Methadone Linctus

Definition

 

Methadone Linctus is an oral solution containing 0.04% w/v of Methadone Hydrochloride in a suitable vehicle with a tolu flavour.

 

The linctus complies with the requirements stated under Oral Liquids and with the following requirements.

 

Content of methadone hydrochloride, C21H27NO,HCl

 

0.036 to 0.044% w/v.

 

Identification

 

To 50 ml add 30 ml of water  and add 1M sulphuric acid until the solution is acidic to litmus paper . Extract with two 20 ml quantities of petroleum spirit (boiling range, 40 to 60), discarding the extracts, and add 5M sodium hydroxide until the solution is alkaline to litmus paper . Add 4 g of sodium chloride, shake to dissolve, extract with two 25 ml quantities of ether  and wash the combined ether extracts with five 20 ml quantities of water . Dry with anhydrous sodium sulphate, filter, evaporate to dryness and dry the residue over phosphorus pentoxide at a pressure of 2 kPa. The residue complies with the following tests.

 

A.    The infrared absorption spectrum, Appendix II A, is concordant with the reference spectrum of methadone (RS 218).

 

B.    To 5 mg add 0.05 ml of dinitrobenzene solution and 0.05 ml of a 50% w/v solution of sodium hydroxide. A purple colour is produced which changes slowly to dark brown.

 

Assay

 

To 30 g add 1 ml of glacial acetic acid and dilute to 100 ml with water . To 10 ml of the resulting solution add 10 ml of a 0.4% w/v solution of picric acid and 10 ml of phosphate buffer pH 4.9, extract with three 15 ml quantities of chloroform and dilute the combined chloroform extracts to 50 ml with chloroform. To 10 ml add sufficient chloroform to produce 20 ml and measure the absorbance of the resulting solution, Appendix II B, at the maximum at 350 nm using in the reference cell a solution prepared in the same manner but using 10 ml of a 1% v/v solution of glacial acetic acid and beginning at the words 'add 10 ml¼'. Calculate the content of C21H27NO,HCl taking 448 as the value of A (1%, 1 cm) at the maximum at 350 nm. Determine the weight per ml, Appendix V G, and calculate the content of C21H27NO,HCl, weight in volume.

 

Labelling

 

The label indicates the pharmaceutical form as 'oral solution'.