Phenobarbital (tablets 0.1 g)
Tabulettae Phenobarbitali 0.1
International not patented name
Phenobarbital
Pharmacotherapeutic group
Sedative and soporific preparations. Anticonvulsants.
Composition
1 tablet contains 100 mg of phenobarbital.
Pharmacologic action
Pharmacodynamics
Phenobarbital has a sedative, soporific, anti-convulsive, spasmolytic effects. It enhances the GABA hindering effect. It interacts with membranes and changing their physico-chemical characteristics reduces the epileptogenic focus neurons excitability and the nervous impulses spread. It has an anti-convulsive activity. It suppresses the cerebral cortex sensor zones, reduces the motor activity, suppresses the cerebral functions. The preparation induces the sleep development. Phenobarbital decreases the GIT not-striated muscles tonus.
Pharmacokinetics
When taken per os phenobarbital is absorbed completely though relatively slowly: the maximal blood plasma concentration is observed in 1 – 2 hours after the preparation intake. About 50% is fixed on plasma proteins. Phenobarbital penetrates through placenta well. The period of half elimination from blood plasma of adults is 2 – 4 days (up to 7 days in newborns). The preparation is excreted slowly from the body thus creating predisposition for accumulation. Phenobarbital is metabolized by the liver microsomal enzymes. Not active metabolite is excreted by the kidneys in form of glucuronide. About 25% of phenobarbital is excreted unchanged.
Indications for appliance
Phenobarbital has a pronounced soporific action and if applied for sleep disturbances managing. Phenobarbital in small doses has a tranquilizing effect and in combinations with other preparations (spasmolytics, vasodilative preparations) is applied in case of neurovegetative disturbances.
Because of the phenobarbital anti-convulsive effect it is prescribed for chorea, spastic paralyses, various convulsive reactions. The preparation is considered to be one of the most efficient anti-epileptic drugs. It is widely used for generalized tonicoclonic attacks (grand mal) as well as for focal attacks in adults and children.
Mode of appliance and dosage regime
As a soporific preparation phenobarbital is prescribed to adults in dose 0.1 – 0.2 g for an intake as a rule 1/2 – 1 hour before going to sleep. The soporific action duration is 6 – 8 hours.
As a tranquilizing and spasmolytic preparation phenobarbital is prescribed in dose 0.01 – 0.03 – 0.05 g 2 – 3 times a day.
As an anti-epileptic preparation it is prescribed to adults the starting dose being 0.05 g 2 times a day, than the dose is increased little by little until the attacks stop but the total dose should not exceed 0.5 g a day. Children are prescribed smaller doses in accordance with their ages (not exceeding the maximal single and 24 hours doses). The treatment lasts for a long time. The phenobarbital intake under epilepsy is withdrawn little by little as the preparation abrupt withdrawal may provoke attacks and even lead to epileptic status development. Phenobarbital is often prescribed in combinations with other medicinal preparations. Those combinations are usually selected individually considering the patient’s general state.
Special warnings
In case of epilepsy phenobarbital should be withdrawn little by little (the preparation abrupt withdrawal may provoke attacks and even lead to epileptic status development).
Side effects
When treating with phenobarbital especially when the preparation has been taken for a long time feeling oneself jaded, asthenia, ataxia, hypotension, nystagmus, allergic reactions (skin eruptions and other manifestations), blood formula changes may appear.
Contraindications
Phenobarbital is contraindicated under severe liver and kidneys damages their functions disturbed, under alcoholism, narcotic dependence, myasthenia, during the first 3 months of pregnancy. One should bear in mind that phenobarbital taken by breast feeding mothers is found in large quantities in milk – the preparation should not be taken during the lactation period (the breast feeding should be stopped for the treatment period).
Caution measures
The preparation should be prescribed in smaller doses to patients with the kidneys changed function.
Interaction with other medicinal preparations
Phenobarbital may provoke enzymes “induction” and enhance the liver monoxygenase enzymes system activity – this should be considerd when the preparation is applied simultaneously with other medicinal preparations their action may become weaker. Phenobarbital decreases the blood plasma indirect anticoagulants, corticosteroids, griseofulvin, doxicyclin, estrogens levels.
Acetazolamide weakens phenobarbital effect (it hinders resorption on the kidneys), sedative preparations enhance the same (breathing suppression is possible). Phenitoin, valproic acid derivatives increase the phenobarbital blood plasma concentration.
Overdosing
Intake of 1 g of phenobarbital may provoke symptoms of intoxication (nystagmus, ataxia, dizziness, slow reactions, anxiety, headache, breathing suppression, hypothermia, hypotension, reflexes absence or suppression, pupils stenosis followed by paralytic dilatation, tachycardia, cyanosis, weakness, lungs edema, coma, arrhythmia, heart failure).
Treatment: symptomatic (no specific antidote exists). Support of vital functions.
Dosage form
100 mg tablets № 12
