Which medication is the more effective: efavirenz or nevirapine? Why must nevirapine be taken 2x a day and efavirenz only 1x? After started, how long does nevirapine take to become safe to the liver?
The effectiveness is probably similar, but nevirapine can have more severe early toxicity, including serious liver and skin toxicity. In a head-to-head comparison trial (2NN), nevirapine was “not non-inferior” to efavirenz, which is a confusing statistical way of saying that it failed to meet the criteria for non-inferiority (comparability), probably due to early nevirapine toxicity.
Nevirapine toxicity is an even more important issue today than it was in the past. Since nevirapine toxicity is a hypersensitivity reaction, it is more likely to occur if your immune system is relatively healthy. We’re now treating people at higher CD4 counts than we used to, and the higher your CD4 count is, the greater the risk of toxicity. Nevirapine toxicity tends to occur during the first 4-6 weeks of therapy. After that, it becomes a safe and well tolerated drug.
Nevirapine does not need to be taken twice a day. In the U.S. and elsewhere, a 400 mg extended-release formulation has been approved (see photo). If it’s not available to you, it’s probably OK to take both of the 200 mg tablets at the same time, especially once you’ve made it through the first few weeks. But no matter which form you take, you have to start with 200 mg once a day, increasing to 400 mg only after the first two weeks, assuming you’re not experiencing any toxicity.