What is the difference between an indication and a contraindication in pharmacology?

• A. Indication is a side effect; contraindication is the drug's mechanism of action.
• B. Indication is a reason to give a drug; contraindication is a condition that makes giving it unsafe.
• C. Indication is the route of administration; contraindication is the patient's age.
• D. Indication is the cost of drug; contraindication is the dosage.

Answer: (B)

Understanding when to use a drug versus when to avoid it hinges on two ideas: indication and contraindication. An indication is a medical reason to give a drug—the condition or situation in which the drug has proven benefit and is considered appropriate therapy. A contraindication is a factor that makes giving the drug unsafe or inappropriate—the condition, circumstance, or risk that would make treatment more likely to cause harm than benefit.

So this choice is the best because it states that an indication is a reason to administer the drug, while a contraindication is a condition that makes giving it unsafe. For example, aspirin has the indication of helping in suspected myocardial infarction, but a contraindication would be an active internal bleeding or a known aspirin allergy, which would make giving it unsafe. Other options mix up these ideas: one confuses indication with a side effect or mechanism, another with route or age, and another with cost or dosage.