New medical drugs have to be tested and trialled before being used to…

The idea

Before a new medical drug can be prescribed to patients, it must pass through testing and clinical trials. Testing first uses laboratory studies, including cells and tissues, to look for harmful effects. If results are promising, trials move to healthy volunteers at low dose to check safety, then to patients to see whether the drug actually treats the condition. Safety means the drug does not cause unacceptable harm; effectiveness means it produces the intended therapeutic benefit at a suitable dose. For example, a new antibiotic might kill bacteria in culture, then be given to volunteers to check side effects, then to patients to compare recovery with an existing treatment. Only after evidence from all stages is reviewed may the drug be approved for medical use.

What earns the marks

• Testing before medical use identifies harmful effects such as organ damage or severe side effects, so safety can be judged.
• Trials establish whether the drug works against the target condition, which is what effective means in this context.
• Laboratory testing on cells, tissues or animals can screen a candidate drug before any human exposure.
• Clinical trials in humans normally begin with healthy volunteers at low dose to assess safety and tolerance.
• Later trials use patients who have the condition so that therapeutic effect can be compared with existing treatments or a placebo.
• Evidence from all stages is reviewed before a drug is approved for prescribing to the general public.

Common mistakes and how to put them right

• Thinking that a drug only needs to be tested for safety.

  Put it right: Effectiveness must also be demonstrated, because a safe drug that does not treat the condition is not useful.

• Assuming human trials always start with patients.

  Put it right: Early human trials usually use healthy volunteers to check safety before patients are exposed.

• Believing that laboratory testing alone is enough for approval.

  Put it right: Human trials are required because effects in cells or animals do not always predict effects in people.

Exam tips

• Link each stage of testing to its purpose: safety, effectiveness or finding a suitable dose.
• Use the terms safe and effective precisely; safe means absence of unacceptable harm, effective means the drug treats the condition.
• When describing a sequence, make clear why healthy volunteers are used before patients rather than simply listing stages.