Which of the following drugs can be used to treat or prevent severe chemotherapy-induced emesis, motion sickness, dystonias, and hay fever?

Which of the following drugs can be used to treat or prevent severe chemotherapy-induced emesis, motion sickness, dystonias, and hay fever?

(A) diphenhydramine
(B) diphenoxylate
© metoclopramide
(D) ondansetron
(E) scopolamine

Explanation:

(A) Diphenhydramine, an older H1-blocking antihistamine, has actions on multiple receptors, including H1 (but not H2) histamine receptors, alpha adrenoceptors, muscarinic receptors, and dopamine receptors. Its value in reducing emesis in the situations listed has been reported extensively, and it is a first-line agent for acute dystonias associated with antipsychotic drugs. It is one of the most sedating antihistamines and has been used as a night-time hypnotic in hospitals. It is the only drug in the list with the broad spectrum of effects described. Diphenoxylate (choice B) is an opioid with primarily gastrointestinal effects (it is the primary ingredient in Lomotil) but no analgesic or addicting effects. Metoclopramide (choice C) is a dopamine antagonist that has some efficacy in preventing chemotherapy-induced vomiting. Ondansetron (choice D) is a 5-HT3 antagonist that is very useful in chemotherapy-induced vomiting. Scopolamine (choice E) is effective in preventing motion sickness.