Domperidone, ondansetron and olanzapine can prolong the QT interval. The clinical use of combinations of these drugs is not uncommon. Our study aimed to determine the presence of any QTc prolonging effect of the combination when used as antiemetic in patients receiving cancer chemotherapy. We carried out a prospective, observational study of patients with malignancy who were to receive domperidone, ondansetron and olanzapine-containing antiemetic regimen. Electrocardiograms were recorded before and during the administration of antiemetics, for three consecutive days. A blinded assessor determined the QTc interval using Bazett and Fridericia formulae. Thirty-six patients completed the study; 23 (63.9%) were females. There was a statistically significant change in QTc with time (Fridericia, χ2(4) = 15.629, p = 0.004; Bazett, χ2(4) = 15.910, p = 0.003); QTc on Day 1 was more than that during baseline (p < 0.001); these differences were significant in females (Fridericia, χ2(4) = 13.753, p = 0.008; Bazett, χ2 (4) = 13.278, p = 0.010) but not in males (Fridericia, χ2 (4) = 4.419, p = 0.352; Bazett, χ2(4) = 4.280, p = 0.369). Two female patients had an absolute QTc prolongation (Bazett correction) of > 500 ms. However, no clinically significant adverse events occurred. The findings show that QTc prolongation is a concern with olanzapine alone and in combination with domperidone and ondansetron, and needs to be investigated further.
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