10th July 2026

Therapeutic drug monitoring

Therapeutic drug monitoring describes the process of tailoring drug regimens for individual patients by monitoring the drug concentrations or drug effects. This is vital, particularly for drugs with a narrow therapeutic window, and where pharmacokinetics are disturbed (i.e. in renal impairment). When a patient with renal impairment is prescribed a drug primarily with renal excretion, the dosing can be adjusted by: 

• Dose reduction
• Extending the dose intervals
• A combination of both above.

Dose adjustment should normally only be carried out if the creatinine clearance is <60mL/min. For drugs with serious adverse effects or a narrow therapeutic index, plasma drug concentrations should be monitored as a guide. The following drug alterations are according to the BNF.