NEW DELHI // Tablets linked to the deaths of more than a dozen women who visited a sterilisation camp in India probably contained a chemical compound commonly used in rat poison.

A preliminary finding suggests that zinc phosphide got mixed with antibiotic Ciprocin tablets given to the women, said Amar Agarwal, health minister of Chhatisgarh state. Government laboratories are expected to give a final report by Monday.

Dozens of women became ill after being operated on at the camp in Bilaspur district of Chhatisgarh, and at least 13 died this past week. The others are still being treated.

SK Mandal, the state’s chief medical officer, said on Saturday that post-mortem reports did not suggest any surgery faults in sterilisation procedures.

The doctor who operated on the women, RK Gupta, has been accused of performing too many procedures in one day and remains in custody. He has denied responsibility for the deaths and blamed the medication. He said he used to perform up to 10 times more surgeries a day than allowed under government protocols.

On Friday, police arrested the director of the drug manufacturing firm, Ramesh Mahawar of Mahawar Pharma, and his son and charged them with fraud.

Authorities tested the Ciprocin tablets after being informed that zinc phosphide was found at the Mahawar factory.

Samples of the drugs have been sent to laboratories in Delhi and Kolkata to verify that the tablets were contaminated as the preliminary report suggested, said Siddhartha Pardeshi, chief administrator of Bilaspur district.

“But, this is what we anticipate,” he said. “Symptoms shown by the patients also conform with zinc phosphide [poisoning].”

Mahawar, run from an upscale residential street in state capital Raipur, had been barred from manufacturing medicines for 90 days in 2012 after it was found in to have produced substandard drugs, but it did not lose its licence.

An investigation is now under way into why the drugs were bought locally when there was enough stock of the medicine with the state’s central procurement agency, said Mr Agarwal, the state health minister.

“There was no incentive to procure locally so we need to investigate why it was done. This means something is wrong.”

More possible victims arrived at hospitals from villages on Thursday and Friday, some clutching medicine strips from Mahawar and complaining of vomiting, dizziness and swelling, a doctor at Bilaspur’s main public hospital said.

The new patients had not attended the sterilisation camps, but had consumed the drugs separately, the doctor said.

The state government said it had seized 200,000 tablets of Ciprocin 500 and more than 4 million other tablets manufactured by Mahawar.

India is the world’s top steriliser of women, and efforts to rein in population growth have been described as the most draconian after China. Indian birth rates fell in recent decades, but population growth remains among the world’s fastest.

Sterilisation is popular because it is cheap and effective, and sidesteps cultural resistance to and problems with distribution of other types of contraception in rural areas.

Experts say India lacks oversight in its public health system and that government incentives to undergo sterilisation can lead to coercion among poor women. Few Indian men choose to undergo vasectomies, due to cultural taboos.

* Associated Press and Reuters