VPT 321: Veterinary Neuropharmacology (2+1) copy 1

SEMISYNTHETIC AND SYNTHETIC ANTIMUSCARINIC DRUGS

• Natural antimuscarinic alkaloids have some disadvantages like lack specificity, long duration of action and potential adverse effects.
• Hence they have been largely displaced by semisynthetic and synthetic antimuscarinic drugs.

Mydriatics

• These drugs are tertiary amines that are instilled into the conjunctival sac to produce mydriasis and or cycloplegia.
• Unlike atropine and hyoscine these drugs have shorter duration of action and are devoid of systemic effects when applied in to the eye.

Homatropine

• It is a semisynthetic drug that is produced from atropine. It is about 10 times less potent than atropine. Has rapid onset (30-45 min) and short duration of action.

Eucatropine

• Has rapid onset and shorter duration of action (about 1 hour) of action . It produces mydriasis without cycloplegia.

Antisecretory – Antispasmodic - Antimuscarinic Drugs

• Quaternary compounds
  • Being quaternary compounds, they are not absorbed from gut, and do not cross BBB and conjunctival barrier.
  • Hence, side effects on eye and CNS are minimal. These drugs have some ganglionic blocking activity, which partly contribute to their antispasmodic effects.

Propantheline

• In the GI tract it reduces spasm and gastric secretions at doses these produces minimal side effects. In the urinary system it reduces the frequency of urination and urgency.
• Clinically propantheline is used as antisecretory antispasmodic in GI disorders. Also indicated in urinary inconsistency.

Isorpropamide

• Used for its antiemetic, antidiarrrhoeal, anticholinergic effects.
• Gylopyrronium (Glycopyrrolate)
• Primarily used an adjunct to general anesthesia to reduce to reduce secretions and to treat sinus bradycardia.

Ipratropium

• It acts selectively on bronchial muscles without altering volume or consistency of respiratory secretions. Used as bronchodilator in treating chronic obstructive pulmonary disease.

Tertiary Amines

• Tertiary amine antimuscarinic drugs in addition to their antimuscarinic actions also have some non- specfic direct relaxant effect on smooth muscles.
• In therapeutic doses, they reduce spasm of the GI tract, biliary tract, ureter and uterus.

Oxybutinin

• Oxybutinin has good antispasmodic and antisecretory effects; the antispasmodoic effect is more prominent on the urinary bladder.

Dicyclomine

• Has some direct smooth muscle relaxant effect in addition to antispasmodic action.
• It decreases spasm of most smooth muscles without producing atropine like effects on the heart, eyes, salivary and sweat glands.

Antiparkinsonian Drugs

• These drugs cross BBB and act on basal ganglion and extra pyramidal system to reduce the involuntary movements and rigidity of parkinson’s disease.
• These are also used to treat the extra pyramidal side effects of antipsychotic drugs.
• These have feeble peripheral effects and hence are more selective for central effects.
  • Eg. Benzhexol, Benztropine, Procylidine etc.