Par Pharmaceutical Cos. Inc. gained exclusive rights in the U.S. to a Phase III drug from Immtech Pharmaceuticals Inc. for treating pneumocystis pneumonia in AIDS patients.

Par is paying Immtech $3 million up front in a deal that includes up to $29 million in milestone payments to Immtech through FDA approval, up to $115 million in sales-based milestone payments and royalties on sales. In return, Par gets exclusive rights to the oral agent pafuramidine maleate (DB289), which is being tested in a 270-patient Phase III trial.

Peter Wolf, director of corporate communications at Par, said the Phase III trial is expected to be completed by the end of this year.

"If all were to go well, if the data are as encouraging as in the Phase II trial, then it's reasonable to expect some sort of expedited review process," Wolf told BioWorld Today. "It could be approved by the end of 2008."

The Phase III study is testing pafuramidine against the standard of care, trimethoprim-sulfamethoxazole (TMP-SMX), in patients with pneumocystis pneumonia, or PCP, which the companies described as a fungal infection in the lungs and the most common opportunistic infection in people living with HIV. The goal is to demonstrate comparable efficacy with a reduced side-effect profile.

The trial is being run under a special protocol assessment from the FDA, which also granted pafuramidine orphan status in that indication.

Immtech, of New York, said the market opportunity for PCP treatment is about $40 million to $50 million. The companies also said they may collaborate on development of the drug in the much larger market of preventing PCP in at-risk patients, an effort that would be subject to a separate agreement, Wolf said.

Specifics of the $29 million nearer-term milestone potential for Immtech include $5 million on positive Phase III data, $8 million upon a new drug application filing with the FDA and $16 million upon FDA approval, Wolf said. Further details were not provided on the potential $115 million in sales-based milestones. The companies also said Immtech retained an option to co-market pafuramidine in the U.S.

Immtech officials said they could not comment on the news due to quiet-period restrictions related to a 10-K filing expected today. Immtech also is testing pafuramidine in Phase II studies in treating malaria, and in preventing malaria in travelers; and in a pivotal Phase III trial for treating trypanosomiasis, or African sleeping sickness. The remainder of Immtech's pipeline, also targeting infectious diseases, is in the preclinical or research stages of development.

The malaria and trypanosomiasis indications are not covered by the deal with Par, which Wolf said has no intention of establishing deals covering markets outside the U.S.

Par, of Woodcliff Lake, N.J., markets more than 110 generic drugs and one branded drug, the appetite stimulant Megace ES for treating the wasting conditions of anorexia and cachexia in AIDS patients.

Wolf said the license deal with Immtech "makes a lot of sense for us. It fits our existing therapeutic focus in AIDS supportive care. We have the sales force in place and would not require any additional infrastructure."

He said Par has about 124 sales representatives calling on about 15,000 physicians who prescribe regularly to AIDS patients.

Immtech said that while pafuramidine's mechanism of action is not completely understood, the drug is an aromatic cationic compound that binds to segments of DNA, thus interfering with the activity of enzymes needed for microbial growth.

Another dicationic drug, pentamidine, was used as the basis for development of pafuramidine, with the idea to eliminate toxicity and improve other properties - including oral bioavailability - of the predecessor compound. The tablet formulation also is designed to withstand tropical conditions, Immtech said.

The better side effect profile would appear to put pafuramidine, too, in a favorable competitive position against TMP-SMX and other treatment options for PCP that are not well tolerated, Wolf said, a result that would lead to increased patient compliance.

Wolf said estimates show there currently are 27,000 HIV patients in the U.S. being treated for PCP. Another 147,000 HIV patients are undergoing prophylactic treatment for PCP, he said.

Par estimated mortality rates in individuals with AIDS during the initial PCP infection at 10 percent to 20 percent, with substantially higher rates when mechanically assisted breathing is needed.

The mortality rate for PCP is even higher among non-AIDS patients with compromised immune systems, such as those receiving chemotherapy or organ transplantations, Par noted.

Pafuramidine is being developed by a consortium that includes the University of North Carolina, Georgia State University, the Swiss Tropical Institute and the University of Glasgow. Development also has been supported by grant funding from U.S government agencies and others.

Immtech's stock (AMEX:IMM) gained 36 cents Tuesday, or 5.2 percent, to close at $7.25. Par's stock (NYSE:PRX) gained 8 cents to close at $28.81.