Benzoic acid derivatives

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Chapter: Medicinal Chemistry : Local Anaesthetics

a. Cocaine b. Hexylcaine hydrochloride (Synonym: Cyanine) c. Meprylcaine and Isobucaine HCl d. Cyclomethycaine sulphate c. Piperocaine (Synonym: Metycaine)


SYNTHESIS AND DRUG PROFILE


Benzoic acid derivatives


a. Cocaine


Properties and uses: Cocaine is the first local anaesthetic discovered; it is an alkaloid obtained from the leaves of Erythroxylon cocca. It is a white crystalline powder (or colourless crystals), very soluble in water, freely soluble in alcohol, and slightly soluble in methylene chloride. Though it is considered too toxic for any anaesthetic procedure requiring injection, it is still employed topically as a 1% or 2% solution for the anaesthesia of the ear, nose, throat, rectum, and vagina because of its intense vasoconstrictive action.

Assay: Dissolve the substance in a mixture of 0.01 M hydrochloric acid and alcohol. Perform potentiometric titration using 0.1 M sodium hydroxide.

Storage: It should be stored in well-closed airtight containers and protected from light.

Synthesis


Dose: Employed topically in a 1% or 2% solution for anaesthesia of the ear, nose, throat, rectum, and vagina.

Dosage forms: Cocaine eye drops B.P.


b. Hexylcaine hydrochloride (Synonym: Cyanine)


Synthesis


Properties and uses: It is a white powder, soluble in water, and chloroform. It is regarded as an all-purpose soluble local anaesthetic agent. The onset and duration of action is almost similar to that of lignocaine. It is mainly used as surface anaesthetic .

Dose: For infiltration anaesthesia, 1%; for nerve block anaesthesia, 1% and 2% solution; and for topical application to skin and mucous membrane, 1% to 5%.


c. Meprylcaine and Isobucaine HCl


Synthesis



d. Cyclomethycaine sulphate


Synthesis

Route I. From: p-Chlorobenzoyl chloride


Route II. From: p-Hydroxy benzoic acid


Properties and uses: It is a white crystalline powder, soluble in water, and chloroform. Used to releive pain from damaged skin, mucous membrane of rectum, vagina, and urinary bladder.

Dose: The usual dose for topical purpose is 0.25% to 1% in suitable form.


e. Piperocaine (Synonym: Metycaine)


Synthesis


Properties and uses: Piperocaine is small, white, crystalline powder, soluble in water and chloroform. It is used as surface anasthesia for eyes, throat and caudal analgesia.


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