Drugmakers are owned more than 1.1 billion euros (771 million pounds) by Greek hospitals and the state-run health insurer, after not being paid since December, but have promised to keep supplying the country on humanitarian grounds.

The European Federation of Pharmaceutical Industries and Associations (Efpia), representing 40 drug companies, said it stood by a commitment made last week to ensure supplies continued for the coming month.

Imports of life-saving medicines - along with fuel - top the list of products at risk as Greece struggles with bank closures and the threat of an exit from the euro zone. Nearly all Greek medicine is imported.

Efpia warned last week, however, that shortages could still emerge on the ground, given the fragmented nature of the Greek supply chain, adding this could be exacerbated if drugs were re-exported.

A spokeswoman for AstraZeneca (>> AstraZeneca plc) said the company was preparing contingency plans but operations for now were continuing as normal.

"At present, there is no impact on our supply chain as, while the banks are closed, bank transfers to and within Greece are still possible," she said.

Pfizer (>> Pfizer Inc.) said current recorded stock levels in Greece should ensure that patients did not suffer any interruption in supply to its medicines in the short term.

Roche (>> Roche Holding Ltd.) also said both its medicines and diagnostics were currently available to patients. "Roche is working to understand the full implications of yesterday’s referendum decision and will both review and take steps to revise its operating plans as needed," the company said.

(Additional reporting by Paul Arnold in Zurich; Editing by Susan Fenton)

By Ben Hirschler

Stocks treated in this article : Pfizer Inc., AstraZeneca plc, Roche Holding Ltd.