Phenobarbital (Phenobarbitalum, Luminal, Adonal, Aephenal, Barbenyl, Barbinal, Barberhen, Dormiral, Epanal, Episedal, Fenemal, Fenobarbital, Gardenal, Hypnotal, Lepinal, Luminal, Mephabarbital, Neurobarb, Nirvonal, Omnibarb, Phenobarbitone, Sedonal, Sevenal, Somonal, Zadonal) is a strong long-acting barbiturate.
History of discovery
Bayer marketed phenobarbital in 1912 under the trade name Luminal. The new barbiturate was synthesized by the German chemist Emil Fischer in 1904, 2 years after the first barbiturate, barbiturate, was synthesized. Luminal remained a common sedative and hypnotic until the advent of benzodiazepines in the 1950s.
Phenobarbital is usually regarded as a sleeping pill. Indeed, it has a markedly soporific effect and is used in sleep disorders. However, at present the drug is most important as an antiepileptic agent.
In small doses phenobarbital has a sedative effect and in combination with other drugs (antispasmodics, vasodilators) it is used in neurovegetative disorders.
Due to anticonvulsant effect phenobarbital is also prescribed for chorea, spastic paralysis, various convulsive reactions.
When administered orally phenobarbital is completely, but relatively slowly absorbed. Peak blood concentrations are observed 1-2 hours after intake. About 50% is bound by plasma proteins. The drug is evenly distributed in different organs and tissues; lower concentrations are found in brain tissues. The half-life period in plasma in adults is 2-4 days (up to 7 days in newborns). It is slowly excreted from the body, which creates the preconditions for cumulation. It is metabolized by microsomal liver enzymes. Inactive metabolite (4-oxyphenobarbital) is excreted by kidneys as glucuronide, and about 25% – unchanged.
As a sleeping pill, phenobarbital is prescribed to adults in a dose of 0.1-0.2 g per dose usually 1/2-1 h before bedtime. The duration of hypnotic action is 6-8 hours. In children, depending on age, 0.005 to 0.0075 g is prescribed.
The hypnotic effect of phenobarbital is similar to that of other barbiturates. An undesirable feature of phenobarbital is that its use may have pronounced aftereffects: general depression, continued somnolence, nystagmus, ataxia, etc.
As a sedative and antispasmodic agent phenobarbital is prescribed in a dose of 0.01-0.03-0.05 g 2-3 times a day. It is usually used in combination with antispasmodics, vasodilators and other agents (Andipal, Bellataminal, Theophedrine tablets, etc.). It is part of the preparations Corvalol and Valokordin.
Prolonged use of phenobarbital and preparations containing it as sleeping pills and sedatives should be avoided due to the possibility of their cumulation and development of addiction.
Recently, a number of finished dosage forms containing phenobarbital (tablets “Pyraminal”, “Diafein”, “Lupaverin”, “Theodinal”, “Mikroiod with phenobarbital”, etc.) have been excluded from the nomenclature of medicines.
For the treatment of patients with epilepsy, phenobarbital was first used in 1912 and is still considered one of the most effective antiepileptic drugs. It is widely used in generalized tonic-clonic seizures (grand mal), as well as in focal seizures in adults and children.
In adults, it is prescribed at a dose of 0.05 g 2 times a day and gradually increasing the dose until seizures cease, but not more than 0.6 g per day. In children the drug is prescribed in smaller doses according to age (not exceeding the higher single and daily doses). Treatment shall be prolonged. Withdrawal of phenobarbital in epilepsy should be gradual, since a sudden withdrawal of the drug may cause the development of seizures and even epileptic status.
To treat epilepsy phenobarbital is often prescribed in combination with other drugs. Usually these combinations are chosen individually, depending on the form and course of epilepsy and the general condition of the patient. There are, however, and ready-made combined drugs (gluferal, pagluferal, falilepsin, etc.).
Domestic psychiatrist M. Y. Sereisky offered an extemporaneous combination (Sereisky mixture), which is still used to treat patients with epilepsy.
One of the properties of phenobarbital is its ability to cause “induction” of enzymes and increase the activity of monooxygenase enzyme system of the liver, which should be considered when using it simultaneously with other drugs, the effect of which may be weakened (see Benzonal). The same feature of phenobarbital is associated with its ability to reduce hyperbilirubinemia, which is the basis of its use for the treatment and prevention of hemolytic disease in infants.
When treating with phenobarbital, especially when taking it for a long time, side effects caused not only by CNS depression, but also by a decrease in BP, allergic reactions (skin rash, etc.), shifts in blood count are possible.
Simultaneous use of phenobarbital with other sedative agents leads to increased sedative-hypnotic effect and may be accompanied by respiratory depression.
The drug is contraindicated in severe liver and kidney impairment, in alcoholism, drug addiction and myasthenia. It should not be prescribed in the first 3 months of pregnancy (in order to avoid teratogenic effects). It should also be taken into account that in breastfeeding mothers when taking phenobarbital it is found in significant amounts in milk.