Labels for two types of medications — methotrexate, used to treat cancer and autoimmune disorders, and acid reducing proton pump inhibitors — will be updated to warn of a potential interaction, Health Canada says.

Using both drugs at the same time many increase the amount of methotrexate in the blood leading to side-effects, including kidney failure, low red blood cell count, inflammation of the digestive tract, irregular heartbeat, muscle pain, infections and diarrhea.

Using both methotrexate and proton pump inhibitors at the same time many increase the amount of methotrexate in the blood leading to side-effects, Health Canada says. (CBC)

"While a definite association between PPI use and an increase in methotrexate has not been confirmed, there have been a number of studies suggesting a possible interaction between PPIs and methotrexate," the department said in a release on Friday.

"The potential for an increased risk of methotrexate side-effects is very likely, which is why Health Canada is informing Canadians and Canadian health care practitioners of this change in labelling."

Patients should not stop taking the medication unless a health care professional advises them to do so.

Proton pump inhibitors sold in Canada include:

• Dexlansoprazole (sold under the brand name Dexilant).
• Esomeprazole (sold under the brand name Nexium and its generic equivalent).
• Omeprazole (sold under the brand name Losec and its generic equivalents).
• Lansoprazole (sold under the brand name Prevacid and its generic equivalents).
• Pantoprazole (sold under the brand names Pantoloc and Panto IV, and their generic equivalent(s).
• Pantoprazole/magnesium (sold under the brand name Tecta).
• Rabeprazole (sold under the brand name Pariet and its generic equivalents).

Proton pump inhibitors are also available in combination with other drugs such as Vimovo (contains esomeprazole and naproxen).