ceftriaxone
Meaning of ceftriaxone: Broad coverage is not complete coverage, and what ceftriaxone misses, including Pseudomonas and enterococci, matters as much as what it reaches.
Definition of ceftriaxone
Ceftriaxone is a broad spectrum antibiotic of the third generation cephalosporin group, given by injection into a vein or a muscle rather than by mouth. It kills bacteria by blocking construction of their cell wall, and it reaches most tissues including the fluid around the brain and spinal cord. A long duration of action allows once daily dosing.
How does it kill bacteria?
Like every cephalosporin, ceftriaxone carries a beta lactam ring that binds the enzymes bacteria use to cross link their cell wall. Without those cross links the wall cannot contain the pressure inside the cell, and the organism bursts. Human cells have no such wall, which is why the drug attacks bacteria while leaving the body's own cells intact. Third generation cephalosporins were developed to resist many of the enzymes bacteria produce to destroy earlier beta lactams. That widened their reach among gram negative organisms, at the cost of some of the activity against staphylococci that the first generation of the class had.
What is it used for?
| Infection | Why ceftriaxone suits it |
|---|---|
| Bacterial meningitis | Reaches the fluid around the brain and spinal cord at levels that kill the usual organisms |
| Pneumonia acquired outside hospital | Covers the common causes, and is usually paired with a drug active against those it misses |
| Gonorrhea | Remains reliably active where many older options have lost their effect |
| Urinary, skin, bone and abdominal infection | Broad coverage with dosing simple enough to continue outside hospital |
Once daily dosing is unusual for an injected antibiotic and follows from an unusually long duration of action, which makes treatment at home or in a clinic practical. Ceftriaxone is cleared partly by the kidneys and partly into the bile, so unlike many comparable drugs it does not generally need its dose reduced when kidney function is poor.
What does it not cover?
Its range is wide but far from complete. Ceftriaxone has no useful activity against Pseudomonas aeruginosa, against enterococci or against Listeria, and no cephalosporin touches organisms that have no cell wall at all. Methicillin resistant staphylococci also fall outside its reach, so serious skin and bloodstream infection often calls for a second drug alongside it. Common unwanted effects include diarrhea and rash, and a reaction can occur in someone allergic to penicillin because the two share the beta lactam structure, although genuine cross reaction is far less frequent than the caution around it implies. The drug can also settle in the gallbladder as sludge that mimics gallstones and clears once treatment stops.
Also known as
Used in a sentence
Ceftriaxone was administered intravenously to treat the patient's community-acquired pneumonia.
Good to know
Ceftriaxone reaches the fluid surrounding the brain and spinal cord better than many other antibiotics, which is part of why it is used for suspected bacterial meningitis. It forms a precipitate with calcium containing intravenous fluids, a hazard specific to newborn infants.