Prazosin Hydrochloride is a pharmaceutical active ingredient belonging to the quinazoline-derived alpha-1 adrenergic antagonist class. It is the hydrochloride salt of prazosin and is primarily used in the manufacture of antihypertensive pharmaceutical formulations. Prazosin reduces peripheral vascular resistance by blocking postsynaptic alpha-1 adrenergic receptors.
The exact API form is Prazosin Hydrochloride, with CAS Number 19237-84-4, molecular formula C₁₉H₂₁N₅O₄·HCl and molecular weight 419.86 g/mol. The USP monograph specifies 97.0%–103.0%, calculated on the anhydrous basis.
Prazosin is a selective peripheral alpha-1 adrenergic receptor antagonist. By inhibiting alpha-1-mediated vasoconstriction, it produces relaxation of vascular smooth muscle and decreases peripheral vascular resistance. Prazosin Hydrochloride is therefore an established pharmaceutical API for cardiovascular formulations.
The substance has a dedicated USP monograph and is also included in the Japanese Pharmacopoeia. Both USP and JP specify the assay on an anhydrous basis, which is particularly important because Prazosin Hydrochloride can occur in different hydration states, including polyhydrate forms.
Product Name: Prazosin Hydrochloride
Pharmaceutical Form: Prazosin Hydrochloride
CAS Number: 19237-84-4
Molecular Formula: C₁₉H₂₂ClN₅O₄
Molecular Weight: 419.86 g/mol
Active Moiety: Prazosin
Free-Base CAS: 19216-56-9
Free-Base Molecular Weight: 383.40 g/mol
Class: Alpha-1 Adrenergic Antagonist
Physical Form: White or almost white crystalline powder
The USP and Japanese Pharmacopoeia identify CAS 19237-84-4 and molecular weight 419.86 g/mol for Prazosin Hydrochloride.
Prazosin Hydrochloride is the monohydrochloride salt of prazosin. Its chemical structure contains a quinazoline ring, piperazine moiety, furan carbonyl group and methoxy substituents. The hydrochloride salt should be distinguished from the free base when preparing API specifications, certificates and regulatory documentation.
An important characteristic of Prazosin Hydrochloride is its ability to exist in different crystalline and hydration states. Historical solid-state studies describe anhydrous forms as well as a polyhydrate containing approximately 8–15% water, with approximately 12–15% water described for a preferred polyhydrate form.
Consequently, the assay should be expressed on the anhydrous basis, rather than incorrectly treating the water content of a polyhydrate as an impurity.
Prazosin Hydrochloride API is primarily used in pharmaceutical products for the treatment of hypertension. Prazosin acts through alpha-1 adrenergic blockade, resulting in vasodilation and reduced vascular resistance.
Prazosin has also been investigated and used clinically for other conditions, including symptoms associated with trauma-related nightmares, although the principal established pharmaceutical classification remains that of an alpha-1 adrenergic antagonist.
Prazosin Hydrochloride has established pharmacopoeial analytical controls. The current USP monograph specifies an assay of 97.0%–103.0% on anhydrous basis and uses liquid chromatography for quantitative determination. The USP analytical procedure uses UV detection at 254 nm.
The European Pharmacopoeia specifies 98.5%–101.0% on the anhydrous substance and controls related substances, iron, loss on drying and sulfated ash. The Ph Eur monograph specifies impurity A at NMT 0.2%, unspecified individual impurities at NMT 0.10% each, and total impurities at NMT 0.5%.
The Japanese Pharmacopoeia describes Prazosin Hydrochloride as a white crystalline powder and specifies 97.0%–103.0% after drying. It also reports a melting point of approximately 270°C with decomposition.
Manufacturing Prazosin Hydrochloride requires controlled synthesis, purification, salt formation and crystallization. Because the material can occur in different hydration states, control of crystallization and moisture is important for maintaining consistent batch quality.
A pharmaceutical-grade API specification should clearly identify whether the material is supplied as anhydrous material or a polyhydrate and should report assay on the appropriate anhydrous basis.
Analytical quality control may include HPLC assay, related substances, identification by IR/UV, water or loss-on-drying testing, residue on ignition or sulfated ash, elemental impurities and physical characterization.
Prazosin Hydrochloride should be protected from light and stored in suitable tightly closed pharmaceutical containers. The USP monograph specifically requires preservation in tight, light-resistant containers.
This is particularly relevant because pharmacopoeial information notes that Prazosin Hydrochloride can gradually become pale yellowish-white on exposure to light.
Typical API documentation may include:
Prazosin Hydrochloride is a well-established pharmaceutical API with recognized USP, Ph Eur and JP quality requirements. Its defined assay, impurity profile and solid-state characteristics make careful control of purity, hydration state and storage conditions important for pharmaceutical manufacturing.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 97.0–103.0% |
| Loss on Drying | NMT 0.5% |
| Residue on Ignition | NMT 0.1% |
| Heavy Metals | NMT 20 ppm |
| Individual Impurity | NMT 0.10% |
| Total Impurities | NMT 0.50% |
| Melting Point | About 270°C with decomposition |