An Audit of Therapeutic Drug Monitoring Services for Older Antiseizure Medications in a Tertiary Care Hospital in India

Historically, the practice of therapeutic drug monitoring (TDM) started with the older antiseizure medications (ASMs) and is still widely utilized for these drugs. The present study was planned as an audit of the TDM services for the older ASMs of a tertiary care hospital in Northern India. An audit for the TDM services was performed from January 2015 to June 2021 for the requisitions received for the older ASMs. Additionally, a critical appraisal for the services was also performed to evaluate the effectiveness of the services along with a trend analysis. A total of 996 TDM service requests were received in the study period; 798 records were included for the analysis. The maximum number of requests were for phenytoin across all age groups, accounting for 59.8% of the total requisitions except the neonatal age group where phenobarbitone was the most common (100%). Maximum concordance with reason for TDM and laboratory result was obtained for phenytoin toxicity (73.6%), whereas most discordance was observed for phenobarbitone (25%), which could be possibly explained by clinical deterioration in the neonates. A gradual decline was observed in the TDM requests received for carbamazepine over the 5-year study period, which may indicate a decrease in the usage of this drug, due to increased physician awareness of the safety signals like SJS-TEN. TDM of older ASMs still hold relevance in a resource-constrained setting and can be the steppingstone for academic centers planning to set up their own TDM services.