Pharmacology of Ganglion Drugs

Ganglion-stimulating drugs

• Include nicotine, DMPP and others.
• Stimulate both sympathetic and parasympathetic ganglia, effects include tachycardia, increased blood pressure and variable effects on GI motility and secretions.
• Therapeutic use limited to nicotine to assist in quitting smoking.

Ganglion-blocking drugs

• Include Hexamethonium and Trimetaphan.
• Block all autonomic ganglia and enteric ganglia.
• Main effects include hypotension, loss of cardiovascular reflexes, inhibition of secretions, gastrointestinal paralysis, and impaired micturition.
• Clinically obsolete, except for the occasional use of Trimetaphan for controlled hypotension during anesthesia.

Scopolamine (Hyoscine)

• Causes urinary retention, dry mouth, blurred vision, constipation, tachycardia, and CNS disturbances such as restlessness, agitation and hallucinations.
• Slows gastric emptying, may worsen gastric ulcer symptoms and lead to food delay.
• Contraindicated in glaucoma, BPH, and caution is advised for infants with fever.
• Crosses the blood-brain barrier and causes CNS depression.
• Well absorbed from the GIT and skin, used in transdermal patches to treat motion sickness.
• Drug of choice for motion sickness.

Hyoscine-N-butyl bromide

• Synthetic derivative of scopolamine.
• Has CNS stimulant action.
• Effective in relaxing smooth muscles, used as an antispasmodic for the GIT, biliary system and urinary tract.

Dicycloverine

• Similar to atropine.
• Primarily used as an antispasmodic agent.

Cyclopentolate and Tropicamide

• Tertiary amines developed for ophthalmic use, acting as mydriatics.
• Shorter duration of action than atropine and scopolamine, lasting approximately 6 hours.

Effects of Atropine on the Eye

• Causes pupil dilation (mydriasis) making pupils unresponsive to light.
• Paralysis of accommodation (cycloplegia), inhibiting ciliary muscle, resulting in blurred vision.
• Can increase intraocular pressure (IOP) in susceptible patients.

Effects of Atropine on the Gastrointestinal Tract

• Inhibits gastrointestinal motility, requiring higher doses than other transmitters such as ACh.
• Used in cases where there is excessive gastrointestinal motility.

Effects of Atropine on Other Smooth Muscles

• Relaxes bronchial smooth muscles, preventing reflex bronchoconstriction.
• Relaxes biliary and urinary tract smooth muscles.
• Can lead to urinary retention, especially in elderly men with BPH.

Effects of Atropine on the Central Nervous System (CNS)

• Primarily produces excitatory effects on the CNS.
• Causes mild restlessness at low doses.
• Leads to agitation and disorientation at high doses.
• In poisoning cases in young children, marked excitement and irritability can develop, sometimes leading to atropine fever.

Pharmacological Effects of Muscarinic Antagonists

• Atropine is the prototype drug.
• Atropine inhibits secretions from salivary, lacrimal, bronchial and sweat glands at low doses.
• Slightly reduces gastric secretions.
• Inhibits mucociliary clearance in the bronchi, causing residual secretions to accumulate in the lungs, which is blocked by Ipratropium.
• Causes tachycardia through the blockade of cardiac mAChRs (M2) up to 80-90 beats per minute.
• At very low doses, atropine can cause paradoxical bradycardia possibly due to central action and inhibition of presynaptic M₂ receptors (that normally have an autoinhibitory effect on acetylcholine release).
• The heart's response to exercise is unaffected.
• Arterial blood pressure is unaffected.

Atropine

• Belladonna alkaloid, non-selective muscarinic receptor antagonist.
• Readily absorbed from GIT.
• Partially metabolized and 60% excreted unchanged in urine.
• Crosses the BBB, causing CNS stimulation.
• Half-life is approximately 2 hours, but its effect on the eye can last 3 days to 1 week.
• Blocks muscarinic receptors, reducing secretions and causing bronchodilation.
• Used as an adjunct in anesthesia, antidote for anticholinesterase poisoning, treatment for bradycardia and gastrointestinal hypermotility.
• Low doses cause sedation, high doses cause excitation.
• Can affect the extrapyramidal system, reducing involuntary movement and rigidity in Parkinson’s patients.

Atropine Poisoning

• Symptoms include dry mouth, mydriasis (dilated pupils), blurred vision, tachycardia, hot and flushed skin, agitation, delirium, dry skin, and hyperthermia.
• Atropine flush may be a diagnostic sign.
• Physostigmine is the antidote, use with caution and only for indicated patients as it may cause convulsions.
• Side effects are generally less severe than the effects of atropine poisoning, including dry mouth, constipation and blurred vision.
• Centrally acting muscarinic antagonists (Benztropine, Benzhexol, Procyclidine, and Biperiden) effect the extrapyramidal system and are used to reduce tremors, involuntary movements and rigidity in Parkinson's disease patients, they can also counteract extrapyramidal side effects of some antipsychotic medication.

This quiz covers the pharmacological effects and therapeutic uses of ganglion-stimulating and ganglion-blocking drugs. It includes detailed discussions on drugs like nicotine, Hexamethonium, and Scopolamine, highlighting their impact on the autonomic system. Ideal for students in pharmacology and medicine.