Description:
Barbiturates belong to a group of drugs called Central Nervous System (CNS) depressants. They can act both in the brain and in the CNS producing effects that can be both positive and harmful. This depends on the individual condition of each person and their response to the dose of the medicine taken, which should be exclusively recommended by a doctor .
Some of the barbiturates can be used before surgery to relieve anxiety or tension. In addition, some of these are used as anticonvulsants to help control some symptoms such as epilepsy, which is a disease that afflicts many people around the world .
They have also been used to treat insomnia ; but if they are used regularly, they will not be effective after two weeks of consecutive intake. Barbiturates have also been used to relieve nervousness or disturbance during the day. However, they have mostly been replaced by safer medication since if it is used in large quantities, or for long periods, it produces a habit.
They are among the most addictive drugs. They are generally a substitute for alcohol (as it produces similar effects). People use them to get a feeling of euphoria and relaxation. However, its use is illegal without prescription and medical supervision.
Barbiturates were the first class of sedative-hypnotic agents known and were once extremely popular as drugs of abuse. Today, benzodiazepines have largely replaced these for patient therapy, creating a decline in barbiturate abuse. Another important factor was the reinforcement of the laws to restrict their sale.
History:
Barbiturates are synthetic products derived from barbituric acid obtained by Bayer in 1863 . The first barbiturate introduced into therapeutics at the beginning of this century was barbital .
More than 2,500 barbiturates have been synthesized, and at the peak of their popularity, about 50 were brought to market for human use. Today, about a dozen are still used by medicine.
Barbiturates produce a broad spectrum of CNS depression, from mild sensation to coma, and have been used as sedatives, hypnotics , anesthetics , and anticonvulsants. The main difference between many of these products is the speed with which they produce the effect and for how long that effect persists. They are classified as ultra short, short, intermediate and long action.
Categories:
Ultra short-acting barbiturates:
• produce anesthesia within one minute after being administered intravenously.
• Those currently under medical use are: category IV drug methohexital (Brevital), Category III thiamil (Surital) and thiopental (Pentothal).
Barbiturate abusers prefer short- and intermediate-acting categories II:
• Which include amobarbital (Amyta),
• pentobarbital (Nembutal),
• secobarbital (Seconal),
• and Tuinal (a combination of amobarbital / secobarbital ).
Other short and intermediate acting but Category III barbiturates include:
• butalbital (Fiorina),
• butabarbital (Butisol),
• talbutal (Lotusate),
• and passbital (Alurate).
• After oral administration, the action begins between 15 to 40 minutes, and the effects last up to 6 hours.
• These drugs are used primarily for insomnia and pre-surgical sedatives. Veterinarians use pentobarbital for anesthesia and for euthanasia.
Long-acting barbiturates include:
• phenobarbital (Luminal)
• and mephobarbital (Mebaral),
• both are in category IV.
• The effects of these drugs occur after about an hour and last for about 12 hours, and are used mainly as daytime sedatives and treatment for disorders.
By His Action
Anticonvulsants –Amobarbital (parenteral only); Mephobarbital; Metabital; Pentobarbital (parenteral only); Phenobarbital; Secobarbital (parenteral only) Antihyperbilirubinemics –Phenobarbital Sedative-hypnotics –Amobarbital; Approvebital; Butabarbital; Pentobarbital; Phenobarbital (parenteral only); Secobarbital
Effects edit
Short-term effects: (last for 15 hours after ingestion)
• Relief of tension and anxiety
• Drowsiness
• Feeling of drunkenness / intoxication
• Unclear speech
• Inability to control simple bodily functions (walking, balance, etc.)
• Decreased memory
• Emotional Instability
Long-term effects:
• Chronic tiredness
• Lack of general coordination
• Vision problems
• dizziness
• Decreased reflexes and response
• Sexual dysfunction
• Menstrual irregularities
• Respiratory disorders
Tolerance:
• Develops very quickly
• It may take up to 10 times the original dose to produce the same state
Withdrawal Symptoms:
• Hallucinations
• Eating disorders
• Disorientation
• vomiting
• Sleep disorders
Barbiturates along with other depressants:
Combining barbiturates with other drugs is very dangerous (especially when combined with other CNS depressants such as Demerol, heroin, morphine, and codeine). Barbiturates produce many of the same effects as alcohol, and the combination of the two is often fatal. There is a hidden danger with using barbiturates, especially if you have allergies. Antihistamines (found in most allergy, cold, and sinus medications) are another type of CNS depressant, and when taken in combination with barbiturates, they can cause respiratory failure.
Barbiturates with stimulants:
Barbiturates are often counteracted with high doses of amphetamines or cocaine (both stimulants). This mixture is extremely dangerous, as it can accelerate the heart rate and lead to coronary failure.
Pathophysiology:
Barbiturates bind to a specific site on gamma-aminobutyric acid (GABA) sensitive ion channels found in the CNS, where they allow chloride to enter cell membranes and subsequently hyperpolarize the postsynaptic neuron.
GABA is the major inhibitory neurotransmitter in the CNS. Barbiturates produce 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 enhancing and prolonging the actions of GABA. In high doses, barbiturates stimulate GABA A receptors directly in the absence of GABA. Barbiturates also block glutamate (excitatory neurotransmitter) receptors in the CNS.
Barbiturates can be functionally grouped into long and short acting agents (forming ultra short, short, and intermediate acting agents). Compared to long-acting agents, those of short duration are more fat soluble, more protein bound, higher pKa, faster action speed and shorter duration, and are almost entirely metabolized in the liver to inactivate metabolites (which are excreted as glucuronides in urine). Long-acting agents, which are less fat soluble, accumulate more slowly in tissues and are more rapidly excreted by the kidney as an active drug. Incidentally, urinary excision accounts for 20-30% of phenobarbital elimination. and 15-42% for primidone (both long-acting).
Short-acting agents have an elimination half-life of less than 40 hours compared to long-acting agents, which have an elimination half-life greater than 40 hours.
Barbiturates stimulate the liver cytochrome P-450 system mixed with the microsomal enzyme oxidase; therefore, they affect the drug levels of medications that are dependent on this system (eg, coumadin).
Effects on the Central Nervous System
Barbiturates act primarily in the CNS and consequently affect other organ systems. The direct effects include being sedative and hypnotic in low doses. Lipophilic barbiturates, such as thiopental, cause rapid anesthesia by their tendency to penetrate brain tissue rapidly. Barbiturates are all anticonvulsants since they hyperpolarize cell membranes; and therefore they are effective in the treatment of epilepsy.
Pulmonary Effects
Barbiturates can cause depression of the respiratory medullary center and induce respiratory depression. LK Patients with chronic respiratory obstruction diseases (COPD) are more susceptible to these effects, even at doses that would be considered therapeutic in healthy individuals. Overdose fatality is generally secondary to respiratory depression.
Cardiovascular Effects
Cardiovascular depression can occur due to the depression of the vasomotor spinal centers; Patients with congestive heart failure (CHF) are more susceptible to these effects. At high doses, cardiac contractility and the vascular atom are compromised, which can result in cardiovascular collapse.
Mortality / Morbidity:
Fatality associated with barbiturate overdose is rare, but complications abound. Morbidity includes pneumonia, shock, hypoxia, and coma.