Acute dystonia following the two-injection start of aripiprazole once-monthly

We present a case of an acute dystonic reaction (ADR) following the two-injection start of aripiprazole once-monthly (AOM) in a patient who previously tolerated equivalent doses of oral aripiprazole (20 mg daily). The ADR occurred two times within 3 weeks of the two-injection start and was effectively treated with benztropine each time. The patient tolerated maintenance treatments of AOM 400 mg without recurrent ADR. A key risk factor in this patient was a prior ADR to a different antipsychotic. We also speculate on the potential roles of strenuous physical activity and infection in increasing the sensitivity to the two-injection initiation regimen compared with the conventional one-injection start. The two-injection start of AOM has been approved by regulatory bodies on the basis of population pharmacokinetic modelling. Our case may, therefore, identify a new safety concern with this alternative initiation option that was not captured in the modelling.