Therapeutic Drug Monitoring: Comparison of Direct Proportion Approach Versus Conventional Method for Dose Adjustment of Carbamazepine
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Abstract
Introduction: Therapeutic Drug Monitoring (TDM) is useful and significant for drugs with a narrow therapeutic index. One of the common drugs requiring TDM is carbamazepine. Conventional pharmacokinetic approach in drug dosage adjustment presents a problem of applying a rather complex formula and multiple steps in calculating the dosage adjustment. This study aimed to determine the magnitude of difference and the level of agreement between the conventional pharmacokinetic equation method and the direct proportion approach in CBZ dose adjustment. Materials and methods: This was a retrospective study conducted at Therapeutic Drug Monitoring Department, Sultan Abdul Halim Hospital, Kedah, Malaysia. Patients’ demographic and related clinical data was collected using pre-designed case report form. Results: A total of 5 patients who fulfilled the inclusion criteria were included for analysis. The propose dose adjustments were identical using the conventional (multiple steps) approach and the direct proportional method (1 step), p = 1.00. One sample T test was used to analyze the mean differences of proposed dose adjustments based on direct proportion method to a value of zero (no difference). The mean differences of proposed dose adjustments were non statistically significant (p > 0.05). Bland-Alman analysis showed good agreement of the proposed dose adjustments by direct proportion method with the conventional (standard) approach, p = 1.00. Conclusion: The results from this study gave strong assurance and evidence that direct proportion method could be used safely as an alternative to the conventional pharmacokinetic equation method (standard) in the calculation of new maintenance dose for CBZ.
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