|Systematic (IUPAC) name|
|Pregnancy cat.||B (U.S.), C (Au)|
|Legal status||Prescription Only (S4) (AU) ℞-only (U.S.)|
|Protein binding||95 to 99%|
|Half-life||30 to 60 min|
|Mol. mass||178.271 g/mol|
|(what is this?)|
Propofol (INN, marketed as Diprivan by AstraZeneca) is a short-acting, intravenously administered hypnotic/amnestic agent. Its uses include the induction and maintenance of general anesthesia, sedation for mechanically ventilated adults, and procedural sedation. Propofol is also commonly used in veterinary medicine. Propofol is approved for use in more than 50 countries, and generic versions are available.
Chemically, propofol is unrelated to barbiturates and has largely replaced sodium thiopental (Pentothal) for induction of anesthesia because recovery from propofol is more rapid and "clear" when compared with thiopental. Propofol is not considered an analgesic, so opioids such as fentanyl may be combined with propofol to alleviate pain. Propofol has been referred to as milk of amnesia (a play on words of milk of magnesia), because of the milk-like appearance of its intravenous preparation.
Propofol was originally developed in the UK by Imperial Chemical Industries as ICI 35868. Clinical trials followed in 1977, using a form solubilised in cremophor EL. However, due to anaphylactic reactions to cremophor, this formulation was withdrawn from the market and subsequently reformulated as an emulsion of a soya oil/propofol mixture in water. The emulsified formulation was relaunched in 1986 by ICI (now AstraZeneca) under the brand name Diprivan (abbreviated version of diisopropyl intravenous anesthetic). The currently available preparation is 1% propofol, 10% soybean oil, and 1.2% purified egg phospholipid as an emulsifier, with 2.25% of glycerol as a tonicity-adjusting agent, and sodium hydroxide to adjust the pH. Diprivan contains EDTA, a common chelation agent, that also acts alone (bacteriostatically against some bacteria) and synergistically with some other antimicrobial agents. Newer generic formulations contain sodium metabisulfite or benzyl alcohol as antimicrobial agents. Propofol emulsion is a highly opaque white fluid due to the scattering of light from the tiny (~150 nm) oil droplets that it contains.
A water-soluble prodrug form, fospropofol, has recently been developed and tested with positive results. Fospropofol is rapidly broken down by the enzyme alkaline phosphatase to form propofol. Marketed as Lusedra, this new formulation may not produce the pain at injection site that often occurs with the traditional form of the drug. The US Food and Drug Administration approved the product in 2008.
Mechanism of action
Propofol has been proposed to have several mechanisms of action, both through potentiation of GABAA receptor activity, thereby slowing the channel-closing time, and also acting as a sodium channel blocker. Recent research has also suggested that the endocannabinoid system may contribute significantly to propofol's anesthetic action and to its unique properties. EEG research upon those undergoing general anesthesia with propofol finds that it causes a prominent reduction in the brain's information integration capacity at gamma wave band frequencies.
Researchers at Washington University School of Medicine in St. Louis and Imperial College London have identified the site where propofol binds to GABAA receptors in the brain.
Propofol is highly protein-bound in vivo and is metabolised by conjugation in the liver. The half life of elimination of propofol has been estimated at between 2 and 24 hours. However, its duration of clinical effect is much shorter, because propofol is rapidly distributed into peripheral tissues. When used for IV sedation, a single dose of propofol typically wears off within minutes. Propofol is versatile; the drug can be given for short or prolonged sedation as well as for general anesthesia. Its use is not associated with nausea as is often seen with opioid medications. These characteristics of rapid onset and recovery along with its amnestic effects have led to its widespread use for sedation and anesthesia.
Propofol is used for induction anesthesia, having largely replaced sodium thiopental for this indication. Propofol can also be administered as part of an anaesthesia maintenance technique called TIVA (Total Intravenous Anaesthesia) using computer controlled infusion pumps in a process called target controlled infusion or TCI. Propofol is also used to sedate individuals who are receiving mechanical ventilation who are not undergoing surgery, such as patients in the intensive care unit. In critically ill patients, propofol has been found to be superior to lorazepam both in effectiveness as well as overall cost. Propofol is also used for procedural sedation, for example during endoscopic procedures. Its use in these settings results in a faster recovery compared to midazolam. Due to its fast induction and recovery time, propofol is also widely used for sedation of infants and children undergoing MRI.
The Missouri Supreme Court decided to allow the use of propofol to execute prisoners condemned to death. However, the first execution by administration of a lethal dose of propofol was halted on October 11, 2013 by governor Jay Nixon following threats from the European Union to limit the drug's export if it were used for that purpose.
There are reports of self-administration of propofol for recreational purposes. Short-term effects include mild euphoria, hallucinations, and disinhibition. Long-term use has been reported to result in addiction. Such use of the drug has been described amongst medical staff, such as anesthetists who have access to the drug. Recreational use is reported to be more common among anesthetists on rotations with short rest periods, as recreational users report rousing to a well-rested state. Recreational use of the drug is relatively rare due to its potency and the level of monitoring required to take it safely. Propofol has not been scheduled by the US Drug Enforcement Administration. The steep dose-response curve of the drug makes potential misuse very dangerous without proper monitoring, and at least three deaths from self-administration have been recorded.
Attention to the risks of off-label use of propofol increased in August 2009 due to the Los Angeles County coroner's conclusion that pop icon Michael Jackson died from a mixture of propofol and the benzodiazepine drugs lorazepam on top of diazepam ingested earlier. According to a July 22, 2009 search warrant affidavit unsealed by the district court of Harris County, Texas, Jackson's personal physician, Conrad Murray, administered 25 milligrams of propofol diluted with lidocaine shortly before Jackson's death.
Aside from low blood pressure related to vasodilation, and transient apnea following induction doses, one of propofol's most frequent side effects is pain on injection, especially in smaller veins. This pain arises from activation of the pain receptor, TRPA1, found on sensory nerves and can be mitigated by pretreatment with lidocaine. Patients show great variability in their response to propofol, at times showing profound sedation with small doses. A more serious but rare side effect is dystonia. Mild myoclonic movements are common, as with other intravenous hypnotic agents. Propofol appears to be safe for use in porphyria, and has not been known to trigger malignant hyperpyrexia.
It has been reported that the euphoria caused by propofol is unlike that caused by other sedation agents, "I even remember my first experience using propofol: a young woman who was emerging from a MAC anesthesia looked at me as though I were a masked Brad Pitt and told me that she felt simply wonderful." —C.F. Ward, M.D.
Propofol administration to achieve the recommended level of sedation suppresses the REM sleep stage and further worsens the poor sleep quality of these patients.
Propofol infusion syndrome
Another recently described rare, but serious, side effect is propofol infusion syndrome. This potentially lethal metabolic derangement has been reported in critically ill patients after a prolonged infusion of high-dose substance in combination with catecholamines and/or corticosteroids.
Contraindications and interactions
The respiratory effects of propofol are potentiated by other respiratory depressants, including benzodiazepines. As with any other general anesthetic agent, propofol should be administered only where appropriately trained staff and facilities for monitoring are available, as well as proper airway management, a supply of supplemental oxygen, artificial ventilation and cardiovascular resuscitation.
On 4 June 2010, Teva Pharmaceutical Industries Ltd., an Israel-based pharmaceutical firm and a major supplier of the drug, announced that the firm would no longer manufacture it. This aggravates an already existing shortage, caused by manufacturing difficulties at Teva and Hospira. A Teva spokesperson attributed the halt to ongoing process difficulties, and a number of pending lawsuits related to the drug. In Switzerland, various preparations of the drug are supplied by Fresenius-Kabi, a German company.
By incorporation of an azobenzene unit, a photoswitchable version of propofol (AP2) was developed in 2012 that allows for optical control of GABAA receptors with light. In 2013, a propofol binding site on mammalian GABAA receptors has been identified by photolabeling using a Diazirine derivative. Additionally, it was shown that the hyaluronan polymer present in the synovia can be protected from free-radical depolymerization by propofol.
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