Gail Itokazu, Pharm.D

Goals and Objectives.

By the end of the lecture the student should be able to discuss the following about cephalosporin antibiotics:

1. Describe their mechanism of action and pharmacologic properties.

2. Describe their spectrum of activity.

3. Describe their major side effects.

4. Discuss their use in the clinical setting.

Required readings.

The goal of this reading is to reinforce the clinical application of cephalosporins.

Gram-negative Sepsis and Septic Shock. Chapter 112, pages 2237-2250.

CephalosporinDoseRouteDosing IntervalRenal

Cephalosporins are beta-lactam compounds in which the beta-lactam ring is fused to a 6-membered dihydrothiazine ring, thus forming the cephem nucleus. Side chain modifications to the cephem nucleus confers 1) an improved spectrum of antibacterial activity, 2) pharmacokinetic advantages, and 3) additional side effects. Based on their spectrum of activity, cephalosporins can be broadly categorized into four generations.


  1. Prevents cell wall synthesis by binding to enzymes called penicillin binding proteins (PBPs). These enzymes are essential for the synthesis of the bacterial cell wall.

  2. Bactericidal.

  3. Concentration-independent bactericidal activity, with maximal killing at 4-5 times the MIC of the organism.

  4. Clinically significant post-antibiotic effect is not observed.

    Given these pharmacodynamic properties (concentration-independent bactericidal activity and lack of a post-antibiotic effect, optimal dosing regimens should be designed to continuously maintain drug levels above the MIC of pathogens.


In general, 1st generation cephalosporins have better activity against gram-positive bacteria and less gram-negative activity, while 3rd generation agents, with a few exceptions, have better gram-negative activity and less gram-positive activity. The only fourth generation agent has both gram-positive and gram-negative activity.


It is not uncommon for several resistance mechanisms to be operating simultaneously.

  1. destruction of beta-lactam ring by beta-lactamases; an intact beta-lactam ring is essential for antibacterial activity
  2. altered affinity of cephalosporins for their target site, the penicillin binding proteins
  3. decreased penetration of antibiotic to the target site, the PBPs. This is only applicable to gram-negative bacteria because gram-positive bacteria lack an outer cell membrane, and therefore penetration to the target site is not a problem.



PHARMACOKINETICS: Generally distributes well into the lung; kidney; urine; synovial, pleural, and pericardial fluids. Penetration into the cerebral spinal fluid (CSF) of some 3rd generation cephalosporins (cefotaxime, ceftriaxone, and ceftazidime) is adequate to effectively treat bacterial meningitis.
Elimination is primarily via the kidneys,
though a few exceptions include cefoperazone and ceftriaxone which have significant biliary elimination.

GENERAL CLINICAL USES: Their broad spectrum of activity and safety profile make the cephalosporins one of the most widely prescribed class of antimicrobials. The earlier generation cephalosporins are commonly used for community-acquired infections, while the later generation agents, with their better spectrum of activity against gram-negative bacteria make them useful for hospital-acquired infections or complicated community-acquired infections.

A. Hypersensitivity reactions manifested by rashes, eosinophilia, fever (1-3%); interstitial nephritis. Given the structural similarity of cephalosporins and penicillins, an estimated 1-7% of patients with penicillin allergies will also be hypersensitive to cephalosporins. Cephalosporins should be avoided in patients with immediate allergic reactions to penicillins (eg: anaphylaxis, bronchospasm, hypotension, etc.). Cephalosporins may be tried with caution in patients with delayed or mild reactions to penicillin.

B. Thrombophlebitis (1-5%).


SPECTRUM OF ACTIVITY. Gram-positive aerobic cocci: Very active against Streptococci pyogenes (Group A strep), Streptococcus agalactiae (Group B strep), viridans streptococci. Methicillin-resistant Staphylococci, Enterococci, penicillin-resistant Streptococcus pneumoniae are resistant.

Gram-negative aerobes: Commonly active against Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae, though susceptibilities may vary. Inadequate activity against Moraxella catarrhalis and Hemophilus influenzae.

Anaerobes: Active against most penicillin-susceptible anaerobes found in the oral cavity, except those belonging to the Bacteroides fragilis group.

GENERAL CLINICAL USES. Uncomplicated, community-acquired infections of the skin and soft tissue and urinary tract. Useful for respiratory tract infections caused by pencillin-sensitive Streptococcus pneumoniae but not for Hemophilus influenzae and Moraxella catarrhalis. While effective for these infections, other less expensive alternatives should be used when appropriate because of their efficacy and narrower spectrum of activity (eg: penicillins, trimethoprim/sulfamethoxazole). Parenteral 1st generation agents are used for surgical wound prophylaxis.

A. Cefazolin (Ancef , Kefzol, Cephalothin (Keflin , Vantage, Cephpirin (Cefadyl). IV/IM formulations. Spectrum of cephalothin and cefazolin are similar except that cefazolin is slightly more active against Escherichia coli and Klebsiella species. The longer half-life of cefazolin allows less frequent dosing.

B. Cephalexin (Keflex, Keftab, Biocef), Cephradine (Anspor, Velosef), Cefadroxil (Duricef, Ultracef). PO formulations. Less frequent dosing with cefadroxil.


There are 2 groups within the 2nd generation agents that differ in their: 1) spectrum of activity and 2) adverse reaction profile. These groups are the "true" second generation cephalosporins (cefamandole, cefuroxime) and the cephamycins (cefoxitin, cefotetan, cefmetazole).

SPECTRUM OF ACTIVITY. Gram-positive aerobic cocci: In general, true 2nd generation agents are comparable to 1st generation agents against nonenterococcal streptococci; are less active invitro, but still have adequate activity against MSSA. Compared to the 1st generation agents, the cephamycins are less active against gram-positive cocci. Both groups of cephalosporins are inactive against methicillin-resistant Staphylococci and Enterococci.

Gram-negative aerobes. The "true" cephalosporins are more active than 1sts for Hemophilus influenzae, Moraxella catarrhalis, Neisseria meningitidis, and some Enterobacteriaceae. The cephamycins in some instances (eg: cefotetan) have improved activity against Enterobacteriaceae.

Anaerobes: Cephamycins are active against most anaerobes found in the mouth as well as colon (eg: Bacteroides species, including Bacteroides fragilis).

GENERAL CLINICAL USES. The "true" 2nd generation agents are useful for community-acquired infections of the respiratory tract (Hemophilus influenzae, Moraxella catarrhalis, Streptococcus pneumoniae) and uncomplicated urinary tract infections (Escherichia coli). The cephamycin group is useful for mixed aerobic/anaerobic infections of the skin and soft tissues, intra-abdominal, and gynecologic infections, and surgical prophylaxis.

SIDE EFFECTS/PRECAUTIONS. The cephamycin agents have a side chain called the methylthiotetrazole (MTT) group which predisposes patients to:

1) hypoprothrombinemia and bleeding by disturbing synthesis of vitamin-k dependent clotting factors.

Risk factors are renal or hepatic disease, poor nutrition, the elderly, and cancer.

2) alcohol intolerance by causing a disulfiram-like reaction, avoid alcohol products for several days after antibiotics have stopped.

A. Cefamandole (MandolR). (IV/IM) formulations. Better activity against selected methicillin-susceptible Staphylococcus aureus than cefazolin. May not be reliable therapy for Hemophilus influenzae. Although not a cephamycin, it contains an NMTT side chain.

B. Cefurxoime (Zinacef, Kefurox). IV/IM/PO formulations. Somewhat less potent against Staphylococcus aureus, but more potent against Streptococcus pneumoniae and Streptococcus pyogenes than 1st generation cephalosporins. Active against Hemophilus influenzae, Moraxella catarrhalis, Escherichia coli, Proteus mirabilis, Klebsiella species.

Although cefuroxime has been used for the treatment of bacterial meningitis caused by H. influenzae, it is not recommended because studies show neurologic deficits are more frequent in children treated with cefuroxime versus selected 3rd generation cephalosporins (cefotaxime, ceftriaxone). This finding is related to delayed sterilization of cerebral spinal fluid.
C. Cefonicid (Monocid
R). IV/IM formulation. Similar to cefamandole and cefuroxime, though less active against gram-positive cocci (methicillin-susceptible Staphylococcus aureus, Group A strep, Streptococcus pneumoniae). Long half-life allows once daily dosing.

D. Cefoxitin (MefoxinR). IV/IM formulations. A cephamycin, which is less active than 1st generation agents against gram-positive bacteria. Active against Neisseria gonorrhea, but less active than "true" second generation cephalosporins against Hemophilus influenzae.

E. Cefotetan (CefotanR). IV/IM formulations. A cephamycin with similar activity to cefoxitin. Compared to second generation cephalosporins and cefoxitin, has improved activity against Enterobacteriaceae including Enterobacter. Also active against Hemophilus influenzae, Neisseria gonorrhea, Neisseria meningitidis. Generally 2-4 fold less active than cefoxitin against gram-positive cocci. For Bacteroides fragilis, is comparable to cefoxitin; but less active than cefoxitin against non-Bacteroides fragilis species within the Bacteroides fragilis group; the clinical significance of which is unknown. Used in surgical wound prophylaxis when activity against Bacteroides fragilis is needed.

F. Cefmetazole (ZefazoneR). IV/IM formulations. A cephamycin, similar to cefoxitin and cefotetan. Similar to cefoxitin and more active than cefotetan against methicillin-susceptible Staphylococcus aureus. 2-4 fold more active than cefoxitin against Enterobacteriaceae (eg: Escherichia coli, Klebsiella sp, Proteus mirabilis). Also active against Hemophilus influenzae and Moraxella catarrhalis. Bacteroides fragilis is similar to cefoxitin, against other Bacteroides species, is similar or slightly less active than cefoxitin. Used in surgical wound prophylaxis when activity against Bacteroides fragilis is needed, repeat dose would be necessary in procedures lasting more than 4 hours.

G. Cefaclor (Ceclor), Cefprozil (Cefzil), Loracarbef(Lorabid), Cefpodoxime proxetil (Vantin). PO formulations. Cefaclor is more commonly associated with a serum sickness like illness. Loracarbef is a new category of compounds called the carbacephems, which are analogues of cephalosporins. Loracarbef is the carbacephem analogue of cefaclor.

H. Cefuroxime axetil (CeftinR). PO formulation of cefuroxime. Is the oral ester of cefuroxime that is hydrolyzed to cefuroxime during absorption.


Improved activity against Enterobacteriaceae associated with hospital-acquired infections; some agents are also active against Pseudomonas aeruginosa which is a frequent cause of hospital-acquired pneumonia.

SPECTRUM OF ACTIVITY. Gram-positive aerobic cocci: Cefotaxime, ceftriaxone, and ceftizoxime are active against methicillin-susceptible Staphylococcus aureus (though less than 1st and some 2nd generation agents), very active against Groups A and B streptococci, and viridans streptococci. Cefotaxime and ceftriaxone are more active than ceftizoxime against Streptococcus pneumoniae, particularly intermediately-penicillin resistant Streptococcus pneumoniae. None are active against methicillin-resistant Staphylococci, Enterococci, and Listeria monocytogenes.

Gram-negative aerobes: Very active against Hemophilus influenzae, Moraxella catarrhalis, Neisseria meningitidis, and Enterobacteriaceae (eg: Escherichia coli, Klebsiella species, Proteus mirabilis, Providencia)found in hospital and community-acquired infections. Some Enterobacter species have a tendency to become resistant during cephalosporin therapy, and thus cephalosporins are not the drugs of choice for Enterobacter infections.

Only and ceftazidime and cefoperazone are active against Pseudomonas aeruginosa, and ceftazidime is preferred because it is more potent than cefoperazone against gram-negative bacteria.

Anaerobes: Cefotaxime, ceftriaxone, and ceftizoxime are adequate for oral anaerobes.

GENERAL CLINICAL USES. For infections involving gram-negative bacteria, particularly hospital-acquired infections or complicated community-acquired infections of the respiratory tract, blood, intra-abdominal, skin and soft tissue, and urinary tract. Because of their activity includes the aerobic gram negative bacteria covered by aminoglycosides, they may be an alternative to aminoglycosides in some patients with renal dysfunction.

The clinical situations requiring use of 3rd generation cephalosporins are likely to be encountered in patients who are hospitalized, have recently received antibiotics, or are immunocompromised.

A. Cefotaxime (Claforan), Ceftriaxone (Rocephin), Ceftizoxime (cefizox) . IV/IM formulations. Activity against Enterobacteriaceae (eg: Escherchia coli, Klebsiella pneumoniae) are similar. None are active against Pseudomonas aeruginosa. Only cefotaxime and ceftriaxone achieve adequate drug levels in the cerebral spinal fluid to constitute reliable empiric therapy for bacterial meningitis. Ceftriaxone is eliminated to a significant degree by the biliary system, and as a result, biliary pseudo-lithiasis has been reported as a side effect of this agent.

B. Ceftazidime (Fortaz, Tazidime, Tazicef), Cefoperazone (Cefobid). IV/IM formulations. Spectrum includes Pseudomonas aeruginosa (against which ceftazidime is more active) and Enterobacteriaceae covered by the 3rd generation agents in item A above. Disadvantages of cefoperazone are: 1) the least active 3rd generation agent against Enterobacteriaceae and 2) contains MTT side chain (see SIDE EFFECTS/PRECAUTIONS under 2nd generation agents).

C. Cefixime (Suprax), Ceftibuten (Cedax) .PO formulations administered once or twice daily. Inactive against methicillin-susceptible Staphylococcus aureus, thus not good choices for skin and soft tissue infections. Generally very active against gram-negative bacteria causing community-acquired infections(Hemophilus influenzae, Moraxella catarrhalis). Cefixime is effective as a single dose therapy for uncomplicated Neisseria gonorrhea infection. While used in otitis media, cefixime may not routinely eradicate Streptococcus pneumoniae.


Has the excellent activity against Enterobacteriaceae and Pseudomonas aeruginosa which is similar to ceftazidime. In addition, it also has better gram-positive activity than ceftazidime.

SPECTRUM OF ACTIVITY. Gram-positive aerobic cocci: Active against Streptococcus pneumoniae, and Groups A and B streptococci. Though active against methicillin-susceptible Staphylococcus aureus, it is less potent than the 1st and 2nd generation agents.
Gram-negative aerobes: Similar to ceftazidime.

Anaerobes: Not active against Bacteroides fragilis.

GENERAL CLINICAL USES. Similar to 3rd generation agents.
A. Cefepime (Maxipime
R). IV/IM formulations.