Improved physicochemical characteristics of artemisinin-nicotinamide solid dispersions by solvent evaporation and freeze dried methods.

Artemisinin (ARMN) is a drug of choice against drug-resistant malaria especially due to Plasmodium falciparum. Being poorly soluble in water, its solid dispersions with nicotinamide (NA) were prepared at various drug-carrier ratios (1:1, 1:4, 1:6, 1:8, 1:10) by solvent evaporation and freeze drying methods. These solid dispersions were characterized by differential scanning calorimetery (DSC), fourier transform infrared spectroscopy (FTIR), X-ray diffraction patterns (XRD), phase solubility and dissolution studies. Artemisinin and nicotinamide both were found completely crystalline as shown by their XRD patterns. Physical mixtures (PMs) showed decreased intensity in their XRD patterns while solid dispersions by solvent evaporation method (SLVPs) exhibited displaced angles and decreased intensity whereas freeze dried solid dispersions (FDSDs) showed least number of peaks having low intensity and maximum displaced angles. DSC thermograms of drug-carrier ratios at 1:1-1:4 showed lower melting temperature than artemisinin and nicotinamide in all preparations. Endothermic temperature of artemisinin in PMs and SLVPs increased with rise of nicotinamide content upto 1:6 ratio followed by decline. All samples showed crystallization temperature below the artemisinin except drug-carrier ratio 1:6 of PMs while δH value was minimum at this ratio. FDSDs produced lowest endothermic temperature than corresponding PMs and SLVPs. SLVPs exhibited band shifting in both functional and fingerprint region compared to respective PMs as exhibited by their FTIR spectra. FDSDs and SLVPs showed different nature of bonding among artemisinin and nicotinamide. FDSDs produced strongest CONH(2) bonding followed by SLVPs and PMs respectively. PMs produced significantly higher aqueous solubility and rate of dissolution as compared to artemisinin alone. SLVPs exhibited improved solubility and dissolution profile corresponding to PMs. FDSDs showed highest release rate and aqueous solubility followed by SLVPs and PMs at all ratios. PMs and SLVPs showed their highest dissolution profile at 1:6 drug-carrier ratio followed by gradual decrease while FDSDs progressed in dissolution rate with increase of nicotinamide content successively upto maximum at 1:10 ratio.