Primary drug resistance in antiretroviral-naïve injection drug users☆

Received 22 January 2008; received in revised form 2 August 2008; accepted 31 August 2008. published online 29 December 2008.

Summary

Objectives

We evaluated the prevalence of primary HIV drug resistance in a population of 128 injection drug users (48 female) prior to initiating antiretroviral therapy.

Methods

Genotypic and phenotypic profiles were obtained retrospectively for the period June 1996 to February 2007. Genotypic drug resistance was defined as the presence of a major mutation (IAS-USA table, 2007 revision), adding revertants at reverse transcriptase (RT) codon 215. Phenotypic drug resistance was defined as the fold change associated with ≥80% loss of the wild type virologic response due to viral resistance based on virtual phenotype analysis.

Results

Genotypic drug resistance was uncommon, and was only identified in six (4.7%) cases, all in the RT gene (L100I, K103N, Y181C, M184V, Y188L, and T215D). There were no cases of multi-class or protease inhibitor (PI) resistance. However, polymorphisms in the protease and RT genes were extremely common. Phenotypic drug resistance was also identified in six (4.7%) patients, four in the RT gene (in patients with mutations K103N, Y181C, M184V and Y188L) and two the protease gene (in two patients with minor PI mutations). In addition, 25 (19.5%) of the patients had reduced susceptibility to PIs, defined as resistance >20% but <80% of the wild type virologic response, with no primary PI mutations detected in all these patients.

Conclusion

The prevalence of primary HIV drug resistance was low in this population of injection drug users.

Corresponding Editor: Mark Holodniy, California, USA

Keywords: HIV, Primary drug resistance, Injection drug users, Antiretroviral therapy, Directly observed therapy

a Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, 2176 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada

b Department of Statistics and Actuarial Science, University of Waterloo, Waterloo, Canada

c Viral Hepatitis Clinical Research Program, National Centre in HIV Epidemiology and Clinical Research, Sydney, Australia

d Pender Community Health Centre, Vancouver Coastal Health, Vancouver, Canada

Corresponding author. Tel.: +1 604 822 7684; fax: +1 604 822 6012.

☆ This study was presented in part at the 15th Annual Canadian Conference on HIV/AIDS Research, May 25–28, 2006, Quebec City, Canada (P248).

PII: S1201-9712(08)01557-9

doi:10.1016/j.ijid.2008.08.028

11 of 58