Design: Double blind, crossover food challenge with crude peanut oil and refined peanut oil.

Setting: Dedicated clinical investigation unit in a university hospital.

Subjects: 60 subjects allergic to peanuts; allergy was confirmed by challenge tests.

Outcome measures: Allergic reaction to the tested peanut oils

Results: None of the 60 subjects reacted to the refined oil; six (10%) reacted to the crude oil. Supervised peanut challenge caused considerably less severe reactions than subjects had reported previously.

Conclusions: Crude peanut oil caused allergic reactions in 10% of allergic subjects studied and should continue to be avoided. Refined peanut oil did not pose a risk to any of the subjects. It would be reasonable to recommend a change in labelling to distinguish refined from crude peanut oil.

University Department of Child Health,
Mailpoint 803,
Southampton General Hospital,
Southampton SO16 6YD
Jonathan O'B Hourihane, clinical research fellow
Simon J Bedwani, medical student
Taraneh P Dean, senior research fellow
John O Warner, professor

Correspondence to: Dr Hourihane.

Design: Quantitative systematic review of published randomised controlled trials.

Data sources: Seven trials from 1991 to January 1996 retrieved from a systematic literature search (Medline, reference lists, hand searching of anaesthetic journals, manufacturer's database); no restriction on language.

Main outcome measures: Estimation of efficacy (incidence of complete control of further nausea and vomiting) by using odds ratios and the "number needed to treat" method for early (within 6 hours of administration) and late (within 24 hours) periods.

Results: Four placebo controlled trials with 1043 patients studied intravenous ondansetron 1 mg, 4 mg, or 8 mg. All doses were more efficacious than placebo in preventing further episodes of nausea or vomiting. For combined data, the point estimates for the number needed to treat were between 3.1 (8 mg) and 3.8 (1 mg) for early efficacy and between 4.1 (8 mg) and 4.8 (1 mg) for late efficacy, without significant differences between doses. No difference was found between ondansetron and droperidol in two trials with 129 patients or between ondansetron and metoclopramide in one trial with 80 patients.

Conclusions: Further nausea and vomiting could be prevented with ondansetron compared with placebo in 25% of patients who had nausea or vomiting (number needed to treat, about 4). There was no evidence of a clinically relevant dose-response between 1 mg and 8 mg or a difference between ondansetron and either droperidol or metoclopramide in a limited dataset. A false impression of ondansetron's efficacy may arise because a quarter of all relevant published reports are duplicates, and reporting of study results is uncritical.

Pain Research, Nuffield Department of Anaesthetics,
Churchill Oxford Radcliffe Hospital,
Oxford OX3 7LJ
Martin R Tramèr, research fellow
R Andrew Moore, consultant biochemist
Henry J McQuay, clinical reader in pain relief

Department of Clinical Pharmacology,
Radcliffe Infirmary,
Oxford OX2 6HE
D John M Reynolds, consultant clinical pharmacologist