A risk for obstruction of the airways in the parenteral use of levomepromazine with benzodiazepine

Arrhythmogenic effects of phenothiazines appear to be associated with sudden death, whereas respiratory complications have received little attention. In this report we describe 5 cases with accompanying obstruction of the airways after intramuscular injections of levomepromazine (LPZ), a potent sedative phenothiazine, in combination with intravenous injections of benzodiazepine (BZ) during a 3-month period in a psychiatric intensive care unit. Two out of 5 cases were unpredictable because obstruction of the airways occurred 2 hours or more after the last injection. As compared with patients who received parenteral (intravenous or intramuscular) injections during the same period, the dose of intramuscular LPZ was significantly large in the 5 cases with obstruction of the airways. All 5 of these cases received intramuscular LPZ 0.52 mg/kg or more. In contrast, there was no patient with obstruction of the airways who received only intramuscular LPZ, the combination of LPZ and HDL, or BZ and HDL. The occurrence of obstruction of the airways among patients who received both intramuscular LPZ and intravenous BZ was significantly higher than among patients who received other drug regimes. These preliminary results suggest that the intramuscular use of LPZ with intravenous BZ may be a risk for obstruction of the airways.