Drugs and Drug Development

Painkillers

• Relieve symptoms (reduce pain) but do NOT kill pathogens or cure the disease
• Examples: paracetamol, aspirin, ibuprofen, morphine
• They work by blocking nerve signals that carry pain messages to the brain

Antibiotics

• Kill or inhibit the growth of bacteria inside the body
• Examples: penicillin, amoxicillin, tetracycline
• Each antibiotic is effective against certain types of bacteria
• Antibiotics do NOT work against viruses — viruses reproduce inside host cells, so antibiotics cannot target them without destroying the host cells

Antivirals

• Drugs that slow down the replication of viruses
• They do NOT kill viruses but reduce their ability to reproduce
• Difficult to develop because viruses use host cell machinery
• Example: antiretrovirals for HIV

Other Drug Categories

• Antiseptics — kill microorganisms outside the body (e.g., on surfaces, skin)
• Antihistamines — reduce allergic reactions
• Anaesthetics — block nerve signals to prevent pain during surgery

Many drugs were originally discovered from natural sources:

Today, most new drugs are synthesised (chemically manufactured) in laboratories, though natural products often inspire their design.

Before a new drug can be prescribed to patients, it must undergo a rigorous testing process that takes many years. This ensures the drug is safe and effective.

Stage 1: Discovery and Pre-clinical Testing

1. Identify a potential drug (from natural sources, computer modelling, or chemical synthesis)
2. Test in the laboratory using cells and tissues grown in the lab (in vitro testing)
   • Checks if the drug has any effect on the target disease
3. Test on animals (in vivo testing)
   • Required by law in the UK
   • Tests for toxicity (harmful effects), efficacy (does it work?), and dosage (how much is needed)
   • Ensures the drug is safe enough to proceed to human testing
   • Controversial — animal rights groups oppose this

Stage 2: Clinical Trials (Human Testing)

If pre-clinical tests are successful, the drug progresses to clinical trials with human volunteers:

Phase 1 — Safety

• Tested on a small group of healthy volunteers
• Determines if the drug is safe and identifies side effects
• Very low doses are used initially

Phase 2 — Efficacy

• Tested on a small group of patients with the target disease
• Determines if the drug actually works against the disease
• Establishes the optimal dose

Phase 3 — Large-scale trials

• Tested on a large number of patients (hundreds or thousands)
• Compares the drug to existing treatments or a placebo
• Provides robust evidence of effectiveness and identifies rare side effects

The Placebo Effect

• A placebo is a substance that looks like the real drug but contains no active ingredient (e.g., a sugar pill)
• Some patients feel better after taking a placebo because they believe they are receiving treatment — this is the placebo effect
• Clinical trials use placebos to distinguish between the actual effect of the drug and the placebo effect

Double-Blind Trials

• In a double-blind trial, neither the patients nor the doctors know who is receiving the real drug and who is receiving the placebo
• This eliminates bias — doctors cannot unconsciously treat patients differently, and patients cannot be influenced by knowing which group they are in
• The data is only "unblinded" after the trial is completed

Peer Review

• After clinical trials, the results are published in scientific journals and undergo peer review
• Other scientists evaluate the methods, data, and conclusions
• This ensures the findings are valid and reliable before the drug is approved

• If clinical trials are successful, the drug is submitted to regulatory authorities (e.g., MHRA in the UK, FDA in the US) for approval
• Even after approval, the drug is monitored for long-term side effects (post-market surveillance)
• The entire process from discovery to prescription can take 10–15 years and cost billions of pounds

(Covered in detail in the Immune System and Vaccination topic, but summarised here for completeness.)

The Problem

• Overuse and misuse of antibiotics has led to bacteria evolving resistance
• Resistant bacteria survive antibiotic treatment and reproduce, spreading resistance genes
• MRSA is an example of a multi-drug-resistant "superbug"

Why It Matters

• If antibiotics stop working, common infections could become life-threatening
• Surgery and cancer treatment (which rely on antibiotics to prevent infection) become much riskier

Solutions

• Only prescribe antibiotics when necessary (not for viral infections)
• Patients must complete the full course of antibiotics
• Develop new antibiotics (though this is slow and expensive)
• Reduce antibiotic use in agriculture
• Improve hygiene in hospitals to prevent spread of resistant bacteria

Recreational Drugs

• Drugs taken for their effects on the mind or body, not for medical reasons
• Can be legal (e.g., alcohol, caffeine, nicotine) or illegal (e.g., cannabis, cocaine, heroin, ecstasy)
• Can cause addiction — a physical or psychological dependence on the drug
• Can cause tolerance — the body adapts, requiring higher doses for the same effect
• Can cause withdrawal symptoms — unpleasant physical effects when the drug is stopped

Alcohol and Tobacco

• Alcohol: depressant that slows brain function; long-term damage to liver (cirrhosis), brain, and heart; social effects
• Tobacco/Nicotine: highly addictive; contains carcinogens; causes lung cancer, COPD, cardiovascular disease; tar damages cilia in airways

Question: Describe the stages of drug testing before a new drug can be prescribed to patients. (4 marks)

Solution:

First, the drug is tested in the laboratory on cells and tissues to check it has an effect on the target disease. Then it is tested on animals to assess its toxicity, efficacy, and appropriate dosage. If safe in animals, the drug enters clinical trials on human volunteers. In Phase 1, it is tested on healthy volunteers to check safety. In Phase 2, it is tested on patients with the disease to check effectiveness. In Phase 3, large-scale trials compare it to a placebo or existing treatment using a double-blind method to eliminate bias. Results are then peer-reviewed before the drug can be approved.

• Remember the order of drug testing: lab (cells/tissues) → animals → human clinical trials (Phase 1, 2, 3).
• Always mention double-blind and placebo when describing clinical trials — these are key exam terms.
• Know the difference between painkillers (treat symptoms) and antibiotics (treat cause of bacterial infections).
• For antibiotic resistance questions, always mention random mutation as the cause of resistance — bacteria don't "decide" to become resistant.

• Painkillers relieve symptoms; antibiotics kill bacteria (but NOT viruses); antivirals slow virus replication.
• Many drugs were discovered from nature: aspirin (willow bark), penicillin (Penicillium mould), digitalis (foxglove).
• Drug testing follows: lab testing → animal testing → clinical trials (Phases 1–3) with placebos and double-blind methods.
• Antibiotic resistance is a growing threat; responsible prescribing and completing courses are essential.
• Clinical trial results undergo peer review before drugs are approved for public use.