Abacavir (Ziagen)

Published January 23, 2001; Updated October 2016
Susa Coffey, MD
Selected References
12. Khanlou  H, Yeh  V, Guyer  B, Farthing  C.
Early virologic failure in a pilot study evaluating the efficacy of therapy containing once-daily abacavir, lamivudine, and tenofovir DF in treatment-naive HIV-infected patients. AIDS Patient Care STDS. 2005 Mar;19(3):135-40
[PubMed ID: 15798380]
Previous investigational data using abacavir (ABC), lamuvidine (3TC), and zidovudine has suggested the possibility of triple nucleoside analogue reverse transcriptase inhibitors (NRTI) therapy as an option in the treatment of HIV infection. We performed a pilot study to assess the potency of once daily ABC+ 3TC+ tenofovir (TDF) in the treatment of HIV-infected naive patients. CD4 and HIV-viral load (VL) were followed monthly. Patients were considered to be nonresponder/failing if there was no reduction in VL by >/= 2 log(10) by week 8 and/or a rebound in VL after initial suppression. Resistance testing was then obtained. Nineteen patients naive to antiretroviral therapy (3 women and 16 men) were enrolled, of whom, 2 did not return (withdrew from study at week 2). Median VL and CD4 count at baseline were 147,167 copies per milliliter (5.16 log(10); [range, 7650->750,000]) and 277 cells/mm(3) (range, 59-598). Eight patients had VL > 100000 at baseline. Of 17 patients eligible for follow-up, 5 (27%) were responders (virologic success). Twelve patients (63%) were considered nonresponders and/or with virologic failure. The study was prematurely interrupted because of a high rate of treatment failure. Resistance testing available for 11 nonresponders (58%) showed: 2 patients with wild-type, 5 patients with M184V (reducing susceptibility to 3TC and ABC), 4 patients with M184V+K65R (K65R is responsible for reducing susceptibility to ABC, 3TC and TDF), and none with K65R alone. In conclusion, the combination of ABC, 3TC and TDF cannot be recommended for the initial regimen in HIV treatment-naive patients.
13. Delaunay  C, Brun-V├ęzinet  F, Landman  R, Collin  G, Peytavin  G, Trylesinski  A, Flandre  P, Miller  M, Descamps  D.
Comparative selection of the K65R and M184V/I mutations in human immunodeficiency virus type 1-infected patients enrolled in a trial of first-line triple-nucleoside analog therapy (Tonus IMEA 021). J Virol. 2005 Aug;79(15):9572-8
[PubMed ID: 16014919]
Tonus was a pilot study in which previously untreated human immunodeficiency virus type 1 (HIV-1)-infected patients received the combination of abacavir, lamivudine, and tenofovir once a day. There was a high rate of early virological failure, and the M184V and K65R mutations were frequently detected at week 12 (W12). The objective of this study was to examine the selection dynamics of the K65R and M184V/I mutations. Bulk sequencing of the reverse transcriptase (RT) gene was performed on plasma HIV-1 RNA at baseline, W4, and W12 for 21 patients with detectable viral loads. The RT genes from baseline, W4, and W12 plasma samples from five patients who developed both M184V and K65R but with different mutational patterns were also cloned and screened for the K65R mutation by selective real-time PCR. At baseline, bulk sequencing and clonal analysis showed only wild-type RT sequences. At W4, M184V/I was detected in 12/19 patients and K65K/R in 2 patients by bulk sequencing. At W12, M184V/I was found in 18/20 patient, together with the K65R in 13 patients. At W4, clonal analysis revealed the K65R mutation in 0.6 to 48% of clones in the five patients studied. At W12, the K65R mutation was found in 30 to 100% of clones. K65R and M184V/I seemed to arise in separate clones, followed by an enrichment of viruses containing both mutations. The clinical relevance of this independent evolution is unclear. M184V/I was selected more frequently than K65R at W4. However, K65R was also detected early using a clone-sensitive genotyping method. All three nucleoside analogs are known to select the K65R and/or M184V/I mutation. This convergent genetic pathway to resistance, associated with lower antiretroviral potency, may explain the high selection rate of these mutations in this trial.