Levofloxacin: Package Insert and Label Information (Page 6 of 9)

12.4 Microbiology

Mechanism of Action
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 inhibition of bacterial topoisomerase IV and DNA gyrase (both of which are type II topoisomerases), enzymes required for DNA replication, transcription, repair and recombination.
Resistance
Fluoroquinolone resistance can arise through mutations in defined regions of DNA gyrase or topoisomerase IV, termed the Quinolone-Resistance Determining Regions (QRDRs), or through altered efflux.
Fluoroquinolones, including levofloxacin, 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 levofloxacin due to spontaneous mutation in vitro is a rare occurrence (range: 10-9 to 10-10). Cross-resistance has been observed between levofloxacin and some other fluoroquinolones, some microorganisms resistant to other fluoroquinolones may be susceptible to levofloxacin.
Antimicrobial Activity
Levofloxacin has in vitro activity against Gram-negative and Gram-positive bacteria.
Levofloxacin has been shown to be active against most isolates of the following bacteria both in vitro and in clinical infections as described in Indications and Usage (1):
Aerobic bacteria
Gram-Positive Bacteria
Enterococcus faecalis
Staphylococcus aureus (methicillin-susceptible isolates)
Staphylococcus epidermidis (methicillin-susceptible isolates)
Staphylococcus saprophyticus
Streptococcus pneumoniae (including multi-drug resistant isolates [MDRSP]1)
Streptococcus pyogenes
Gram-Negative Bacteria
Enterobacter cloacae
Escherichia coli
Haemophilus influenzae
Haemophilus parainfluenzae
Klebsiella pneumoniae
Legionella pneumophila
Moraxella catarrhalis
Proteus mirabilis
1 MDRSP (Multi-drug resistant Streptococcus pneumoniae) isolates are isolates resistant to two or more of the following antibiotics: penicillin (MIC ≥2 mcg/mL), 2nd generation cephalosporins, e.g., cefuroxime; macrolides, tetracyclines and trimethoprim/sulfamethoxazole.
Pseudomonas aeruginosa
Serratia marcescens
Other microorganisms
Chlamydophila pneumoniae
Mycoplasma pneumoniae
The following in vitro data are available, but their clinical significance is unknown: Levofloxacin exhibits in vitro minimum inhibitory concentrations (MIC values) of 2 mcg/mL or less against most (≥90%) isolates of the following microorganisms; however, the safety and effectiveness of levofloxacin in treating clinical infections due to these bacteria have not been established in adequate and well-controlled clinical trials.
Aerobic bacteria
Gram-Positive Bacteria
Staphylococcus haemolyticus
β-hemolytic Streptococcus (Group C/F)
β-hemolytic Streptococcus (Group G)
Streptococcus agalactiae
Streptococcus milleri
Viridans group streptococci
Bacillus anthracis
Gram-Negative Bacteria
Acinetobacter baumannii
Acinetobacter lwoffii
Bordetella pertussis
Citrobacter koseri
Citrobacter freundii
Enterobacter aerogenes
Enterobacter sakazakii
Klebsiella oxytoca
Morganella morganii
Pantoea agglomerans
Proteus vulgaris
Providencia rettgeri
Providencia stuartii
Pseudomonas fluorescens
Yersinia pestis
Anaerobic bacteria
Gram-Positive Bacteria
Clostridium perfringens
Susceptibility Tests
For specific information regarding susceptibility test interpretive criteria and associated test methods and quality control standards recognized by FDA for this drug, please see: https://www.fda.gov/STIC.

13 NONCLINICAL TOXICOLOGY

13.1 Carcinogenesis & Mutagenesis & Impairment Of Fertility

In a lifetime bioassay in rats, levofloxacin exhibited no carcinogenic potential following daily dietary administration for 2 years; the highest dose (100 mg/kg/day) was 1.4 times the highest recommended human dose (750 mg) based upon relative body surface area. Levofloxacin did not shorten the time to tumor development of UV-induced skin tumors in hairless albino (Skh-1) mice at any levofloxacin dose level and was therefore not photo-carcinogenic under conditions of this study. Dermal levofloxacin concentrations in the hairless mice ranged from 25 to 42 mcg/g at the highest levofloxacin dose level (300 mg/kg/day) used in the photo-carcinogenicity study. By comparison, dermal levofloxacin concentrations in human subjects receiving 750 mg of levofloxacin averaged approximately 11.8 mcg/g at Cmax .
Levofloxacin was not mutagenic in the following assays: Ames bacterial mutation assay (S. typhimurium and E. coli), CHO/HGPRT forward mutation assay, mouse micronucleus test, mouse dominant lethal test, rat unscheduled DNA synthesis assay, and the mouse sister chromatid exchange assay. It was positive in the in vitro chromosomal aberration (CHL cell line) and sister chromatid exchange (CHL/IU cell line) assays.
Levofloxacin caused no impairment of fertility or reproductive performance in rats at oral doses as high as 360 mg/kg/day, corresponding to 4.2 times the highest recommended human dose based upon relative body surface area and intravenous doses as high as 100 mg/kg/day, corresponding to 1.2 times the highest recommended human dose based upon relative body surface area.

13.2 Animal Pharmacology & OR Toxicology

Levofloxacin and other quinolones have been shown to cause arthropathy in immature animals of most species tested [see Warnings and Precautions (5.12)]. In immature dogs (4 to 5 months old), oral doses of 10 mg/kg/day for 7 days and intravenous doses of 4 mg/kg/day for 14 days of levofloxacin resulted in arthropathic lesions. Administration at oral doses of 300 mg/kg/day for 7 days and intravenous doses of 60 mg/kg/day for 4 weeks produced arthropathy in juvenile rats. Three-month old beagle dogs dosed orally with levofloxacin at 40 mg/kg/day exhibited clinically severe arthrotoxicity resulting in the termination of dosing at Day 8 of a 14-day dosing routine. Slight musculoskeletal clinical effects, in the absence of gross pathological or histopathological effects, resulted from the lowest dose level of 2.5 mg/kg/day (approximately 0.2-fold the pediatric dose based upon AUC comparisons). Synovitis and articular cartilage lesions were observed at the 10 and 40 mg/kg dose levels (approximately 0.7-fold and 2.4-fold the pediatric dose, respectively, based on AUC comparisons). Articular cartilage gross pathology and histopathology persisted to the end of the 18-week recovery period for those dogs from the 10 and 40 mg/kg/day dose levels.
When tested in a mouse ear swelling bioassay, levofloxacin exhibited phototoxicity similar in magnitude to ofloxacin, but less phototoxicity than other quinolones.
While crystalluria has been observed in some intravenous rat studies, urinary crystals are not formed in the bladder, being present only after micturition and are not associated with nephrotoxicity.
In mice, the CNS stimulatory effect of quinolones is enhanced by concomitant administration of non-steroidal anti-inflammatory drugs.
In dogs, levofloxacin administered at 6 mg/kg or higher by rapid intravenous injection produced hypotensive effects. These effects were considered to be related to histamine release.
In vitro and in vivo studies in animals indicate that levofloxacin is neither an enzyme inducer nor inhibitor in the human therapeutic plasma concentration range; therefore, no drug metabolizing enzyme-related interactions with other drugs or agents are anticipated.

14 CLINICAL STUDIES

14.1 Nosocomial Pneumonia

Adult patients with clinically and radiologically documented nosocomial pneumonia were enrolled in a multicenter, randomized, open-label study comparing intravenous levofloxacin (750 mg once daily) followed by oral levofloxacin (750 mg once daily) for a total of 7 to 15 days to intravenous imipenem/cilastatin (500 to 1000 mg every 6 to 8 hours daily) followed by oral ciprofloxacin (750 mg every 12 hours daily) for a total of 7 to 15 days. Levofloxacin-treated patients received an average of 7 days of intravenous therapy (range: 1 to 16 days); comparator-treated patients received an average of 8 days of intravenous therapy (range: 1 to 19 days).
Overall, in the clinically and microbiologically evaluable population, adjunctive therapy was empirically initiated at study entry in 56 of 93 (60.2%) patients in the levofloxacin arm and 53 of 94 (56.4%) patients in the comparator arm. The average duration of adjunctive therapy was 7 days in the levofloxacin arm and 7 days in the comparator. In clinically and microbiologically evaluable patients with documented Pseudomonas aeruginosa infection , 15 of 17 (88.2%) received ceftazidime (N = 11) or piperacillin/tazobactam (N = 4) in the levofloxacin arm and 16 of 17 (94.1%) received an aminoglycoside in the comparator arm. Overall, in clinically and microbiologically evaluable patients, vancomycin was added to the treatment regimen of 37 of 93 (39.8%) patients in the levofloxacin arm and 28 of 94 (29.8%) patients in the comparator arm for suspected methicillin-resistant S. aureus infection.
Clinical success rates in clinically and microbiologically evaluable patients at the post-therapy visit (primary study endpoint assessed on day 3 to 15 after completing therapy) were 58.1% for levofloxacin and 60.6% for comparator. The 95% CI for the difference of response rates (levofloxacin minus comparator) was [-17.2, 12]. The microbiological eradication rates at the posttherapy visit were 66.7% for levofloxacin and 60.6% for comparator. The 95% CI for the difference of eradication rates (levofloxacin minus comparator) was [-8.3, 20.3]. Clinical success and microbiological eradication rates by pathogen are detailed in Table 9. Table 9: Clinical Success Rates and Bacteriological Eradication Rates (Nosocomial Pneumonia)

Pathogen

N

Levofloxacin No. (%) of Patients Microbiologic/ Clinical Outcomes

N

Imipenem/Cilastatin No. (%) of Patients Microbiologic/ Clinical Outcomes

MSSA*

21

14 (66.7)/13 (61.9)

19

13 (68.4)/15 (78.9)

P. aeruginosa

17

10 (58.8)/11 (64.7)

17

5 (29.4)/7 (41.2)

S. marcescens

11

9 (81.8)/7 (63.6)

7

2 (28.6)/3 (42.9)

E. coli

12

10 (83.3)/7 (58.3)

11

7 (63.6 )/8 (72.7)

K. pneumoniae

11

9 (81.8)/5 (45.5)

7

6 (85.7)/3 (42.9)

H. influenzae

16

13 (81.3)/10 (62.5)

15

14 (93.3)/11 (73.3)

S. pneumoniae

4

3 (75)/3 (75)

7

5 (71.4)/4 (57.1)

* Methicillin-susceptible S. aureus
See above text for use of combination therapy
The observed differences in rates for the clinical and microbiological outcomes may reflect other factors that were not accounted for in the study

14.2 Community-Acquired Pneumonia: 7 to 14 day Treatment Regimen

Adult inpatients and outpatients with a diagnosis of community-acquired bacterial pneumonia were evaluated in 2 pivotal clinical studies. In the first study, 590 patients were enrolled in a prospective, multi-center, unblinded randomized trial comparing levofloxacin 500 mg once daily orally or intravenously for 7 to 14 days to ceftriaxone 1 to 2 grams intravenously once or in equally divided doses twice daily followed by cefuroxime axetil 500 mg orally twice daily for a total of 7 to 14 days. Patients assigned to treatment with the control regimen were allowed to receive erythromycin (or doxycycline if intolerant of erythromycin) if an infection due to atypical pathogens was suspected or proven. Clinical and microbiologic evaluations were performed during treatment, 5 to 7 days posttherapy, and 3 to 4 weeks posttherapy. Clinical success (cure plus improvement) with levofloxacin at 5 to 7 days posttherapy, the primary efficacy variable in this study, was superior (95%) to the control group (83%). The 95% CI for the difference of response rates (levofloxacin minus comparator) was [-6, 19]. In the second study, 264 patients were enrolled in a prospective, multi-center, non-comparative trial of 500 mg levofloxacin administered orally or intravenously once daily for 7 to 14 days. Clinical success for clinically evaluable patients was 93%. For both studies, the clinical success rate in patients with atypical pneumonia due to Chlamydophila pneumoniae, Mycoplasma pneumoniae, and Legionella pneumophila were 96%, 96%, and 70%, respectively. Microbiologic eradication rates across both studies are presented in Table 11.Table 11: Bacteriological Eradication Rates Across 2 Community Acquired Pneumonia Clinical Studies

Pathogen

No. Pathogens

Bacteriological Eradication Rate (%)

H. influenzae

55

98

S. pneumoniae

83

95

S. aureus

17

88

M. catarrhalis

18

94

H. parainfluenzae

19

95

K. pneumoniae

10

100

Community-Acquired Pneumonia Due to Multi-Drug Resistant Streptococcus pneumoniae
Levofloxacin was effective for the treatment of community-acquired pneumonia caused by multi-drug resistant Streptococcus pneumoniae (MDRSP). MDRSP isolates are isolates resistant to two or more of the following antibacterials: penicillin (MIC ≥2 mcg/mL), 2nd generation cephalosporins (e.g., cefuroxime, macrolides, tetracyclines and trimethoprim/sulfamethoxazole). Of 40 microbiologically evaluable patients with MDRSP isolates, 38 patients (95%) achieved clinical and bacteriologic success at post-therapy. The clinical and bacterial success rates are shown in Table 12.Table 12: Clinical and Bacterial Success Rates for Levofloxacin-Treated MDRSP in Community Acquired Pneumonia Patients (Population Valid for Efficacy)

Screening Susceptibility

Clinical Success

Bacteriological Success*

n/N

%

n/N

%

Penicillin-resistant

16/17

94.1

16/17

94.1

2nd generation Cephalosporin resistant

31/32

96.9

31/32

96.9

Macrolide-resistant

28/29

96.6

28/29

96.6

Trimethoprim/Sulfamethoxazole resistant

17/19

89.5

17/19

89.5

Tetracycline-resistant

12/12

100

12/12

100

* One patient had a respiratory isolate that was resistant to tetracycline, cefuroxime, macrolides and TMP/SMX and intermediate to penicillin and a blood isolate that was intermediate to penicillin and cefuroxime and resistant to the other classes. The patient is included in the database based on respiratory isolate.
n= the number of microbiologically evaluable patients who were clinical successes; N= number of microbiologically evaluable patients in the designated resistance group.
n= the number of MDRSP isolates eradicated or presumed eradicated in microbiologically evaluable patients; N= number of MDRSP isolates in a designated resistance group.
Not all isolates were resistant to all antimicrobial classes tested. Success and eradication rates are summarized in Table 13. Table 13: Clinical Success and Bacteriologic Eradication Rates for Resistant Streptococcus pneumoniae (Community Acquired Pneumonia)

Type of Resistance

Clinical Success

Bacteriologic Eradication

Resistant to 2 antibacterials

17/18 (94.4%)

17/18 (94.4%)

Resistant to 3 antibacterials

14/15 (93.3%)

14/15 (93.3%)

Resistant to 4 antibacterials

7/7 (100%)

7/7 (100%)

Resistant to 5 antibacterials

0

0

Bacteremia with MDRSP

8/9 (89%)

8/9 (89%)

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