Analog-computer method for rapid estimates of theophylline clearance using presteady-state plasma concentrations

Area of Science:

• Pharmacokinetics
• Computational Modeling
• Clinical Pharmacology

Background:

• Accurate estimation of plasma theophylline concentration and total body clearance is crucial for effective aminophylline therapy.
• Traditional methods for determining these parameters often require steady-state conditions, delaying therapeutic adjustments.
• Theophylline, a bronchodilator, has a narrow therapeutic index, necessitating precise dosing.

Purpose of the Study:

• To describe and validate an analog-computer method for predicting steady-state plasma theophylline concentration and total body clearance before steady-state is achieved.
• To assess the accuracy and efficiency of this novel analog-computer approach compared to established methods.
• To demonstrate the potential clinical utility of the method for early optimization of aminophylline dosage.

Main Methods:

• An analog computer was programmed to simulate the single-compartment disposition of plasma theophylline under constant rate infusion and initial bolus conditions.
• Simulations were algebraically summed and displayed on an oscilloscope to model pre-steady-state pharmacokinetics.
• The method was validated using previously published patient data, comparing analog-computer-derived values with those obtained through nonlinear least-squares regression analysis.

Main Results:

• The analog-computer method demonstrated a high degree of accuracy in fitting pre-steady-state plasma concentration-time data (r² = 0.99995 for 72 data points).
• Estimates of total body clearance using the analog-computer method showed favorable comparison with nonlinear least-squares regression analysis (r² = 0.86 for 16 pre-steady-state patient data points).
• The simulations effectively defined the rate of theophylline administration for the analog-computer rate constant.

Conclusions:

• The developed analog-computer method provides reliable pre-steady-state estimates of plasma theophylline concentration and total body clearance.
• This approach enables clinicians to make timely adjustments to aminophylline doses early in therapy.
• Early dose adjustments can lead to the achievement of optimal therapeutic plasma theophylline concentrations, improving patient outcomes.