Prediction of theophylline clearance using condition correction factors.

The predictive ability of different mathematical manipulations of condition correction factors in estimating total body clearance of theophylline in acutely ill hospitalized patients was evaluated. Fifty acutely ill patients who were treated with constant aminophylline infusions were evaluated. Twenty-one patients were evaluated prospectively. Initial serum theophylline concentrations were ordered, and second concentrations were obtained at steady state. Twenty-nine patients were evaluated retrospectively and were included if two steady-state serum theophylline concentrations had been obtained. Each condition correction factor was determined by calculating the predicted normal clearance using a literature-derived clearance value and dividing it into the actual clearance obtained. The FDA condition correction factors were obtained by dividing the theophylline dose recommended for patients with a particular disease by the dose recommended for a normal patient. Pearson correlation coefficients for 15 mathematical manipulations were used to examine the relationship between the predicted clearance and actual clearance. The predictability of theophylline clearance using the mathematical manipulations decreased as the number of condition correction factors increased. The mean actual clearance for four patients with no condition correction factors was only 2% greater than the mean standard clearance found in a previous study. The use of 0.041 L/hr/kg as a standard clearance appears justified for calculating initial theophylline dosages in all patients. Patients with only one condition correction factor may use this factor to adjust dosage, but when more than one factor is present, the use of the other manipulations studied may result in either subtherapeutic or toxic serum concentrations.