|How resistance is Norvir?
Mar 22, 2001
I've been on Norvir for a while, but it's failing on me now. My doctor wants to put me on a combination of low dose of the Norvir, but add Indinavir too. He says I am only a little bit resistant to the Norvir, so I should be o.k. with the combo. Is this true?
Response from Dr. Little
Actually, in this setting the presence or absence of drug resistance to ritonavir (Norvir) is less relevant than you might expect. The use of ritonavir as a second low dose agent with another protease inhibitor is primarily as a booster of the other protease inhibitor's drug concentration in the blood as a result of a drug/drug interaction. That is, even if you were fully resistant to ritonavir, the use of low dose ritonavir could still be used to boost (increase) the levels of certain other protease inhibitors to more effective levels that would provide antiviral efficacy and more convenient dosing. HOWEVER, in this case, there is substantial cross resistance between indinavir and ritonavir, thus, you may get adequate levels of indinavir, but your virus may be essentially resistant to its activity by virtue of the resistance it carries to ritonavir. So, in this setting, the "degree" of resistance to ritonavir becomes quite important. I would be concerned about the prospect of using a indinavir/ritonavir combination in someone who had a drug resitance mutation at position 82 of the protease gene. I hope this is helpful.
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