BARCELONA, May 14 (Reuters) - Spanish drug maker Grifols , battling a plunge in its share price this year, on Tuesday posted a first-quarter net profit of 21 million euros ($22.71 million), in a swing from a year-ago loss as revenues rose 4.1%.

Since early January, short-sheller fund Gotham City Research has released several reports accusing Grifols of overstating earnings and understating debt. Grifols' market value has shed several billion euros since then. The company has denied any wrongdoing although it has announced governance changes.

($1 = 0.9246 euros) (Reporting by Joan Faus, Editing by Andrei Khalip)