[Absolute bioavailability of theophylline (Euphylline)]

Area of Science:

• Pharmacology
• Drug Delivery Systems
• Clinical Pharmacy

Background:

• Theophylline is a widely used bronchodilator.
• Understanding its pharmacokinetic profile across different dosage forms is crucial for effective therapeutic use.
• Variability in bioavailability can impact patient outcomes.

Purpose of the Study:

• To investigate and compare the pharmacokinetics and absolute bioavailability of theophylline.
• To evaluate different oral formulations: standard tablet, enteric-coated retard tablet, and suppository.
• To compare these formulations against an intravenous preparation.

Main Methods:

• Eight healthy subjects participated in the study.
• Theophylline was administered via intravenous injection, standard tablet, retard tablet, and suppository.
• Plasma concentrations were measured over time to determine pharmacokinetic parameters.
• Peak plasma concentrations and time to peak were recorded for each formulation.

Main Results:

• Peak plasma concentrations were achieved at 1.5 hours (tablet), 6 hours (retard tablet), and 4 hours (suppository).
• Absolute bioavailability was highest for the standard tablet (105% ± 25%), followed by the retard tablet (81% ± 23%), and the suppository (74% ± 25%).
• Observed variations in bioavailability were mainly attributed to other pharmacokinetic parameters rather than solely to absorption.

Conclusions:

• The standard oral theophylline tablet demonstrates superior bioavailability compared to retard tablets and suppositories.
• Dosage form significantly influences the pharmacokinetic profile and bioavailability of theophylline.
• Further research into optimizing retard tablet and suppository formulations may be warranted to improve their therapeutic equivalence.