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Phenobarbyl - General Information: A barbituric acid derivative that acts as a nonselective central nervous system depressant. It promotes binding to inhibitory gamma-aminobutyric acid subtype receptors, and modulates chloride currents through receptor channels. It also inhibits glutamate induced depolarizations. [PubChem] Pharmacology: Phenobarbyl, the longest-acting barbiturate, is used for its anticonvulsant and sedative-hypnotic properties in the management of all seizure disorders except absence (petit mal). Phenobarbyl for patients Practitioners should give the following information and instructions to patients receiving barbiturates: 1. The use of phenobarbital carries with it an associated risk of psychological and/or physical dependence. The patient should be warned against increasing the dose of the drug without consulting a physician. 2. Phenobarbital may impair mental and/or physical abilities required for the performance of potentially hazardous tasks (e.g., driving, operating machinery, etc.). 3. Alcohol should not be consumed while taking phenobarbital. Concurrent use of phenobarbital with other CNS depressants (e.g., alcohol, narcotics, tranquilizers, and antihistamines) may result in additional CNS depressant Phenobarbyl Interactions Most reports of clinically significant drug interactions occurring with the barbiturates have involved phenobarbital. 1. Anticoagulants: Phenobarbital lowers the plasma levels of dicumarol (name previously used: bishydorxycoumarin) and causes a decrease in anticoagulant activity as measured by the prothrombin time. Phenobarbital can induce hepatic microsomal enzymes resulting in increased metabolism and decreased anticoagulant response of oral anticoagulants (e.g., warfarin, acenocournarol, dicumarol, and phenprocoumon). Patients stabilized on anticoagulant therapy may require dosage adjustments if phenobarbital is added to or withdrawn from their dosage regimen. 2. Corticosteroids: Phenobarbital appears to enhance the metabolism of exogenous corticosteroids probably through the induction of hepatic microsomal enzymes. Patients stabilized on corticosteroid therapy may require dosage adjustments if phenobarbital is added to or withdrawn from their dosage regimen. 3. Griseofulvin: Phenobarbital appears to interfere with the absorption of orally administered griseofulvin, thus decreasing its blood level. The effect of the resultant decreased blood levels of griseofulvin on therapeutic response has not been established. However, it would be preferable to avoid concomitant administration of these drugs. 4. Doxycycline: Phenobarbital has been shown to shorten the half- life of doxycycline for as long as 2 weeks after barbiturate therapy is discontinued. This mechanism is probably through the induction of hepatic microsomal enzymes that metabolize the antibiotic. If phenobarbital and doxycycline are administered concurrently, the clinical response to doxycycline should be monitored closely. 5. Phenytoin, sodium valproate, valproic acid: The effect of phenobarbital on the metabolism of phenytoin appears to be variable. Some investigators report an accelerating effect, while others report no effect. Because the effect of phenobarbital on the metabolism of phenytoin is not predictable, phenytoin and phenobarbital blood levels should be monitored more frequently if these drugs are given concurrently. Sodium valproate and valproic acid appear to decrease phenobarbital metabolism; therefore, phenobarbital blood levels should be monitored and appropriate dosage adjustments made as indicated. 6. Central nervous system depressants: The concomitant use of other central nervous system depressants including other sedatives or hypnotics, antihistamines, tranquilizers, or alcohol, may produce additive depressant effects. 7. Monoamine oxidase inhibitors (MAOIs): MAOIs prolong the effects of phenobarbital probably because metabolism of the phenobarbital is inhibited. 8. Estradiol, estrone, progesterone and other steroidal hormones: Pretreatment with or concurrent administration of phenobarbital may decrease the effect of estradiol by increasing its metabolism. There have been reports of patients treated with antiepileptic drugs (e.g., phenobarbital) who became pregnant while taking oral contraceptives. An alternate contraceptive method might be suggested to women taking phenobarbital. Phenobarbyl Contraindications Phenobarbital is contraindicated in patients with known phenobarbital sensitivity or a history of manifest or latent porphyria.Additional information about PhenobarbylPhenobarbyl Indication: For the treatment of all types of seizures except absence seizures. Mechanism Of Action: Phenobarbyl acts on GABAA receptors, increasing synaptic inhibition. This has the effect of elevating seizure threshold and reducing the spread of seizure activity from a seizure focus. Phenobarbyl may also inhibit calcium channels, resulting in a decrease in excitatory transmitter release. The sedative-hypnotic effects of phenobarbital are likely the result of its effect on the polysynaptic midbrain reticular formation, which controls CNS arousal. Drug Interactions: Not Available Food Interactions: Avoid alcohol.Avoid excessive quantities of coffee or tea (Caffeine).Increase dietary intake of magnesium, folate, vitamin B6, B12, and/or consider taking a multivitamin. Generic Name: Phenobarbital Synonyms: Phenobarbitol; Phenobarbituric Acid; Phenylethylbarbiturate; Phenylethylbarbituric Acid; Phenylethylmalonylurea; Fenobarbital Where to order Phenobarbital (and Phenobarbyl analogs) online: Drug Category: Hypnotics and Sedatives; Anticonvulsants Drug Type: Small Molecule; Approved Other Brand Names containing Phenobarbital: Adonal; Aephenal; Agrypnal; Amylofene; Aphenylbarbit; Aphenyletten; Barbenyl; Barbinal; Barbiphen; Barbiphenyl; Barbipil; Barbita; Barbivis; Barbonal; Barbophen; Bardorm; Bartol; Bialminal; Blu-Phen; Cabronal; Calmetten; Calminal; Cardenal; Chinoin; Codibarbita; Coronaletta; Cratecil; Damoral; Dezibarbitur; Dormina; Dormiral; Dormital; Doscalun; Duneryl; Ensobarb; Ensodorm; Epanal; Epidorm; Epilol; Episedal; Epsylone; Eskabarb; Etilfen; Euneryl; Fenbital; Fenemal; Fenosed; Fenylettae; Gardenal; Gardepanyl; Glysoletten; Haplopan; Haplos; Helional; Hennoletten; Henotal; Hypnaletten; Hypnette; Hypno-Tablinetten; Hypnogen; Hypnolone; Hypnoltol; Hysteps; Lefebar; Leonal; Lephebar; Lepinal; Lepinaletten; Linasen; Liquital; Lixophen; Lubergal; Lubrokal; Lumen; Lumesettes; Lumesyn; Luminal; Lumofridetten; Luphenil; Luramin; Molinal; Neurobarb; Nirvonal; Noptil; Nova-Pheno; Nunol; Parkotal; Pharmetten; Phen-Bar; Phenaemal; Phenemal; Phenemalum; Phenobal; Phenobarbyl; Phenoluric; Phenolurio; Phenomet; Phenonyl; Phenoturic; Phenyletten; Phenyral; Phob; Polcominal; Promptonal; Seda-Tablinen; Sedabar; Sedicat; Sedizorin; Sedlyn; Sedofen; Sedonal; Sedonettes; Sevenal; Sinoratox; Solfoton; Solfoton Talpheno; Solu-Barb; Sombutol; Somnolens; Somnoletten; Somnosan; Somonal; Spasepilin; Starifen; Starilettae; Stental; Stental Extentabs; Talpheno; Teolaxin; Teoloxin; Thenobarbital; Theoloxin; Triabarb; Tridezibarbitur; Triphenatol; Versomnal; Zadoletten; Zadonal; Absorption: Absorbed in varying degrees following oral, rectal or parenteral administration. The salts are more rapidly absorbed than are the acids. The rate of absorption is increased if the sodium salt is ingested as a dilute solution or taken on an empty stomach. Toxicity (Overdose): CNS and respiratory depression which may progress to Cheyne-Stokes respiration, areflexia, constriction of the pupils to a slight degree (though in severe poisoning they may wshow paralytic dilation), oliguria, tachycardia, hypotension, lowered body temperature, and coma. Typical shock syndrome (apnea, circulatory collapse, respiratory arrest, and death) may occur. Protein Binding: 20 to 45% Biotransformation: Hepatic (mostly via CYP2C19). Half Life: 53 to 118 hours (mean 79 hours) Dosage Forms of Phenobarbyl: Tablet OralElixir OralSolution Intramuscular Chemical IUPAC Name: 5-ethyl-5-phenyl-1,3-diazinane-2,4,6-trione Chemical Formula: C12H12N2O3 Phenobarbital on Wikipedia: http://en.wikipedia.org/wiki/Phenobarbital Organisms Affected: Humans and other mammals
Practitioners should give the following information and instructions to patients receiving barbiturates: 1. The use of phenobarbital carries with it an associated risk of psychological and/or physical dependence. The patient should be warned against increasing the dose of the drug without consulting a physician. 2. Phenobarbital may impair mental and/or physical abilities required for the performance of potentially hazardous tasks (e.g., driving, operating machinery, etc.). 3. Alcohol should not be consumed while taking phenobarbital. Concurrent use of phenobarbital with other CNS depressants (e.g., alcohol, narcotics, tranquilizers, and antihistamines) may result in additional CNS depressant
Most reports of clinically significant drug interactions occurring with the barbiturates have involved phenobarbital. 1. Anticoagulants: Phenobarbital lowers the plasma levels of dicumarol (name previously used: bishydorxycoumarin) and causes a decrease in anticoagulant activity as measured by the prothrombin time. Phenobarbital can induce hepatic microsomal enzymes resulting in increased metabolism and decreased anticoagulant response of oral anticoagulants (e.g., warfarin, acenocournarol, dicumarol, and phenprocoumon). Patients stabilized on anticoagulant therapy may require dosage adjustments if phenobarbital is added to or withdrawn from their dosage regimen. 2. Corticosteroids: Phenobarbital appears to enhance the metabolism of exogenous corticosteroids probably through the induction of hepatic microsomal enzymes. Patients stabilized on corticosteroid therapy may require dosage adjustments if phenobarbital is added to or withdrawn from their dosage regimen. 3. Griseofulvin: Phenobarbital appears to interfere with the absorption of orally administered griseofulvin, thus decreasing its blood level. The effect of the resultant decreased blood levels of griseofulvin on therapeutic response has not been established. However, it would be preferable to avoid concomitant administration of these drugs. 4. Doxycycline: Phenobarbital has been shown to shorten the half- life of doxycycline for as long as 2 weeks after barbiturate therapy is discontinued. This mechanism is probably through the induction of hepatic microsomal enzymes that metabolize the antibiotic. If phenobarbital and doxycycline are administered concurrently, the clinical response to doxycycline should be monitored closely. 5. Phenytoin, sodium valproate, valproic acid: The effect of phenobarbital on the metabolism of phenytoin appears to be variable. Some investigators report an accelerating effect, while others report no effect. Because the effect of phenobarbital on the metabolism of phenytoin is not predictable, phenytoin and phenobarbital blood levels should be monitored more frequently if these drugs are given concurrently. Sodium valproate and valproic acid appear to decrease phenobarbital metabolism; therefore, phenobarbital blood levels should be monitored and appropriate dosage adjustments made as indicated. 6. Central nervous system depressants: The concomitant use of other central nervous system depressants including other sedatives or hypnotics, antihistamines, tranquilizers, or alcohol, may produce additive depressant effects. 7. Monoamine oxidase inhibitors (MAOIs): MAOIs prolong the effects of phenobarbital probably because metabolism of the phenobarbital is inhibited. 8. Estradiol, estrone, progesterone and other steroidal hormones: Pretreatment with or concurrent administration of phenobarbital may decrease the effect of estradiol by increasing its metabolism. There have been reports of patients treated with antiepileptic drugs (e.g., phenobarbital) who became pregnant while taking oral contraceptives. An alternate contraceptive method might be suggested to women taking phenobarbital.
Phenobarbital is contraindicated in patients with known phenobarbital sensitivity or a history of manifest or latent porphyria.
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