🌡️ Pharmacokinetics (What the body does to the drug)

4 processes:

1. Absorption – from GI tract → bloodstream
• Disintegration: break drug into particles
• Dissolution: dissolve in fluid
• Methods:
• Passive (diffusion, facilitated)
• Active (needs carrier + energy)
• Pinocytosis (engulfing drug particles)
• Factors: blood flow, pain/stress, pH, food, exercise, route
• First-pass effect: liver metabolism before reaching circulation
• Bioavailability: % of drug that actually reaches circulation
2. Distribution – drug movement from blood → tissues
• Influenced by protein binding, free drug levels, blood-brain barrier, placenta transfer
3. Metabolism (Biotransformation) – drug chemically changed (mainly in liver)
• Prodrug = inactive until metabolized
• Half-life (t½) = time for drug level to fall by 50%
• Steady state = consistent drug level
• Loading dose = large first dose to reach effect quickly
4. Excretion (Elimination) – main routes: kidneys, liver (bile), lungs, saliva, sweat, breast milk

💊 Pharmacodynamics (What the drug does to the body)

• Primary effect = desired therapeutic response
• Secondary effect = can be helpful or harmful

Drug Response Concepts:

• Potency – how much drug is needed
• Maximal efficacy – maximum effect drug can give
• Therapeutic index – margin between effective and toxic dose
• Onset, Peak, Duration – how fast, how strong, how long drug acts
• Therapeutic monitoring:
• Peak = highest plasma concentration
• Trough = lowest level before next dose

Receptor Theory:

• Agonist – activates receptor → response
• Partial agonist – weaker effect, blocks stronger drugs
• Antagonist – blocks receptor → no response

Other Mechanisms:

• Stimulation, Depression, Irritation, Replacement, Cytotoxic, Antimicrobial, Immune modification

Side Effects & Risks:

• Side effects – secondary effects (mild, expected)
• Adverse reactions – severe, unexpected, harmful
• Toxicity – drug levels above therapeutic range
• Tolerance – less response over time → higher dose needed
• Tachyphylaxis – rapid decrease in response
• Placebo effect – response due to expectation, not drug

🔄 Drug Interactions

• Pharmacokinetic (absorption, distribution, metabolism, excretion changes)
• Pharmacodynamic:
• Additive = sum of two drugs
• Synergistic = effect much greater together
• Antagonistic = one drug blocks/reduces the other
• Other interactions:
• Drug-food (e.g., delayed absorption)
• Drug-lab (false test results)
• Drug-induced photosensitivity

🧠 Clinical Judgment (PK & PD)

• Recognize cues: Look for possible interactions, check patient’s meds
• Analyze: Anxiety, knowledge gaps
• Generate solutions: Patient explains why regimen is important
• Take action:
• No high-fat food before enteric-coated meds
• Monitor drugs with narrow therapeutic ranges
• Notify provider of antagonistic combinations
• Evaluate: Check if outcomes met safely

✅ In short:

• Pharmacokinetics = ADME (Absorption, Distribution, Metabolism, Excretion).
• Pharmacodynamics = drug effects (agonists, antagonists, therapeutic effects, side/adverse effects).
• Nurses monitor interactions, therapeutic ranges, and patient teaching to keep drug therapy safe.