Methohexital

Question 1

What is the trade name of Methohexital?

Answer 1

Brevital

Question 2

What is the formal drug class of Methohexital?

Answer 2

Barbiturate/ Oxybarbiturate

Question 3

What are the clinical uses of Methohexital?

Answer 3

• IV/IM/Rectal induction and IV maintenance of anesthesia in short procedures with minimal painful stimuli
• treatment of Increased ICP

Question 4

What is the MOA of Methohexital?

Answer 4

• produces sedative-hypnotic effects via interaction with GABA in the CNS and by depressing the RAS
• GABAa increases transmembrane chloride, resulting in hyperpolarization of the post-synaptic cell membrane and thus inhibition of the post-synaptic neurons
• also targets glutamate, adenosine and neuronal nicotinic receptors
• selectively depresses transmission in SNS ganglia resulting in decreased BP during IV administration

Question 5

How is Methohexital metabolized?

Answer 5

• Occurs in the liver through N-dealkylation and oxidation to inactive metabolites
• side chain oxidation to form the inactive metabolite, 4-hydromethohexital is the most important biotransformation involved in termination of biologic activity

Question 6

What is the elimination 1/2 life?

Answer 6

4 hours

Question 7

How is Methohexital cleared?

Answer 7

-much higher hepatic extraction ratio (compared with TPL) therefore hepatic blood flow and cardiac output more likely to influence metabolism

Question 8

What is the redistribution of Methohexital?

Answer 8

• IV administration results in rapid uptake by the brain (within 30 secs) and rapid induction of sleep
• early awakening is a result of redistribution away from CNS

Question 9

What is the DOA of Methohexital?

Answer 9

5-10 minutes as a result of its lipid solubility and rapid redistribution into muscle and organs with high blood flow

Question 10

How is Methohexital eliminated?

Answer 10

clearance 9.3-12.1 mL/kg/min

Excreted via the kidneys

Question 11

What is the volume of distribution of Methohexital?

Answer 11

Vd is 1.9-2.2 L/kg

Question 12

Is Methohexital protein bound?

Answer 12

approximately 73%

Question 13

What are the CNS side effects of Methohexital?

Answer 13

• Hiccups, coughing, and/or muscle twitching
• produces a dose-dependent decrease in CMRO2 by up to 50% of normal
• Reduction in O2 requirements may offer protection during transient focal ischemic events
• seizures may be elicited in those with previous history of convulsive activity, especially partial seizure disorder
• cerebral vasoconstriction with reduction in cerebral blood flow and ICP- cerebral perfusion pressure maintained because reduction in ICP exceeds MAP
• pain on injection

Question 14

What are the respiratory side effects of Methohexital?

Answer 14

• Depressed ventilatory response to hypercarbia or hypoxemia as a result of central depression
• dose dependent decrease in RR and TV- apnea may result for 30-90 seconds after a sleep dose

Question 15

What are the CV effects of Methohexital?

Answer 15

-following induction, temporary dose-dependent decrease in ABP and CO, and reflex tachycardia

Question 16

What are the contraindications to the use of Methohexital?

Answer 16

• Contraindicated in patients who cannot tolerate GA
• Porphyria
• known sensitivity

Question 17

When should Methohexital be used with caution?

Answer 17

in patients with:
asthma
obstructive pulm. disease
severe HTN or hypotension
Hypovolemia
Myocardial disease
CHF
Severe anemia
Extreme obesity

Question 18

Metabolism of Methohexital is influenced by what other drugs?

Answer 18

Phenytoin
Halothane
Anticoagulants
Corticosteroids
Ethyl Alcohol
Opioids
Propylene Glycol

Question 19

What should NOT be mixed with Methohexital?

Answer 19

Succinylcholine and other

Acidotic medications because precipitation will occur

Question 20

What is the induction dose of Methohexital?

Answer 20

1 - 2 mg/kg IV of 1% solution

Question 21

What is the maintenance IV dosage of Methohexital?

Answer 21

Intermittent injections of 20-40mg of 0.2% or 1% solution every 4-7 minutes, or as required

Question 22

What is the rectal dose of Methohexital and when is it usually used?

Answer 22

20 - 30 mg/kg for induction of anesthesia in uncooperative or pediatric patients

Question 23

What is an important airway consideration of Methohexital?

Answer 23

-it does not completely obtund a/w reflexes; asthmatics may develop bronchospasm and lightly anesthetized patient may develop laryngospasm