**Preface to "Solid Dispersions for Drug Delivery: Applications and Preparation Methods"**

The use of solid dispersions has expanded in recent years to include different pharmaceutical applications such as oral drug delivery and drug delivery to the lungs. The success of this technology has allowed this expansion and requires an update of current understandings. Thus, the aim of this book is to summarize the achievements in the area of solid dispersions and suggest potential future applications. The formation of solid dispersions, where poorly soluble active pharmaceutical ingredients are dispersed in a solid carrier, is one of the strategies to improve drug dissolution profiles and to enhance bioavailability. These solid drug dispersions can be formulated with the use of water-soluble or -insoluble polymers as well as some materials with small molecular weight such as surfactants, sugars, and other drugs. Recent advances in this area of research have shown the potential of the application of co-amorphous and polymeric amorphous solid dispersions to enhance solubility as well as to deliver combination treatments. Likewise, pharmaceutical co-crystals have attracted significant interest to deliver combination treatments. The drug present in amorphous dispersions typically undergoes rapid dissolution, which may result in its better bioavailability. There are several methods used to prepare solid drug dispersions, which include solvent evaporation, melting, and supercritical fluid technology. Numerous solvent evaporation approaches may also involve the use of spray-drying, lyophilization, co-precipitation, electrospraying, electrospinning, etc. There are also several melting approaches such as hot-melt extrusion and melt agglomeration.

This book represents a collection of three reviews and seven original research papers contributed by different authors. Elshadeey and El-Dahmy [1] reported the formulation of oral fast-dissolving films containing nanosuspension of paroxetine. They characterized these films using in vitro techniques, studied ex vivo drug permeation, and demonstrated their applicability for buccal drug delivery in healthy human volunteers. Mudie and co-workers [2] described the streamlined in vitro and in silico approaches to formulate tablets based on solid dispersions of Calquence® (crystalline acalabrutinib). Shan et al. [3] reported the use of poly(N-vinyl pyrrolidone), poly(2-methyl-2-oxazoline), poly(2-ethyl-2-oxazoline), poly(2-n-propyl-2-oxazoline), and poly(2-isopropyl-2-oxazoline) to formulate solid dispersions with ibuprofen. They explored the effects of hydrogen bonding and polymer hydrophobicity on the inhibition of ibuprofen crystallization. In another study, Mudie and co-workers [4] formulated Calquence® as immediate-release tablets with spray-dried amorphous solid drug dispersions comprising 50% acalabrutinib and 50% hydroxypropyl methylcellulose acetate succinate, and they studied these in dogs. El-Helaly et al. [5] reported the development of solid dispersions of raloxifene using multilayered core-sheath nanofibers using an electrospinning technique and formulated it in the form of buccal films. Eedara et al. [6] prepared solid dispersions of fexofenadine hydrochloride using poly(ethylene glycol) 20 kDa and Poloxamer 188 and reported their improved dissolution properties. Oliveira et al. [7] reported the use of hydroxypropyl methylcellulose, poly(ethylene glycol) and poly(vinyl pyrrolidone) for formulating solid dispersions of naphthoquinone with physical mixing, kneading, and rotary evaporation methods. In addition to physicochemical characterization of these dispersions, they also evaluated antiparasitic activity in Trypanosoma cruzi Y strains in vitro.

Al-Obaidi et al. [8] reviewed recent advancements in the use of solid dispersions of anticancer and antimicrobial drugs for drug delivery to the lungs. The review covered the current state of the art for formulating drugs for inhalation with a focus on co-amorphous solid dispersions and cocrystals to deliver inhaled drugs. Qian et al. [9] reviewed the dissolution of amorphous solid dispersions and the theory of the formation of metastable drug-rich phases. The authors discussed the additional benefits of amorphous solid dispersions that induced drug-rich phases for bioavailability enhancements. Oliveira et al. [10] reviewed recent advancements in therapeutical applications of solid dispersions. The authors showed the breadth of applications of solid dispersions such as anticancer, anti-inflammatory, and antimicrobial applications that were reported in previous in vitro and in vivo studies.

This book can be particularly useful for researchers as well as postgraduate students in formulation sciences and drug delivery. Undergraduate students will also find elements of this book very relevant to scientific fundamentals such as solubility and crystallization of amorphous materials as well as drug delivery challenges.

#### **References**

1. Elshafeey AH, El-Dahmy RM. Formulation and Development of Oral Fast-Dissolving Films Loaded with Nanosuspension to Augment Paroxetine Bioavailability: In Vitro Characterization, Ex Vivo Permeation, and Pharmacokinetic Evaluation in Healthy Human Volunteers. Pharmaceutics. 2021;13(11):1869.

2. Mudie DM, Stewart AM, Rosales JA, Adam MS, Morgen MM, Vodak DT. In Vitro-In Silico Tools for Streamlined Development of Acalabrutinib Amorphous Solid Dispersion Tablets. Pharmaceutics. 2021;13(8):1257.

3. Shan X, Moghul MA, Williams AC, Khutoryanskiy VV. Mutual Effects of Hydrogen Bonding and Polymer Hydrophobicity on Ibuprofen Crystal Inhibition in Solid Dispersions with Poly(N-vinyl pyrrolidone) and Poly(2-oxazolines). Pharmaceutics. 2021;13(5):659.

4. Mudie DM, Stewart AM, Rosales JA, Biswas N, Adam MS, Smith A, Craig CD, Morgen MM, Vodak DT. Amorphous Solid Dispersion Tablets Overcome Acalabrutinib pH Effect in Dogs. Pharmaceutics. 2021;13(4):557.

5. Nageeb El-Helaly S, Abd-Elrasheed E, Salim SA, Fahmy RH, Salah S, EL-Ashmoony MM. Green Nanotechnology in the Formulation of a Novel Solid Dispersed Multilayered Core-Sheath Raloxifene-Loaded Nanofibrous Buccal Film; In Vitro and In Vivo Characterization. Pharmaceutics. 2021;13(4):474.

6. Eedara BB, Nyavanandi D, Narala S, Veerareddy PR, Bandari S. Improved Dissolution Rate and Intestinal Absorption of Fexofenadine Hydrochloride by the Preparation of Solid Dispersions: In Vitro and In Situ Evaluation. Pharmaceutics. 2021;13(3):310.

7. Oliveira VdS, Dantas ED, Queiroz ATdS, Oliveira JWdF, Silva MdSd, Ferreira PG, Siva FdCd, Ferreira VF, Lima AANd. Novel Solid Dispersions of Naphthoquinone Using Different Polymers for ´ Improvement of Antichagasic Activity. Pharmaceutics. 2020;12(12):1136.

8. Al-Obaidi H, Granger A, Hibbard T, Opesanwo S. Pulmonary Drug Delivery of Antimicrobials and Anticancer Drugs Using Solid Dispersions. Pharmaceutics. 2021;13(7):1056.

9. Qian K, Stella L, Jones DS, Andrews GP, Du H, Tian Y. Drug-Rich Phases Induced by Amorphous Solid Dispersion: Arbitrary or Intentional Goal in Oral Drug Delivery? Pharmaceutics. 2021;13(6):889.

10. Oliveira VdS, de Almeida AS, Albuquerque IdS, Duarte F´IC, Queiroz BCSH, Converti A, Lima AANd. Therapeutic Applications of Solid Dispersions for Drugs and New Molecules: In Vitro ´ and In Vivo Activities. Pharmaceutics. 2020;12(10):933.

**Vitaliy Khutoryanskiy, Hisham Al-Obaidi**

*Editors*
