Allergic reaction to depot risperidone but not to oral risperidone.

Sir: Oral risperidone is an effective and well-tolerated atypi-cal antipsychotic 1 that has been in widespread clinical usage for over 10 years. In recent years, a long-acting injectable form of depot risperidone with a delivery system different from other depot antipsychotics became available in the United States following several years of marketing in other countries. This formulation consists of risperidone microencapsulated in 7525 polylactide-co-glycolide (PLG) at a concentration of 381 mg of risperidone per gram of microspheres 2 ; the PLG slowly hy-drolyzes to release risperidone, allowing administration every 2 weeks. Depot risperidone has been shown to be therapeutically equivalent to oral risperidone and is also well tolerated. 3,4 We describe a patient who developed a severe allergic reaction concomitant with administration of depot risperidone, although he had taken oral risperidone with no side effects. Case report. Mr. A, a 46-year-old man with a long history of schizophrenia, was hospitalized in January 2005 with paranoia and disorganization of thought processes after stopping his medication (ziprasidone, 80 mg b.i.d.) and using cocaine. Review of his records revealed that he had been taking several different antipsychotics, including risperidone, 4 mg at bedtime, in an attempt to better control his symptoms. However, he eventually stopped taking the medication, leading to his hospitalization. He had no history of any drug allergies or hypersensitivity reactions. Because of Mr. A's history of noncompliance, plans were made to initiate treatment with depot risperidone. He was given oral risperidone, 3 mg daily, for 3 days without problems and was then given depot risperidone, 25 mg IM. Within 4 to 6 hours of the injection, he developed urticaria with an erythema-tous, raised pruritic rash covering large areas of his body. He was administered oral diphenhydramine, 50 mg t.i.d., and topical hydrocortisone cream (1%). The next day, the rash had worsened and faint expiratory wheezing was present bilaterally. He was given dexamethasone, 4 mg IM, and the rash began to improve over the next 48 hours, resolving after about 5 days. Mr. A was then treated with ziprasidone and was ultimately discharged on a dosage of 80 mg b.i.d. A MEDLINE search and review of published articles on depot risperidone revealed no reports of allergic reactions to the formulation. A study using doses as high as 75 mg did not report the occurrence of rash or similar reactions. 5 In the present case, the rapid onset of rash concomitant with …