Research paperInhalable highly concentrated itraconazole nanosuspension for the treatment of bronchopulmonary aspergillosis
Graphical abstract
Itraconazole is insoluble in aqueous media. Using wet-milling with organic grinding media and polysorbate 80 in water, a stable nanosuspension was generated with up to 20% itraconazole, which can be nebulized with standard inhaler technology. An inhaled dose of 45 mg/kg administered once daily for 7 days was well tolerated in rats. Inhalation resulted in high lung exposure with >24 h tissue half-life in rats.
Introduction
Cystic fibrosis (CF) is a recessive genetic disease affecting primarily the lungs, but also the pancreas, liver, and intestine. It is characterized by abnormal transport of chloride and sodium across epithelium, leading to thick, viscous secretions [1]. The hallmark pulmonary symptoms of CF are accumulation of thick, sticky mucus, frequent chest infections and coughing or shortness of breath [2]. Such pulmonary infections are the primary cause of morbidity and mortality among patients with CF; endobronchial infection with Pseudomonas aeruginosa is difficult to treat since aminoglycosides active against P. aeruginosa penetrate sputum poorly. While before 1995, it was necessary to administer high intravenous doses of antibiotics to achieve therapeutic levels in sputum of CF patients, the introduction of an aqueous inhalable formulation of tobramycin has resulted in a substantial improvement of the antibacterial therapy in CF patients, directly targeting the endobronchial infection and reducing systemic toxicity such as ototoxicity [3]. Indeed, the use of inhaled tobramycin is now standard for maintenance therapy of CF patients [4], and the inhaled administration in non-CF patients has also been reported to be advantageous [5].
Aspergillus is a ubiquitous mold representing between 0.1% and 22% of the total air spores sampled [6]. There are approximately 250 species of Aspergillus, but only a few are human pathogens [7]. The respiratory tract is the main target organ for Aspergillus infections. Inhaled spores are able to germinate under the ideal conditions (e.g., high humidity, oxygen, and carbon dioxide) present in the lung [8], [9]. Depending on the immunological status of an affected individual and the pathogenicity of the strain, the respiratory diseases caused by Aspergillus colonization are classified as saprophytic (aspergilloma), allergic (allergic Aspergillus sinusitis, allergic bronchopulmonary aspergillosis—ABPA), and invasive (airway invasive aspergillosis, chronic necrotizing pulmonary aspergillosis) [10].
The stiff mucus and the impaired mucociliary clearance in CF patients is an ideal environment not only for Pseudomonas, but also for Aspergillus species. Indeed, up to 57% of patients with CF are colonized in the lower respiratory tract with Aspergillus fumigatus [11]. While this colonization is often asymptomatic, it can result in the development of ABPA, a hypersensitivity reaction to A. fumigatus antigens characterized by type I and type III hypersensitivity reactions. About 10–20% of CF patients colonized with A. fumigatus develop manifest symptoms of ABPA resulting in a prevalence of 7.8% in this population [12]. ABPA is also found in patients with chronic asthma with an incidence rate of up to 6% [13]. In ABPA patients, repeated episodes of bronchial obstruction, inflammation, and mucoid impaction can lead to bronchiectasis, fibrosis, and respiratory compromise [12].
While the introduction of inhaled tobramycin has changed the therapeutic approach to bacterial lung infections aiming at reducing or eradicating the bacterial burden in affected patients, the standard therapy of ABPA is currently focused on controlling the allergy associated symptoms by administration of glucocorticoids, to prevent chronic lung damage [14]. The fact that the lung is colonized by A. fumigatus is not yet a therapeutic focus. The antifungal azole itraconazole (ITRA) has been successfully used as high dose oral treatment of ABPA [15], either as monotherapy or in combination with glucocorticoids. It is now accepted that systemic administration of ITRA is capable of reducing the required dose of glucocorticoids in patients suffering from ABPA [14].
ITRA is a poorly soluble weak base with a calculated log P of 6.2. Its aqueous solubility is estimated at approximately 1 ng/ml at neutral pH and approximately 4 μg/ml at pH 1 [16]. To prevent germination of fungal spores ITRA levels of greater than 0.5 μg/g of lung tissue or 0.5 μg/ml of blood [17] is generally required. It is difficult to obtain suitable systemic concentrations of ITRA using currently used oral formulations because of its poor and erratic absorption characteristics [18], [19], [20]. Therefore, an inhalable formulation of ITRA would represent an interesting treatment option for ABPA. The challenge to overcome is the high dose to be administered to achieve therapeutic concentrations [14], [15]. We, therefore, focused on aqueous nebulizer systems, where the volumes of 1–8 ml are nebulized per administration. Three different technologies are now available. Pressurized air nebulizers represent a well-established technology, which was recently upgraded by inducing the breath activated nebulization to control and minimize the amount of wasted medication. Vibrating mesh nebulizers offer the advantages of higher respirable fractions when compared with pressurized air nebulizers [21]. A third technology is ultrasonic wave nebulization, where a piezoelectric element is in contact with a liquid reservoir, and its high frequency vibration is sufficient to produce a vapor mist [22]. The aim of this study was to develop an aqueous ITRA nanosuspension, which can be nebulized with all three inhalation device platforms capable of achieving high lung concentrations.
Section snippets
Preparation of nanosuspension
A wet-milling process using a pearl mill to generate a stable nanosuspension of ITRA was selected. For this purpose, microcrystalline ITRA (Matrix Laboratories Ltd, Secunderabad, India) was pre-suspended in distilled water at a concentration of 5–20% by weight with addition of a suitable stabilizer using a high shear mixer (Ultra-Turrax homogenizer, IKA-Werke GmbH & Co., Staufen, Germany). As suspension stabilizers poloxamer 188 (Fagron GmbH, Barsbüttel, Germany), Solutol® HS 15 (BASF AG,
Selection of the stabilizing excipient
The aim was to develop a stable ITRA suspension with a high drug concentration of up to 20% and a low concentration of stabilizing excipients. Polysorbate 80, Solutol® HS 15, and poloxamer 188 were compared in a first series of experiments. The ITRA concentration was selected to be 5% or 20%, and stabilizer concentrations of 25% and 100% relative to ITRA were selected. Organic grinding media were used, and the milling time was set to 240 min. While with poloxamer 188, no measurable particle size
Discussion
The main route of infection for Aspergillus spp. is through the lungs, and inhaled spores are able to germinate on bronchial and alveolar epithelium, due to the high humidity and the presence of oxygen and carbon dioxide in the lung [8], [9]. While in immune competent individuals, an Aspergillus infection is immediately limited, and spores are phagocytized by alveolar macrophages, an immune-compromised patient is often not capable of fighting the infection effectively.
While pulmonary derived
Conclusions
The novel ITRA nanosuspension for inhalation represents an interesting novel tool for the treatment of ABPA in patients with CF. The formulation is tasteless and nonirritant. Due to the high concentration of ITRA in the suspension, a dose of 100 mg or more can be easily inhaled using standard nebulizer technology. High lung concentrations are reached, enabling once daily administration. Pulmonary administration of anti-infective agents was successfully established to treat Pseudomonas infections
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Current address: Baxter Oncology GmbH Halle/Westfalen, Germany.