CLINICAL PHARMACOLOGY
Mechanism Of Action
Levofloxacin is a member of the
fluoroquinolone class of anti-microbial drug (See Microbiology).
Pharmacokinetics
Levofloxacin concentration in
plasma was measured in 14 healthy adult volunteers during a 16Âday course of
treatment with IQUIX® solution. The dosing schedule was 1-2 drops per eye once
in the morning on Days 1 and 16; 1-2 drops per eye every two hours Days 2
through 8; and 1-2 drops per eye every four hours Days 9 through 15. The mean
levofloxacin concentration in plasma 1 hour post dose ranged from 3.13 ng/mL on
Day 1 to 10.4 ng/mL on Day 16.
Maximum mean levofloxacin concentrations increased from
3.22 ng/mL on Day 1 to 10.9 ng/mL on Day 16, which is more than 400 times lower
than those reported after standard oral doses of levofloxacin.
Levofloxacin concentration in tears was measured in 100
healthy adult volunteers at various time points following instillation of 2
drops of IQUIX® solution. Mean tear concentration measured 15 minutes after
instillation was 757 mcg/mL.
Microbiology
Levofloxacin is the L-isomer of the racemate, ofloxacin,
a quinolone antimicrobial agent. The antibacterial activity of ofloxacin
resides primarily in the L-isomer. The mechanism of action of levofloxacin and
other fluoroquinolone antimicrobials involves the inhibition of bacterial
topoisomerase IV and DNA gyrase (both of which are type II topoisomerases),
enzymes required for DNA replication, transcription, repair, and recombination.
Levofloxacin has in vitro activity against a wide range
of Gram-negative and Gram-positive microorganisms and is often bactericidal at
concentrations equal to or slightly greater than inhibitory concentrations.
Fluoroquinolones, including levofloxacin, differ in
chemical structure and mode of action from Ã-lactam antibiotics and
aminoglycosides, and therefore may be active against bacteria resistantto
Ã-lactam antibiotics and aminoglycosides. Additionally, Ã-lactam antibiotics
andaminoglycosides may be active against bacteria resistant to levofloxacin.
Resistance tolevofloxacin due to spontaneous mutation in vitro is a rare
occurrence (range: 10 -9 to 10-10).
Levofloxacin has been shown to be active against most
strains of the following microorganisms, both in vitro and in clinical
infections as described in the INDICATIONS AND USAGE section .
Aerobic Gram-positive Microorganisms
Corynebacterium species*
Staphylococcus aureus
Staphylococcus epidermidis
Streptococcus pneumoniae
Viridans group streptococci*
Aerobic Gram-negative Microorganisms
Pseudomonas aeruginosa
Serratia marcescens*
*Efficacy for this organism was studied in fewer than 10
infections.
The following in vitro data are also available, but their
clinical significance in ophthalmic infections is unknown. The safety and
effectiveness of levofloxacin in treating ophthalmological infections due to
these microorganisms have not been established in adequate and well controlled
trials.
These organisms are considered susceptible when evaluated
using systemic breakpoints. However, a correlation between the in vitro systemic
breakpoint and ophthalmological efficacy has not been established. The list of
organisms is provided as guidance only in assessing the potential treatment of
corneal ulcer. Levofloxacin exhibits in vitro minimal inhibitory concentrations
(MICs) of 2 mcg/mL or less (systemic susceptible breakpoint) against most
( ≥ 90%) strains of the following ocular pathogens:
Aerobic Gram-positive Microorganisms
Enterococcus faecalis (many strains are only
moderately susceptible)
Staphylococcus saprophyticus
Streptococcus agalactiae
Streptococcus pyogenes
Streptococcus (Group C/F)
Streptococcus (Group G)
Aerobic Gram-negative Microorganisms
Acinetobacter baumannii
Acinetobacter lwoffii
Citrobacter koseri
Citrobacter freundii
Enterobacter aerogenes
Enterobacter cloacae
Escherichia coli
Haemophilus influenzae
Haemophilus parainfluenzae
Klebsiella oxytoca
Klebsiella pneumonia
Legionella pneumophila
Moraxella catarrhalis
Morganella morganii
Neisseria gonorrhoeae
Pantoea agglomerans
Proteus mirabilis
Proteus vulgaris
Providencia rettgeri
Providencia stuartii
Pseudomonas fluorescens
Clinical Studies
In two randomized, double-masked, multi-center,
controlled clinical trials of 280 patients with positive cultures, subjects
were dosed with IQUIX® or ofloxacin 0.3% ophthalmic solution. Dosing occurred
on Days 1 through 3 every two hours while awake and 4 and 6 hours after
retiring. Dosing occurred on Day 4 through treatment completion 4 times daily
while awake. Clinical cure was defined as complete re-epithelialization and no
progression of the infiltrate for two consecutive visits. The IQUIX® treated
subjects had an approximately equal mean clinical cure rate of 80% (73% to 87%)
compared to 84% (82% to 86%) for the subjects treated with ofloxacin 0.3%
ophthalmic solution.