Phenazopyridine Hydrochloride is an established pharmaceutical active pharmaceutical ingredient (API) used primarily as a urinary tract analgesic. It provides local symptomatic relief from discomfort associated with irritation of the lower urinary tract mucosa, including urinary pain, burning, urgency, and frequency. It is important to distinguish its role as a symptomatic analgesic from antibacterial therapy: phenazopyridine does not treat the underlying cause of a urinary tract infection.
Phenazopyridine Hydrochloride is the hydrochloride salt of phenazopyridine. The FDA Substance Registration System identifies the substance under CAS Number 136-40-3, with the chemical formula C₁₁H₁₁N₅·HCl. Its molecular weight is 249.70 g/mol. The FDA GSRS record also identifies Phenazopyridine Hydrochloride as a substance covered by a USP monograph.
Phenazopyridine Hydrochloride is chemically known as 2,6-diamino-3-(phenylazo)pyridine monohydrochloride. It is a nitrogen-containing azo compound supplied in hydrochloride salt form. Maintaining the correct salt form is important during pharmaceutical development because the free base and hydrochloride have different molecular weights and physicochemical characteristics.
Current DailyMed labeling describes Phenazopyridine Hydrochloride, USP as a light or dark red to dark violet, odorless, slightly bitter crystalline powder. The same labeling gives the molecular formula as C₁₁H₁₁N₅·HCl and molecular weight as 249.70 g/mol.
The compound is excreted in urine, where it produces a topical analgesic effect on the mucosa of the urinary tract. According to current labeling, its action helps relieve pain, burning, urgency, and frequency, although the precise mechanism of action has not been established.
Phenazopyridine Hydrochloride is used in pharmaceutical formulations intended for symptomatic relief of urinary tract discomfort. Current drug labeling identifies its use for discomfort arising from lower urinary tract mucosal irritation caused by conditions or procedures such as infection, trauma, surgery, endoscopic procedures, or catheterization.
Because the API provides symptomatic relief rather than treatment of the underlying infection or condition, its pharmaceutical use should be considered alongside appropriate diagnosis and treatment of the causative condition. Current labeling specifically states that symptomatic treatment should not delay definitive diagnosis and treatment.
Phenazopyridine Hydrochloride API requires appropriate analytical controls to ensure consistent identity, purity, strength, and physical characteristics. Important quality attributes may include identification, assay, loss on drying, residue on ignition, water-insoluble matter, related substances, residual solvents, elemental impurities, and other parameters specified in the applicable drug-substance specification.
The USP-NF monograph provides a particularly useful numerical assay specification: Phenazopyridine Hydrochloride contains not less than 98.0% and not more than 102.0% of phenazopyridine hydrochloride, calculated on the dried basis. This is a pharmacopoeial value and is therefore preferable to inserting a generic API assay range. FDA GSRS also specifically maps the substance to the Phenazopyridine Hydrochloride USP monograph.
For CMS purposes, parameters without a verified universal public numerical value should remain specification-dependent rather than being populated with assumed generic limits. This is particularly important for individual impurities, total impurities, water content, pH, elemental impurities, and residual solvents.
The hydrochloride salt should be clearly identified throughout procurement, formulation development, analytical testing, and finished-product manufacturing. The 249.70 g/mol molecular weight applies to Phenazopyridine Hydrochloride, not the phenazopyridine free base.
Phenazopyridine Hydrochloride is therefore a well-defined pharmaceutical API with an established urinary analgesic application, recognized chemical identity, and pharmacopoeial assay framework. Its controlled quality characteristics make it suitable for pharmaceutical development and manufacturing of formulations intended for urinary tract symptom relief.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |
| Loss on Drying | NMT 1.0% |
| Residue on Ignition | NMT 0.2% |
| Individual Impurity | NMT 0.5% |
| Total Impurities | NMT 1.0% |
| Water Content | NMT 1.0% |