Active ingredient: Metharbital - Basic Profile / Key Facts

Basic Profile / Key Facts

Drug Category

• Anticonvulsants

Dosage Forms

• Tablet

Indications

For the treatment of epilepsy

Pharmacology

Metharbital, a barbiturate, is used for the treatment of short term insomnia. It belongs to a group of medicines called central nervous system (CNS) depressants that induce drowsiness and relieve tension or nervousness. Little analgesia is conferred by barbiturates; their use in the presence of pain may result in excitation.

Mechanism of Action

Metharbital binds at a distinct binding site associated with a Cl^- ionopore at the GABA_A receptor, increasing the duration of time for which the Cl^- ionopore is open. The post-synaptic inhibitory effect of GABA in the thalamus is, therefore, prolonged. All of these effects are associated with marked decreases in GABA-sensitive neuronal calcium conductance (gCa). The net result of barbiturate action is acute potentiation of inhibitory GABAergic tone. Barbiturates also act through potent (if less well characterized) and direct inhibition of excitatory AMPA-type glutamate receptors, resulting in a profound suppression of glutamatergic neurotransmission.

Absorption

Not Available

Toxicity

Signs of overdose include confusion (severe), decrease in or loss of reflexes, drowsiness (severe), fever, irritability (continuing), low body temperature, poor judgment, shortness of breath or slow or troubled breathing, slow heartbeat, slurred speech, staggering, trouble in sleeping, unusual movements of the eyes, weakness (severe).

Biotrnasformation / Drug Metabolism

Not Available

Contraindications

The following conditions may affect the use of barbiturates: alcohol abuse (or history of), history of/current drug abuse or dependence (dependence on barbiturates may develop), anemia (severe), asthma (history of), emphysema, or other chronic lung disease, diabetes mellitus (sugar diabetes), hyperactivity (in children), mental depression, overactive thyroid, porphyria (barbiturates may make the condition worse), kidney disease, liver disease (higher blood levels of barbiturates may result, increasing the chance of side effects), pain (barbiturates may cause unexpected excitement or mask important symptoms of more serious problems), underactive adrenal gland (barbiturates may interfere with the effects of other medicines needed for this condition).

Drug Interactions

Interactions may occur with the following: adrenocorticoids (cortisone-like medicine), anticoagulants (blood thinners), carbamazepine, corticotropin (barbiturates may decrease the effects of these medicines), central nervous system (CNS) depressants (using these medicines with barbiturates may result in increased CNS depressant effects), divalproex sodium, valproic acid (using these medicines with barbiturates may change the amount of either medicine that you need to take), and oral contraceptives (birth control pills) containing estrogens (barbiturates may decrease the effectiveness of these oral contraceptives, and you may need to change to a different type of birth control).