Actions of Phenobarbitone GPO in details
Rhea Phenobarbitone GPO is an anticonvulsant, hypnotic, sedative drug. This medication is a long-acting barbiturate. It is believed that the effects of Phenobarbitone GPO, like other barbiturates, due to the ability to increase and / or mimic the inhibitory effect of GABA on synaptic transmission. Sedative-hypnotic effect due to the suppression of sensory cortex, decrease motor activity, changes in the functional state of the brain. Although the mechanism of action is not fully installed, Phenobarbitone GPO, like other barbiturates apparently is particularly active at the level of the thalamus, which suppresses the rising holding in the reticular formation, thereby preventing transmission of impulses in the cerebral cortex. Anticonvulsant effect is due to suppression of the monosynaptic and polysynaptic transmission in the CNS.
Rhea Phenobarbitone GPO causes a dose-dependent respiratory depression.
Phenobarbitone GPO reduces the concentration of serum bilirubin.
Like other barbiturates, this medicine contributes to the induction of microsomal liver enzymes, thereby enhancing or altering the metabolism of other drugs.
How should I take Phenobarbitone GPO?
Take exactly as prescribed by your doctor. Do not take in larger or smaller amounts or for longer than recommended. Follow the directions on your prescription label.
Take this medicine with a full glass of water.
If you are taking this medicine to treat insomnia, take it only at bedtime. Do not use Phenobarbitone GPO for longer than 2 weeks to treat insomnia, unless your doctor has told you to.
Take Phenobarbitone GPO only when you are getting ready for several hours of sleep. You may fall asleep very quickly after taking the medicine.
Do not change your dose of Phenobarbitone GPO without your doctor's advice. Tell your doctor if the medication does not seem to work as well in treating your condition.
If you are taking Phenobarbitone GPO to treat seizures, keep taking the medication even if you feel fine. You may have increased seizures or withdrawal symptoms if you stop using Phenobarbitone GPO suddenly. You will need to use less and less before you stop the medication completely.
If you use this medication long-term, your blood will need to be tested often. Visit your doctor regularly.
Store at room temperature away from moisture and heat.
Keep track of the amount of medicine used from each new bottle. Phenobarbitone GPO is a drug of abuse and you should be aware if anyone is using your medicine improperly or without a prescription.
Phenobarbitone GPO administration
Take exactly as prescribed by your doctor. Do not take in larger or smaller amounts or for longer than recommended. Follow the directions on your prescription label.
Take this medicine with a full glass of water.
If you are taking this medicine to treat insomnia, take it only at bedtime. Do not use Phenobarbitone GPO for longer than 2 weeks to treat insomnia, unless your doctor has told you to.
Take Phenobarbitone GPO only when you are getting ready for several hours of sleep. You may fall asleep very quickly after taking the medicine.
Do not change your dose of Phenobarbitone GPO without your doctor's advice. Tell your doctor if the medication does not seem to work as well in treating your condition.
If you are taking Phenobarbitone GPO to treat seizures, keep taking the medication even if you feel fine. You may have increased seizures or withdrawal symptoms if you stop using Phenobarbitone GPO suddenly. You will need to use less and less before you stop the medication completely.
If you use this medication long-term, your blood will need to be tested often. Visit your doctor regularly.
Store at room temperature away from moisture and heat.
Keep track of the amount of medicine used from each new bottle. Phenobarbitone GPO is a drug of abuse and you should be aware if anyone is using your medicine improperly or without a prescription.
Phenobarbitone GPO pharmacology
Phenobarbitone GPO is capable of producing all levels of CNS mood alteration, from excitation to mild sedation to hypnosis, and deep coma. Overdosage can produce death. In high enough therapeutic doses, Phenobarbitone GPO induces anesthesia. Phenobarbitone GPO depresses the sensory cortex, decreases motor activity, alters cerebellar function, and produces drowsiness, sedation, and hypnosis. Phenobarbitone GPO-induced sleep differs from physiological sleep. Sleep laboratory studies have demonstrated that Phenobarbitone GPO reduces the amount of time spent in the rapid eye movement (REM) phase of sleep or the dreaming stage. Also Stages III and IV sleep are decreased. Following abrupt cessation of Phenobarbitone GPO used regularly, patients may experience markedly increased dreaming, nightmares and/or insomnia. Therefore, withdrawal of a single therapeutic dose over 5 or 6 days has been recommended to lessen the REM rebound and disturbed sleep which contribute to drug withdrawal syndrome (for example, decrease the dose from 3 to 2 doses a day for 1 week).
Phenobarbitone GPO might be expected to lose its effectiveness for inducing and maintaining sleep after about 2 weeks.
Phenobarbitone GPO has little analgesic action at subanesthetic doses. Rather, in subanesthetic doses, this drug may increase the reaction to painful stimuli. All barbiturates exhibit anticonvulsant activity in anesthetic doses. However, of the drugs in this class, only Phenobarbitone GPO, mephobarbital, and metharbital are effective as oral anticonvulsants in subhypnotic doses.
Phenobarbitone GPO is a respiratory depressant. The degree of respiratory depression is dependent upon the dose. With hypnotic doses, respiratory depression produced by Phenobarbitone GPO is similar to that which occurs during physiologic sleep with slight decrease in blood pressure and heart rate. Studies in laboratory animals have shown that Phenobarbitone GPO causes reduction in the tone and contractility of the uterus, ureters, and urinary bladder. However, concentrations of the drug required to produce this effect in humans are not reached with sedative-hypnotic doses.
Phenobarbitone GPO does not impair normal hepatic function but has been shown to induce liver microsomal enzymes, thus increasing and/or altering the metabolism of barbiturates and other drugs.
Pharmacokinetics
Phenobarbitone GPO is 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.
Duration of action, which is related to the rate at which Phenobarbitone GPO is redistributed throughout the body varies among persons and in the same person from time to time. Long-acting Phenobarbitone GPO has onset of action of 1 hour or longer and duration of actions of 10 to 12 hours.
No studies have demonstrated that the different routes of administration are equivalent with respect to bioavailability.
Phenobarbitone GPO is a weak acid that is absorbed and rapidly distributed to all tissues and fluids with high concentrations in the brain, liver, and kidneys. The more lipid soluble the drug is, the more rapidly it penetrates all tissues of the body.
Phenobarbitone GPO has the lowest lipid solubility, lowest plasma binding, lowest brain protein binding, the longest delay in onset of activity, and the longest duration of action in the barbiturate class.
Phenobarbitone GPO has a plasma half-life of 53 to 118 hours (mean: 79 hours). For children and newborns the plasma half-life is 60 to 180 hours (mean: 110 hours). (Half-life values were determined for newborn age being defined as 48 hours or less.)
Phenobarbitone GPO is metabolized primarily by the hepatic microsomal enzyme system, and the metabolic products are excreted in the urine, and less commonly, in the feces. Approximately 25 to 50 percent of a dose of Phenobarbitone GPO is eliminated unchanged in the urine, whereas the amount of other barbiturates excreted unchanged in the urine is negligible. The excretion of unmetabolized barbiturate is one feature that distinguishes the long-acting category from those belonging to other categories which are almost entirely metabolized. The inactive metabolites of the barbiturates are excreted as conjugates of glucuronic acid.
References
- NCIt. "Phenobarbital: NCI Thesaurus (NCIt) provides reference terminology for many systems. It covers vocabulary for clinical care, translational and basic research, and public information and administrative activities.". https://ncit.nci.nih.gov/ncitbrowser... (accessed September 17, 2018).
- EPA DSStox. "Phenobarbital: DSSTox provides a high quality public chemistry resource for supporting improved predictive toxicology.". https://comptox.epa.gov/dashboard/ds... (accessed September 17, 2018).
Reviews
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Information checked by Dr. Sachin Kumar, MD Pharmacology
