Nursing Pharmacology: Drug Action

• Study notes for Level 1 Nursing Students, Pharmacology Lec2, 2024-2025

Pharmacodynamics of Drugs

• Focuses on actions of drugs within the body
• Explores drug actions, mechanisms, and adverse effects

Drug Mechanisms

• Examines how drugs create biochemical/physiological changes in the body
• Drugs interact with cellular components, like complex cell membrane proteins
• Drug interactions with target receptors represents drug action
• The drug effect is the response from this action

Factors Affecting Drug Action

• Patient size and age
• Genetic and nutritional factors
• Gender, health conditions, emotional status, and other drug interactions

Mechanisms of Drug Actions

• Centers around receptor interactions
• A drug (ligand) interacts with a receptor, which affects the body
• The receptor is a target molecule that a drug combines with to produce specific effects
• Receptor occupation may or may not result in receptor activation

Drug-Receptor Theory and Major Receptor Families

• Ligand-gated ion channels mediate ion flow across cell membranes
• G protein-coupled receptors activate intracellular signaling pathways
• Enzyme-linked receptors trigger enzymatic cascades
• Intracellular receptors bind to drugs inside the cell

Drug Action on Receptors: Agonists

• Agonist drugs are characterized by an attraction, or affinity, for a receptor and stimulate it
• Involves the drug's ability to initiate a response
• Includes full agonists and partial agonists

Antagonists

• Drugs having affinity for a receptor, but displaying little or no intrinsic activity
• Prevents responses from occurring
• Can be competitive, noncompetitive, chemical, or functional

Drug Dependence

• An aspect of drug abuse where individuals depend on a drug
• Stopping the drug can cause withdrawal symptoms
• Classified as psychological or physical

Drug Tolerance

• Decreased response to a drug's usual dose after repeated use

Drug-Drug Interactions

• Occurs when two drugs are administered
• Additive effect results if they have similar effects (1+1=2)
• Synergism occurs when combined net effect is greater than individual effects (1+1>2)

Potentiation

• Involves a drug with no affect by itself which then increases the effect of another active drug
• (0+1>1)

Antagonism

• Drugs with opposing effects are given together

Drug Potency

• The relative amount of a drug needed for a desired response
• Drug potency is also used to compare and contrast 2 drugs

Dose-Response Curve

• Illustrates relationship between drug dose and the response
• Low doses correlate with low responses
• Incremental doses lead to increased drug response until a maximum effectiveness reaches the maximum effect level

Therapeutic Index and Margin of Safety

• Therapeutic Index is a ratio of a drug that produces toxicity and/or therapeutic response
• Ratios of less than 2 are considered to be toxic
• It is safer for there to be a higher ratio of 10 or greater versus a 2 or lower ratio

Autonomic Nervous System (ANS)

• Regulates involuntary functions like heart rate, respiratory rate, and digestion
• Controlled by sympathetic and parasympathetic systems

Types of Drugs for ANS Disorders

• Cholinergic, anticholinergic, adrenergic, and adrenergic blocking drugs

Cholinergic Agonists (Parasympathomimetics)

• Act like acetylcholine (Ach)
• Classified as cholinergic agonists, which mimic Ach
• Anticholinesterase drugs inhibit acetylcholine destruction

Classification of Parasympathomimetics

• Choline Esters: Bethanechol
• Includes activating atonic bladders and treating post-operative urinary retention

Cholinomimetic Alkaloids

• Pilocarpine is stable and used to lower intraocular pressure (IOP)
• Nicotine has N actions, which stimulate ganglia at small doses and block ganglia at larger doses

Indirect Acting Anticholinesterases

• Physostigmine treats glaucoma and atropine poisoning
• Neostigmine is the DOC (Directly Observed Therapy) for Mythenia gravis
• Galantamine and Donepezil will treat Alzheimer's