Degradation kinetics of artesunate for the development of an ex-tempore intravenous injection

Abstract

Background Artesunate is recommended by the World Health Organization (WHO) for parenteral treatment of severe Plasmodium falciparum malaria. However, artesunate is inherently unstable in an aqueous solution and hydrolyses rapidly after its preparation for injection. Therefore, the aim of the study was to evaluate the stabilizing effects of phosphate buffer and mannitol against short-term (ex-tempore) artesunate hydrolysis. Methods A HPLC–UV isocratic method was developed using a reversed-phase fused core column (HALO RP-C18) and a mobile phase consisting of a mixture of 45% ammonium formate 10 mM in water (pH 4.5) and 55% methanol. Artesunate was formulated as aqueous solutions using a design of experiment (DOE) to investigate the artesunate stabilizing effects of pH (8–10), phosphate buffer strength (0.3–0.5 M), and mannitol (0–0.22 mmol/mL). The solutions were incubated at predefined temperatures (5, 25, and 40 °C) with subsequent analysis. Arrhenius equation was applied to model and evaluate the stability results. Results The developed HPLC-based method using fused-core stationary phase allowed to selectively quantify artesunate in the presence of its main hydrolysis degradants; namely β-dihydroartemisinin (β-DHA) and α-dihydroartemisinin (α-DHA) within 10 min. By applying the Arrhenius equation, the rate of hydrolysis of the drug increased approximately by 3.4 as the temperature raised by 10 °C. Buffer strength was found to be the main factor affecting the hydrolysis rate constants at 5 and 25 °C (p < 0.05), the activation energy (p = 0.009), and the frequency factor (p = 0.045). However, the effect of the buffer was predominant on the activation energy and hydrolysis rate constants, revealing its stabilizing effect on the drug at lower buffer strength (0.3 M). Within the investigated range (pH = 8–10), pH was found to influence the activation energy, with a positive stabilizing effect in the pH range of 8–9. The addition of mannitol as stabilizing agent into artesunate aqueous formulation did not show an improved response. Conclusion Phosphate buffer was the main stability determining factor of artesunate in the aqueous intravenous (i.v.) formulation and was found to be more effective in stabilizing artesunate at a buffer strength of 0.3 M in pH 8–9, while mannitol lacked stabilizing effect.

Differential Anti-Fibrotic and Remodeling Responses of Human Dermal Fibroblasts to Artemisia sp., Artemisinin, and Its Derivatives

“…The degradation of AS to DHA and then DHA to dART reflects the instability of AS in aqueous media [36]. AS is a form of ART acylated with succinate in order to make the drug more bioavailable, but it is also readily hydrolyzed to DHA, which is the bioactive metabolite against malaria (see review by Morris et al [37]).…”

Synthesis and Characterization of Dimeric Artesunate Glycerol Monocaprylate Conjugate and Formulation of Nanoemulsion Preconcentrate

“…Chemically, ARTs are attributed to the sesquiterpene lactone class, having an endoperoxide bridge which is pharmacologically significant for anti-malarial activity [ 8 ]. Among the ART analogs, artesunate (AS) demonstrated the most versatile semisynthetic derivative due to its broader therapeutic potential, rapid action, and better water solubility [ 9 , 10 , 11 ]. Apart from its wide therapeutic use, AS exhibits a short plasma half-life and low bioavailability, which undermine the effectiveness of optimal therapeutic efficacy [ 12 ].…”

“…Chemically, ARTs are attributed to the sesquiterpene lactone class, having an endoperoxide bridge which is pharmacologically significant for anti-malarial activity [8]. Among the ART analogs, artesunate (AS) demonstrated the most versatile semisynthetic derivative due to its broader therapeutic potential, rapid action, and better water solubility [9][10][11].…”