Lingual distonia due to quetiapine and valproate interaction: A case report

Acute dystonic reactions (ADS) are characterized by sustained abnormal postures or muscle spasm that develop in association with the use of dopaminergic receptor-blocking agents. Possible risk factors of ADR are: male gender, young age, diagnosis of bipolar disorder, disuse of anticholinergic prophylaxis. Atypical antipsychotics carry a minimal risk of ADS compared to typical neuroleptics. AC, 17-year-old boy was hospitalized for the first manic episode. He was diagnosed bipolar disorder manic episode due to DSM-IV criteria. Quetiapine 900 mg/day and valproic add 1500 mg/day was initiated. 13 days after the initiation of the treatment lingual distonia which was improved within 20 minutes following 5 mg biperiden injection was observed. We stopped quetiapine and started olanzapine 10 mg/day-valproate 1500 mg/day. At 25 day of hospitalization, our patient's symptoms calmed down and he was discharged. No side effects have been observed during control assesments for the next three months. Quetiapine causes a similar degree of EPS as placebo was stated in many case reports. Besides this, there are some case studies that has reported extrapyramidal syndromes during queitapine. Quetiapine is mostly metabolized in the liver via the cytochrome p450 isoenzyme CYP3A4 and, in a smaller part, via CYP2D6. In vitro studies showed that valproic acid inhibits CYP2C and, to a smaller degree, also CYP3A4. A clinical study published in 2006, showed that comedication with valproic acid increases plasma concentration of quetiapine by approximately 77%. In this case, lingual dystonia that was observed 13 days after the initiation of the treatment due to elevated quetiapine plasma concentration is linked to quetiapine and valproate interaction. Limitation of the study was the lack of the measurement of plasma concentration of quetapine. Considering this case it is important to underline that atypical antipsychotics may cause ADS. Clinicians must be careful about the comedication with valproic add because of drug interactions.