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Phenobarbital in the serum
Medical expert of the article
Last reviewed: 23.04.2024
The concentration of phenobarbital in the serum when used in therapeutic doses is 10-40 mg / l (65-172 μmol / l). Toxic concentration is more than 45 mg / l (more than 194 μmol / l).
The half-life of phenobarbital in adults is 96 hours, in children 62 hours, in newborns - 103 hours. The time of reaching the equilibrium state of the drug in the blood is 3-4 weeks.
Phenobarbital is mainly used as an anticonvulsant. It is taken orally, the drug is almost completely (up to 80%) absorbed into the small intestine. The maximum concentration of the drug is achieved in 2-8 hours after a single oral intake through 1.5-2 hours after intramuscular injection. In the blood plasma phenobarbital is bound by proteins by 40-60%. Metabolism occurs in the liver by oxidation with the micro-rosomal system of cytochromes P450. Approximately 50% of the drug is excreted by the kidneys unchanged. Phenobarbital monitoring is performed in patients with epilepsy receiving this drug.
Rules of blood sampling for research. The material for the study is serum. For the study, take a sample of venous blood before receiving the next dose of the drug. The first measurement of the drug concentration is carried out 2 hours after intravenous (initial) administration, and then 3-4 weeks after the start of treatment. Regular control studies of the drug in the blood are performed in the following cases:
- changes in the dose of phenobarbital;
- introduction of another antiepileptic drug into the course of treatment;
- the appearance of signs of intoxication;
- the resumption of epileptic seizures;
- in pregnant women every 2-4 weeks.
Signs of drug overdose: drowsiness, impaired coordination, ataxia, nystagmus.
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