10/19/2012 11:20 EDT | Updated 12/19/2012 05:12 EST

Drugs for heartburn, cancer may interact to cause adverse effects: Health Canada

OTTAWA - Health Canada is updating safety warnings on labelling of a cancer drug and a class of heartburn medications because of a potential interaction between the products that could cause serious health problems.

The drug methotrexate is used in the treatment of cancer and autoimmune diseases, while proton pump inhibitors such as Losec and Nexium are acid reducers used to treat heartburn or acid indigestion.

Taking methotrexate and a proton pump inhibitor (PPI) at the same time may increase the amount of methotrexate in the blood, leading to adverse health effects, Health Canada said in an advisory Friday.

The possible risks to health include kidney failure, low red blood cell count, inflammation of the digestive tract, irregular heartbeat, muscle pain, infections and diarrhea.

While a definitive association between the use of PPIs and an increase in methotrexate has not been confirmed, there have been a number of studies suggesting a possible interaction between the drugs.

Health Canada called the potential for an increased risk of methotrexate side-effects "very likely."

Patients should not stop taking their medication unless advised to do so by their health-care provider. Patients using PPIs and methotrexate should consult with their doctor if they have any concerns about their health or these products.

Health Canada also reminds medical practitioners that PPIs should be prescribed at the lowest dose and for the shortest duration of therapy appropriate to the condition being treated.

The following proton pump inhibitors are available in Canada:

Dexilant (dexlansoprazole)

Nexium and its generic equivalent (esomeprazole)

Losec and its generic equivalents (omeprazole)

Prevacid and its generic equivalents (lansoprazole)

Pantoloc and Panto IV, and their generic equivalents (pantoprazole)

Tecta (pantoprazole/magnesium)

Pariet and its generic equivalents (rabeprazole)

PPIs are also available in combination with other drugs. For example, Vimovo contains esomeprazole and naproxen.