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)/mm3) occurred in 25 (9%) patients, and moderate thrombocytopenia (platelet count of 40-100 x 103/mm3) occurred in 6 (2%) patients. Age older than 65 years (p=0.02) and VPA dosage greater than 1,000 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 receiving VPA, with the elderly at greatest risk.