Antibiotic Resistance – Why You Should Finish the Course

What it shows

Most bacteria in this infection are sensitive to drug A, but a few carry mutations that raise their minimum inhibitory concentration (MIC): low-level mutants need three times more drug, high-level mutants thirty times more. The antibiotic does not cause these mutations; it acts as a selective agent, killing sensitive bacteria first and leaving the tougher ones. If treatment stops while survivors remain, they multiply again and the new population contains a larger share of resistant bacteria. A full course, a high enough dose, or two drugs together can kill every bacterium, because resistance to both drugs at once is extremely rare.

How to use

Press Run to follow the first course with the default settings, and watch the coloured curves on the logarithmic graph and the drug level strip below it. When the infection returns, press New course to treat again and compare the rows in the table. Then press New patient and change Dose (peak / MIC), Course length, Taking the drug or Treatment.

Parameters you can change

• Antibiotic dose (peak concentration relative to MIC) 2–20 × MIC
• Length of the course 2–14 days
• How the drug is taken Every dose, for the full course, Stop when feeling better, Often misses doses (1 in 3 skipped)
• Treatment One drug (drug A), Combination of two drugs (A + B)

Questions to explore

1. Why does feeling better not mean that all the bacteria are gone?
2. Does the antibiotic cause resistance mutations, or does it only select mutations that were already there?
3. Why is it much harder for bacteria to become resistant when two drugs are given together?