Calculation of Active Drug Moiety
The following formula may be used to calculate the active drug moiety portion of a drug compound:
$$ Drug \ Moiety \ (fraction) = {Drug\ Moiety (g/mole ) \over Drug \ compound \ (g/mole)} $$
|
Solved Problem: The chemical formula of methadone hydrochloride is C21H27NO.HCl a) Calculate the molecular weights of the base and the salt form.
Answer: 309.22 g/mole; 345.67 g/mole |
||||||||||||||||
|
b) Calculate the fraction of active moiety in the compound. Approach: $$ {309.22 (g/mole) \over 345.67 (g/mole)} =0.895, fraction \ of \ methadone \ base $$ Answer: 0.895 | ||||||||||||||||
|
c) Calculate the percent of active moiety in the compound. Approach:
$$ {0.895 \times 100}=89.5 % methadone base $$ Answer: 89.5 % | ||||||||||||||||
|
d) Calculate the quantity of methadone in a 10 mg tablet of methadone hydrochloride. Approach: .
$${10 \ mg \over 345.67 (g/mole)} = {x\ mg \over 309.22 (g/mole)} $$ Answer: 8.95 mg methadone |
||||||||||||||||
|
e) Calculate the quantity of methadone hydrochloride needed to supply a 10 mg dose of methadone. Approach:
$${10 \ mg \over 309.22 (g/mole)} = {x \ mg \over 345.67 (g/mole)} $$ Answer: 11.18 mg methadone hydrochloride |