Open-label, Dose-escalation Study to Evaluate the Pharmacokinetics of Inhaled Teicoplanin in Cystic Fibrosis Patients

INTRODUCTION \& STATE-OF-ART Cystic Fibrosis (CF) is the most common autosomal recessive lethal disorders affecting 1 in 2.500 newborns among Caucasians. CF lung disease reflects a failure in the capacity of airway epithelia to normally hydrate their surface. Poor hydration of airways surfaces leads to reduced mucociliary clearance, adhesion of mucus to airway surfaces and, ultimately, chronic bacterial infection.

On regard the therapeutic strategy, lung infection in CF was mainly treated with antibiotics, anti-inflammatory medicines, bronchodilators and mucolytics. In addition, patients with cystic fibrosis were often given other types of medicines such as pancreatic enzymes and food supplements. They were also advised to exercise and to have physiotherapy.

Patients with CF are peculiarly susceptible to infection and colonization of the respiratory tract with patho-gens. In particular, methicillin-resistant Staphylococcus aureus (MRSA) has become the third most prevalent bacterium in cystic fibrosis (CF) in the United States and has been increasing in other countries. Apart from the difficulty of treating the infection because of its antimicrobial resistances, MRSA is transmissible between individuals with and without CF.

With increasing survival due to improvements of care, an increased frequency of pulmonary infections with new and resistant pathogens has been identified. In particular, the prevalence of Methicillin-resistant Staphylococcus aureus (MRSA) in respiratory cultures of CF patients has increased over the past decade. MRSA pneumonia is likely to be severe and life threatening, with high mortality, compared with non-MRSA pneumonia.

The impact of MRSA on outcomes in CF is not fully understood. In a large epidemiologic study was shown that lung function decline is more rapid in CF children and adolescents with persistent MRSA compared with those without MRSA. Epidemiologic evidence suggests that persistent infection with MRSA is associated with increased use of intra-venous antibiotics, increased hospitalizations, a faster decline of lung function, as well as shortened life expectancy.

During chronic infection, MRSA shows the adaptive mode of growth, which enhances the bacterias' ability to withstand the immune system and antibiotic therapy. In the setting of chronic infection, however, reduction in bacterial density in sputum and increased clinical stability may be appropriate outcomes.

Chronic MRSA infection is associated with worse outcomes, and treatment/eradication is challenging. Antibiotic dosing and choices should be optimized to minimize further resistance and to maximize chances of successful therapy. Yet, MRSA has several mechanisms to escape clearance by the immune system and antibiotic killing. For these reasons, a better understanding of preventive measures and early therapy is of key importance.

Different approaches have been considered in the prevention and management of MRSA infections among patients with CF. In consideration of all these assessments there is an emerging consensus that MRSA is an important pathogen in CF rather than simply a marker of severe disease. However, to date there are no guidelines or recommendations on the choice of antibiotics for MRSA in CF.

Glycopeptides are an important class of antibiotics active against Gram-positive pathogens. Teicoplanin and vancomycin, are two glycopeptide antibiotics currently in widespread use and are active against MRSA. Teicoplanin susceptibility is considered when minimal inhibition concentration (MIC) is < 2 ug/mL. Teicoplanin is produced by Actynoplanes teichomycietus and acts by inhibition of cell wall synthesis. Teicoplanin is often preferred to vancomycin for intravenous treatment because of its better safety profile but its use in MRSA lung infection is limited by its limited lung penetration. Teicoplanin has been marketed for >20 years in most EU countries. Teicoplanin is mainly used for injection/infusion; the oral route of administration is used only for the treatment of pseudomembranous colitis by Clostridium difficilis.

Inhalation of anti-microbial drugs is a cornerstone in the treatment of patients with CF, by providing high drug concentrations locally in the lung while minimizing systemic exposure and thus the potential for side effects. Nebulized antibiotic therapy directly targets airways and lung parenchyma, thereby resulting in increased local concentrations and hence potentially improving efficacy. In CF, inhaled antibiotics decrease the rate of decline of lung function, improve the quality of life, and reduce the frequency of exacerbations and hospital admissions.

Delivery of nebulized Teicoplanin directly to the bronchial tree may offer improved efficacy. It is expected that, using the inhalation route, lung concentrations will be higher than MICs for most bacteria, improving efficacy and reducing the risk of resistance. At present, no antibiotic active against MRSA is available as an inhaled formulation; vancomycin dry powder for inhalation is currently under clinical investigation in the U.S.A. for the treatment of MRSA lung infection.

SUMMARY OF NON-CLINICAL PHARMACOLOGY Teicoplanin inhibits the growth of susceptible organisms by interfering with cell wall biosynthesis at a site different from that affected by beta-lactams. Specific binding to D-alanyl-D-alanine residues blocks peptidoglycan synthesis. The spectrum of activity of Teicoplanin, like that of vancomycin, is restricted to Gram-positive aerobic and anaerobic bacteria. Teicoplanin is generally more active than vancomycin against streptococci and Gram-positive anaerobes; the two agents exhibit similar activity against S. aureus (including MRSA).

Resistance to Teicoplanin is rare but not unknown. SUMMARY OF CLINICAL DATA In clinical trials, Teicoplanin is associated with fewer side effects than vancomycin, while caution is recommended in the elderly, patients with compromised renal function, pre-existing hearing problems or with a history of allergic reactions to vancomycin. Common adverse reactions (≥1/100 to <1/10) include rash, erythema, pruritis, pain at injections site and pyrexia while less common reactions (≥1/1,000 to <1/100) include leucopenia, thrombocytopenia, eosinophilia, anaphylactic reactions dizziness, headache, phlebitis, bronchospasm, diarrhoea, vomiting, nausea and transient increases in transaminases.

Renal failure has been reported in patients treated with Teicoplanin; patients with renal insufficiency, and/or in those receiving Teicoplanin in conjunction with or sequentially with other medicinal products with known nephrotoxic potential (aminoglycosides, colistin, amphotericin B, cyclosporin, and cisplatin) should be carefully monitored, and should include auditory tests. Since Teicoplanin is mainly excreted by the kidney, the dose of Teicoplanin must be adapted in patients with renal impairment.

As with other glycopeptides, ototoxicity (deafness and tinnitus) has been reported in patients treated with Teicoplanin. Patients who develop signs and symptoms of impaired hearing or disorders of the inner ear during treatment with Teicoplanin should be carefully evaluated and monitored, especially in case of prolonged treatment and in patients with renal insufficiency. Patients receiving Teicoplanin in conjunction with or sequentially with other medicinal products with known neurotoxic/ototoxic potential (amino-glycol¬sides, cyclosporin, cisplatin, furosemide and ethacrynic acid) should be carefully monitored and the benefit of Teicoplanin evaluated if hearing deteriorates.

The safety of Teicoplanin has been confirmed by pharmacovigilance data based on approximately 30 years of use in Gram-positive severe infections. There are no human data concerning the use of inhaled Teicoplanin.

SUMMARY OF CLINICAL PHARMACOKINETICS Teicoplanin is currently administered primarily by the parenteral route (intravenous, IV or intra¬muscular, IM). Following intravenous administration, the disposition kinetics are tri-exponential, and the majority of drug is excreted unchanged by glomerular filtration. In patients with normal renal function, the terminal half-life is 87 h. The volume of distribution at steady-state is 860 mL/kg, clearance is 11.4 mL/h/kg and renal clearance is 8.3 mL/h/kg. Teicoplanin is highly bound in plasma to albumin (fraction unbound = 0.1). The pharmacokinetics are linear over a wide dose range (2 to 26 mg/kg). As expected, clearance is higher in children than in adults, and lower in the elderly, associated with a decrease in glomerular filtration rate with advancing years.

Teicoplanin is not absorbed from the gastrointestinal tract and shows negligible oral bioavailability. After IM administration, the bioavailability of Teicoplanin is 90%. After six daily IM administrations at 200 mg, the mean ± SD maximum Teicoplanin concentration (Cmax) is 12.1 ± 0.9 mg/L and occurs at 2h after administration.

RATIONALE FOR THE STUDY The objective of this phase I, first-in-man clinical study is to identify the dose providing, after single inhalation administration, a sputum Teicoplanin concentrations exceeding the drug concentration required to inhibit bacterial growth for at least 8 hours, while minimizing the development of resistance. To this end, the study is designed with single daily escalating doses in subjects with CF. Up to now, no Teicoplanin product for nebulization has been approved either in EU or U.S.A.. Nevertheless, Teicoplanin containing solutions are often used off-label to manage MRSA lung infections in patients with Cystic Fibrosis, usually with nebulization of 200 mg in 3 ml.

Inhalation by nebulization is a typical topical therapy and its efficacy depends on the physicochemical characteristics of the drug solution and of the nebuliser used to generate the aerosol.

In this trial the first dose has been selected after aerodynamic assessment of nebulised aerosol in accordance with European Pharmacopoeia 9th and USP 28. A starting dose of 150 mg will be most likely well tolerated and possibly able to reach the expected concentration in the target tissue.

On the basis of PK features of Teicoplanin (elimination half-life of the product varies from 100 to 170 hours in blood), of time-dependent killing characteristic, of the mechanism of action and of the expected MIC, an AUC0-12 h of more 300 μg/mL*h in the sputum will be effective in controlling MRSA infection. This value is thus an appropriate end point for a preliminary pilot study after single local administration and will likely allow optimal evaluation of the doses to be applied to test clinical efficacy on the basis of the following considerations:

• Repeated administrations, to be applied in later studies, will produce proportionally higher AUC values than single administration;
• Local ratio between AUC and MIC necessary to achieve killing of MRSA are likely lower than systemic ratio;
• Teicoplanin "off-label" experience is usually based on administration of doses unlikely to produce a AUC0-12 h above 300 μg/mL*h in the sputum.

In conclusion, on the basis of literature data an AUC0-12 h above 300 μg/mL*h in the sputum is achievable within the planned protocol, is likely to be clinically relevant in patients with MRSA lung infection and is likely well tolerated even by patients with chronic lung inflammation as those who will be enrolled in the proposed study.