Pfizer Inc reported that a number of the company’s compounds have shown activity against some of the world’s leading infectious diseases—malaria, severe acute respiratory syndrome (SARS), and pox viruses.

The Phase II clinical trials against drug-resistant malaria using a combination of Zithromax and chloroquine, an older, commonly used malaria treatment, have shown very promising results. The combination has been shown to be three times more effective than chloroquine alone. Based on these encouraging data, Pfizer plans to conduct much larger, Phase III clinical trials worldwide.

At least 10 Pfizer compounds have shown significant activity against the SARS virus in laboratory tests. The company will now selecte the best candidates for continuing development and potential studies in humans.

Pfizer said it has shared an experimental medicine with Harvard Medical School because of potential utility in treating smallpox.

“Taken together, we are making inroads against three of the world’s most-feared diseases,” said Pfizer Chairman and Chief Executive Hank McKinnell. “We are able to do because our scientific operations are unmatched in their global scale. With more than two million compounds in our research library and the ultra-high throughput systems to rapidly screen them against diseases, we have a very good chance of emerging with at least some credible candidates against these and other unexpected threats.”

For malaria, Pfizer will begin Phase III clinical trials, the final stage of human testing, on three continents to definitively demonstrate the efficacy of Zithromax combined with chloroquine. Pfizer cautioned that there are no guarantees that any of these compounds will result in a viable medicine for patients.

“There are tremendous risks and high costs involved in any pharmaceutical research and development project,” McKinnell said. “The complexity of this research is enormous, and my best guess is that none of these candidates has a significant commercial market. But the human stakes are so high that we must continue our investment and seek partnerships through all phases of development and distribution if we are to save lives.”