Injection site reactions after intramuscular administration of haloperidol decanoate 100 mg/mL

The authors report four cases of injection site reaction after intramuscular administration of haloperidol decanoate 100 mg/mL. In each case, the injection site became edematous, red, pruritic, and tender, and a palpable mass remained for up to 3 months. No systemic symptoms were reported. All four patients had previously received the 50 mg/mL haloperidol decanoate injection without incident. Two of these events followed the initial injection of haloperidol decanoate 100 mg/mL. Rechallenge with the 100 mg/mL product in one case and the 50 mg/mL product in two resulted in similar reactions. The incidence of this reaction at the authors' facility is estimated to be 7.7%. The authors speculate that the reaction is most likely to be related to the concentration of haloperidol decanoate in the injection.