In September 2014, Janssen Inc. began marketing a new medicine called Prezcobix in Canada. This medicine contains the following two drugs:
- darunavir 800 mg (also called Prezista) – an HIV protease inhibitor
- cobicistat 150 mg – a boosting agent
Prezcobix is meant to be used as part of a regimen of anti-HIV drugs in adults. Prezcobix is taken once daily with food; the type or amount of food does not matter. For some people with HIV, combining darunavir and cobicistat can help simplify regimens by putting two drugs into one pill. The price of Prezcobix will be the same as the current combined price of darunavir and low-dose ritonavir. Darunavir without cobicistat will continue to be available.
Darunavir is the leading anti-HIV protease inhibitor in Canada and Western Europe. It has been used by thousands of people over the past eight years. In clinical trials, darunavir-based regimens have been shown to be powerful and generally safe when used as directed. Darunavir-based regimens have been tested in people new to HIV medicines as well as people who have used treatment in the past. Darunavir has been taken with a low dose of another drug called ritonavir (Norvir). The purpose of the low dose of ritonavir is to boost and maintain the levels of darunavir in the blood. In this way, darunavir need only be taken once daily. When drugs such as ritonavir are used in this way they are called boosters or boosting agents. Ritonavir has been commonly used for the past decade to boost other HIV protease inhibitors such as atazanavir (Reyataz) and lopinavir (Kaletra). Now, an alternative to boosting with ritonavir has become available—the drug cobicistat.
Cobicistat is a relatively new boosting agent. It is sufficiently powerful that only a once-daily dose is needed to boost and maintain the level of darunavir in the blood. Cobicistat is also used as a booster in another HIV medicine called Stribild, where it boosts the level of a drug called elvitegravir. To date cobicistat has only been available coformulated with another drug.
In studies that have occurred or are underway, cobicistat-boosted regimens have been found to be similarly effective as ritonavir-boosted regimens. In particular, regimens containing cobicistat-boosted darunavir have been found to be similar in effectiveness and safety to regimens containing ritonavir-boosted darunavir.
Clinical trials have found that the absorption of the ingredients in Prezcobix is similar to that seen when ritonavir-boosted darunavir is taken.
In one phase III clinical trial (called GS-US-216-0130) researchers evaluated the safety and effectiveness of Prezcobix together with two nucleoside analogues (nukes). In this study, all medicines were taken once daily with food. Researchers recruited 313 participants—295 who had never previously used treatment and 18 others who were treatment experienced. The majority of participants were men (89%) and 11% were women.
Researchers found that after 24 weeks of this therapy, 82% of participants had a viral load less than 50 copies/ml. This degree of overall response is similar to what has been seen in clinical trials of ritonavir-boosted darunavir or other modern anti-HIV drugs. About 12% of participants had virologic failure and the remaining participants left the study for different reasons.