Methadone analogues

Methadone analogues

a. Methadone

Synthesis

Metabolism: Methadone metabolizes to form an active α-dinormethadol and dinor-L-α-acetylmethadol (LAAM), then it undergoes N-demethylation to form inactive pyrrolidines an pyrrolines which are excreted in urine.

Properties and uses: It is a white or almost white crystalline powder, freely soluble in ethanol and soluble in water. Even methadone, which looks structurally different from other opioid agonists, has steric forces that produce a configuration that closely resembles the opioid agonists. Methadone is more active and more toxic than morphine. It can be used for the relief of many types of pain. In addition, it is used as narcotic substitute treatment because it prevents morphine abstinence syndrome. The toxicity of methadone is three to ten times that of morphine, but its analgesic effect is twice that of morphine and ten times that of meperidine.

Assay: Dissolve the sample in a mixture of 0.01 M hydrochloric acid and anhydrous ethanol by using 0.1 M sodium hydroxide to perform potentiometric titration.

Storage: It should be stored in well-closed airtight containers and protected from light.

Dosage forms: Methadone HCl injection I.P., Methadone HCl tablets I.P., Methadone injection B.P., Methadone Linctus B.P., Methadone oral solution (1 mg/ml), B.P., Methadone tablets B.P.

b. Dextromoramide

Synthesis

Properties and uses: It is a white amorphous or crystalline powder, soluble in water and sparingly soluble in alcohol. Used as an opioid receptor agonist , and thus, acts as an analgesic.

Assay: Dissolve the sample in anhydrous acetic acid and titrate with 0.05 M perchloric acid using naphtholbenzein solution as indicator.

Dosage forms: Dextromoramide tablets B.P.

c. Dextropropoxyphene (Propoxyphene hydrochloride, Neurovon, Proxytab, Spasma Neurovon)

Synthesis

Properties and uses: It is a white or almost white crystalline powder, very soluble in water and freely soluble in alcohol. It has no anti-inflammatory or antipyretic action and has little antitussive activity despite the fact that its levo isomer is used for this purpose. It is used to control mild-to-moderate pain and used along with other analgesics having anti-inflammatory and antipyretic properties, such as paracetamol and aspirin.

Assay: Dissolve the sample in acetic anhydride and titrate with 0.1M perchloric acid. Determine the end point potentiometrically.

Storage: It should be stored in well-closed airtight containers and protected from light.

Dose: The usual does is 65 mg, 3 or 4 times/day.

Dosage forms: Co-proxamol tablets B.P.