Table 1.

NRTIs currently used in clinical therapy ^a.

Common name	Abbrev.	Structural name	Natural analog	Year FDA approved	Common resistance mutations selected b	Mechanism of resistance
zidovudine	ZDV, AZT	β-d-(+)-3′-azido-3′-deoxythymidine	dTTP	1987	M41L, D67N, K70R, L210W, T215F/Y, K219Q/E	excision
didanosine	ddI	β-d-(+)-2′,3-dideoxyinosine	dATP	1991	K65R, L74V	discrimination
stavudine	d4T	β-d-(+)-2′,3′-didehydro-3′-deoxythymidine	dTTP	1994	M41L, D67N, K70R, L210W, T215F/Y, K219Q/E	excision
lamivudine	3TC	β-l-(−)-2′,3′-dideoxy-3′-thiacytidine	dCTP	1995	K65R, M184V/I	discrimination
abacavir	ABC	(1S,4R)-4-[2-amino-6-(cyclopropyl-amino)-9H-purin-9-yl]-2-cyclopentene-1-methanol succinate	dGTP	1998	K65R, L74V, Y115F, M184V	discrimination
tenofovirc	TFV	({[(2R)-1-(6-amino-9H-purin-9-yl)propan-2-yl]oxy}methyl)phosphonic acid	dATP	2001	K65R, K70E	discrimination
emtricitabine	FTC	β-l-(−)-2′,3′-dideoxy-5-fluoro-3′-thiacytidine	dCTP	2003	K65R, M184V/I	discrimination

^aAll NRTIs shown are approved by the U.S. Food and Drug Administration (FDA). Zalcitabine (ddC), which is not currently in use, is also FDA approved;

^bFrom the current listing of mutations associated with antiretroviral drug resistance compiled by the International AIDS Society—USA, Drug Resistance Mutations Group [19];

^cProdrug is tenofovir disoproxil fumarate (TDF).