1. Overview
Drugs are substances that interact with the body's internal chemistry to alter how it functions. This topic focuses on the role of antibiotics in treating bacterial infections and the growing global concern of antibiotic resistance, which challenges our ability to treat previously curable diseases.
Key Definitions
- Drug: Any substance taken into the body that modifies or affects chemical reactions in the body.
- Antibiotic: A chemical substance, derived from a microorganism or produced synthetically, that kills or inhibits the growth of bacteria.
- Resistant Bacteria: Bacteria that have mutated so that they are no longer affected by a specific antibiotic.
- Pathogen: A disease-causing organism (e.g., bacteria, viruses, fungi).
Core Content
The Nature of Drugs
A drug is defined by its ability to interfere with metabolic pathways. When a drug enters the system, it travels through the blood to target specific cells or enzymes, changing the rate of chemical reactions.
Antibiotics: Fighting Bacterial Infections
- Antibiotics are used specifically to treat bacterial infections.
- They work by disrupting processes unique to bacteria, such as the production of the bacterial cell wall or protein synthesis within the bacterial cell.
- Description: A diagram showing a bacterium with a cell wall, cytoplasm, and floating DNA loops (plasmids). Next to it, a virus consisting only of a protein coat (capsid) and a strand of genetic material. Labels point to the bacterial cell wall as the "Target for Antibiotics" and the virus as "Lacking targets for Antibiotics."
Antibiotics vs. Viruses
- Antibiotics do not affect viruses.
- Reasoning: Viruses do not have their own metabolism or cell structure (like cell walls or ribosomes). They "hide" inside host cells and use the host's machinery to replicate. Therefore, antibiotics have no target to attack in a virus.
Antibiotic Resistance
- Some bacteria are resistant to antibiotics.
- When a population of bacteria is exposed to an antibiotic, the resistant individuals survive and reproduce.
- This reduces the effectiveness of the drug, as the antibiotic can no longer kill the newly formed population of resistant bacteria.
Extended Content (Extended Curriculum Only)
Development of Resistant Bacteria (e.g., MRSA)
Resistance is an example of natural selection. If antibiotics are used too frequently or incorrectly, the pressure on the bacterial population increases the prevalence of resistant strains.
How MRSA (Methicillin-resistant Staphylococcus aureus) develops:
- Mutation: A random change occurs in the DNA of a bacterium, giving it resistance to an antibiotic.
- Selection Pressure: When the antibiotic is used, it kills all the non-resistant (susceptible) bacteria.
- Survival: The resistant bacterium survives and has more resources and space.
- Reproduction: The survivor multiplies, passing the resistance gene to its offspring.
- Spread: The resistant strain (like MRSA) becomes the dominant strain in the environment (e.g., hospitals).
Limiting Resistance
To ensure antibiotics remain effective, their use must be limited to essential cases only:
- Complete the course: Patients must take all prescribed doses to ensure all bacteria are killed, leaving none to mutate.
- Avoid over-prescription: Doctors should not prescribe antibiotics for viral infections like the common cold or flu.
- Agricultural restrictions: Limiting the use of antibiotics in livestock feed to prevent the jump of resistant strains from animals to humans.
Key Equations
There are no mathematical equations for this specific sub-topic. However, you may be asked to calculate percentage increases in resistance or ratios of resistant vs. non-resistant bacteria from provided data tables.
Common Mistakes to Avoid
- ❌ Wrong: Thinking that the human body becomes resistant to antibiotics.
- ✓ Right: The bacteria become resistant to the drug, not the human patient.
- ❌ Wrong: Prescribing antibiotics to "cure" a cold or the flu.
- ✓ Right: Colds and flu are caused by viruses, which are unaffected by antibiotics.
- ❌ Wrong: Thinking antibiotics "kill" viruses.
- ✓ Right: Antibiotics only kill bacteria; antiviral drugs are needed for viruses.
Exam Tips
- Command Word - "State": This appears most frequently (10x in past papers). When asked to "State the use of antibiotics," a simple "to treat bacterial infections" is sufficient.
- Definition Questions: Be precise with the definition of a "drug." Ensure you mention that it affects "chemical reactions in the body."
- The MRSA Context: MRSA is the most common real-world example used in the Extended curriculum. Always link it to the idea of "natural selection" or "survival of the fittest bacteria."
- Graph Analysis: Expect questions showing a graph of antibiotic use vs. the number of resistant cases. Always describe the trend (usually as use increases, resistance also increases).