Image caption The 'quad' is the first multi-pill to include a type of anti-HIV drug known as an integrase inhibitor

A new once-a-day pill which combines four HIV drugs into a single daily treatment is safe and effective, according to a US study.

It is hoped the four-in-one "quad pill" will make it easier for patients to stick to their medication, improving the effects of their treatment.

A study in the Lancet said it could be an "important new treatment option".

A UK expert said the pill was "great news" and was part of a movement towards once-daily doses.

HIV is incurable, but managing the infection requires combination therapy - multiple drugs used to control the virus.

This can mean taking several pills at different times of the day - and missing them means the body can lose the fight against the virus.

Researchers and drug companies have combined some drugs into single pills so that taking the correct medication at the right time of day is easier.

The quad pill is the first to include a type of anti-HIV drug known as an integrase inhibitor, which stops the virus replicating.

Without a doubt the achievement of a one-a-day pill has been a big advance in tackling HIV Dr Steve Taylor, Birmingham Heartlands Hospital

'Safe, simple, effective'

Paul Sax, clinical director at Brigham and Women's Hospital, in Boston, Massachusetts, and associate professor at Harvard Medical School, said: "Patient adherence to medication is vital, especially for patients with HIV, where missed doses can quickly lead to the virus becoming resistant to medication."

He led research comparing the effect of the quad pill with the current best treatment in 700 patients. He said the quad pill was as safe and effective, although there was a higher level of kidney problems among those taking it.

"Our results provide an additional highly potent, well-tolerated treatment option and highlight the simplicity of treatment resulting from combining several antiretrovirals in a single pill.

Dr Steve Taylor, an HIV specialist at Birmingham Heartlands Hospital, said: "Without a doubt the achievement of a one-a-day pill has been a big advance in tackling HIV.

"We've come a long way from people taking up to 40 pills three times a day."

He said the new tablet was "great news" for people with HIV and would increase options for treatment.

However, he warned that too many people still had undiagnosed HIV. A quarter of people with HIV in the UK do not know they are infected.

The researcher was funded by the biotechnology company Gilead Sciences.