Clinical Pharmacology for Ocuflox
Mechanism Of Action
The primary mechanism of action of ofloxacin appears to be the specific inhibition of DNA gyrase (topoisomerase II). This enzyme is responsible for the negative supercoiling of bacterial DNA and OCUFLOX (ofloxacin) consequently for its topological configuration, governing functions such as RNA transcription, protein synthesis, DNA replication and repair functions.
Pharmacodynamics
The general pharmacological activities of ofloxacin have been studied in several mammalian species. At the maximum therapeutic dose levels, no effects on the central nervous system, cardiovascular and respiratory system, autonomic response or smooth and skeletal muscle were observed. These results are consistent with the infrequent occurrence of serious adverse effects with systemic clinical use of ofloxacin. Any pharmacological effects observed were frequently associated with doses at least 1000 times the anticipated maximal daily ocular dose.
Pharmacokinetics
Human
Systemic Pharmacokinetics
Absorption
In systemic pharmacokinetic studies following oral dosing, ofloxacin was rapidly absorbed into the blood stream, with peak serum concentrations (Cmax) increasing in a dose-related manner. There was no significant increase in peak serum ofloxacin concentration following multiple oral administrations.
Following administration of 0.3% ofloxacin topically 4 times daily to the eyes of 30 normal healthy adults, mean serum plateau levels of 0.97 ng/mL after the first dose (day 1) and 1.66 ng/mL after the 41st dose (day 11) were achieved. The maximum serum level from multiple topical dosing (1.9 ng/mL) was approximately 2000-fold less than the maximum serum level achieved from treatment with a single 300 mg oral dose (4620 ng/mL). Time to reach 90% of the plateau serum concentration was 0.9 hours after the initial dose on Day 1 compared with 0.5 hours on Day 11, indicating a change in the rate of systemic absorption from ophthalmic dosing.
Metabolism And Elimination
The metabolism of ofloxacin was studied in five healthy adult male volunteers receiving a single oral dose of a 600 mg mixture of ofloxacin and deuterium-labeled ofloxacin. Ofloxacin and its metabolites were identified, confirmed and quantified using thin layer chromatography, UV spectrophotometry, high pressure liquid chromatography, fluorometry and other methods. Urinary concentration of ofloxacin increased to a maximum of 686.6 mcg/mL at 2-4 hours after dosing and was maintained above 273.9 mcg/mL 4-24 hours after dosing.
Cumulative urinary excretion of ofloxacin was 79.5% at 48 hours after dosing. Urinary concentrations of desmethyl ofloxacin were 10.4 and 6.6 mcg/mL at 2-4 and 12-24 hours after dosing, concentrations of ofloxacin N-oxide were 7.8 and 2.7 mcg/mL at 2-4 and 12-24 hours after dosing. Urinary concentrations of these metabolites were less than 2.5% of the excreted concentration of ofloxacin at each time interval.
The results of this study indicate that ofloxacin exists mainly as parent drug in vivo, and is excreted mainly unchanged in the urine in humans.
Ocular Pharmacokinetics
Absorption
Administering 0.3% ofloxacin topically 4 times daily to the eyes of 30 normal healthy adults resulted in tear ofloxacin concentrations ranging from 1.2 to 22 mcg/g (mean 9.2 mcg/g) four hours after the first dose on the eleventh day of treatment. The mean tear concentration varied between 5.7 and 31 mcg/g during the time period between 5 and 40 minutes after instillation of the second dose on day 11.
Storage, Stability And Disposal
OCUFLOX is sterile in the unopened package, and is stable for 24 months when stored at 15 to 25°C. Keep bottle tightly closed when not in use.
Keep out of reach and sight of children.
Special Handling Instructions
There are no special handling instructions.
PrOCUFLOX®
Ofloxacin ophthalmic solution  Solution, 0.3% w/v, for ophthalmic use  USP
Antibacterial Agent (ATC code: S01AE01)
Clinical Trials
Clinical Trials by Indication
No clinical trial information is available for this product.
Microbiology
Ofloxacin has in vitro activity against both gram-positive and gram-negative organisms. The primary mechanism of action of ofloxacin appears to be the specific inhibition of DNA gyrase (topoisomerase II). This enzyme is responsible for the negative supercoiling of bacterial DNA and consequently for its topological configuration, governing functions such as RNA transcription, protein synthesis, DNA replication and repair functions.
In a four-site study using a modified tube-dilution procedure, the in vitro activity of ofloxacin was evaluated against 419 ocular bacterial isolates of 55 species, in media supplemented with Ca++ and Mg++. Table 2 includes MIC values for five major ocular pathogens.
Table 2 : In Vitro Antibacterial Activity of Ofloxacin Against Five Major Ocular Pathogens in Studies Conducted in the USA
| Minimum Inhibitory Concentration Range (mcg /mL) |
| ORGANISMS (Number) |
MINIMUM |
MAXIMUM |
MIC90 |
| Staphylococcus aureus (79)1 |
0.125 |
4 |
0.5 |
| Staphylococcus epidermidis (68) |
0.125 |
16 |
0.5 |
| Pseudomonas aeruginosa (68) |
0.25 |
8 |
4 |
| Streptococcus pneumoniae (21) |
0.125 |
2 |
2 |
| Haemophilus influenzae (18) |
0.25 |
4 |
4 |
| 1 Number of isolates in parentheses. |
In Vitro Study Of Ocular Isolates From Japanese Clinical Studies
An in vitro evaluation of the activity (MIC) of ofloxacin was conducted using a broth dilution technique, with 2,678 organisms cultured from the infected eyes of subjects enrolled in three clinical trials conducted in the clinics of public hospitals in Japan. The minimum concentrations necessary to inhibit 90% of the strains (MIC90) was 3.13 mcg/mL or less for all species tested except various Pseudomonas species and for Streptococcus sanguis isolates. MIC90 values for ocular isolates are listed in Table 3.
Table 3 : Ocular Isolates from Japanese Clinical Studies (Ofloxacin MIC90 Values)
| Bacterial species |
N |
MIC90 (mcg/mL) |
| Acinetobacter var. anitratum |
44 |
0.39 |
| Acinetobacter var. lwoffii |
33 |
0.39 |
| Alcaligenes denitrificans |
10 |
1.56 |
| Alcaligenes faecalis |
24 |
0.78 |
| Bacillus species |
111 |
0.20 |
| Corynebacterium species |
379 |
3.13 |
| Enterobacter species (3: cloacae, aerogenes and agglomerans) |
44 |
0.20 |
| Escherichia coli |
8 |
0.10 |
| Flavobacterium species |
22 |
3.13 |
| Haemophilus aegyptius |
59 |
0.20 |
| Haemophilus influenzae |
44 |
0.20 |
| Klebsiella species (3: oxytoca, pneumoniae and ozaenae) |
21 |
0.10 |
| Micrococcus species |
73 |
1.56 |
| Moraxella species |
25 |
0.20 |
| Propionibacterium acnes |
66 |
1.56 |
| Proteus species (5: including mirabilis, vulgaris and morganii) |
30 |
0.20 |
| Pseudomonas acidovorans |
21 |
1.56 |
| Pseudomonas aeruginosa |
11 |
1.56 |
| Pseudomonas alcaligenes |
32 |
3.13 |
| Pseudomonas cepacia |
75 |
1.56 |
| Pseudomonas fluorescens |
44 |
0.78 |
| Pseudomonas maltophilia |
36 |
3.13 |
| Pseudomonas paucimobilis |
31 |
0.39 |
| Pseudomonas putida |
29 |
0.78 |
| Pseudomonas species (6: including vescularis and diminuta) |
16 |
50.5 |
| Pseudomonas stutzeri |
20 |
0.78 |
| Serratia marcescens |
46 |
0.39 |
| Staphylococcus aureus |
335 |
0.39 |
| Staphylococcus epidermidis |
735 |
0.39 |
| Streptococcus beta-hemolytic |
17 |
1.56 |
| Streptococcus faecalis (Enterococcus faecalis) |
14 |
1.56 |
| Streptococcus pneumoniae |
101 |
3.13 |
| Streptococcus sanguis |
96 |
6.25 |
| Streptococcus species (inc. pyogenes) |
35 |
3.13 |
Ofloxacin is bactericidal (3 log reduction in 1-2 hours) at 1 to 4 times the MIC.
Susceptibility Testing
Laboratory results from standard single disc susceptibility tests with a 5 mcg ofloxacin disc should be interpreted according to the following criteria:
| Zone Diameter (mm) |
Interpretation |
| ≥ 16 |
Susceptible |
| 13-15 |
Moderately susceptible |
| ≤ 12 |
Resistant |
Bacterial Resistance
The development of resistance to ofloxacin appears to be related to modification of bacterial DNA gyrase or to permeability changes in the bacterial outer cell membrane. Resistance to ofloxacin in vitro usually develops slowly (multiple-step mutation). Plasmid-mediated resistance or enzymatic inactivation have not been reported. Cross resistance among the fluoroquinolones has been observed, but development of clinically significant cross resistance to nonquinolone drugs appears to be uncommon.
Non-Clinical Toxicology
General Toxicology
Ofloxacin was administered in repeated doses in rats, dogs and monkeys for periods of up to 52 weeks. The most notable effect seen in these studies was the effect of ofloxacin on articular cartilage in immature animals. Several special studies of the effects of ofloxacin on articular cartilage were conducted. Orally administered ofloxacin had no effect on articular cartilage in mature rats and dogs. However, in immature animals, daily treatment for 7 days with ofloxacin at 300 mg/kg (but not at 100 mg/kg) in rats and at 10 mg/kg (but not at 5 mg/kg) in dogs produced arthropathic effects.
Studies were conducted to elucidate the mechanism of action, onset, recovery and effects of age and dosage on arthropathy associated with ofloxacin and other quinolones. The studies indicate that toxicity to weight-bearing joints is dose-related at oral dosages far higher than topical ophthalmic dosages and that toxic effects are seen only in growing animals. Damage to joints was partially repairable, although some damage appeared to be permanent. Damage such as erosion of the cartilage occurs in weight-bearing joints where “bubbles” (inconsistencies in growth) have developed in the cartilage.
Carcinogenicity
Because ophthalmic ofloxacin solution is not intended for chronic use, specific carcinogenicity studies were not carried out. Chronic ophthalmic toxicity studies showed no evidence of carcinogenic potential.
Genotoxicity
Predictive tests included: Ames test, REC-Assay, micronucleus test, sister chromatid exchange in cultured Chinese hamster cells and in human peripheral blood lymphocytes, unscheduled DNA repair synthesis test, dominant lethal assay, and in vitro and in vivo cytogenetic tests.
Extensive tests for mutagenicity showed no mutagenic potential. Mutagenicity tests were conducted with ofloxacin by a number of techniques, both in vitro and in vivo. Dose-related damage to the DNA of Bacillus subtilis was seen in tests using the REC assay technique. The damage to B. subtilis DNA is consistent with the mechanism of action of the drug in bacteria and is not predictive of mutagenic potential in eukaryotic cells. No evidence of significant mutagenic effects was seen in other tests in a variety of eukaryotic somatic or germ cells.
Human blood samples were examined after oral dosing with 200 mg/day of ofloxacin for 1 to 10 weeks (equivalent to 50 times the maximum recommended daily ophthalmic dose). No chromosome-damaging effect was seen in the peripheral blood leukocytes.
Reproductive And Developmental Toxicology
The effects of ofloxacin on fertility, reproduction and fetal toxicity were studied in rats and rabbits. No adverse effects on fertility and general reproductive performance were seen in male or female rats from administration of ofloxacin in dosages of 10 mg/kg/day to 360 mg/kg/day, beginning well before mating and continuing through the seventh day of gestation in females.
Ofloxacin has not been shown to be teratogenic at doses as high as 810 mg/kg/day (equivalent to 13500 times the maximum recommended daily ophthalmic dose) and 160 mg/kg/day (equivalent to 2600 times the daily ophthalmic dose) when administered to pregnant rats and rabbits, respectively. Additional studies in rats with doses up to 360 mg/kg/day during late gestation showed no adverse effect on late fetal development, labor, delivery, lactation, neonatal viability, or growth of the newborn. Doses of 810 mg/kg/day and 160 mg/kg/day resulted in decreased fetal body weight and increased fetal mortality in rats and rabbits, respectively. Minor fetal skeletal variations were reported in rats receiving doses of 810 mg/kg/day.
Special Toxicity Studies
Ocular Toxicity
Ocular toxicity studies were conducted in rabbits and monkeys with ofloxacin ophthalmic solutions. Results indicate that ofloxacin ophthalmic solutions are not toxic to the eyes under the conditions tested, including dosing up to 16 times per day. No local or systemic toxicity was observed as a result of ocular administration of ofloxacin for up to six months in rabbits or monkeys.
Other Special Toxicity Studies
No evidence of ototoxicity, antigenicity or skin sensitization was seen in guinea pigs. Studies in rabbits revealed no evidence of nephrotoxicity.
Special Studies Of Tissue Distribution And Accumulation
Special studies of tissue distribution and accumulation, with special reference to the eye tissues, were conducted due to the tendency of ofloxacin to bind to the pigment melanin, which is present in some ocular structures. Studies with the topical solution showed definite binding to melanin which decreased slowly after withdrawal of the drug. In vitro studies with bovine melanin showed the affinity of ofloxacin for melanin to be greater than that of timolol and pilocarpine, but less than that of chloroquine and befunolol. The binding was reversible. A four-week study in pigmented rats revealed no evidence of ocular toxicity after daily oral doses of 100 mg/kg/day. Results of this study were consistent with the lack of ocular toxicity seen in multi-dose ocular and systemic toxicity studies in dogs and monkeys.