['To determine if the timing of administration affects the dose of dolasetron necessary to prevent postoperative nausea and vomiting (PONV).', 'Pooled data from 8 randomized, multicenter, double-blind, placebo-controlled studies with common endpoints.', 'University hospital.', 'A total of 4,587 ASA physical status I, II, and III patients, including 4,124 females undergoing primarily gynecologic procedures and 463 males undergoing various procedures (i.e., thyroidectomy or orthopedic, ophthalmologic, urologic, ENT, or laparoscopic surgery).', 'Balanced general anesthesia was used during all procedures. Patients received a dose of dolasetron either for prevention of PONV (25 or 50 mg IV at induction; 25, 50, 100, or 200 mg orally 1 to 2 hours pre-induction; or 12.5, 25, 50, or 100 mg IV at end of anesthesia) or for treatment of PONV (12.5, 25, 50, or 100 mg IV). One PONV prevention study had an ondansetron (comparator) group.', 'Outcome measures over a 24-hour study period included complete response (defined as no vomiting/retching and no need for rescue medication), percentage of patients without nausea [defined as nausea visual analog scale (VAS) score < 5 mm], and maximum nausea according to VAS score.', 'A 12.5-mg IV dose of dolasetron resulted in a complete response rate that was statistically significantly higher than placebo and comparable to higher dolasetron doses (25 mg to 100 mg IV) when administered either near the end of anesthesia for prevention of PONV or at the onset of symptoms for treatment of PONV. In contrast, when administered at induction of anesthesia, a statistically significant treatment response was observed with dolasetron 50 mg IV, but not at a lower dose.'] Does timing of administration of dolasetron affect dose necessary to prevent postoperative nausea and vomiting?