Prevalence and risk of thrombocytopenia with valproic acid: Experience at a psychiatric teaching hospital

Study Objective. To investigate the prevalence and potential risk factors of thrombocytopenia in hospitalized patients receiving valproic acid (VPA) for psychiatric indications (excluding epilepsy). Design. Retrospective study. Setting. University-affiliated psychiatric facility. Patients. Two hundred sixty-four patients treated with VPA. Intervention. Data from patients hospitalized between January 1, 1994, and December 31, 1998, who were receiving VPA and had at least one platelet count recorded. Measurements and Main Results. Of 264 VPA-treated patients, 31 (12%) met our criteria for thrombocytopenia. Mild thrombocytopenia (platelet count of 101-150 x 10(3)/mm(3)) occurred in 25 (9%) patients, and moderate thrombocytopenia (platelet count of 40-100 x 10(3)/mm(3)) occurred in 6 (2%) patients. Age older than 65 years (p=0.02) and VPA dosage greater than 1000 mg/day (p <0.001) were identified as significant risk factors for developing thrombocytopenia. Conclusion. The estimated prevalence of thrombocytopenia is 12% in the general psychiatric population recieving VPA, with the elderly at greatest risk.