Also Known As: Sodium Pentothal, Thiopental, Sodium thiopental, Thiopentone sodium, Trapanal
Sodium thiopental, better known as Sodium Pentothal (a trademark of Abbott Laboratories), thiopental, thiopentone sodium, or Trapanal (also a trademark), is a rapid-onset short-acting barbiturate general anaesthetic. Thiopental is a core medicine in the World Health Organization's "Essential Drugs List", which is a list of minimum medical needs for a basic healthcare system. It is also usually the first of three drugs administered during most lethal injections in the United States.
Thiopental is an ultra-short-acting barbiturate and has been used commonly in the induction phase of general anesthesia. Its use in the United States and elsewhere has been largely replaced with that of propofol. Following intravenous injection the drug rapidly reaches the brain and causes unconsciousness within 30–45 seconds. At one minute, the drug attains a peak concentration of about 60% of the total dose in the brain. Thereafter, the drug distributes to the rest of the body and in about 5–10 minutes the concentration is low enough in the brain such that consciousness returns.
A normal dose of thiopental (usually 4–6 mg/kg) given to a pregnant woman for operative delivery (caesarian section) rapidly makes her unconscious, but the baby in her uterus remains conscious. However, larger or repeated doses can depress the baby.
Thiopental is not used to maintain anesthesia in surgical procedures because, in infusion, it displays zero-order elimination kinetics, leading to a long period before consciousness is regained. Instead, anesthesia is usually maintained with an inhaled anesthetic (gas) agent. Inhaled anesthetics are eliminated relatively quickly, so that stopping the inhaled anesthetic will allow rapid return of consciousness. Thiopental would have to be given in large amounts to maintain an anesthetic plane, and because of its 11.5–26 hour half-life, consciousness would take a long time to return.
In veterinary medicine, thiopental is used to induce anesthesia in animals. Since thiopental is redistributed to fat, certain breeds of dogs – primarily the sight hounds – can have accelerated recoveries from thiopental due to their lack of body fat and their lean body mass. Similarly, overweight or obese animals will have prolonged recoveries from thiopental. Thiopental is always administered intravenously, as it can be fairly irritating; severe tissue necrosis and sloughing can occur if it is injected incorrectly into the tissue around a vein.
Medically induced coma
In addition to anesthesia induction, thiopental was historically used to induce medical comas. It has now been superseded by drugs such as propofol.
Thiopental has a long Context Sensitive Half Time (CSHT), meaning infusions saturate peripheral compartments (fat, muscle etc.). When the infusion is stopped, the drug redistributes from the peripheral tissues back into the blood, prolonging the effect.
Thiopental also exhibits zero order kinetics at higher doses. The rate of elimination becomes constant.
Patients with brain swelling, causing elevation of the intracranial pressure, either secondary to trauma or following surgery, may benefit from this drug. Thiopental, and the barbiturate class of drugs, decrease neuronal activity and therefore decrease the production of osmotically active metabolites, which in turn decreases swelling. Patients with significant swelling have improved outcomes following the induction of coma. Reportedly, thiopental has been shown to be superior to pentobarbital in reducing intracranial pressure.This phenomena is also termed as Reverse steal Effect.
Thiopental is used intravenously for the purposes of euthanasia. The Belgians and the Dutch have created a protocol that recommends sodium thiopental as the ideal agent to induce coma, followed by pancuronium bromide.
Intravenous administration is the most reliable and rapid way to accomplish euthanasia. A coma is first induced by intravenous administration of 20 mg/kg thiopental sodium (Nesdonal) in a small volume (10 ml physiological saline). Then, a triple dose of a non-depolarizing skeletal muscle relaxant is given, such as 20 mg pancuronium bromide (Pavulon) or 20 mg vecuronium bromide (Norcuron). The muscle relaxant should be given intravenously to ensure optimal availability but pancuronium bromide may be administered intramuscularly at an increased dosage level of 40 mg.
Along with pancuronium bromide and potassium chloride, thiopental is used in 34 states of the U.S. to execute prisoners by lethal injection. A very large dose is given to ensure rapid loss of consciousness. Although death usually occurs within ten minutes of the beginning of the injection process, some have been known to take longer. The use of sodium thiopental in execution protocols was challenged in court after a study in the medical journal The Lancet reported autopsies of executed inmates showed the level of thiopental in their bloodstream was insufficient to cause unconsciousness.
On December 8, 2009, the State of Ohio became the first to use a single dose of sodium thiopental for its capital execution, following the failed use of the standard three-drug cocktail during a recent execution, due to inability to locate suitable veins. Kenneth Biros was executed using the single-drug method. Death was pronounced at 11:47 a.m., about ten minutes after the single-dose injection was administered. Including the time required to insert the IV lines and prepare the inmate, the entire process lasted 43 minutes. Ohio executed a second man using sodium thiopental on January 7, 2010. Vernon Smith was pronounced dead eight minutes after the time of injection. A third man was executed using the single-drug method on April 20, 2010. Daryl Durr was pronounced dead at 10:36 am. Most recently, William Garner was executed in Ohio with sodium thiopental.
The state of Washington is now the second state in the U.S. to use the single-dose sodium thiopental injections for death penalty executions. On September 10, 2010, Cal Coburn Brown was executed. His was the first execution in the state to use a single dose, single drug injection. His death was pronounced approximately one and a half minutes after the intravenous administration of five grams of the drug.
Following a shortage that led a court to delay an execution in California, a company spokesman for Hospira, the sole American manufacturer of the drug, objected to the use of thiopental in lethal injection. "Hospira manufactures this product because it improves or saves lives, and the company markets it solely for use as indicated on the product labeling. The drug is not indicated for capital punishment, and Hospira does not support its use in this procedure." On January 21, 2011, the company announced that it would stop production of sodium thiopental from its plant in Italy because it could not guarantee Italian authorities that the drug would not be used in executions. Italy was the only viable place where the company could produce sodium thiopental, leaving the United States without a supplier.
States such as Nebraska and South Dakota have turned to an Indian supplier of the drug but this move has been criticized on the grounds the chemical may deteriorate in transit to the United States.
A request from Gary Locke to export thiopental for lethal injections was denied by the German government.
Thiopental (Pentothal) is still used in some places as a truth serum to weaken the resolve of the subject and make them more compliant to pressure. The barbiturates as a class decrease higher cortical brain functioning. Some psychiatrists hypothesize that because lying is more complex than telling the truth, suppression of the higher cortical functions may lead to the uncovering of the truth. The drug tends to make subjects loquacious and cooperative with interrogators; however, the reliability of confessions made under thiopental is questionable.