Pfizer Inc said on Thursday that data from its late-stage trials showed its experimental combination of antibiotics was effective in treating some infections caused by drug-resistant bacteria.

The late-stage studies compared the experimental combination of the antibiotics aztreonam-avibactam (ATM-AVI) with a combination of two other antibiotics - meropenem and colistin - for the treatment of complicated intra-abdominal infections and types of hospital-acquired pneumonia.

Pfizer said the data from the studies shows the antibiotic combination of aztreonam-avibactam is effective and well-tolerated in treating infections caused by gram-negative bacteria.

Hospital-acquired pneumonia occurs in patients at least two-three days after being admitted, or in those who have life-threatening lung infections with high mortality rates, and who are on mechanical breathing machines.