Adrenergic and Cholinergic Drugs

Adrenergic Agonists

• Enhance the natural action at adrenergic receptors (alpha 1 & 2, beta 1 & 2).
• Examples:
  • Epinephrine: Works at alpha 1 & 2, beta 1 & 2; increases activity of all receptors.
  • Norepinephrine
  • Albuterol
  • Terbutaline
  • Phenylephrine
  • Pseudoephedrine
  • Clonidine: An adrenergic agonist, but works at the alpha-two receptor (negative feedback receptor). Activation leads to a lowering of blood pressure.

Adrenergic Antagonists

• Blocker medications.
• Examples:
  • Metoprolol: Beta blocker (more commonly referred to as). A beta one selective blocker.
  • Prazosin: Alpha one blocker.

Expected Responses to Adrenergic Agonists (excluding clonidine)

• Mimic the sympathetic response (running from a predator).
  • Increased blood pressure.
  • Increased heart rate.
  • Bronchodilation in the lungs.

Albuterol

• Used for bronchospasms and asthma to cause bronchodilation.
• Side effects involve increased heart rate or heart palpitations because it's a beta-2 adrenergic agonist stimulating beta receptors in both the lungs and the heart.

Norepinephrine

• Used in hypotension and shock, particularly hypovolemic shock.
• Increases heart rate and blood pressure in emergency situations to support cardiovascular function.

Terbutaline

• Used in asthma, similar to albuterol.

Phenylephrine & Pseudoephedrine

• Used for nasal congestion and sinus pressure.
• Side effects:
  • Increased blood pressure due to alpha and beta agonist activity.
• Contraindicated in patients with:
  • Hypertension.
  • Unstable angina (can worsen due to vasoconstriction).
  • Closed-angle glaucoma (can trigger constriction of vessels responsible for clearing aqueous humor).

Metoprolol (Beta-1 Antagonist/Beta Blocker)

• Lowers blood pressure.
• Used in heart failure or angina.
• Beta-1 selective blocker.
• Non-selective beta blockers (block beta 1 and beta 2) can cause bronchoconstriction because beta 2 receptors are located in the lungs and cause bronchodilation.
• Use selective beta blockers in patients with asthma or COPD to avoid exacerbating respiratory conditions.

Prazosin (Alpha-1 Antagonist)

• Lowers blood pressure by causing vasodilation (opposite of pseudoephedrine).
• Can be used to treat Raynaud's syndrome by improving blood flow.
• Common Side Effect:
  • Orthostatic hypotension (blood pressure drops when changing positions).

First Dose Phenomenon

• The first dose of a new medication causes a drop in blood pressure and orthostatic hypotension.
• More common with cardiac medications.
• Patients can continue to experience orthostatic hypotension even after the first dose.
• First dose phenomenon and orthostatic hypotension can occur separately.

Clonidine

• Adrenergic agonist at alpha-two receptors, causes negative feedback, leading to decreased blood pressure and heart rate.
• Side effects: dry mouth and fatigue.
• Used in patients undergoing alcohol withdrawal to lower blood pressure; can be pulled back quickly because the blood pressure adjusts rapidly.
• Dangerous for children: can cause fatal decreases in heart rate and blood pressure if ingested.

Cholinergic Drugs

• Muscarinic receptors are cholinergic receptors, but there are also nicotinic receptors.
• Work in the parasympathetic nervous system (rest and digest).
• An adrenergic agonist and a cholinergic antagonist produce the same effect in the body.
• An adrenergic antagonist and a cholinergic agonist produce the same effects, but they're working in different systems.

Actions of the Parasympathetic Nervous System

• Decrease in blood pressure.
• Increase in GI secretions.
• Calming of the whole system.

Cholinergic Agonists

• Stimulate parasympathetic receptors.
• Examples:
  • Bethanycol
  • Edrophonium: Used as a test drug to determine if a patient is experiencing myasthenia gravis or a cholinergic crisis, not a treatment.

Bethanycol

• Used to treat urinary retention, particularly post-anesthesia when the bladder is atonic.
• Contraindicated in patients with peptic ulcer disease because it increases stomach acid secretion.

Cholinergic Antagonists

• Examples:
  • Atropine
  • Oxybutynin
  • Succinylcholine

Atropine

• Can be used to treat a cholinergic crisis.

Cholinergic Crisis Symptoms

• Muscle weakness
• Bradycardia

Atropine (cont.)

• Can be used to treat bradycardia or excessive oral secretions.

Causes of Cholinergic Crisis

• Organophosphate poisoning (pesticides).

Oxybutynin

• Used for overactive bladder.
• Side effects: blurry vision and light sensitivity (photophobia).

Succinylcholine

• Used for Anesthesia to bring about muscle paralysis.
• Short-acting muscle relaxant.
• Absolute contraindications: Hyperkalemia releases additional potassium from cells, which is dangerous when potassium is already high.

Other Important Points

• Malignant hyperthermia: Caused by succinylcholine, symptoms include muscle rigidity, tachycardia, and high fever.
• Cholinergic crisis or overdose: Symptoms include low heart rate (bradycardia), cramping, and diarrhea.
• Anticholinergic side effects: Dry mouth, urinary retention, constipation, and blurry vision.