Phendimetrazine is a synthetic sympathomimetic amine and anorectic compound belonging to the morpholine class. For pharmaceutical use, the active ingredient is commonly provided as Phendimetrazine Tartrate, the L-(+)-tartrate salt of phendimetrazine. The USP-NF recognizes Phendimetrazine Tartrate as a defined pharmaceutical substance with the molecular formula C12H17NO·C4H6O6 and molecular weight 341.36 g/mol.
Phendimetrazine itself has the molecular formula C12H17NO and molecular weight 191.27 g/mol. PubChem identifies it as a morpholine derivative and lists CAS RN 634-03-7 for the active base.
The pharmaceutical tartrate form has CAS RN 50-58-8 and is chemically described as (2S,3S)-3,4-dimethyl-2-phenylmorpholine L-(+)-tartrate (1:1).
Phendimetrazine Tartrate has historically been used as an anorectic agent for short-term weight management in conjunction with dietary measures. It is pharmacologically related to sympathomimetic amines and is subject to controlled-substance regulations in jurisdictions where it is marketed.
For an API product page, it is important to use Phendimetrazine Tartrate rather than treating the free base and tartrate salt as interchangeable materials. Their molecular weights, CAS numbers and assay calculations are different.
The USP-NF monograph for Phendimetrazine Tartrate specifies that the material contains NLT 98.0% and NMT 102.0% of Phendimetrazine Tartrate, calculated on the dried basis.
Importantly, the USP assay is not an HPLC assay. The official procedure uses titration with 0.1 N perchloric acid in glacial acetic acid, with each mL equivalent to 34.14 mg of Phendimetrazine Tartrate.
This distinction is important for CMS specifications: the assay should be listed as 98.0–102.0% by USP titration, not incorrectly described as “98–102% HPLC.”
The current USP specification uses infrared spectroscopy, UV-visible spectroscopy and a specific identification test for tartrate. The UV identification solution is 1 mg/mL in methanol.
Organic impurities are evaluated by TLC. The USP procedure requires the sample chromatogram to correspond to the USP reference standard and specifies that no other spot is obtained under the prescribed test conditions.
The USP monograph also specifically controls the L-erythro isomer at NMT 0.1% using gas chromatography with flame-ionization detection.
Phendimetrazine Tartrate has a USP melting range of 182–188°C with decomposition, with the beginning-to-end melting range not exceeding 3°C. Specific rotation is +32° to +36°, measured using a 100 mg/mL aqueous solution. The pH is specified as 3.0–4.0 in a 1-in-40 solution.
Loss on drying is controlled at NMT 0.5%, with drying to constant weight at 105°C. Residue on ignition is NMT 0.1%. Chloride and sulfate are controlled at NMT 0.035% and NMT 0.01%, respectively.
These values provide a strong basis for a pharmaceutical CMS specification because they are taken from the current USP 2025 presentation of the Phendimetrazine Tartrate monograph rather than generic research-grade specifications.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |
| Loss on Drying | NMT 0.5% |
| Residue on Ignition | NMT 0.2% |
| Individual Impurity | NMT 0.5% |
| Total Impurities | NMT 1.0% |
| Water Content | NMT 0.5% |
| Melting Point | 182–188° |