Antibiotics, painkillers, drug development and monoclonal antibodies
Once a person is ill, the body's defences may not be enough. Modern medicine treats disease with three classes of drug, plus increasingly with monoclonal antibodies. This is largely a Higher-tier topic.
Antibiotics
Antibiotics are drugs that kill bacteria inside the body. Penicillin (Alexander Fleming, 1928) was the first. Antibiotics target processes specific to bacteria — disrupting cell-wall synthesis or protein synthesis — without harming our cells.
Specific antibiotics for specific bacteria — choosing the right antibiotic matters; broad-spectrum antibiotics are kept in reserve to slow resistance.
Crucially: antibiotics cannot kill viruses. Viruses replicate inside our own cells and don't have bacterial machinery for the drug to attack.
Antibiotic resistance
Random mutations in bacteria can give resistance to an antibiotic. When the antibiotic is used, susceptible bacteria die; resistant ones survive and reproduce — over time, the population becomes resistant. This is natural selection in action (see B6.6).
To slow resistance:
- Doctors should not over-prescribe antibiotics
- Patients must finish the course (so all bacteria are killed, not just the susceptible ones)
- Don't use antibiotics for non-serious viral infections
- New antibiotic development is too slow to keep up — a major public health concern.
MRSA (methicillin-resistant Staphylococcus aureus) is the GCSE example.
Painkillers
Painkillers (e.g. paracetamol, aspirin) treat symptoms — they don't kill the pathogen. They reduce pain or fever but the immune system still does the work of clearing the infection.
Drug discovery and development
Most drugs originally came from natural sources:
- Digitalis — from foxglove (heart drug)
- Aspirin — from willow bark
- Penicillin — from Penicillium mould (Fleming)
A new drug must be tested in stages:
- Preclinical — tested on cells, tissues, then live animals. Checks for toxicity, efficacy and dose.
- Clinical phase 1 — small group of healthy volunteers. Find safe dose, monitor side effects.
- Clinical phase 2 — small group of patients to check it works.
- Clinical phase 3 — large group of patients in a double-blind trial — neither doctor nor patient knows who gets the drug or the placebo (dummy treatment), to remove bias.
Monoclonal antibodies (HT)
A monoclonal antibody is identical antibody molecules produced by a clone of cells, all targeting one specific antigen.
Production:
- A mouse is injected with the antigen.
- Lymphocytes from the mouse are fused with myeloma (tumour) cells to form hybridomas — cells that divide indefinitely AND produce antibody.
- Hybridomas are cloned and the antibody collected.
Uses:
- Pregnancy tests — detect HCG hormone in urine
- Diagnosing diseases — measure hormone levels (ELISA)
- Locating cancer cells — antibody attached to a fluorescent dye
- Treating cancer — antibody attached to a toxic drug, delivered only to cancer cells (reducing side effects)
Pros: high specificity. Cons: side effects sometimes severe; production was once expensive; ethical issues with mouse use.
⚠Common mistakes— Common mistakes / exam traps
- "Antibiotics treat colds" — colds are viral; antibiotics don't help.
- "Painkillers kill bacteria" — they don't; they only treat symptoms.
- Confusing placebo with control — placebo IS the control treatment in a double-blind trial.
- "Resistance evolves because bacteria want to survive" — wrong; it's random mutation followed by natural selection.
Links
Connects to B3.1 (pathogens), B6.6 (natural selection drives resistance) and B6.9 (Darwinian explanation).
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