Introduction
During the fag end of 2019, Wuhan – the most densely populated city and capital of Hubei Province – China was witnessing pneumonia whose etiology was unknown. At the beginning of 2020, the pathogen was successfully identified and was named as the 2019 novel corona virus (2019-nCoV) [1,2]. Later, on 20 February 2020, the International Committee on Taxonomy of Viruses (ICTV) named it as Severe Acute Respiratory Syndrome Corona virus 2 (SARS-CoV-2), a new variant of SARS-CoV, and the disease caused was corona virus disease 2019 (COVID-19) [3]. Since then the whole world is on ‘High Alert’ due to this new viral threat. Millions of people have been (self) quarantined to prevent it from further spreading [4]. Nonetheless, the individuals infected by corona virus are augmenting everyday [5]. There are absolutely no drugs that are approved by regulatory agencies across the globe. In India, the Indian Council of Medical Research (ICMR) strongly recommended the usage of hydroxychloroquine for asymptomatic purposes [6]. Followed by this development, emergency use authorization was granted by United States Food and Drug Administration (USFDA) to promote the usage of chloroquine phosphate or hydroxychloroquine sulfate for treating COVID-19 [7]. World Health Organization (WHO) identified and recommended usage of remdesivir, lopinavir–ritonavir with or without interferon, immunotherapy, and recuperative sera. WHO also launched SOLIDARITY trials for the above-prescribed drugs to support that they are effective in treating COVID-19 [8]. In addition, novel chemical entities against the corona virus protease were also proposed by some researchers [9] and some have proposed various integrated Chinese and Western medicines for treating this pandemic [10].
While the research is going on to identify an active agent for COVID-19. Identifying the mode of delivering the active moieties to patients and healthy subjects cannot be ignored. At present, there are several drug delivery systems, whereas the most novel and transformative drug delivery/carrier system is orodispersible films (ODFs). European Pharmacopoeia (Ph. Eur.) defines ODFs as ‘single or multilayered sheets of suitable materials, to be placed in the mouth where they disperse rapidly’ [11]. They are a type of oromucosal preparations which are ultra-thin, elegant, stamp sized, portable, patient friendly, and attractive dosage forms across all the age groups [12]. Clinical Data Interchange Standards Consortium (CDISC) defines ODFs as ‘A thin layer or coating which is susceptible to being dissolved when in contact with a liquid’ [13]. On the contrary, United States Pharmacopoeia (USP) employs a different terminology and called them as ‘Oral Films’ and defined as ‘Thin sheets that are placed in the oral cavity. They contain one or more layers. A layer might or might not contain API’ [14]. ODFs undergo rapid disintegration/dissolution and are usually swallowed along with saliva and a small amount of the drug gets absorbed via the oral mucosa due to its high vasculature [15,16].
ODFs are excellent and attractive carriers for delivery of various over the counter (OTC) or prescription drugs [17], herbal extracts [18–21], vaccines [22], probiotics [23], and vitamins [24]. Drugs are either directly introduced [25–28] in the formulation of ODFs or size reduced and converted to solid dispersions [29] or nanoparticles [30,31] or solid lipid microparticles [32] or micronized and surface modified using silica [33] which not only help in enhancing the amount of drug that could be loaded on to ODFs but also help in enhancing the release rate and, bioavailability of the drug. At present, ODFs are used as an excellent carrier system for delivering various therapeutically active agents. The composition of ODFs includes a drug substance (natural or synthetic), a film-forming agent and plasticizer. Additionally, it also includes saliva stimulating agent, organoleptic agents, and stabilizers [12]. The critical quality characteristics of ODFs are its appearance, stability, water content, uniformity of the active agent, color, taste, aftertaste, and mouthfeel. Most importantly, it shall not cause irritation of mucosa when administered [34]. The authors provided an overview on characterization of ODFs to determine various quality parameters of ODFs and also introduced a 3D printed disintegration test apparatus for testing the disintegration time of ODFs using sensor technology [35]. ODFs are capable for drug delivery in patients with swallowing problems, mentally retarded patients, subjects with Parkinson’s disease, bed-ridden patients, oral cancer patients, and uncooperative patients [36–38]. The present review is focused on critically analyzing the potential of ODFs as carriers for delivering antiviral drugs/herbs/vaccines with a potential for treatment of COVID-19, the global pandemic.