Barbiturates

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Chapter: Medicinal Chemistry : Anticonvulsants

Anticonvulsants - Barbiturates - Synthesis and Drug Profile - a. Phenobarbitol (Gardenal, Phenetone, Phenorbarb) b. Mephobarbitone or Methyl phenobarbital c. Primidone (Mysoline) - Structure, Properties, uses, Synthesis, Assay, Storage, Dosage forms, Dose | Synthesis and Drug Profile


SYNTHESIS AND DRUG PROFILE


Barbiturates

Mode of action: The mechanism is facilitated by GABA receptor mediated synaptic inhibition, opens the chloride channels, and inhibits the calcium dependent release of neurotransmitters. In addition, at very high concentrations, barbiturates depress sodium and potassium channels and reduce the abnormal discharge of electrical impulse.

Metabolism of barbiturates is discussed in Section III, Chapter Sedatives and Hypnotics.


a. Phenobarbitol (Gardenal, Phenetone, Phenorbarb)


Dose: The usual dose is 1 to 5 mg/kg daily.

Synthesis and drug profile is discussed in section III, Chapter Sedatives and Hypnotics.


b. Mephobarbitone or Methyl phenobarbital


Synthesis and drug profile is discussed in section III, Chapter ‘Sedatives and Hypnotics.


c. Primidone (Mysoline)


Synthesis


Properties and uses: It is a white or almost white crystalline powder. It dissolves in alkaline solutions, slightly soluble in water and ethanol. It is an active antiepileptic but is less potent and less toxic than Phenobarbital. The most frequent side effects include ataxia and vertigo; these tend to disappear with continued or reduced therapy. It is an effective agent for treatment of all types of epilepsy except absence seizures. It is used in combination with Phenytoin or Carbamazepine.

Assay: Dissolve the sample in ethanol, cool, and dilute with the same solvent. Prepare a reference solution in the same manner using 60.0 mg of primidone. Measure the absorbance of the 2 solutions at the absorption maximum of 257 nm. Calculate the content of primidone from the absorbances measured and the concentrations of the solutions.

Dose: The usual dose is 500 mg/day, gradually increasing to a maximum of 2 g daily.

Dosage forms: Primidone oral suspension B.P., Primidone tablets B.P.

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