Urinary excretion: does it accurately reflect relative differences in bioavailability/systemic exposure when renal...

Area of Science:

• Pharmacokinetics
• Drug Metabolism and Disposition
• Renal Physiology

Background:

• Accurate assessment of systemic exposure and bioavailability is critical in drug development.
• Urinary excretion data offers a non-invasive method for pharmacokinetic evaluation.
• The influence of nonlinear renal clearance on urinary data interpretation requires careful consideration.

Purpose of the Study:

• To evaluate how nonlinear renal clearance affects the accuracy of urinary excretion data in determining relative systemic exposure.
• To assess the impact of nonlinear renal clearance on the accuracy of urinary data for bioavailability estimations.

Main Methods:

• Simulated serum concentration and urinary excretion profiles using a one-compartmental model.
• Incorporated linear nonrenal clearance with either linear or nonlinear (saturable) renal clearance.
• Varied doses over a 100-fold range and analyzed ratios of key pharmacokinetic parameters.

Main Results:

• Linear renal clearance allowed accurate estimation of systemic exposure and bioavailability from urinary data.
• Nonlinear renal clearance led to significant errors (-53% to +125%) in estimating relative bioavailability and systemic exposure when renal clearance was 5% of total.
• Minimal errors were observed in bioavailability estimation when renal clearance was 95% of total under nonlinear conditions.

Conclusions:

• Urinary excretion data accuracy for assessing systemic exposure and bioavailability is compromised by nonlinear renal clearance.
• Establishing the relationship between serum concentration and renal clearance is essential before relying on urinary data.
• The contribution of renal clearance to total clearance influences the magnitude of errors introduced by nonlinearity.