Following oral administration, the bioavailability of ofloxacin in the tablet
formulation is approximately 98%. Maximum serum concentrations are achieved
one to two hours after an oral dose. Absorption of ofloxacin after single or
multiple doses of 200 to 400 mg is predictable, and the amount of drug absorbed
increases proportionately with the dose. Ofloxacin has biphasic elimination.
Following multiple oral doses at steady-state administration, the half-lives
are approximately 4-5 hours and 20-25 hours. However, the longer half-life represents
less than 5% of the total AUC. Accumulation at steady-state can be estimated
using a half-life of 9 hours. The total clearance and volume of distribution
are approximately similar after single or multiple doses. Elimination is mainly
by renal excretion. The following are mean peak serum concentrations in healthy
70-80 kg male volunteers after single oral doses of 200, 300, or 400 mg of ofloxacin
or after multiple oral doses of 400 mg.
| Oral Dose |
Serum Concentration
2 Hours After Admin. (μg/mL) |
Area Under the Curve (AUC(0-8 ))
(μg•h/mL) |
| 200 mg single dose |
1.5 |
14.1 |
| 300 mg single dose |
2.4 |
21.2 |
| 400 mg single dose |
2.9 |
31.4 |
| 400 mg steady-state |
4.6 |
61.0 |
Steady-state concentrations were attained after four oral doses, and the area
under the curve (AUC) was approximately 40% higher than the AUC after single
doses. Therefore, after multiple-dose administration of 200 mg and 300 mg doses,
peak serum levels of 2.2 μg/mL and 3.6 μg/mL, respectively, are predicted
at steady-state.
In vitro, approximately 32% of the drug in plasma is protein bound.
The single dose and steady-state plasma profiles of ofloxacin injection were
comparable in extent of exposure (AUC) to those of ofloxacin tablets when the
injectable and tablet formulations of ofloxacin were administered in equal doses
(mg/mg) to the same group of subjects. The mean steady-state AUC(0-12)
attained after the intravenous administration of 400 mg over 60 min was 43.5
μg•h/mL; the mean steady-state AUC(0-12) attained after the
oral administration of 400 mg was 41.2 μg•h/mL (two one-sided t-test,
90% confidence interval was 103-109). (See following chart.)
Between 0 and 6 h following the administration of a single 200 mg oral dose
of ofloxacin to 12 healthy volunteers, the average urine ofloxacin concentration
was approximately 220 μg/mL. Between 12 and 24 hours after administration,
the average urine ofloxacin level was approximately 34 μg/mL.
Following oral administration of recommended therapeutic doses, ofloxacin has
been detected in blister fluid, cervix, lung tissue, ovary, prostatic fluid,
prostatic tissue, skin, and sputum. The mean concentration of ofloxacin in each
of these various body fluids and tissues after one or more doses was 0.8 to
1.5 times the concurrent plasma level. Inadequate data are presently available
on the distribution or levels of ofloxacin in the cerebrospinal fluid or brain
tissue.
Ofloxacin has a pyridobenzoxazine ring that appears to decrease the extent
of parent compound metabolism. Between 65% and 80% of an administered oral dose
of ofloxacin is excreted unchanged via the kidneys within 48 hours of dosing.
Studies indicate that less than 5% of an administered dose is recovered in the
urine as the desmethyl or N-oxide metabolites. Four to eight percent of an ofloxacin
dose is excreted in the feces. This indicates a small degree of biliary excretion
of ofloxacin.
The administration of FLOXIN® with food does not affect the Cmax and AUC∞
of the drug, but Tmax is prolonged.
Clearance of ofloxacin is reduced in patients with impaired renal function
(creatinine clearance rate ≤ 50 mL/min), and dosage adjustment is necessary.
(See PRECAUTIONS: General and DOSAGE
AND ADMINISTRATION.)
Following oral administration to healthy elderly subjects (65-81 years of age),
maximum plasma concentrations are usually achieved one to two hours after single
and multiple twice-daily doses, indicating that the rate of oral absorption
is unaffected by age or gender. Mean peak plasma concentrations in elderly subjects
were 9-21% higher than those observed in younger subjects. Gender differences
in the pharmacokinetic properties of elderly subjects have been observed. Peak
plasma concentrations were 114% and 54% higher in elderly females compared to
elderly males following single and multiple twice-daily doses. [This interpretation
was based on study results collected from two separate studies.] Plasma concentrations
increase dose-dependently with the increase in doses after single oral dose
and at steady state. No differences were observed in the volume of distribution
values between elderly and younger subjects. As in younger subjects, elimination
is mainly by renal excretion as unchanged drug in elderly subjects, although
less drug is recovered from renal excretion in elderly subjects. Consistent
with younger subjects, less than 5% of an administered dose was recovered in
the urine as the desmethyl and N-oxide metabolites in the elderly. A longer
plasma half-life of approximately 6.4 to 7.4 hours was observed in elderly subjects,
compared with 4 to 5 hours for young subjects. Slower elimination of ofloxacin
is observed in elderly subjects as compared with younger subjects which may
be attributable to the reduced renal function and renal clearance observed in
the elderly subjects. Because ofloxacin is known to be substantially excreted
by the kidney, and elderly patients are more likely to have decreased renal
function, dosage adjustment is necessary for elderly patients with impaired
renal function as recommended for all patients. (See PRECAUTIONS:
General and DOSAGE AND ADMINISTRATION.)
Microbiology
Ofloxacin is a quinolone antimicrobial agent. The mechanism of action of ofloxacin
and other fluoroquinolone antimicrobials involves inhibition of bacterial topoisomerase
IV and DNA gyrase (both of which are type II topoisomerases), enzymes required
for DNA replication, transcription, repair and recombination.
Ofloxacin has in vitro activity against a wide range of gram-negative
and gram-positive microorganisms. Ofloxacin is often bactericidal at concentrations
equal to or slightly greater than inhibitory concentrations.
Fluoroquinolones, including ofloxacin, differ in chemical structure and mode
of action from aminoglycosides, macrolides and β-lactam antibiotics, including
penicillins. Fluoroquinolones may, therefore, be active against bacteria resistant
to these antimicrobials.
Resistance to ofloxacin due to spontaneous mutation in vitro is a rare
occurrence (range: 10-9 to 10-11). Although cross-resistance
has been observed between ofloxacin and some other fluoroquinolones, some microorganisms
resistant to other fluoroquinolones may be susceptible to ofloxacin.
Ofloxacin 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
Staphylococcus aureus (methicillin-susceptible strains)
Streptococcus pneumoniae (penicillin-susceptible strains)
Streptococcus pyogenes
Aerobic Gram-negative microorganisms
Citrobacter (diversus) koseri
Enterobacter aerogenes
Escherichia coli
Haemophilus influenzae
Klebsiella pneumoniae
Neisseria gonorrhoeae
Proteus mirabilis
Pseudomonas aeruginosa
As with other drugs in this class, some strains of Pseudomonas aeruginosa
may develop resistance fairly rapidly during treatment with ofloxacin.
Other microorganisms
Chlamydia trachomatis
The following in vitro data are available, but their clinical significance
is unknown.
Ofloxacin exhibits in vitro minimum inhibitory concentrations (MIC values)
of 2 μg/mL or less against most ( ≥ 90%) strains of the following microorganisms;
however, the safety and effectiveness of ofloxacin in treating clinical infections
due to these microorganisms have not been established in adequate and well-controlled
trials.
Aerobic Gram-positive microorganisms
Staphylococcus epidermidis (methicillin-susceptible strains)
Staphylococcus saprophyticus
Streptococcus pneumoniae (penicillin-resistant strains)
Aerobic Gram-negative microorganisms
Acinetobacter calcoaceticus
Bordetella pertussis
Citrobacter freundii
Enterobacter cloacae
Haemophilus ducreyi
Klebsiella oxytoca
Moraxella catarrhalis
Morganella morganii
Proteus vulgaris
Providencia rettgeri
Providencia stuartii
Serratia marcescens
Anaerobic microorganisms
Clostridium perfringes
Other microorganisms
Chlamydia pneumoniae
Gardnerella vaginalis
Legionella pneumophila
Mycoplasma hominis
Mycoplasma pneumoniae
Ureaplasma urealyticum
Ofloxacin is not active against Treponema pallidum (See WARNINGS.)
Many strains of other streptococcal species, Enterococcus species, and
anaerobes are resistant to ofloxacin.
Susceptibility Tests
Dilution Techniques:
Quantitative methods are used to determine antimicrobial minimum inhibitory
concentrations (MIC values). These MIC values provide estimates of the susceptibility
of bacteria to antimicrobial compounds. The MIC values should be determined
using a standardized procedure. Standardized procedures are based on a dilution
method1 (broth or agar) or equivalent with standardized inoculum
concentrations and standardized concentrations of ofloxacin powder. The MIC
values should be interpreted according to the following criteria:
For testing Enterobacteriaceae, methicillin-susceptible Staphylococcus
aureus, and Pseudomonas aeruginosa:
| MIC (μ g/mL) |
Interpretation |
| ≤ 2 |
Susceptible (S) |
| 4 |
Intermediate (I) |
| ≥ 8 |
Resistant (R) |
For testing Haemophilus influenzae:a
| MIC (μ g/mL) |
Interpretation |
| ≤ 2 |
Susceptible (S) |
| a This interpretive standard
is applicable only to broth microdilution susceptibility tests with Haemophilus
influenzae using Haemophilus Test Medium1 |
The current absence of data on resistant strains precludes defining any results
other than “Susceptible”. Strains yielding MIC results suggestive
of a “nonsusceptible” category should be submitted to a reference
laboratory for further testing.
For testing Neisseria gonorrhoeae:b
| MIC (μ g/mL) |
Interpretation |
| ≤ 0.25 |
Susceptible (S) |
| 0.5-1 |
Intermediate (I) |
| ≥ 2 |
Resistant (R) |
| b These interpretive standards
are applicable only to agar dilution tests using GC agar base and 1% defined
growth supplement incubated in 5% CO2. |
For testing Streptococcus pneumoniae and Streptococcus pyogenes:c
| MIC (μ g/mL) |
Interpretation |
| ≤ 2 |
Susceptible (S) |
| 4 |
Intermediate (I) |
| &ge8 |
Resistant (R) |
| c These interpretive standards
are applicable only to broth microdilution susceptibility tests using
cation-adjusted Mueller-Hinton broth with 2-5% lysed horse blood. |
A report of “Susceptible” indicates that the pathogen is likely to
be inhibited if the antimicrobial compound in the blood reaches the concentration
usually achievable. A report of "Intermediate" indicates that the result should
be considered equivocal, and, if the microorganism is not fully susceptible
to alternative, clinically feasible drugs, the test should be repeated. This
category implies possible clinical applicability in body sites where the drug
is physiologically concentrated or in situations where a high dosage of drug
can be used. This category also provides a buffer zone which prevents small
uncontrolled technical factors from causing major discrepancies in interpretation.
A report of "Resistant" indicates that the pathogen is not likely to be inhibited
if the antimicrobial compound in the blood reaches the concentration usually
achievable; other therapy should be selected.
Standardized susceptibility test procedures require the use of laboratory control
microorganisms to control the technical aspects of the laboratory procedures.
Standard ofloxacin powder should provide the following MIC values:
| Microorganism |
|
MIC Range (μ g/mL) |
| Escherichia coli |
ATCC 25922 |
0.015-0.12 |
| Haemophilus influenzae |
ATCC 49247d |
0.016-0.06 |
| Neisseria gonorrhoeae |
ATCC 49226e |
0.004-0.016 |
| Pseudomonas aeruginosa |
ATCC 27853 |
1-8 |
| Staphylococcus aureus |
ATCC 29213 |
0.12-1 |
| Streptococcus pneumoniae |
ATCC 49619f |
1-4 |
d This quality control range
is applicable to only H. influenzae ATCC 49247 tested by a microdilution
procedure using Haemophilus Test Medium (HTM)1.
e This quality control range is applicable only to N. gonorrhoeae
ATCC 49226 tested by an agar dilution procedure using GC agar base with
1% defined growth supplement incubated in 5% CO2.
f This quality control range is applicable to only S. pneumoniae
ATCC 49619 tested by a microdilution procedure using cation-adjusted Mueller-Hinton
broth with 2-5% lysed horse blood. |
Diffusion Techniques:
Quantitative methods that require measurement of zone diameters also provide
reproducible estimates of the susceptibility of bacteria to antimicrobial compounds.
One such standardized procedure2 requires the use of standardized
inoculum concentrations. This procedure uses paper disks impregnated with 5-μg
ofloxacin to test the susceptibility of microorganisms to ofloxacin.
Reports from the laboratory providing results of the standard single-disk susceptibility
test with a 5-μg ofloxacin disk should be interpreted according to the following
criteria:
For testing Enterobacteriaceae, methicillin-susceptible Staphylococcus
aureus, and Pseudomonas aeruginosa:
| Zone Diameter (mm) |
Interpretation |
| ≥ 16 |
Susceptible (S) |
| 13-15 |
Intermediate (I) |
| ≤ 12 |
Resistant (R) |
For testing Haemophilus influenzae:g
| Zone Diameter (mm) |
Interpretation |
| ≥ 16 |
Susceptible (S) |
| g This zone diameter standard
is applicable only to disk diffusion tests with Haemophilus influenzae
using Haemophilus Test Medium (HTM)2 incubated in
5% CO2. |
The current absence of data on resistant strains precludes defining any results
other than “Susceptible”. Strains yielding zone diameter results suggestive
of a “nonsusceptible” category should be submitted to a reference
laboratory for further testing.
For testing Neisseria gonorrhoeae:h
| Zone Diameter (mm) |
Interpretation |
| ≥ 31 |
Susceptible (S) |
| 25-30 |
Intermediate (I) |
| &le24 |
Resistant (R) |
| h These zone diameter standards
are applicable only to disk diffusion tests using GC agar base and 1%
defined growth supplement incubated in 5% CO2 |
For testing Streptococcus pneumoniae and Streptococcus pyogenes:i
| Zone Diameter (mm) |
Interpretation |
| ≥ 16 |
Susceptible (S) |
| 13-15 |
Intermediate (I) |
| ≤ 12 |
Resistant (R) |
| i These zone diameter standards
are applicable only to disk diffusion tests performed using Mueller-Hinton
agar supplemented with 5% defibrinated sheep blood and incubated in 5%
CO2. |
Interpretation should be as stated above for results using dilution techniques.
Interpretation involves correlation of the diameter obtained in the disk test
with the MIC for ofloxacin.
As with standardized dilution techniques, diffusion methods require the use
of laboratory control microorganisms that are used to control the technical
aspects of the laboratory procedures. For the diffusion technique, the 5-μg
ofloxacin disk should provide the following zone diameters in these laboratory
quality control strains:
| Microorganism |
|
Zone Diameter (mm) |
| Escherichia coli |
ATCC 25922 |
29-33 |
| Haemophilus influenzae |
ATCC 49247j |
31-40 |
| Neisseria gonorrhoeae |
ATCC 49226k |
43-51 |
| Pseudomonas aeruginosa |
ATCC 27853 |
17-21 |
| Staphylococcus aureus |
ATCC 25923 |
24-28 |
| Streptococcus pneumoniae |
ATCC 49619l |
16-21 |
j This quality control range
is applicable only to H. influenzae ATCC 49247 tested by a disk
diffusion procedure using Haemophilus Test Medium (HTM)2
incubated in 5% CO2.
k This quality control range is applicable only to N. gonorrhoeae
ATCC 49226 tested by a disk diffusion procedure using GC agar base with
1% defined growth supplement incubated in 5% CO2.
l This quality control range is applicable only to S. pneumoniae
ATCC 49619 tested by a disk diffusion procedure using Mueller-Hinton agar
supplemented with 5% defibrinated sheep blood and incubated in 5% CO2.
|
ANIMAL PHARMACOLOGY
Ofloxacin, as well as other drugs of the quinolone class, has been shown to
cause arthropathies (arthrosis) in immature dogs and rats. In addition, these
drugs are associated with an increased incidence of osteochondrosis in rats
as compared to the incidence observed in vehicle-treated rats. (See WARNINGS.)
There is no evidence of arthropathies in fully mature dogs at intravenous doses
up to 3 times the recommended maximum human dose (on a mg/m² basis or 5
times based on mg/kg basis), for a one-week exposure period.
Long-term, high-dose systemic use of other quinolones in experimental animals
has caused lenticular opacities; however, this finding was not observed in any
animal studies with ofloxacin.
Reduced serum globulin and protein levels were observed in animals treated
with other quinolones. In one ofloxacin study, minor decreases in serum globulin
and protein levels were noted in female cynomolgus monkeys dosed orally with
40 mg/kg ofloxacin daily for one year. These changes, however, were considered
to be within normal limits for monkeys.
Crystalluria and ocular toxicity were not observed in any animals treated with
ofloxacin.
REFERENCES
1.National Committee for Clinical Laboratory Standards.
Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow
Aerobically - Fourth Edition. Approved Standard NCCLS Document M7-A4, Vol. 17,
No. 2, NCCLS, Wayne, PA, January, 1997.
2.National Committee for Clinical Laboratory Standards.
Performance Standards for Antimicrobial Disk Susceptibility Tests - Sixth Edition.
Approved Standard NCCLS Document M2-A6, Vol. 17, No. 1, NCCLS, Wayne, PA, January
1997.
Last updated on RxList: 1/3/2008