Labetalol Tablets

General Notices

Action and use

Alpha- and beta-adrenoceptor antagonist.

Definition

Labetalol Tablets contain Labetalol Hydrochloride.

The tablets comply with the requirements stated under Tablets and with the following requirements.

Content of labetalol hydrochloride, C19H24N2O3,HCl

95.0 to 105.0% of the stated amount.

Identification

A. To a quantity of the powdered tablets containing 50 mg of Labetalol Hydrochloride add 50 mL of 0.1m hydrochloric acid and heat on a water bath for 30 minutes. Cool, filter, add 10 mL of ammonia buffer pH 10.0 and extract with three 15-mL quantities of dichloromethane. Shake the combined extracts with 5 g of 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 labetalol (RS 199).
B. The light absorption, Appendix II B, in the range 250 to 400 nm of a 0.004% w/v solution in 0.1m sodium hydroxide of the residue obtained in test A exhibits a maximum only at 333 nm.

Tests

Related substances

Carry out the method for thin-layer chromatography, Appendix III A, using the following solutions.

(1) Shake a quantity of the powdered tablets containing 0.5 g of Labetalol Hydrochloride with 10 mL of methanol, filter and use the filtrate.
(2) Dilute 1 volume of solution (1) to 100 volumes with methanol.
(3) Dilute 1 volume of solution (2) to 2 volumes with methanol.
chromatographic conditions
(a) Use as the coating silica gel GF254.
(b) Use the mobile phase as described below.
(c) Apply 20 µL of each solution.
(d) Develop the plate to 15 cm.
(e) After removal of the plate, dry it in a current of warm air, heat at 105° for 30 minutes, cool and examine under ultraviolet light (254 nm).
mobile phase

5 volumes of 13.5m ammonia, 25 volumes of methanol and 75 volumes of dichloromethane.

limits

Any secondary spot in the chromatogram obtained with solution (1) is not more intense than the spot in the chromatogram obtained with solution (2) (1%) and not more than one such spot is more intense than the spot in the chromatogram obtained with solution (3) (0.5%).

Assay

Weigh and powder 20 tablets. Shake a quantity of the powdered tablets containing 1 g of Labetalol Hydrochloride with 250 mL of 0.05m sulfuric acid for 30 minutes. Dilute the mixture to 500 mL with 0.05m sulfuric acid, mix, filter and dilute 10 mL of the filtrate to 250 mL with 0.05m sulfuric acid. Measure the absorbance of the resulting solution at the maximum at 302 nm, Appendix II B. Calculate the content of C19H24N2O3,HCl taking 86 as the value of A(1%, 1 cm) at the maximum at 302 nm.