Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1   Pharmacodynamic properties
Pharmacotherapeutic group: Antibacterials for systemic use, Aminoglycoside antibacterials, ATC Code: J01GB01
Mechanism of action
Tobramycin is an aminoglycoside antibiotic produced by Streptomyces tenebrarius. It acts primarily by disrupting protein synthesis leading to altered cell membrane permeability, progressive disruption of the cell envelope and eventual cell death. It is bactericidal at concentrations equal to or slightly greater than inhibitory concentrations.
Breakpoints
Established susceptibility breakpoints for parenteral administration of tobramycin are inappropriate in the aerosolised administration of the medicinal product.
Sputum from cystic fibrosis exhibits an inhibitory action on the local biological activity of inhaled aminoglycosides. This necessitates sputum concentrations of tobramycin after inhalation to be about ten-fold above the minimum inhibitory concentration (MIC) or higher for P.
aeruginosa suppression. In the active-controlled study, at least 89% of patients had P. aeruginosa isolates with MICs at least 15 times lower than mean post-dose sputum concentration, both at baseline and at the end of the third active treatment cycle.
Susceptibility
In the absence of conventional susceptibility breakpoints for the inhaled route of administration, caution must be exercised in defining organisms as susceptible or insusceptible to inhaled tobramycin.
The clinical significance of changes in MICs of tobramycin for P. aeruginosa has not been clearly established in the treatment of cystic fibrosis patients. Clinical studies with inhaled tobramycin solution (TOBI) have shown a small increase in tobramycin, amikacin and gentamicin Minimum Inhibitory Concentrations for P. aeruginosa isolates tested. In the open label extensions, each additional 6 months of treatment resulted in incremental increases similar in magnitude to that observed in the 6 months of placebo-controlled studies.
Resistance to tobramycin involves different mechanisms. The main resistance mechanisms are drug efflux and drug inactivation by modifying enzymes. The unique characteristics of chronic P.
aeruginosa infections in CF patients, such as anaerobic conditions and high frequency of genetic mutations, may also be important factors for reduced susceptibility of P. aeruginosa in CF patients.
Based upon in vitro data and/or clinical trial experience, the organisms associated with pulmonary infections in CF may be expected to respond to TOBI Podhaler therapy as follows: Susceptible                                         Pseudomonas aeruginosa Haemophilus influenzae
Staphylococcus aureus
Insusceptible                                       Burkholderia cepacia Stenotrophomonas maltophilia
Alcaligenes xylosoxidans

Clinical experience
The TOBI Podhaler Phase III clinical development program consisted of two studies and 612 treated patients with a clinical diagnosis of CF, confirmed by quantitative pilocarpine iontophoresis sweat chloride test or well-characterised disease causing mutations in each cystic fibrosis transmembrane regulator (CFTR) gene, or abnormal nasal transepithelial potential difference characteristic of CF.
In the placebo controlled study, patients were aged 6 - ≤22 years with an FEV1 at screening of between 25% and 84% of predicted normal values for their age, sex and height based upon Knudson criteria. In the active controlled studies, all patients were aged >6 years old (range 6-66 years) with an FEV1 % predicted at screening of between 24% and 76%. In addition, all patients were infected with P. aeruginosa as demonstrated by a positive sputum or throat culture (or bronchoalveolar lavage) within 6 months prior to screening, and also in a sputum culture taken at the screening visit.
In a randomised, double-blind, placebo-controlled, multicentre study, TOBI Podhaler 112 mg (4 x 28 mg capsules) was administered twice daily, for three cycles of 28 days on-treatment and 28 days off-treatment (a total treatment period of 24 weeks). Patients who were randomised to the placebo treatment group received placebo during the first treatment cycle and TOBI Podhaler in the subsequent two cycles. Patients in this study had no exposure to inhaled tobramycin for at least 4 months prior to study start.
TOBI Podhaler significantly improved lung function compared with placebo, as shown by the relative increase in percent predicted FEV1 of about 13% after 28 days of treatment. The improvements in lung function achieved during the first treatment cycle were maintained during the two subsequent cycles of treatment with TOBI Podhaler.
When patients in the placebo treatment group were switched from placebo to TOBI Podhaler at the start of the second treatment cycle, they experienced a similar improvement from baseline in percent predicted FEV1. Treatment with TOBI Podhaler for 28 days resulted in a statistically significant reduction in P. aeruginosa sputum density (mean difference with placebo about 2.70 log10 in colony forming units/CFUs).
In a second open-label, multicentre study, patients received treatment with either TOBI Podhaler (112 mg) or tobramycin 300 mg/5 ml nebuliser solution (TOBI), administered twice daily for three cycles. A majority of the patients were tobramycin-experienced adults with chronic pulmonary P. aeruginosa infection.
Treatment with both TOBI Podhaler and tobramycin 300 mg/5 ml nebuliser solution (TOBI) resulted in relative increases from baseline to day 28 of the third treatment cycle in percent predicted FEV1 of 5.8% and 4.7%, respectively. The improvement in percent predicted FEV1 was numerically greater in the TOBI Podhaler treatment group and was statistically non-inferior to TOBI nebuliser solution. Although the magnitude of improvements in lung function was smaller in this study, this is explained by the previous exposure of this patient population to treatment with inhaled tobramycin. Over half of the patients in both the TOBI Podhaler and TOBI nebuliser solution treatment groups received new (additional) anti-pseudomonal antibiotics (64.9% and 54.5% respectively, the difference consisting mainly of oral ciprofloxacin use). The proportions of patients requiring hospitalisation for respiratory events were 24.4% with TOBI Podhaler and 22.0% with TOBI nebuliser solution.
A difference in FEV1 response by age was noted. In the patients aged <20 years the increase from baseline percent predicted FEV1 was larger: 11.3% for TOBI Podhaler and 6.9% for the nebuliser solution after 3 cycles. A numerically lower response in patients aged ≥20 years was observed: the change from baseline FEV1 observed in the patients aged ≥20 years was smaller (0.3% with TOBI Podhaler and 0.9% with TOBI nebuliser solution).
Furthermore, an improvement of 6% in percent predicted FEV1 was obtained in about 30% versus 36% of the adult patients in the TOBI Podhaler and TOBI nebuliser solution group respectively.
Treatment with TOBI Podhaler for 28 days resulted in a statistically significant reduction in P.
aeruginosa sputum density (-1.61 log10 CFUs), as did the nebuliser solution (-0.77 log10 CFUs).
Suppression of sputum P. aeruginosa density was similar across age groups in both arms. In both studies, there was a trend for a recovery of P. aeruginosa density after the 28 days off-treatment period, which was reversed after a further 28 days on-treatment.
In the active-controlled study, administration of a TOBI Podhaler dose was faster with a mean difference of approximately 14 minutes (6 minutes vs. 20 minutes with the nebuliser solution).
Patient-reported convenience and overall treatment satisfaction (as collected through a patient- reported outcomes questionnaire) were consistently higher with TOBI Podhaler compared with tobramycin nebuliser solution in each cycle.
For safety results see section 4.8.

Paediatric population

See section 4.2 for information on paediatric use.

Pharmacokinetic Properties

5.2 Pharmacokinetic properties

Absorption
The systemic exposure to tobramycin after inhalation of TOBI Podhaler is expected to be primarily from the inhaled portion of the medicinal product as tobramycin is not absorbed to any appreciable extent when administered via the oral route.
Serum concentrations
After inhalation of a 112 mg single dose (4 x 28 mg capsules) of TOBI Podhaler in cystic fibrosis patients, the maximum serum concentration (Cmax) of tobramycin was 1.02 ± 0.53 μg/ml (mean ± SD) and the median time to reach the peak concentration (Tmax) was one hour. In comparison, after inhalation of a single dose of tobramycin 300 mg/5 ml nebuliser solution (TOBI), Cmax was 1.04 ± 0.58 μg/ml and median Tmax was one hour. The extent of systemic exposure (AUC) was also similar for the 112 mg TOBI Podhaler dose and the 300 mg tobramycin nebuliser solution dose. At the end of a 4-week dosing cycle of TOBI Podhaler (112 mg twice daily), maximum serum concentration of tobramycin 1 hour after dosing was 1.99 ± 0.59 μg/ml.
Sputum concentrations
After inhalation of a 112 mg single dose (4 x 28 mg capsules) of TOBI Podhaler in cystic fibrosis patients, sputum Cmax of tobramycin was 1047 ± 1080 μg/g (mean ± SD). In comparison, after inhalation of a single 300 mg dose of tobramycin nebuliser solution (TOBI), sputum Cmax was 737.3 ± 1028.4 μg/g. The variability in pharmacokinetic parameters was higher in sputum as compared to serum.
Distribution
A population pharmacokinetic analysis for TOBI Podhaler in cystic fibrosis patients estimated the apparent volume of distribution of tobramycin in the central compartment to be 84.1 liters for a typical CF patient. While the volume was shown to vary with body mass index (BMI) and lung function (as FEV1% predicted), model-based simulations showed that peak (Cmax) and trough (Ctrough) concentrations were not impacted markedly with changes in BMI or lung function.
Biotransformation
Tobramycin is not metabolised and is primarily excreted unchanged in the urine.
Elimination
Tobramycin is eliminated from the systemic circulation primarily by glomerular filtration of the unchanged compound. The apparent terminal half-life of tobramycin in serum after inhalation of a 112 mg single dose of TOBI Podhaler was approximately 3 hours in cystic fibrosis patients and consistent with the half-life of tobramycin after inhalation of tobramycin 300 mg/5 ml nebuliser solution (TOBI).
A population pharmacokinetic analysis for TOBI Podhaler in cystic fibrosis patients aged 6 to 66 years estimated the apparent serum clearance of tobramycin to be 14 liters/h. This analysis did not show gender or age-related pharmacokinetic differences