Halothane

IUPAC nomenclature

2-Bromo-2-chloro-1,1,1-trifluoroethane

Classification

Halothane is a hydrocarbon inhalational anesthetic.

Physiochemical Properties

Mechanism of Action

• Halothane produces actions on multiple ion channels due to which, there is depression in the nerve conduction, breathing and cardiac contractility.
• It binds with potassium channels and produces immobilizing effects.
• They also bind with NMDA and calcium channels and causes hyperpolarization.

Structure Activity Relationship

The SAR for inhaled anesthetics can be summarized as follows:

• Halogenations of the hydrocarbons and ether increase the anesthetic potency.
• Halogenations of the hydrocarbons tends to induce arrhythmia in the following order F<Cl<Br<I.
• Due to presence of asymmetric halogenated carbon in ether, they are better anesthetics.
• Halogenated methyl ethyl ethers are more stable, more potent and have better clinical profile than halogenated diethyl ether.
• Fluorination increases the stability and decreases the flammability.
• Compete halogenations of the alkane or ether decreases the anesthetic potency and increases the convulsant potency
• Presence of double bond increases chemical reactivity and toxicity.

Method of synthesis

i. Hydrogen fluoride is added to trichloroethylene and on simultaneous substitution of chloride atoms in presence of antimony(III) chloride at 130_­^oC produces 2-chloro-1,1,1-trifluoroethane.

ii. The above formed compound undergoes bromination at 450^oC to produce halothane. [1]

Therapeutic Uses

Halothane is used for:

• As a potent anesthetic

Side Effects

Side effects of halothane are: 

• Liver problems
• Irregular heart beats
• Halothane hepatitis
• Decreased efforts to breath

MCQs

Q.1 “2-Bromo-2-chloro-1,1,1-trifluoroethane” is the IUPAC nomenclature of which drug?

a) Chlorpromazine

b) Halothane

c) Dutasteride

d) Fulvestrant

Q.2 Correct melting point of the drug Halothane is?

a) 155°C

b) 50.2°C

c) 115.6°C

d) 15.7°C

Q.3 Match the following with correct classifications of the drugs.

 a) i-A, ii-C, iii-D, iv-B

b) i-C, ii-A, iii-B, iv-D

c) i-D, ii-C, iii-A, iv-B

d) i-A, ii-D, iii-C, iv-B

Q.4 Mechanism of action of drug Halothane includes?

I. Binding with acetylcholine receptors

II. Binding with potassium channels

III. Promoting the prostaglandin production

IV. Binding with NMDA

a) I, IV

b) II, IV

c) I, III, IV

d) I, II

Q.5   Correct sequence for True and False for the given statements related with the SAR of Inhaled anesthetics drugs?

• Halogenations of the hydrocarbons and ether decrease the anesthetic potency.
• Halogenations of the hydrocarbons tends to induce arrhythmia in the following order F<Cl<Br<I.
• Due to presence of asymmetric halogenated carbon in ether, they are better anesthetics.
• Halogenated methyl ethyl ethers are more stable, more potent and have better clinical profile than halogenated diethyl ether.

a) FFTT

b) TFTF

c) TFFT

d) FTTT

Q.6 Which drug is formed on bromination of 2-chloro-1,1,1-trifluoroethane?

a) Halothane

b) Benzazepam

c) Phensuximide

d) Cetrizine 

Q.7 The drug Halothane is mainly used for?

a) As an anesthetic

b) Treatment of pain

c) As an anti-inflammatory agent

d) All of the above

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ANSWERS

1-b

2-b

3-c

4-b

5-d

6-a

7-a

REFERENCES