By Veronika Gulyas

BUDAPEST--Richter Gedeon Nyrt. (RICHTER.BU), Hungary's largest home-grown pharmaceutical firm, issued a profit warning on Tuesday after the Russian ruble weakened sharply against core currencies.

Late Monday, the Russian central bank raised the country's key policy rate to 17% from 10.5% effective from Tuesday in an effort to stem the ruble's decline.

Richter generates about one-third of its revenue in Russia. The company now said this revenue and group operating profit are likely to drop in euro terms.

"The significant devaluation of the Russian ruble is expected to negatively impact the company's fourth quarter 2014 results," Richter said in a stock exchange filing.

If the ruble exchange rate remains close to where it is now, Richter expects a "substantial" one-off financial loss at the end of the year, it said.

The ruble hit its weakest-ever level of 66 against the dollar around 0836 GMT on Tuesday, compared with a level of 59.55 at the market's opening, as a decline in oil prices eclipsed the central bank's massive increase in interest rates overnight.

Andrey Ostroukh in Moscow contributed to this article.

Write to Veronika Gulyas at veronika.gulyas@wsj.com; Twitter: @VeronikaGulyas1