RESEARCH TRIANGLE PARK, N.C. – Antiviral therapeutics company Chimerix has licensed rights to its HIV drug candidate to pharmaceutical giant Merck (NYSE:MRK) in a deal that gives Chimerix an up-front payment of $17.5 million.

RTP-based Chimerix stands to gain up to $151 million more in milestone payments depending on the progress of CMX157. The company would also receive royalties on sales of a successfully commercialized drug. Merck receives exclusive global rights to the compound and takes on the responsbility for developing and commercializing a new HIV drug.

The deal is the second announced by Merck this week. The company also signed a separate deal on Tuesday to develop an antiviral compound from Japan-based Yamasa Corporation. Merck also announced plans to take its own HIV antiviral candidate MK-1439 into a phase 2b clinical study.

Chimerix’s CMX157 is in a class of antiretroviral drugs called nucleoside reverse transcriptase inhibitors, or NRTIs. The compound delivers concentrations of the active antiviral agent tenofovir diphosphate into cells. CMX157 could offer an alternative to Gilead Sciences’ (NASDAQ:GILD) HIV drug Viread.

Chimerix says its compound is more than 200 times more potent than Viread against all major HIV subtypes that are resistant to current therapies and might work against viruses that are resistant to Viread. CMX157 has has completed phase 1 clinical trials.

Chimerix has raised more than $100 million in venture capital financing including a $45 million series F round last year. The deal with Merck allows Chimerix to focus on its lead antiviral drug candidate CMX001, which is being studied as a way to fight certain DNA viruses in patients who have had stem cell and solid organ transplants.

Chimerix has already met with the Food and Drug Administration to discuss that compound and CEO Kenneth Moch said in a statement that the company plans to begin enrolling patients in a phase 3 study early next year.