Levofloxacin clinical pharmacology

# CLINICAL PHARMACOLOGY

# Mechanism of Action=
Levofloxacin is a member of the fluoroquinolone class of antibacterial agents .

## Pharmacokinetics
The mean SD pharmacokinetic parameters of levofloxacin determined under single and steady-state conditions following oral tablet, oral solution, or intravenous (IV) doses of LEVAQUIN are summarized in Table 10.
1 clearance/bioavailability
2 volume of distribution/bioavailability
3 healthy males 1853 years of age
4 60 min infusion for 250 mg and 500 mg doses, 90 min infusion for 750 mg dose
5 healthy male and female subjects 1854 years of age
6 500 mg every 48h for patients with moderate renal impairment (CLCR 2050 mL/min) and infections of the respiratory tract or skin
7 dose-normalized values (to 500 mg dose), estimated by population pharmacokinetic modeling
8 healthy males 2275 years of age
9 healthy females 1880 years of age
10 young healthy male and female subjects 1836 years of age
11 healthy elderly male and female subjects 6680 years of age
12 healthy males and females 1955 years of age.
- Absolute bioavailability; F=0.99  0.08 from a 500 mg tablet and F=0.99  0.06 from a 750 mg tablet;
ND=not determined.

## Absorption
Levofloxacin is rapidly and essentially completely absorbed after oral administration. Peak plasma concentrations are usually attained one to two hours after oral dosing. The absolute bioavailability of levofloxacin from a 500 mg tablet and a 750 mg tablet of LEVAQUIN are both approximately 99%, demonstrating complete oral absorption of levofloxacin. Following a single intravenous dose of LEVAQUIN to healthy volunteers, the mean SD peak plasma concentration attained was 6.2 1.0 mcg/mL after a 500 mg dose infused over 60 minutes and 11.5 4.0 mcg/mL after a 750 mg dose infused over 90 minutes. LEVAQUIN Oral Solution and Tablet formulations are bioequivalent.
Levofloxacin pharmacokinetics are linear and predictable after single and multiple oral or IV dosing regimens. Steady-state conditions are reached within 48 hours following a 500 mg or 750 mg once-daily dosage regimen. The mean SD peak and trough plasma concentrations attained following multiple once-daily oral dosage regimens were approximately 5.7 1.4 and 0.5 0.2 mcg/mL after the 500 mg doses, and 8.6 1.9 and 1.1 0.4 mcg/mL after the 750 mg doses, respectively. The mean SD peak and trough plasma concentrations attained following multiple once-daily IV regimens were approximately 6.4 0.8 and 0.6 0.2 mcg/mL after the 500 mg doses, and 12.1 4.1 and 1.3 0.71 mcg/mL after the 750 mg doses, respectively. Oral administration of a 500 mg dose of LEVAQUIN with food prolongs the time to peak concentration by approximately 1 hour and decreases the peak concentration by approximately 14% following tablet and approximately 25% following oral solution administration. Therefore, LEVAQUIN Tablets can be administered without regard to food. It is recommended that LEVAQUIN Oral Solution be taken 1 hour before, or 2 hours after eating.
The plasma concentration profile of levofloxacin after IV administration is similar and comparable in extent of exposure (AUC) to that observed for LEVAQUIN Tablets when equal doses (mg/mg) are administered. Therefore, the oral and IV routes of administration can be considered interchangeable(see Figure 2 and Figure 3).

## Distribution
The mean volume of distribution of levofloxacin generally ranges from 74 to 112 L after single and multiple 500 mg or 750 mg doses, indicating widespread distribution into body tissues. Levofloxacin reaches its peak levels in skin tissues and in blister fluid of healthy subjects at approximately 3 hours after dosing. The skin tissue biopsy to plasma AUC ratio is approximately 2 and the blister fluid to plasma AUC ratio is approximately 1 following multiple once-daily oral administration of 750 mg and 500 mg doses of LEVAQUIN, respectively, to healthy subjects. Levofloxacin also penetrates well into lung tissues. Lung tissue concentrations were generally 2- to 5- fold higher than plasma concentrations and ranged from approximately 2.4 to 11.3 mcg/g over a 24-hour period after a single 500 mg oral dose.
In vitro, over a clinically relevant range (1 to 10 mcg/mL) of serum/plasma levofloxacin concentrations, levofloxacin is approximately 24 to 38% bound to serum proteins across all species studied, as determined by the equilibrium dialysis method. Levofloxacin is mainly bound to serum albumin in humans. Levofloxacin binding to serum proteins is independent of the drug concentration.

## Metabolism
Levofloxacin is stereochemically stable in plasma and urine and does not invert metabolically to its enantiomer, D-ofloxacin. Levofloxacin undergoes limited metabolism in humans and is primarily excreted as unchanged drug in the urine. Following oral administration, approximately 87% of an administered dose was recovered as unchanged drug in urine within 48 hours, whereas less than 4% of the dose was recovered in feces in 72 hours. Less than 5% of an administered dose was recovered in the urine as the desmethyl and N-oxide metabolites, the only metabolites identified in humans. These metabolites have little relevant pharmacological activity.

## Excretion
Levofloxacin is excreted largely as unchanged drug in the urine. The mean terminal plasma elimination half-life of levofloxacin ranges from approximately 6 to 8 hours following single or multiple doses of levofloxacin given orally or intravenously. The mean apparent total body clearance and renal clearance range from approximately 144 to 226 mL/min and 96 to 142 mL/min, respectively. Renal clearance in excess of the glomerular filtration rate suggests that tubular secretion of levofloxacin occurs in addition to its glomerular filtration. Concomitant administration of either cimetidine or probenecid results in approximately 24% and 35% reduction in the levofloxacin renal clearance, respectively, indicating that secretion of levofloxacin occurs in the renal proximal tubule. No levofloxacin crystals were found in any of the urine samples freshly collected from subjects receiving LEVAQUIN.

## Geriatric
There are no significant differences in levofloxacin pharmacokinetics between young and elderly subjects when the subjects' differences in creatinine clearance are taken into consideration. Following a 500 mg oral dose of LEVAQUIN to healthy elderly subjects (66  80 years of age), the mean terminal plasma elimination half-life of levofloxacin was about 7.6 hours, as compared to approximately 6 hours in younger adults. The difference was attributable to the variation in renal function status of the subjects and was not believed to be clinically significant. Drug absorption appears to be unaffected by age. LEVAQUIN dose adjustment based on age alone is not necessary .

## Pediatrics
The pharmacokinetics of levofloxacin following a single 7 mg/kg intravenous dose were investigated in pediatric patients ranging in age from 6 months to 16 years. Pediatric patients cleared levofloxacin faster than adult patients, resulting in lower plasma exposures than adults for a given mg/kg dose. Subsequent pharmacokinetic analyses predicted that a dosage regimen of 8 mg/kg every 12 hours (not to exceed 250 mg per dose) for pediatric patients 6 months to 17 years of age would achieve comparable steady state plasma exposures (AUC024 and Cmax) to those observed in adult patients administered 500 mg of levofloxacin once every 24 hours.

## Gender
There are no significant differences in levofloxacin pharmacokinetics between male and female subjects when subjects' differences in creatinine clearance are taken into consideration. Following a 500 mg oral dose of LEVAQUIN to healthy male subjects, the mean terminal plasma elimination half-life of levofloxacin was about 7.5 hours, as compared to approximately 6.1 hours in female subjects. This difference was attributable to the variation in renal function status of the male and female subjects and was not believed to be clinically significant. Drug absorption appears to be unaffected by the gender of the subjects. Dose adjustment based on gender alone is not necessary.

## Race
The effect of race on levofloxacin pharmacokinetics was examined through a covariate analysis performed on data from 72 subjects: 48 white and 24 non-white. The apparent total body clearance and apparent volume of distribution were not affected by the race of the subjects.

## Renal Impairment
Clearance of levofloxacin is substantially reduced and plasma elimination half-life is substantially prolonged in adult patients with impaired renal function (creatinine clearance < 50 mL/min), requiring dosage adjustment in such patients to avoid accumulation. Neither hemodialysis nor continuous ambulatory peritoneal dialysis (CAPD) is effective in removal of levofloxacin from the body, indicating that supplemental doses of LEVAQUIN are not required following hemodialysis or CAPD .

## Hepatic Impairment=
Pharmacokinetic studies in hepatically impaired patients have not been conducted. Due to the limited extent of levofloxacin metabolism, the pharmacokinetics of levofloxacin are not expected to be affected by hepatic impairment .

## Bacterial Infection
The pharmacokinetics of levofloxacin in patients with serious community-acquired bacterial infections are comparable to those observed in healthy subjects.

## Drug-Drug Interactions
The potential for pharmacokinetic drug interactions between LEVAQUIN and antacids warfarin, theophylline, cyclosporine, digoxin, probenecid, and cimetidine has been evaluated