Drug action
Encyclopedia
The action of drugs on the human body is called pharmacodynamics
, and what the body does with the drug is called pharmacokinetics
. The drugs that enter the human tend to stimulate certain receptors, ion channels, act on enzymes or transporter proteins. As a result, they cause the human body to react in a specific way.
There are two different types of drugs:
Once the receptors are activated, they either trigger a particular response directly on the body, or they trigger the release of hormones and/or other endogenous drugs in the body to stimulate a particular response.
These interactions are very basic, just like that of other chemical bondings:
) or quaternary ammonium (e.g. acetylcholine
), and the dissociated carboxylic acid group. Similarly, the dissociated carboxylic acid group on the drug can bind with amino groups on the receptor.
This type of bonds are very strong, and varies with
so it could act over large distances.
Cation-π interactions can also be classified as ionic bonding. This occurs when a cation, e.g. acetylcholine, interacts with the negative π bonds on an aromatic group of the receptor.
Ion-dipole and dipole-dipole bonds have similar interactions, but are more complicated and are weaker than ionic bonds.
Only act over short distances, and are dependent on the correct alignment between functional groups.
Of course, drugs not only just act on receptors. They also act on ion channels, enzymes and cell transporter proteins.
Receptors are located on all cells in the body. The same receptor can be located on different organ, and even on different types of tissues.
There are also different subtypes of receptor which ellicit different effects in response to the same agonist, e.g.
There are two types of Histamine receptor; H1 and H2, activation of H1 subtype causes contraction of smooth muscle whereas activation of the H2 receptors stimulates gastric secretion.
It is this phenomenon that gives rise to drug specificity.
An example is the endogenous
drug acetylcholine (ACh). ACh is used by the parasympathetic nervous system
to activate muscarinic receptors and by the neuromuscular system to activate nicotinic receptors. However, the compounds muscarine and nicotine can each preferentially interact one of the two receptor types, allowing them to activate only one of the two systems where ACh itself would activate both.
Pharmacodynamics
Pharmacodynamics is the study of the biochemical and physiological effects of drugs on the body or on microorganisms or parasites within or on the body and the mechanisms of drug action and the relationship between drug concentration and effect...
, and what the body does with the drug is called pharmacokinetics
Pharmacokinetics
Pharmacokinetics, sometimes abbreviated as PK, is a branch of pharmacology dedicated to the determination of the fate of substances administered externally to a living organism...
. The drugs that enter the human tend to stimulate certain receptors, ion channels, act on enzymes or transporter proteins. As a result, they cause the human body to react in a specific way.
There are two different types of drugs:
- AgonistAgonistAn agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance...
s - they stimulate and activate the receptors - AntagonistReceptor antagonistA receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses...
s - they stop the agonists from stimulating the receptors
Once the receptors are activated, they either trigger a particular response directly on the body, or they trigger the release of hormones and/or other endogenous drugs in the body to stimulate a particular response.
Short Note on Receptors
The drugs interact at receptors by bonding at specific binding sites. Most receptors are made up of proteins, the drugs can therefore interact with the amino acids to change the conformation of the receptor proteins.These interactions are very basic, just like that of other chemical bondings:
Ionic Bonds
Mainly occur through attractions between opposite charges. For example, between protonated amino (on salbutamolSalbutamol
Salbutamol or albuterol is a short-acting β2-adrenergic receptor agonist used for the relief of bronchospasm in conditions such as asthma and chronic obstructive pulmonary disease. It is marketed as Ventolin among other brand names....
) or quaternary ammonium (e.g. acetylcholine
Acetylcholine
The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
), and the dissociated carboxylic acid group. Similarly, the dissociated carboxylic acid group on the drug can bind with amino groups on the receptor.
This type of bonds are very strong, and varies with
so it could act over large distances.Cation-π interactions can also be classified as ionic bonding. This occurs when a cation, e.g. acetylcholine, interacts with the negative π bonds on an aromatic group of the receptor.
Ion-dipole and dipole-dipole bonds have similar interactions, but are more complicated and are weaker than ionic bonds.
Hydrogen bonds
Refer to the attraction between Hydrogen atoms and polar functional groups e.g. The Hydroxyl (-OH) group.Only act over short distances, and are dependent on the correct alignment between functional groups.
Of course, drugs not only just act on receptors. They also act on ion channels, enzymes and cell transporter proteins.
Receptors are located on all cells in the body. The same receptor can be located on different organ, and even on different types of tissues.
There are also different subtypes of receptor which ellicit different effects in response to the same agonist, e.g.
There are two types of Histamine receptor; H1 and H2, activation of H1 subtype causes contraction of smooth muscle whereas activation of the H2 receptors stimulates gastric secretion.
It is this phenomenon that gives rise to drug specificity.
How shape of Drug Molecules affect drug action
When talking about the shape of molecules, the scientists are mainly concerned with the 3D conformation of drug molecules. There are many isomers of a particular drug, and each one will have their own effects. This effect is not only what the drug activates, but also changes the potency of each drug.Potency
Potency is a measure of how much a drug is required in order to produce a particular effect. Therefore, only a small dosage of a high potency drug is required to induce a large response. The other terms used to measure the ability of a drug to trigger a response are:- Intrinsic Activity which defines:
- Agonists as having Intrinsic Activity = 1
- Antagonists as having Intrinsic Activity = 0
- and, Partial Agonist as having Intrinsic Activity between 0 and 1
- Intrinsic Efficacy also measures the different activated state of receptors, and the ability for a drug to cause maximum response without having to bind to all the receptors.
The specificity of drugs
Drug companies invest significant effort in designing drugs that interact specifically with particular receptors , since non-specific drugs can cause more side effects.An example is the endogenous
Endogenous
Endogenous substances are those that originate from within an organism, tissue, or cell. Endogenous retroviruses are caused by ancient infections of germ cells in humans, mammals and other vertebrates...
drug acetylcholine (ACh). ACh is used by the parasympathetic nervous system
Parasympathetic nervous system
The parasympathetic nervous system is one of the two main divisions of the autonomic nervous system . The ANS is responsible for regulation of internal organs and glands, which occurs unconsciously...
to activate muscarinic receptors and by the neuromuscular system to activate nicotinic receptors. However, the compounds muscarine and nicotine can each preferentially interact one of the two receptor types, allowing them to activate only one of the two systems where ACh itself would activate both.