Hong Kong Med J 2001;7:15-21 | Number 1, March 2001
Valproic acid and thrombocytopenia: cross-sectional study
CH Ko, CK Kong, PWT Tse
Developmental Disabilities Unit, Department of Paediatrics, Caritas Medical Centre, 111 Wing Hong Street, Shamshuipo, Hong Kong
OBJECTIVES. To investigate the relationship between platelet count and serum valproic acid level, age, duration of valproic acid therapy, and polytherapy, and to determine the clinical significance of thrombocytopenia associated with high-dosage valproic acid therapy.
DESIGN. Cross-sectional study.
SETTING. Residential unit for neurologically impaired children and paediatric out-patient clinic, Hong Kong.
PATIENTS. Ninety-six neurologically impaired children who were treated with valproic acid between 1 July 1991 to 3 June 1999. The comparison group consisted of 48 children receiving antiepileptic drugs other than valproic acid.
INTERVENTION. Low- or high-dosage valproic acid, using the threshold value of 40 mg/kg/d.
MAIN OUTCOME MEASURES. Platelet count and liver function, duration of valproic acid treatment, dosage, and trough serum valproic acid concentration.
RESULTS. Seventeen (17.7%) patients in the treatment group developed thrombocytopenia, compared with two (4.2%) in the comparison group (P450 micromol/L or a daily dose of >40 mg/kg were more likely to develop thrombocytopenia. Thrombocytopenia was mild in most cases.
CONCLUSIONS. A trough valproic acid level of >450 micromol/L or a daily dose of >40 mg/kg should alert the clinician to the risk of developing thrombocytopenia. The risk is further increased for older children. The platelet count should be monitored for patients receiving a high concentration of valproic acid who are also receiving drugs that would affect homeostasis, or who are undergoing surgical procedures.
Key words: Anticonvulsants/adverse effects; Thrombocytopenia/chemically induced; Valproic acid/adverse effects
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