Table 5. Fusion inhibitor resistance mutations^*.

	G36	I37	V38	Q40	N42	N43	L44	L45
Enfuvirtide	DEVS	V	EAMG	H	T	DKS	M	M

^*Mutations in bold reduce enfuvirtide susceptibility > 10-fold in site-directed mutants and most clinical isolates. N42S is the only common polymorphism between codons 36 to 45. It occurs in about 15% of untreated isolates and does not decrease enfuvirtide susceptibility²⁶⁹. Most other mutations at these positions are likely to have been selected by enfuvirtide, although their effect on enfuvirtide susceptibility may not have been reported. Several accessory mutations in the HR2 region corresponding to the peptide sequence of enfuvirtide including N126K, N137K, and S138A have been shown to emerge to improve fitness in combination with specific mutations at positions 36 to 45²⁷⁴-²⁷⁷.