Visual Compatibility of Various Injectable Neuroleptic Agents with Benztropine and Lorazepam in Polypropylene Syringes

Background: The nursing staff at the authors’ hospital are frequently called upon to administer medications by intramuscular injection during psychiatric emergencies. Many of these medications are considered incompatible when mixed together, and up to 3 separate injections may be required for a single patient. The need for multiple injections increases the risk of needle-stick injury in these situations. Objectives: The visual compatibility of various combinations of haloperidol, loxapine, chlorpromazine, benztropine, and lorazepam was studied, with the aim of reducing the number of injections required and hence reducing the risk to staff and increasing patient comfort. Methods: To emulate the setting of a nursing unit, single syringes of selected combinations of medications were prepared on a clean tabletop under fluorescent light at room temperature. The syringes were visually inspected for haze, immiscibility, precipitation, and colour change at 15, 30, and 45 min and at 1, 2, 3, and 4 h after mixing. Results: The haloperidol–benztropine mixtures and the haloperidol–benztropine–lorazepam mixtures were compatible on visual inspection throughout the observation period. The loxapine–benztropine and loxapine–lorazepam mixtures showed immediate incompatibility, as did the chlorpromazine–lorazepam and benztropine–lorazepam mixtures. A table of compatibilities was produced for quick reference on nursing units. Conclusions: Mixtures of haloperidol and benztropine and of haloperidol, benztropine, and lorazepam are compatible for periods of up to 4 h. The combinations of loxapine and benztropine, loxapine and lorazepam, chlorpromazine and lorazepam, and benztropine and lorazepam should not be mixed before administration.