British Pharmacopoeia 2025 (Ph. Eur. 11.6 update)
Action and Use
Anticholinergic.
DEFINITION
Homatropine Eye Drops are a sterile solution of Homatropine Hydrobromide in Purified Water.
The eye drops comply with the requirements stated under Eye Preparations and with the following requirements.
Content of homatropine hydrobromide, C₁₆H₂₁NO₃,HBr:
90.0 to 110.0% of the stated amount.
IDENTIFICATION
A. To a volume containing 60 mg of Homatropine Hydrobromide add 3 mL of 5M ammonia, extract with 15 mL of chloroform, dry the chloroform over anhydrous sodium sulfate, filter and evaporate the filtrate to dryness. The infrared absorption spectrum of the residue, Appendix II A, is concordant with the reference spectrum of homatropine (RS 175).
B. In the Assay, the chromatogram obtained with solution (2) shows a peak with the same retention time as the peak derived from homatropine hydrobromide in the chromatogram obtained with solution (3).
C. To 1 mL of the eye drops, diluted with water if necessary to give a solution containing 1% w/v of Homatropine Hydrobromide, add 1 mL of 5M ammonia, shake with chloroform and evaporate the chloroform solution to dryness on a water bath. To the residue add 1.5 mL of a 2% w/v solution of mercury(II) chloride in ethanol (60%). A yellow colour is produced which becomes red on gentle warming (distinction from most other alkaloids except atropine and hyoscyamine).
TESTS
Tropine
Carry out the method for thin-layer chromatography, Appendix III A, using the following solutions.
(1): Use the eye drops diluted, if necessary, with water to contain 1% w/v of Homatropine Hydrobromide.
(2): 0.0050% w/v of tropine.
CHROMATOGRAPHIC CONDITIONS
(a) Use as the coating silica gel G.
(b) Use the mobile phase as described below.
(c) Apply 40 µL of each solution.
(d) Develop the plate to 15 cm.
(e) After removal of the plate, dry it at 100° to 105° until the solvent has evaporated, allow to cool and spray with dilute potassium iodobismuthate solution until spots appear.
MOBILE PHASE
33 volumes of anhydrous formic acid, 33 volumes of water and 134 volumes of ethyl acetate.
LIMITS
Any spot corresponding to tropine in the chromatogram obtained with solution (1) is not more intense than the spot in the chromatogram obtained with solution (2) (0.5%).
ASSAY
Carry out the method for gas chromatography, Appendix III B. Prepare a 2% w/v solution of atropine sulfate BPCRS (internal standard) in methanol (solution A).
(1): Add 1 mL of solution A and 1 mL of 5M ammonia to a volume of the eye drops containing 20 mg of Homatropine Hydrobromide, diluted if necessary to 5 mL with water. Extract with two 5-mL quantities of chloroform, shake the combined extracts with 1 g of anhydrous sodium sulfate, filter and evaporate the filtrate to dryness. Dissolve the residue in 10 mL of dichloromethane. To 1 mL of this solution add 0.2 mL of a mixture of 4 volumes of N,O-bis(trimethylsilyl)acetamide and 1 volume of trimethylchlorosilane, mix and allow to stand for 30 minutes.
(2): Prepare in the same manner as solution (1) but omitting the addition of solution A.
(3): Add 1 mL of solution A and 1 mL of 5M ammonia to 5 mL of a 0.4% w/v solution of homatropine hydrobromide BPCRS. Complete the procedure described under solution (1), beginning at the words ‘Extract with two 5-mL quantities of chloroform…’.
CHROMATOGRAPHIC CONDITIONS
(a) Use a glass column (1.5 m × 4 mm) packed with acid-washed, silanised diatomaceous support (80 to 100 mesh) coated with 3% w/w of phenyl methyl silicone fluid (50% phenyl) (OV-17 is suitable).
(b) Use helium as the carrier gas at 1.7 mL per minute.
(c) Use isothermal conditions maintained at 220°.
(d) Use an inlet temperature of 220°.
(e) Use a flame ionisation detector at a temperature of 220°.
(f) Inject 1 µL of each solution.
DETERMINATION OF CONTENT
Calculate the content of C₁₆H₂₁NO₃,HBr using the ratios of the peaks and the declared content of C₁₆H₂₁NO₃,HBr in homatropine hydrobromide BPCRS.
