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In the Resistance and Topism session, Prof Jonathan Shapiro gave an excellent summary on HIV resistance titled: “Resistance: what’s new and on the horizon, and a time to teach old dogs new tricks?”
Professor Shapiro explained that assessing viral resistance enabled better choices for patients and better new drugs that provided more durable lines of treatment.
Resistance testing was developed because, in early ART, many patients were failing virologically and individual mutations helped to guide future treatment. The benefit of resistance testing over and above expert opinion based on previous treatment experience was shown by studies such as Viradapt, GART and Havana.
Over recent years there have been more drugs available, new drugs without class cross-resistance, newer drugs with better resistance patterns and tolerability and simpler regimens, better adherence.
The SPREAD study in Europe showed that acquisition of resistant HIV virus had increased 35% from 2003 to 2013, even though overall prevalence of resistance hadn’t.
There was concern with the roll-out and widespread use of ART in low and middle income countries, resistant rates could sharply increase, but in low and middle income countries, resistance has remained stable 5-15%.
These days there is a need for resistance testing to optimise NRTI use in 2nd and 3rd line therapy and fine tune use of PIs e.g. to use darunavir once or twice daily.
Also resistance can be helpful in patients failing raltegravir or elvitegravir and deciding on dose of dolutegravir to use.
There is new technology that can provide for point of care testing for resistance by looking at specific mutations. Depending on requirements, specific point mutations are provided in a tiered kit: for Tier 1, mutations are suited for 1st time failure; Tier 2 guidance for suspected transmitted resistance; Tier 3 for NRTI choice in 2nd or 3rd line failure; and Tier 4 for PI resistance.
Laboratories providing resistance testing need to improve the format of reporting of resistance testing to make it more user-friendly and clinically relevant.
In the future, reporting will provide not only which drug are okay to use, but also what dose and how many active drugs are needed to be included in the regimen.