To evaluate the safety and efficacy of trimetrexate glucuronate with leucovorin protection in pediatric patients with Pneumocystis carinii pneumonia (PCP) who are refractory to or have demonstrated severe or life-threatening toxicities to standard therapies (e.g., TMP/SMX or parenteral pentamidine).

Patients receive intravenous infusions of trimetrexate glucuronate and leucovorin for 21 days. Leucovorin is continued for 3 additional days after discontinuation of trimetrexate glucuronate. Patients are followed for 1 month.

Inclusion Criteria

Patients must have:

• Pneumocystis carinii pneumonia (PCP) confirmed within 15 days prior to study entry.
• Serious intolerance and/or resistance to standard therapies (such as trimethoprim/sulfamethoxazole and parenteral pentamidine) during the course of therapy for the current episode of PCP, OR a documented history of such intolerance during a prior episode.

Exclusion Criteria

Patients with the following prior conditions are excluded:

History of Type I hypersensitivity (i.e., urticaria, angioedema, or anaphylaxis), exfoliative dermatitis, or other life-threatening reactions due to trimetrexate glucuronate.