What are bacteriostatic antibiotics?

Antibiotics (also referred to as ‘antibacterial drugs’) are drugs used in the treatment of bacterial infections. However, not all antibiotics work in the same way. In fact, their mechanisms and mode of action can differ quite significantly.

One of the ways we can categorise antibacterial drugs is by assessing whether they kill bacteria or whether they simply inhibit the bacterial growth. The latter mechanism helps the body to deplete microbial levels in the long-term.

And that is precisely the difference between bactericidal and bacteriostatic drugs. Bactericidal drugs are medicines that actively kill the bacterium. Bacteriostatic drugs are, in contrast, drugs that inhibit the growth and multiplication of the bacterial load.

This allows the body’s natural immune system to combat the remaining bacterial load.

Which drugs are bacteriostatic?

Antibiotics pharmacology is, then, often classified along these lines.

However, we must add some small addendums.

  • A drug that is bactericidal is often no better than a drug that is bacteriostatic. In other words, both drugs can have the same clinical impact.
  • Also, it’s worth bearing in mind that the distinction between bactericidal and bacteriostatic antibiotics is somewhat blurred. Low doses of bactericidal agents can act in a bacteriostatic way, and high doses of bacteriostatic agents can act in a bactericidal manner.

So, we shouldn’t assess the clinical impact of a drug based on whether it belongs to the bactericidal class of antibiotics or to bacteriostatic antibiotics. But this distinction is by no means irrelevant. To the contrary, it informs us how the drug works.

Let’s take a quick look at drugs that fall into each of these antibiotic groups:

Bacteriostatic & Bactericidal Antibacterials

Again, consider the above caveats. Clinical outcomes should always be considered above and beyond other forms of classification – and that includes the antibiotic classification we’re describing here.

Related substances

The terms ‘bacteriostatic’ and ‘bactericidal’ don’t just apply to antibiotics. They also apply to other substances that kill microorganisms.

For example, antiseptics and disinfectants are often classified as ‘bactericidal’, highlighting that their composition has the effect of killing microorganisms. Similarly, substances, such as preservatives, can be described as ‘bacteriostatic’, in that they can limit bacterial growth.

If you’d like to learn more about the antibiotic classes tabled above, check out these antibiotics pharmacology rapid revision slides for more information!



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