Drug Dosing in Renal Diseases: Dose Adjustments Based on Drug Clearance and Elimination Rate Constant

In renal disease, dosage adjustments are essential to maintain therapeutic plasma drug concentrations.

Pharmacokinetic changes in uremia, such as prolonged elimination half-lives and altered apparent volume of distribution, require careful dosage regimen modification.

One approach to dose adjustment focuses on changes in total body clearance.

To maintain the desired average concentration in uremic patients, the dose must be adjusted accordingly.

For intravenous infusions, maintaining a steady-state concentration comparable to patients with normal renal function requires adjusting the infusion rate based on renal clearance in uremic patients.

Another method adjusts for decreased elimination rate constant in uremic patients.

In a multiple-dose regimen, where the apparent volume of distribution and dosing interval remain constant, the uremic dose becomes a fraction of the normal dose.

When the elimination rate constant cannot be measured directly, it is the sum of the nonrenal rate and renal rate constants. By rearranging the renal clearance equation and using specific assumptions and substitutions, the overall elimination rate constant can be calculated.