Which covariates are commonly considered in population PK analyses?

• A. Only weight and height.
• B. Weight, age, body size, sex, renal function, hepatic function, concomitant drugs
• C. Renal function and hepatic function only.
• D. Dose history and genetic factors only.

Answer: (B)

Population PK uses covariates to explain why individuals differ in drug exposure by accounting for how factors like physiology and co-medications modify typical PK parameters (like clearance and volume of distribution). The most commonly included covariates are weight or body size (captured through allometric scaling to reflect size-related differences in distribution and clearance), age (maturation effects in the young and aging effects in adults), body size measures in general, sex (differences in body composition and enzyme activity), renal function (impacting clearance for drugs cleared renally), hepatic function (affecting metabolism and clearance for drugs processed by the liver), and concomitant drugs (drug–drug interactions that can induce or inhibit metabolic enzymes or transporters). In some models, genetic factors and dose history may be considered, but the set above represents the typical, broadly applicable covariates used to explain interindividual variability in population PK analyses.