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Antimicrob Agents Chemother. 2011 June; 55(6): 2636–2640.
PMCID: PMC3101414

Pharmacokinetics and Safety of MP-376 (Levofloxacin Inhalation Solution) in Cystic Fibrosis Subjects[down-pointing small open triangle]


The pharmacokinetics and tolerability of nebulized MP-376 (levofloxacin inhalation solution [Aeroquin]) were determined in cystic fibrosis (CF) subjects. Ten CF subjects received single 180-mg doses of two formulations of MP-376, followed by a multiple-dose phase of 240 mg once daily for 7 days. Serum and expectorated-sputum samples were assayed for levofloxacin content. Safety was evaluated following the single- and multiple-dose study phases. Nebulized MP-376 produced high concentrations of levofloxacin in sputum. The mean maximum plasma concentration (Cmax) ranged between 2,563 and 2,932 mg/liter for 180-mg doses of the 50- and 100-mg/ml formulations, respectively. After 7 days of dosing, the mean Cmax for the 240-mg dose was 4,691 mg/liter. The mean serum levofloxacin Cmax ranged between 0.95 and 1.28 for the 180-mg doses and was 1.71 for the 240-mg dose. MP-376 was well tolerated. Nebulized MP-376 produces high sputum and low serum levofloxacin concentrations. The pharmacokinetics, safety, and tolerability were similar for the two formulations. MP-376 240 mg (100 mg/ml) is being advanced into late-stage clinical development.


Patients with cystic fibrosis (CF) suffer from recurrent and chronic infections of the lower respiratory tract. Pseudomonas aeruginosa in particular has been implicated as a major risk factor for declining lung function and associated morbidity and mortality in CF patients (5). Aerosol delivery of an antibiotic directly to the lung increases the local concentration of the drug at the site of infection, thereby enhancing bacterial killing and reducing the selection of resistance compared to the outcomes of systemic administration. Currently, a tobramycin solution for inhalation (TOBI; Novartis Pharmaceuticals, East Hanover, NJ) and aztreonam lysine for inhalation (Cayston; Gilead Pharmaceuticals, Seattle, WA) are the two aerosol antibiotics approved in the United States for the management of CF patients with P. aeruginosa. For a number of reasons, including decreased efficacy, drug intolerance, new emerging pathogens, and inconvenient dosing regimens, there is a need for alternative inhaled therapies to treat CF patients with pulmonary infections caused by P. aeruginosa and other bacteria.

Levofloxacin is a fluoroquinolone antibiotic with potent activity against key pathogens in CF patients, including P. aeruginosa. Unlike tobramycin, levofloxacin's activity is not reduced in CF sputum (8). In addition, levofloxacin has greater antimicrobial activity than tobramycin and aztreonam in biofilms produced by P. aeruginosa (8). Extensive in vitro and animal pharmacokinetic-pharmacodynamic studies, as well as both retrospective and prospective clinical studies, have established a clear link between the exposure to fluoroquinolones and clinical response (1). While not conducted in patients with CF, studies with levofloxacin show that bacterial killing and clinical efficacy is linked to the plasma area under the concentration-time curve (AUC)/MIC ratio or maximum plasma concentration (Cmax)/MIC ratio and that high peak concentrations relative to the MIC may reduce the selection of drug-resistant bacteria in vitro and in vivo (6, 7). Aerosol administration of levofloxacin produces Cmax/MIC and AUC/MIC ratios in the airways that are substantially greater than those that can be obtained with parenteral or oral administration. High levofloxacin concentrations delivered to the lung may be active against even highly resistant organisms and may also reduce the selection of resistant bacteria (9).

MP-376 is a novel solution formulation of levofloxacin for aerosol administration, developed for the management of CF patients with chronic infections due to Pseudomonas aeruginosa. Pharmacokinetic studies in animals show that the formulation promotes the retention of active drug in the lung, which results in enhanced efficacy compared to the efficacies of other aerosol or systemic formulations of levofloxacin in animal models of infection (11). MP-376 is a preservative-free, pH 5 to 7 and 350 to 500 mosmol (slightly hyperosmotic) solution that has been optimized for administration using a customized, investigational, high-efficiency Pari eFlow nebulizer for rapid delivery using once- or twice-daily dosage regimens. The purpose of this study was to evaluate and compare the safety, tolerability, and pharmacokinetic profiles of two formulations of MP-376 (50 and 100 mg/ml) at two dose levels in CF subjects in order to facilitate the design of further clinical trials of MP-376.



The entry criteria for this study included an age of 16 years or older with a diagnosis of CF, baseline forced expiratory volume in 1 s (FEV1) ≥40% of the predicted value, clinically stable with a stable medication regimen, no use of an investigational agent within 4 weeks before the first study visit, and no aerosol or systemic antibiotics within 7 days before the first visit (other than maintenance oral azithromycin). The Institutional Review Board at each site approved the study, and all patients or their guardians provided written informed consent.

Study design.

This was a multicenter, randomized, single-blind, crossover study of two concentrations of MP-376 (50 mg/ml and 100 mg/ml; 180-mg dose) administered via inhalation using a customized, investigational, Pari eFlow nebulizer, followed by 7 days of daily treatment with a 240-mg (100 mg/ml) dose. After completing the screening procedures, qualified patients were randomized to one of the treatment sequences as shown in Table 1. Subjects received, in an order specified by a randomization schedule, a single 180-mg dose of one formulation in period 1 of the study, followed by a 7-day wash-out period and a single 180-mg dose of the other formulation in period 2. On the days when pharmacokinetic samples were obtained, patients rinsed their mouths and swallowed 15 ml of Maalox (400 mg magnesium hydroxide, 400 mg aluminum hydroxide) 5 min prior to and 5 min after dosing in order to minimize oral absorption of any swallowed levofloxacin. This was done so that serum levofloxacin levels would better reflect the intrapulmonary deposition and absorption from the airways. After an additional 7-day wash-out period, the third and final period of the trial consisted of seven consecutive days of once-daily 240-mg dosing using the 100-mg/ml formulation.

Table 1.
Study design sequence

Blood samples were collected before dosing, at the end of the inhalation (1 to 8 min), and at 0.167 (10 min), 0.25 (15 min), 0.5 (30 min), 1, 2, 4, 8, and 24 h after the start of dosing in periods 1 and 2 and after the last dose in period 3. Sputum samples were collected before dosing and at 0.25, 0.5, 1, 2, 4, 8, and 24 h after dosing.

Analytical methods.

The concentrations of levofloxacin in serum and in the sputum were determined using the validated high-performance liquid chromatography (HPLC) method using fluorescence detection (Anapharm, Québec, Canada). Briefly, levofloxacin and an internal standard (difloxacin) were extracted from a 0.1-ml aliquot of human serum or sputum using dichloromethane-isopropyl alcohol (90/10), using a liquid-liquid extraction. The extracted samples were injected into a liquid chromatograph equipped with a Zorbax SB C8, 4.6- by 150-mm, 5-μm column. The mobile phase was a mixture of deionized water-acetonitrile (75/25), 7.5 mM potassium dihydrogen orthophosphate, pH 3.50. Standard curves were obtained using a weighted least squares linear regression analysis of the peak area ratios (levofloxacin/internal standard) versus the nominal concentration of the standard curve. Two standard curves were prepared, one for serum and one for sputum. Sample concentrations were determined by interpolation from the standard curve. The serum standard curve was linear from 5 to 1,000 ng/ml, with a between- and within-day precision of <8.0%. The sputum standard curve was linear from 100 to 50,000 ng/ml, with a between- and within-day precision of <4.0%.

Pharmacokinetic methods.

All pharmacokinetic parameters were calculated using noncompartmental analysis. The Cmax and time to Cmax (Tmax) were identified directly from the data. The elimination rate constant, λz, was calculated as the negative of the slope of the terminal log-linear segment of the plasma concentration-time curve. The range of data used for calculation in each subject and treatment was determined by visual inspection of a semilogarithmic plot of concentration versus time. Pharmacokinetic parameters were calculated using SAS for Windows, version 9.1.3.

Safety evaluation.

Patients were seen a total of 9 times during the study; a screening visit, 2 visits around each of the single-dose periods, 3 visits during the multiple-dose period, and a follow-up visit. Adverse events (AEs) were collected at each visit. Safety was assessed by evaluating AEs and changes from baseline in physical examinations, vital signs, electrocardiograms (ECGs), pulse oximetry results, spirometry, and laboratory test results.


Ten CF subjects enrolled in the study, and all subjects completed the study successfully. Patient characteristics were similar across the two treatment sequences and are shown in Table 2. The overall mean age was 32.4 years, 60% of the patients were female, all were Caucasian, and there were no clinically relevant differences in medical history or screening physical examination findings. The average baseline percent predicted FEV1 for all patients was 67.1%, with similar mean baseline FEV1 values in each treatment sequence.

Table 2.
Demographic characteristics of CF subjects in this study

Pharmacokinetics. (i) Serum.

The mean serum levofloxacin concentrations for all three doses are shown in Fig. 1. A comparison of the mean serum and sputum exposures is shown in Fig. 2. After the administration of 180 mg MP-376, the mean Cmax and AUC from 0 h to infinity (AUC0-∞) values for the 100-mg/ml formulation were 35% and 22% higher than the corresponding values for the 50-mg/ml formulation, respectively (Table 3), but the differences were not statistically significant. There was a 1.33-fold increase in the mean Cmax after the administration of 240 mg versus 180 mg as the 100-mg/ml formulation, exactly proportional to the increase in dose. There was a corresponding 1.71-fold increase in the mean AUC0-∞ after the 240-mg dose versus the 180-mg dose.

Fig. 1.
Serum levofloxacin levels after aerosol dosing of 180 or 240 mg MP-376.
Fig. 2.
Levofloxacin serum and sputum AUCs after aerosol dosing of MP-376, and comparative data for a 750-mg oral levofloxacin dose (750 PO [per os]) in CF subjects (3).
Table 3.
Summary of serum pharmacokinetic parameters for levofloxacin after administration of single 180-mg doses of MP-376 as 50- or 100-mg/ml inhalation solutions and after administration of 240 mg as a 100-mg/ml inhalation solution to patients with CF

(ii) Sputum.

The sputum pharmacokinetic parameters are shown in Table 4. Inhalation of a 180-mg dose as either the 50- or 100-mg/ml formulation resulted in similar mean sputum levofloxacin Cmax and AUC values (Table 4). After 7 days of 240-mg-per-day dosing with the 100-mg/ml formulation, the increases in Cmax and AUC were both slightly greater than dose proportional (1.6-fold and 2.3-fold increase, respectively, versus a dose increase of 1.33-fold). The mean half-life (t1/2) was comparable for all three doses, ranging from 3.55 h to 4.58 h (Table 3).

Table 4.
Summary of sputum pharmacokinetic parameters for levofloxacin after administration of single 180-mg doses of MP-376 as 50- or 100-mg/ml inhalation solutions and after administration of 240 mg as a 100-mg/ml inhalation solution to patients with CF


MP-376 was very well tolerated with both concentrations and doses. A total of 26 AEs were reported by 7 of the 10 patients during the study. The number of patients reporting an AE was similar across each treatment period (60%, 50%, and 40% for periods 1, 2, and 3, respectively). Adverse events that were reported in 2 or more patients are as follows: dysgeusia was noted in 4 of 10 patients with the 180-mg single dose (50 mg/ml), in 4 of 10 with the 180-mg single dose (100 mg/ml), and in 4 of 10 during the 240-mg multiple-dose (100 mg/ml) period. Hemoptysis occurred in 1 of 10 patients with the 180-mg single dose (50 mg/ml) and 1 of 10 patients with the 180-mg single dose (100 mg/ml). No patients experienced hemoptysis during the multiple-dose period. Of the 26 AEs, 25 were mild and one was moderate. The moderate AE was back pain and was judged not to be related to the study drug. Nineteen events in 4 patients were considered related to the study drug (either possibly or probably). A similar AE profile, with respect to event, severity, and relationship, was observed across treatment periods. No patient experienced a serious adverse event, and no patient discontinued the study due to an AE. There were no clinically relevant changes in physical exam findings, vital signs, ECGs, pulse oximetry, spirometry, or laboratory results.

Nebulization time.

The mean delivery time for MP-376 was 5.5 min for the 180-mg dose (50 mg/ml), 3.0 min for the 180-mg dose (100 mg/ml), and 4.8 min for the 240-mg dose.


Both formulations of MP-376 tested produced very high sputum concentrations with low systemic exposure. The 180- and 240-mg doses using the 100-mg/ml formulation produced 24-h serum AUCs (AUC0–24) of 9.05 and 14.77 mg · hr/liter, respectively. These measures of serum levofloxacin exposure from MP-376 are only 12 to 19% of the 24-hour serum AUC achieved in another study of CF patients dosed with 750 mg oral levofloxacin (AUC0–24 = 76.6 mg · hr/liter) (3). Systemic absorption from the lung was very rapid, with serum Tmax occurring within 20 min of dose administration.

For CF patients who spend considerable time taking their prescribed daily inhaled medications, it is important to consider the treatment burden when developing new therapies. This pharmacokinetic study showed that the 100-mg/ml formulation of MP-376 produced serum and sputum levels of levofloxacin that were similar to those obtained with the 50-mg/ml formulation and required less time for nebulization.

After 7 days of 240 mg daily dosing using the 100-mg/ml formulation, the serum and sputum exposures were approximately dose proportional with those obtained with the 180-mg dose with regard to Cmax and seemed higher than dose proportional with regard to AUC values. However, there was very high intersubject variability, with standard deviations approximating or exceeding the mean values, making it difficult to evaluate dose proportionality. This high degree of variability can be seen in most studies of aerosol drugs and stems from factors that include breathing patterns during drug inhalation (tidal volume, inspiratory flow, and respiratory rate) and disease severity (degree and location of airway obstruction) (4). Sputum concentrations of inhaled antibiotics are frequently measured in clinical trials as a guide to ensure that they exceed the MIC of the bacteria. However, as a measure of deposited dose in the airways, sputum levels can be misleading, as the drug is not evenly distributed in the airways and the exact source of sputum may differ between specimens, leading to more variability (4).

Aerosol dosing with MP-376 produced a mean sputum AUC of 4,500 mg/liter and a mean sputum Cmax of 4,700 mg · hr/liter after a 240-mg dose. Extensive in vitro and animal pharmacokinetic-pharmacodynamic studies, as well as both retrospective and prospective clinical studies, have established a clear link between exposure to fluoroquinolones and antibacterial effects. Studies with levofloxacin show that bacterial killing and clinical efficacy are linked to the plasma drug area under the curve (AUC)/MIC ratio or the Cmax/MIC ratio (6, 7, 10, 12). Studies with levofloxacin also show that high levels of exposure relative to the MIC can reduce the selection of drug-resistant bacteria in vitro and in vivo (7, 12). Based on a MIC90 to P. aeruginosa of 16 mg/liter for levofloxacin, aerosol administration of MP-376 resulted in a sputum AUC/MIC90 ratio of 280 and a Cmax/MIC90 ratio of 290. These sputum exposures are greater than those that can be achieved with either parenteral or oral administration.

While sputum levofloxacin exposures were very high, serum exposures were only 10 to 16% of those previously reported with 750 mg oral dosing (Fig. 2). (3) With lower systemic exposures, aerosol MP-376 should improve the safety and tolerability profile compared to that of either parenteral or oral administration of levofloxacin.

Overall, this study demonstrated that aerosol administration of MP-376 was well tolerated and produced sputum levofloxacin exposures that should maximize bacterial killing while minimizing the development of resistance. Based on these data, the 100-mg/ml formulation of MP-376 was advanced into phase 2 studies (2).


[down-pointing small open triangle]Published ahead of print on 28 March 2011.


1. Ambrose P. G., et al. 2007. Pharmacokinetics-pharmacodynamics of antimicrobial therapy: it's not just for mice anymore. Clin. Infect. Dis. 44:79–86 [PubMed]
2. Conrad D., et al. 2010. Phase 2b study of inhaled MP-376 (Aeroquin, levofloxacin inhalation solution) in stable cystic fibrosis (CF) patients with chronic Pseudomonas aeruginosa (PA) lung infection, abstr. A102. Am. J. Respir. Crit. Care Med. 181(Meeting abstr.):A2339
3. Geller D. E., et al. 2006. Pharmacokinetics of oral levofloxacin (LVX) in stable adult CF subjects. Pediatr. Pulmonol. 41(S29):328
4. Geller D. E. 2008. The science of aerosol delivery in cystic fibrosis. Pediatr. Pulmonol. 43(Suppl. 9):S5–S17
5. Gibson R. L., Burns J. L., Ramsey B. W. 2003. Pathophysiology and management of pulmonary infections in cystic fibrosis. Am. J. Respir. Crit. Care Med. 168:918–951 [PubMed]
6. Griffith D. C., et al. 2006. Pharmacodynamics of levofloxacin against Pseudomonas aeruginosa with reduced susceptibility due to different efflux pumps: do elevated MICs always predict reduced in vivo efficacy? Antimicrob. Agents Chemother. 50:1628–1632 [PMC free article] [PubMed]
7. Jumbe N., et al. 2003. Application of a mathematical model to prevent in vivo amplification of antibiotic-resistant bacterial populations during therapy. J. Clin. Invest. 112:275–285 [PMC free article] [PubMed]
8. King P., Lomovskaya O., Griffith D. C., Burns J. L., Dudley M. N. 2010. In vitro pharmacodynamics of levofloxacin and other aerosolized antibiotics under multiple conditions relevant to chronic pulmonary infection in cystic fibrosis. Antimicrob. Agents Chemother. 54:143–148 [PMC free article] [PubMed]
9. King P., et al. 2008. In vitro PK-PD of levofloxacin (LVX): a new dosing paradigm for aerosolized antibiotics, abstr. A-042. Abstr. 48th Intersci. Conf. Antimicrob. Agents Chemother American Society for Microbiology, Washington, DC
10. Preston S., et al. 1998. Pharmacodynamics of levofloxacin: a new paradigm for early clinical trials. JAMA 279:125–129 [PubMed]
11. Sabet M., et al. 2009. Efficacy of aerosol MP-376 (levofloxacin inhalation solution) in mouse lung infection models due to Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 53:3923–3928 [PMC free article] [PubMed]
12. Tam V. H., et al. 2005. Bacterial-population responses to drug-selective pressure: examination of garenoxacin's effect on Pseudomonas aeruginosa. J. Infect. Dis. 192:420–428 [PubMed]

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