Solanaceous alkaloids and analogues

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Chapter: Medicinal Chemistry : Anticholinergic Drugs

Anticholinergic Drugs : Solanaceous alkaloids and analogues - Synthesis and Drug Profile - i. Atropine (Atp, Tropine) ii. Scopolamine iii. Homatropine (Isopto) iv. Ipratropium Bromide (Ipneb, Ipranaseaq, Ipratop) - Structure, Properties, uses, Synthesis, Assay, Storage, Dosage forms, Dose | Synthesis and Drug Profile


SYNTHESIS AND DRUG PROFILE


Solanaceous alkaloids and analogues


i. Atropine (Atp, Tropine)


Properties and uses: It is a white crystalline powder or colourless crystals, freely soluble in alcohol and well soluble in water. It is the tropine ester of racemic tropic acid and is optically inactive. The greater molar potency of atropine helps it to block several moles of acetylcholine. The umbrella-like atropine molecule may mechanically or electrostatically inactivate adjacent receptors on the cell surface so that these receptors are also unavailable for acetylcholine or other parasympathomimetic stimulants. Atropine has all the actions and uses of antimuscarinic drugs.

Synthesis


Assay: Dissolve the sample in anhydrous acetic acid and warm it, if necessary. Cool the solution and titrate with 0.1 M perchloric acid. Determine the end point potentiometrically.

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

Dose: In Bradycardia: Adult: 500 μg every 3–5 min totally 3 mg.

Dosage forms: Atropine methonitrate injection I.P., Atropine sulphate injection I.P., Atropine sulphate tablets I.P., Atropine sulphate ointment I.P., Atropine Eye drops B.P., Atropine Eye ointment B.P., Atropine injection B.P., Atropine tablets B.P., Morphine and Atropine injection B.P.


ii. Scopolamine


Synthesis


Properties and uses: It exists as colourless or white crystals or white granular powder, odourless, slightly efflorescent in dry air, and is an anhydrous salt, soluble in water or alcohol and in chloroform, insoluble in ether. Scopolamine is the levo component of the racemic mixture that is known as Hyoscine. It is effective in the prevention of motion sickness. It is a competitive blocking agent of the parasympathetic nervous system like atropine, but it differs markedly from atropine in its action on the higher nerve centres.


iii. Homatropine (Isopto)


Synthesis


Properties and uses: It is a white crystalline powder or colourless crystals, sparingly soluble in alcohol, but freely soluble in water. It is used topically on the ciliary structure of the eye and to effect mydriasis.

Assay: Dissolve the sample 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, protected from light.

Dose: Topically for adult, to the conjunctiva, 1 drop of a 2%–5% solution given three times at 10 min intervals.

Dosage forms: Homatropine eye drops B.P.


iv. Ipratropium Bromide (Ipneb, Ipranaseaq, Ipratop)


(±)-endo-3-(3-Hydro-1-oxo-2-phenyl propyl)-8-methyl-8-(1-methyl ethyl-8-azoniabicyclo octane bromide

Synthesis


Properties and uses: It is a white or almost white crystalline powder, freely soluble in methanol, soluble in water, but slightly soluble in ethanol. It is used in the inhalation therapy to produce dilation of bronchial smooth muscle for acute asthmatic attacks. It produces broncho-dilation by competitive inhibition of cholinergic receptors bound to the smooth muscles of the bronchioles.

Assay: Dissolve the sample in water and add 3 ml of dilute nitric acid. Titrate with 0.1 M silver nitrate and determine the end point potentiometrically.

Dose: For inhalation reversible airways obstruction and COPD, maximum dose is 320 μg daily as nebulized solution.

Dosage forms: Ipratropium Nebuliser solution B.P., Ipratropium powder for inhalation B.P., Ipratropium pressurized inhalation B.P.


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