Ceftriaxone
Ceftriaxone is a 3rd generation cephalosporin, which is known for its longer half-life when compared with other cephalosporins as well as broader gram-negative bacteria cover than 1st and 2nd generation cephalosporins. Its structure is shown below
Mechanism Of Action
Ceftriaxone crosses cell wall and enters the periplasmic space where it will bind to penicillin binding protein (PBP) on the cell membrane of bacteria. The PBP are responsible for mitosis and cell structure integrity. Inhibition of PBP results in prevention of cell division, resulting in filament formation which cause leakages of bacteria cell content. Ceftriaxone primarily binds to PBP 3
Antimicrobial Activity
Gram positive cocci
Staphylococcus aureus, Streptococcus Pyogenes, Streptococcus pneumoniae are all susceptible to ceftriaxone
Methicillin-resistant Staphylococcus aureus (MRSA) and Enterococci are exceptions which are not susceptible to Ceftriaxone
Gram positive bacilli
Very few species and include Listeria Monocytogenes
Gram positive anaerobes
Peptococcus, Propionibacterium acnes, Clostridium perfringens are susceptible
Clostridium difficile is resistant
Gram negative cocci
Ceftriaxone has excellent activity against Neisseria meningitidis and Neisseria gonorrhea
Gram negative bacilli
Haemophilus influenzae, Salmonella enterica, Shigella spp, Vibrio Cholerae are susceptible
Campylobacter jejuni and C. Coli are resistant to Ceftriaxone
Ceftriaxone shows little to no activity against Pseudomonas Aeruginosa.
Indications
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Absorption
Ceftriaxone is poorly absorbed after oral administration, hence its available for i.m. or i.v.
The dry powder is reconstituted with water or lignocaine to reduce pai at injection site
Following i.m. administration it is almost immediately absorbed
Distribution
It is well absorbed throughout the body including lungs, ears, kidneys. It even crosses the placenta
It penetrates well in the Cerebral Spinal Fluid in patients with inflamed meninges
About 80-95% is protein bound
Volume of distribution is 6-14L
i.m. peak serum time is 2-3hrs
i.v. peak serum time is 30minutes
Metabolism and Elimination
Low concentration of it is metabolized in the liver
About 333-67% is excreted in urine as unchanged drug
Since it is highly protein bound, it has a slow renal clearance. It is mainly excreted by glomerular filtration
The remaining drug is excreted in feces
Ceftriaxone has a half-life of 5-9hours in people with normal hepatic and renal function
Interactions
Ceftriaxone is not to be mixed with Calcium containing solution such as Ringers or Harmann solutions. This is because Ceftriaxone and calcium form a salt precipitate which is damaging to the lungs and kidneys
Therefore, ceftriaxone and Calcium containing solution administration should be spaced at least 48hrs?
Ceftriaxone increases anticoagulation activity of heparin/enoxaparin, and it should be avoided or an alternative be used
Side Effects
Ceftriaxone side effects are few and include the following
Induration after i.m. administration
Diarrhea, hypersensitivity reactions and vomiting
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