Oral sustained-release aminophylline in medical inpatients: factors related to toxicity and plasma theophylline concentrations

Toxicity of theophylline depends on plasma concentration by single and also repeated dosing in rats

The purpose of this study was to evaluate the relationship between the in vivo toxicity and plasma concentration of theophylline. Theophylline was administered intravenously in single doses ( 50, 100, 150 and 200 mg kg(-1)once a day) or repeated doses (12.5, 25 and 90 mg kg(-1)/day for 28 days) in rats. Plasma concentrations of theophylline increased dose-dependently in both single and repeated doses, and there were no differences due to effects of 28-times repeated administration. Neither single dose at 50 mg kg(-1)nor repeated dose at 12.5 mg kg(-1)/day injections of theophylline showed toxic signs, in which plasma concentrations of theophylline were less than 110 and 22.5 microg ml(-1), respectively. Theophylline induced myocardial fibrosis in 25 mg kg(-1)/day and more treated groups: in which plasma concentrations of theophylline were more than 50 microg ml(-1). At doses of 100 mg kg(-1)(single) and 90 mg kg(-1)/day (repeated), theophylline caused tachypnea and excitement of movement. Each theophylline concentration in plasma was more than 194 microg ml(-1)in single 100 mg kg(-1)and 162 microg ml(-1)in repeated 90 mg kg(-1)/day injections, respectively. Death was observed at a dose of 200 mg kg(-1), in which the plasma concentration of theophylline was more than 264 microg ml(-1). Moreover, the recovery period from signs of toxic poisoning to normality in the 200 mg kg(-1)treated group was greater than that in the 150 mg kg(-1)and less treated groups. The results indicated that the in vivo toxicity of theophylline is highly dependent on plasma concentrations in rats which received single and also repeated doses of theophylline.

Aminophylline toxicity

Aminophylline therapy has undergone change in the past decade. With the changes in usage and dosage forms, the frequency of toxicity in the pediatric population, especially in adolescents, has increased dramatically. Two distinct patterns, chronic and acute, have been recognized and treatment methods for both are changing. Table 4 summarizes the emerging state-of-the-art therapy for aminophylline toxicity. Judging from the activity seen in the literature, investigation into aminophylline toxicity will continue to be a priority. We will see a greater understanding of the disease process and a refining of the therapeutic process. The ultimate goal is the elimination of mortality and the minimization of morbidity from aminophylline toxicity.

Clinical predictors of theophylline blood levels in asthmatic patients

To determine the usefulness of clinical information in predicting theophylline levels, 21 parameters were studied in 204 asthmatic patients. The best single parameter for predicting theophylline levels was the last outpatient level (r = 0.484), which was within +/- 5 micrograms/mL of the presenting theophylline level in 62.5% of cases. However, there was considerable variability in theophylline levels in the other 37.5% of cases. The best combination of predictors was the last outpatient level and time since the last dose in patients taking a short-acting preparation. Even with this combination, however, 20.8% of predicted levels fell outside a range of +/- 5 micrograms/mL of the presenting theophylline levels. The only patients in whom a theophylline level could be predicted reliably were those who reported taking a sustained-release or short-acting preparation more than 15 or 8 hours prior to evaluation, respectively. In these patients, all presenting theophylline levels were in the subtherapeutic range (ie, less than 10 micrograms/mL), with 92% of the levels less than 5 micrograms/mL. Except for these patients, readily available theophylline determinations are necessary in order to optimize theophylline therapy with minimal risk of toxicity.

An in vivo single- and multiple-dose study of several marketed brands of conventional and controlled-release theophylline

In a single-dose study, 18 healthy adult males consumed each of six dosage forms of theophylline. A conventional-release tablet, a syrup, and four competing brands of controlled-release theophylline were studied. Serial serum samples were obtained and analyzed via high pressure liquid chromatography (HPLC). After achieving steady state, 15 healthy adult males consumed each of five dosage forms of theophylline in a multiple-dose study. Serial blood samples were obtained between 0 and 72 hours and subjected to analysis with HPLC. The results indicated that the controlled-release products were not bioequivalent, although they achieved longer time-to-peak values than did the immediate-release syrup and the conventional-release tablet. A single sustained-release product was uniquely different on most pharmacokinetic parameters when compared with the remaining three controlled-release products. In general, the dosage form variation exceeded the individual subject variation on the single-dose study, but the opposite was true for the multiple-dose study.

Prediction of maintenance oral theophylline dosage using single oral doses in patients with obstructive airways disease

This study was designed to test whether single oral doses of theophylline, rather than the specified single intravenous infusions, could be used with a nomogram designed to predict the maintenance oral dose necessary to establish plasma theophylline concentrations of 10 micrograms ml (Koup et al., 1979) in patients with obstructive airways disease. A test dose of theophylline (5 mg kg) was administered on two separate occasions as an oral elixir and as an intravenous infusion. Exactly 6 h after each test dose, plasma theophylline concentration was measured, and the result used to predict daily maintenance dose requirements. During subsequent oral administration, a sustained-release preparation was given in equally divided 12-hourly doses, and 'steady-state' concentrations were measured at trough. Nineteen patients completed the study, and on doses ranging from 4.2 to 21.1 mg kg-1 day-1, trough concentrations of 5.4 to 15.8 micrograms ml (mean 10.0 +/- 0.7 micrograms ml) were achieved. No significant differences were noted between the dose predictions made following either the oral or the intravenous test doses, and the predictive accuracy using the oral route was not compromised. This would suggest that the test dose of theophylline may be administered orally, instead of intravenously, with this nomogram without reducing its efficiency.