Sterilization of corticosteroids for ocular and pulmonary delivery with supercritical carbon dioxide
Graphical abstract
Introduction
Sterility is a requisite for ocular formulations including suspensions (EDQM., 2011a) and it has recently become mandatory also for many inhalatory formulations such as nasal liquids and single-dose products for nebulization (QWP, 2012).
It can be obtained through a sterilization process that can be defined as a procedure affording at least a 6 order of magnitude reduction of the microbial bioburden.
Glucocorticosteroids, a class of drugs used in the treatment of allergies, airways inflammation and inflammatory ocular diseases, are often difficult to sterilize due to their inherent sensibility to heat or irradiation induced degradation (Bosela et al., 2010, Bussey et al., 1983, Hayes et al., 2011, Kane and Tsuji, 1983). Being often in form of suspension, obviously the final medicinal product cannot be sterilized by filtration.
Patent literature reports different attempts to set suitable conditions for obtaining sterile glucocorticoids without altering the physico-chemical characteristics of the drug with particular respect to particle size, purity and crystallinity (Bussey et al., 1983, Gentile et al., 2003). However, the cited examples are mainly based on the use of heat for a prolonged period of time as sterilizing agent.
The effectiveness of supercritical CO2 (SC-CO2) based method for the sterilization of food and biomedical materials is well documented in the literature (Ballestra and Cuq, 1998, Ballestra et al., 1996, Ferrentino et al., 2012, Ferrentino and Spilimbergo, 2011, Garcia-Gonzalez et al., 2007, Jimenez et al., 2008, Reverchon et al., 2010, Spilimbergo et al., 2002).
The actual mechanism involved in the sterilization with supercritical carbon dioxide is still matter of debate (Andras et al., 2010, Dillow et al., 1999, Enomoto et al., 1997, Nakamura et al., 1994, Spilimbergo et al., 2002).
Whatever would be the mechanism beyond the methods of sterilization with sub- or supercritical CO2, it is evident that SC-CO2 can be suitably exploited for sterilizing medical devices (Hemmer, 2005, Jiménez and Matthews, 2007, Reverchon et al., 2010) and drug delivery systems (Dillow et al., 1999, Jimenez et al., 2008, Pasquali and Bettini, 2008).
Few data are available on the use of SC-CO2 for the sterilization of active pharmaceutical ingredients in powder form in particular of corticosteroids (Burns et al., 2011, Howell et al., 2012, Pavese, 2005).
In particular, Pavese (Pavese, 2005) claims the sterilization of micronized powders of glucocorticoids, in particular beclometasone dipropionate, by treating in an autoclave the material with carbon dioxide at 80 bar and 125 °C for 25 min. It is worthy underscoring that standard steam sterilization in autoclave is carried out at 121 °C for 15 min (EDQM., 2011c), thus the addition of SC-CO2 seems to be only related to the creation of a non-oxidative environment inside the autoclave. Therefore, a specific role of the supercritical status is hardly seen here.
Burns and co-workers described a method for effective sterilization of drugs implying controlled pressurization and depressurization in the presence of a sterilization additive such as hydrogen peroxide, acetic acid, peracetic acid or trifluoroacetic acid (Burns et al., 2011).
A similar approach has been recently reported by Howell et al. who described the simultaneous drying and sterilization of active pharmaceutical ingredients directly in a dispensing container with SC-CO2 and peracetic acid (Howell et al., 2012).
The aim of the present work was to investigate the suitability of SC-CO2 at mild temperature (40 or 55 °C) for the decontamination of corticosteroid powders both in dry or wet form. Beclometasone dipropionate anhydrous (9-Chloro-11β-hydroxy-16β-methyl-3,20-dioxopregna-1,4-diene-17,21-diyl dipropanoate) and budesonide, a mixture of the C-22S (epimer A) and the C-22R (epimer B) epimers of (16α,17[(1RS)-butylidenebis(oxy)]-11β,21-dihydroxypregna-1,4-diene-3,20-dione) were taken as model drugs and the influence of the decontamination process on the physico-chemical properties of such drugs was studied in detail: chemical integrity was investigated by HPLC, whereas the effect of the sterilization treatments on solid-state properties (crystal phase, degree of crystallinity, content of water and particle size distribution) was investigated by Differential Scanning Calorimetry, DSC, Thermo-Gravimetric Analysis, TGA, Powder X-Ray Diffraction, PXRD, Karl-Fischer titration and laser light diffraction.
Section snippets
Test microorganisms
The antimicrobial potential of CO2 treatment was investigated against Gram-positive bacteria Staphylococcus epidermidis ATCC12228, Bacillus pumilus BGSC 8E2 and spores of Bacillus subtilis ATCC 6633, used to contaminate pharmaceutical powders.
The selected strains of S. epidermidis and B. pumilus were incubated overnight in Mueller Hinton Broth (Oxoid Ltd, Basingstoke, Hampshire, England) at 37 °C. The bacterial cultures were added with glycerol at the concentration of 10% (v/v) and stored at −80
Effect of temperature
Preliminary, the effect of temperature on the supercritical sterilization of a BDP dry powder contaminated with S. epidermidis was investigated by submiting the samples to a single pressurization cycle at 200 bar for 3 h at 40 or 55 °C.
The degree of contamination before and after thermal or supercritical treatments are reported in Table 1.
Data reported in Table 1 relevant to the degree of contamination of the treated materials present quite a high standard deviation, which reflects the large
Conclusions
From the presented data it can be concluded that SC treatment in wet environment is a suitable method for reducing by at least six orders of magnitude the degree of contamination of powdered steroidal drugs when vegetative bacteria are concerned. The method is very effective even when the powders are highly contaminated.
The findings of this work are of particular interest for the application in the case of aqueous suspension of steroids for aerosol therapy or ocular delivery, where the
Acknowledgement
The financial support of Eratech is kindly acknowledged.
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