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Penetrex

Discontinued Warning IconPlease Note: This Brand Name drug is no longer available in the US.
(Generic versions may still be available.)

CLINICAL PHARMACOLOGY

Following oral administration to healthy subjects, peak plasma enoxacin concentrations were achieved within 1 to 3 hours. Absolute oral bioavailability of enoxacin is approximately 90%. Maximum plasma concentrations of enoxacin average 0.93 µg/mL and 2.0 µg/mL after single 200 mg and 400 mg doses, respectively. Enoxacin plasma half-life is 3 to 6 hours. Enoxacin is excreted primarily via the kidney. After a single dose, greater than 40% was recovered in urine by 48 hours as unchanged drug. In elderly patients, the mean peak enoxacin plasma concentration was 50% higher than that in young adult volunteers receiving comparable single doses of enoxacin. This appears to correspond to age-associated reduction of renal function in the elderly population. Five metabolites of enoxacin have been identified in human urine and account for 15% to 20% of the administered dose.

Enoxacin diffuses into cervix, fallopian tube, and myometrium at levels approximately 1-2 times those achieved in plasma, and into kidney and prostate at levels approximately 2-4 times those achieved in plasma. Studies have not been conducted to assess the penetration of enoxacin into human cerebrospinal fluid.

Enoxacin is approximately 40% bound to plasma proteins in healthy subjects and is approximately 14% bound to plasma proteins in patients with impaired renal function.

The effect of food on the absorption of enoxacin from the tablet formulation has not been studied.

Some isozymes of the cytochrome P-450 hepatic microsomal enzyme system are inhibited by enoxacin. This inhibition results in significant drug/drug interactions with theophylline and caffeine. Enoxacin interferes with the metabolism of theophylline, resulting in a dose-related decrease in theophylline clearance. Elevated serum theophylline concentrations may increase the risk of theophylline-related adverse reactions. (See PRECAUTIONS : Drug Interactions . )

Clearance of enoxacin is reduced in patients with impaired renal function (creatinine clearance ≤30 mL/min/1.73 m 2 ), and dosage adjustment is necessary. (See DOSAGE AND ADMINISTRATION.)

MICROBIOLOGY

Enoxacin is an inhibitor of the bacterial enzyme DNA gyrase and is a bactericidal agent. Enoxacin may be active against pathogens resistant to drugs that act by different mechanisms.

Enoxacin has been shown to be active against most strains of the following organisms both in vitro and in clinical infections: (See INDICATIONS AND USAGE.)

Gram-positive aerobes: Staphylococcus epidermidis, Staphylococcus saprophyticus.

Gram-negative aerobes: Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, Neisseria gonorrhoeae, Proteus mirabilis, Pseudomonas aeruginosa.

The following in vitro data are available but their clinical significance is unknown.

In addition, enoxacin exhibits in vitro minimum inhibitory concentrations (MICs) of 2.0 µg/mL or less against most strains of the following organisms; however, the safety and effectiveness of enoxacin in treating clinical infections due to these organisms have not been established in adequate and well-controlled trials.

Gram-negative aerobes: Aeromonas hydrophila, Citrobacter diversus, Citrobacter freundii, Citrobacter koseri, Enterobacter aerogenes, Haemophilus ducreyi, Klebsiella oxytoca, Klebsiella ozaenae, Morganella morganii, Proteus vulgaris, Providencia stuartii, Providencia alcalifaciens, Serratia marcescens, Serratia proteomaculans (formerly S. liquefaciens )

Many strains of Streptococcus species and anaerobes are usually resistant to enoxacin.

The activity of enoxacin against Treponema pallidum has not been evaluated; however, other quinolones are not active against T. pallidum. (See WARNINGS.)

Cross-resistance with other quinolones has been demonstrated.

The addition of human serum has no effect on the in vitro MIC values; however, enoxacin activity is decreased in acidic (pH 5.5) environments.

Susceptibility Testing

Diffusion Techniques:   Quantitative methods that require measurement of zone diameters give the most precise estimate of susceptibility of bacteria to antimicrobial agents. One such standardized procedure 1 that has been recommended for use with disks to test susceptibility of organisms to enoxacin uses the 10-µg enoxacin disk.

Interpretation involves the correlation of the diameter obtained in the disk test with the minimum inhibitory concentration (MIC) for enoxacin.

Reports from the laboratory giving results of the standard single-disk susceptibility test with a 10-µg enoxacin disk should be interpreted according to the following criteria:

 

Zone Diameter (mm)
Interpretation
≥18
(S) Susceptible
15-17
(MS) Moderately susceptible
≤14
(R) Resistant

A report of "Susceptible" indicates that the pathogen is likely to be inhibited by generally achievable blood concentrations. A report of "Moderately susceptible" suggests that the organism would be susceptible if high dosage is used or if the infection is confined to tissues or fluids in which high antimicrobial levels are attained. A report of "Resistant" indicates that achievable drug concentrations are unlikely to be inhibitory, and other therapy should be selected.

Standardized susceptibility test procedures require the use of laboratory control organisms. The 10-µg enoxacin disk should give the following zone diameters:

 

Organism
Zone Diameter (mm)
Escherichia coli (ATCC 25922)
28-36
Neisseria gonorrhoeae (ATCC 49226)
43-51
Pseudomonas aeruginosa (ATCC 27853)
22-28
Staphylococcus aureus (ATCC 25923)
22-28

Other quinolone antibacterial disks should not be substituted when performing susceptibility tests for enoxacin because of spectrum differences. The 10-µg enoxacin disk should be used for all in vitro testing of isolates for enoxacin susceptibility using diffusion techniques.

Dilution Techniques:   Use a standardized dilution method 2 (broth, agar, or microdilution) or equivalent with enoxacin powder. The MIC values obtained should be interpreted according to the following criteria:

 

MIC (µg/mL)
Interpretation
≤2
(S) Susceptible
4
(MS) Moderately susceptible
≥8
(R) Resistant

As with standard diffusion methods, dilution procedures require the use of laboratory control organisms. Standard enoxacin powder should give the following MIC values:

 

Organism
MIC (µg/mL)
Enterococcus faecalis (ATCC 29212)
2-16
Escherichia coli (ATCC 25922)
0.06-0.25
Neisseria gonorrhoeae (ATCC 49226)
0.015-0.06
Pseudomonas aeruginosa (ATCC 27853)
2-8
Staphylococcus aureus (ATCC 29213)
0.5-2

ANIMAL PHARMACOLOGY

Enoxacin and other members of the quinolone class have been shown to cause arthropathy in immature animals of most species tested. (See WARNINGS.)

Last reviewed on RxList: 12/8/2004
This monograph has been modified to include the generic and brand name in many instances.

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