Phenobarbital plasma concentrations

Kerrick JlvL Wolff DL, Risinger MW, Graves NM. Increased phenobarbital plasma concentrations a r felbamate initiation Epilepsia ( 99A) 35 (Suppl 8), 96. 

Mephobarbital and Phenobarbital Plasma Concentrations in Epileptic Patients Treated with Mephobarbital Ther. Drug Monit. 1(1) 117-122 (1979) CA 91 168094m... 

Pharmacokinetics Primidone is readily absorbed from the Gl tract. Phenobarbital appears in plasma after several days of continuous therapy. Therapeutic plasma concentrations are 5 to 12 mcg/mL for primidone and 15 to 40 mcg/mL for phenobarbital. PEMA and phenobarbital have longer half-lives (10 to 18 hours and... 

Drugs that might decrease plasma concentrations of lopinavir/ritonavir include rifampin, phenobarbital, carbamazepine, phenytoin, azole antifungals, delavirdine, rifabutin, St. John s wort, efavirenz, nevirapine, and corticosteroids. 

Inducers of CYP3A4 such as St. John s wort preparations (H. perforatum), phenobarbital, carbamazepine, and rifampin may reduce plasma concentrations of estrogens, possibly resulting in a decrease in therapeutic effects and/or changes in the uterine bleeding profile ... 

Delavirdine is extensively metabolized to inactive metabolites by the CYP3A and CYP2D6 enzymes. However, it also inhibits CYP3 A and thus inhibits its own metabolism. In addition to its interactions with other antiretroviral agents (see Table 49 1), delavirdine will result in increased levels of numerous agents (Table 49-3). Dose reduction of indinavir and saquinavir should be considered if they are administered concurrently with delavirdine. Delavirdine plasma concentrations are reduced in the presence of antacids, phenytoin, phenobarbital, carbamazepine, rifabutin, and rifampin concentrations are increased during coadministration with clarithromycin, fluoxetine, dexamethasone, and ketoconazole. 

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... 

ALMOTRIPTAN, ELETRIPTAN PHENOBARBITAL Possible 1 plasma concentrations of almotriptan and risk of inadequate therapeutic efficacy One of the major metabolizing enzymes of almotriptan - CYP3A4 isoenzymes - is induced by rifampicin. As there are alternative metabolic pathways, the effect may not be significant and can vary from individual to individual Be aware of possibility of 1 response to triptan, and consider t dose if considered to be due to interaction... 

CARMUSTINE ANTIEPILEPTICS -PHENOBARBITAL 1 plasma concentrations of carmustine and 1 anti-tumour effect in animal experiments Attributed to induction of liver metabolizing enzymes of carmustine by phenobarbitone, particularly with long-term therapy Avoid concurrent use. As this study did not show any interaction with phenytoin, phenytoin may be a suitable alternative antiepileptic... 

ETOPOSIDE ANTIEPILEPTICS - PHENYTOIN, PHENOBARBITAL Significantly i plasma concentrations of etoposide (clearance may be >170%) and considerable risk of loss of therapeutic efficacy Due to potent induction of the hepatic microsomal enzymes that metabolize etoposide Do not co-administer. Consider use of alternative antiepileptics that do not induce hepatic microsomal enzymes, e.g. valproic acid... 

IRINOTECAN 1. ANTIBIOTICS-rifampicin 2. ANTICANCER AND IMMUNOMODULATING DRUGS - dexamethasone 3. ANTIDEPRESSANTS -St John s wort 4. ANTI EPILEPTICS -carbamazepine, phenobarbital, phenytoin 1 plasma concentrations of irinotecan and risk of 1 therapeutic efficacy. The effects may last for 3 weeks after discontinuation of CYP-inducer therapy Due to induction of CYP3A4-mediated metabolism of irinotecan Avoid concomitant use when ever possible if not, t dose of irinotecan by 50%... 

LOMUSTINE ANTIEPILEPTICS-PHENOBARBITAL 1 plasma concentrations of lomustine and risk of inadequate therapeutic response Phenobarbital induces the metabolism of lomustine by the CYP450 isoenzymes Avoid concurrent use. If necessaiy, t dose of lomustine and monitor therapeutic effects... 

PACLITAXEL 1. ANTIBIOTICS-rifampicin 2. ANTIDEPRESSANTS-St John s wort 3. ANTIEPILEPTICS -carbamazepine, phenobarbital, phenytoin 1 plasma concentration of paclitaxel and 1 efficacy of paclitaxel Due to induction of hepatic metabolism of paclitaxel by the CYP isoenzymes Monitor for clinical efficacy and need to T dose if inadequate response is due to interaction... 

TAMOXIFEN ANTIEPILEPTICS -CARBAMAZEPINE, PHENYTOIN, PHENOBARBITAL i plasma concentrations of tamoxifen and risk of inadequate therapeutic response Due to induction of metabolism of tamoxifen by the CYP3A isoenzymes by phenytoin Avoid concurrent use if possible. Otherwise monitor for clinical efficacy of tamoxifen by t dose of tamoxifen... 

CORTICOSTEROIDS ANTIEPILEPTICS -CARBAMAZEPINE, PHENYTOIN, PHENOBARBITAL 1 plasma concentrations of corticosteroids and risk of poor or inadequate therapeutic response, which would be undesirable if used for e.g. cerebral oedema Due to induction of the hepatic metabolism by the CYP3A4 isoenzymes Closely monitor therapeutic response - clinically, by ophthalmoscopy and radiologically - and t dose of corticosteroids for desired therapeutic effect... 

All were treated with albendazole 7.5 mg/kg every 12 hours on 8 consecutive days. Phenytoin, carbamaze-pine, and phenobarbital all induced the oxidative metabolism of albendazole to a similar extent in a non-enantioselective manner. In consequence, there was a significant reduction in the plasma concentration of the active metabolite of albendazole, albendazole sulfoxide. 

Concomitant use of inducers of cytochrome P450, such as rifampicin, rifabutin, phenytoin, phenobarbital, or carba-mazepine, should be avoided, since they significantly reduce delavirdine plasma concentrations (4). 

Phenobarbital stimulates the microsomal enzymes in the liver. This results in increases in liver enzyme concentrations and more rapid metabolism of not only phenobarbital but also other concurrently administered drugs. In the horse, it has been shown that the half-life of phenobarbital decreases (to around 11 h) following repeated oral dosing (Knox et al 1982). Dosage adjustments of phenobarbital may be required to maintain plasma concentrations within the therapeutic window and can be made using the equation ... 

Potassium bromide is the oldest and chemically the simplest of the anticonvulsants. It was first used in 1857 to treat seizures in people. It was the sole effective anticonvulsant drug until the early 1900s when less-sedative drugs became available. Although it is rarely used in humans because of its toxicity, potassium bromide has become popular as a second anticonvulsant drug when seizures continue to occur in dogs and cats despite adequate plasma concentrations of phenobarbital (Dowling 1994). 

With chronic exposure, side effects may include rash, thrombocytopenia, leukopenia, and a lupus-like disorder. Chronic therapy is likely to result in tolerance, and withdrawal symptoms if primidone therapy is abruptly stopped. Doses in excess of 1500 mg (twice the maximum recommended daily dose) should be considered toxic. Less common side effects are hypotension, hypothermia, and dermal bullae. Encephalopathy has been observed in an epileptic patient with high plasma levels and poor renal function. With plasma concentrations exceeding 80pgml primidone may precipitate and cause crystalluria. Plasma levels >10 rgpml are associated with toxic effects. The therapeutic range is reportedly 5-10pgml , but clinical effects correlate more closely with phenobarbital blood levels. 

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