Chemistry in Everyday Life

Therapeutic Action of Different Classes of Drugs

We know that drugs help us diagnose and cure numerous illnesses. But any drug consumed by humans can actually have two kinds of effects – therapeutic effects and side effects. The goal is to prescribe the ideal drug, the one that only has a therapeutic effect. So let us learn about different classes of drugs and their therapeutic action.

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Our stomach produces acid to facilitate the digestion process. However, at times there is an overproduction of acid in the stomach. This leads to irritation, pain and discomfort. In the long run, it may also result in more severe problems such as stomach ulcers.

Until a few years ago, the only drugs available to cure this excessive acidity were sodium hydrogen carbonate or in some cases aluminum and magnesium hydroxide. These would react with the acid and make the stomach more alkaline. But these would just cause the stomach to produce more acid. The other drug available was metal hydroxides, which were insoluble. They only treated the symptoms of acidity, without altering the pH levels of the stomach.

Then in the recent years, we came up with a better form of antacids for therapeutic actions. We learned that histamine is the chemical messenger that stimulates the secretion of the various digestive acids such as pepsin and HCl. So a drug called cimetidine was invented. The drug blocks the interaction between histamine and the receptors in the stomach. This ensures that fewer acids are released into the stomach, hence preventing hyperacidity. Even today, antacids remain the most consumed drug in the world.

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 Learn Drugs and their Classification here. 


First, let us understand the functions of histamines. They are powerful vasolidators, i.e. they expand the blood vessels of a region and stimulate the blood flow. Histamines are produced by the immune system whenever it is triggered by an allergen. Histamines are stored in the mast cells of our body, in lungs, nose, gut, mouth etc. When released they interact with specific receptors in the body and performs its actions.

Antihistamines are the drugs we take to tame the effects of histamines. Antihistamines work by blocking the effect of histamines by not allowing the receptors to bind with histamine. This, in turn, will prevent the cells from inflammation, excessive blood circulation etc. The major use of antihistamines is in prevention and control of allergies. Some common drugs used as antihistamine are brompheniramine, cetirizine, and terfenadine.

Image result for cetirizine chemical structure

(source: researchgate)


These are chemically synthesized drugs that help humans fight a variety of mental diseases such as stress, anxiety, mental fatigue, depression etc. They are identified as neurologically active drugs. There are several types of tranquillizers and they all have different chemical structures to help with different problems.

Let us take the example of depression. There is a hormone which is responsible for mood changes known as noradrenaline. If the levels of noradrenaline get too low, a person may feel depressed. So drugs like chlordiazepoxide or Equanil inhibit the enzyme that is responsible for breaking down noradrenaline. The hormone remains in the system longer, helping with depression.


These are drugs we commonly identify as painkillers. They mains interact with elements of the nervous system. They reduce or extinguish any pain or discomfort felt anywhere in the body, but without impairing consciousness or causing incoordination. There are two basic types of analgesic

  • Non-narcotic Analgesic: Also known as the simple analgesic, they are not opioids. These include anti-inflammatory drugs and aspirin and paracetamol. They help relieve pain, swelling and even control fevers. They mainly reduce the production of a chemical known as Prostaglandins, which is normally produced in response to tissue damage.
  • Narcotic Analgesics: These are opioid medication. These are helpful in moderate to severe main management. They basically attach to the receptors in your brain and reduce the perception of the pain. Some can also increase the patient’s threshold of pain. In high doses, they are very dangerous and addictive as well. Some examples include morphine, oxycodone, fentanyl etc.

Image result for morphine chemical structure

Chemical structure of Morphine


Very often diseases are often caused due to foreign bodies entering our systems. These can be various types of bacteria, fungi, parasites etc. Antimicrobial drugs destroy or prevent such microbes or hamper their pathogenic actions in our bodies. There are broadly three types of antimicrobial therapeutic drugs,

  • Antibiotics: These are specifically targeted towards bacteria, they are harmless to fungi. They work in two ways, they either kill the bacteria (bactericidal). Or they inhibit the growth and the actions of bacteria (bacteriostatic). And then there are broad-spectrum antibiotics that target a diverse variety of bacteria, while the narrow spectrum ones target only a few specific bacteria. Examples include Sulphonamides and penicillin.
  • Antiseptics: These are drugs we use on the surface of living things to kill the microbes on it. So we use them on cuts, wounds, scrapes and such to destroy all the microorganisms and prevent them from entering our body. One very common example is Dettol (chloroxylenol and terpineol). Antiseptics are for external use only, they are not ingested.
  • Disinfectants: These are used on the surface of inanimate objects like floors, sinks etc. The principal is the same, to kill the microorganism. Only the chemicals are used in a higher concentration.

Learn the Concept of Drug Target Interaction here.

Solved Example for You

Question: Chloramphenicol is which of the following?

  1. Antihistamine
  2. Antifertility
  3. Broad spectrum antibiotic
  4. Disinfectant

Answer: The answer is C. Chloramphenicol is a broad spectrum antibiotic and so can be used against a variety of gram-positive and gram-negative bacteria.

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