[Importance of the laboratory in optimizing anti-asthma therapy with theophylline].

In relation to antiasthmatic treatment of hospitalized patients with theophyllines, results concerning: a) a retrospective analysis of plasma levels observed over a 18-month period; b) a pharmacokinetic study and consequent determination of an efficient individual posology are reported. On the 194 serum drug tests (each comprehensive of the trough and peak concentrations) evaluated, 58 (30%) entered the retrospective study, after screening by predetermined criteria. 96 out of 194 (49%) tests were eliminated because of inappropriate sample collection or irrational dosage regimen. The theophylline blood levels, distinguished by drug formulation and posology, were spread over very large ranges (coefficient of variation up to 88%, mean of 55%), so that many concentrations were subtherapeutic or potentially toxic. The kinetic study, undergone by 22 patients, was carried out by administering and intravenous test-dose of aminophylline, followed by collection of blood samples at determined times. Elimination half-life, clearance and volume of distribution were then calculated by means of the plasma theophylline concentrations and subsequently an individual optimized dosage regimen (so as to keep the blood drug levels within the 8-16 mg.l-1 range) was determined. The considerable variability of elimination rate observed among patients (extreme values of half-life and clearance differ 10-fold) mainly account for the unforeseeability of plasma levels obtainable with a given posology. Even if the factors affecting the elimination rate of theophylline (i.e. cigarette smoking, obesity, congestive heart failure, chronic obstructive pulmonary disease, pneumonia) are taken into account, the blood concentrations are frequently unforeseeable. Therefore, the monitoring of plasma levels is necessary for every patient treated with theophyllines and a pharmacokinetic study is desirable in some cases.