Background Patients in the acute phase of agitation can require the administration of multiple drugs by intramuscular injection in order to temporarily stabilise their condition. Administration of multiple psychotropic medications in a single syringe can be beneficial to both the patient and healthcare professionals. However, there are very little data in the literature regarding psychotropic drug compatibility in syringes for acute agitation.

Objective The aim of this study was to assess the visual compatibility of various combinations of 12 intramuscular psychotropic medications in syringes, and to validate compatibility with the use of a particle counter. The medications evaluated were benztropine mesylate, diazepam, dimenhydrinate, diphenhydramine hydrochloride, haloperidol lactate, hydroxyzine, lorazepam, loxapine, methotrimeprazine, midazolam, olanzapine and zuclopenthixol acetate.

Methods Compounded solutions of medication combinations underwent visual inspection initially and after 0.25, 0.5, 1, 2 and 4 hours using a white background and a black background. In order to validate the compatibility results, the presence of particulate matter was determined by light obscuration.

Results This study identified 35 combinations that were visually compatible and 35 that were visually incompatible. We chose eight highly clinically relevant combinations to test using the requirements of the United States Pharmacopoeia (USP) chapter <788> (Particulate Matter in Injections). Of those eight, six were physically compatible, including the triple combinations of lorazepam and haloperidol with either benztropine or diphenhydramine.

Conclusion These physical compatibility results will give healthcare professionals an idea of the possible compatible combinations of psychotropic drugs in syringes, and thus complete some of the missing data in the literature.