Background: While dosing theophylline in asthmatics, we should consider that a lot of medicines, substances, conditions and diseases affect the clearance of theophylline, such as smoking, macrolide antibiotics, barbiturates, oral contraceptives, heart and liver insufficiency, alcohol, calcium-antagonists, pneumonia, viral infections, hypoxemia, etc.
Aim: The aim of the study is to investigate the concentrations of theophylline during the day in smoking and nonsmoking patients with asthma.
Material and methods: We have estimated the concentrations of theophylline 6 times daily by the HPLC method (Keith Muir, J Chromatography) in 20 smoking and 20 nonsmoking asthmatic patients, who were treated with theophylline sustained-release tablets 175 mg twice daily.
Results: In the first group of 20 nonsmoking patients we obtained constant therapeutic and optimal concentrations of theophylline. In the second group of 20 smoking asthmatics the concentration of theophylline in plasma, in 8pm and 8am the next day was very low.
Conclusion: Because in smokers we have increased clearance and the decreased half- life of theophylline, and in order to prevent the night time life-threatening attacks, it is necessary to recommend maximal doses of theophylline, especially in the evening. According to the study, dosage should be individualized in order to optimize the treatment based on the measurement of theophylline concentration in plasma.
Keywords: asthma; cigarette smoking; plasma concentration; theophylline; theophylline clearance.