Influence of Polymers on the Physical and Chemical Stability of Spray-dried Amorphous Solid Dispersion: Dipyridamole Degradation Induced by Enteric Polymers

Amorphous solid dispersions (ASDs) are inherently unstable because of high internal energy. Evaluating physical and chemical stability during the process and storage is essential. Numerous researches have demonstrated how polymers influence the drug precipitation and physical stability of ASDs, while the influence of polymers on the chemical stability of ASDs is often overlooked. Therefore, this study aimed to investigate the effect of polymers on the physical and chemical stability of spray-dried ASDs using dipyridamole (DP) as a model drug. Proper polymers were selected by assessing their abilities to inhibit drug recrystallization in supersaturated solutions. HPMC E5, Soluplus®, HPMCP-55, and HPMCAS-LP were shown to be effective stabilizers. The optimized formulations were further stored at a high temperature (60 °C) and high humidity (40 °C, 75% RH) for 2 months, and their physical and chemical stability was evaluated using polarizing optical microscopy, FTIR, HPLC, and mass spectrometry (MS). In general, crystallization was observed in all samples, which indicated the physical instability under stressed storage conditions. Also, it was noted that the polymers in ASDs rather than physical mixtures, induced a dramatic drug degradation after being exposed to a high temperature (HPMCP-55 > 80% and HPMCAS-LP > 50%) and high humidity (HPMCP-55 > 40% and HPMCAS-LP > 10%). The MS analysis further confirmed the degradation products, which might be generated from the reaction between dipyridamole and phthalic anhydride decomposed from HPMCP-55 and HPMCAS-LP. Overall, the exposure of ASDs to stressed conditions resulted in recrystallization and even the chemical degradation induced by polymers.

Development and evaluation of solid dispersion of spironolactone using fusion method

Introduction:

Solubility and dissolution of a poor water-soluble drug are the two major barriers for formulation scientists in development of drug delivery. Many of the potent drugs do not show the therapeutic effects due to solubility issues but may show toxicity issues when used in high doses. Solid dispersion (SD) technology is an excellent tool for enhancing the solubility and dissolution and hence related bioavailability.

Materials and Methods:

SD of spironolactone (SPL) was developed using an inert carrier polyethylene glycol 4000 (PEG 4000) by the conventional fusion method and characterized for various characterization parameters.

Results:

Solubility of pure drug and SD of SPL in water was found to be 23.54 ± 1.75 μg/mL and 61.73 ± 1.26 μg/mL, respectively. The maximum cumulative percentage release from pure drug, SPL marketed product (tablet), physical mixture, and SPL SD at 60 min was 27.25 ± 1.83%, 35.64 ± 3.65%, 47.72 ± 2.45%, and 74.24 ± 3.25%, respectively in 0.1 N HCl.

Conclusions:

SD of SPL was developed successfully. The solubility of SPL SD was found to be significantly increased (P < 0.05) as compared to SPL active pharmaceutical ingredient (API) and physical mixture of PEG 4000 and SPL. The current study indicated that SD of SPL was a better option for enhancing solubility of a poorly soluble therapeutic agent.