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To determine the maximal tolerable dosage of trimetrexate for treatment of pneumocystis pneumonia, 25 patients were treated each day with 45 mg/m2 of trimetrexate and 80 mg/m2 of leucovorin; 10 received 60 mg/m2 and 80 mg/m2; 12 received 60 mg/m2 and 160 mg/m2; and 6 received 90 mg/m2 and 160 mg/m2, respectively. Leucovorin was increased twofold and trimetrexate reduced by 50% or suspended briefly for various levels of neutropenia and thrombocytopenia until blood counts increased. Dosage-modifying hematologic toxicity occurred in 12 (46%), 8 (80%), 9 (75%), and 4 (67%) patients with the respective groups. Cytopenias were in each case reversible and other toxicities were well tolerated. All survivors but one were able to receive a full 21 doses of trimetrexate. Twenty-four (92%), 10 (100%), 7 (58%), and 4 (80%) of patients in the respective groups survived. Thus, the 45 mg/m2/day dosage of trimetrexate with 80 mg/m2/day of leucovorin resulted in the least dosage-modifying toxicity and excellent efficacy. This combination should be selected for studies to compare trimetrexate with other therapies for pneumocystis pneumonia.

Twenty patients with the acquired immune deficiency syndrome (AIDS) and suspected Pneumocystis carinii pneumonia were evaluated by gallium67 (Ga67 scintigraphy and fiberoptic bronchoscopy for initial diagnosis and response to therapy. Lung uptake of Ga67 was demonstrated in 100% of AIDS patients with P. carinii pneumonia, including those with subclinical infection. Fiberoptic bronchoscopy identified P. carinii in the bronchial washings of 100% of cases (19 patients), whereas only 13 of 16 (81%) patients had P. carinii in lung tissue obtained by transbronchial biopsy. Repeat fiberoptic bronchoscopy was performed in 16 of 20 patients. After 2 to 4 wk of therapy, P. carinii was identified in bronchial washings in 8 of 16 (50%) patients and in transbronchial biopsy in 1 of 10 (10%) patients examined. Bronchial washing has a higher yield than transbronchial biopsy in demonstrating P. carinii in patients with AIDS and may evolve as the procedure of choice in such patients. Based on the clinical course and results of Ga67 scintigraphy and fiberoptic bronchoscopy in AIDS patients with P. carinii pneumonia, optimal therapy may require at least 3 wk of treatment.

Fifty bronchial washing specimens from 36 patients with acquired immune deficiency syndrome (AIDS) were retrospectively reviewed to assess the sensitivity of the various special stains used to diagnose Pneumocystis carinii. In 76% of the cases, the Diff-Quik stain was positive; it was the easiest and most rapid of the special stains used. The sensitivity was increased to 92%, 96% and 100%, respectively, by also doing cresyl echt violet, Grocott's Gomori methenamine silver and both the cresyl violet and Grocott stains in addition to the Diff-Quik stain. We conclude that the Diff-Quik stain is a fairly reliable and rapid screening procedure for making the diagnosis of Pneumocystis infection in bronchial washings from AIDS patients. The routine Papanicolaou stain gave less sensitive results in the smears of the washing specimens, but does give a markedly improved yield in bronchoalveolar lavage specimens.

Preclinical studies have demonstrated that trimetrexate is a potent inhibitor of dihydrofolate reductase from Pneumocystis carinii. On the basis of this evidence, this lipid-soluble antifolate was used as an antipneumocystis agent in 49 patients with the acquired immunodeficiency syndrome (AIDS) and pneumocystis pneumonia. Simultaneous treatment with the reduced folate leucovorin was used as a specific antidote to protect host tissues from the toxic effects of the antifolate without affecting the antipneumocystis action of trimetrexate. Patients were assigned to three groups and treated for 21 days: in Group I, trimetrexate with leucovorin was used as salvage therapy in patients in whom standard treatments (both pentamidine isethionate and trimethoprim-sulfamethoxazole) could not be tolerated or had failed (16 patients); in Group II, trimetrexate with leucovorin was used as initial therapy in patients with a history of sulfonamide inefficacy or intolerance (16 patients); and in Group III, trimetrexate with leucovorin plus sulfadiazine was used as initial therapy (17 patients). The response and survival rates were, respectively, 69 percent and 69 percent in Group I; 63 percent and 88 percent in Group II; and 71 percent and 77 percent in Group III. Trimetrexate therapy had minimal toxicity; transient neutropenia or thrombocytopenia occurred in 12 patients and mild elevation of serum aminotransferases in 4. We conclude that the combination of trimetrexate and leucovorin is safe and effective for the initial treatment of pneumocystis pneumonia in patients with AIDS and for the treatment of patients with intolerance or lack of response to standard therapies.

In vitro studies have shown that trimetrexate, a lipid-soluble analogue of methotrexate, is 1500 times more potent than trimethoprim as an inhibitor of dihydrofolate reductase from Pneumocystis carinii. Furthermore, trimetrexate is readily taken up by P carinii, while performed folates such as leucovorin are not. These observations suggest that the combination of trimetrexate plus leucovorin, which can specifically protect mammalian host tissues from the toxic effects of the antifolate, may be useful in the treatment of pneumocystis pneumonia. This concept was tested in a clinical study of 49 patients with acquired immunodeficiency syndrome (AIDS) and P carinii pneumonia who were treated for 21 days with trimetrexate and leucovorin. Patients were divided into three groups: 16 patients who were unable to tolerate or had failed both pentamidine isethionate and trimethoprim-sulfamethoxazole therapy were treated with trimetrexate plus leucovorin (Group I); 16 patients who were unable to tolerate sulfonamide therapy were treated with trimetrexate with leucovorin as initial therapy (Group II); and 17 patients in whom trimetrexate with leucovorin plus sulfadiazine was used as initial therapy (Group III). Response and survival rates were 69% and 69% in Group I; 63% and 88%, respectively, in Group II; and 71% and 76%, respectively, in Group III. Toxicity was minimal. The results indicate that trimetrexate with leucovorin is safe and effective for initial therapy in AIDS patients with P carinii pneumonia and in those intolerant or unresponsive to standard therapies.