Molecular formula. C₁₉H₂₄N₂O₂

Relative molecular mass. 312.4

Graphic formula.

Chemical name. 2-(Cyclohexylcarbonyl)-1,2,3,6,7, 11b-hexahydro-4H-pyrazino-[2,1-α]isoquinolin-4-one; CAS Reg. No. 55268-74-1.

Description. A white or almost white, crystalline powder; odourless or with a faint characteristic odour.

Solubility. Very slightly soluble in water; freely soluble in ethanol (~750 g/l) TS.

Category. Antischistosomal drug.

Storage. Praziquantel should be kept in a well-closed container, protected from light.

Requirements

Definition. Praziquantel contains not less than 98.5% and not more than 101.0% of C₁₉H₂₄N₂O₂, calculated with reference to the dried substance.

Identity tests

• Either test A or tests B and C may be applied.

A. Carry out the examination as described under 1.7 Spectrophotometry in the infrared region. The infrared absorption spectrum is concordant with the spectrum obtained from praziquantel RS or with the reference spectrum of praziquantel.

B. See the test below under "Related substances". The principal spot obtained with solution A corresponds in position, appearance, and intensity with that obtained with solution B.

C. Melting temperature, about 138°C.

Heavy metals. Use 1.0 g for the preparation of the test solution as described under 2.2.3 Limit test for heavy metals, Procedure 3; determine the heavy metals content according to Method A; not more than 20 μg/g.

Sulfated ash. Not more than 1.0 mg/g.

Loss on drying. Dry at 50°C under reduced pressure (not exceeding 0.6 kPa or about 5 mm of mercury) for 2 hours; it loses not more than 5.0 mg/g.

Related substances. Carry out the test as described under 1.14.1 Chromatography, Thin-layer chromatography, using silica gel R5 as the coating substance and a mixture of 85 volumes of toluene R and 15 volumes of methanol R as the mobile phase. Use an unlined chamber. Apply separately to the plate, in a current of nitrogen R, 10 μl of each of 2 solutions in chloroform R containing (A) 50 mg of the test substance per mL and (B) 50 mg of praziquantel RS per mL; further apply 2 μl of each of 2 solutions in chloroform R containing (C) 0.5 mg of praziquantel RS per mL and (D) 1.0 mg of praziquantel RS per mL. Allow the mobile phase to ascend 7 cm. After removing the plate from the chromatographic chamber, allow it to dry in a current of warm air, place the plate in a chamber with iodine vapours and allow to stand for 20 minutes. Examine the chromatogram immediately in daylight. Any spot obtained with solution A, other than the principal spot, is not more intense than that obtained with solution C, except one spot above the main spot which is not more intense than that obtained with solution D.

Assay. Dissolve about 0.04 g, accurately weighed, in sufficient ethanol (~750 g/l) TS to produce 100 mL. Measure the absorbance of a 1-cm layer at the maximum at about 265 nm. Calculate the amount of C₁₉H₂₄N₂O₂ in the substance being tested by comparison with praziquantel RS, similarly and concurrently examined.