol