Trimetrexate Plus Leucovorin Calcium Rescue Versus Sulfamethoxazole-Trimethoprim in the Treatment of Pneumocystis Carinii Pneumonia (PCP) in Patients With AIDS

Inclusion Criteria Concurrent Medication: Allowed: * Acetaminophen 650 mg prescribed as necessary for temperature \> 38.7 degrees C. Acetaminophen q4h should not be prescribed as a standing order for more than 48 hours. Prior Medication: Allowed: * Zidovudine as long as such therapy is suspended prior to randomization and not reinstituted until therapy for the acute episode is completed. * Prophylaxis for Pneumocystis carinii pneumonia (PCP). * Unequivocal diagnosis of Pneumocystis carinii pneumonia (PCP) by morphologic confirmation of three or more typical P. carinii organisms in sputum, bronchoalveolar lavage fluid, or lung tissue obtained by transbronchial or open-lung biopsy within 3 days before or after randomization. If morphologic confirmation is not possible prior to therapy, patients may be randomized if the investigator believes there is a high suspicion of PCP based on clinical presentation. If morphologic diagnosis cannot be established within 6 days of randomization, the patient will be withdrawn from study therapy. * Resting alveolar-arterial oxygen differences = or \> 30 mm Hg on room air. Exclusion Criteria Patients with the following are excluded: * Inability to have alveolar blood gas analysis on room air. * Medically unable to receive a liter of intravenous fluid (5 percent dextrose in water) per 24 hours. This procedure is required in order to maintain blinding. Prior Medication: Excluded within 14 days of study entry: * Systemic steroids excee…