Methohexital is a barbiturate, the structure of which is that of barbituric acid substituted at N-1 by a methyl group and at C-5 by allyl and 1-methylpent-2-ynyl groups. It has a role as an intravenous anaesthetic and a drug allergen. It is a member of barbiturates and an acetylenic compound. It is a conjugate acid of a methohexital(1-).
Safety information is for reference only and does not replace the supplier’s Safety Data Sheet (SDS), applicable regulations, or professional assessment.
GHS classification
GHS Classification · 4 items
Danger
H301 (100%): Toxic if swallowed [Danger Acute toxicity, oral]
P264, P270, P301+P316, P321, P330, P405, and P501 (click each P-code to see the statement)
Aggregated GHS information provided per 39 reports by companies from 1 notifications to the ECHA C&L Inventory.
Hazard information
Regulatory InformationDEA schedule IV controlled substance
Hazard Classes and CategoriesAcute Tox. 3 (100%)
Toxicology
Treatment · 1 item
Establish an airway and ensure oxygenation and ventilation. Resuscitative measures should be initiated promptly. For hypotension, intravenous fluids should be administered and the patient's legs raised. If desirable increase in blood pressure is not obtained, vasopressor and/or inotropic drugs may be used as dictated by the clinical situation. For convulsions, diazepam intravenously and phenytoin may be required. If the seizures are refractory to diazepam and phenytoin, general anesthesia and paralysis with a neuromuscular blocking agent may be necessary. Protect the patient's airway and support ventilation and perfusion. Meticulously monitor and maintain, within acceptable limits, the patient's vital signs, blood gases, serum electrolytes, etc. Absorption of drugs from the gastrointestinal tract may be decreased by giving activated charcoal, which, in many cases, is more effective than emesis or lavage; consider charcoal instead of or in addition to gastric emptying. Repeated doses of charcoal over time may hasten elimination of some drugs that have been absorbed. Safeguard the patient's airway when employing gastric emptying or charcoal. (L1712)
Chemistry & industry
Pharmacology
ATC Code · 4 items
N - Nervous system
N - Nervous system
QN - Nervous system
QN - Nervous system
Protein Binding73%
Pharmacodynamics · 1 item
Methohexital, a barbiturate, is used for the induction of anesthesia prior to the use of other general anesthetic agents and for induction of anesthesia for short surgical, diagnostic, or therapeutic procedures associated with minimal painful stimuli. Little analgesia is conferred by barbiturates; their use in the presence of pain may result in excitation.
Mechanism of Action · 1 item
Methohexital binds at a distinct binding site associated with a Cl<sup>-</sup> ionopore at the GABA<sub>A</sub> receptor, increasing the duration of time for which the Cl<sup>-</sup> ionopore is open. The post-synaptic inhibitory effect of GABA in the thalamus is, therefore, prolonged.
Biological Half-Life5.6 ± 2.7 minutes
Metabolism/Metabolites · 2 items
Metabolism occurs in the liver through demethylation and oxidation. Side-chain oxidation is the most important biotransformation involved in termination of biologic activity.
Metabolism occurs in the liver through demethylation and oxidation. Side-chain oxidation is the most important biotransformation involved in termination of biologic activity.
Route of Elimination: Excretion occurs via the kidneys through glomerular filtration.
Half Life: 5.6 ± 2.7 minutes
FDA Pharmacological Classification · 5 items
E5B8ND5IPE
METHOHEXITAL
Established Pharmacologic Class [EPC] - Barbiturate
6.1 C · 6.1C - Combustible acute toxic Cat.3toxic compounds or compounds which causing chronic effects
Hazard Classifications
3 Oral · Acute Tox. 3 Oral
Toxicity
An ultra-short-acting i.v. anesthetic. Because its use causes respiratory depression, apnea, and hypotension, establishment and maintenance of airways, oxygen administration, etc. are required. Various allergic responses have sometimes been reported with its use.
Health Effects
They cause slurred speech, disorientation and "drunken" behavior. They are physically and psychologically addictive.
Adverse Effects · 1 item
The adverse effects of methohexital include respiratory depression, apnea, hiccups, cardiovascular depression, and laryngospasm. In critically ill preload-dependent patients, methohexital may reduce systemic vascular resistance and cardiac output; however, the incidence of these events is low. The ventilatory and cardiovascular depressant effects of methohexital are dose-dependent; however, they vary with the patient's preexisting disease. The respiratory depressant effect may result from both central and peripheral mechanisms. Methohexital can alter upper airway tone, leading to obstruction, and affect the brainstem respiratory centers, resulting in apnea and hypoventilation. Hypotension has also been noted during methohexital administration and is mediated by peripheral vasodilation, resulting in decreased afterload and preload and a negative inotropic effect on the heart. Methohexital is commonly associated with pain when injected into smaller veins. A study demonstrated that dissolving the drug in a lipid emulsion before administration resulted in pain resolution with no change in potency. Mean arterial pressure is not significantly affected after administration of methohexital and appears to be more hemodynamically stable when compared to other agents. As methohexital is a commonly used agent during ECT, it is essential to note that it has dose-dependent anticonvulsant properties and may adversely affect seizure procurement in a subset of patients with high seizure thresholds.
Exposure RoutesParenteral (intramuscular, intravenous).
The absolute bioavailability following rectal administration of methohexital is 17%.
Toxicity Summary · 2 items
Signs and Symptoms of Overdose
Methohexital binds at a distinct binding site associated with a Cl<sup>-</sup> ionopore at the GABA<sub>A</sub> receptor, increasing the duration of time for which the Cl<sup>-</sup> ionopore is open. The post-synaptic inhibitory effect of GABA in the thalamus is, therefore, prolonged.
Signs and Symptoms · 1 item
The onset of toxicity following an overdose of intravenously administered methohexital will be within seconds of the infusion. If methohexital is administered rectally or is ingested, the onset of toxicity may be delayed. The manifestations of an ultrashort-acting barbiturate in overdose include central nervous system depression, respiratory depression, hypotension, loss of peripheral vascular resistance, and muscular hyperactivity ranging from twitching to convulsive-like movements. Other findings may include convulsions and allergic reactions.
Carcinogen ClassificationNo indication of carcinogenicity to humans (not listed by IARC).
Effects During Pregnancy and Lactation◉ Summary of Use during Lactation
Safety data
wgk
WGK 3
ridadr
3249
hs_code
2933599550
Toxicity
An ultra-short-acting i.v. anesthetic. Because its use causes respiratory depression, apnea, and hypotension, establishment and maintenance of airways, oxygen administration, etc. are required. Various allergic responses have sometimes been reported with its use.
risk_code
11-23/24/25-39/23/24/25
Signal word
Danger
Symbol(GHS)
GHS06
hazard_code
F,T
safety_code
16-36/37-45
hazard_class
6.1(b)
Storage Class
6.1C - Combustible acute toxic Cat.3toxic compounds or compounds which causing chronic effects
packing_group
III
Hazard statements
H301
Hazard Classifications
Acute Tox. 3 Oral
Precautionary statements
P301+P330+P331+P310
Ultrashort-acting anesthetics that are used for induction. Loss of consciousness is rapid and induction is pleasant, but there is no muscle relaxation and reflexes frequently are not reduced adequately. Repeated administration results in accumulation and prolongs the recovery time. Since these agents have little if any analgesic activity, they are seldom used alone except in brief minor procedures. (From AMA Drug Evaluations Annual, 1994, p174)
Absorption, Distribution and Excretion · 2 items
The absolute bioavailability following rectal administration of methohexital is 17%.
Excretion occurs via the kidneys through glomerular filtration.
Cellular LocationsMembrane
Uses & manufacturing
Uses · 2 items
Use (kg; approx.) in Germany (2009): >10
Methohexital is indicated for use as an intravenous anaesthetic. It has also been commonly used to induce deep sedation. It is only used in hospital or similar settings, under strict supervision.
Applications · 1 item
UsesMethohexital is a short-acting barbiturate used as a sedative. Methohexital is used an anesthetic for oral surgery and dentistry and is also used to induce anesthesia prior to electroconvulsive therapy (ECT). Methohexital is a Controlled Substance.
DefinitionChEBI: A barbiturate, the structure of which is that of barbituric acid substituted at N-1 by a methyl group and at C-5 by allyl and 1-methylpent-2-ynyl groups.
