Formulation, characterisation and in vivo efficacy of dapsone and proguanil in trimethylated chitosan microparticles
Van Heerden, Jacobus
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Malaria is an infectious disease caused by various forms of the Plasmodium parasite. It is responsible for thousands of deaths yearly with 90 % of those deaths being in sub-Saharan Africa, thus making it a disease of global importance. The global burden of malaria is worsened by resistance to current treatment, a lack in funding and limited research outputs. More alternative ways of treatment must be explored and may include the co-formulation of antimalarial drug substances as well as alternative ways of drug delivery. Antifolates are drugs which interfere with an organism’s folate metabolism by inhibiting dihydropteroate synthase (DHPS) or dihydrofolate reductase (DHFR). Dapsone is a synthetic sulfone which has a mechanism of action that is very similar to that of sulphonamides. The mechanism of action is characterised by the inhibition of folic acid synthesis through the inhibition of dihydropteroate synthase (DHPS). Another antifolate drug, proguanil, is the prodrug of cycloguanil. Its mechanism involves the inhibition of dihydrofolate reductase (DHFR), thus inhibiting the malaria parasite to metabolise folates and therefore stunting its growth. Unfortunately, dapsone has a serious side-effect in people with a deficiency of the enzyme glucose-6-phosphate dehydrogenase (G6PD) causing oxidative stress on the red blood cells leading to the rupturing of these cells. The main objective of this study was to formulate and characterise TMC-TPP microparticles loaded with the effective but toxic drug combination of dapsone and proguanil and to determine if these drug-containing microparticles had in vivo efficacy against malaria. N-trimethyl chitosan chloride (TMC), a partially quaternised chitosan derivative, shows good water solubility across a wide pH range thus having mucoadhesive properties and excellent absorption enhancing effects even at neutral pH. A faster, more efficient microwave irradiation method was developed as an alternative to the conventional synthesising method of TMC. TMC with the same degree of quaternisation (DQ), ± 60 %, was obtained in a quarter of the reaction time (30 min) by using the newly developed method. The TMC synthesised with the microwave irradiation method also exhibited less degradation of the polymer structure, thus limiting the chance for the formation of any unwanted by-products (Omethylation, N,N-dimethylation and N-monomethylation). The formation of complexes by ionotropic gelation between TMC and oppositely charged macromolecules, such as tripolyphosphate (TPP), has been utilised to prepare microparticles which are a suitable drug delivery system for the dapsone-proguanil combination. Both these drugs were successfully entrapped. These particles were characterised and the in vivo efficacy against the malaria parasites was determined. The microparticles with both the drugs, separately and in combination, displayed similar or better in vivo efficacy when compared to the drugs without the TMC microparticles. An in vitro dissolution study was also performed by subjecting the dapsone and proguanil TMC formulations to 0.1N HCl dissolution medium. Samples were withdrawn after predetermined time points and the drug concentration was determined with HPLC. It was found that the TMC microparticles resulted in a sustained release profile since only 73.00 ± 1.70 % (dapsone) and 55.00 ± 1.90 % (proguanil) was released after 150 minutes. The in vivo bioavailability of the dapsone and proguanil TMC formulations was evaluated in mice by collecting blood samples at predetermined time points and analysing the samples with a sensitive and accurate LC-MS/MS method. The in vivo bioavailability of the dapsone TMC formulation relative to the normal dapsone formulation was found to be 244 % and 123 % for the proguanil TMC formulation relative to the normal proguanil formulation. These TMC-TPP microparticles formulations showed better in vivo efficacy and bioavailability when compared to the normal formulation. Together with the sustained release, these formulations may be a promising cheaper and more effective treatment against malaria.
- Health Sciences