TABLE 1.

HIV-1 resistance to protease inhibitors

Drug	Position(s) in protease		Reference(s)
	Critical substitutions	Secondary substitutionsa
Saquinavir	48, 90	10, 36, 63, 71	43
Ritonavir	82, 84	20, 36, 46, 54, 63, 71, 90	59, 65
Indinavir	46, 82	10, 20, 24, 32, 54, 63, 71, 84, 90	10, 90
Nelfinavir	30	46, 63, 71, 88, 90	73, 74
Amprenavir	50	10, 46, 47	71

^aThe role of secondary substitutions in the development of resistance is not completely understood. Some substitutions are known to be compensatory, enhancing the replicative efficiency of the virus. Other changes exist as naturally occurring polymorphisms in untreated patients.