Principles of pharmacology
Pharmacology explains how drugs move through the body and how they act. Safe medication practice depends on these principles. For study only, not clinical guidance: always follow your programme, current local protocols, and supervising clinicians.
Drug names
Every drug has a chemical name, a generic name (the official non-proprietary name, such as ibuprofen), and often one or more brand names (such as Advil). Nurses should know generic names, since brands differ between countries and manufacturers.
Pharmacokinetics
Pharmacokinetics is what the body does to a drug, summarised as ADME: absorption (entering the bloodstream), distribution (travelling to tissues), metabolism (chemical change, mainly in the liver), and excretion (removal, mainly by the kidneys). Liver or kidney disease can cause drugs to build up to toxic levels.
First-pass effect and routes
Oral drugs pass through the liver before reaching general circulation, where some is metabolised (the first-pass effect), so oral doses may be higher than IV doses. Intravenous drugs act fastest because they enter the blood directly. Other routes include intramuscular, subcutaneous, sublingual, topical, inhaled, and rectal.
Half-life
A drug's half-life is the time for its blood concentration to fall by half. It determines dosing frequency. After about four to five half-lives, a drug is mostly eliminated; similarly, with regular dosing, steady state is reached after about four to five half-lives.
Pharmacodynamics
Pharmacodynamics is what a drug does to the body: its mechanism of action and effects. Many drugs bind receptors. Agonists activate receptors (morphine at opioid receptors); antagonists block them (naloxone blocks opioid receptors, reversing overdose).
Therapeutic index
The therapeutic index compares the dose that causes toxicity with the dose that produces the desired effect. Drugs with a narrow therapeutic index, such as digoxin, lithium, warfarin, and some antiepileptics, need careful dosing and often blood level monitoring.
Adverse effects and allergies
Side effects are predictable, usually mild, unwanted effects (drowsiness from antihistamines). Adverse drug reactions are harmful. Allergic reactions involve the immune system and range from rash to anaphylaxis, a life-threatening emergency with airway swelling and low blood pressure, treated urgently with intramuscular adrenaline (epinephrine).
Special populations
Children need weight-based dosing. Older adults often have reduced kidney and liver function and take multiple medications (polypharmacy), increasing interaction and fall risks; the Beers Criteria list drugs often inappropriate for older adults. In pregnancy, some drugs can harm the fetus and need careful review.
Key takeaways
Use generic drug names. Pharmacokinetics is absorption, distribution, metabolism, and excretion; liver and kidney disease affect it. The first-pass effect reduces oral bioavailability; IV acts fastest. Half-life guides dosing; steady state takes about four to five half-lives. Agonists activate receptors; antagonists block them. Narrow therapeutic index drugs need monitoring. Recognise allergies and anaphylaxis. Adjust for children, older adults, and pregnancy.
Flashcard
Official non-proprietary drug name
Check your understanding
Why might a patient with kidney failure need a lower dose of a drug excreted by the kidneys?