Pharmacology principles
Consider indication, dose, interactions, contraindications, organ function and adverse effects before prescribing. Reconcile the full medicines list.
Understand
Absorption, distribution, metabolism and elimination determine exposure; pharmacodynamics determines effect. Therapeutic benefit must be balanced against interactions, allergies, adverse effects and renal or hepatic function.
Assess
Reconcile prescribed, over-the-counter and recreational agents and clarify the indication. Distinguish a genuine immune allergy from a predictable side effect or intolerance without dismissing reported reactions.
Apply
Check the current BNF or formulary and patient-specific contraindications before prescribing. Use the narrowest appropriate indication, document advice and review effectiveness or adverse effects.
Key distinctions
An adverse drug reaction may be dose-related, idiosyncratic or immune-mediated. The medicine's indication also signals an underlying condition: an antiresorptive for metastatic cancer and one for osteoporosis have different contexts. When prescribing, weigh absolute benefit against harm and use current dose information; a remembered regimen can become outdated.
Think through a case
A patient reports a “penicillin allergy” described as nausea years ago. Clarify the reaction and timing, then make a safe prescribing decision using the current formulary.
The distinction to remember
Do not choose an antibiotic before deciding whether one is indicated. Also check drug interactions, pregnancy, renal function and the patient's stated allergy.
Test your recall
What two factors commonly alter drug exposure?
Show answer
Renal or hepatic function and interacting medicines.