Pharmacology of Adrenergic and Cholinergic Drugs

Drugs Acting on ANS

• The nervous system regulates and coordinates body functions like movement, digestion, sleep, and waste elimination.
• The nervous system has two main divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).
• The CNS (brain and spinal cord) receives, integrates, and interprets nerve impulses.
• The PNS (nerves outside the brain and spinal cord) connects all body parts to the CNS.

Peripheral Nervous System

• The peripheral nervous system includes the somatic nervous system (SNS) and the autonomic nervous system (ANS).
• The SNS controls voluntary movement, such as walking, chewing, and writing. Sensory parts of the SNS send messages to the brain regarding internal/external environment (heat, pain, pressure).
• The ANS controls involuntary body functions critical for survival. These systems are automatic and not consciously controlled. Blood pressure, heart rate, gastrointestinal activity, and glandular secretions are regulated by the ANS.

Autonomic Nervous System (ANS)

• The ANS is divided into the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS).
• The sympathetic nervous system (SNS) increases energy expenditure during stressful situations, like danger or illness. It is responsible for speeding up bodily functions like increasing heart rate and diverting energy.
• The parasympathetic nervous system (PNS) conserves energy and promotes bodily rest and repair. It's associated with slower bodily functions like decreasing heart rate and promoting digestion.

Neurotransmitters

• Neurohormones are chemical substances that facilitate the transmission of nerve impulses at nerve endings.
• The two neurohormones in the sympathetic nervous system are epinephrine and norepinephrine. Epinephrine is released by the adrenal medulla, while norepinephrine is primarily released at nerve endings of sympathetic (adrenergic) fibers.
• The parasympathetic nervous system uses acetylcholine (ACh) and acetylcholinesterase (AChE) as neurohormones. ACh is responsible for nerve impulse transmission to effector cells in the parasympathetic system. AChE rapidly deactivates ACh, preventing prolonged nerve stimulation.

Cholinergic Drugs

• Cholinergic drugs mimic the parasympathetic nervous system's activity.
• Direct-acting cholinergics act like ACh, while indirect-acting ones inhibit AChE, prolonging ACh's activity.
• Uses include treating glaucoma, myasthenia gravis, and urinary retention. Glaucoma treatment usually involves eye drops. Myasthenia gravis involves skeletal muscle fatigue, often treated with drugs that enhance acetylcholine action. Urinary retention problems can also be addressed with cholinergic drugs.

Adverse Reactions and Precautions

• Oral/Parenteral administration of cholinergic drugs can cause nausea, diarrhea, abdominal cramping, salivation, skin flushing, cardiac arrhythmias, and muscle weakness.
• Topical application may result in temporary visual acuity reduction and headache.
• Cholinergic drugs are contraindicated for those with hypersensitivity to the drugs, asthma, peptic ulcer disease, coronary artery disease, and hyperthyroidism.
• Use cautiously in patients with hypertension, epilepsy, cardiac arrhythmias, bradycardia, recent coronary occlusion, or megacolon
• Avoid during pregnancy, breastfeeding, and in children, as safety is not fully proven for those groups.

Cholinergic Crisis

• A cholinergic crisis is a severe reaction to cholinergic drugs and involves symptoms like abdominal cramping, diarrhea, excessive salivation, muscle weakness, rigidity, spasms, and jaw clenching.
• Immediate medical help and an antidote (e.g., atropine) are crucial.

Cholinergic Blocking Drugs

• Cholinergic blocking drugs (anticholinergics) inhibit acetylcholine activity, often having the opposite effects of cholinergic drugs.
• They affect numerous systems including eyes, respiratory and gastrointestinal tracts, heart and bladder
• Examples include atropine, scopolamine, and propantheline.

Actions of Cholinergic Blocking Drugs

• Inhibit acetylcholine activity in parasympathetic nerve fibers. This leads to reduced nerve impulse transmission.
• Various effects, such as dreamless sleep, drowsiness.
• Increased pupil dilation, reduced accommodation.
• Decrease in secretions from respiratory tract.
• Decreased in stomach secretions and gastrointestinal motility.
• Increase in heart rate.
• Increased bladder contraction
• These effects are due to reduced parasympathetic activity.

Uses of Cholinergic Blocking Drugs

• Used to treat conditions such as pylorospasm, peptic ulcer, ureteral and biliary colic, vagally induced bradycardia, Parkinsonism.
• Reduced secretions in the upper respiratory tract before general anesthesia.
• Used in pre-anesthetic sedation and motion sickness.
• Also for certain situations like peptic ulcers.

Adrenergic Drugs

• Mimic the effects of the sympathetic nervous system. They're also called sympathomimetic drugs.
• Primarily contain epinephrine and norepinephrine, naturally occurring neurohormones.
• Synthetic versions are also available in medicine.
• Examples include metaraminol (Aramine), isoproterenol (Isuprel), and ephedrine.

Actions of Adrenergic Drugs

• General effects include wakefulness, quick reaction to stimuli, reflexes, reduction in stomach/intestinal movement, and increased heart rate.
• Effects on the central nervous system (CNS) and peripheral nervous system (PNS) to different extents, modifying various body functions.
• Adrenergic nerve fibers have alpha (α) and beta (β) receptors, where drugs act.

Uses of Adrenergic Drugs

• Used in hypovolemic and septic shock, moderately severe hypotension.
• Control superficial bleeding in surgical or dental procedures.
• Bronchial asthma
• Cardiac decompensation and arrest.
• Allergic reactions (e.g., anaphylaxis)
• Heart block, ventricular arrhythmias.
• Nasal congestion (topical use). Local anesthetic prolongations.

Adrenergic blocking Drugs

• These drugs either block alpha (α), beta (β), or both. This leads to effects on various bodily systems including the cardiovascular system with changes in heart rate and blood pressure.
• α-blocking agents can cause vasodilation.
• β-blockers can reduce heart rate and workload.

Uses of Adrenergic Blocking Drugs

• Treating hypertension
• Treating cardiac arrhythmias.
• Preventing reinfarction after myocardial infarction.
• Migraine headaches and angina pectoris.
• Glaucoma (topical use)

Adverse Reactions & Precautions

• May lead to nausea, vomiting, headache, and other side effects.
• Contraindications vary depending on the drug, often associated with hypersensitivity to certain drugs, including conditions like asthma and coronary artery disease.
• Precautions include considerations like pregnancy or renal failure, where their use could be restricted.

Specific Drugs and their Uses

• (Specific examples of action, adverse effects, and specific uses of drugs, as shown in the notes, are listed.)

Shock

• Inadequate blood flow and oxygen delivery to tissues and vital organs.
• Five types: hypovolemic, cardiogenic, septic, obstructive, and neurogenic.

Clinical Manifestations of Shock

• Include cool, clammy skin, rapid heartbeat, low blood pressure, and other signs of decreased blood flow and oxygen delivery to peripheral vessels and vital organs.

Antiadrenergic Drugs

• Inhibit norepinephrine release or act centrally to decrease sympathetic nervous system activity.
• Certain cardiac arrhythmias and hypertension are possible treatment areas.
• Adverse effects include dry mouth, drowsiness, anorexia and other symptoms. Avoid use in individuals with active hepatic disease, liver dysfunction or renal conditions due to increased risk.

α-Adrenergic Blocking Drugs

• Opposite of typical adrenergic effects, causing vasodilation instead of vasoconstriction.
• They are useful in situations like hypertension associated with pheochromocytoma, a tumor that releases excessive catecholamines. Prevents or treats extravasation damage from infiltration during intravenous drug administration.
• Certain adverse effects can include weakness, orthostatic hypotension and tachycardia.

Test your knowledge on the pharmacological effects of adrenergic and cholinergic drugs, their uses, receptor subtypes, and associated adverse effects. This quiz covers key concepts related to cardiovascular actions, metabolic effects, and clinical uses of various drug types.