Which of the following is the most common type of receptor mechanism by which drugs produce their therapeutic effects?

Question

Accepted Answer

C. G-protein coupled receptors. ## Receptor Types and Prevalence

**Key Point:** G-protein coupled receptors (GPCRs) account for approximately 30–40% of all drug targets and are the most frequently exploited receptor class in clinical pharmacology.

### Classification of Receptor Mechanisms

| Receptor Type | Mechanism | Prevalence | Clinical Examples |
|---|---|---|---|
| G-protein coupled receptors | Heterotrimeric G-protein activation | ~30–40% of drugs | β-blockers, ACE inhibitors, dopamine agonists |
| Ligand-gated ion channels | Direct ion channel opening | ~5–10% of drugs | Benzodiazepines, succinylcholine |
| Tyrosine kinase receptors | Autophosphorylation & cascade | ~5–10% of drugs | Trastuzumab, erlotinib |
| Nuclear receptors | Gene transcription regulation | ~13% of drugs | Corticosteroids, thyroid hormone |

### Why GPCRs Dominate

1. **Structural diversity** — GPCRs comprise the largest protein family (>800 members in humans)
2. **Versatile signalling** — activate multiple downstream pathways (G~s~, G~i~, G~q~, G~12~)
3. **Tissue distribution** — expressed on virtually all cell types
4. **Druggability** — small molecules easily cross cell membranes to access the receptor

**High-Yield:** Approximately **30–40%** of FDA-approved drugs target GPCRs. This is the single most exploited receptor class in therapeutics.

**Clinical Pearl:** Common GPCR-targeting drugs include:
- Cardiovascular: β-blockers (propranolol), α~2~-agonists (clonidine)
- CNS: dopamine agonists (bromocriptine), serotonin antagonists (ondansetron)
- Endocrine: GnRH agonists (leuprolide)

### Why Other Receptors Are Less Common

- **Ligand-gated ion channels** — limited tissue distribution, slower onset, mainly for acute CNS/neuromuscular effects
- **Tyrosine kinase receptors** — mostly growth factor signalling; fewer endogenous ligands; mainly targeted in oncology
- **Nuclear receptors** — slower onset (gene transcription); limited to lipophilic drugs; ~13% of drug targets

Answer

A. Ligand-gated ion channels

Answer

B. Tyrosine kinase receptors

Answer

D. Nuclear receptors

Which of the following is the most common type of receptor mechanism by which drugs produce their therapeutic effects?

Explanation

Receptor Types and Prevalence

Classification of Receptor Mechanisms

Why GPCRs Dominate

Why Other Receptors Are Less Common

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Receptor Type	Mechanism	Prevalence	Clinical Examples
G-protein coupled receptors	Heterotrimeric G-protein activation	~30–40% of drugs	β-blockers, ACE inhibitors, dopamine agonists
Ligand-gated ion channels	Direct ion channel opening	~5–10% of drugs	Benzodiazepines, succinylcholine
Tyrosine kinase receptors	Autophosphorylation & cascade	~5–10% of drugs	Trastuzumab, erlotinib
Nuclear receptors	Gene transcription regulation	~13% of drugs	Corticosteroids, thyroid hormone