If the drug is found to be safe, further clinical trials are carried out…

The idea

Once early clinical trials show that a drug is safe, further trials are carried out to find the optimum dose. The optimum dose is the amount that gives the best balance between treating the condition and causing acceptable side effects. Researchers test different doses in groups of patients and compare how well each dose works and how many side effects occur. For example, a trial might compare 10 mg, 20 mg and 40 mg doses. The optimum dose is not simply the largest dose; a higher dose may cause more harm without extra benefit. Finding the optimum dose allows the drug to be prescribed at a level that is effective and as safe as possible.

What earns the marks

• Further clinical trials are carried out only after the drug has been shown to be safe in earlier trials.
• The purpose of these further trials is to find the optimum dose of the drug.
• The optimum dose gives the best balance between effectiveness and acceptable side effects.
• Different doses are compared in groups of patients to see which works best with fewest problems.
• The optimum dose is not always the highest dose, because larger doses can cause more side effects.

Common mistakes and how to put them right

• Believing the optimum dose is the maximum dose.

  Put it right by explaining that the optimum dose balances benefit against side effects.

• Thinking safety testing and optimum-dose testing happen at the same time.

  Put it right by stating that optimum-dose trials follow safety trials.

• Assuming all patients need the same dose.

  Put it right by noting that trials compare doses to find the best overall dose for the drug.

Exam tips

• Define the optimum dose in terms of both effectiveness and side effects, not just one of these.
• Use comparative language such as 'different doses are compared' when describing how the optimum dose is found.
• Make the sequence clear: safety first, then further trials for the optimum dose.