Drug information of Thiopental

Thiopental


Thiopental Sodium is a thiobarbiturate, the sulfur analogue of sodium pentobarbital .

Mechanism of effect

Thiopental binds at a distinct binding site associated with a Cl- ionopore at the GABAA receptor, increasing the duration of time for which the Cl- ionopore is open. The post-synaptic inhibitory effect of GABA in the thalamus is, therefore, prolonged.

Pharmacodynamic

Thiopental is a barbiturate . it slows the activity of brain and nervous system. Thiopental is used to help to relax before receiving general anesthesia with an inhaled medication. its activity is Depresses CNS to produce hypnosis and anesthesia without analgesia.

Pharmacokinetics

is an ultrashort-acting depressant of the central nervous system that induces hypnosis and anesthesia, but not analgesia. It produces hypnosis within 30 to 40 seconds of intravenous injection. Recovery after a small dose is rapid, with some somnolence and retrograde amnesia.
Repeated intravenous doses lead to prolonged anesthesia because fatty tissues act as a reservoir; they accumulate Pentothal in concentrations 6 to 12 times greater than the plasma concentration, and then release the drug slowly to cause prolonged anesthesia.
The half-life of the elimination phase after a single intravenous dose is three to eight hours. Approximately 80% of the drug in the blood is bound to plasma protein. Pentothal is largely degraded in the liver and to a smaller extent in other tissues, especially the kidney and brain.

Dosage

Usual Adult Dose for Anesthesia
When used for induction in balanced anesthesia with a skeletal muscle relaxant and an inhalation agent:
The total dose can be estimated and then injected in two to four fractional doses. With this technique, brief periods of apnea may occur which may require assisted or controlled pulmonary ventilation. As an initial dose, 210 to 280 mg (3 to 4 mg/kg) is usually required for rapid induction in the average adult (70 kg).
When used as the sole anesthetic agent:
Moderately slow induction can usually be accomplished in the "average" adult by injection of 50 to 75 mg (2 to 3 mL of a 2.5% solution) at intervals of 20 to 40 seconds, depending on the reaction of the patient. Once anesthesia is established, additional injections of 25 to 50 mg can be given whenever the patient moves. The desired level of anesthesia can be maintained by injection of small repeated doses as needed or by using a continuous intravenous drip in a 0.2% or 0.4% concentration. With continuous drip, the depth of anesthesia is controlled by adjusting the rate of infusion.
Usual Adult Dose for Seizures
For the control of convulsive states following anesthesia (inhalation or local) or other causes, 75 to 125 mg (3 to 5 mL of a 2.5% solution) should be given as soon as possible after the convulsion begins. Convulsions following the use of a local anesthetic may require 125 to 250 mg given over a ten minute period. Usual Adult Dose for Coma Induction
In neurosurgical patients, intermittent bolus injections of 1.5 to 3.5 mg/kg of body weight may be given to reduce intraoperative elevations of intracranial pressure, if adequate ventilation is provided. Usual Adult Dose for Psychosis
For narcoanalysis and narcosynthesis in psychiatric disorders, premedication with an anticholinergic agent may precede administration of thiopental. After a test dose, thiopental is injected at a slow rate of 100 mg/min (4 mL/min of a 2.5% solution) with the patient counting backwards from 100. Shortly after counting becomes confused but before actual sleep is produced, the injection is discontinued.
Allow the patient to return to a semidrowsy state where conversation is coherent. Alternatively, thiopental may be administered by rapid IV drip using a 0.2% concentration in 5% dextrose and water. At this concentration, the rate of administration should not exceed 50 mL/min.
Usual Pediatric Dose for Anesthesia
Induction anesthesia:
less than 1 month: 3 to 4 mg/kg intravenously
less than 1 year: 5 to 8 mg/kg intravenously
1 year to 12 years: 5 to 6 mg/kg intravenously
over 12 years: 3 to 5 mg/kg intravenously
Maintenance anesthesia:
1 year and older: 1 mg/kg intravenously as needed
Usual Pediatric Dose for Seizures
1 year or older: 2 to 3 mg/kg/dose intravenously, repeat as needed.
Usual Pediatric Dose for Head Injury
1 year or older: 1.5 to 5 mg/kg/dose intravenously; repeat as needed to control intracranial pressure - larger doses (30 mg/kg) to induce coma after hypoxic-ischemic injury do not appear to improve neurologic outcome.

Drug contraindications

patients with porphyria

Interactions

probenecid , Ethchlorvynol

Alerts

This drug should be administered only by persons qualified in the use of intravenous anesthetics.
Avoid extravasation or intra-arterial injection.
Observe aseptic precautions at all times in preparation and handling of Pentothal (Thiopental Sodium for Injection) solutions.
If used in conditions involving relative contraindications, reduce dosage and administer slowly.
Care should be taken in administering the drug to patients with advanced cardiac disease, increased intracranial pressure, ophthalmoplegia plus, asthma, myasthenia gravis and endocrine insufficiency (pituitary, thyroid, adrenal, pancreas).

Points of recommendation

You should not use thiopental if you are allergic to it, or if you have :
• porphyria (a genetic enzyme disorder that causes symptoms affecting the skin or nervous system);
• Addison's disease (an adrenal gland disorder);
• liver or kidney disease;
• severe anemia (low red blood cells);
• a thyroid disorder;
• myasthenia gravis;
• asthma; or
• if you are allergic to other barbiturates (amobarbital, butabarbital, mephobarbital, secobarbital, phenobarbital).
To make sure thiopental is safe for you, tell your doctor if you have :
• severe heart disease;
• pituitary gland disorder;
• a pancreas disorder;
• head injury, brain tumor, or other condition that causes increased pressure inside the skull;
• problems with the muscles in or around your eyes; or
• if you take a blood thinner (warfarin, Coumadin, Jantoven).
Avoid drinking alcohol for at least 24 hours after you leave the hospital or surgery center.
Thiopental can cause severe drowsiness or dizziness, which may last for several hours. You will need someone to drive you home after your surgery or procedure. Do not drive yourself or do anything that requires you to be awake and alert for at least 24 hours.

Pregnancy level

C


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