Samidorphan is a synthetic opioid receptor antagonist used as a pharmaceutical active ingredient, primarily in combination with olanzapine. The pharmaceutical drug substance is supplied as Samidorphan L-Malate, also known as Samidorphan Malate, and is identified by CAS No. 1204592-75-5. The free-base form of Samidorphan is identified separately by CAS No. 852626-89-2. FDA regulatory documentation identifies Samidorphan L-Malate as the active substance used in LYBALVI, an oral fixed-dose combination containing olanzapine and samidorphan.
Samidorphan is a structurally related opioid antagonist with high affinity for opioid receptors. It is particularly associated with the pharmacological management of olanzapine-associated weight gain when used as part of the olanzapine/samidorphan combination. Samidorphan itself is not an antipsychotic; olanzapine provides the antipsychotic activity while samidorphan is included to reduce olanzapine-associated weight gain.
The API is generally manufactured as the L-malate salt, which consists of Samidorphan and L-malic acid in a 1:1 salt relationship. FDA identifies the substance using the molecular representation C21H26N2O4·C4H6O5 and a molecular mass of 504.53 g/mol. PubChem similarly identifies the complete salt as C25H32N2O9 with a molecular weight of approximately 504.5 g/mol.
Samidorphan belongs to the morphinan-related class of synthetic opioid receptor antagonists. The molecule contains a cyclopropylmethyl-substituted morphinan structure with hydroxyl, ketone and carboxamide functionalities. The L-malate salt provides the pharmaceutical salt form used in the approved drug substance.
FDA describes Samidorphan as a white to off-white powder, while the L-malate substance is described as a white to off-white solid. Regulatory data report a melting point of approximately 199°C for Samidorphan L-Malate and a pH of 3.78 for a 1% aqueous solution. The substance is soluble in water and only slightly soluble in organic solvents such as ethanol.
Samidorphan L-Malate is primarily used in the manufacture of oral pharmaceutical products containing olanzapine and samidorphan. The FDA-approved combination is indicated for the treatment of schizophrenia in adults and for the acute treatment of manic or mixed episodes associated with bipolar I disorder in adults. Samidorphan is included in the combination to reduce olanzapine-associated weight gain.
For pharmaceutical manufacturing, control of the Samidorphan active moiety, L-malate salt formation, stereochemical integrity, related substances, moisture and residual solvents is important. Because Samidorphan contains several stereochemical centers, appropriate analytical control of stereochemical identity and purity is also relevant to API quality.
Quality control of Samidorphan L-Malate can include identity testing by infrared spectroscopy and chromatography, HPLC assay, related-substance testing, water or moisture determination, residual-solvent analysis, elemental impurities and salt-related characterization.
FDA's chemistry review confirms that Samidorphan L-Malate was evaluated as a defined drug substance and that the manufacturing process includes assessment of known impurities, degradation products and potential process impurities. The regulatory review also discusses control of potentially mutagenic impurities according to ICH M7 principles.
A current universal USP or BP monograph with numerical release specifications for Samidorphan L-Malate could not be verified. Therefore, commercial API specifications should not be incorrectly presented as pharmacopoeial limits.
Manufacturing Samidorphan L-Malate requires controlled synthesis, purification and salt formation using L-malic acid. Important quality attributes include chemical purity, stereochemical integrity, related substances, salt composition, moisture and residual solvents.
For pharmaceutical API manufacturing, validated chromatographic methods can be used to monitor the main compound and process-related impurities. Batch-specific quality documentation may include a Certificate of Analysis, specification sheet, chromatograms, impurity profile, residual-solvent information and technical documentation.
Samidorphan L-Malate should be protected from contamination, excessive moisture and unsuitable environmental conditions. Because the substance is water soluble and has a defined salt form, appropriate moisture-protective packaging is recommended.
Commercial storage conditions should be based on validated stability data and the manufacturer's approved specification rather than applying research-reagent storage conditions universally.
Typical Samidorphan API documentation may include:
Samidorphan L-Malate is a specialized pharmaceutical API used in combination with olanzapine and has a clearly defined regulatory identity. Its controlled salt form, stereochemistry and impurity profile make analytical characterization important for pharmaceutical manufacturing.
Reliable production of Samidorphan L-Malate requires consistent control of chemical purity, salt formation, stereochemical quality, related substances, moisture and residual solvents. Appropriate validated analytical procedures and batch documentation help support quality assessment and downstream pharmaceutical manufacturing.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |