Appropriateness of therapeutic drug monitoring of valproic acid in Hospital Tengku Ampuan Rahimah / Nurul-Shazalina Zubir

TDM, although very useful in individualizing dose regimen, are often done inappropriately. For a drug lacking extensive research and having less predictable pharrnacokinetics such as VPA, there is always the potential of overlooking certain factors while ensuring its optimum use. The main aim of this study is to compare the methods applied by the pharmacists in HT AR in individualizing dose regimen to the methods applied by the researcher based on literature review. Retrospective review of both TDM forms and laboratory values of HT AR in-patients taking VP A for epilepsy were carried out. Calculations of expected levels, loading dose and maintenance dose made by both the researcher and the TDM pharmacists in HTAR are compared using Wilcoxon Signed Ranks Test (p < 0.05) to detect significant difference between the two median values. There were significant difference (p<0.05) for both expected level (z ratio= ±6.900) and maintenance dose (z ratio= ±5.232) but no significant difference was found (p>0.05) for the loading dose (z ratio = ± 0.980). For expected level and loading dose, the calculation methods differ from those applied by HT AR pharmacist only in the choice of values of pharmacokinetic parameters and the target steady-state concentration respectively. However, the researcher has found that two important factors, hepatic function and concomitant use of hepatic enzyme inducers were not taken into account in the calculations of maintenance dose of VPA applied in HTAR. A guideline for the calculations of VP A was proposed along with this research.