Levodopa Tablets

General Notices

Action and use

Dopamine precursor; treatment of Parkinson’s disease.

Definition

Levodopa Tablets contain Levodopa.

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

Content of levodopa, C9H11NO4

95.0 to 105.0% of the stated amount.

Identification

A. Dissolve as completely as possible a quantity of the powdered tablets containing 0.5 g of Levodopa in 25 mL of 1m hydrochloric acid and filter. Adjust to pH 3 with 5m ammonia, added dropwise with stirring, and allow to stand for several hours, protected from light. Filter, wash the precipitate with water and dry it at 105°. The infrared absorption spectrum of the residue, Appendix II A, is concordant with the reference spectrum of levodopa (RS 201).
B. Comply with test B for Identification described under Levodopa Capsules, but using as solution (1) a solution obtained by shaking a quantity of the powdered tablets containing 0.1 g of Levodopa with 10 mL of 1m hydrochloric acid and filtering.
C. Shake a quantity of the powdered tablets containing 20 mg of Levodopa with 5 mL of 0.1m hydrochloric acid. Add 0.1 mL of iron(iii) chloride solution R1; a green colour is produced. To half of the solution add an excess of 5m ammonia; a purple colour is produced. To the remainder of the solution add an excess of 5m sodium hydroxide; a red colour is produced.

Tests

Dissolution

Comply with the requirements for Monographs of the British Pharmacopoeia in the dissolution test for tablets and capsules, Appendix XII B1, using as the medium 900 mL of 0.1m hydrochloric acid and rotating the basket at 100 revolutions per minute. Withdraw a sample of 10 mL of the medium and filter. For tablets containing 0.25 g of Levodopa or less, filter and dilute 2 mL of the filtrate to 10 mL with 0.1m hydrochloric acid. For tablets containing more than 0.25 g of Levodopa, filter and dilute 1 mL of the filtrate to 10 mL with 0.1m hydrochloric acid. Measure the absorbance of the solution, Appendix II B, at 280 nm using 0.1m hydrochloric acid in the reference cell. Calculate the total content of C9H11NO4 in the medium taking 142 as the value of A(1%, 1 cm) at the maximum at 280 nm.

Specific optical rotation

–38.5 to –41.5, Appendix V F, when determined in the following manner. Shake a quantity of the finely powdered tablets containing 1.25 g of Levodopa with 25 mL of 0.5m hydrochloric acid for 30 minutes, centrifuge and filter the supernatant liquid (Whatman No. 42 filter paper is suitable). To 10 mL of the filtrate add 10 mL of a 21.5% w/v solution of aluminium sulfate, 20 mL of a 21.8% w/v solution of sodium acetate and sufficient water to produce 50 mL and measure the optical rotation. Further dilute 5 mL of the filtrate to 200 mL with 0.1m hydrochloric acid, mix well and dilute 10 mL to 200 mL with 0.1m hydrochloric acid. Measure the absorbance of the resulting solution at the maximum at 280 nm, Appendix II B. Calculate the concentration of levodopa, C9H11NO4, in the filtrate taking 142 as the value of A(1%, 1 cm) at the maximum at 280 nm and hence calculate the specific optical rotation.

Related substances

Comply with the test described under Levodopa Capsules using as solution (1) a solution prepared immediately before use by shaking a quantity of the powdered tablets containing 0.1 g of Levodopa with 10 mL of a mixture of equal volumes of anhydrous formic acid and methanol.

Assay

Weigh and powder 20 tablets. Dissolve as completely as possible a quantity of the powder containing 0.6 g of Levodopa in 10 mL of anhydrous formic acid, add 80 mL of anhydrous acetic acid, mix and carry out Method I for non-aqueous titration, Appendix VIII A, using oracet blue 2R solution as indicator. Each mL of 0.1m perchloric acid VS is equivalent to 19.72 mg of C9H11NO4.

When l-dopa tablets are prescribed or demanded, Levodopa Tablets shall be dispensed or supplied.