Image caption HIV drug costs have been driven down over the years

Rises in the use of cheaper, non-branded HIV drugs could potentially see more patients with treatment failure, claim US researchers.

They say, based on modelling and trial data, that generic medicines may be slightly less effective.

And as they require users to take three daily pills instead of one, this ups the risk some patients may miss doses.

But others say firm conclusions cannot be made from the Annals of Internal Medicine study.

The HIV information site Aidsmap says because the study is based on modelling it raises too many uncertainties.

A spokesman was concerned that reports such as this could unduly alarm people with HIV on these medicines.

He said the move to generics should be supported.

Generic drugs These are less expensive copies of branded drugs

They usually work in the same way and contain the same active ingredients as the branded version, although some have slight differences

Generic medicines are usually cheaper because there are fewer research and development costs

They still require vigorous safety and regulatory checks

Experts agree that generic antiretroviral drugs have already made a big contribution to managing HIV globally, particularly in the developing world.

The authors of the study say that they used a worst-case scenario for their modeling and much will depend on how well patients comply with taking their tablets - for those who do, the generic option would be a bit more complex but could be as effective as the standard regimen.

Introducing generic medications would be one way for the health service to reduce expenditure, but this must not be at the expense of patient health Jason Warriner of the Terrence Higgins Trust

By their calculations, reduced treatment efficacy could result in 4.4 months of life lost per patient lifetime.

At the same time the lifetime financial savings would be $42,500 (£26,500) per patient, say the Massachusetts General Hospital investigators.

The currently recommended treatment for newly diagnosed patients is a single pill (Atripla) taken dailythat combines three brand-name antiretrovirals - tenofovir (Viread), emtricitabine (Emtriva) and efavirenz (Sustiva).

A generic form of a drug that has a similar mechanism of action to emtricitabine became available in January 2012, and a generic version of efavirenz is expected in the relatively near future.

Patients could soon take these two less expensive generic drugs alongside the brand drug tenofovir.

Lead researcher Dr Rochelle Walensky said: "This is a trade-off that many of us will find emotionally difficult, and perhaps even ethically impossible, to recommend."

She said this trade-off might be more acceptable if the financial savings were redirected to other aspects of HIV medicine.

The researchers calculate that for every 15 patients switched to the generic-based regimen, one who is also infected with hepatitis C could be treated and potentially cured of that infection.

Jason Warriner, of the Terrence Higgins Trust, a UK HIV charity, said: "We welcome this research, which couldn't be more timely.

"There are around 7,000 people diagnosed annually in the UK, meaning the cost of anti-HIV drugs is rising year on year.

"With the NHS under unprecedented financial pressure, the spread of the epidemic is a challenge not just for public health but for the public purse.

"Introducing generic medications would be one way for the health service to reduce expenditure, but this must not be at the expense of patient health.

"Anything that compromises the effectiveness of anti-HIV drugs, or makes people less likely to stick to treatments, would be a false economy.

"Currently, ensuring people with HIV are diagnosed and on treatment is a cornerstone of HIV prevention efforts.

"Effective medications not only keep those living with the virus fit and well, they also help to keep down new infections."

SharonannLynch, HIV/AIDS Policy Advisor for MSF said: "This study fails to take into account the fact that drug patents are what prevent patients from being able to stay on an easier-to-take and more affordable combination pill.

"Generic versions of this combination exist for $200 per person per year in countries where patents do not block their use - less than one percent of what they cost in the US.

"MSF and PEPFAR use these generics that are quality-assured by the World Health Organization and the US FDA, and work just as well as the brand versions."