Isoflurane

IUPAC nomenclature

(RS)-2-Chloro-2-(difluoromethoxy)-1,1,1-trifluoro-ethane

Classification

Isoflurane is an inhalational anesthetic.

Physiochemical Properties

Mechanism of Action

• Isoflurane decreases the gap junction channel opening times and increases gap junction channel closing time which induces reduction in junctional conductance.
• The drug also increases the fluidity of the lipid membrane and thus, activates calcium dependent ATPase in the sarcoplasmic reticulum.
• Isoflurane also binds with D subunit of ATP synthase, GABA receptors, glutamate receptors , glycine receptors, the large conductance Calcium ion activated potassium channel and NADH dehydrogenase.

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. 2,2,2-trifluoroethanol undergoes methylation by dimethylsulfate to give methyl ether.

ii. Methyl ether is chlorinated by molecular chlorine to produce 2-(dichloromethoxy)-1,1,1-trifluoroethane.

iii. Chlorine atoms are replaced by fluorine atoms on subsequent interaction with hydrogen fluoride in presence of antimony(V) chloride.

iv. Resulting ether undergoes chlorination by molecular chlorine to produce isoflurane.

Therapeutic Uses

Isoflurane is used for:

• Induction and maintenance of general anesthesia in adult and pediatric patients.

Side Effects

Side effects of Isoflurane are: 

• Cardiac disorders
• Hepatobiliary disorders

MCQs

Q.1 Choose the correct option related with the mechanism of action of drug Isoflurane?

a) Increases the gap junction channel opening time

b) Decreases the gap junction channel closing time

c) Increases the fluidity of the lipid membrane

d) All of the above

Q.2 Therapeutic use of drug Isoflurane is/are?

a) Control of seizures

b) As an anesthetic

c) Prevention of Diarrhea

d) All of the above

Q.3 Which amongst the following are the correct statements with respect to the SAR of drug Isoflurane?

I. Due to presence of asymmetric halogenated carbon in ether, they are lesser anesthetics.

II. Halogenated methyl ethyl ethers are less stable, less potent and have lesser clinical profile than halogenated diethyl ether.

III. Fluorination increases the stability and decreases the flammability.

IV. Compete halogenations of the alkane or ether decreases the anesthetic potency and increases the convulsant potency

a) I, IV

b) II, III

c) III, IV

d) I, III

Q.4 Number of chiral carbons present in the structure of isoflurane is?

a) 0

b) 1

c) 2

d) 3

Q.5 Correct sequence for the True/False for the physiochemical properties of the drug Isoflurane is?  

I. Molecular weight = 184.49 gm/mol

II. Melting point = 140.2^oC

III. White powder

IV. Ring structure absent

a) FFTF

b) TFFT

c) FTTF

d) TFFF

Q.6 Correct statements for the IUPAC nomenclatures of the drugs are?

I. Isoflurane: (RS)-2-Chloro-2-(difluoromethoxy)-1,1,1-trifluoro-ethane.

II. Carvedilol: 1-(Aminomethyl)cyclohexaneacetic acid

III. Procyclidine: 8-chloro-6-(4-methylpiperazin-1-yl)benzo[b][1,4]benzoxazepine

IV. Codeine: 5-ethyl-5-pentan-2-yl-2-sulfanylidene-1,3-diazinane-4,6-dione

a) I

b) II, III, IV

c) II , III

d) III, IV 

Q.7 Match the following drugs with their correct classifications-

a) i-B, ii-D, iii-C, iv-A

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

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

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

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ANSWERS

1-c

2-b

3-c

4-b

5-b

6-a

7-d

REFERENCES