Prediction of theophylline clearance using condition correction factors

Area of Science:

• Pharmacokinetics
• Clinical Pharmacology
• Mathematical Modeling

Background:

• Theophylline is a critical medication for acutely ill patients.
• Accurate estimation of theophylline clearance is essential for safe and effective dosing.
• Existing methods for adjusting theophylline dosage based on patient conditions have variable predictive abilities.

Purpose of the Study:

• To evaluate the predictive accuracy of various mathematical manipulations of condition correction factors for estimating theophylline total body clearance.
• To determine the reliability of using standard clearance values versus adjusted values in acutely ill patients.

Main Methods:

• Prospective and retrospective evaluation of 50 acutely ill patients receiving constant aminophylline infusions.
• Measurement of initial and steady-state serum theophylline concentrations.
• Calculation of predicted clearance using 15 different mathematical manipulations of condition correction factors.
• Analysis of Pearson correlation coefficients to assess the relationship between predicted and actual clearance.

Main Results:

• Predictive ability of theophylline clearance decreased as the number of condition correction factors increased.
• Patients with no condition correction factors showed actual clearance only 2% greater than the mean standard clearance.
• The use of a standard clearance of 0.041 L/hr/kg appears justified for initial dosing.

Conclusions:

• Mathematical manipulations of condition correction factors generally reduce the predictability of theophylline clearance.
• A standard clearance value is likely adequate for initial theophylline dosage calculations in most acutely ill patients.
• Over-adjustment using multiple condition correction factors can lead to subtherapeutic or toxic drug levels.