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.
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.
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
The label indicates the pharmaceutical form as 'oral