The sponsor has developed the test formulation. This study is being conducted to compare the bioavailability and characterize the Pharmacokinetic profile of the  sponsor’s formulatons (Nevirapine Prolonged Release 400 mg tablets) with reference formulation (VIRAMUNE Prolonged Release 400 mg tablets) in HIV-I Infected patients under fasting conditions, stabilized on Nevirapine based regimen either immediate release or prolonged release to assess the bioequivalence. The most serious adverse reactions associated with nevirapine are hepatitis, hepatic failure, Stevens- Johnson syndrome, toxic epidermal necrolysis, and hypersensitivity reactions. Hepatitis/hepatic failure may be isolated or associated with signs of hypersensitivity which may include severe rash or rash accompanied by fever, general malaise, fatigue, muscle or joint aches, blisters, oral lesions, conjunctivitis, facial edema, eosinophilia, granulocytopenia, lymphadenopathy, or renal dysfunction etc.,   regulatory authorities are recommending that studies should be conducted on  HIV-I infected patients.    Since the formaulation being studied is a modified release formaulation, a multiple dose, stady state study is being conducted as per applicable regulatory guidance. The study is being conducted on schizophrenic patients who are on a stable dose of Nevirapine based regimen, and the patient cannot be deprived of the Nevirapine treatment during the washout period of the study. Hence, the study has been planned to be a continuous administration of the test and reference formulation without any intervening washout period. Objective: To evaluate the pharmacokinetic bioequivalence of the test and reference products and to monitor safety of the patients. The total number of patients to enroll is around 36 from India.