Sciences - Co-ordinated (Double) (0654) | Drugs

B14 Drugs: Understanding How Medicines Affect the Body

Welcome to the chapter on Drugs! Don't worry, we aren't just talking about illegal substances; in Biology, a 'drug' is any powerful chemical that changes how your body works. Understanding drugs, especially antibiotics, is essential for tackling diseases and appreciating modern medicine. Let's dive into how these substances interact with your body's chemical reactions!

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1. What Exactly Is a Drug? (Core)

In the context of biology and medicine, a drug has a precise definition.

Definition of a Drug

• A drug is defined as any substance taken into the body that modifies or affects chemical reactions in the body.

Think of your body as a massive factory running thousands of specific chemical reactions (your metabolism). A drug is a chemical signal or substance designed to step in and either speed up, slow down, or block one of these specific reactions.

Example: The active ingredient in pain relief medication modifies the chemical reactions that signal pain to your brain, effectively reducing the sensation of pain.

2. Antibiotics: Targeting Bacterial Infections (Core)

One of the most important types of therapeutic drugs are antibiotics. They revolutionised medicine, allowing us to treat deadly bacterial diseases effectively.

Use of Antibiotics

The primary use of antibiotics is for the treatment of bacterial infections. They work by killing the bacteria or stopping them from reproducing.

• Antibiotics target the unique structures in bacteria (like the cell wall or processes in the cytoplasm) that are different from human cells. This means they can kill the infectious agent without harming your cells.

The Crucial Distinction: Bacteria vs. Viruses (Core)

This is a very common point tested in examinations. You must know the difference between what antibiotics can treat and what they cannot.

Antibiotics kill bacteria, but they do NOT affect viruses.

Viruses (like the common cold, flu, or COVID-19) are fundamentally different from bacteria. They hijack your own cells to reproduce and lack the specific metabolic machinery that antibiotics target.

Analogy: If bacteria are like enemy soldiers on the street (easy to target with antibiotics), viruses are like tiny spies hiding inside your houses (your cells). If you use antibiotics, you only destroy the soldiers on the street; if you try to destroy the spies hiding inside, you end up destroying your own house!

3. The Growing Problem of Antibiotic Resistance (Core & Supplement)

While antibiotics are life-savers, their widespread use has created a new challenge: antibiotic resistance.

What is Resistance? (Core)

• Some bacteria develop the ability to survive exposure to an antibiotic. These bacteria are described as resistant.
• When bacteria become resistant, it reduces the effectiveness of antibiotics, making infections much harder, or sometimes impossible, to treat.

Imagine: An antibiotic is like a poisonous spray. Most bacteria die when sprayed. However, due to natural variation, a few bacteria might have a slight genetic mutation that makes them immune to the spray. These are the resistant ones.

How Resistance Develops and Spreads (Supplement)

The rapid development of resistance is a major public health concern. The key concept here is natural selection (B17.2).

1. Variation: Within a large population of bacteria, there is natural genetic variation. A few individual bacteria might possess genes that give them slight resistance to an antibiotic.
2. Selection (Using the Drug): When an antibiotic is used, all the non-resistant (weak) bacteria are killed.
3. Survival of the Fittest: The few resistant bacteria survive the drug treatment.
4. Reproduction: These surviving resistant bacteria reproduce rapidly, passing on the resistance genes to their offspring.
5. Evolution: Soon, the entire infection is caused by a resistant strain, and the original antibiotic is now useless.

This explains how using antibiotics only when essential can limit the development of resistant bacteria (Supplement 5). If the antibiotic is only used when truly needed (i.e., for a bacterial infection, not a virus), the chances of the bacteria being exposed and evolving resistance are much lower.

Case Study: MRSA (Supplement)

MRSA (Methicillin-resistant Staphylococcus aureus) is a specific example of a highly dangerous resistant bacteria (a 'superbug').

• MRSA is a type of bacterium that often causes infections in hospitals.
• It is resistant to many common antibiotics, including methicillin, making infections very difficult to treat effectively and increasing the risk of death.