An Indian court has sentenced two pharmaceutical company executives to two-and-half years in jail for exporting substandard drugs to Vietnam a decade ago, months after the WHO linked their cough syrups to the deaths of children in Gambia.

India suspended production at Maiden Pharmaceuticals in October last year for violations of manufacturing standards after the World Health Organization said four of its cough syrups may have killed dozens of children in Gambia.

The company has denied its drugs were at fault for the deaths in Gambia and tests by an Indian government laboratory found there were no toxins in them.

The company had been facing legal difficulties for years over suspected shoddy products.

A court in Sonipat, near New Delhi, where Maiden has its main production facility, ordered jail for company founder Naresh Kumar Goel and technical director M.K. Sharma for exporting heartburn medicine “not of standard quality” to Vietnam.

"This court has come to the conclusion that the complainant/prosecution has duly proved the charge ... beyond a shadow of reasonable doubt,” the judge, Sanjeev Arya, told the court in its ruling last week.

The written judgement was posted online this week. The court has given them until March 23 to appeal to a higher court.

The two were also fined 100,000 rupees ($1,209) each for exporting the medicine, Ranitidine Tablets B.P (Mantek-150), to Vietnam.

Goel did not answer calls to his telephone. The company said it had no immediate comment on the convictions and declined to provide Sharma's contact details.

Their lawyer told the court that as both Goel and Sharma were over the age of 60 and had been facing court proceedings for the seven years, it should take a “lenient view” on their punishment, according to the judgement.

Indian authorities started investigating the company in 2014 after the Consulate General of India in Vietnam told India's Drug Controller General that Vietnam had blacklisted many Indian companies, including Maiden, for quality violations.