Barbiturate
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Barbiturates are drugs that act as central nervous system depressants, and by virtue of this they produce a wide spectrum of effects, from mild sedation to anesthesia. Some are also used as anticonvulsants.
Barbiturates are derivatives of barbituric acid.
History
Barbituric acid was first synthesised on December 4, 1864, by German researcher Adolf von Baeyer. This was done by condensing urea (an animal waste product) with diethyl malonate (an ester derived from the acid of apples). There are several stories about how the substance got its name. The most likely story is that von Baeyer and his colleagues went to celebrate their discovery in a tavern where the town's artillery garrison were also celebrating the day of Saint Barbara — the patron saint of artillerists. An artillery officer is said to have christened the new substance by amalgamating Barbara with urea. [2]
Barbituric acid itself is not pharmacologically active, but chemists immediately began making a great variety of derivatives for potential use as drugs. No substance of medical value was discovered, however, until 1903 when two German chemists working at Bayer, Emil Fischer and Joseph von Mering, discovered that barbital was very effective in putting dogs to sleep. Barbital was then marketed by Bayer under the trade name Veronal. It is said that Von Mering proposed this name because the most peaceful place he knew was the Italian city of Verona. [3]
In 1912, Bayer introduced another barbituric acid derivative, Phenobarbital, under the trade name Luminal, as a sedative-hypnotic.
In the 1950s and 1960s, reports began to be published about side effects and dependence related to barbiturates.
In 1970 several barbiturates were designated in the United States as controlled substances with the passage of the American Controlled Substances Act of 1970. Pentobarbital, secobarbital and amobarbital were designated schedule II drugs, butabarbital schedule III, and barbital and phenobarbital schedule IV.
In 1971 the Convention on Psychotropic Substances was signed in Vienna. Designed to regulate amphetamines, barbiturates, and other synthetics, the treaty today regulates amobarbital (schedule III), butalbital (III), cyclobarbital (III), pentobarbital (III), allobarbital (IV), methylphenobarbital (IV), phenobarbital (IV), secobarbital (IV), and vinylbital (IV) as scheduled substances.
Table of Barbiturates
| Short Name | R1 | R5 | R5 | Full Name |
|---|---|---|---|---|
| Allobarbital | H | CH2CH1CH2 | CH2CH1CH2 | 5,5-diallylbarbiturate |
| Amobarbital | H | CH2CH3 | CH2CH2 CH(CH3)2 | 5-ethyl-5-isopentyl-babiturate |
| Aprobarbital | H | CH2CH1CH2 | CH(CH3)2 | 5-allyl-5-isopropyl-barbiturate |
| Alphenal | H | CH2CH1CH2 | C6H5 | 5-allyl-5-phenyl-barbiturate |
| Barbexaclone | H | CH2CH3 | C6H5 | 5-ethyl-5-phenyl-barbiturate |
| Barbital | H | CH2CH3 | CH2CH3 | 5,5-diethylbarbiturate |
| Brallobarbital | H | CH2CH1CH2 | CH2CBr1CH2 | 5-allyl-5-(2-bromo-allyl)-barbiturate |
| Phenobarbital | H | CH2CH3 | C6H5 | 5-phenyl-5-ethylbarbiturate |
Mechanism of Action
The principal mechanism of action of barbiturates is believed to be their affinity for the GABAA receptor. GABA is the principal inhibitory neurotransmitter in the mammalian Central Nervous System (CNS). Barbiturates bind to the GABAA receptor at a binding site distinct from GABA itself and also distinct from the benzodiazepine binding site. Like benzodiazepines, barbiturates potentiate the effect of GABA at this receptor. In addition to this GABA-ergic effect, barbiturates also block the AMPA receptor, a subtype of glutamate receptor. Glutamate is the principal excitatory neurotransmitter in the mammalian CNS. Taken together, the findings that barbiturates potentiate inhibitory GABAA receptors and inhibit excitatory AMPA receptors can explain the CNS-depressant effects of these agents.[1]
Therapeutic use
Barbiturates like pentobarbital and phenobarbital were long used as anxiolytics and hypnotics. Today benzodiazepines have largely supplanted them for these purposes, because benzodiazepines have less potential for abuse and less danger of lethal overdose. Today, fewer than 10 percent of all sedative/hypnotic prescriptions in the United States are for barbiturates.
Barbiturates are still widely used in surgical anesthesia, especially to induce anesthesia.
Phenobarbital is used for as an anticonvulsant for people suffering from seizure disorders such as febrile seizures, tonic-clonic seizures, status epilepticus, and eclampsia.[2]
Potential for addiction
Barbiturates are habit forming and lead to physical withdrawal symptoms. These can include tremors, anxiety, weakness, restlessness, nausea and vomiting, delirium, tonic-clonic or grand mal seizures, and cardiac arrest. Death can result from seizures or cardiac arrest.
Effects on the Body
Barbiturates are classified as ultrashort-, short-, intermediate-, and long-acting, depending on how quickly they act and how long their effects last. Ultrashort barbiturates such as thiopental (Pentothal) produce unconsciousness within about a minute of intravenous (IV) injection. These drugs are used to prepare patients for surgery; other general anesthetics like nitrous oxide are then used to keep the patient from waking up before the surgery is complete. Because Pentothal and other ultrashort-acting barbiturates are typically used in hospital settings, they are not very likely to be abused, noted the DEA.
Abusers tend to prefer short-acting and intermediate-acting barbiturates. The most commonly abused are amobarbital (Amytal), pentobarbital (Nembutal), and secobarbital (Seconal). A combination of amobarbital and secobarbital (called Tuinal) is also highly abused. Short-acting and intermediate-acting barbiturates are usually prescribed as sedatives and sleeping pills. These pills begin acting fifteen to forty minutes after they are swallowed, and their effects last from five to six hours. Veterinarians use pentobarbital to anesthetise animals before surgery; in large doses, it can be used to euthanise animals.
Long-acting barbiturates such as phenobarbital (Luminal) and mephobarbital (Mebaral) are prescribed for two main reasons. When taken at bedtime, they help treat insomnia. When taken during the day, they have sedative effects that can aid in the treatment of tension and anxiety. These same effects have been found helpful in the treatment of convulsive conditions like epilepsy. Long-acting barbiturates take effect within one to two hours and last twelve hours or longer.
Similarity to Alcohol
Recreational users report that a barbiturate high makes them feel "relaxed, sociable, and good-humored," according to an Independent article. Users typically describe feelings of decreased anxiety, a loss of inhibitions, and an increased sense of confidence. Physical effects include slowed breathing and a lowering of both blood pressure and heart rate.
Like alcohol, barbiturates are intoxicating. During the stage after mild intoxication, the user's speech may be slurred and a loss of coordination may become noticeable. Stumbling and staggering are common. Other symptoms include shallow breathing, fatigue, frequent yawning, and irritability.
When taken in high doses, barbiturates can cause serious side effects, including "unpredictable emotional reactions and mental confusion," noted the Independent. Judgment becomes severely impaired and the user may experience mood swings.
The mental effects of barbiturates generally depend on the amount of the drug taken and the strength of the dosage. Generally, a person falls asleep when taking a prescribed dosage at bedtime. But barbiturates remain in the system for a long time. "At normal doses," explained Cynthia Kuhn and her coauthors in Buzzed: The Straight Facts about the Most Used and Abused Drugs from Alcohol to Ecstasy, "the major concern is that they can have sedative effects that outlast their sleep-inducing properties. Driving, flying an airplane, or other activities requiring muscle coordination can be impaired for up to a day after a single dose." Some barbiturates can be detected in a user's urine sample days or even weeks after the drug was consumed.
Truth Serum
Thiopental is a barbiturate that is marketed under the name Sodium Pentothal, but it is probably best known as "truth serum." When dissolved in water, it can be swallowed or administered by intravenous injection. In large doses, it is one of three drugs used in the United States to execute prisoners on death row. In lower doses, it is sometimes used as a truth serum.
Drug experts claim that truth serum does not force people to tell the truth. It merely decreases their inhibitions, making them more likely to be "caught off guard" when questioned by authorities. People being questioned may slip up and expose a lie or give more information on a subject or event than they intended.
Dependance, Tolerance, and Overdose
Barbiturate use can lead to both psychological and physical dependence. Psychological addiction can occur quickly. Signs of drug dependence include relying on a drug regularly for a desired effect. The addicted abuser believes he or she must take a barbiturate to sleep, relax, or just get through the day. Continued use of barbiturates leads to physical dependence.
As people develop a tolerance for barbiturates, they may need more of the drug or a higher dosage to get the desired effect. This can lead to an overdose, which results when a person takes a larger-than-prescribed dose of a drug. "People who get in the habit of taking sleeping pills every night to fall sleep," noted Andrew Weil and Winifred Rosen in From Chocolate to Morphine, "might start out with one a night, progress to two, then graduate to four to get the same effect. One night the dose they need to fall asleep might also be the dose that stops their breathing." Generally, barbiturate overdoses "occur because the effective dose of the drug is not too far away from the lethal dose," explained Dr. Eric H. Chudler on the Neuroscience for Kids Web site.
Symptoms of an overdose typically include severe weakness, confusion, shortness of breath, extreme drowsiness, an unusually slow heartbeat, and darting eye movements. The amount of a fatal dosage of barbiturate varies from one individual to another. However, the lethal dose is usually ten to fifteen times as large as a usual dose. An overdose affects the heart and the respiratory system. The user then falls into a coma and dies.
Clayton pointed out that barbiturates "can have a 'multiplying' effect when taken with other depressants. For example, if someone drinks alcohol and takes a barbiturate, the effect may be ten times stronger than either one taken separately." According to Weil, "many people have died because they were ignorant of this fact."
Older adults and pregnant women should consider the risks associated with barbiturate use. When a person ages, the body becomes less able to rid itself of barbiturates. As a result, people over the age of sixty-five are at higher risk of experiencing the harmful effects of barbiturates, including drug dependence and accidental overdose. When barbiturates are taken during pregnancy, the drug passes through the mother's bloodstream to her fetus. After the baby is born, it may experience withdrawal symptoms and have trouble breathing. In addition, nursing mothers who take barbiturates may transmit the drug to their babies through breast milk.
Recreational use
Barbiturates were very popular in the first half of the twentieth century. In moderate amounts, these drugs produce a state of intoxication that is remarkably similar to alcohol intoxication. Symptoms include slurred speech, loss of motor coordination, and impaired judgment. Depending on the dose, frequency, and duration of use, one can rapidly develop tolerance, physical dependence, and psychological dependence on barbiturates. With the development of tolerance, the margin of safety between the effective dose and the lethal dose becomes very narrow. That is, in order to obtain the same level of intoxication, the tolerant abuser may raise his or her dose to a level that may result in coma or death. Although many individuals have taken barbiturates therapeutically without harm, concern about the addiction potential of barbiturates and the ever-increasing number of fatalities associated with them led to the development of alternative medications, namely benzodiazepines.
Other non-therapeutical use
Barbiturates in high doses are used for physician-assisted suicide (PAS), and in combination with a muscle relaxant for euthanasia and for capital punishment by lethal injection.
References
cs:Barbiturát da:Barbiturat de:Barbiturat gl:Barbitúricos hr:Barbiturati he:ברביטורט nl:Barbituraat no:Barbiturat nn:Barbiturat sl:Barbiturat sr:Барбитурати fi:Barbituraatti sv:Barbiturater uk:Барбітурати