Different classes of HIV drugs
Two of the drugs used in many HIV treatment combinations belong to a class of drugs called nukes (nucleoside analogues, or NRTIs). Because the two nukes in a combination usually need to be taken at the same time, drug manufacturers have produced several co-formulations—that is, two or more nukes in a single pill, such as Truvada (tenofovir + FTC) and Kivexa (abacavir + 3TC).
A third drug from a different class is added to these two to create an effective combination that attacks HIV at different points.
Integrase inhibitors, another class of antiretroviral drugs, have several advantages: When taken as part of combination therapy they quickly suppress the amount of HIV in the blood. They generally cause relatively few side effects and are less likely to interact with other medicines.
Protease inhibitor (PI)–based combinations tend to involve more pills than other combinations and may have to be taken with food. One advantage of PIs is that if your HIV develops resistance to one PI, other PIs can still be effective, providing future treatment options.
A small dose of another drug—either ritonavir (Norvir) or cobicistat—is almost always added to a PI combination. This is called “boosting” because it boosts the levels of the PI in the blood, and usually allows for once-daily dosing. Note that “boosters” can interact with recreational drugs, such as ecstasy, crystal meth, K, benzodiazepines and erectile dysfunction drugs such as Viagra.
Non-nukes are another class of antiretroviral drugs. Resistance to a non-nuke sometimes develops more easily than to drugs from other classes, and HIV that is resistant to one non-nuke is sometimes resistant to other drugs in this class.
The only fusion inhibitor currently available is T-20 (enfuvirtide, Fuzeon). This powerful drug, which has to be taken twice a day by injection, is currently used only rarely—by some people who have developed resistance to many other HIV drugs.
Similarly, CCR5 inhibitors are used mostly by people who have previously tried other treatment combinations. A simple screening test can determine whether a person has the strain of HIV against which this class of drug is effective. If so, CCR5 inhibitors may be an option.