Science - Combined (0653) | Drugs

Welcome to the world of pharmacology! This chapter might sound complicated, but we are just learning about how different substances interact with the incredible chemical system inside your body. Understanding drugs is not only vital for your exam, but also for making informed, healthy choices in real life. Let’s get started!

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B13.1 Drugs: The Basics (Core Content)

1. What is a Drug?

Before we dive into specific types, we need a clear definition. This is a common exam question, so make sure you know it!

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

• Modify or Affect: Drugs work by changing the speed, outcome, or process of the normal chemical reactions happening in your cells.
• Example: Think of a painkiller. When you feel pain, it’s because of chemical signals traveling to your brain. A drug like paracetamol works by interfering with (modifying) those chemical signals, so your brain doesn’t register the pain as strongly.

Key Takeaway: Drugs aren't just medicines; they are any substance (like alcohol, nicotine, or caffeine) that causes a biochemical change when consumed.

2. The Important Role of Antibiotics (Core Content)

When you get sick, it’s often due to an infection. But infections can be caused by different things, most commonly bacteria or viruses. This distinction is crucial for understanding antibiotics.

A. Use of Antibiotics (Core 2)

Antibiotics are a special type of drug used specifically for the treatment of bacterial infections.

They work by killing the bacteria or preventing them from reproducing. They target structures that bacteria have, but human cells do not (like the bacterial cell wall).

B. Antibiotics vs. Viruses (Core 4)

It is extremely important to remember this rule:

Antibiotics kill bacteria but do not affect viruses.

• Bacteria: These are living cells that antibiotics can target and destroy.
• Viruses: These are not technically living cells; they are just genetic material inside a protein coat. They hijack your own cells to reproduce. Since antibiotics target bacterial cell structures, they cannot affect the virus hidden inside your own cells.
• Common Mistake Alert! Taking an antibiotic for a cold or flu (which are caused by viruses) will not help you get better and contributes to a serious global problem.

Analogy: Imagine your immune system is a police force. Antibiotics are specialized tools designed to arrest the gang members (bacteria). If the criminals are aliens (viruses), those tools are useless!

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B13.1 Antibiotic Resistance (Core & Supplement Content)

3. The Problem of Resistance (Core 3)

We rely heavily on antibiotics, but their overuse means they are becoming less effective. Why?

Some bacteria are naturally resistant to antibiotics. This resistance greatly reduces the effectiveness of the drug.

How Resistance Develops:

Step 1: Exposure: A person takes an antibiotic to kill a group of bacteria.
Step 2: Survival: Most bacteria die, but a few individuals naturally have a random mutation that makes them slightly resistant (they survive the drug).
Step 3: Multiplication: These surviving resistant bacteria now have no competition. They multiply rapidly, passing their resistance trait to the next generation.
Step 4: Superbug: The antibiotic is now useless against this new, resistant population.

This process is an example of natural selection happening very quickly among bacteria.

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4. Limiting the Development of Resistance (Supplement 5)

This section is crucial for students aiming for the highest grades (Extended syllabus). We need strategies to slow down the evolution of these 'superbugs'.

The main way to limit the development of resistant bacteria (like the famously resistant MRSA - Methicillin-resistant Staphylococcus aureus) is to ensure we use antibiotics only when essential.

Practical Steps to Limit Resistance:

1. Prescription Only: Ensure antibiotics are only prescribed by a doctor for confirmed bacterial infections, not for viral infections like colds.
2. Completing the Course: Patients must finish the full course of antibiotics, even if they feel better quickly.

Step-by-Step Explanation for Completing the Course:

1. If you stop taking the antibiotic early, you might kill the weakest bacteria, but the slightly stronger ones might just be damaged, not dead.
2. These surviving, partially resistant bacteria recover and multiply.
3. The next time you get sick, the entire population of bacteria in your body is now stronger and harder to kill, speeding up the development of full resistance.

By using them only when essential and ensuring every prescribed course is finished, we minimize the chances of the bacteria adapting and surviving exposure.