📘 Medicinal Chemistry – Lecture 3: Antibiotics (Antibacterial Drugs)

By PharmaEasyNotes 💙

🔹 Introduction

When we get fever, infection, or wounds 🤒
Doctor gives us… Antibiotics 💊

👉 Antibiotics = Drugs that kill or stop bacteria

They:
✔️ Treat infections
✔️ Save lives
✔️ Control bacteria growth

⚠️ They do NOT work on viruses (cold, flu).

🔹 What is Bacteria?

Bacteria → Enter Body
        ↓
Multiply
        ↓
Cause Infection

👉 Antibiotics stop this process.

🔹 Mechanism of Action (Easy Flowchart)

Antibiotics
     ↓
Attack Bacteria
     ↓
Cell Wall / Protein / DNA Damage
     ↓
Bacteria Die
     ↓
Patient Gets Better 😌

🔹 Main Targets of Antibiotics

Target	Action
Cell Wall	Break wall → Kill bacteria
Protein	Stop growth
DNA	Stop multiplication
Metabolism	Block energy

🔹 Classification (Flowchart Style)

Antibiotics
     |
--------------------------------
|       |        |        |
Penicillin Cephalo  Tetra   Macrolide
|         |        |        |
Amoxicillin Cefixime Doxy  Azithromycin

✅ 1. Penicillins

Example: Amoxicillin
✔️ Most common
✔️ Safe
✔️ Broad spectrum

✅ 2. Cephalosporins

Example: Cefixime
✔️ Stronger than penicillin
✔️ Less resistance

✅ 3. Tetracyclines

Example: Doxycycline
✔️ Acne + infection
✔️ Broad spectrum

✅ 4. Macrolides

Example: Azithromycin
✔️ Used in throat & lung infection
✔️ Good alternative

🔹 Important Antibiotics (Must Know ⭐)

Drug	Use
Amoxicillin	General infection
Azithromycin	Throat / Chest
Ciprofloxacin	UTI
Doxycycline	Skin / Acne
Cefixime	Typhoid

🔹 Therapeutic Uses

Antibiotics are used in:

✅ Fever
✅ Typhoid
✅ UTI
✅ Pneumonia
✅ Skin infection
✅ Wound infection

🔹 Side Effects ⚠️

Common:

❗ Nausea
❗ Diarrhea
❗ Allergy
❗ Stomach upset

Serious:

❗ Resistance
❗ Liver damage
❗ Kidney problem

👉 Always take full course ✔️

🔹 Antibiotic Resistance (Very Important 🔥)

What is Resistance?

Incomplete Dose
      ↓
Weak Bacteria Survive
      ↓
Become Strong
      ↓
Medicine Stops Working

👉 Biggest medical problem today 😨

How to Prevent?

✔️ Complete full course
✔️ No self-medication
✔️ Doctor advice only

🔹 Structure–Activity Relationship (SAR – Easy)

Basic Features:

✔️ Beta-lactam ring → Penicillin
✔️ Side chain → Potency
✔️ Lipophilic group → Absorption

👉 Important for exams ⭐⭐

📝 Exam-Oriented Points

✅ Antibiotics kill bacteria
✅ Not useful in viral disease
✅ Act on cell wall/protein/DNA
✅ Resistance is major problem
✅ Full dose is necessary

👉 5–8 marks ready 💯

🌟 Memory Trick

👉 “ACDC” Trick

A – Amoxicillin
C – Cefixime
D – Doxycycline
C – Ciprofloxacin

Easy to remember