Category. Antibacterial and antimalarial drug.

Storage. Doxycycline capsules should be kept in a tightly closed container.

Labelling. The designation on the container of doxycycline capsules should state that the active ingredient is in the hyclate form and the quantity should be indicated in terms of the equivalent amount of doxycycline (C₂₂H₂₄N₂O₈).

Additional information. Strengths in the current WHO Model list of essential medicines (EML): 50 mg, 100 mg (as hyclate). Strengths in the current WHO EML for children: 50 mg, 100 mg (as hyclate).

Requirements

Complies with the monograph for Capsules .

Definition. Doxycycline capsules contain Doxycycline hyclate. They contain not less than 90.0% and not more than 110.0% of the amount of doxycycline (C₂₂H₂₄N₂O₈) stated on the label.

Identity tests

• Either tests A and E or tests B and E or tests C, D and E may be applied.

1. Carry out the test as described under 1.14.1 Chromatography, Thin-layer chromatography using silica gel R4 as the coating substance and a mixture of 12 volumes of ethyl acetate R, 12 volumes of acetic acid glacial R, 8 volumes of methanol R and 2 volumes of ammonia R as the mobile phase. Apply separately to the plate 2 μL of each of the following three solutions. For solution (A), shake a quantity of the contents of the capsules containing the equivalent of about 8 mg of doxycycline in 10 mL of methanol R, filter and use the resulting solution. For solution (B), dissolve 10 mg of doxycycline hyclate RS in methanol R and dilute to 10 mL with the same solvent. For solution (C), dissolve 10 mg of tetracycline hydrochloride RS in 10 mL of solution (B). After removing the plate from the chromatographic chamber, allow it to dry in a current of air and examine the chromatogram in ultraviolet light (254nm).

   The principal spot obtained with solution (A) corresponds in position, appearance and intensity with that obtained with solution (B). The test is not valid unless the chromatogram obtained with solution (C) shows two clearly separated spots.

2. See the method described below under "Assay". The retention time of the principal peak in the chromatogram obtained with solution (1) corresponds to that in the chromatogram obtained with solution (2).

3. To a quantity of the contents of the capsules containing the equivalent of about 2 mg of doxycycline, add about 5 mL of sulfuric acid (~1760 g/L) TS; an intense yellow colour is produced.

4. To a quantity of the contents of the capsules containing the equivalent of about 0.1 g of doxycycline, add 10 mL of water R and filter. Reserve part of the filtrate for test D. To 2.0 mL of the filtrate, add 1 drop of ferric chloride (25 g/L) TS; a dark red-brown colour is produced.

5. To 1.0 mL of the filtrate from test C, add 5 drops of silver nitrate (40 g/L) TS; a white, curdy precipitate is formed which dissolves in 1.0 mL of ammonia (~100 g/L) TS.

Dissolution. Carry out the test as described under 5.5 Dissolution test for solid oral dosage forms using as the dissolution medium, 500 mL of dissolution buffer, pH 6.8, TS and rotating the paddle at 75 revolutions per minute. At 30 minutes, withdraw a sample of 10 mL of the medium through an in-line filter. Measure the absorbance (1.6) of a 1 cm layer of the filtered sample, suitably diluted if necessary, at the maximum at about 274 nm. At the same time, measure the absorbance at the maximum at about 274 nm of a suitable solution of doxycycline hyclate RS in dissolution buffer, pH 6.8, TS, using the same buffer as the blank.

For each of the capsules tested, calculate the total amount of doxycycline (C₂₂H₂₄N₂O₈) in the medium. Evaluate the results as described under 5.5 Dissolution test for solid oral dosage forms, Acceptance criteria. The amount of doxycycline released is not less than 75% (Q) of the amount declared on the label.

Related substances. Carry out the test as described under 1.14.1 Chromatography, High-performance liquid chromatography using the chromatographic conditions and preparing the solutions as described under "Assay".

Inject 20 μL of solution (5). The test is not valid unless the resolution between the first peak (metacycline) and the second peak (6-epidoxycycline) is greater than 1.25 and the resolution between the second peak and the third peak (doxycycline) is greater than 2.0. If necessary, adjust the tert-butanol R content in the mobile phase to obtain a long retention time for doxycycline and to improve the separation of doxycycline and related substances. The test is not valid unless the symmetry factor for the third peak is less than 1.25.

In the chromatogram obtained with solution (1), the area of any peak corresponding to metacycline or to 6-epidoxycycline is not greater than the area of the corresponding peak in the chromatogram obtained with solution (6) (2% with reference to doxycycline hyclate), the area of any peak appearing between the solvent peak and the peak corresponding to metacycline and the area of any peak appearing on the tail of the main peak is not greater than 0.25 times the area of the peak corresponding to 6-epidoxycycline in the chromatogram obtained with solution (6) (0.5% with reference to doxycycline hyclate).

Assay. Carry out the test as described under 1.14.1 Chromatography, High-performance liquid chromatography using a stainless steel column (25 cm×4.6 mm) packed with particles of styrene divinylbenzene copolymer (8-10 μm). As the mobile phase, use a solution prepared as follows: transfer 60.0 g of tert-butanol R with the aid of 200 mL water R to a 1000 mL volumetric flask. Add 400 mL of phosphate buffer, pH 8.0 (0.05 mol/L), TS, 50 mL of a solution of 10 mg of tetrabutylammonium hydrogen sulfate R per mL adjusted to pH 8.0 with sodium hydroxide (~80g/L) TS and 20 mL of sodium edetate (20 g/L) TS adjusted to pH 8.0 with sodium hydroxide (~80 g/L) TS. Dilute to 1000 mL with water R.

Prepare the following solutions in hydrochloric acid (0.01 mol/L) VS. For solution (1), use an amount of the mixed contents of 20 capsules to produce a solution containing the equivalent of 0.70 mg of doxycycline per mL. Solution (2) contains 0.80 mg of doxycycline hyclate RS per mL, solution (3) 0.80 mg of 6-epidoxycycline hydrochloride RS per mL and solution (4) 0.80 mg of metacycline hydrochloride RS per mL. For solution (5), mix 4.0 mL of solution (2) with 1.5 mL of solution (3) and 1.0 mL of solution (4) and dilute to 25 mL with hydrochloric acid (0.01 mol/L) VS and for solution (6) mix 2.0 mL of solution (3) and 2.0 mL of solution (4) and dilute to 100 mL with hydrochloric acid (0.01 mol/L) VS.

Operate with a flow rate of about 0.9 mL per minute. As a detector, use an ultraviolet spectrophotometer set at a wavelength of about 254 nm. Maintain the temperature of the column at 60^°C.

Inject 20 μL of solution (5). The assay is not valid unless the resolution between the first peak (metacycline) and the second peak (6-epidoxycycline) is greater than 1.25 and the resolution between the second peak and the third peak (doxycycline) is greater than 2.0. If necessary, adjust the tert-butanol R content in the mobile phase. The test is not valid unless the symmetry factor for the third peak is less than 1.25.

Inject alternately 20 μL each of solutions (1) and (2).

Measure the areas of the peak responses in the chromatograms obtained with solutions (1) and (2) and calculate the content of doxycycline (C₂₂H₂₄N₂O₈) in the capsules, taking into account the declared content of C₂₂H₂₄N₂O₈ in doxycycline hyclate RS.

Impurities

The impurities limited by the requirements of this monograph include those listed in the monograph for Doxycycline hyclate.