Pharmacodynamics Mechanism of Drug Action, Receptors, Therapeutic Index, Potency, Efficacy, Drug Interactions

💊 Pharmacodynamics Mechanism of Drug Action, Receptors, Therapeutic Index, Potency, Efficacy, Drug Interactions — 

━━━━━━━━━━━━━━━━━━━

🌟 Introduction to Pharmacodynamics

🔹 Pharmacodynamics = “Drug body पर क्या effect डालती है”

🔹 Pharmacodynamics mainly बताती है:

✔ Drug कहाँ act करती है

✔ Drug कैसे effect produce करती है

✔ Drug effect कितना strong होगा

✔ Drug toxic कब होगी

✔ Drug response क्यों बदलता है

━━━━━━━━━━━━━━━━━━━

🧠 Basic Concept of Drug Action

⚡ Fundamental Principle

Drug effect तभी आता है जब:

✔ Drug target तक पहुँचे

✔ Target से bind करे

✔ Cellular change produce करे

━━━━━━━━━━━━━━━━━━━

🎯 Drug Targets in Body

Drug mainly इन targets पर act करती है:

✔ Receptors

✔ Enzymes

✔ Ion channels

✔ Transporters

✔ Nucleic acids

✔ Structural proteins

━━━━━━━━━━━━━━━━━━━

📌 Why Drug Action Occurs?

Drug effect इसलिए आता है क्योंकि:

➡ Drug की chemical structure body molecule जैसी होती है

इसलिए drug:

✔ Receptor को activate कर सकती है

✔ Enzyme block कर सकती है

✔ Ion movement रोक सकती है

━━━━━━━━━━━━━━━━━━━

🌟 TYPES OF MECHANISM OF DRUG ACTION

① Non-Receptor Mediated Drug Action

② Receptor Mediated Drug Action

━━━━━━━━━━━━━━━━━━━

💥 ① NON-RECEPTOR MEDIATED DRUG ACTION

📌 Meaning

Drug बिना receptor bind किए directly action करती है।

━━━━━━━━━━━━━━━━━━━

🧪 A. Drug Action by Physical Action

📌 Mechanism

Drug अपनी physical property से action करती है।

━━━━━━━━━━━━━━━━━━━

💊 Mannitol

⚙ Mechanism

✔ Osmotic diuretic

Mannitol kidney tubule में water को hold करता है।

➡ Water reabsorption नहीं होती

➡ Urine output increase

❓ ऐसा क्यों होता है?

✔ Mannitol highly osmotic substance है

✔ Tubule membrane से absorb नहीं होती

इसलिए:

➡ Water बाहर निकलता रहता है

💊 Uses

✔ Cerebral edema

✔ Increased intracranial pressure

━━━━━━━━━━━━━━━━━━━

💊 Activated Charcoal

⚙ Mechanism

Poisons को surface पर adsorb करता है।

➡ Poison absorption कम

❓ ऐसा क्यों होता है?

✔ Activated charcoal की surface area बहुत ज्यादा होती है

इसलिए:

➡ Toxin particles bind हो जाते हैं

━━━━━━━━━━━━━━━━━━━

💊 Sucralfate

⚙ Mechanism

Ulcer surface पर protective coating बनाता है।

❓ ऐसा क्यों होता है?

✔ Acidic medium में polymerize होकर sticky gel बनाता है

➡ Ulcer protection

━━━━━━━━━━━━━━━━━━━

🧪 B. Drug Action by Chemical Action

📌 Mechanism

Drug directly chemical reaction करती है।

━━━━━━━━━━━━━━━━━━━

💊 Antacids

Examples

✔ Magnesium hydroxide

✔ Aluminum hydroxide

✔ Sodium bicarbonate

⚙ Mechanism

Gastric HCl neutralize

Mg(OH)2 + 2HCl → MgCl2 + 2H2O

➡ Acidity decrease

❓ ऐसा क्यों होता है?

✔ H⁺ ion acid का main component है

Antacid:

➡ H⁺ neutralize कर देता है

इसलिए:

✔ Gastric irritation कम

━━━━━━━━━━━━━━━━━━━

💊 Chelating Agents

Examples

✔ EDTA

✔ Dimercaprol

✔ Penicillamine

✔ Deferoxamine

⚙ Mechanism

Metal ion से stable complex बनाते हैं।

❓ ऐसा क्यों होता है?

Heavy metals proteins से bind करके toxicity करते हैं।

Chelator:

➡ Metal को पकड़ लेता है

➡ Urine से excrete करा देता है

💊 Important Examples

✔ EDTA → Lead poisoning

✔ Deferoxamine → Iron poisoning

✔ Penicillamine → Copper poisoning (Wilson disease)

━━━━━━━━━━━━━━━━━━━

💊 Protamine Sulfate

⚙ Mechanism

Negatively charged heparin को neutralize करता है।

❓ ऐसा क्यों होता है?

✔ Protamine positively charged होता है

➡ Ionic complex formation

━━━━━━━━━━━━━━━━━━━

🧬 C. Drug Action Through Enzymes

Drug:

✔ Enzyme inhibit

✔ Enzyme activate

✔ False substrate बन सकती है

━━━━━━━━━━━━━━━━━━━

💊 Aspirin

⚙ Mechanism

Cyclooxygenase (COX) irreversibly inhibit

➡ ↓ Prostaglandin synthesis

❓ ऐसा क्यों होता है?

Prostaglandins:

✔ Pain

✔ Fever

✔ Inflammation

produce करते हैं।

जब COX inhibit:

➡ Prostaglandin कम

इसलिए:

✔ Pain कम

✔ Fever कम

✔ Inflammation कम

━━━━━━━━━━━━━━━━━━━

💊 Statins

Examples

✔ Atorvastatin

✔ Rosuvastatin

⚙ Mechanism

HMG-CoA reductase inhibit

➡ Cholesterol synthesis decrease

❓ ऐसा क्यों होता है?

Liver cholesterol कम बनने पर:

➡ LDL receptors increase

➡ Blood LDL decrease

━━━━━━━━━━━━━━━━━━━

💊 Sildenafil

⚙ Mechanism

PDE-5 inhibit

➡ cGMP increase

➡ Vasodilation

❓ ऐसा क्यों होता है?

✔ cGMP smooth muscle relaxation करता है

✔ PDE-5 normally cGMP destroy करता है

जब PDE-5 inhibit:

➡ cGMP ज्यादा

➡ Penile blood flow increase

━━━━━━━━━━━━━━━━━━━

💊 Acetazolamide

⚙ Mechanism

Carbonic anhydrase inhibit

❓ ऐसा क्यों होता है?

✔ Bicarbonate reabsorption decrease

➡ Diuresis increase

━━━━━━━━━━━━━━━━━━━

⚡ D. Drug Action Through Ion Channels

📌 Mechanism

Drug ion flow बदलती है।

━━━━━━━━━━━━━━━━━━━

💊 Local Anesthetics

Examples

✔ Lidocaine

✔ Bupivacaine

✔ Procaine

⚙ Mechanism

Voltage-gated Na⁺ channels block

➡ Nerve impulse stop

❓ ऐसा क्यों होता है?

Na⁺ entry जरूरी है:

➡ Action potential generation के लिए

Na⁺ block:

➡ Depolarization नहीं

➡ Pain signal नहीं

━━━━━━━━━━━━━━━━━━━

💊 Calcium Channel Blockers

Examples

✔ Verapamil

✔ Diltiazem

✔ Amlodipine

⚙ Mechanism

L-type calcium channels block

➡ Smooth muscle relaxation

❓ ऐसा क्यों होता है?

Calcium:

✔ Muscle contraction के लिए जरूरी

Calcium entry कम:

➡ Contraction कम

➡ Vasodilation

➡ BP decrease

━━━━━━━━━━━━━━━━━━━

💊 Sulfonylureas

Examples

✔ Glibenclamide

✔ Glimepiride

⚙ Mechanism

ATP-sensitive K⁺ channels close

➡ Insulin release increase

❓ ऐसा क्यों होता है?

K⁺ channel close:

➡ Cell depolarization

➡ Ca²⁺ influx

➡ Insulin secretion

━━━━━━━━━━━━━━━━━━━

🚚 E. Drug Action Through Transporters

💊 SSRIs

Examples

✔ Fluoxetine

✔ Sertraline

✔ Escitalopram

⚙ Mechanism

Serotonin transporter inhibit

➡ Serotonin synapse में increase

❓ ऐसा क्यों होता है?

Low serotonin:

➡ Depression से associated

Serotonin increase:

➡ Mood improve

━━━━━━━━━━━━━━━━━━━

💊 Digoxin

⚙ Mechanism

Na⁺/K⁺ ATPase inhibit

❓ ऐसा क्यों होता है?

Na⁺ increase:

➡ Na⁺/Ca²⁺ exchange reduce

➡ Intracellular calcium increase

➡ Cardiac contraction strong

━━━━━━━━━━━━━━━━━━━

💊 Cocaine

⚙ Mechanism

Dopamine reuptake inhibit

❓ ऐसा क्यों होता है?

Dopamine accumulation:

➡ Euphoria

➡ Addiction potential high

━━━━━━━━━━━━━━━━━━━

🛡 F. Drug Action Through Antibody Production

💉 Vaccines

Examples

✔ BCG

✔ Rabies vaccine

✔ Hepatitis B vaccine

✔ COVID vaccines

⚙ Mechanism

Immune system activate

➡ Antibody production

➡ Memory cell formation

❓ ऐसा क्यों होता है?

Body antigen को foreign समझती है।

➡ B-cells activated

➡ Plasma cells antibodies बनाते हैं

━━━━━━━━━━━━━━━━━━━

🌟 RECEPTOR MEDIATED DRUG ACTION

🧠 Receptor Definition

Receptor = Specialized protein molecule

जो:

✔ Drug recognize करता है

✔ Signal produce करता है

━━━━━━━━━━━━━━━━━━━

📌 Why Receptors Important?

✔ Most drugs receptors पर act करती हैं

━━━━━━━━━━━━━━━━━━━

🎯 Characteristics of Receptors

✔ Specificity

✔ Selectivity

✔ Saturability

✔ Reversibility

✔ Affinity

━━━━━━━━━━━━━━━━━━━

❓ Receptor Saturation क्यों होता है?

✔ Receptors limited number में होते हैं

जब सारे receptors occupied:

➡ Maximum effect achieved

━━━━━━━━━━━━━━━━━━━

🧪 Drug-Receptor Interaction

🔹 Agonist

Receptor activate

Examples

✔ Adrenaline

✔ Salbutamol

━━━━━━━━━━━━━━━━━━━

🔹 Antagonist

Receptor block

Examples

✔ Propranolol

✔ Atropine

━━━━━━━━━━━━━━━━━━━

🔹 Partial Agonist

Weak activation

Examples

✔ Buprenorphine

✔ Pindolol

━━━━━━━━━━━━━━━━━━━

🔹 Inverse Agonist

Opposite effect produce

Example

✔ Some antihistamines

━━━━━━━━━━━━━━━━━━━

🧬 TYPES OF RECEPTORS

① Ligand-Gated Ion Channel Receptors

📌 Fastest receptors

⏰ Response: Milliseconds

⚙ Mechanism

Drug binds

⬇

Channel opens/closes

⬇

Ion flow changes

⬇

Membrane potential changes

━━━━━━━━━━━━━━━━━━━

💊 Nicotinic Receptor

Ligand

✔ Acetylcholine

Channel

✔ Na⁺

❓ ऐसा क्यों होता है?

Na⁺ influx:

➡ Depolarization

➡ Muscle contraction

━━━━━━━━━━━━━━━━━━━

💊 GABA-A Receptor

Channel

✔ Cl⁻

Drugs

✔ Diazepam

✔ Lorazepam

✔ Alprazolam

❓ ऐसा क्यों होता है?

Cl⁻ influx:

➡ Hyperpolarization

➡ Neuron firing decrease

➡ Sedation

━━━━━━━━━━━━━━━━━━━

💊 NMDA Receptor

Ligand

✔ Glutamate

❓ Important

Overactivation:

➡ Excitotoxicity

➡ Epilepsy

➡ Neurodegeneration

━━━━━━━━━━━━━━━━━━━

② G-Protein Coupled Receptors (GPCR)

📌 Most important receptor family

लगभग 50% drugs GPCR पर act करती हैं।

⚙ Mechanism

Drug binds receptor

⬇

G-protein activated

⬇

Second messenger formed

⬇

Cell response

━━━━━━━━━━━━━━━━━━━

🧪 Important Second Messengers

✔ cAMP

✔ IP3

✔ DAG

✔ Calcium

━━━━━━━━━━━━━━━━━━━

🔬 Types of G Proteins

🔹 Gs

➡ Adenylyl cyclase activate

➡ ↑ cAMP

Examples

✔ β1 receptor

✔ β2 receptor

❓ Effect क्यों?

cAMP:

➡ Protein kinase activate

➡ Cellular stimulation

━━━━━━━━━━━━━━━━━━━

🔹 Gi

➡ ↓ cAMP

Examples

✔ α2 receptor

✔ M2 receptor

━━━━━━━━━━━━━━━━━━━

🔹 Gq

➡ ↑ IP3 + DAG

Examples

✔ α1 receptor

✔ H1 receptor

❓ Effect क्यों?

IP3:

➡ Ca²⁺ release

➡ Muscle contraction

━━━━━━━━━━━━━━━━━━━

💊 Important GPCR Examples

✔ Salbutamol → β2 → Bronchodilation

✔ Adrenaline → α + β → Sympathetic stimulation

✔ Dopamine → D receptor → CNS effect

✔ Histamine → H1 → Allergy

✔ Morphine → Opioid receptor → Analgesia

━━━━━━━━━━━━━━━━━━━

③ Enzyme-Linked Receptors

📌 Also called Catalytic receptors

⚙ Mechanism

Drug binds

⬇

Tyrosine kinase activation

⬇

Protein phosphorylation

⬇

Gene activation

━━━━━━━━━━━━━━━━━━━

💊 Insulin Receptor

❓ ऐसा क्यों होता है?

Phosphorylation:

➡ GLUT4 translocation

➡ Glucose uptake increase

━━━━━━━━━━━━━━━━━━━

💊 Growth Hormone Receptor

➡ JAK-STAT pathway activation

━━━━━━━━━━━━━━━━━━━

💊 Erythropoietin Receptor

➡ RBC production increase

━━━━━━━━━━━━━━━━━━━

④ Nuclear Receptors

📌 Intracellular receptors

⚙ Mechanism

Lipid soluble drug enters cell

⬇

Binds receptor

⬇

Complex enters nucleus

⬇

Gene transcription altered

⬇

Protein synthesis changes

━━━━━━━━━━━━━━━━━━━

❓ Slow action क्यों?

✔ New proteins synthesize होने में time लगता है

━━━━━━━━━━━━━━━━━━━

💊 Important Examples

✔ Corticosteroids

✔ Thyroxine

✔ Vitamin D

✔ Estrogen

✔ Progesterone

━━━━━━━━━━━━━━━━━━━

💊 Steroid Mechanism

Prednisolone:

➡ Lipocortin synthesis increase

➡ Phospholipase A2 inhibition

➡ Inflammation decrease

━━━━━━━━━━━━━━━━━━━

📈 Dose Response Curve

📌 Importance

बताती है:

✔ Drug potency

✔ Drug efficacy

✔ Safety

━━━━━━━━━━━━━━━━━━━

💥 Drug Potency

📌 Definition

Effect produce करने के लिए required dose

❓ High potency क्यों?

✔ Receptor affinity high

➡ कम dose में effect

💊 Examples

✔ Fentanyl > Morphine

✔ Clonazepam > Diazepam

━━━━━━━━━━━━━━━━━━━

🔥 Drug Efficacy

📌 Definition

Maximum effect produced

❓ High efficacy क्यों?

✔ Drug receptor activation capacity ज्यादा

💊 Example

Morphine:

✔ Severe pain relief

Aspirin:

✔ Mild pain relief

इसलिए:

➡ Morphine efficacy ज्यादा

━━━━━━━━━━━━━━━━━━━

🧲 Affinity

📌 Definition

Drug की receptor से bind होने की ability

❓ High affinity क्यों important?

✔ Strong binding

✔ Lower dose required

━━━━━━━━━━━━━━━━━━━

📌 Intrinsic Activity

Drug receptor activate कितनी अच्छी तरह करती है

━━━━━━━━━━━━━━━━━━━

🪟 Therapeutic Window

📌 Definition

Effective concentration और toxic concentration के बीच range

❓ Narrow therapeutic window dangerous क्यों?

✔ Small dose increase → toxicity

━━━━━━━━━━━━━━━━━━━

💊 Important Narrow TI Drugs

✔ Digoxin

✔ Lithium

✔ Warfarin

✔ Phenytoin

✔ Theophylline

━━━━━━━━━━━━━━━━━━━

📊 Therapeutic Index

TI = TD50 / ED50

❓ High TI safer क्यों?

✔ Toxic dose बहुत ज्यादा होती है compared to effective dose

━━━━━━━━━━━━━━━━━━━

🤝 Combined Effect of Drugs

① Additive Effect

📌 1 + 1 = 2

Examples

✔ Paracetamol + Aspirin

━━━━━━━━━━━━━━━━━━━

② Synergism

📌 1 + 1 > 2

Important Examples

✔ Sulfamethoxazole + Trimethoprim

✔ Levodopa + Carbidopa

✔ Amoxicillin + Clavulanic acid

❓ Synergism क्यों होता है?

✔ Drugs different pathways block करती हैं

━━━━━━━━━━━━━━━━━━━

💊 TMP-SMX Mechanism

TMP:

➡ Dihydrofolate reductase inhibit

SMX:

➡ Dihydropteroate synthase inhibit

Sequential blockade:

➡ Strong antibacterial effect

━━━━━━━━━━━━━━━━━━━

③ Antagonism

📌 One drug दूसरे का effect कम करती है

━━━━━━━━━━━━━━━━━━━

🧪 Types of Antagonism

🔹 Chemical Antagonism

Example

✔ Protamine vs Heparin

━━━━━━━━━━━━━━━━━━━

🔹 Physiological Antagonism

Example

✔ Insulin vs Glucagon

━━━━━━━━━━━━━━━━━━━

🔹 Pharmacological Antagonism

✔ Competitive

Example

✔ Atropine vs Acetylcholine

❓ Competitive क्यों?

✔ Same receptor competition

━━━━━━━━━━━━━━━━━━━

✔ Noncompetitive

Example

✔ Phenoxybenzamine

━━━━━━━━━━━━━━━━━━━

🔹 Pharmacokinetic Antagonism

Example

✔ Rifampicin + Oral contraceptive

❓ ऐसा क्यों?

Rifampicin:

➡ Liver enzymes induce

➡ OCP metabolism increase

➡ OCP failure

━━━━━━━━━━━━━━━━━━━

⚡ Tachyphylaxis

📌 Rapid tolerance

Examples

✔ Ephedrine

✔ Nitroglycerin

❓ क्यों होता है?

✔ Neurotransmitter depletion

✔ Receptor exhaustion

━━━━━━━━━━━━━━━━━━━

🔥 Drug Tolerance

📌 Gradual decrease in response

Examples

✔ Morphine

✔ Alcohol

✔ Benzodiazepines

❓ क्यों होता है?

✔ Receptor downregulation

✔ Enzyme induction

━━━━━━━━━━━━━━━━━━━

🚨 Receptor Upregulation

📌 Receptors increase

Example

✔ Long-term β blocker withdrawal

━━━━━━━━━━━━━━━━━━━

🚨 Receptor Downregulation

📌 Receptors decrease

Example

✔ Chronic β agonist use

━━━━━━━━━━━━━━━━━━━

🧠 Spare Receptors

📌 Meaning

Maximum effect before all receptors occupied

❓ क्यों important?

✔ Small amount drug भी maximum response दे सकती है

━━━━━━━━━━━━━━━━━━━

📚 Important Exam Comparison

💥 Potency vs Efficacy

✔ Potency = Dose needed

✔ Efficacy = Maximum effect

✔ Potency depends on affinity

✔ Efficacy depends on intrinsic activity

✔ Clinical importance of efficacy > potency

Examples

✔ Fentanyl = More potent

✔ Morphine = More efficacious

━━━━━━━━━━━━━━━━━━━

📚 Receptor Quick Revision

✔ Ligand gated receptor → Ion flow → Milliseconds → GABA-A

✔ GPCR → Second messenger → Seconds → β receptors

✔ Enzyme linked receptor → Phosphorylation → Minutes → Insulin

✔ Nuclear receptor → Gene transcription → Hours → Steroids

━━━━━━━━━━━━━━━━━━━

🏁 Conclusion

🔹 Pharmacodynamics explains:

✔ Drug कैसे काम करती है

✔ Receptor activation कैसे होता है

✔ Drug effect क्यों आता है

✔ Toxicity क्यों होती है

✔ Drug interactions कैसे होते हैं

🔹 Most important exam topics:

✔ GPCR

✔ Therapeutic index

✔ Potency vs efficacy

✔ Nuclear receptors

✔ Synergism and antagonism

✔ Receptor mechanisms

🔹 Pharmacodynamics understanding helps:

✔ Rational therapy

✔ Safe prescribing

✔ Toxicity prevention

✔ Better patient outcome