Barbiturates belong to the group of medicines called central nervous system (CNS) depressants (medicines that cause drowsiness). They act on the brain and CNS to produce effects that may be helpful or harmful. This depends on the individual patient's condition and response and the amount of medicine taken.
Some of the barbiturates may be used before surgery to relieve anxiety or tension. In addition, some of the barbiturates are used as anticonvulsants to help control seizures in certain disorders or diseases, such as epilepsy.
The barbiturates have been used to treat insomnia; but if they are used regularly for insomnia, they are usually not effective for longer than 2 weeks. The barbiturates have also been used to relieve nervousness or restlessness during the daytime. However, the barbiturates have generally been replaced by safer medicines for the treatment of insomnia and daytime nervousness or tension.
If too much of a barbiturate is used, it may become habit-forming.
Barbiturates are some of the most addictive drugs. They are often a substitute for alcohol (as similar effects are produced.) People use Barbiturates to get a sense of euphoria and relaxation. However, it is illegal to take barbiturates with out a doctor's prescription and supervision.
Barbiturates are the earliest known class of sedative-hypnotic agents and were once extremely popular drugs to abuse. Benzodiazepines largely have replaced barbiturates for outpatient medical therapy, which has created a decline in barbiturate abuse. Stricter guidelines dictating barbiturate use have led to decreased availability as well.
History:
Barbiturates are synthetic products that derive barbituric acid which was obtained by Bayer in 1863. Barbiturates were first introduced for medical use in the early 1900s. More than 2,500 barbiturates have been synthesized, and at the height of their popularity, about 50 were marketed for human use. Today, about a dozen are in medical use. Barbiturates produce a wide spectrum of central nervous system depression, from mild sedation to coma, and have been used as sedatives, hypnotics, anesthetics, and anticonvulsants. The primary differences among many of these products are how fast they produce an effect and how long those effects last. Barbiturates are classified as ultrashort, short, intermediate, and long-acting.
The ultrashort-acting barbiturates:
• produce anesthesia
• within about one minute after intravenous administration.
• Those in current medical use are: Schedule IV drug methohexital (Brevital®),
Schedule III drugs thiamyl (Surital®)
and thiopental (Pentothal®).
Barbiturate abusers prefer the Schedule II short-acting and intermediate-acting barbiturates:
• that include amobarbital (Amyta®),
• pentobarbital (Nembutal®),
• secobarbital (Seconal®),
• and Tuinal (an amobarbital/secobarbital combination product).
Other short and intermediate-acting barbiturates are in Schedule III and include:
• butalbital (Fiorina®),
• butabarbital (Butisol®),
• talbutal (Lotusate®),
• and aprobarbital (Alurate®).
• After oral administration, the onset of action is from 15 to 40 minutes, and the effects last up to six hours.
• These drugs are primarily used for insomnia and preoperative sedation. Veterinarians use pentobarbital for anesthesia and euthanasia.
Long-acting barbiturates include:
• phenobarbital (Luminal®)
• and mephobarbital (Mebaral®),
• both of which are in Schedule IV.
• Effects of these drugs are realized in about one hour and last for about 12 hours, and are used primarily for daytime sedation and the treatment of seizure disorders.
- Anticonvulsant --Amobarbital (parenteral only); Mephobarbital; Metharbital; Pentobarbital (parenteral only); Phenobarbital; Secobarbital (parenteral only)
- Antihyperbilirubinemic --Phenobarbital
- Sedative-hypnotic --Amobarbital; Aprobarbital; Butabarbital; Pentobarbital; Phenobarbital (parenteral only); Secobarbital
Brand Names
Some commonly used brand names are:
In the U.S.
Alurate Aprobarbital
Amytal Amobarbital
Barbita Phenobarbital
Luminar Phenobarbital
Solfoton - Phenobarbital
Busodium Butabarbital
Butalan- Butabarbital
Butisol Butabarbital
Sarisol No. 2 Butabarbital
Mebaral Mephobarbital
Nembutal Pentobarbital
Seconal Secobarbital
Tuinal - Secobarbital and Amobarbital
In Canada
Amytal Amobarbital
Butisol Butabarbital
Mebaral Mephobarbital
Nembutal - Pentobarbital
Nova Rectal - Pentobarbital
Novopentobarb Pentobarbital
Ancalixir - Phenobarbital
Novosecobarb Secobarbital
Seconal Secobarbital
Tuinal - Secobarbital and Amobarbital
Dosage Forms:
These medicines are available only with doctor's prescription, in the following dosage forms:
Oral
- Amobarbital
- Capsules ( U.S. and Canada )
- Tablets ( U.S. and Canada )
- Aprobarbital
- Elixir (U.S.)
- Butabarbital
- Capsules (U.S.)
- Elixir (U.S.)
- Tablets ( U.S. and Canada )
- Mephobarbital
- Tablets ( U.S. and Canada )
- Metharbital
- Tablets (Other countries)
- Pentobarbital
- Capsules ( U.S. and Canada )
- Elixir (U.S.)
- Phenobarbital
- Capsules (U.S.)
- Elixir ( U.S. and Canada )
- Tablets ( U.S. and Canada )
- Secobarbital
- Capsules ( U.S. and Canada )
- Secobarbital and Amobarbital
- Capsules ( U.S. and Canada )
Parenteral
- Amobarbital
- Injection ( U.S. and Canada )
- Pentobarbital
- Injection ( U.S. and Canada )
- Phenobarbital
- Injection ( U.S. and Canada )
- Secobarbital
- Injection (U.S.)
Rectal
- Pentobarbital
- Suppositories ( U.S. and Canada )
Barbs, downers, sleepers, stumblers, blues, yellow jackets, purple hearts, red dolls, rainbows, tootsies, Amytal, Nembutal, Seconal, reds, red birds, phennies, yellows
Effects:
Short Term Effects of Barbiturates: (last for 15 hours after ingestion)
• Relief of tension and anxiety
• Sleepiness
• Feeling of drunkenness / intoxication
• Slurred speech
• Inability to control simple bodily functions (walking, balance, etc...)
• Memory impairment
• Emotional instability
Long Term Effects of Barbiturates:
• Chronic tiredness
• General uncoordination
• Vision problems
• Dizziness
• Slowed reflexes and response
• Sexual dysfunction
• Menstrual irregularities
• Breathing disorders
Tolerance:
• Develops very rapidly
• Ten times the original dosage may be required to produce the same high
Withdrawal symptoms:
• Hallucinations
• Eating disorders
• Disorientation
• Vomiting
• Sleep disorders
Barbiturates and other depressants:
The combination of barbiturates and other drugs is very dangerous (especially when combined with other CNS Depressants like Demerol, heroin, morphine, and codeine). Barbiturates produce many of the same effects as alcohol, and the combination of the two is often lethal. There is a hidden danger with barbiturate use, especially if you suffer from allergies. Antihistamines (found in most allergy, cold, and sinus medicine) are another type of CNS Depressants, and when taken with barbiturates, can cause respiratory arrest.
Barbiturates and stimulants:
Barbiturates are often used to counteract large doses of amphetamines or cocaine (both stimulants). This mixture is extremely dangerous, as it can increase heart rate, and cause coronary arrest.
Barbiturates bind to specific sites on gamma-aminobutyric acid (GABA)-sensitive ion channels found in the central nervous system (CNS), where they allow an influx of chloride into cell membranes and, subsequently, hyperpolarize the postsynaptic neuron.
GABA is the major inhibitory neurotransmitter in the CNS. Barbiturates enhance GABA-mediated chloride currents by binding to the GABA A receptor-ionophore complex and increasing the duration of ionophore opening; barbiturates inhibit neuronal depolarization by potentiating and prolonging the actions of GABA. At high doses, barbiturates stimulate GABA A receptors directly in the absence of GABA. Barbiturates also block glutamate (excitatory neurotransmitter) receptors in the CNS.
Barbiturates may be grouped functionally into long-acting and short-acting agents (consisting of ultrashort, short, and intermediate-acting agents). Compared to long-acting agents, short-acting agents are more lipid soluble, more protein bound, have a higher pKa, a more rapid onset and shorter duration of action, and are metabolized almost entirely in the liver to inactive metabolites (which are excreted as glucuronides in the urine). Long-acting agents, which are less lipid soluble, accumulate more slowly in tissue and are excreted more readily by the kidney as active drug. For instance, urinary excretion accounts for 20-30% of phenobarbital and 15-42% of primidone elimination (both long-acting agents).
Short-acting agents have an elimination half-life less than 40 hours compared to long-acting agents, which have an elimination half-life longer than 40 hours.
Barbiturates stimulate the hepatic cytochrome P-450 mixed function oxidase microsomal enzyme system; thus, barbiturates affect the drug levels of medications that are dependent on this system (eg, coumadin).
Central nervous system effects
Barbiturates mainly act in the CNS and, as a consequence, affect other organ systems. Direct effects include sedation and hypnosis at lower dosages. The lipophilic barbiturates, such as thiopental, cause rapid anesthesia because of their tendency to penetrate brain tissue quickly. Barbiturates all have anticonvulsant activity because they hyperpolarize cell membranes; therefore, they are effective adjuncts in the treatment of epilepsy.
Pulmonary effects
Barbiturates can cause a depression of the medullary respiratory center and induce a respiratory depression. Patients with underlying chronic obstructive pulmonary disease (COPD) are more susceptible to these effects, even at doses that would be considered therapeutic in healthy individuals. Barbiturate overdose fatality is usually secondary to respiratory depression.
Cardiovascular effects
Cardiovascular depression may occur following depression of the medullary vasomotor centers; patients with underlying congestive heart failure (CHF) are more susceptible to these effects. At higher doses, cardiac contractility and vascular tone are compromised, which may cause cardiovascular collapse.
Mortality/Morbidity:
Fatality associated with barbiturate overdose is rare, but complications are abundant. Morbidity includes pneumonia, shock, hypoxia, and coma.
Webliography
http://www.secffaa.mil.do/drogas/hipnoticos.htm
http://www.gwu.edu/~cade/barbiturates.htm
http://www.emedicine.com/emerg/topic52.htm
http://www.drogas.com/index-espanol.html
http://www.dea.gov/concern/barbiturates.html
http://www.nlm.nih.gov/medlineplus/druginfo/uspdi/202081.html