Blood concentration, efficacy, and adverse events of phenobarbital: A prospective study in rural China

This study evaluated the relationship between blood concentration of phenobarbital (PB) and its efficacy as well as adverse events in people with epilepsy in rural China.

People with epilepsy being treated with PB monotherapy were recruited and followed up for averagely 2.5 years. Data of clinical characteristics were collected using a standardized questionnaire by face-to-face interviews both at baseline and follow-up. Plasma concentration of PB was detected by the high-performance liquid chromatography.

Data on treatment response and PB blood concentration was obtained from 225 subjects. Among them, 119 (52.9%) were recognized as effective cases and 106 (47.1%) as ineffective cases. In the effective group, the blood concentration of 95% subjects ranged from 1.22 μg/ml to 41.36 μg/ml with a median at 13.18 μg/ml (IQR = 8.32-20.19 μg/ml). The PB concentration of 95% of the subjects in the ineffective group ranged from 2.73 μg/ml to 70.16 μg/ml with a median at 19.80 μg/ml (IQR = 11.30-30.40 μg/ml), which was significantly higher than that of the effective group (p < 0.001). Multivariate logistic regression analysis showed that PB concentration ≥26.38 μg/ml was related to a 4.5-fold (95% confidence interval [CI], 1.85-11.08) higher risk of inefficacy. A receiver operation characteristic curve was performed to determine the cutoff value of concentration for PB efficacy at 19.02 μg/ml.

Blood concentration may be an important indicator for clinical decision making when PB monotherapy cannot achieve a good efficacy and more attention should be paid on it in clinical practice especially in resource-poor settings.