📚 Lecture 7: Drug–Receptor Interaction (Simple & Exam-Focused Notes) medicinal pharmaceutical chemistry

✨ Introduction

Drug–Receptor Interaction is one of the most important and scoring topics in Medicinal Pharmaceutical Chemistry.

Understanding this concept helps students easily learn advanced topics like SAR, agonists, antagonists, potency, and efficacy.

👉 If you understand this lecture well, half of medicinal chemistry becomes easy.

🔬 What is a Receptor?

A receptor is a specific biological target (usually a protein) present in the body that interacts with a drug to produce a pharmacological response.

📌 In simple words:

Drug = Key 🔑

Receptor = Lock 🔐

Only the correct drug can activate the correct receptor.

🧪 Types of Drug–Receptor Interactions

1️⃣ Covalent Bonding

• Strongest type of interaction

• Mostly irreversible

• Produces long-lasting effects

📝 Example:

✔ Aspirin binds with COX enzyme

📌 Exam Point:

Covalent bonding drugs are potent but may cause toxicity.

2️⃣ Ionic (Electrostatic) Interaction

• Occurs between oppositely charged ions

• Stronger than hydrogen bonding but weaker than covalent bonding

📝 Example:

✔ Acetylcholine with muscarinic receptors

3️⃣ Hydrogen Bonding

• Common type of interaction

• Moderate strength

• Improves drug selectivity

📝 Example:

✔ Morphine with opioid receptors

4️⃣ Van der Waals Forces

• Weakest interaction

• Acts over short distance

• Requires perfect shape compatibility

📌 Remember:

Better fit = Better drug action

⚖ Factors Affecting Drug–Receptor Binding

🔹 1. Shape of the Drug

The shape of the drug must match the receptor site.

This is explained by the Lock and Key Theory.

🔹 2. Functional Groups

Functional groups like –OH, –NH₂, –COOH increase binding affinity and biological activity.

🔹 3. Stereochemistry

Optical isomers may show different pharmacological actions.

📝 Example:

✔ One isomer may be active while the other may be inactive or toxic.

📊 Importance of Drug–Receptor Interaction

✔ Determines drug potency

✔ Helps in drug design

✔ Predicts side effects

✔ Forms the basis of SAR and QSAR studies

🧠 Exam-Oriented Quick Notes

• Strong binding does not always mean safe drug

• Selective drugs produce fewer side effects

• Weak interactions are usually reversible

❓ Self-Assessment MCQs

Q1. Which is the weakest drug–receptor interaction?

a) Covalent

b) Ionic

c) Hydrogen

d) Van der Waals ✔

Q2. Lock and Key Theory explains:

✔ Drug–receptor interaction

📌 One-Minute Summary

• Receptors are biological targets

• Drug action depends on binding type

• Covalent bonds are strongest

• Van der Waals forces are weakest

• Shape and functional groups play key roles

🚀 Why Pharmacy Students Must Learn This Topic

Drug–receptor interaction is the foundation of medicinal chemistry.

Without this concept, understanding agonists, antagonists, and SAR becomes difficult.

🔔 Coming Next (Lecture 8)

👉 Agonists, Antagonists & Partial Agonists – with real drug examples