What is the effect of first pass metabolism on drug bioavailability?

Correct Answer: D

Rationale: First pass metabolism refers to the metabolism of a drug in the liver before it reaches systemic circulation. This process greatly reduces the fraction of unchanged drug that reaches systemic circulation, as the drug may be metabolized or broken down before it can exert its effects. This leads to lower bioavailability of the drug. Choice A is incorrect because first pass metabolism does affect the fraction of unchanged drug reaching systemic circulation. Choice B is incorrect as first pass metabolism does not necessarily impact the half-life of the drug in plasma. Choice C is incorrect because first pass metabolism does not accelerate the absorption rate of the drug; instead, it may decrease it by metabolizing the drug before it can be absorbed.

Correct Answer: D

Rationale: The correct answer is D, Cetirizine hydrochloride. Cetirizine is an antihistamine used to treat allergies and does not have any effect on reducing gastric acid production. Aluminium hydroxide (A) is an antacid that neutralizes stomach acid. Cimetidine (B) is an H2 blocker that reduces acid production. Omeprazole (C) is a proton pump inhibitor that also decreases stomach acid production. Therefore, D is the correct answer as it does not have any impact on gastric acid levels.

Correct Answer: A

Rationale: First-pass metabolism occurs when drugs are absorbed from the gastrointestinal tract and pass through the liver before reaching the systemic circulation. The oral route is affected by first-pass metabolism as drugs are metabolized in the liver before entering the bloodstream. Sublingual bypasses the liver due to absorption through the oral mucosa. Intravenous administration delivers drugs directly into the bloodstream, avoiding first-pass metabolism. Rectal administration partially bypasses the liver, but some drug metabolism can still occur. Therefore, the correct answer is A (Oral), as it is affected by first-pass metabolism.

Correct Answer: C

Rationale: Increased binding of drugs to plasma proteins leads to a decrease in the concentration of free drug available for elimination. This results in a longer half-life of the drug as it takes longer for the bound drug to be released and metabolized. This does not directly impact drug-drug interactions or renal filtration, as binding to plasma proteins affects the distribution and elimination of the drug. Therefore, the correct answer is C.

Correct Answer: A

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.