Pentamidine Isethionate is a pharmaceutical active ingredient belonging to the aromatic diamidine antiprotozoal class. It is the bis-isethionate salt of pentamidine and is used in pharmaceutical formulations for specific protozoal and opportunistic infections. Pentamidine isethionate has established applications in the treatment of Pneumocystis jirovecii pneumonia (PCP) and in the management of certain parasitic infections, depending on the dosage form and approved indication.
Pentamidine Isethionate has the CAS Number 140-64-7, molecular formula C23H36N4O10S2, and molecular weight 592.68 g/mol. Chemically, it consists of pentamidine associated with two equivalents of 2-hydroxyethanesulfonic acid (isethionic acid).
Pentamidine isethionate is described as a white or almost white crystalline powder or crystals. It is readily soluble in water, and aqueous solutions have an acidic pH range. PubChem reports a pH of approximately 4.5–6.5 for a 5% aqueous solution, consistent with pharmacopoeial specifications.
The active pentamidine moiety has the molecular formula C19H24N4O2 and molecular weight 340.40 g/mol. The isethionate salt contains two isethionic acid components, giving the complete salt a molecular weight of approximately 592.68 g/mol.
Pentamidine Isethionate is an established antiprotozoal pharmaceutical ingredient. It has been used for the treatment of Pneumocystis pneumonia and certain parasitic diseases including African trypanosomiasis and leishmaniasis, depending on the clinical setting and approved product.
The API is used in different pharmaceutical dosage-form applications, including preparations intended for parenteral administration and inhalation. The exact finished-product requirements depend on the dosage form, route of administration and applicable regulatory standard.
Pentamidine Isethionate is recognized by major pharmacopoeial standards. The USP has a dedicated monograph for Pentamidine Isethionate. A USP revision proposal specifies a modern LC assay with an acceptance range of 98.0–102.0%, replacing the earlier titration-based acceptance range of 98.5–101.5%.
The Indian Pharmacopoeia 2010 monograph specifies 98.5–101.0% of Pentamidine Isethionate calculated on the dried basis. It also specifies pH 4.5–6.5, loss on drying NMT 4.0%, and sulphated ash NMT 0.1%.
Historical USP requirements specify individual organic impurities at NMT 0.4% and total impurities at NMT 0.7%, together with pH 4.5–6.5 and loss on drying NMT 4.0%.
Pentamidine Isethionate can be characterized using infrared spectroscopy and chromatographic techniques. The USP revision proposal describes an LC procedure using an L1 column and UV detection, with pentamidine retention at approximately 3 minutes.
Indian Pharmacopoeia describes a liquid chromatographic procedure using an octadecylsilane bonded silica column and UV detection at 265 nm for related-substance testing.
Because different pharmacopoeias can prescribe different analytical procedures and acceptance criteria, the applicable specification should always be identified when preparing a commercial API specification or certificate of analysis.
Pentamidine Isethionate should be handled under controlled pharmaceutical conditions. The historical USP monograph specifies storage in tight containers, protected from light, at controlled room temperature. The Indian Pharmacopoeia also specifies protection from moisture.
For pharmaceutical manufacturing, appropriate controls should be maintained for moisture, light exposure, container closure, impurity profile and microbiological quality according to the intended dosage form and applicable regulatory requirements.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | Conforms to USP identification tests |
| Assay (HPLC) | 98.0% – 102.0% |
| Loss on Drying | NMT 4.0% |
| Residue on Ignition | NMT 0.1% |
| Heavy Metals | NMT 10 ppm |
| Individual Impurity | NMT 0.4% |
| Total Impurities | NMT 0.7% |
| Melting Point | Approximately 187–191°C |