Pharmaceutical NanotechnologyEvaluation of the physical properties and stability of two lipid drug delivery systems containing mefloquine
Graphical abstract
Introduction
Due to an increase in demand for more effective and safer drugs, drug delivery systems development has increased in the last decades (Buszello and Müller, 2000, Ranade and Hollinger, 2004). These systems can transport drugs for site specific delivery leading to enhanced efficacy and bioavailability, decrease adverse reactions and improve patient compliance (Date et al., 2007, Mahato, 2007, Ranade and Hollinger, 2004). Colloidal drug carriers consist of a dispersed phase in a continuous phase and have been investigated for targeted delivery (Buszello and Müller, 2000, Date et al., 2007, Mahato, 2007).
The most extensively researched colloidal system is liposomes (Sharma and Sharma, 1997). The vesicles are composed of a lipid bilayer with an aqueous compartment (New, 1990, Sharma and Sharma, 1997) and can entrap both hydrophilic and lipophilic drugs increasing the versatility of liposomes (Date et al., 2007, New, 1990). Liposome properties vary considerably with lipid composition, size and method of preparation (Betageri et al., 1993). Liposomes differ in size from 80 nm to 100 μm and can be manipulated according to specific requirements (New, 1990, Sharma and Sharma, 1997). Site specific delivery, sustained release and reduction in toxicity are some of the advantages of this lipid drug delivery system (Betageri et al., 1993, Date et al., 2007, New, 1990). Research into the application of liposomes in malaria include artemether (Joshi et al., 2008a, Joshi et al., 2008b), artesunate (Gabriels and Plaizier-Vercammen, 2003), chloroquine (Qiu et al., 2008) and primaquine (Stensrud et al., 2000).
Pheroid™ technology is a patented colloidal delivery system consisting of a dispersed phase of plant and essential fatty acid in a nitrous oxide saturated continuous water phase. Pheroid™ also consists of a lipid bilayer that is dynamic and constantly changing, but has high stability. Like liposomes, Pheroid™ can entrap both hydrophilic and lipophilic drugs. Pheroid™ lipid carrier system can be manipulated in formulation, structure and size for various applications (Grobler et al., 2007). Pheroid™ has been successfully used in nasal peptide delivery (Du Plessis et al., 2010), transdermaly (Gerber et al., 2008, Grobler et al., 2007, Saunders et al., 1999) and cosmetic application (Grobler et al., 2007).
Malaria affects billions of people in 109 countries worldwide, almost half situated in Africa (WHO, 2010a, WHO, 2010b)(WHO, 2010a, WHO, 2010c). Malaria is responsible for 20% of deaths in children (WHO, 2010b). Anti-parasitic disease drug discovery only accounts for 1% of new drug development (Date et al., 2007). Mefloquine, a blood schizonticidal drug, is used as treatment and chemoprophylaxis of malaria (Basco, 2007, Rosenthal, 2004). Mefloquine in combination with artemisinins showed to be highly effective with good tolerability (Bouyou-Akotet et al., 2010, Congpuong et al., 2010). Adverse reactions include gastrointestinal and neurological disturbances (Rosenthal, 2004). Neurotoxicity has been demonstrated in vitro (Dow et al., 2003), in vivo (Dow et al., 2006) and numerous reports of neurological symptoms in humans exist (Arguin and Steele, 2010, Rendi-Wagner et al., 2002). Mefloquine has been successfully formulated in emulsions with satisfactory stability and high antimalarial activity (Mbela et al., 1998, Mbela et al., 1994). Stability is mainly evaluated to ensure the product will remain in a state of adequate quality throughout its shelf life and is most difficult to attain (Rhodes, 1979). Stability testing under different environmental factors provides evidence of the quality of the product needed for registration (ICH, 2006).
These lipid based colloidal drug delivery systems is similar in structure, size and drug loading ability. The present study is intended to evaluate the physical stability of mefloquine loaded Pheroid™ vesicles and liposomes under different storage condition for three months. Characteristics under investigation include the flow cytometric evaluation of size, entrapment efficacy by means of UV-spectrophotometry and pH.
Section snippets
Materials
Vitamin F ethyl ester was obtained from Chemimpo (South Africa), Cremophor® RH40 from BASF (Germany) and dl-α-tocopherol from DSM (Basel, Switzerland). High grade chloroform and methanol were obtained from Rochelle Chemicals (South Africa). The following were purchased from Sigma–Aldrich® (St. Louis, MO, USA): cholesterol; l-α-phosphatidylcholine; Nile Red; and Sephadex® G50. Mefloquine hydrochloride (MQ) was purchased from Sifaviton S.p.A (Mairano, Italy). Flow Cytometry Size Calibration Kit
Size determination
Size determination of lipid drug delivery systems are usually conducted with dynamic light scattering (Sintov and Botner, 2006, Vicentini et al., 2010) but large sample volumes are needed and is based on the equivalent sphere principle (Gaumet et al., 2008). Flow cytometry can measure and analyse physical characterizations, like size of a single particle as it passes through a beam of light (BD Biosciences, 2002). Flow cytometry technology is a reliable and accurate quantitative tool for
Discussion
The aim of the study was to determine the stability of liposomes and Pheroid™ vesicles by determination of pH, particle size and entrapment efficacy over a three month period. A limiting problem of liposomes is the physical stability including aggregation of vesicles to form larger particles (Sharma and Sharma, 1997). Results of this study showed an increase in size of liposomes at different temperatures with significant changes at 30 °C. The liposomes remained structurally stable as seen with
Conclusion
MQ was successfully entrapped in Pheroid™ vesicles both during and after manufacturing and proved to be stable during three month stability testing. Results of size determination at the different storage conditions for both Pheroid™ vesicle formulations was around 3 μm. MQ interfered with the size and structural integrity of the liposomes with low stability compared to Pheroid™ vesicles. The liposome formulations were double the initial size of Pheroid™ vesicles increasing over time. Liposomes
Acknowledgements
The authors are grateful to the Innovation Fund (Project number: T60042) for financial support.
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