When sourcing Trimethoprim (CAS No. 738-70-5), buyers must ensure the product complies with international pharmacopoeia standards such as USP (United States Pharmacopeia), BP (British Pharmacopoeia), or EP (European Pharmacopoeia). Key technical parameters include an assay purity of 98.5% to 101.0%, strictly controlled impurity profiles (e.g., Impurity A and B), and specific particle size distributions (micronized vs. non-micronized) depending on the final dosage form. Always request a Certificate of Analysis (COA) for every batch to verify these metrics.