Therapeutic Action of Medical Drugs

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will describe the three general ways by which drugs can exert their therapeutic action. You'll learn about drugs like antibiotics as well as agonists and antagonists.

Therapeutic Effects

When we think of a drug's effect on the body we tend to think of two main categories of effect. The therapeutic effects and the negative side effects. The therapeutic effects are the intended beneficial effects of the drug while the negative side effects are the unwanted effects of the drug. For example, non-steroidal anti-inflammatory drugs, like Advil, can help ease minor aches and pains resulting from running around too much. That's their therapeutic effect. A potential negative side effect is gastrointestinal ulceration. Gastrointestinal ulceration is a term that describes the formation of deep defects (like sores) in the digestive system.

How this therapeutic action of a drug occurs varies from drug to drug but we can simplify the therapeutic classification scheme of drugs into three general categories that we cover in this lesson.

Action On Pathogens

Think back to the last time you had something like a skin infection or perhaps a minor skin abscess. That infection was most likely caused by pathogenic bacteria. A pathogen is an agent of disease. This isn't limited to bacteria, however. Viruses, fungi, and parasitic worms are included as well.

Now, how did you treat that skin infection? Well, your doctor may have given you a topical antibiotic, a cream or ointment of some sort infused with antibiotics. Antibiotics are drugs that target bacteria. Their therapeutic action lies in how they target the bacteria. In other words, some therapeutic drug action has less to do with targeting receptors or other structures of your body's cells and more to do with targeting those types of structures and molecules on the pathogen. To emphasize this point, this doesn't mean that the drug has no interaction with your body whatsoever. This is not true at all. However, its major intended therapeutic effect lies in its direct action on the pathogen, not on your body. Along the same lines, it also means that the drug is more toxic to the pathogen than it is to your body (when the proper amount is used over a given period of time).

Drugs that act by targeting pathogens include the antibiotics, antivirals, antifungals, and antiparasitics. The way they act differs from drug to drug and from pathogen to pathogen. Here is a general idea of some of the various ways by which they work:

  • They can affect the protective membrane or covering of the pathogen. This would be akin to severely compromising your own skin, which would be deadly.
  • They can affect the ability of the pathogens to reproduce.
  • They can put an end to important energetic or enzymatic processes that help power the pathogen.

This image shows a test plate where bacteria have been inhibited from growing in a zone around an antibiotic-infused disk.

Action On The Body

That being said, many drugs do not act on any pathogen and, instead, act on your body. Their therapeutic action varies widely. Here is how they may exert their effects.

Some drugs are agonists. An agonist is a drug that binds a receptor in order produce an intended biological response. Think of the drug as a key and the receptor as a lock. The key inserts into the lock (binds the receptor) and then turns the lock to open it (produces a response). For instance, some analgesics (pain relievers) work by activating opioid receptors to relieve pain.

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