Pharmacology: Pharmacodynamics: As a phosphonic acid derivative, fosfomycin inhibits bacterial wall synthesis (bactericidal) by inactivating the enzyme, pyruvyl transferase, which is critical in the synthesis of cell walls by bacteria; the trometamol salt is preferable to the calcium salt due to its superior absorption.
It is active in vitro against a range of gram-positive and gram-negative bacteria including Staphylococcus aureus, some streptococci, most Enterobacteriaceae, Haemophilus influenzae, Neisseria spp., and some strains of Pseudomonas aeruginosa although some are resistant. Bacteroides spp. are not sensitive.
Phamacokinetics: Absorption: Well absorbed.
Bioavailability: 34% to 58%.
Distribution: Vd: 2 L/kg; high concentrations in urine; well into other tissues; crosses maximally into CSF with inflamed meninges.
Protein binding: <3%.
Half-life elimination: 4-8 hours; Clcr <10 mL/minute: 50 hours.
Time to peak, serum 2 hours.
Excretion: Urine (as unchanged drug); high urinary levels (100 mcg/mL) persist for >48 hours.