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Dose-Finding Study of Once-Daily Indinavir/Ritonavir Plus Zidovudine and Lamivudine in HIV-Infected Patients.

Mallolas, Josep; Blanco, José L.; Sarasa, María; Giner, Vicenç; Martinez, Esteban; Garcia-Viejo, Miguel A.; Arnaiz, Joan A.; Cruceta, Anna; Soy, Dolors; Tuset, Montse; Soriano, Alex; Codina, Carles; Pumarola, Tomás; Carné, Xavier; Gatell, Josep M.

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Background: Strategies for treatment of HIV need to be considered in terms of combining potency, safety, and convenience of dosage. However, regimens including once-daily protease inhibitors are not yet available. We have performed a pilot study to determine an indinavir/ritonavir (IND/RTV) regimen for once-daily dosing, by monitoring plasma levels.

Methods: Antiretroviral-naive HIV-infected adults were eligible. Therapy was zidovudine/lamivudine 1 pill twice daily plus IND/RIT (liquid formulation) 800/100 mg twice daily with food. At 4-week intervals, plasma levels were measured and dosage of IND/RIT switched to 1000/100 mg daily and then 800/200 mg daily. If 12-hour minimum concentrations (Cmin12h) of IND were too low (<0.1 [mu]g/ml) with IND/RIT 1000/100 mg once daily in the first half of the patients, it was planned to switch directly to 800/200 mg once daily in the other half.

Results: In all, 27 patients were recruited. Mean baseline CD4+ lymphocyte count was 107 x 106/L (range, 4-623 x 106/L). Eleven patients (40%) discontinued the study medication within the first 4 weeks due to clinical progression (n = 3) or grade 1-2 RTV related side effects (n = 8). Nine patients (group A) switched from 800/100 mg twice daily to 1000/100 mg once daily and then to 800/200 mg once daily. Seven patients (group B) switched directly to 800/200 mg once daily. At week 32, viral load was <5 copies/ml in 15 of 16 patients (94%). RTV levels were always <2.1 [mu]g/ml. The mean and 95% confidence interval for IND Cmin and Cmax in [mu]g/ml was: using IND/RTV 800/100 mg twice daily (n = 16) 1.4 (0.5-2.3) and 6.7 (4.4-9.1), respectively; using IND/RTV 1000/100 mg once daily (n = 9) 0.18 (0-0.41) and 8.6 (3.3-14), respectively; and using 800/200 mg once daily (n = 16) 0.38 (0-0.9), and 7.5 (0.8-14.8). For all 16 patients who received IND/RTV 800/100 mg twice daily, the Cmin value for IND was >=0.1 [mu]g/ml. Conversely, IND Cmin was <0.1 [mu]g/ml in 4 of 9 receiving 1000/100 mg once daily but in only 1 of 16 receiving 800/200 mg once daily.

Conclusion: Once-daily regimen of IND/RIT is feasible and deserves further evaluation in larger randomized trials. Liquid formulation of RIT was not well tolerated by our antiretroviral-naive patients despite lower than suggested doses.

(C) 2000 Lippincott Williams & Wilkins, Inc.


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