Ultra-short-acting barbiturate

The ultra-short-acting barbiturates include methohexital sodium (Brevi-tal) and thiopental sodium (Pentothal). These agents are used as anesthetics and are administered intravenously. Barbiturates with short-to-intermediate duration of action are used for their sedative-hypnotic effect in the treatment of anxiety. These medications include amobarbital (Amytal), butabarbital (Butisol), sodium pentobarbital (Nembutal), and secobarbital (Seconal). 

Clinical reports of patients who underwent chloroform anesthesia indicated that premedication with morphine caused serious respiratory depression when chloroform was co-administered. Thiopentone (thiopental Na, an ultra-short-acting barbiturate anesthetic) was associated with increased incidences of hypotension in chloroform-anesthetized patients (Whitaker and Jones 1965). 

Anaesthesia The ultra short acting barbiturates produce general anaesthesia (details are given in chapter General anaesthetics ). 

They are well absorbed from the GIT. They are widely distributed in body. Rate of entry into CNS is dependent on lipid solubility. Ultra short acting barbiturates are highly lipid soluble and quickly enter the brain. Redistribution to various tissues terminate their action and they are slowly released from the tissues and gradually metabolised in the liver. They are partly metabolised and partly excreted unchanged in urine. 

For general anaesthesia Ultra short acting barbiturates are used. 

Anesthesia Selection of a barbiturate is strongly influenced by the desired duration of action. The ultra-short-acting barbiturates, such as thiopental, are used intravenously to induce anesthesia. 

Thiopental Sodium, USP. Thiopental. sodium, sodium S-ethyl-S-(l-methylbutyl)-2-lhiobarbilurale (Pentothal Sodium). is the mo.st widely u.sed ultra-short-acting anc.sthctic barbiturate. Additionally, the compound is the prototype for the ultra-short-acting barbiturates. Most discussions of how structure influences duration of action in this group of agents relate specifically to it. The compound s onset of action is about equal to the time required for it to travel to the brain from the site of administration. Consciousness is regained within 30 minutes. 

Ultrashort-acting Ultra-short-acting barbiturates (thiopental sodium Pentothal) are an anesthetic... 

The ultra-short-acting barbiturates, thiopental, thiamylal, and methohexital, quickly cross the blood-brain barrier but are rapidly redistributed from the brain to other body tissues, first to highly perfused visceral organs (liver, kidneys, heart) and muscle, and later to fatty tissues. 

As soon as a drug finds its way into the blood stream, it tries to approach the site of biological action. Hence, the distribution of a drug is markedly influenced by such vital factors as tissue distribution and membrane penetration, which largely depends on the physico-chemical characteristics of the drug. For instance, the effect of the ultra-short acting barbiturate thiopental may be explained on its dissociation constant and lipid solubility. It is worthwhile to observe here that the dmation of thiopental is not influenced by its rate of excretion or metabolism, but by its rate of distribution. 

It belongs to the category of ultra-short-acting barbiturates which are usually administered intravenously for the production of complete anaesthesia of a short duration. It is also used as a basal anaesthesia. 

It is an ultra-short acting barbiturate mainly used for intravenous anaesthesia in conditions of comparatively short-duration. It is also effective for the termination of convulsions of unknown origin. 

With increased doses, the patient experiences a hypnotic effect causing the patient to fall asleep. Even higher doses of sedative-hypnotics anesthetize the patient. Such is the case of the ultra-short-acting barbiturate thiopental sodium (Pentothal) that produces anesthesia. 

Various barbiturates such as the short acting agent pentobarbital and the ultra-short acting agents thiopental and methohexital are used for anesthesia induction. They produce loss of consciousness without analgesia and with little effects on the cardiovascular system. Unconsciousness is combined with respiratory depression as the barbiturates produce non-selective CNS depression. 

Succinylcholine is an ultra-short-acting depolarizing skeletal muscle relaxant. The neuromuscular block remains for as long as sufficient quantities of succinylcholine remain. After i.v. administration, the onset of action is typically within Imin and lasts for 2-3 min. Succinylcholine is metabolized by plasma cholinesterases to choline and the weakly active succinylmono-choline, which is primarily excreted in the urine (Plumb 1995). Succinylcholine should be administered i.v. at a dose rate of 0.088mg/kg (Plumb 1995). Succinylcholine can also be added to an overdose of barbiturate to produce euthanasia in horses. This is accompanied by a minimal amount of postmortem muscular contraction, making the addition of succinylcholine desirable for use during euthanasia when the client is present. 

Barbiturates are classified according to their duration of action. These are ultra short-acting (thiopental and methohexital), short- to intermediate-acting (pentobarbital, secobarbital, and amobarbital), and long-acting (phenobarbital). 

Ultra-short-acting hypnotic agents are obtained in some instances by alkylation of a ring nitrogen of the barbiturate. l-Methyl-5-allyl-5-(l-methyl-2-pentynyl)barbituric acid (methohexitone, methohexital, Brietal, Brevital, Metharbital) is one such example, which is used as an anaesthetic of very short duration. Patients are usually awake in 5-10 min, and ambulatory in 15 min. Some iV-methylated barbiturates, such as the 5-ethyl-5-phenyl... 

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