Dimenhydrinate

Chemical composition

Diphenhydramine (53-55.5%) + 8-Chlorotheophylline (44-47%)

IUPAC nomenclature

2-benzhydryloxy-N,N-dimethylethanamine;8-chloro-1,3-dimethyl-7H-purine-2,6-dione

Classification

• H1-receptor antihistamine
• Ethanolamine ether antihistamine

Physiochemical Properties

Mechanism of Action

• The antiemetic property is due to H1 antagonism in the vestibular system.
• Excitatory effects of drug is due to adenosine receptor blockade by 8-chlorotheophylline.

Structure Activity Relationship

Structure activity of ethanolamine ethers can be summarized as:

• 8-chlorotheophyllinate salt of diphenhydramine is used for treatment of motion sickness
• Compounds with p-Cl-Ph and 2-pyridyl aryl groups are carboxamine, which is a potent anti-histamine drug.
• Substitution of the methyl group at the carbon alpha to the ether function gives a related compound known as doxylamine.
• An additional carbon atom between oxygen and nitrogen produces clemastine which has lower sedative properties.
• In setastine, alkyl amine substituent is incorporated into seven-membered hexahydroazepine ring, having lower sedative properties.
• With increase in alkyl group size at C-2’, there is decrease in antihistaminic activity and increases in anticholinergic activity..
• Introduction of alkyl substituents at C-4’results in decrease in anticholinergic activity and increase in antihistaminic activity. [1]

Method of synthesis

i. Reaction of benzhydrylbromide and 2-dimethylaminoethanol produces diphenhydramine.

ii. Theophylline anhydrous is warmed up to 50-60^oC and dissolved in water, drip N-chlorosuccimide to get a crude product. The product is then dissolved in 5% NaOH aqueous solution to get Chlorotheophyline. [2]

Medicinal Uses

Dimenhydrinate is used for treatment of:

• Nausea
• Vomiting
• Dizziness
• Motion sickness 

Side Effects

Side effects of dimenhydrinate are:

• Asthma
• Bronchitis
• Emphysema
• Glaucoma
• Liver diseases
• Kidney diseases
• Enlarged prostate
• Urination problems
• High blood pressure
• Overactive thyroid
• Heart diseases. 

MCQs 

Q.1 Dimenhydrinate is the mixture of?

a) Diphenhydramine and Epinephrine

b) Xylometazoline and Bicalutamide

c) Diphenhydramine and 8-chlorotheophylline

d) 8-chlorotheophylline and brompheniramine

Q.2 Which amongst the following statements is/are incorrect related to the SAR of ethanolamine ethers antihistamine drugs?

I. 8-chlorotheophyllinate salt of diphenhydramine is used for treatment of motion sickness

II. Compounds with p-Cl-Ph and 2-pyridyl aryl groups are carboxamine, which is a potent anti-histamine drug.

III. Substitution of the methyl group at the carbon alpha to the ether function gives a related compound known as doxylamine.

IV. An additional carbon atom between oxygen and nitrogen produces clemastine which has higher sedative properties.

a) I, II

b) II, IV

c) I, II, IV

d) IV

Q.3 Type of rings present in the structure of dimenhydrinate?

I. Pyridine

II. Purine

III. Phenyl

IV. Pyrimidine

a) II, III

b) I, IV

c) I, III

d) II, IV

Q.4 Side effects of drug dimenhydrinate is/are?

a) Asthma

b) Heart diseases

c) Enlarged prostate

d) All of the above

Q.5 Match the following drugs with their correct melting point-

 a. i-A, ii-D, iii-C, iv-B

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

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

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

Q.6 An example of drug from class ethanolamine ether antihistamines is?

a) Dimenhydrinate

b) Dobutamine

c) Ethosuximide

d) All of the above 

Q.7 Dimenhydrinate is used for the treatment of?

a) Nausea

b) Vomiting

c) Dizziness

d) All of the above

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ANSWERS

1-c

2-d

3-a

4-d

5-b

6-a

7-d

REFERENCES