Primary: To quantify the influence of single-dose and steady-state tipranavir/ritonavir 500/200 mg on intestinal and hepatic cytochrome P450 (CYP) and P-glycoprotein (P-gp) biomarkers, as a means of predicting drug interactions. The AUCs for biomarkers caffeine, warfarin, omeprazole, dextromethorphan, midazolam, and digoxin will be assessed.

Inclusion Criteria:

1. Signed informed consent
2. Healthy subjects aged between 18 years and 45 years inclusive
3. Weighing at least 50 kg
4. Volunteers must be hospitalized on Days 1-4, 7-9, and 17-20 for pharmacokinetic assessments for each biomarker and TPV/r (Days 7-9 and 17-20)
5. Volunteers must be willing to complete all study-related activities
6. Each volunteer must have a valid social security number
7. Each volunteer must have acceptable medical history, physical examination and laboratory test

Exclusion Criteria:

1. History or presence of allergy to the study drugs or their components or drugs of their class, or a history of drug or other allergy that, in the opinion of the physician responsible, contraindicates their participation
2. Any finding of the medical examination (including blood pressure, pulse rate and electrocardiogram) deviating from normal and of clinical relevance
3. History or diagnosis of any significant medical conditions: Including but not limited to gastrointestinal, hepatic, renal, respiratory, cardiovascular, metabolic, immunologic, hematological, psychiatric, neurological, oncological or hormonal disorders
4. Known elevated liver enzymes in past clinical trials with any compound (experimental or marketed)
5. Clinically relevant laboratory abnormalities (e.g. Hgb<11g/dL, Hct<30g/dL, total cholesterol >240mg/dL, triglycerides >500mg/dL, fasting glucose >130mg/dL, liver function tests >2.5x upper limit of normal, baseline international normalized ratio >1.2)
6. History of evidence of clinically significant hepatic, cardiac, pulmonary, endocrine, immunological, gastrointestinal, hematological, vascular or collagen disease
7. History of alcohol abuse or use of any illicit drugs
8. Unable to abstain from more than one beer or alcohol equivalent per day for the duration of the study
9. Use of tobacco products and/or history of smoking within the past 2 months
10. Pregnant or breast feeding
11. Sexually active women of childbearing age who do not use an acceptable barrier method of birth control
12. Hypersensitivity to caffeine, warfarin, vitamin K, omeprazole, dextromethorphan, midazolam, tipranavir, ritonavir or their excipients
13. Concomitant treatment with other experimental compounds
14. Concomitant administration of any prescription or over the counter medications known to alter P450 enzyme or P-gp activity
15. Concomitant administration of any prescription or over the counter medications known to be highly dependent on P450 or P-gp for clearance for which elevated plasma concentrations are known to be associated with serious toxicity
16. Concomitant administration of any food product known to alter P450 enzyme or P-gp activity such as grapefruit juice, Seville oranges
17. Concomitant administration of any drug that could affect bleeding (e.g., aspirin, clopidogrel, ticlopidine, warfarin, heparin, low-molecular weight heparin)
18. Concomitant administration of oral contraceptives (may be included with 7-day washout period)
19. Concomitant administration of any herbal medications
20. Inadequate venous access
21. Renal or hepatic insufficiency
22. Clinically unacceptable result at the screening physical examination
23. Use of investigational medications within 30 days before study entry
24. HIV-positive
25. Body Mass Index (BMI) > 30 kg/m²