How would you approach dosing a drug that has both hepatic clearance and significant renal clearance in a patient with hepatic impairment and CKD?

• A. Use PK model with both clearance pathways; adjust for impairment in each; simulate exposures to determine safe dose/interval
• B. Use standard dosing
• C. Stop drug
• D. Only hepatic impairment considered

Answer: (B)

The key idea is that when a drug is cleared by both hepatic and renal pathways, dosing in someone with hepatic impairment and CKD must account for the combined impact on both routes rather than assuming one pathway predominates. Use a pharmacokinetic model that separates hepatic and renal clearance, apply impairment factors to each (reduced hepatic clearance due to liver dysfunction and reduced renal clearance due to CKD), and then simulate drug exposure for various doses and dosing intervals. The goal is to find a regimen that achieves the target exposure (such as a desired AUC or trough concentration) without leading to accumulation, all while recognizing that changes in protein binding, transporter activity, or nonrenal elimination can further influence exposure. In practice, you would start with a model-informed dose, consider therapeutic drug monitoring if available, and adjust based on observed exposure or clinical response. This approach avoids under- or overexposure that can occur with standard dosing in the presence of organ impairment and reflects a patient-specific strategy.