Trough Level
The lowest concentration of a drug in the blood, measured just before the next scheduled dose. Trough levels indicate whether drug concentrations remain above the minimum effective level throughout the dosing interval. For peptide drugs with long half-lives, maintaining adequate trough levels supports consistent efficacy.
Technical Context
Ctrough (Cmin) is measured by collecting a blood sample immediately before the next scheduled dose. For drugs where efficacy requires maintaining concentrations above a minimum threshold (like antibiotics), Ctrough monitoring ensures adequate coverage. For peptide drugs with long half-lives (semaglutide: Ctrough is approximately 80% of Cmax due to the long t1/2 and flat PK profile), trough fluctuation is minimal. For shorter-acting peptides, the Ctrough-to-Cmax ratio may be much lower, and clinical effects may wane before the next dose. Vancomycin trough monitoring (target 15-20 mg/L for serious infections) is the most common example of trough-based therapeutic drug monitoring for a peptide drug.