How many different antibiotics are there?

This is difficult to answer, as new antibiotics are being developed continually (although very few novel antibiotics have been marketed in the last few years).

It is easier to discuss broad groups of antibiotics (which may contain many specific compounds, all of which act in the same way and are able to treat the same types of infections).

Some commonly encountered groups of antibiotics are:

• Beta Lactams: This is the largest group of antibiotics, and there are four subdivisions within this group:

  1. Penicillins: penicillin, amoxicillin, cloxacillin etc.

  2. Cephalosporins: cefazolin, cefuroxime, cefotaxime, ceftazidime, cefepime, cefpirome etc.

  3. Monobactams: a relatively small group – aztreonam

  4. Carbapanems: meropenem, imipenem

• Aminoglycosides: gentamicin, amikacin, tobramycin, netilmicin etc
• Quinolones: ciprofloxacin, ofloxacin, gatifloxacin, moxifloxacin etc
• Glycopeptides: vancomycin, teicoplanin
• Macrolides: erythromycin, azithromycin, clarithromycin etc

These are just some examples of commonly used antibiotics and groups of antibiotics. I have elected to use generic names rather than trade names to avoid confusion.

Many people are more familiar with trade names, but some antibiotics are manufactured by more than one company, and thus have more than one name. To include all the trade names for each antibiotic would thus be very cumbersome, and difficult to read.

If you have been prescribed an antibiotic, you can find what ingredients it has (ie what generic compound it contains) on the box or the package insert. For example, the antibiotic commonly called Taravidâ is the same as ofloxacin.

The following sections provide some information on the different types of antibiotics. Not all antibiotics are included here, but I have endeavoured to include all those that are commonly used to treat common infections, as well as some of the less common ones that are still valuable in treating severe or unusual infections.