BACKGROUND. Recent studies have suggested that antiemetic therapy with a triple combination of the neurokinin-1 receptor antagonist MK-869, a serotonin (5-HT3) antagonist, and dexamethasone provides enhanced control of cisplatin-induced emesis compared with standard therapy regimens. The authors compared the antiemetic activity of a dual combination of MK-869 and dexamethasone with that of a standard dual combination of ondansetron and dexamethasone to characterize further the efficacy and tolerability profile of MK-869. METHODS. This was a multicenter, double-blind, randomized, active agent-controlled study of 177 cisplatin-naïve patients with malignant disease. On Day 1, MK-869 was given intravenously as its water-soluble prodrug, L-758,298. Patients were randomized to one of three groups as follows. Group I received L-758,298 100 mg intravenously (i.v.), then dexamethasone 20 mg i.v., and cisplatin ≤ 70 mg/m2 on Day 1 followed by 300 mg MK-869 (tablet) orally on Days 2-5; Group II received L-758,298 100 mg i.v., then dexamethasone 20 mg i.v., and cisplatin ≤ 70 mg/m2 on Day 1 followed by placebo on Days 2-5; and Group III received ondansetron 32 mg i.v., then dexamethasone 20 mg i.v., and cisplatin ≤ 70 mg/m2 on Day 1 followed by placebo on Days 2-5. Emesis was recorded over Days 1-5 in a diary. Nausea was assessed every 24 hours by visual analog scale. Additional medication was available for emesis or nausea at any time. The primary efficacy parameters of interest were the proportion of patients without emesis and the proportion without emesis or rescue therapy on Day 1 (acute phase) and on Days 2-5 (delayed phase). RESULTS. No serious adverse events were attributed to L-758,298 or MK-869. On Day 1, the proportions of patients with no emesis and no use of rescue medication were 44% of patients in Group I, 36% of patients in Group II, 40% of patients in Groups I and II combined, and 83% of patients in Group III (P < 0.001 for Group III vs. the combined Groups I and II). The proportions of patients with no emesis and no use of rescue medication on Days 2-5 were 59% of patients in Group I, 46% of patients in Group II, and 38% of patients in Group III (P < 0.05 for Group I vs. Group III). The proportions of patients who were without emesis on Day 1 were 49% of patients in Group I, 47% of patients in Group II, and 84% of patients in Group III (P < 0.01 for Group I or II vs. Group III). On Days 2-5, however, the proportions of patients who were without emesis on Days 2-5 were 65% of patients in Group I, 61% of patients in Group II, and 41% of patients in Group III (P < 0.05 for Group I or II vs. Group III). Nausea scores in the acute phase were lower for Group III than for Group I, Group II, or Groups I and II combined (P < 0.05), although there was no significant difference among groups either for the delayed phase or overall for Days 1-5. CONCLUSIONS. Although the L-758,298 and dexamethasone combination reduced acute (Day 1) emesis compared with historic rates, dual therapy with ondansetron and dexamethasone was superior in controlling acute emesis. Continued dosing with MK-869 may enhance control of other measures of delayed emesis, such as the use of rescue medication, although confirmation is required before a definitive conclusion may be drawn. MK-869 given as dual therapy with dexamethasone was superior to ondansetron with dexamethasone for the control of delayed emesis (Days 2-5) and control of the need for rescue medication on Days 2-5. © 2002 American Cancer Society.