Which of the following is NOT a phase I drug metabolising process?

Correct Answer: B

Rationale: The correct answer is B: Conjugation. Phase I drug metabolizing processes involve functionalization reactions to make the drug more polar for easier elimination. Conjugation reactions, on the other hand, occur in Phase II metabolism and involve the addition of endogenous molecules to the drug to further enhance its solubility for elimination. Hydrolysis, reduction, and oxidation are all Phase I processes that involve breaking down or modifying the drug molecule without conjugation. Therefore, Conjugation is NOT a phase I drug metabolizing process.

Correct Answer: A

Rationale: The correct answer is A: Serotonin (5-HT) is NOT a monoamine neurotransmitter. Monoamine neurotransmitters have a single amino group and are derived from amino acids like tyrosine. Serotonin, however, is derived from tryptophan and belongs to the indoleamine class. Dopamine, Noradrenaline, and Adrenaline are all monoamine neurotransmitters derived from tyrosine and phenylalanine. Therefore, Serotonin does not fit the criteria for being a monoamine neurotransmitter, making choice A the correct answer.

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.