Cephalosporins: Classification, Types, Side Effects, Pharmacology, Warnings and Precautions

They are a large group of antibiotics derived from the Acremonium fungus (formerly called Cephalosporium) that function similarly to penicillins.

This fungus produced three main compounds, historically called cephalosporin N and C, and P, from which the first cephalosporins were derived. Cephalosporins are bactericidal (kill bacteria) and belong to a class known as beta-lactams.

They bind and block the activity of the enzymes responsible for the manufacture of Peptidoglycan, an important component of the bacterial cell wall.

They are called broad spectrum antibiotics because they are effective against a wide variety of bacteria.

These medications are used to treat bacterial infections, which include:

  • Ear infections
  • Pneumonia.
  • Infections of the skin.
  • Kidney infections
  • Sexually transmitted infections such as gonorrhea .
  • Bone infections
  • Streptococcal pharyngitis and other throat infections.
  • Meningitis.

They share a molecular similarity with penicillins, so they can cause a bad reaction in people allergic to penicillins.

What are some examples?

  • Ancef y Kefazol (cefazolin).
  • Ceclor and Cefaclor (cefaclor).
  • Cefdinir.
  • Ceftin y Zinacef (cefuroxime).
  • Duricef (cefadroxilo).
  • Keflex and Keftabs (cefalexin).
  • Maxipime (cefepime).
  • Rocephin (ceftriaxona).
  • Suprax (cefixima).
  • Teflaro (ceftaroline fosamil).

How are they classified?

They are classified in generations. First-generation drugs are effective mainly against gram-positive organisms. The higher generations generally have expanded spectra against aerobic gram-negative bacilli.

Since the first cephalosporin was discovered in 1945, scientists have been improving the structures to make them more effective against a wider range of bacteria.

Each time the structure changes, a new “generation” of cephalosporins is produced.

The first-generation ones work mainly against infections that are considered easy to treat, while the latest-generation cephalosporins tend to be reserved for more serious bacterial infections.

So far there are five generations and all these start with cef , CEPH or kef .

Types of cephalosporins

  • First generation
  • Second generation
  • Third generation
  • Fourth generation.

First generation cephalosporins.

They refer to the first group of cephalosporins discovered. Its optimal activity is against gram-positive bacteria such as staphylococci and streptococci.

They have little activity against gram-negative bacteria. These drugs have an excellent activity against gram-positive cocci.

First-generation oral cephalosporins are commonly used for uncomplicated skin and soft tissue infections, which are usually due to staphylococci and streptococci.

Some are:

  • Cefadroxilo.
  • Cefradina.
  • Cephalexin.
  • Cefazolina.

Second generation cephalosporins.

They are active against Gram-positive coconuts and certain gram-negative bacilli.

These medications may be slightly less active against gram-positive cocci than first-generation cephalosporins.

They are often used for polymicrobial infections that include gram-negative bacilli and gram-positive cocci. They can be used in intra-abdominal sepsis, decubitus ulcers and diabetic foot infections.

Second-generation cephalosporins followed those of first generation and some of them are:

  • Bullet.
  • Cefuroxima.
  • Cefprozil.
  • Loracarbef.
  • Cefoxitina.

Third generation cephalosporins.

These followed the second generation. No third generation of cephalosporins treats all scenarios of infectious diseases.

Cefotaxime and Ceftizoxime offer the best gram-positive coverage of all third-generation agents; Ceftazidime and Cefoperazone are unique in that they provide antipseudomonal coverage.

Ceftriaxone has a long half-life that allows administration once a day and all third-generation cephalosporins with the exception of Cefoperazone penetrate the cerebrospinal fluid.

These drugs are active against Haemophilus influenzae and some Enterobacteriaceae that do not produce AmpL-type beta-lactamase or extended-spectrum beta-lactamase.

Some third-generation cephalosporins have a relatively poor activity against gram-positive cocci. If they are used for skin and soft tissue infections, they should be restricted to uncomplicated infections due to streptococci.

These cephalosporins have many clinical uses, as does the fourth-generation cephalosporin.

Fourth generation of cephalosporins.

They refer to the fourth group of cephalosporins discovered. They are structurally related to the third generation, but have an additional group of ammonium, which allows them to quickly penetrate through the outer membrane of Gramnegative bacteria, improving their activity.

They are also active against beta-lactamase-producing bacteria that can inactivate third-generation cephalosporins.

They have an excellent activity against gram-positive bacteria such as methicillin-sensitive staphylococci, penicillin-resistant pneumococci and viridans group streptococci.

Cefepime is the only fourth-generation cephalosporin available in the United States.


Cephalosporins penetrate well in most body fluids and in the FEC of most tissues, especially when inflammation is present, because it increases diffusion.

However, the only ones that reach levels of cerebrospinal fluid high enough to treat meningitis are:

  • Ceftriaxona.
  • Cefotaxima.
  • Ceftazidime.
  • Cefepime.

Most cephalosporins are excreted mainly in the urine, so their doses should be adjusted in patients with renal failure. Cefoperazone and Ceftriaxone, which have significant biliary excretion, do not require such dose adjustment.

What are the most common side effects?

  • Stomach ache.
  • Nausea or vomiting
  • Diarrhea.
  • Thrush (white fungus in the mouth), yeast infection or other fungal infection.
  • Blood abnormalities.
  • Rash or itching

Warnings and precautions

People who are allergic to penicillins, or any inactive ingredient found in these drugs, should not take them.

As with all antibiotics, it is important that you finish the entire course prescribed, even if you feel better. This is the only way to guarantee that the infection disappears completely.

Otherwise, the infection could come back and be much harder to treat the second time.