Cefazolin

Cefazolin belongs to the first-generation cephalosporins, a family within the beta-lactam antibiotics. At the heart of the molecule, the beta-lactam ring binds to bacterial enzymes called penicillin-binding proteins, or PBPs. By binding to these PBPs, cefazolin blocks the transpeptidation reaction, the step that links together the chains of peptidoglycan. Without this cross-linking, the bacterial wall can no longer be built or repaired.

Deprived of its wall, the bacterium can no longer withstand its own internal pressure and dies: the effect is bactericidal. This bactericidal action of the cephalosporins follows directly from the inhibition of cell wall synthesis. Cefazolin thus targets a structure specific to bacteria, absent from our own cells, which explains why it strikes them without affecting the host in the same way.

Cefazolin acts on Gram-positive cocci, particularly methicillin-sensitive Staphylococcus aureus and streptococci, as well as on some Gram-negative bacteria such as Escherichia coli, Klebsiella and Haemophilus influenzae. Methicillin-resistant staphylococci and many Enterobacter strains, on the other hand, are resistant to it. This spectrum of activity directly guides its indications.

It is prescribed for respiratory, urinary, skin, biliary, bone and joint infections. It is also used as antibiotic prophylaxis before contaminated surgery, where it remains the cephalosporin of choice. The use of cefazolin depends on the suspected organism, the site of the infection and its presumed susceptibility.

Cefazolin is given by injection, intravenous or intramuscular, and never by mouth. The question of taking it with or between meals therefore does not arise, since it is the care team who performs the injections. The usual dosage ranges from 500 mg to 1 g every 6 to 8 hours for moderate to severe infections.

Its serum half-life is around 1.8 hours after intravenous injection, which justifies these repeated doses through the day to maintain an effective concentration. Keeping to the schedule and completing the full prescribed duration matters as much as the dose, even when symptoms improve before the end. Stopping treatment too soon risks a relapse and encourages the emergence of resistance.

Digestive disturbances are among the most frequent effects: diarrhea, and more rarely a pseudomembranous colitis linked to the bacterium Clostridioides difficile, an effect known across all the cephalosporins. Allergic reactions can also occur, from simple hives to serious forms such as anaphylaxis or Stevens-Johnson syndrome. These hypersensitivity reactions remain uncommon, somewhat more reported with the first- and second-generation cephalosporins.

On the laboratory side, blood abnormalities may be seen, such as neutropenia or thrombocytopenia, along with a transient rise in urea, creatinine and transaminases. These variations generally return to normal after treatment is stopped. A skin rash, swelling or diarrhea that persists warrants telling the care team without delay.

Part of our vitamin K is produced by the bacteria that populate the lower part of the intestine. Prolonged antibiotic treatment disrupts this flora and can, in some cases, reduce this supply and lead to a vitamin K deficiency. This vitamin is essential for blood coagulation.

In addition, the cephalosporins can be associated with a decrease in prothrombin activity, especially in people already at risk of vitamin K deficiency. This is why prothrombin time and INR are monitored when the situation requires it, with vitamin K supplied if needed. Food remains a simple support for vitamin K intake.

Cefazolin is eliminated mainly by the kidney: about 60 % of the drug passes into the urine within the first six hours, then 70 to 80 % within twenty-four hours. In case of kidney failure, the dosage is reduced to avoid accumulation. Each gram of cefazolin sodium also provides 48 mg of sodium, that is 2 mEq, a load to consider in people who must limit salt, in cases of heart failure, hypertension or kidney failure.

Monitoring covers allergic signs, such as hives, itching, swelling or anaphylaxis, and kidney function, all the more so since the kidney handles most of the elimination. Depending on the situation, prothrombin time and INR are also checked. Any unusual reaction should be reported to the care team.