Title: Therapeutic Drug Monitoring of Carbamazepine and Phenytoin: Monotherapy versus Combination Therapy
Authors: Dr Rupali Bandagi, Dr Bharti Daswani, Dr Balasaheb Ghongane
DOI: https://dx.doi.org/10.18535/jmscr/v5i5.230
Abstract
Objectives: To study serum concentration of carbamazepine and phenytoin, when given singly and together.
Method: This is a non-interventional, cross-sectional, analytical study done in a tertiary care hospital. Consenting epileptics on stable antiepileptic regime for at least past 2 weeks and taking carbamazepine 200mg BD (group I) or phenytoin 100mg BD (group II) or carbamazepine (200)+phenytoin (100)mg BD (group III) were included. There were 20 patients in each group. Blood samples were collected 12 hours after the last dose and serum was analyzed for carbamazepine, phenytoin concentrations using HPLC method and data was compared using unpaired t-test.
Results: Mean serum carbamazepine concentration in group I was (7.37±3.67)mcg/ml and in group III (5.65±2.37) mcg /ml (p=0.09). Mean serum phenytoin in group II was (15.16±6.48) mcg /ml and in group III (12.66±5.5) mcg/ml (p=0.2). When used singly carbamazepine showed 30% subtherapeutic and 20 % toxic concentrations. Whereas in combination group the plasma concentrations of carbamazepine were found to be therapeutic, subtherapeutic and toxic ranges in 55%, 40% and 5% patients, respectively. In phenytoin monotherapy group the concentrations were subtherapeutic in 15%, therapeutic in 65% and in toxic range in 20% patients, whilst in combination group the concentrations obtained were 50%, 40 and 10% respectively.
Conclusion: Co-administration of carbamazepine and phenytoin do not affect the serum concentrations of either group significantly. It’s possible that Indian population has different therapeutic range of antiepileptic drugs from that given in standard literature. But larger study needs to be done to confirm the results.
Keywords: Therapeutic drug monitoring, HPLC, Phenytoin, Carbamazepine.
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