Wellington, Aug 1 NZPA - A drug used to treat rheumatoid arthritis will now be offered to a wider range of people suffering a variety of ailments, Pharmac says.

The Government drug-buying agency said from today Humira (adalimumab) would be funded to treat auto-immune and inflammatory conditions ankylosing spondylitis, psoriatic arthritis, psoriasis and Crohn's disease.

About 600 people use the drug and the number is expected to double over the next year.

Pharmac said Humira belonged to the TNF-alpha inhibitors class of drugs which were typically very expensive -- costing up to $20,000 per patient per year -- and often needed to be administered at hospital.

Humira could be injected by patients themselves at home.

The drug could have "a significant impact on people's lives," Pharmac medical director Dr Peter Moodie said.

"However that positive effect had to be balanced against its substantial cost."

Pharmac said it could not say how much the increased number of treatments would cost but with the Government adding $41 million to Pharmac's pharmaceutical budget yesterday, there was no need to reduce funding in other areas to cover the extra spending.

"In addition Pharmac has a savings programme in place to reduce the cost of existing treatments so it can afford to pay for some of these new drugs," a spokesman said.

Arthritis New Zealand welcomed the funding decision .

"More people now have access to a treatment that can help prevent their disease from developing to a debilitating level.

"While that means small things like having the ability to open car doors, it means big things in terms of quality of life and independence," chief executive Sandra Kirby said.