(Ph. Eur. 11.6 update)
Action and use
Local anaesthetic; Class I antiarrhythmic.
DEFINITION
Lidocaine Gel is a sterile solution of Lidocaine Hydrochloride Monohydrate in a suitable water-miscible basis.
The gel complies with the requirements stated under Topical Semi-solid Preparations and with the following requirements.
Content of anhydrous lidocaine hydrochloride, C14H22N2O,HCl
95.0 to 105.0% of the stated amount.
IDENTIFICATION
To a quantity of the gel containing the equivalent of 80 mg of anhydrous lidocaine hydrochloride add 4 mL of hydrochloric acid and heat on a water bath for 10 minutes. Allow to cool, transfer to a separating funnel with the aid of 20 mL of water, add 5M sodium hydroxide until precipitation is complete and extract with two 20-mL quantities of chloroform. Filter the chloroform extracts through anhydrous sodium sulfate and evaporate the filtrate to dryness on a water bath using a current of nitrogen. The residue complies with the following tests.
A. The infrared absorption spectrum, Appendix II A, is concordant with the reference spectrum of lidocaine (RS 202).
B. Dissolve 20 mg in 1 mL of ethanol (96%), add 0.5 mL of a 10% w/v solution of cobalt(II) chloride and 0.5 mL of 5M sodium hydroxide and shake for 2 minutes. A bluish-green precipitate is produced.
C. Dissolve 40 mg in 5 mL of a 1% w/v solution of cetrimide and add 1 mL of 5M sodium hydroxide and 1 mL of bromine water. A yellow colour is produced.
TESTS
2,6-Dimethylaniline
Mix a quantity of the gel containing the equivalent of 15 mg of anhydrous lidocaine hydrochloride with sufficient water to produce 3 mL using a rotary vortex mixer. To 2 mL of the resulting solution add 1 mL of a freshly prepared 1% w/v solution of 4-dimethyl-aminobenzaldehyde in methanol, mix thoroughly using a rotary vortex mixer, add 2 mL of glacial acetic acid and allow to stand for 10 minutes. The yellow colour produced is not more intense than that obtained using a mixture of 2 mL of a solution of 2,6-dimethylaniline in methanol containing 2 μg per mL in place of the solution of the gel.
Sterility
Complies with the test for sterility, Appendix XVI A.
ASSAY
Disperse a quantity containing the equivalent of 10 mg of anhydrous lidocaine hydrochloride in 20 mL of water. Add 5 mL of acetate buffer pH 2.8, 120 mL of chloroform and 5 mL of dimethyl yellow and oracet blue 2R solution and titrate with 0.005M dioctyl sodium sulfosuccinate VS, swirling vigorously. Near the end point add the titrant dropwise and, after each addition, swirl vigorously, allow to separate and swirl gently for 5 seconds. The end point is indicated when the colour of the chloroform layer changes from green to pinkish-grey. Repeat the operation without the preparation being examined. The difference between the titrations represents the amount of dioctyl sodium sulfosuccinate required. Each mL of 0.005M dioctyl sodium sulfosuccinate VS is equivalent to 1.354 mg of C14H22N2O,HCll. Determine the weight per mL of the gel, Appendix V G, and calculate the percentage of C14H22N2O,HCl, weight in volume.
STORAGE
Lidocaine Gel should be stored in accordance with the manufacturer’s instructions.
LABELLING
The quantity of active ingredent is stated in terms of the equivalent amount of anhydrous lidocaine hydrochloride.
