LEXINGTON, Mass. (AP) — Cubist Pharmaceuticals Inc. said Thursday its net income fell more than 80 percent in the first quarter after it acquired the rights to market an experimental antibiotic in more countries.

During the quarter Cubist paid $25 million to gain the right to market an experimental drug called ceftolozane in some Middle-Eastern and Asia-Pacific countries. The deal gave Cubist full worldwide rights to the drug in all countries. Cubist is studying ceftolozane and another drug, tazobactam, as a treatment for a variety of different types of serious infections including complicated intra-abdominal infections and complicated urinary tract infections.

Astellas Pharma of Japan still has right to milestone and royalty payments related to ceftolozane.

Cubist said its income shrank to $6.1 million, or 9 cents per share, from $32.8 million, or 45 cents per share. Excluding one-time charges the company said it earned 34 cents per share. Revenue rose 9 percent, to $229.9 million from $211.7 million.

Analysts were forecasting adjusted net income of 33 cents per share on $243.7 million in revenue, according to FactSet.

Cubist gets most of its revenue from Cubicin, a treatment for skin infections like the MRSA “superbug” and blood infections. The company said U.S. sales of Cubicin rose 9 percent to $202 million during the quarter. Sales of its constipation drug Entereg increased to $11.2 million from $9.4 million.

Cubist shares declined 61 cents to $45.42 Thursday and lost another penny to $45.41 in aftermarket trading following the release of the earnings report.