Action and use
Beta-adrenoceptor antagonist; treatment of glaucoma.
DEFINITION
Timolol Eye Drops are a sterile solution of Timolol Maleate in Purified Water.
The eye drops comply with the requirements stated under Eye Preparations and with the following requirements.
Content of timolol, C13H24N4O3S
90.0 to 110.0% of the stated amount.
IDENTIFICATION
A. Add a volume of the eye drops containing the equivalent of 50 mg of timolol to an equal volume of carbonate buffer pH 9.7 and extract with two 40-mL quantities of dichloromethane. Reserve the aqueous layer for test B, dry the extracts with anhydrous sodium sulfate, evaporate to dryness using a rotary evaporator and dry at 60° under reduced pressure for 15 minutes. The infrared absorption spectrum of the residue, Appendix II A, is concordant with the reference spectrum of timolol (RS 339).
B. Evaporate the aqueous solution reserved in test A to about 1 mL. Add 1 mL of bromine solution, heat in a water bath for 10 minutes, boil, cool and add 0.1 mL of the solution to a solution of 10 mg of resorcinol in 3 mL of sulfuric acid. A
bluish black colour is produced on heating in a water bath for 15 minutes.
TESTS
Acidity or alkalinity
pH, 6.5 to 7.5, Appendix V L.
Related substances
Carry out the method for liquid chromatography, Appendix III D, using the following solutions.
(1) Use the eye drops undiluted.
(2) Dilute 1 volume of the eye drops to 250 volumes with the mobile phase.
(3) Dilute 1 volume of the eye drops to 500 volumes with the mobile phase.
(4) 0.30% w/v of maleic acid in the mobile phase.
CHROMATOGRAPHIC CONDITIONS
(a) Use a stainless steel column (25 cm × 4 mm) packed with end-capped octadecylsilyl silica gel for chromatography (10 μm) (Nucleosil C18 is suitable).
(b) Use isocratic elution and the mobile phase described below.
(c) Use a flow rate of 2 mL per minute.
(d) Use an ambient column temperature.
(e) Use a detection wavelength of 295 nm.
(f) Inject 20 μL of each solution.
(g) Allow the chromatography to proceed for 4 times the retention time of the principal peak.
MOBILE PHASE
42.5 volumes of 0.02M sodium octanesulfonate and 57.5 volumes of methanol, adjusted to pH 3.0 using glacial acetic acid.
LIMITS
In the chromatogram obtained with solution (1): the area of any secondary peak, other than the peak corresponding to maleic acid, is not greater than the area of the peak obtained with solution (2) (0.4%); not more than two such peaks have an area greater than that of the peak obtained with solution (3) (0.2%).
ASSAY
Dilute a volume containing the equivalent of 25 mg of timolol to 50 mL with water. To 5 mL add 15 mL of carbonate buffer pH 9.7 and extract with three 20-mL quantities and one 10-mL quantity of toluene. Wash each extract successively with the same 10 mL volume of carbonate buffer pH 9.7, combine the toluene extracts and extract with four 20-mL quantities of 0.05M sulfuric acid. Combine the extracts, dilute to 100 mL, filter and measure the absorbance at the maximum at 295 nm, Appendix II B, using in the reference cell a solution prepared by treating 5 mL of water in the same manner, beginning at the words ‘add 15 mL…’. Calculate the content of C13H24N4O3S taking 279 as the value of A(1%, 1 cm) at the maximum at 295 nm.
LABELLING
The quantity of active ingredient is stated in terms of the equivalent amount of timolol.
