Drug Mechanism of Action | 9 Types and Their Effects

There are many medicines in the world and of them drugs of modern medicine are widely used.

They are highly prescribed compared to alternative medicine. This is because of the advantage of faster relief from the symptoms.

But on negative side some of these drugs have severe side effects limiting prolonged and wide spread use.

These drugs are chemically diverse and even their mode of action is quite different.

For health conscious people it will be quite interesting to study the mechanism of action of drugs we regularly use.

Drug Mechanism of Action

Based on the mode of action, drugs can be categorized as following types

A. Physically acting drugs: These are the drugs which do not react in the body with fluids or other biochemical substances. But they exert their effect just by being physically present at the location.

Ex; 1) Bisacodyl: A drug of choic prescribed for peptic ulcer. This drug physically binds to the portion of ulcer surface in the stomach. There by prevents further attack of gastric acid on to it. Due to lack of further exposure to acid, the ulcer portion of stomach gets healed faster.Drug Mechanism of Action

2) Charcoal; The activated charcoal is used as an antidote to poisons. Scientifically it is called activated as it in powered form and made to readily adsorb matter.

This charcoal neither gets digested not absorbed in the gut. But it has a special tendency to adsorb substances. In case of poison it physically adsorbs poison in the gut and prevent it from being absorbed into blood. Thus it minimizes poison effect.

Thus the above drugs act by being physically present in the location of problem.

B) Drugs acting by chemical reactions: Here drugs act to produce relief by reacting chemically with some or other body fluids.

Ex; 1.When you have acidity in the stomach, you are advised to drink a solution of sodium bicarbonate. Acidity is caused due to release of HCL in the stomach. HCl as we know is a strong acid. So when sodium bicarbonate a base (alkali) is consumed, it reacts with excess acid and neutralizes it to salt. Thus acidic pain is reduced. Other examples in this case are antacids tablets of aluminum hydroxide, magnesium hydroxide etc.

2. When there are kidney stones, physician advice consumption of lot of citrus fruit juices like lemon, orange etc. These juices are acidic in nature. The kidney stones are mostly made of Calcium salts. Calcium is an alkaline substance. So when acidic juice is taken in large quantities, it reacts with calcium (a alkali element) in the kidney stone and dissolves it. Also any chances of further growth of the stone is inhibited by this citric juice.

C) Drugs acting by physiological modifications: Here drugs produce some physiological effect and relieve from symptoms of disease.  This can be of three types.

1. Those producing opposite effect: In case of severe diarrhea (loose motions without pain), the intestinal motility (movement) is very high. The movement is such that any food material in intestine is pushed downwards i.e. towards rectum for faster defecation. In this condition, doctors prescribes Morphine related drugs ( Ex; Loperamide).

Morphine has a special property in the gut. When taken orally, it reverses intestinal movement and instead of contents traveling downward they travel up towards stomach and mouth. (Hence morphine consumption orally has symptoms like vomiting even undigested waste from mouth). For sever diarrhea, weaker derivatives of morphine are given to slow down the intestinal run downward and stop loose motion.

2. Those producing related effects: Here the body physiology is modified temporarily to bring down any adverse disorder.

Ex; In patients with high blood pressure, diuretics are given. Blood pressure is one which exerts pressure on the blood vessels. When blood volume increases, the pressure also increases. So the drugs are given to enhance urine out put. Due to this blood volume decreases there by reducing the blood pressure.

3. Those producing unrelated effect: Here the symptoms are mitigated by producing unrelated changes in physiology.

Ex of such drugs are Zandu balm, iodex and other pain relieving balms. These gels show this unrelated mechanism of drug action. The volatile or essential oils present in these drugs produce irritation and redness in the region of application. Hence they are called as rubefacients. They are also called counter irritants.

When there is pain, if the balm or gel is applied at the point of pain, they produce irritable and burning sensation at the place of application. This leads to high blood circulation at the point, causing redness and swelling of the region.  Hence the actual pain is nullified or forgot due to new irritating or burning feeling.

D) Drugs acting through receptors: This is a common method by which most drugs used in important disorders function. Receptors are situated at cellular surface or rarely inside. When drugs binds to them, they bring changes in the cellular level and help relieve symptoms.

Ex; Most drugs used in depression, schizophrenia, anxiety and drugs of abuse function through this mechanism.

E) Drugs acting by replacement: Many vital drugs like anti-Parkinson’s,  anti-epileptics etc. act by this mechanism.

Ex; In Parkinson’s disorder, there is low concentration ratio of Dopamine with that of acetylcholine in the brain. Hence the Parkinson symptoms are present. To minimize them, Levodopa is given. This is similar to dopamine in chemistry. In the brain it breaks down into dopamine and enhances the concentration. Thus the imbalance in the ratio of dopamine and acetyl choline is minimized. Due to this the Parkinson symptoms subside.

F) Drugs acting by substitution: This is the mechanism of action of anticancer, antiviral,  antibiotic drugs. They substitute a vital metabolite of cell physiology with a function-less molecule and lead to death of cancer cells, bacteria and virus.

This is a list of all the possible mode of drug actions. Most of the drugs fall into one or other category of mechanism of action as mentioned above.

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