 The purpose of the study is to find out if high dose antibiotic meropenem, MERREM I.V., along with another drug called an aminoglycoside a different type of antibiotic is effective in decreasing or reducing the rate of antibiotic resistant Pseudomonas aeruginosa, Acinetobacter germs that can cause pneumonia, and the rate of resistance in other difficult to treat germs which may cause hospital-acquired pneumonia requiring mechanical ventilatory support. The study hopes to show that by increasing the amount of meropenem administered and increasing the duration of infusion release of the drug into the bloodstream, levels of the drug will stay at target levels in the bloodstream and decrease the ability of difficult to treat germs to resist, or not be killed by, the treatment using this antibiotic meropenem or other antibiotics. 