Bayer has failed in the last round of its effort to block the sale of a cheap generic version of its cancer drug Nexavar in India.

In a Dec. 12 decision, the country's Supreme Court upheld earlier court rulings, dismissing Bayer's challenge against a compulsory license that would allow India's Natco Pharma to sell a cheaper generic version of the medicine used to treat kidney and liver cancer.

The ruling is seen as a blow for global drugmakers' efforts to hold on to exclusivity on high-price medicines in India.

Under a global Trade-Related Aspects of Intellectual Property Rights agreement, countries such as India can issue compulsory licenses on certain drugs that are deemed unaffordable to a large section of their populations.

However, Bayer has consistently fought compulsory licensing, arguing that it weakens the international patent system and endangers pharmaceutical research.

The German group said it was disappointed by the Supreme Court decision and its legal experts were evaluating the verdict before determining any future course of action.

Natco was first given permission by the Indian patents office in 2012 to sell a generic version of Nexavar at 8,800 rupees ($141) for a month's dose, a fraction of Bayer's price of 280,000 rupees. Bayer challenged this decision in the long-running case.

In a much higher profile case last year, Swiss drugmaker Novartis suffered another defeat in the Indian Supreme Court when its attempt to win patent protection for its cancer drug Glivec was dismissed.

Indian courts in recent years also have revoked patents granted to other international drugmakers, including Pfizer, Roche and Merck & Co.