|Intravenous (most common), oral or rectal|
|Elimination half-life||5.5-26 hours|
|Chemical and physical data|
|Molar mass||264.32 g·mol−1|
|3D model (JSmol)|
Sodium thiopental, also known as Sodium Pentothal (a trademark of Abbott Laboratories, not to be confused with pentobarbital), thiopental, thiopentone, or Trapanal (also a trademark), is a rapid-onset short-acting barbiturate general anesthetic that is an analogue of thiobarbital. Sodium thiopental was a core medicine in the World Health Organization's List of Essential Medicines, which is a list of minimum medical needs for a basic healthcare system, but was supplanted by propofol. Despite this thiopental is still listed as an acceptable alternative to propofol, depending on local availability and cost of these agents. It was previously the first of three drugs administered during most lethal injections in the United States, but the U.S. manufacturer Hospira stopped manufacturing the drug and the EU banned the export of the drug for this purpose. Although thiopental abuse carries a dependency risk, its recreational use is rare.
Sodium thiopental is an ultra-short-acting barbiturate and has been used commonly in the induction phase of general anesthesia. Its use has been largely replaced with that of propofol, but retains popularity as an induction agent for rapid sequence intubation and in obstetrics. 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 that consciousness returns.
A normal dose of sodium 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.
Sodium 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. Sodium thiopental would have to be given in large amounts to maintain an anesthetic plane, and because of its 11.5- to 26-hour half-life, consciousness would take a long time to return.
In veterinary medicine, sodium thiopental is used to induce anesthesia in animals. Since it is redistributed to fat, certain lean breeds of dogs such as sight hounds will have prolonged recoveries from sodium thiopental due to their lack of body fat and their lean body mass. Conversely, obese animals will have rapid recoveries, but it will be some time before it is entirely removed (metabolized) from their bodies. Sodium 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.
Sodium thiopental decreases the cardiac stroke volume, which results in a decrease in cardiac output. The decrease in cardiac output occurs in conjunction with a decrease in systemic vascular resistance, which results in hypotension. However, in comparison with propofol, the reflex tachycardia seen during states of hypotension is relatively spared (a bradycardia is common after administration of propofol) and therefore the observed fall in blood pressure is generally less severe.
Medically induced coma
In addition to anesthesia induction, sodium thiopental was historically used to induce medical comas. It has now been superseded by drugs such as propofol because their effects wear off more quickly than thiopental. Patients with brain swelling, causing elevation of intracranial pressure, either secondary to trauma or following surgery, may benefit from this drug. Sodium 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 phenomenon is also called a reverse steal effect.
In refractory status epilepticus, thiopental may be used to terminate a seizure.
Sodium thiopental is used intravenously for the purposes of euthanasia. In both Belgium and the Netherlands, where active euthanasia is allowed by law, the standard protocol recommends sodium thiopental as the ideal agent to induce coma, followed by pancuronium bromide to paralyze muscles and stop breathing.
Intravenous administration is the most reliable and rapid way to accomplish euthanasia. Death is quick. 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 neuromuscular blocking drug 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 United States 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, Ohio became the first state 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.
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. This 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.
After its use for execution of Jeffrey Landrigan in the U.S., the UK introduced a ban on the export of sodium thiopental in December 2010, after it was established that no European supplies to the U.S. were being used for any other purpose. The restrictions were based on "the European Union Torture Regulation (including licensing of drugs used in execution by lethal injection)". From 21 December 2011 the European Union extended trade restrictions to prevent the export of certain medicinal products for capital punishment, stating that "the Union disapproves of capital punishment in all circumstances and works towards its universal abolition".
Thiopental (Pentothal) is still used in some places as a truth serum to weaken the resolve of a 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.
Psychiatrists have used thiopental to desensitize patients with phobias, and to "facilitate the recall of painful repressed memories." One psychiatrist who worked with thiopental is the Dutch Professor Jan Bastiaans, who used this procedure to help relieve trauma in surviving victims of the Holocaust.
Mechanism of action
Sodium thiopental is a member of the barbiturate class of drugs, which are relatively non-selective compounds that bind to an entire superfamily of ligand-gated ion channels, of which the GABAA receptor channel is one of several representatives. This superfamily of ion channels includes the neuronal nAChR channel, the 5HT3R channel, the GlyR channel and others. Surprisingly, while GABAA receptor currents are increased by barbiturates (and other general anesthetics), ligand-gated ion channels that are predominantly permeable for cationic ions are blocked by these compounds. For example, neuronal nAChR channels are blocked by clinically relevant anesthetic concentrations of both sodium thiopental and pentobarbital. Such findings implicate (non-GABA-ergic) ligand-gated ion channels, e.g. the neuronal nAChR channel, in mediating some of the (side) effects of barbiturates. The GABAA receptor is an inhibitory channel that decreases neuronal activity, and barbiturates enhance the inhibitory action of the GABAA receptor.
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 Italian authorities couldn't guarantee that exported quantities of 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.
Thiopental rapidly and easily crosses the blood brain barrier as it is a lipophilic molecule. As with all lipid-soluble anaesthetic drugs, the short duration of action of sodium thiopental is due almost entirely to its redistribution away from central circulation towards muscle and fat tissue, due to its very high fat:water partition coefficient (aprx 10), leading to sequestration in fat tissue. Once redistributed, the free fraction in the blood is metabolized in the liver. Sodium thiopental is mainly metabolized to pentobarbital, 5-ethyl-5-(1'-methyl-3'-hydroxybutyl)-2-thiobarbituric acid, and 5-ethyl-5-(1'-methyl-3'-carboxypropyl)-2-thiobarbituric acid.
The usual dose range for induction of anesthesia using thiopental is from 3 to 6 mg/kg; however, there are many factors that can alter this. Premedication with sedatives such as benzodiazepines or clonidine will reduce requirements, as do specific disease states and other patient factors. Among patient factors are: age, sex, and lean body mass. Specific disease conditions that can alter the dose requirements of thiopentone and for that matter any other intravenous anaesthetic are: hypovolemia, burns, azotemia, hepatic failure, hypoproteinemia, etc.
As with nearly all anesthetic drugs, thiopental causes cardiovascular and respiratory depression resulting in hypotension, apnea and airway obstruction. For these reasons, only suitably trained medical personnel should give thiopental in an environment suitably equipped to deal with these effects. Side effects include headache, agitated emergence, prolonged somnolence, and nausea. Intravenous administration of sodium thiopental is followed instantly by an odor and/or taste sensation, sometimes described as being similar to rotting onions, or to garlic. The hangover from the side effects may last up to 36 hours.
Co-administration of pentoxifylline and thiopental causes death by acute pulmonary edema in rats. This pulmonary edema was not mediated by cardiac failure or by pulmonary hypertension but was due to increased pulmonary vascular permeability.
Sodium thiopental was discovered in the early 1930s by Ernest H. Volwiler and Donalee L. Tabern, working for Abbott Laboratories. It was first used in human beings on March 8, 1934, by Dr. Ralph M. Waters in an investigation of its properties, which were short-term anesthesia and surprisingly little analgesia. Three months later, Dr. John S. Lundy started a clinical trial of thiopental at the Mayo Clinic at the request of Abbott. Abbott continued to make the drug until 2004, when it spun off its hospital-products division as Hospira.
Thiopental is famously associated with a number of anesthetic deaths in victims of the attack on Pearl Harbor. These deaths, relatively soon after the drug's introduction, were said to be due to excessive doses given to shocked trauma patients. However, recent evidence available through freedom of information legislation was reviewed in the British Journal of Anaesthesia, which has suggested that this story was grossly exaggerated. Of the 344 wounded that were admitted to the Tripler Army Hospital only 13 did not survive and it is unlikely that thiopentone overdose was responsible for more than a few of these.
- Russo H, Brès J, Duboin MP, Roquefeuil B (1995). "Pharmacokinetics of thiopental after single and multiple intravenous doses in critical care patients". Eur. J. Clin. Pharmacol. 49 (1–2): 127–37. doi:10.1007/BF00192371. PMID 8751034.
- Morgan DJ, Blackman GL, Paull JD, Wolf LJ (June 1981). "Pharmacokinetics and plasma binding of thiopental. II: Studies at cesarean section". Anesthesiology. 54 (6): 474–80. doi:10.1097/00000542-198106000-00006. PMID 7235275.
- "WHO Model List of Essential Medicines 16th list, March 2009" (PDF). Geneva, Switzerland: World Health Organization. March 2009. Retrieved 25 August 2017.
- "WHO Model List of Essential Medicines 20th List (March 2017)" (PDF). Geneva, Switzerland: World Health Organization. March 2017. Retrieved 25 August 2017.
- "Death Penalty Opposition: EU Set to Ban Export of Drug Used in US Executions". Spiegel Online International. Retrieved 23 January 2014.
- Substance abuse : inpatient and outpatient management for every clinician. Kaye, Alan David,, Vadivelu, Nalini,, Urman, Richard D.,. New York. ISBN 1493919512. OCLC 897466425.
- Gleason, Christine A; Juul, Sandra E (12 August 2011). Avery's Diseases of the Newborn. Elsevier Health Sciences. p. 169. ISBN 9781455727148. Retrieved 13 August 2016.
- Morgan, DJ; Blackman, GL; Paull, JD; Wolf, LJ (1981). "Pharmacokinetics and plasma binding of thiopental. II: Studies at cesarean section". Anesthesiology. 54 (6): 474–80. doi:10.1097/00000542-198106000-00006. PMID 7235275.
- Toyama, Takeko. "TRAUMA.ORG: Critical Care: Barbiturate Coma". trauma.org. Retrieved 18 August 2016.
- Pérez-Bárcena J, Barceló B, Homar J, et al. (February 2005). "[Comparison of the effectiveness of pentobarbital and thiopental in patients with refractory intracranial hypertension. Preliminary report of 20 patients]" (PDF). Neurocirugia (Astur) (in Spanish). 16 (1): 5–12; discussion 12–3. PMID 15756405. Archived from the original (PDF) on 2007-09-28. Retrieved 2008-07-18.
- Royal Dutch Society for the Advancement of Pharmacy (1994). "Administration and Compounding of Euthanasic Agents". The Hague. Archived from the original on 2008-08-21. Retrieved 2008-07-18.
- "Ohio executes inmate with 1-drug lethal injection". Associated Press. December 2001. Retrieved 2009-12-08.
- Martinez, Edecio (8 December 2009). "Kenneth Biros Execution: Ohio Man First to Die Under 1-Drug Thiopental Sodium Method". CBS News.
- Sullivan, Jennifer (10 September 2010). "Killer on death row 16-1/2 years is executed". The Seattle Times.
- "Drug sold in UK to be used for execution in Georgia". bbc.co.uk. BBC News. 24 January 2011. Retrieved 18 August 2016.
- Casciani, Dominic (29 November 2010). "US lethal injection drug faces UK export restrictions". bbc.co.uk. BBC News. Retrieved 18 August 2016.
- "Controls on torture goods - Detailed guidance - GOV.UK". gov.uk. Retrieved 18 August 2016.
- EU Council Regulation (EU) No 1352/2011
- "Truth serum used on 'serial child killers'". Sydney Morning Herald. Reuters. January 12, 2007.
- Anne Bannon; Stevens, Serita Deborah (2007). The Howdunit Book of Poisons (Howdunit). Cincinnati: Writers Digest Books. ISBN 1-58297-456-X.
- Pearlman, T. (1980). "Behavioral desensitization of phobic anxiety using thiopental sodium". The American Journal of Psychiatry. American Psychiatric Association. 137 (12): 1580–1582. doi:10.1176/ajp.137.12.1580. PMID 6108082.
- "Drugged Future?". TIME. February 24, 1958.
- Snelders, Stephen (1998). "The LSD Therapy Career of Jan Bastiaans, M.D". Newsletter of the Multidisciplinary Association for Psychedelic Studies. Multidisciplinary Association for Psychedelic Studies. 8 (1): 18–20.
- Weber, M; Motin, L; Gaul, S; Beker, F; Fink, RH; Adams, DJ (January 2005). "Intravenous anesthetics inhibit nicotinic acetyl-choline receptor-mediated currents and Ca2+ transients in rat intracardiac ganglion neurons". British Journal of Pharmacology. 144 (1): 98–107. doi:10.1038/sj.bjp.0705942. PMC 1575970
. PMID 15644873.
- Franks, NP; Lieb, WR (23 November 1998). "Which molecular targets are most relevant to general anaesthesia?". Toxicology Letters. 100–101 (1–2): 1–8. doi:10.1016/S0378-4274(98)00158-1. PMID 10049127.
- "Anesthesia and Analgesia". University of Virginia School of Medicine. Retrieved 2007-08-05.
- McKinley, Jesse (28 September 2010). "Judges Question California's Motivation on Execution". New York Times.
- "U.S. Drug Maker Discontinues Key Death Penalty Drug". Fox News. 21 January 2011.
- WINTERS WD, SPECTOR E, WALLACH DP, SHIDEMAN FE (July 1955). "Metabolism of thiopental-S35 and thiopental-2-C14 by a rat liver mince and identification of pentobarbital as a major metabolite". J. Pharmacol. Exp. Ther. 114 (3): 343–57. PMID 13243246. Retrieved 2008-07-18.
- Bory C, Chantin C, Boulieu R, et al. (1986). "[Use of thiopental in man. Determination of this drug and its metabolites in plasma and urine by liquid phase chromatography and mass spectrometry]". Comptes Rendus de l'Académie des Sciences, Série III (in French). 303 (1): 7–12. PMID 3093002.
- "Pentothal (thiopental)". eMedicineHealth. April 12, 2009.
- M. F. M. James; R. J. Hift (July 1, 2000). "Porphyrias". bja.oxfordjournals.org. Retrieved September 25, 2013.
- Pereda J, Gómez-Cambronero L, Alberola A, et al. (October 2006). "Co-administration of pentoxifylline and thiopental causes death by acute pulmonary oedema in rats". Br. J. Pharmacol. 149 (4): 450–5. doi:10.1038/sj.bjp.0706871. PMC 1978439
. PMID 16953192.
- "This Month in Anesthesia History: March". Anesthesia History Association. Archived from the original on 2011-05-01.
- Steinhaus, John E (September 2001). "The Investigator and His 'Uncompromising Scientific Honesty'". ASA Newsletter. American Society of Anesthesiologists. 65 (9): 7–9. Archived from the original on 2011-05-13.
- Lundy, John S. (1966). "From this point in time: Some memories of my part in the history of anesthesia". Journal of the American Association of Nurse Anesthetists. American Association of Nurse Anesthetists. 24 (2): 95–102. Archived from the original on 2011-05-01.
- Thatcher, Virginia S. (1953). "Chapter 7: Illegal or Legal?". History of Anesthesia with Emphasis on the Nurse Specialist. J.B. Lippincott. ISBN 0-8240-6525-5. Archived from the original (PDF) on 2011-05-01.
- Bennetts FE (September 1995). "Thiopentone anaesthesia at Pearl Harbor". Br J Anaesth. 75 (3): 366–8. doi:10.1093/bja/75.3.366. PMID 7547061. Retrieved 2008-07-18.
- PubChem Substance Summary: Thiopental
- Vassallo, Susi, M.D. "THIOPENTAL IN LETHAL INJECTION" (Archive). Fordham Urban Law Journal. June 18, 2008. p. 957-.