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A Guide to 5 Common Antibiotic Classes: From Penicillin to Macrolides…

Most of us have taken antibiotics at some point in our lives, whether to combat acne, conjunctivitis, a urinary tract infection (UTI) or one of the many other ailments physicians use antibiotics to treat. However, there are a vast number of different antibiotics available, with a wide variety of uses, side effects, drawbacks, and benefits, which can make understanding these drugs a challenge for even the most informed patients. 

Antibiotics are anti-infectives, but more specifically, they are used to treat bacterial infections, for example, those caused by Strep. E. Coli and Staph. A common misconception is that antibiotics may be used to treat coughs, the flu, and colds, but these conditions are generally caused by viral infections, which renders antibiotics and their bactericidal (bacteria killing) or bacteriostatic (stopping bacteria multiplying) qualities ineffective. 

While there are many medical uses for antibiotics, correct usage and administration are vital to minimize side effects and the risk of antibiotic resistance. Patients who develop resistance to antibiotics may find treatment with these drugs less effective at a later date, leaving them in need of other more complex or expensive treatments. Earlier this year, the US Food and Drug Administration's (FDA's) director of the Office of In Vitro Diagnostics and Radiological Health Alberto Gutierrez PhD, warned: "Unnecessary antibiotic use may contribute to the rise in antibiotic-resistant infections."

Despite this, antibiotics offer a highly effective form of treatment to myriad ailments and infections when used correctly and appropriately. Among the numerous diseases and conditions treated with antibiotics are conjunctivitis, acne, ear infections, UTIs, skin infections, upper respiratory tract infections, strep throat and travelers diarrhea.  More than 100 antibiotics exist, and these are separated into different categories according to their properties, composition, and effects. Below is our guide to five of the most common antibiotic drug classes.


Perhaps the most famous form of antibiotics, penicillins (also known as beta-lactam antibiotics) are used for a wide range of medical treatments. These drugs are regularly prescribed to deal with dental infections, skin infections, ear infections, UTIs and respiratory tract infections. Among the most common drugs to fall into their category are: penicillin V potassium, (phenoxymethylpenicillin), Novamox (amoxicillin), Tazocin (piperacillin), and Floxapen (flucloxacillin).


Cephalosporins have similar uses and methods of action to penicillins, yet their chemical structure is different, which gives them a different range of antibacterial activity. They are grouped into "generations", according to their antimicrobial qualities and have an extensive variety of uses. 

In addition to treating skin infections, gonorrhea, and UTIs, they also have surgical uses and may be utilized to treat bone infections and, in the case of fifth generation varieties, to combat Staphylococcus aureus (MRSA).  Among the most common cephalosporins are Ceftin (cefuroxime), Duricef (cefadroxil), Rocephin (ceftriaxone) and Zevtera (ceftobiprole).


Quinolones, also called fluoroquinolones, are bactericidal antibiotics with a broad range of uses. They are synthetic and are often used when other treatment options prove ineffective. Hospital-acquired pneumonia and UTIs are among the conditions quinolone antibiotics are considered particularly useful for treating. 

However, in 2016, the FDA issued a warning about the potential side effects of these drugs, noting the potential severity of the side effects often outweighs the benefits of these drugs. It suggested the use of quinolones should be reserved for patients lacking other treatment options. Among the drugs falling into this category are Cipro (ciprofloxacin), Avelox (moxifloxacin) and Levaquin (levofloxacin).


Tetracyclines are bacteriostatic antibiotics used to treat and prevent a variety of conditions, including UTIs, intestinal tract infections, infections of the respiratory tract, Lyme disease and STDs. They are also commonly prescribed to treat acne and rosacea. 

There is a small risk of an allergic reaction to tetracyclines and side effects sometimes include headaches and vision problems. Some of the most commonly prescribed tetracyclines are Vibramycin (doxycycline), Minocin (minocycline) and Terramycin (oxytetracycline).


Macrolides are mainly bacteriostatic antibiotics and are often used to treat respiratory and lung conditions due to their high level of lung penetration. They may also be used to treat gastrointestinal tract infections, pneumonia and skin infections, among other conditions. Some commonly prescribed macrolides include Zithromax (azithromycin), Biaxin (clarithromycin) and Ketek (telithromycin).

Other information and OTC antibiotics

There are many other antibiotic classes, such as carbapenems, aminoglycosides, glycopeptides, sulfonamides, and lincomycins. Most antibiotics are administered orally and are available on prescription only. However, there are a small number of over-the-counter topical treatments, which are used to treat minor skin infections and similar conditions. Examples of these include Neosporin (bacitracin, neomycin, polymyxin B) and Bacitracin (Bacitracin).

For more information about antibiotics, speak to your pharmacist or physician. Always ensure you tell your healthcare providers of any existent conditions and any other medications you are taking before starting a course of antibiotics.