Mechanism of action of Drugs

Mechanism of action of Drugs

Drugs act at the following sites;

Cell surface receptors

They act as the first line of communication between the extracellular environment and the cell’s interior. Cell surface receptors are important for many essential processes in the body, such as cell signaling, cell adhesion, and the regulation of cell growth and differentiation.

lon channels

Ion channels are specialized proteins that form pores in the plasma membrane of cells, allowing the selective passage of ions across the membrane. These channels play a critical role in maintaining the electrical potential of cells, and are essential for many physiological processes, including muscle contraction, neurotransmission, and the regulation of hormone secretion.

Ion channels are selective for specific ions, such as sodium, potassium, calcium, or chloride, and can be gated in different ways. Some ion channels are voltage-gated, meaning they open or close in response to changes in the electrical potential across the membrane. Others are ligand-gated, meaning they open or close in response to the binding of a specific ligand, such as a neurotransmitter or a hormone.

Carrier pumps

Carrier pumps are specialized proteins that are embedded in the plasma membrane of cells, and they play a key role in the active transport of molecules across the membrane. Unlike ion channels, which allow the passive movement of ions across the membrane down their concentration gradient, carrier pumps actively move ions or other molecules against their concentration gradient, requiring energy in the form of ATP.

There are many types of carrier pumps, each with different characteristics and functions. One well-known example is the sodium-potassium pump, which is found in all animal cells and helps to maintain the concentration gradients of sodium and potassium ions across the cell membrane. The pump moves three sodium ions out of the cell for every two potassium ions that it moves into the cell, using the energy of ATP hydrolysis to do so.

e.g. some diuretics act on the Na+/CI- cotransporter in the distal tubules, some diuretics act on the Na+/K+ antiporter in the collecting ducts, some antiulcer/reflux drugs work on the H+/K+ antiporter.


Enzymes are specialized proteins that catalyze, or speed up, biochemical reactions in living organisms. They play a crucial role in many physiological processes, including digestion, metabolism, and DNA replication.

NSAIDs inhibit cyclo-oxygenase which blocks prostaglandin production, ACE inhibitors inhibit angiotensin converting enzyme to decrease blood pressure, HMG-CoA reductase inhibitors inhibit this to reduce lipid concentration.

Nuclear receptors/RNA/DNA

Nuclear receptors are a class of proteins that function as transcription factors, regulating gene expression in response to specific signaling molecules. They are found in the cell nucleus, where they bind to DNA and affect the rate of transcription of target genes.

Intracellular structural proteins

Intracellular structural proteins are a class of proteins that provide mechanical support and shape to cells and cellular structures. They are found within cells and contribute to their overall architecture and function.

One important group of intracellular structural proteins are the cytoskeletal proteins. These include microfilaments, intermediate filaments, and microtubules, which together form a network of fibers that give cells their shape, help them move, and allow them to divide. For example, microfilaments are involved in cell movement and contraction, while microtubules are involved in cell division and transport of organelles within the cell.

After binding to its receptors, the drug produces its action by following mechanisms;


Lipid soluble drugs cross cell membrane and act on intracellular receptors altering the functions of the cells by initiating a series of biochemical & physiological changes that are characteristic of the response to drug.


The drug binds to the receptor which open or close an associated ion channel.


The drug binds to a transmembrane receptor causing activation of a G protein that results in stimulation or inhibition of generation of 2nd messenger (CAMP, GMP,Ca" & IP3).

G protein coupled receptors are membrane bound receptors which are bound to effector system through G protein.

They have 3 subunits

  1. Alpha
  2. beta
  3. gamma.

Based on alpha subunit, they are further classified into;

  • Gs
  • Gi
  • Gq


Stimulates adenylyl cyclase which cause conversion of ATP to CAMP, CAMP activates protein kinase which promote phosphorylation Of proteins (tissue specific enzymes) activation.


  • Sympathetic (beta)
  • Dopamine (D1)
  • Histamine (H2)


Inhibits adenylyl cyclase which cause inhibition of cAMP.


  • Sympathetic (alpha-2)
  • Muscarinic (M2)


Activates Phospholipase C which increase lP3- and which increases Ca++ release from sarcoplasmic reticulum which cause activation of protein kinase C and results in phosphorylation of proteins.


  • Sympathetic (alpha-1)
  • Muscarinic (M1, M3)

Via transmembrane receptor protein:

Some receptors have two parts one present on the surface of the cell and other projecting inside the cell. Drug binds to a site on extracellular domain, conformational change and activation of the cytoplasmic enzyme domain, which may be a protein Tyrosine Kinase, serine kinase or a Guanyl cyclase.


  • Insulin.

Learn more

Mechanism of action of Drugs

What is mechanism of action of Drugs?

What is cell surface receptors?

What is ion channels?

What is carrier pumps?

What is enzymes?

What is nuclear receptors?

What is intracellular structural proteins?

How drug produce its action VIA INTRACELLULAR RECEPTORS?


Classification of alpha subunit

What is Gs?

Examples of Gs

What is Gi?

Examples of Gi

What is Gq?

Examples of Gq

How drug produce its action Via transmembrane receptor protein?

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