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  • Title: Therapeutic equivalence of a generic slow-release theophylline tablet.
    Author: Hendeles L, Breton AL, Beaty R, Harman E.
    Journal: Pharmacotherapy; 1995; 15(1):26-35. PubMed ID: 7739942.
    Abstract:
    STUDY OBJECTIVE: To evaluate the relative bioavailability and clinical efficacy of two slow-release theophylline products. DESIGN: Randomized, double-blind, crossover trial. SETTING: A university-affiliated clinical research center. PATIENTS: Fourteen adults with asthma. INTERVENTIONS: The patients received a generic slow-release theophylline tablet or Theo-Dur at bedtime for 5 nights. MEASUREMENTS AND MAIN RESULTS: Serum drug concentrations were measured after the last dose. Attenuation of exercise-induced bronchospasm (EIB) was included as a surrogate for efficacy. There was no significant difference in extent of absorption. The mean differences between the generic product and Theo-Dur in area under the curve was -13.9 micrograms/ml.hr-1 (95% CI -41 to 12.9, p = 0.3) and in peak concentration (Cmax), -0.5 microgram/ml (95% CI -1.7 to 2.7, p = 0.6). In contrast, the generic product was absorbed more rapidly; the mean differences in the time to peak concentration (Tmax) was -3.0 hours (95% CI -4.3 to -1.7, p = 0.0003), in trough concentration (Cmin), -0.9 microgram/ml (95% CI -1.9 to -0.01, p = 0.05), and in fluctuation between Cmax and Cmin, +128% (95% CI 40 to 217, p = 0.008). Neither product effectively attenuated EIB, since mean serum concentrations during the exercise challenges were unexpectedly below 10 micrograms/ml after both products. CONCLUSION: These two products are not bioequivalent, but the difference in absorption rates is unlikely to be clinically important in most patients (i.e., they are therapeutic equivalents).
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