Massive increase in serum creatine kinase during olanzapine and quetiapine treatment, not during treatment with clozapine

Sir. Within the last years, there have been several publications describing creatine kinase (CPK) increases associated with neuroleptic treatment in the absence of neuroleptic malignant syndrome (NMS). Meltzer et al. (1996) reported a marked increase in CPK levels in approximately 10% of patients treated with clozapine, risperidone, melperone, olanzapine, haloperidol, or loxapine. In three cases, treatment with olanzapine was associated with an increase in CPK without NMS. There have also been reports associating olanzapine with NMS (Johnson and Bruxner 1998; Emborg and Kongevej 1999; Hickey et al 1999). In this letter, we describe a case in which there was a massive CPK increase during olanzapine treatment without symptoms of NMS, which disappeared during treatment with clozapine and returned after starting quetiapine.