Pharmacist‐managed therapeutic drug monitoring service in an intensive care unit

Abstract

Introduction: In the intensive care unit (ICU), drug dosing presents challenges due to variable pharmacokinetics, such as expanded apparent volume of distribution, owing to fluid resuscitation, which can result in inadequate dosing, and end-organ dysfunction, which impacts drug clearance or metabolism. Pharmacists in the ICU are positioned to advise on individual drug dosing using therapeutic drug monitoring to maximise the efficacy of medications while minimising drug toxicity(1). Achieving therapeutic serum concentrations for medications with a narrow therapeutic range is crucial for critically ill patients. Objectives: The aim of this study was to evaluate the impact of a pharmacist-managed therapeutic drug monitoring service in a mixed ICU of an acute general hospital on dosing optimisation and minimisation of potential adverse drug events (ADEs). Methods: The study was conducted over three months in 2023, where clinical pharmacists reviewed the medication charts of patients admitted to the ICU and participated in daily ward rounds as part of the multidisciplinary team. Data about TDM activities carried out by pharmacists were compiled. The pharmacists provided clear guidance on timing of TDM in relation to drug administration, interpreted TDM results and provided specialised pharmacological advice following TDM results, including adjustments in dose or frequency for subse- quent doses, in collaboration with ICU clinicians. Recommendations by pharmacists also took into account the patient’s clinical condition, changes in renal replacement therapies, administration modes, and drug-drug interactions. All pharmacists’ recommendations were evaluated by a panel of experts for their potential to prevent a potential ADE. Results: Over the three-month period, among 164 patients admitted to the ICU, 35 patients needed TDM recommendations from pharmacists, resulting in a total of 93 interventions. The medications most frequently involved in TDM were antimicrobials (71%), comprising aminoglycosides and vancomycin, anti-epileptics (13%) and digoxin (12%). Pharmacist recommendations included requesting TDM (52%), adjusting daily dosage (16%), modifying dosing intervals or infusion rates (17%), withholding medications in cases of supratherapeutic levels (12%), changing method of administration (2%) or proposing alternative therapy in case of severe interactions (1%). The expert panel assessed the interventions to have a medium (20%) or low (80%) probability of preventing a potential ADE. Interventions with a medium probability of preventing a potential ADE included omitting the planned dose of aminoglycoside in a patient with kidney injury who was receiving a continuous replacement therapy free period, and carrying out TDM until the trough was within range; requesting TDM and proposing the need for alternative treatment due to interaction between sodium valproate and meropenem; stopping vancomycin infusion and requesting TDM due to sudden decline in renal function and development of an acute kidney injury in a patient being treated with vancomycin continuous infusion. Conclusions: A pharmacist-managed TDM service helped optimise medication doses for drugs with a narrow therapeutic range and those with a high incidence of toxicity. Timely interpretation and appropriate management of TDM assisted in preventing potential ADEs in critically ill patients.