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• W2087917806 abstract "It is generally accepted that the therapeutic activity of theophylline in patients with reversible airway disease can be maximized by maintaining the plasma concentration above 10 µg/ml. The dosage form of theophylline can influence rate and extent of drug delivery and therefore can influence the plasma level. In this issue of Chest (see page 300) Meyer and co-workers reported on the bioavailability of three different theophylline or aminophylline dosage forms manufactured by one pharmaceutical company. A prior study by another research group1Weinberger M Hendeles L Bighley L The relation of product formulation to absorption of oral theophylline.N Engl J Med. 1978; 299: 852Crossref PubMed Scopus (179) Google Scholar using a different batch of aminophylline (Aminodur Dura-tabs) controlled-release tablets reported only 65 percent bioavailability relative to a reference solution. However, this earlier report was justifiably challenged by the present authors on the basis of inadequate experimental design. In their study, Meyer et al used 12 healthy, nonsmoking male subjects in a cross-over design, administering each drug on an eight-hour dosing schedule and measuring the concentration-time course during the ninth dosing interval. Their results clearly indicate no difference in the mean bioavailability among the three dosage forms with the batches selected for testing. However, one can abstract some additional comparative information from their study. The authors include the SDs about the mean values. Examination of the relative SD can lead to information in the variability of the sustained-release preparation when compared with the elixir. The relative SD of the elixir was 26 percent. Since this solution dosage form is virtually 100 percent bioavailable,1Weinberger M Hendeles L Bighley L The relation of product formulation to absorption of oral theophylline.N Engl J Med. 1978; 299: 852Crossref PubMed Scopus (179) Google Scholar, 2Upton RA Sanson L Guentert TW et al.The evaluation of absorption from 15 commercial products indicating deficiencies in currently applied bioavailability criteria.J Pharmacokin Biopharm. 1980; (In press)Google Scholar this variation is due to variation in elimination clearance of the drug within the population tested. In contrast, the sustained-release capsules showed a 34 percent relative SD, and the tablets 30 percent. Any significant increases in variation are in all likelihood due to dose-to-dose variability in drug absorption from the preparation. These variations may be of minimal clinical significance, yet their effect would be amplified in patients with high elimination clearance (short half-life); those who can best benefit from administration of controlled-release dosage forms. One can calculate the parameters controlling the elimination characteristics of theophylline from the results obtained by Meyer et al (mean clearance = 37±6 ml/kg/hr; volume of distribution=490 ml/kg; half-life, 8.7 hr). These values are virtually identical to the results of earlier studies of Powell et al3Powell JR Bozeh S Hopewell P et al.Theophylline disposition in acutely ill hospitalized patients: affect of smoking, heart failure, severe airway obstruction and pneumonia.Am Rev Resp Dis. 1978; 118: 229PubMed Google Scholar for healthy nonsmokers. Elimination half-lives ranging from 2.4 to more than 20 hours (mean half-life=5.5 hr) have been measured in asthmatics free from other pathologic conditions known to affect theophylline kinetics.2Upton RA Sanson L Guentert TW et al.The evaluation of absorption from 15 commercial products indicating deficiencies in currently applied bioavailability criteria.J Pharmacokin Biopharm. 1980; (In press)Google Scholar, 4Ogilvie RI Clinical pharmacokinetics of theophylline.Clin Pharmacokin. 1978; 3: 267Crossref PubMed Scopus (401) Google Scholar Subjects with shorter half-lives will show larger peak-trough differences. Presuming a dose of the elixir is administered to achieve a peak therapeutic concentration, serum levels in subjects with a half-life less than 5.5 hr will fall below the therapeutic level before their next dose, even on a six-hour schdule and will decline far below therapeutic levels overnight. Drug monitoring and dosage adjustment are more difficult. The use of the sustained-release dosage forms such as reported in this issue is extremely useful in the treatment of patients with high rates of clearance of theophylline (eg, half-lives of less than six hours). Such subjects can be much more effectively controlled using one of the sustained-action dosage forms. The study of Meyers et al used an eight-hour dosing schedule It is likely that Aminodur Dura-tabs can be used on a 12-hour dosing schedule,4Ogilvie RI Clinical pharmacokinetics of theophylline.Clin Pharmacokin. 1978; 3: 267Crossref PubMed Scopus (401) Google Scholar but additional testing is required to validate whether the sustained release capsule can maintain control on a 12-hour dosing schedule, particularly owing to the apparent higher dose-to-dose variability shown with the capsules. Subjects with a long half-life (slow clearance) can be treated with less expensive aminophylline tablets. However, side effects have been noted to be reduced by administration of sustained-release dosage forms, even in this special population. Sustained-release preparations are most clearly indicated in asthmatic subjects, many of whom have great fluctuations in airway caliber. Those with a pattern of severe nocturnal bronchospasm are, in fact, at risk of sudden asthmatic death.5Hetzel MR Clark TJH Braithwaite MA Asthma: analysis of sudden death and ventilatory arrests in hospital.Br Med J. 1978; 1: 808Crossref Scopus (214) Google Scholar The ensurance of therapeutic levels during these hours and the entire 24-hour day is comforting to patient and physician." @default.
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• W2087917806 title "Controlled Release Theophylline" @default.
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• W2087917806 doi "https://doi.org/10.1378/chest.78.2.250" @default.
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