Pakistan health authorities have opened an investigation into the deaths of at least 25 heart patients in one city since last month.

Officials say they suspect the deaths in Lahore – the capital of Punjab province – are a result of a tainted batch of drugs.

Dr. Javed Akram, head of the investigative committee, says 100 other heart patients who have taken the same medicine have been admitted to Lahore hospitals. He said 50 of the patients are in critical condition.

Akram said the problem seems to have occurred in a batch of drugs provided to patients by the Punjab Institute of Cardiology. Health officials have withdrawn the suspected medicines and have sent samples for tests.