Design, formulation and evalauation of liposomes co-loaded with human serum Albumin and Rifampicin
- Authors: Bapolisi, Alain Murhimalika
- Date: 2020
- Subjects: Liposomes , Serum albumin , Rifampin , Mycobacterium tuberculosis
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/161780 , vital:40670
- Description: Tuberculosis (TB) is a devastating infectious disease caused by Mycobacterium tuberculosis and is the leading cause of death from a single infectious agent. The high morbidity and mortality rates of TB are partly due to factors such as the lengthy regimen (of 6–24 months), the development of drug resistance, and the pathogen location within the macrophages. These, with poor physiochemical properties of existing drugs hamper the effectiveness of the treatment despite the existence of potent antibiotics such as Rifampicin (Rif). Hydrophobicity plagues many drugs, including Rif, which are then particularly affected due to inherently poor intracellular availability. Novel drug delivery approaches are therefore needed in order to optimize the cytotoxic potential of said antitubercular drugs. To improve the bioavailability of hydrophobic drugs, numerous delivery strategies have been developed. Amongst these, the coordination of cytotoxic drugs to therapeutic proteins have shown some success for improved efficacy in the management of illnesses including infectious diseases. Of therapeutic proteins, Human Serum Albumin (HSA) is an attractive drug carrier with interestingbenefits such as low immunogenicity, antioxidant properties and improving cellular uptake ofdrugs through HSA-specific binding sites which are expressed on most cells including macrophages, where M. tuberculosis often resides. Hence, combination of Rif to HSA (Rif-HSA)seems a promising approach for improved intracellular delivery of Rif. However, the in vivo stability of colloidal protein-based therapeutics is mostly challenging and an effective vehicle is needed to control the biological fate of such conjugates.Liposomes seem to be appropriate carriers for the Rif-HSA complex due to their reputable applicability for encapsulating diverse materials (i.e., hydrophobic and hydrophilic compounds or small and complex molecules) and preventing chemical and biological degradation of the cargo. Therefore, the main objective of this study was to simultaneously encapsulate Rif and HSA in liposomes, which, to the best of our knowledge, has not been done before. The dual liposomes (Rif-HSA-lip) were made by a modified “Reverse Phase Evaporation” method (REV), following a Design of Experiments (DOE) approach to determine which factors impact the formulation. In addition, liposomes were made from crude soybean lecithin (CSL), rather than expensive and highly purified lipids. The liposomes were fully characterised, and the encapsulation efficiency (î) was monitored using high-performance liquid chromatography (HPLC). The results were correlated with factors such as organic and aqueous phase composition, as well as the in vitro release profile of Rif. Transmission electron microscopy (TEM) results confirmed the formation of spherical dual liposomes nanoparticles of roughly 200 nm. Dynamic light scattering (DLS) and Zeta potential measurements showed a negative charge (<–45 mV) and with satisfactory polydispersity (PDI<0.5). HSA dramatically improved the aqueous solubility of Rif (from1.9 mg/ml in water to around 4.3 mg/ml in HSA 10% solution) mainly due to Rif-HSA hydrophobic interactions. This resulted in a good î of almost 60% for Rif, despite the presence of bulky HSA in the lipid bilayer. These details were confirmed using proton nuclear magnetic resonance (1H NMR) and Fourier-transform infrared spectroscopy (FTIR). Furthermore, energy dispersive X-ray (EDX) and DLS data suggested the presence of HSA poking out on the surface of liposomes, which is encouraging for potential targeted delivery in the future. The in vitro release studies also depicted a substantial improvement in the diffusion of Rif in dual liposomes versus free Rif, from 65% after 12 hours for free Rif to 95% after only 5 hours for Rif- HSA-lip. Finally, stability studies conducted over 30 days at room temperature, showed that the freeze-dried formulations of Rif-HSA-lip exhibited good shelf stability over liposomes with no HSA. This study represents an illustrative example of co-loading of antibiotics and proteins into liposomes, which could encourage further development of novel nanoparticulate tools for the effective management of both drug-susceptible and -resistant infectious diseases such as TB.
- Full Text:
- Date Issued: 2020
Design, formulation and evaluation of liposomes co-loaded with human serum albumin and rifampicin
- Authors: Bapolisi, Alain Murhimalika
- Date: 2020
- Subjects: Liposomes , Rifampin , Antitubercular agents , Serum albumin , Albumins , Tuberculosis -- Treatment
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/163179 , vital:41016
- Description: Tuberculosis (TB) is a devastating infectious disease caused by Mycobacterium tuberculosis and is the leading cause of death from a single infectious agent. The high morbidity and mortality rates of TB are partly due to factors such as the lengthy regimen (of 6–24 months), the development of drug resistance, and the pathogen location within the macrophages. These, with poor physiochemical properties of existing drugs hamper the effectiveness of the treatment despite the existence of potent antibiotics such as Rifampicin (Rif). Hydrophobicity plagues many drugs, including Rif, which are then particularly affected due to inherently poor intracellular availability. Novel drug delivery approaches are therefore needed in order to optimize the cytotoxic potential of said antitubercular drugs. To improve the bioavailability of hydrophobic drugs, numerous delivery strategies have been developed. Amongst these, the coordination of cytotoxic drugs to therapeutic proteins have shown some success for improved efficacy in the management of illnesses including infectious diseases. Of therapeutic proteins, Human Serum Albumin (HSA) is an attractive drug carrier with interesting benefits such as low immunogenicity, antioxidant properties and improving cellular uptake of drugs through HSA-specific binding sites which are expressed on most cells including macrophages, where M. tuberculosis often resides. Hence, combination of Rif to HSA (Rif-HSA) seems a promising approach for improved intracellular delivery of Rif. However, the in vivo stability of colloidal protein-based therapeutics is mostly challenging and an effective vehicle is needed to control the biological fate of such conjugates. Liposomes seem to be appropriate carriers for the Rif-HSA complex due to their reputable applicability for encapsulating diverse materials (i.e., hydrophobic and hydrophilic compounds or small and complex molecules) and preventing chemical and biological degradation of the cargo. Therefore, the main objective of this study was to simultaneously encapsulate Rif and HSA in liposomes, which, to the best of our knowledge, has not been done before. The dual liposomes (Rif-HSA-lip) were made by a modified “Reverse Phase Evaporation” method (REV), following a Design of Experiments (DOE) approach to determine which factors impact the formulation. In addition, liposomes were made from crude soybean lecithin (CSL), rather than expensive and highly purified lipids. iv The liposomes were fully characterised, and the encapsulation efficiency (î) was monitored using high-performance liquid chromatography (HPLC). The results were correlated with factors such as organic and aqueous phase composition, as well as the in vitro release profile of Rif. Transmission electron microscopy (TEM) results confirmed the formation of spherical dual liposomes nanoparticles of roughly 200 nm. Dynamic light scattering (DLS) and Zeta potential measurements showed a negative charge (<–45 mV) and with satisfactory polydispersity (PDI<0.5). HSA dramatically improved the aqueous solubility of Rif (from1.9 mg/ml in water to around 4.3 mg/ml in HSA 10% solution) mainly due to Rif-HSA hydrophobic interactions. This resulted in a good î of almost 60% for Rif, despite the presence of bulky HSA in the lipid bilayer. These details were confirmed using proton nuclear magnetic resonance (1H NMR) and Fourier-transform infrared spectroscopy (FTIR). Furthermore, energy dispersive X-ray (EDX) and DLS data suggested the presence of HSA poking out on the surface of liposomes, which is encouraging for potential targeted delivery in the future. The in vitro release studies also depicted a substantial improvement in the diffusion of Rif in dual liposomes versus free Rif, from 65% after 12 hours for free Rif to 95% after only 5 hours for Rif- HSA-lip. Finally, stability studies conducted over 30 days at room temperature, showed that the freeze-dried formulations of Rif-HSA-lip exhibited good shelf stability over liposomes with no HSA. This study represents an illustrative example of co-loading of antibiotics and proteins into liposomes, which could encourage further development of novel nanoparticulate tools for the effective management of both drug-susceptible and -resistant infectious diseases such as TB.
- Full Text:
- Date Issued: 2020
Understanding the underlying resistance mechanism of Mycobacterium tuberculosis against Rifampicin by analyzing mutant DNA - directed RNA polymerase proteins via bioinformatics approaches
- Authors: Monama, Mokgerwa Zacharia
- Date: 2020
- Subjects: Mycobacterium tuberculosis , Rifampin , Drug resistance , Homology (Biology) , Tuberculosis -- Chemotherapy
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167508 , vital:41487
- Description: Tuberculosis or TB is an airborne disease caused by the non-motile bacilli, Mycobacterium tuberculosis (MTB). There are two main forms of TB, namely, latent TB or LTB, asymptomatic and non-contagious version which according to the World Health Organization (WHO) is estimated to afflict over a third of the world’s population; and active TB or ATB, a symptomatic and contagious version which continues to spread, affecting millions worldwide. With the already high reported prevalence of TB, the emergence of drug-resistant strains has prompted the development of novel approaches to enhance the efficacy of known drugs and a desperate search for novel compounds to combat MTB infections. It was for this very purpose that this study was conducted. A look into the resistance mechanism of Rifampicin (Rifampin or RIF), one of the more potent first-line drugs, might prove beneficial in predicting the consequence of an introduced mutation (which usually occur as single nucleotide polymorphisms or SNPs) and perhaps even overcome it using appropriate therapeutic interventions that improve RIF’s efficacy. To accomplish this task, models of acceptable quality were generated for the WT and clinically relevant, RIF resistance conferring, SNPs occurring at codon positions D516, H526 and S531 (E .coli numbering system) using MODELLER. The models were accordingly ranked using GA341 and z-DOPE score, and subsequently validated with QMEAN, PROCHECK and VERIFY3D. MD simulations spanning 100 ns were run for RIF-bound (complex) and RIF-free (holo) DNA-directed RNA polymerase (DDRP) protein systems for the WT and SNP mutants using GROMACS. The MD frames were analyzed using RMSD, Rg and RMSF. For further analysis, MD-TASK was used to analyze the calculated dynamic residue networks (DRNs) from the generated MD frames, determining both change in average shortest path (ΔL) and betweenness centrality (ΔBC). The RMSD analysis revealed that all of the SNP complex models displayed a level instability higher than that of the WT complex. A majority of the SNP complex models were also observed to have similar compactness to the WT holo when looking at the calculated Rg. The RMSF results also hinted towards possible physiological consequences of the mutations (generally referred to as a fitness cost) highlighted by the increased fluctuations of the zinc-binding domain and the MTB SI α helical coiled coil. For the first time, to the knowledge of the authors, DRN analysis was employed for the DDRP protein for both holo and complex systems, revealing insightful information about the residues that play a key role in the change in distance between residue pairs along with residues that play an essential role in protein communication within the calculated RIN. Overall, the data supported the conclusions drawn by a recent study that only concentrated on RIF-resistance in rpoB models which suggested that the binding pocket for the SNP models may result in the changed coordination of RIF which may be the main contributor to its impaired efficacy.
- Full Text:
- Date Issued: 2020
Ph-responsive liposomal systems for site-specific pulmonary delivery of anti-tubercular drugs
- Authors: Nkanga, Christian Isalomboto
- Date: 2019
- Subjects: Tuberculosis -- Chemotherapy , Lipsomes , Drug carriers (Pharmacy) , Rifampin , Hydrogen-ion concentration , Hydrogen-ion concentration -- Physiological effect
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/125832 , vital:35822
- Description: Tuberculosis (TB) is an infectious disease that has been reported to be the ninth leading cause of death worldwide, even though mostly considered as a poverty related disease. Despite the existence of potent anti-tubercular drugs (ATBDs), such as rifampicin (RIF) and isoniazid (INH), TB remains the major killer among many microbial diseases over the last five years. Although several factors are to be blamed for this deadly status, the most crucial issues encompass both the self-defensiveness of the causative agent (Mycobacterium tuberculosis), including its intra-macrophage location that compromises ATBDs accessibility, and the widespread/off target distribution of ATBDs. The need for novel drug delivery strategies therefore arises to provide selective distribution of ATBDs at the infected site. Among the drug vehicles explored in this field, liposomes have been reported to be the most suitable drug carriers due to their rapid uptake by alveolar macrophages, where M. tuberculosis often resides. Since liposomes experience media of different pH throughout the cell uptake process (endocytosis/phagocytosis), the use of pH change as a stimulus for controlled release looks promising for enhancing intra-macrophage delivery and minimizing premature ‘off-target’ release of ATBDs. However, the costly status of liposome technology, due to the use of sophisticated procedures and expensive materials (especially for pH-dependent delivery, where special lipids are required), may preclude wider developments of liposomal products, especially for the developing world. This study aimed at investigating liposomal encapsulation of pH-sensitive and fluorescent hydrazone derivatives of INH using crude soybean lecithin, as a cost-effective option for site-specific delivery combined with potential bio-imaging features. Another objective was to explore encapsulation of INH hydrazone derivatives with and without RIF in liposomes using a simple and organic solvent-free preparation method. Initially, INH was coupled with 4-hydroxy-benzaldehyde to yield a conjugate (INH-HB) that was encapsulated in liposomes using film hydration method with acceptable encapsulation efficiency (î), about 89 %. The prepared INH-HB loaded liposomes (IHL) were characterized by means of dynamic light scattering (DLS), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The release of INH from IHL was evaluated over 12 hours in media of different pH using dialysis. As hypothesized, pH dependent release of INH from IHL was observed with 22, 69, 83 and 100 % release obtained in media of pH 7.4, 6.4, 5.4 and 4.4, respectively. From this experimental trial, further development was undertaken by conjugating INH to a hydrophobic fluorescent tag, zinc (II) phthalocyanine (PC), through hydrazone linkages. The obtained conjugate (PC-INH) was loaded into liposomes (PIL) that were characterized using various spectroscopic techniques, including UV-Vis absorption and energy dispersive X-ray spectroscopy, which suggested the presence of PC-INH within the lipid bilayers. The release study performed in different pH media revealed 22, 41, 97 and 100 % of INH, respectively released at pH 7.4, 6.4, 5.4 and 4.4. This confirmed the potential of pH-triggered drug release from liposomes loaded with hydrazone drug derivatives. In addition, successful encapsulation of PC-INH using crude soybean lecithin inspired a new opening towards development of multimodal liposomes that could achieve controlled drug release with added benefits of image-guided biological tracking. However, the hydrophobic nature of PC-INH requires an effective strategy that could improve its solubility and favour extensive development. In this context, the tetra-substituted structure of PC-INH brought up the hypothesis that cyclodextrin (CD) complexation would facilitate PC-INH encapsulation in liposomes using an organic solvent-free method, called here the “heating method” (HM). Inclusion complexes of PC-INH with various CDs were therefore investigated, with gamma-CD complex (CP) giving the best results. These complexes were prepared in both solution and solid-state and further comprehensively characterized using UV-Vis spectroscopy, magnetic circular dichroism, NMR spectroscopy, diffusion ordered spectroscopy, DSC, XRD and Fourier transform infrared spectroscopy. CP-loaded liposomes prepared using HM exhibited greater î than film hydration liposomes, about 70 % versus 56 %, respectively. The HM-liposomal system (CPL) exhibited potentially useful nano particulate characteristics (i.e. mean particle size 240 nm and Zeta potential –57 mV), which remained unchanged over 5 weeks of stability study at 4 °C, and pH-dependent INH release behaviour alike PIL. Furthermore, CP was co-encapsulated with rifampicin (RIF) in liposomes using HM to investigate the possibility for future combination therapy. 1H-NMR spectroscopy, DSC, XRD and photophysical studies were performed for molecular assessment of the cargo in CP-RIF co-loaded liposomes (CPRL). The mean particle size, Zeta potential and î of CPRL were respectively 594 nm, –50 mV, 58 % for CP and 86 % for RIF. CPRL exhibited much higher release rates for both INH and RIF at pH 6.4, compared to those tested at pH 7.4. In addition, there was no cytotoxicity on HeLa cells, but attractive lung fibroblasts and epithelial cells uptake and viability. Hence, CPRL are promising for targeted ATBD delivery to alveolar macrophages following pulmonary administration. Overall, the developed pH-responsive liposomal system holds the promise for new openings towards wider developments of multifunctional liposomes for site-specific controlled pulmonary delivery of antimicrobials drugs.
- Full Text:
- Date Issued: 2019
The development, manufacture and evaluation of sustained release gastric-resistant isoniazid and gastroretentive microporous rifampicin microspheres
- Authors: Mwila, Chiluba
- Date: 2018
- Subjects: Biodegradation , Microspheres (Pharmacy) , Drug delivery systems , Rifampin , Isoniazid
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/63497 , vital:28421 , DOI 10.21504/10962/63497
- Description: According to the World Health Organization Global Tuberculosis (TB) 2017 Report, there were an estimated 10.4 million new TB cases worldwide of which, in 2016, 65 % occurred in men, 28.1 % in women and 6.9 % in children. TB is the ninth leading cause of death globally and is the leading cause due to an infectious organism surpassing HIV/AIDS. Treatment is long-term and the use of a combination of medicines is required for success. The concern related to the use of fixed dose combination products for the treatment of TB is the issue of low bioavailability of rifampicin observed from a number of fixed dose combination (FDC) formulations. The hydrolysis of rifampicin, in acidic media, to form insoluble 3-formyl rifamycin SV contributes to poor bioavailability of rifampicin. The degradation of rifampicin to form this poorly absorbed compound is accelerated in the presence of isoniazid via the reversible formation of isonicotinyl hydrazone is a further factor contributing to the poor bioavailability of rifampicin. Therefore, the development of a novel drug delivery technology that prevents interactions between rifampicin and isoniazid in an acidic medium is required. A Box Behnken design was successfully used for the optimisation of a rapid and accurate stability-indicating gradient elution RP-HPLC method for the simultaneous analysis of isoniazid, pyrazinamide and rifampicin. The method was validated using ICH guidelines and the results indicate it can be used for the rapid analysis of commercially available TB FDC formulations containing the active pharmaceutical ingredients, API. The method is precise, sensitive and has the necessary selectivity for use during formulation development and optimisation studies for a combination of rifampicin, isoniazid and pyrazinamide. Initially formulation activities were undertaken with rifampicin and isoniazid for the development of an approach to enhance the effective delivery of these compounds. The characterisation of rifampicin and isoniazid was undertaken using spectroscopic, thermal and microscopic analysis. The studies revealed that the compounds are crystalline and exhibit distinct characteristic sharp peaks in X-ray diffractograms and Differential Scanning Calorimetry thermograms. The thermograms, 13C Nuclear Magnetic Resonance and Fourier Transform Infrared spectroscopy results identified that rifampicin occurs as the form II polymorph however, as there are no significant biopharmaceutic differences between the polymorphic forms of rifampicin this information was used for identification purposes only. The results were used as baseline data for comparative purposes to monitor changes that may occur when rifampicin and isoniazid are used in formulation development, dosage form manufacture and characterisation activities for a FDC technology designed to deliver both compounds simultaneously. Hydroxypropylmethylcellulose acetate succinate (HPMC-AS) and Eudragit® L100 polymers were successfully used for manufacture of isoniazid loaded gastric-resistant sustained release microspheres using an o/o solvent emulsification and evaporation approach. A Hybrid experimental design was used to investigate the influence of input variables viz., homogenisation speed and amount of HPMC-AS and Eudragit® L100 on gastric-resistance, INH release and encapsulation efficiency. The approach of using coating polymers viz., HPMC-AS and Eudragit® L100, to manufacture gastric resistant sustained release microspheres of isoniazid is unique and was efficient for preventing the release of isoniazid in an acidic environment. Only 0.523 % isoniazid was released from the optimised formulation after 2 h exposure to pH 1.2 0.1 M HCl suggesting there is also the possibility of minimising the accelerated degradation of rifampicin that occurs in the presence of isoniazid in acidic media. The microspheres also exhibited sustained release properties without burst release in pH 6.8 0.1 M phosphate buffer as < 5 % isoniazid was released at 0.5 h and only 11 % isoniazid was released at 2 h. The release of isoniazid was sustained over the entire period of dissolution testing with > 85 % isoniazid released at 24 h, implying that the majority of encapsulated isoniazid would be available for absorption. The manufacturing process resulted in the production of hard spherical particles and particle size analysis revealed that the microspheres ranged between 415.76 ± 76.93 μm and 903.35 ± 197.10 μm in diameter. The microspheres exhibited excellent flow properties attributed to the spherical nature of particles. Carr‟s index (CI) was 4.934 ± 0.775 % and the Hausner ratio (HR) was 1.148 ± 0.033 indicating good packability of the microspheres that would help in achieving weight and content uniformity of capsule dosage units. The manufacturing process however produced a low % yield suggesting that scale up difficulties may be encountered. However the high encapsulation efficiency observed may counter the challenges associated with the low yield. The DSC thermograms and FT Raman spectra of 1:1 mixtures of isoniazid, excipients and the microspheres did not reveal any potential detrimental interactions. Microporous floating sustained release microspheres for the delivery of rifampicin in the stomach have been successfully manufactured using emulsification and a diffusion/evaporation process. A novel approach using solvent mixture of acetone and dichloromethane that has not been reported for the manufacture of rifampicin microspheres was successfully used and resulted in the formation of a stable emulsion and the manufacture of rifampicin-loaded microspheres with uniform characteristics. In addition the manufacturing process was shorter than most other reported methods. A Box-Behnken experimental design was successfully used to study the influence of ethylcellulose, Eudragit® RLPO and d-glucose content on the floating properties, encapsulation efficiency and % yield of microspheres. The optimised formulation did not yield desired floating characteristics as the % buoyancy was low and floating lag times were high. The optimised formulation was modified by addition of NaHCO3 to increase the % buoyancy and reduce the floating lag time. Rifampicin release from the microspheres of the modified batch was 87.10 % at 12 h and the microspheres exhibited a % buoyancy of 87.66 ± 1.28 % (n = 6) and floating lag time of 15 ± 3.2 (n = 6) seconds. The microspheres remained buoyant for up to 12 h and an encapsulation efficiency of 88.26 ± 1.25 % was achieved. SEM images of microspheres following exposure to dissolution fluid revealed that the microspheres had numerous pores on their surface. The mean particle size distribution ranged between 423.19 ± 121.86 μm to 620.07 ± 102.67 μm. The microspheres exhibited similar flow characteristics to isoniazid microspheres with a CI of 1.422 ± 0.074 %, and HR of 1.034 ± 0.002. The excellent flow characteristics indicate that filling of the microspheres into hard gelatin capsules was unlikely to pose a challenge in respect of producing a product with uniform content. Rifampicin-excipient compatibility studies did not reveal any potential or significant interactions suggesting that the excipients used for the manufacture of the microspheres were compatible, although long term stability studies would be required to ascertain this is, indeed the case. The microporous floating sustained release microspheres manufactured in these studies has the potential to increase the bioavailability of rifampicin as they may be retained in the stomach where the solubility of rifampicin is high and from which absorption is best achieved. The degradation of rifampicin after 12 h dissolution testing in pH 1.2 0.1 M HCl in the presence of isoniazid gastric-resistant sustained release microspheres was only 4.44%. These results indicate that the degradation of rifampicin in the presence of isoniazid in acidic media can be overcome by encapsulation of both active pharmaceutical ingredients in a manner that ensure release in different segments of the gastrointestinal tract. The use of sustained release microporous gastroretentive rifampicin microspheres in combination with sustained release isoniazid gastric-resistant microspheres revealed that accelerated degradation of rifampicin in the presence of isoniazid is reduced significantly when using this approach and a FDC of rifampicin and isoniazid microspheres has the potential to improve the bioavailability of rifampicin thereby enhancing therapeutic outcomes. In vivo studies would be required to confirm the potential benefits of using this approach to deliver rifampicin in combination with isoniazid. , Thesis (PhD) -- Faculty of Pharmacy, Pharmacy, 2018
- Full Text:
- Date Issued: 2018
The solubility enhancement and the stability assessment of rifampicin, isoniazid and pyrazinamide in aqueous media
- Authors: Chen, Yu-Jen
- Date: 2000
- Subjects: Gel permeation chromatography , Rifampin , Isoniazid , Pyridazines
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4346 , http://hdl.handle.net/10962/d1005009 , Gel permeation chromatography , Rifampin , Isoniazid , Pyridazines
- Description: Tuberculosis (TB) is a highly contagious disease caused by the bacterium known as Mycobacterium tuberculosis which is widely spread in South Africa, especially in the rural areas of the Western Province. Rifampicin, isoniazid and pyrazinamide are the three most effective drugs against this organism. However, most of the current commercial anti-TB formulations are inconvenient to administrate. This results in patient non-compliance which has increased with incomplete tuberculosis treatment and further has intensified the mortality rate. The matter is especially severe amongst the paediatric and geriatric patients. Therefore, creating a "user-friendly" but non-alcoholic liquid formulation should improve the whole situation. The key to a successful formulation relies on sufficient concentrations of the drugs within the formulation together with acceptable stability of these drugs. Therefore, during the pre-formulation stage, the solubility and stability studies of rifampicin, isoniazid and pyrazinamide are to be conducted. Rifampicin, isoniazid and pyrazinamide were fully characterized and identified by means of spectroscopic and thermal techniques. A HPLC method for simultaneous analysis of the three drugs was developed and validated. This HPLC method was employed for all the solubility and stability assessments. Unbuffered HPLC water of pH value 7.01 was chosen as the aqueous solvent. This was decided after the stability of rifampicin, isoniazid and pyrazinamide was studied at a pH range of 2 to 10. The solubility and the stability studies of rifampicin, isoniazid, pyrazinamide, rifampicin with isoniazid, rifampicin with pyrazinamide, isoniazid with pyrazinamide and rifampicin combined with both isoniazid and pyrazinamide were performed in the presence of various agents. These agents can be categorized into three groups: the surfactants (poloxamer 188, poloxamer 407 and sorbitol) which could increase the intrinsic solubility or the drugs by altering the surface tensions of the aqueous solution medium, the suspending agents (carbopol 934 and carbopol 974P) which could enable the amount of dosage required to be homogeneously suspended in the formulation without considering the low intrinsic solubility factor of the drugs, and the complexing agents (ß-cyclodextrin, hydroxypropyl-ß-cyclodextrin and -cyclodextrin) which could initiated the inclusion complex between the host cyclodextrin and the drugs, thus further enhance the solubility of the drugs . The stability assessments were performed after 7-days stability trail with the HPLC method developed. Each drug/combination of drugs were stored in closed ampoules and subjected to 25, 40 and 60° C with or without nitrogen flushing while in the presence of the above mentioned agents. While assessing the solubility/stability of the drugs in the presence of the above mentioned surfactants, the phase-solubility curves indicate that both rifampicin and pyrazinamide fail to achieve the desired concentration. Moreover, the stability-time plots clearly indicate that these surfactants fail to enhance the general stabilities of the drugs. When the stabilizing effects of the above mentioned suspending agents were investigated, it was found that although the desired concentration could be easily accomplished by suspending the drug in the aqueous carbopol solutions, the stabilities of the different drug combinations were still below the regulatory level. Cyclodextrins are well known to form inclusion complexes with less polar drug molecules. The inclusion complexation could enhance both the solubility and the stability of the included drug molecules. The computer force field generated models of the cyclodextrin-drug were used to predict the complexation sites. The results indicated the all the inclusion complexation between the drugs and the cyclodextrins were favourable, but do not necessary protect the potential degradation sites of the drugs. The stability results confirmed the above findings as the cyclodextrins did not enhance the stability of the drugs. Various drug-drug interaction pathways were also predicted from the experimental observations which clearly indicated the stability reductions of these drugs in combination. This leads to the conclusion that a liquid formulation combining rifampicin, isoniazid and pyrazinamide should not initiate the use of aqueous solutions as the protic ions of the solution are able to initiate the degradation of these drugs.
- Full Text:
- Date Issued: 2000