mechanism of action

Barbiturates work by binding to the GABAA receptor at either the alpha or the beta sub unit. These are binding sites that are distinct from GABA itself and also distinct from the benzodiazepine binding site. Like benzodiazepines, barbiturates potentiate the effect of GABA at this receptor. This GABAA receptor binding decreases input resistance, depresses burst and tonic firing, especially in ventrobasal and intralaminar neurons, while at the same time increasing burst duration and mean conductance at individual chloride channels; this increases both the amplitude and decay time of inhibitory postsynaptic currents. In addition to this GABA-ergic effect, barbiturates also block the AMPA receptor, a subtype of glutamate receptor. Glutamate is the principal excitatory neurotransmitter in the mammalian CNS.

drug interactions

Amiloride: Decreases the antiarrhythmic effect of quinidine

Aminophylline: The barbiturate, dihydroquinidine barbiturate, decreases the effect of aminophylline.

Amiodarone: Increases the effect of quinidine

Amitriptyline: Dihydroquinidine barbiturate increases the effect of the tricyclic antidepressant, amitriptyline.

Aripiprazole: Quinidine increases the effect and toxicity of aripiprazole

Atazanavir: Increased risk of cardiotoxicity and arrhythmias

Betamethasone: The barbiturate, dihydroquinidine barbiturate, may decrease the effect of the corticosteroid, betamethasone.

Cimetidine: Increases the effect of quinidine

Cisapride: Increased risk of cardiotoxicity and arrhythmias

Clomipramine: Dihydroquinidine barbiturate increases the effect of the tricyclic antidepressant, clomipramine.

Codeine: Quinidine decreases the analgesic effect of codeine

Cyclosporine: The barbiturate, dihydroquinidine barbiturate, increases the effect of cyclosporine.

Desipramine: Dihydroquinidine barbiturate increases the effect of the tricyclic antidepressant, desipramine.

Dexamethasone: The barbiturate, dihydroquinidine barbiturate, may decrease the effect of the corticosteroid, dexamethasone.

Dextromethorphan: Quinidine increases the toxicity of dextromethorphan

Digoxin: Quinine/quinidine increases the effect of digoxin

Diltiazem: Increases the effect and toxicity of quinidine

Doxepin: Dihydroquinidine barbiturate increases the effect of the tricyclic antidepressant, doxepin.

Doxycycline: The anticonvulsant, dihydroquinidine barbiturate, decreases the effect of doxycycline.

Felodipine: The barbiturate, dihydroquinidine barbiturate, decreases the effect of felodipine.

Fludrocortisone: The barbiturate, dihydroquinidine barbiturate, may decrease the effect of the corticosteroid, fludrocortisone.

Folic Acid: Folic acid decreases the effect of anticonvulsant, dihydroquinidine barbiturate.

Gatifloxacin: Increased risk of cardiotoxicity and arrhythmias

Gefitinib: The CYP3A4 inducer, dihydroquinidine barbiturate, may decrease the serum concentration and therapeutic effects of gefitinib.

Grepafloxacin: Increased risk of cardiotoxicity and arrhythmias

Griseofulvin: The barbiturate, dihydroquinidine barbiturate, decreases the effect of griseofulvin.

Hydrocortisone: The barbiturate, dihydroquinidine barbiturate, may decrease the effect of the corticosteroid, hydrocortisone.

Imipramine: Dihydroquinidine barbiturate increases the effect of the tricyclic antidepressant, imipramine.

Levofloxacin: Increased risk of cardiotoxicity and arrhythmias

Levonorgestrel: Phenobarbital decreases the effect of levonorgestrel

Magnesium: The antiacid decreases the absorption of quinidine

Methadone: The barbiturate, dihydroquinidine barbiturate, decreases the effect of methadone.

Metronidazole: The barbiturate, dihydroquinidine barbiturate, decreases the effect of metronidazole.

Moxifloxacin: Increased risk of cardiotoxicity and arrhythmias

Nelfinavir: Nelfinavir increases the effect and toxicity of quindine

Nifedipine: Decreased quinidine effect, increased nifedipine effect

Nortriptyline: Dihydroquinidine barbiturate increases the effect of the tricyclic antidepressant, nortriptyline.

Ofloxacin: Increased risk of cardiotoxicity and arrhythmias

Oxtriphylline: The barbiturate, dihydroquinidine barbiturate, decreases the effect of oxtriphylline.

Prednisolone: The barbiturate, dihydroquinidine barbiturate, may decrease the effect of the corticosteroid, prednisolone.

Prednisone: The barbiturate, dihydroquinidine barbiturate, may decrease the effect of the corticosteroid, prednisone.

Procainamide: Quinidine increases the effect of procainamide

Propafenone: Quinidine increases the effect of propafenone

Quinidine: The anticonvulsant, dihydroquinidine. barbiturate, decreases the effect of quinidine.

Quinupristin: This combination presents an increased risk of toxicity

Theophylline: The barbiturate, dihydroquinidine barbiturate, decreases the effect of theophylline.

Triamcinolone: The barbiturate, dihydroquinidine barbiturate, may decrease the effect of the corticosteroid, triamcinolone.