Core25: Pharmacodynamic interactions - synergism

➕ High-yield / 要点：Pharmacodynamic synergy means combined drug effect is additive or greater-than-additive. It changes the effect, not necessarily the concentration.

Definition / 定義

• Synergism occurs when the overall effect of a drug combination is:
  • Additive：effect A + effect B.
  • Potentiation：greater than additive.

Examples / 例

Combination	Effect	Type
ACE inhibitor + thiazide diuretic	Stronger antihypertensive effect	Potentiation
Paracetamol + ibuprofen	Stronger analgesia	Additive
Beta blocker + verapamil	Marked AV conduction depression	Potentiation; toxicity risk
Folinic acid + 5-fluorouracil	Enhanced thymidylate synthase inhibition → cytotoxicity	Potentiation
Beta-lactam + aminoglycoside	Stronger bactericidal effect	Potentiation

Clinical meaning / 臨床的意義

• Synergy can be therapeutically useful, e.g. antibiotics or anticancer regimens.
• It can also increase toxicity, e.g. beta blocker + verapamil causing excessive AV block/bradycardia.

Remember / 覚え方

• Synergy = effect stronger together
• Additive = 1 + 1 = 2
• Potentiation = 1 + 1 > 2
• Pharmacodynamic interaction = effect-level interaction