There are many medicines in the medical world and of them, drugs of modern medicine (allopathic) are widely used.
They are highly prescribed compared to alternative medicine. This is because of the benefit of faster relief from the symptoms.
But on the negative side, some of these drugs have severe side effects limiting prolonged and widespread 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 the 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 choice prescribed for peptic ulcer. This drug physically binds to the portion of the ulcer surface in the stomach. Thereby prevents the further attack of gastric acid on to it. Due to lack of further exposure to acid, the ulcer portion of the stomach gets healed faster.
2) Charcoal; The activated charcoal is used as an antidote to poisons. Scientifically it is called activated as it in powdered 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 prevents it from being absorbed into the blood. Thus it minimizes the poison effect.
Thus the above drugs act by being physically present in the location of the 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 the 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 a 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 (an alkali element) in the kidney stone and dissolves it. Also, any chances of further growth of the stone are inhibited by this citric juice.
C) Drugs acting by physiological modifications: Here, drugs produce some physiological effect and relief from symptoms of the disease. This can be of three types.
1. Those producing the 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 the intestine is pushed downwards, i.e., towards rectum for faster defecation. In this condition, doctors prescribe 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 the mouth). For severe 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 output. Due to this, blood volume decreases, thereby reducing blood pressure.
3. Those producing unrelated effect: Here, the symptoms are mitigated by producing unrelated changes in physiology.
Ex of such drugs is 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 counterirritants.
When there is a 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 forgotten due to a 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 the cellular surface or rarely inside. When drugs bind 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 a 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 acetylcholine 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 the 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 the mechanism of action as mentioned above.