We are offering trimethoprim cas no.: 8064-90-2 formula: c14h18n4o3•c10h11n3o3s molecular weight: 543.66 safety description: human poison by ingestion. Moderately toxic experimentally by ingestion and intraperitoneal routes. human systemic effects by ingestion and intravenous routes: decreased urine volume or anuria, skin dermatitis, fever and other metabolic changes. When heated to decomposition it emits very toxic fumes of nox and sox