Phenobarbital Felodipine

Drugs that can decrease carbamazepine serum levels include charcoal, cisplatin, doxorubicin, felbamate, hydantoins, rifampin, phenobarbital, primidone, theophylline. The serum levels of oral contraceptives, haloperidol, bupropion, anticoagulants, felbamate, valproic acid, felodipine, tricyclic antidepressants, acetaminophen, ziprasidone, voriconazole, topiramate, tiagabine, olanzapine, and lamotrigine can be lowered by carbamazepine. 

Phenobarbital Enhances phasic GABAa receptor responses reduces excitatory synaptic responses Nearly complete absorption not significantly bound to plasma proteins peak concentrations in Vi to 4 h no active metabolites tjy2 varies from 75 to 125 h Generalized tonic-clonic seizures, partial seizures, myoclonic seizures, generalized seizures, neonatal seizures, status epilepticus Toxicity Sedation, cognitive issues, ataxia, hyperactivity Interactions Valproate, carbamazepine, felbamate, phenytoin, cyclosporine, felodipine, lamotrigine, nifedipine, nimodipine, steroids, theophylline, verapamil, others... 

CALCIUM CHANNEL BLOCKERS BARBITURATES L plasma concentrations of felodipine, nifedipine, nimodipine, nisoldipine and verapamil with phenobarbital Phenobarbital induces CYP3A4, which metabolizes calcium channel blockers. It also induces intestinal P-gp, which may 1 the bioavailability of verapamil Monitor PR and BP closely watch for Tbp... 

Clinically important, potentially hazardous interactions with amlodipine, anisindione, anticoagulants, aprepitant, atorvastatin, barbiturates, benzodiazepines, butabarbital, carbamazepine, chlordiazepoxide, clarithromycin, clonazepam, dorazepate, corticosteroids, cyclosporine, dexamethasone, diazepam, dicumarol, erythromycin, ethotoin, felodipine, flurazepam, fluvastatin, fosphenytoin, isradipine, itraconazole, ketoconazole, lorazepam, lovastatin, mephenytoin, mephobarbital, midazolam, nicardipine, nifedipine, nimodipine, nisoldipine, oxazepam, pentobarbital, phenobarbital, pimozide, pravastatin, primidone, quazepam, rifampin, secobarbital, simvastatin, St John s wort, temazepam, warfarin... 

Clinically important, potentially hazardous interactions with abacavir, atorvastatin, bepridil, bupropion, carbamazepine, clarithromycin, cyclosporine, dexamethasone, digoxin, felodipine, fluticasone propionate, fosamprenavir, itraconazole, ketoconazole, lovastatin, methadone, midazolam, nicardipine, nifedipine, phenobarbital, phenytoin, rifabutin, simvastatin, sirolimus, St John s wort, systemic lidocaine, tacrolimus, tenofovir, trazodone, vinblastine, vincristine, voriconazole, warfarin, zidovudine... 

CYP2C8 <5 1-2 Disopyramide Amiodarone Clozapine Diclofenac Fluvastatin Nicardipine Paclitaxel Retinoic acid Rosiglitazone Torsemide Repaglinide Amiodarone Celecoxib Felodipine Nicardipine Fluoxetine Ketoconazole Ritonavir Indinavir Troglitazone Zafirlukast Retinoic acid Clotrimazole Phenobarbital Dexamethasone Gemfibrozil Rifampin Phenytoin Ritonavir... 

Limited evidence su ests that phenobarbital greatly reduces the levels and/or increases the clearance of felodipine, nifedipine, ni-modipine, and verapamil. Other calcium-channel blockers are expected to be similar affected. 

After taking felodipine 10 mg daily for 4 days, 10 epileptics (including one who was taking phenobarbital) had markedly reduced plasma felodipine levels (peak levels of 1.6nanomol/L compared with 8.9 nanomol/L in 12 control subjects). The felodipine bioavailability was reduced to 6.6%. ... 

Pbenobarbital markedly reduces felodipine, nifedipine and verapamil levels. A considerable increase in tbe dosage of these calcium-cbannel blockers will probably be needed in patients taking phenobarbital. Nimodipine effects are also markedly reduced by phenobarbital and the manufactarer contraindicates concurrent use. There is no direct information of interactions with other calcium-cbannel blockers, but as they are largely metabolised in the same way (see calcium-cbannel blockers , (p.860)) they would all be expected to interact similarly. 

Konno H, Taylor LS (2006) Influence of diffeient polymers on the crystallization tendency of moleculariy dispersed amorphous felodipine. J Pharm Sci 95 2692-2705 Korhonen O, Bhugra C, Pikal MJ (2008) Correlation between molecular mobility and crystal growth of amorphous phenobaibital and phenobarbital with polyvinylpyrrolidone and L-proline. J Pharm Sci 97 3830-3841... 

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