New Zealand's drug buying agency is alerting almost 36,000 people taking a blood pressure medication that they will need to change treatments due to contamination.

Pharmac has released a statement saying the supply of quinapril with hydrochlorothiazide - branded as Accuretic and supplied by Pfizer - would be stopped due to the detection of a contaminant called nitrosamine.

However, Pharmac's director of operations, Lisa Williams, said they hadn't yet secured a direct alternative drug.

"Unfortunately, because it's a global issue, no alternative brand is available in sufficient volumes for New Zealand and that can be verified as being free from contamination.

"This means there is currently no acceptable direct chemical substitute for New Zealanders taking this medicine," Williams said.

The agency had received clinical advice that losartan with hydrochlorothiazide would be an appropriate alternative for "most patients". This was currently funded and Medsafe approved.

Pharmac said they had assurances from its supplier, Teva, that there was sufficient stock of losartan with hydrochlorothiazide to accommodate patients transitioning from Accuretic.

There was also enough of the other alternative funded angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) to meet the additional demand from people changing from Accuretic, Williams said.

She said Accuretic was a medicine generally used to manage blood pressure and was used by almost 36,000 New Zealanders.

"Medsafe has advised us that there is no immediate risk to people who are taking Accuretic, and they should continue with their treatment until they find an alternative because the risk associated with suddenly halting blood pressure medication exceeds that presented by the contaminant."

Pharmac’s director of operations Lisa Williams has urged patients to consult with their doctors. Photo / Dean Purcell

People taking Accuretic would need to consult their doctor about an alternative treatment when next due for a prescription, the statement said.

Williams said Pharmac had asked health professionals to talk to their patients about changing medicines for their blood pressure.

"We know that our healthcare sector is currently under a huge amount of strain, and that changing this many people to alternative treatments will add to that strain.

"We are asking clinicians to move their patients to alternative medicines as soon as possible, and we really appreciate the support that we know that both clinicians and pharmacists will provide to their patients."

Voluntary recalls were happening in other countries, including in Australia, Europe, the United States, and Canada.

Williams said Pharmac was committed to working closely with healthcare professionals, patient support groups, and other key stakeholders to make this change as easy as possible for patients, including covering the cost of the GP clinic visit and prescription fees.

Pharmac would continue to update the healthcare sector and public, and would keep its website up to date, the statement said.