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| Interactions: | Acenocoumarol
Adverse Effect: decreased anticoagulant effectiveness Clinical Management: With coadministration of phenobarbital and Acenocoumarol , monitor international normalized ratio (INR) and adjust anticoagulant doses accordingly.
Amitriptyline
Adverse Effect: Possible decreased tricyclic antidepressant serum concentrations and possible additive adverse effects Clinical Management: Monitor for efficacy of antidepressant effect. Increases in tricyclic antidepressant dosages may be required. Additionally, monitor for toxicity when either drug is added to or withdrawn from therapy. Serum concentrations may be of value in determining appropriate dosage.
Amoxapine
Adverse Effect: Possible decreased Amoxapine serum concentrations and possible additive adverse effects Clinical Management: Monitor for efficacy of antidepressant effect. Increases in Amoxapine dosages may be required. Additionally, monitor for toxicity when either drug is added to or withdrawn from therapy. Serum concentrations may be of value in determining appropriate dosage.
Betamethasone
Adverse Effect: Decreased betamethasone effectiveness Clinical Management: Monitor for a decreased corticosteroid therapeutic effect; increased doses of the corticosteroid may be necessary.
Bupropion hcl
Adverse Effect: Decrease in the plasma concentration of Bupropion HCL due to the induction of its metabolism # Clinical Management: Monitor for the therapeutic effect and adjust the dose if required.
Carbamazepine
Adverse Effect: Decreased carbamazepine effectiveness with loss of seizure control Clinical Management: With combined carbamazepine-phenobarbital therapy, monitor patients for seizure activity, especially pediatric patients, and adjust doses accordingly.
Chloramphenicol
Adverse Effect: phenobarbital toxicity or decreased chloramphenicol effectiveness Clinical Management: With concurrent use monitor levels of both drugs three to five days after initiation or discontinuation; adjust doses as needed.
Clomipramine
Adverse Effect: Possible decreased tricyclic antidepressant serum concentrations and possible additive adverse effects Clinical Management: Monitor for efficacy of antidepressant effect. Increases in tricyclic antidepressant dosages may be required. Additionally, monitor for toxicity when either drug is added to or withdrawn from therapy. Serum concentrations may be of value in determining appropriate dosage.
Clonazepam
Adverse Effect: Increased clonazepam clearance Clinical Management: Monitor patients on concurrent phenobarbital and clonazepam therapy for decreased effectiveness of clonazepam. If therapy with phenobarbital is discontinued, a sudden increase in clonazepam levels would be expected.
Clozapine
Adverse Effect: Decreased clozapine plasma levels associated with marked worsening of psychosis Clinical Management: When adding phenobarbital therapy to patients stabilized on clozapine, monitor patient closely for worsening of psychotic symptoms. If needed, increase the clozapine dose cautiously on the basis of psychotic symptoms. Conversely, when discontinuing phenobarbital, levels of clozapine may increase significantly.
Cyclophosphamide
Adverse Effect: Decreased cyclophosphamide efficacy
Cyclosporin
Adverse Effect: Decreases Cyclosporine concentrations and reduces its efficacy #Clinical Management: Monitor Cyclosporine concentrations and adjust the dosage accordingly.
Dexamethasone
Adverse Effect: Decreased dexamethasone effectiveness Clinical Management: Monitor for a decreased Dexamethasone therapeutic effect andincreased doses of the Dexamethasone may be necessary.
Disopyramide
Adverse Effect: Decreased disopyramide effectiveness Clinical Management: Monitor therapeutic efficacy of disopyramide with combined therapy. Consider obtaining disopyramide levels within the first three weeks when phenobarbital is added or discontinued from the drug regimen.
Dothiepin
Adverse Effect: Possible decreased tricyclic antidepressant serum concentrations and possible additive adverse effects Clinical Management: Monitor for efficacy of antidepressant effect. Increases in tricyclic antidepressant dosages may be required. Additionally, monitor for toxicity when either drug is added to or withdrawn from therapy. Serum concentrations may be of value in determining appropriate dosage.
Doxepin
Adverse Effect: Possible decreased Doxepin serum concentrations and possible additive adverse effects Clinical Management: Monitor for efficacy of antidepressant effect. Increases in Doxepin dosages may be required. Additionally, monitor for toxicity when either drug is added to or withdrawn from therapy. Serum concentrations may be of value in determining appropriate dosage.
Doxycycline
Adverse Effect: decreased doxycycline effectiveness Clinical Management: If used concurrently, a dosage adjustment for doxycycline may be required in order to maintain or achieve a therapeutic effect.
Dydrogesterone
Enhance the clearance of progesterone and the progestogens
Ethosuximide
Adverse Effect: decreased ethosuximide serum concentrations Clinical Management: Patients should be closely monitored for increased seizure activity, and serum concentrations of ethosuximide should be carefully followed. An increase in the ethosuximide dose may be needed.
Felodipine
Adverse Effect: Decreased felodipine effectiveness Clinical Management: Monitor patient for loss of Felodipine effects, including clinical signs or symptoms of hypertension or angina. Dose increases may be required.
Fludrocortisone acetate
Adverse Effect: Increased metabolic clearance of Fludrocortisone acetate due to the induction of hepatic enzymes by Barbiturates # Clinical Management: Monitor for the possible diminished effect of Fludrocortisone acetate and increase the dosage accordingly
Griseofulvine
Adverse Effect: Decreased effectiveness of griseofulvin Clinical Management: Griseofulvin efficacy should be monitored. Dose of griseofulvin need to be increased, or phenobarbital might be administered in a divided dose three times daily to allow more opportunity for griseofulvin to be absorbed.
Hydrocortisone
Adverse Effect: decreased Hydrocortisone effectiveness Clinical Management: Monitor for a decreased Hydrocortisone therapeutic effect and increase dose may be necessary.
Imipramine
Adverse Effect: Possible decreased Imipramine serum concentrations and possible additive adverse effects Clinical Management: Monitor for efficacy of antidepressant effect. Increases in Imipramine dosages may be required. Additionally, monitor for toxicity when either drug is added to or withdrawn from therapy. Serum concentrations may be of value in determining appropriate dosage.
Itraconazole
Adverse Effect: Loss of itraconazole efficacy Clinical Management: If combination therapy is necessary, monitor antifungal therapy for loss of efficacy.
Lamotrigine
Adverse Effect: Reduced lamotrigine efficacy, loss of seizure control Clinical Management: Higher doses of lamotrigine are needed when given concurrently with enzyme-inducing drugs such as phenytoin and phenobarbital. When given in combination with an enzyme-inducing antiepileptic agent, the manufacturer recommends an initial lamotrigine dose of 50 mg once daily for the first two weeks for adult patients, followed by 50 mg twice daily for the third and fourth weeks, advancing by 100 mg daily every two weeks to a total daily dose of 300 mg to 500 mg administered in two divided doses.
Leucoverin
Adverse Effect: decreased efficacy of phenobarbital Clinical Management: Monitor the patient for seizure control if high doses of leucovorin are administered.
Losartan
Adverse Effect: Decreased losartan serum levels Clinical Management: The coadministration of phenobarbital and losartan may result in a lowering of losartan plasma concentrations, but this effect is not considered to be clinically relevant.
Metoprolol
Adverse Effect: Decreased metoprolol effectiveness Clinical Management: If concurrent therapy is required, monitor for a reduction in the effectiveness of metoprolol. A dosage adjustment may be required. Timolol or atenolol may be an alternative beta-blocker choice because they are not dependent on first-pass hepatic metabolism.
Metronidazole
Adverse Effect: Decreases metronidazole effectiveness Clinical Management: Monitor carefully the clinical response to metronidazole. If the infection is not cleared or recurs after stopping metronidazole, higher doses may be necessary.
Mifepristone
Adverse Effect: Induction of Mifepristone metabolism resulting in decreased serum levels of Mifepristone # Clinical Management: Monitor for the therapeutic effects and adjust the dose accordingly.
Montelukast
Adverse Effect: Due to the hepatic microsomal induction the AUC of Montelukast is decreased by concomitant administration of Phenobarbitone # Clinical Management: Monitor for the therapeutic effects and adjust the dose if required.
Nimodipine
Adverse Effect: Decreased nimodipine effectiveness Clinical Management: Monitor patient for clinical signs or symptoms of continuing neurologic deficit which might be due to inadequate or diminished Nimodipine effect. Dose increases may be required.
Nortriptyline
Adverse Effect: Possible decreased Nortriptyline serum concentrations and possible additive adverse effects Clinical Management: Monitor for efficacy of antidepressant effect. Increases in Nortriptyline dosages may be required. Additionally, monitor for toxicity when either drug is added to or withdrawn from therapy. Serum concentrations may be of value in determining appropriate dosage.
Oxcarbazepine
Adverse Effect: Decrease in the Conc of Oxcarbazepine and increase in the Conc. of Phenobarbital. # Clinical Management: Monitor for therapeutic effects and adjust the dose accordingly.
Oxyphenbutazone
Adverse Effect: Decreased phenylbutazone half-life Clinical Management: Monitor therapeutic efficacy of phenylbutazone. If clinically appropriate, an alternative to phenylbutazone, such as naproxen or ibuprofen, that does not interact with phenobarbital might be considered.
Phenindione
Adverse Effect: decreased anticoagulant effectiveness Clinical Management: With coadministration of phenobarbital and Phenindione , monitor international normalized ratio (INR) and adjust anticoagulant doses accordingly.
Phenylbutazone
Adverse Effect: Decreased phenylbutazone half-life Clinical Management: Monitor therapeutic efficacy of phenylbutazone. If clinically appropriate, an alternative to phenylbutazone, such as naproxen or ibuprofen, that does not interact with phenobarbital might be considered.
Prednisolone
Adverse Effect: Decreased prednisolone effectiveness Clinical Management: Monitor for a decreased Prednisolone therapeutic effect and increased dose may be necessary.
Propranolol
Adverse Effect: Decreased propranolol effectiveness Clinical Management: If concurrent therapy is required, monitor for a reduction in the effectiveness of propranolol. A dosage adjustment may be required. Timolol or atenolol may be an alternative choice for a beta blocker because they are not dependent on hepatic metabolism.
Quinidine
Adverse Effect: Decreased quinidine effectiveness Clinical Management: Monitor quinidine concentration for one to three weeks after starting or discontinuing phenobarbital. A dosage adjustment for quinidine may be required in order to maintain a therapeutic effect.
Selegiline
Adverse Effect: CNS depression (sedation, lethargy, speech difficulties) Clinical Management: Caution should be used when these agents are coadministered. Monitor patients for signs of CNS depression and adjust doses accordingly.
Sodium Valproate
Adverse Effect: Phenobarbital toxicity or decreased valproic acid effectiveness Clinical Management: With the addition of valproic acid therapy in a patient stabilized on phenobarbital, the patient should be monitored for signs of phenobarbital toxicity and serum phenobarbital level obtained. Phenobarbital dosage may need to be decreased in some cases. Due to increased valproic acid metabolism, periodic determinations of valproic acid concentrations should be considered.
Tamoxifen
Adverse Effect: Decreased steady-state serum levels of tamoxifen
Theophylline
Adverse Effect: Decreased theophylline effectiveness Clinical Management: Theophylline serum concentrations should be closely monitored when a barbiturate is added, discontinued, or when dosing changes occur. Dosing adjustments of theophylline may be necessary.
Thioridazine
Adverse Effect: Decreased phenobarbital or thioridazine effectiveness Clinical Management: If concurrent therapy is required, a dosage adjustment for thioridazine or phenobarbital may be required in order to maintain or achieve a therapeutic effect.
Tretinoin
Adverse Effect: decreased efficacy of tretinoin Clinical Management: Monitor patients for signs of tretinoin efficacy. The withdrawal of phenobarbital therapy may be warranted in some cases.
Triamcinolone
Adverse Effect: Decreased Triamcinolone effectiveness Clinical Management: Monitor for a decreased Triamcinolone therapeutic effect and increase the dose if necessary.
Trimipramine
Adverse Effect: possible decreased tricyclic antidepressant serum concentrations and possible additive adverse effects Clinical Management: Monitor for efficacy of antidepressant effect. Increases in tricyclic antidepressant dosages may be required. Additionally, monitor for toxicity.
Verapamil
Adverse Effect: Decreased verapamil effectiveness Clinical Management: Monitor patient for loss of calcium channel blocker effects, including clinical signs or symptoms of hypertension or angina. Dose increases may be required.
Warfarin
Adverse Effect: decreased anticoagulant effectiveness Clinical Management: With coadministration of phenobarbital and Warfarin , monitor international normalized ratio (INR) and adjust Warfarin doses accordingly. |
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