Screening of Antiemetic Drugs

Introduction & rationale

• Definition — Antiemetic screening = the preclinical, mostly in vivo evaluation of candidate compounds for their ability to suppress experimentally-induced emesis (retching + vomiting) or its non-vomiting surrogates, using species with a functional vomiting reflex and standardised emetogenic challenges.
• Why it matters — nausea and vomiting complicate pregnancy, GI/renal/hepatic disease, motion, post-operative states and — most importantly for screening — cytotoxic cancer chemotherapy; emesis is also a protective reflex expelling ingested toxins.
• Three-fold purpose of the models — (i) map the pathways generating nausea and reflex vomiting; (ii) identify pharmacological approaches for new antiemetics; (iii) understand disease states in which nausea/vomiting are cardinal.
• Central constraint — emesis comparable to man occurs only in a few animal species — this single fact drives the entire species-selection logic; apomorphine serves either as the reference emetic standard or as the challenging emetogen.
• Terminology (defines the endpoints) — Nausea — subjective, non-observable urge (inferred only indirectly in animals); retching — rhythmic inspiratory efforts against a closed glottis without expulsion; vomiting — coordinated forced expulsion of gastric contents; where retch frequency is too high to score (e.g. Suncus) these are pooled as emetic episodes.
• Temporal classes — acute (minutes–hours, resolves <24 h) · delayed (>24 h, peaks 48–72 h, responds poorly to 5-HT₃ antagonists) · anticipatory (conditioned, before the stimulus) · breakthrough (despite prophylaxis) — each dictates model choice.