Drug-drug interactions are a major practical concern for physicians treating 
human immunodeficiency virus (HIV) because of the many medications that 
HIV-positive patients must take. Pharmacokinetic drug interactions can occur at 
different levels (absorption, distribution, metabolism, excretion) and are 
difficult to predict. Of all the processes that give rise to drug interactions, 
metabolism by cytochrome P450 (CYP3A) is the most frequent. Moreover, 
medications prescribed to HIV-positive patients may also be CYP3A inhibitors and 
inducers: Tipranavir, in the absence of ritonavir, is a CYP3A inducer, and 
ritonavir is a CYP3A inhibitor. Fortunately, the drug interactions between 
tipranavir coadministered with ritonavir and other antiretroviral medications or 
with other medications commonly used in HIV therapy are well characterized. This 
review summarizes the pharmacokinetic interactions between tipranavir/ritonavir 
and 11 other antiretroviral medications and between tipranavir/ritonavir and 
drugs used to treat opportunistic infections such as fungal infections, 
antiretroviral-treatment-related conditions such as hyperlipidemia, and side 
effects such as diarrhea.