Dozens of diabetes patients in Pakistan suffered vision loss after being given a contaminated drug, a provincial health official said on Tuesday.

Two men behind the supply of the drug, Avastin, have been arrested and 12 government inspectors suspended after an investigation found the medicine was packaged in an unhygienic environment, according to police and health authorities.

"As of now, the injection has severely affected the vision of 68 patients in Punjab," said a spokesperson for the province's health department, who declined to be named.

At least 12 people have reported complete blindness.

"We will only be able to assess the true extent of harm done by the injection once the infections are completely treated," the spokesperson added.

Supplied by the Swiss pharmaceutical company Roche, Avastin is primarily prescribed for the treatment of cancer, however it is given off-label in Pakistan to diabetic patients to block the growth of abnormal vessels in the eye.

It comes in doses of 25mg, but it is divided and repackaged locally into smaller doses as a low-cost option to treat certain eye conditions.

Karsten Kleine, a spokeswoman for Roche in Switzerland, said the drug is not approved for any use in the eye.

"Roche strongly condemns this criminal act of counterfeiting and is doing everything in its power to cooperate with the authorities to protect patients from counterfeits," Kleine said in a statement.

The provincial health ministry has now banned the use of the drug for eye treatment.

One in four adults in Pakistan has diabetes – one of the highest rates in the world – blamed on a lack of excercise and high sugar diet. (AFP)