Pharmacodynamics is the study of how drugs produce their effects on the body. Drugs act by binding to receptors, which are molecules that drugs specifically bind to, producing a physiological effect. There are different types of receptors that drugs can bind to, including G protein-coupled receptors (GPCRs), which have 7 transmembrane domains and are the largest family of receptors, steroid hormone receptors which are intracellular proteins, and neurotransmitter transporter proteins which have 12 transmembrane domains. When a drug binds to a receptor, it forms bonds such as covalent, hydrogen, ionic, or hydrophobic bonds, and this binding exhibits stereospecificity where usually only one enantiomer will bind to the receptor.

1. Pharmacodynamics
Dr. Karun Kumar
JR –II
Dept. of Pharmacology

2. Definition
• Study of the detailed mechanism of action by which
drugs produce their pharmacologic effect
• Provides a scientific basis for the selection & use of
drugs

3. Nature of drug receptors
• Receptor [Recipere  to receive, accept] 1. a
molecular structure within a cell or on the cell
surface and characterized by (1) selective binding of
a specific substance and (2) a specific physiologic
effect that accompanies the binding, e.g.,
membrane receptors for peptide hormones,
neurotransmitters, antigens, complement
fragments, and immunoglobulins, and nuclear
receptors for steroid hormones. 2. a sensory nerve
terminal that responds to stimuli of various kinds;
classified in various ways including by the type of
stimulus (see chemoreceptor, mechanoreceptor,
photoreceptor, and thermoreceptor) and by the
location in the body (see exteroceptor,
interoceptor, and proprioceptor).

4. • Ligand (ligare  to tie or bind)  a molecule that
binds to another molecule, used especially to refer
to a small molecule that binds specifically to a
larger molecule, e.g., an antigen binding to an
antibody, a hormone or neurotransmitter binding
to a receptor, or a substrate or allosteric effector
binding to an enzyme. 2. a molecule that donates
or accepts a pair of electrons to form a coordinate
covalent bond with the central metal atom of a
coordination complex.

5. Types of drug receptors
• GPCRs  Largest family of receptors
• GPCRs  7 transmembrane domains
• Neurotransmitter transporter proteins  12
transmembrane domain proteins (SSRI/SNRI target
them)
• Steroid hormone receptors  Intracellular proteins
that translocate to the nucleus

8. Steroid hormones diffuse through cell membrane
↓
Bind to steroid receptors in cytoplasm
↓
Dimerized steroid hormone-receptor complex is
translocated to the nucleus
↓
Binds to specific sequences on the DNA of a gene
↓
↑ transcription of gene (↑ mRNA)
↓
↑ translation of proteins

9. Drug receptor interactions
• Bonds formed between receptor and drug
1. Strong bonds  Covalent bonds
a) Anti-neoplastic drugs binding to DNA
b) Irreversible anti-chEs (Ops)
2. Weak bonds
a) Hydrogen bonds
b) Ionic bonds
c) Hydrophobic (van der Waals) bonds

10. • Binding exhibits stereospecificity (only 1 of the
enantiomers will form a 3 point attachment with
the receptor)
• Affinity 
• Tendency/ability of a drug to combine with a receptor
• Measure of the strength of the drug-receptor complex

11. Drug receptors (HE MAN)
• Hormone receptors
1. Insulin receptors  Insulin
2. Opioid receptors  Morphine & naltrexone
3. Steroid receptors  Cortisol & Tamoxifen
• Enzyme receptors (ABCDE,X)
1. A  nA,K+ ATPase  Digoxin
2. A  Amine oxidase (MAO)  Phenlzine,
Tranylcypromine, Moclobemide, Clorgyline

12. 1. C  Carbonic anhydrase  Acetazolamide
2. C  chE  Donepezil & Physostigmine
3. C  COX  Aspirin & Celecoxib
4. D  DNA polymerase  Acyclovir & Zidovudine
5. D  DNA topoisomerase  Ciprofloxacin
6. H  HIV protease  Indinavir
7. X  Xanthine oxidase  Allopurinol
• Membrane transport proteins
1. Ligand GIC  Diazepam & Ondansetron
2. Voltage GIC  Lidocaine & Verapamil
3. Ion transporter  Loop & thiazide diuretics
4. Neurotransmitter transporter  Fluoxetine,
Cocaine

13. • Among others 
1. Membrane lipids  Alcohol & Amphotericin B
2. Nucleic acids  Anti-cancer drugs
• Neurotransmitter receptors
1. Adrenoceptors  E & Ppnl
2. Histamine recep.  Cimetidine, Diphenhydramine
3. 5-HT rec.  LSD & Sumatriptan
4. Muscarinic receptors  Atropine, Bethanechol