The quality of evidence is downgraded by study limitations (unclear allocation concealment and lack of blinding).
A Cochrane review [Abstract] 1 included 14 studies with a total of 1 917 adult subjects with 24 different cancers. Thirteen studies examined chemotherapy-induced nausea and vomiting. Oral olanzapine was administered during highly emetogenic or moderately emetogenic chemotherapy (12 studies), chemoradiotherapy (1 study) or palliation (1 study). All participants also received standard antiemetic treatment.
Olanzapine compared to placebo/no treatment: Olanzapine increased the likelihood of no nausea or vomiting during chemotherapy from 25% to 50% (RR 1.98, 95% CI 1.59 to 2.47; NNTB 5, 95% CI 3.3 to 6.6; 3 studies, n=561) when added to standard therapy. There was no statistically significant difference in serious adverse events (RR 2.46, 95% CI 0.48 to 12.55; 7 studies, n=889).Olanzapine seemed to increase statistically non-significantly other adverse events (RR 1.71, 95% CI 0.99 to 2.96; 4 studies, n=332) and increased somnolence and fatigue compared to no treatment or placebo (RR 2.33, 95% CI 1.30 to 4.18; 5 studies, n= 464). There was no difference in breakthrough nausea and vomiting (RR 0.38, 95% CI 0.10 to 1.47; 2 studies, n=501; I² = 54%) compared to placebo or no treatment. Olanzapine reduced delayed nausea (RR 1.71, 95% CI 1.40 to 2.09; 3 studies, n=585) and vomiting (RR 1.28, 95% CI 1.14 to 1.42; 5 studies, n=702).
Other comparisons: Olanzapine increased freedom from overall nausea (RR 2.95, 95% CI 1.73 to 5.02) and overall vomiting (RR 3.03, 95% CI 1.78 to 5.14) compared to metoclopramide (1 study, n=112). Olanzapine increased the likelihood of 50% or greater reduction in nausea or vomiting at 48 hours (RR 1.82, 95% CI 1.11 to 2.97) and 24 hours (RR 1.36, 95% CI 0.80 to 2.34) compared to 5-HT3 antagonists (1 study, n=62). Olanzapine reduced overall nausea (RR 1.73, 95% CI 1.37 to 2.18), overall vomiting (RR 1.27, 95% CI 1.10 to 1.48), delayed nausea (RR 1.66, 95% CI 1.33 to 2.08) and delayed vomiting (RR 1.25, 95% CI 1.07 to 1.45) compard to dexamethasone (1 study, n=229).
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