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Category Antiprotozoal (antimalarial).

          Chloroquine Phosphate Tablets contain not less than 92.5 per cent and not more than 107.5 per cent of the labelled amount of C₁₈H₂₆ClN₃.2H₃PO₄.

Strengths available 150 and 300 mg (base).

Dose
          Suppressive treatment----Adults: 300 mg once weekly starting 1 week before and continuing until 4 weeks after leaving a malarial area.
          Children: 5 mg per kg of body weight, not to exceed the adult dose, once weekly.
          Therapeutic treatment----Adults: 600 mg initially followed by 300 mg in 6 to 8 hours, and 300 mg once a day on the second and third days.

Contra-indication; Warning; Precaution See under Chloroquine Phosphate, p. 70.

Additional information
          1. The medication should be taken with or after meals to minimize gastro-intestinal irritation.
          2. Oral chloroquine can also be used in the treatment of acute and chronic rheumatoid arthritis. The daily dose is up to 2.4 mg per kg of lean body weight.

Packaging and storage Chloroquine Phosphate Tablets shall be protected from light.

Labelling The label on the container states the quantity equivalent to the amount of chloroquine.

Identification
          A. Dissolve a portion of the powdered tablets, containing 100 mg of chloroquine phosphate, in a mixture of 10 ml of water and 2 ml of 2 M sodium hydroxide and extract with two 20-ml portions of chloroform. Wash the chloroform extracts with water, dry with anhydrous sodium sulfate, evaporate to dryness, and dissolve the residue in 2 ml of chloroform: the infrared absorption spectrum of the resulting solution is concordant with the spectrum obtained from Chloroquine Phosphate RS, similarly treated (Appendix 2.1), or with the reference spectrum of Chloroquine.
          B. Extract a portion of the powdered tablets, containing 25 mg of chloroquine phosphate, with 20 ml of water, filter and add 8 ml of trinitrophenol TS to the filtrate: the precipitate, after washing successively with water, ethanol and ether, melts at about 207º (Appendix 4.3).
          C. Extract a portion of the powdered tablets, containing 500 mg of chloroquine phosphate, with 25 ml of water and filter. To the filtrate add 2.5 ml of 5 M sodium hydroxide and extract with three 10-ml portions of ether: the aqueous layer yields the reactions characteristic of phosphates (Appendix 5.1).

Related substances Carry out the test as described in the “Thin-layer Chromatography” (Appendix 3.1), using silica gel GF254 as the coating substance.
          Test solution Shake a quantity of the powdered tablets containing 1 g of chloroquine phosphate with 20.0 ml of water for 30 minutes, centrifuge and use the supernatant liquid; if necessary, filter through a glass fibre paper.
          Reference solution 1 Dilute 1.0 ml of Test solution to 100.0 ml with water.
          Reference solution 2 Dilute 5.0 ml of Reference solution 1 to 10.0 ml with water.
         ​Mobile phase Prepare a mixture of 10 volumes of diethylamine, 40 volumes of cyclohexane and 50 volumes of chloroform.
          Procedure Apply separately to the plate, 2 μl of each of the solutions. After removal of the plate, allow it to dry in air and examine under ultraviolet light (254 nm). Any secondary spot in the chromatogram obtained from Test solution is not more intense than the spot in the chromatogram obtained from Reference solution 1 (1.0 per cent) and not more than one such spot is more intense than the spot in the chromatogram obtained from Reference solution 2 (0.5 per cent).

Dissolution Carry out the test as described in the
“Dissolution Test” (Appendix 4.24).
          Dissolution medium: water; 900 ml.
          Apparatus 2: 100 rpm.
          Time: 45 minutes.
          Procedure Determine the amount of C₁₈H₂₆ClN₃.2H₃PO₄ dissolved from absorbances at the maximum at about 343 nm of filtered portions of the test solution, suitably diluted with Dissolution medium, if necessary, in comparison with a standard solution having a known concentration of Chloroquine Phosphate RS in the same medium (Appendix 2.2).
          Tolerances Not less than 75 per cent (Q) of the labelled amount of C₁₈H₂₆ClN₃.2H₃PO₄ is dissolved in 45 minutes.

Assay Weigh and finely powder not less than 20 Chloroquine Phosphate Tablets. Dissolve an accurately weighed portion of the powder, containing about 500 mg of chloroquine phosphate, in 20 ml of 1 M sodium hydroxide and extract with four 25-ml portions of chloroform. Combine the chloroform extracts and evaporate to a volume of about 10 ml. Add 40 ml of anhydrous glacial acetic acid. Titrate with 0.1 M perchloric acid VS, determining the end-point potentiometrically (Appendix 6.1). Each ml of 0.1 M perchloric acid is equivalent to 25.79 mg of C₁₈H₂₆ClN₃.2H₃PO₄.

Other requirements Comply with the requirements described under “Tablets” (Appendix 1.16).