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The Repurposing of Drugs Involved in the Treatment of COVID-19

By Katie Culver


Drug repurposing is a method of utilizing previously established drugs, and has been used for over three decades. This approach has allowed for experiments and trials in order to understand if previously approved formulations can be used for other medical treatments in a cost-effective and time-saving manner. Drug repurposing allows for the development of new treatments for novel medical diseases/issues through the idea that the drugs being tested have already been developed. This allows for a bypassing of slow and methodical drug development. Since 2020, the rise of the COVID19 pandemic has allowed for drug repurposing to be attempted at a larger scale than ever before. This review offers information regarding the repurposing of two drugs, hydroxychloroquine and ivermectin, both solo and in combination with other drugs, for the treatment of COVID19. Although there is no definitive evidence to suggest that either of these drugs have a substantial impact on the treatment of COVID19, these two drugs offer key examples of how drug repurposing allows for clinical trials and results regarding treatment methods to be completed in a fraction of the time that would be used if entirely new treatments had to be synthesized.  


Literature Review:

This paper functions as a review of the existing knowledge behind the repurposing of drugs for the treatment of COVID19. Specifically, clinical trials regarding the use of hydroxychloroquine and ivermectin are focused on in this regard. This paper aims to display COVID19 as a recent and relevant example for the repurposing of drugs, which is a technique that shows promising outcomes within the future of medicine. Continuation of clinical trials with hydroxychloroquine and ivermectin must be completed in order to understand if these drugs truly have an impact on health outcomes of COVID19 patients, but this review brings to light the contrasting methods used within the different studies, and the different forms of analysis completed in these trials. With this review, I plan to highlight the different trials that have been completed and present information into how drug repurposing offers a hopeful alternative to treatment methods in future medical outcomes.


Drug repurposing has been used for over 30 years in an effort to discover new ways that a particular treatment could potentially have effective outcomes on other areas of an individual's health (Pushpakom et al., 2019), but this process originally began through unintended measures. The first drugs that were repurposed actually arose from positive side-effects that were observed from drugs intended for different outcomes. Since this, scientists and researchers have intentionally tried specific drugs for different clinical outcomes. By definition, drug repurposing is the exploration of new medical uses for existing drugs which have already been FDA approved (Agarwal, 2021). Drug repurposing is a good option when faced with an arising medical concern because it allows for slow drug development to be bypassed. Additionally, it cuts costs in terms of research and drug development materials and has already been deemed safe for usage in humans. Because the drugs that are getting repositioned have already been through all the necessary trials to allow them to be on the market, large amounts of time and money are saved. Drug repurposing has recently become more pertinent due to the COVID19 pandemic that swept the world starting at the beginning of 2020 (CDC, 2022). The COVID19 pandemic brought a novel coronavirus, meaning that there were no known treatment options available for people who became infected. Along with this arose the perfect opportunity to attempt the repurposing of drugs. Due to the impact of COVID19, researchers have tried various drugs in order to combat the effects and symptoms that present upon viral infection of COVID19.

COVID19 is a novel coronavirus, which includes an entire group of viruses that have a single-stranded RNA genome (the largest of all the RNA viruses) within a spherical capsid composed of matrix proteins (Mousavizadeh et al., 2021). RNA is a specific type of nucleic acid that is used to encode the genome of the virus. The RNA encodes specific membrane proteins that give COVID19 its significant characteristics. The most notable membrane proteins include the spike (S), envelope (E), membrane (M), and nucleocapsid (N). Of these 4 membrane proteins, the most noteworthy in terms of infection is the S protein. The S protein contains a complex receptor binding domain, and 6 of these domains are necessary in order for the coronavirus to attach to the ACE2 receptor of host cells (Mohamadian et al., 2021). ACE2 receptors are seen in many different tissue types in mammals. Most of the ACE2 receptors are condensed in tissues of the lungs, kidneys, gastrointestinal tract, heart, and liver. These receptors are necessary for the proper regulation of the renin-angiotensin-aldosterone pathway but for the purpose of this paper, these ACE2 receptors are most necessary for the S proteins to properly attach to the host cell membrane (Mousavizadeh et al., 2021). This binding allows for the entry of COVID19 into the cell, where the RNA genome is translated into viral proteins and replication of the RNA genome occurs.

With the gain in understanding in regard to the pathology of COVID19, many researchers have been interested in the idea that previously marketed drugs may be able to combat the effects of COVID19. Some of the drugs that have recently been popular in terms of potential repurposing include hydroxychloroquine and ivermectin. Clinical trials have been completed with both of these medications in order to see if these drugs could offer potential treatments resulting in better clinical outcomes in individuals that have tested positive for COVID19. The rise of COVID19 has offered a recent and relevant example of how the process of repurposing drugs is a necessary and helpful process in order to attempt to limit COVID19 symptoms and infections worldwide.

Hydroxychloroquine Treatment:

Hydroxychloroquine is an organic synthetic compound that was initially used as an antimalarial drug (Furst, 1996), and has since been used for the treatment of autoimmune diseases, namely  rheumatoid autoimmune disorders (Nirk et al., 2020). Hydroxychloroquine is generally characterized as an immunomodulating/anti-inflammatory drug (Plantone et al., 2018). This drug is a weak base,  known to enter cells and become trapped in endosomes and lysosomes (Ohkuma et al., 1978). In doing so, the pH of the surrounding environment increases, inhibiting activity of cytokines, T cell proliferation and antigen presentation (Sperber et al., 1993), as well as blocking Toll-like receptors (Kyburz et al., 2006). Additionally, the increase in pH that is seen upon hydroxychloroquine exposure potentially affects the ability for viruses like malaria to enter cells, thereby offering a potential mode of treatment (Keyaerts et al., 2006 & Ooi et al., 2004). With these modes of action in mind, specifically the antiviral effects of hydroxychloroquine, this drug has become a potential treatment option for patients with COVID19 (Yao et al., 2020). Studies done in cell culture (in vitro) have shown that hydroxychloroquine may decrease the effectiveness of the coronavirus to enter the cell due to the inhibition of glycosylation that is needed in order for endocytosis of the virus (Pahan & Pahan, 2020). Because of these in vitro results, there are many clinical studies that have been done in regard to the treatment of COVID19 with hydroxychloroquine alone, or in combination with azithromycin. The data, however, is mixed in regard to whether this treatment is actually effective.

Solo Treatment:

In terms of treatment that solely uses hydroxychloroquine, there are trials that have been completed that show varying results. A clinical trial coordinated by a large group of scientists and physicians found that hydroxychloroquine had no significant effect on the recovery of COVID19 patients in comparison to typical treatments (RECOVERY Collaborative Group, 2020). Additionally, a second clinical trial conducted throughout the United States and Canada found that hydroxychloroquine did not prevent COVID19 illness when given after high-risk exposure (Boulware et al., 2020). The RECOVERY trial conducted throughout the UK included an experimental group of 1,561 patients, and a control group of 3,155 patients. At 28 days, the death rates of both groups were analyzed (RECOVERY Collaborative Group, 2020). Results suggest there is no statistical significance between the death rates of the two groups. In terms of the United States and Canada trial, a total of around 800 patients were enrolled, with around 400 in both the experimental and control group. It was found that the incidence of infection between the control and treatment group was not significant after the 14 day follow up (Boulware et al., 2020). Contrastingly, it has been found that hydroxychloroquine was able to successfully decrease rates of COVID19 infection post-exposure in a study completed in Singapore (Seet et al., 2021). This study differed in the way that hydroxychloroquine was given over a 42 day period as compared to the 14 day period. 3,037 patients were included in this trial, and the patients treated with hydroxychloroquine showed significantly lower COVID19 infection compared to those that received other treatments. These are only three examples of the trials completed, but data accumulations heavily point toward the agreement that hydroxychloroquine by itself is not a significantly beneficial treatment for COVID19 (RECOVERY Collaborative Group, 2020, Boulware et al., 2020, Abd-Elsalam et al., 2020, Mitjà et al., 2020, & Self et al., 2020). 

In Combination with Azithromycin:

With the suggestion that hydroxychloroquine alone does not effectively treat or prevent COVID19, the studies in which hydroxychloroquine is used in combination with other drugs must be evaluated. In particular, a clinic trial performed by Gautret et al. (2020), and an additional clinical trial completed by Abbas et al. (2021) showed that in combination with a common antibiotic, azithromycin, hydroxychloroquine significantly reduced viral load and symptoms, and was also associated with an earlier appearance of negative COVID19 tests post-infection. Both of these trials included a 6 day treatment window with the administration of both hydroxychloroquine and azithromycin. Researchers found that after this period, viral load had significantly decreased in comparison to control groups (Gautret et al., 2020 & Abbas et al., 2021). These two studies therefore suggest that although hydroxychloroquine does not work as an isolated treatment, it may be beneficial in combination with azithromycin. That being said, there are other clinical trials that refute this evidence by suggesting that this combination is not beneficial (Cavalcanti et al., 2020; Sivapalan et al., 2020; Rodrigues et al., 2021). In these studies, it was found that the combination of these drugs did not have any significant effect on the length of hospitalization (Sivapalan et al., 2020), viral clearance (Rodrigues et al., 2021), or positive clinical outcomes (Cavalcanti et al., 2020). Overall, these results offer inconclusive evidence, but one downfall of these trials includes the fact that even though some of these articles compare hydroxychloroquine solo to hydroxychloroquine/azithromycin combinations (Gautret et al., 2020, Cavalcanti et al., 2020; Sivapalan et al., 2020), these studies did not include any study groups that only included azithromycin without hydroxychloroquine, so it is unable to be determined if any positive effects are due to azithromycin alone. All of the studies found high rates of viral clearance when combination therapy was used as compared to solo treatment with hydroxychloroquine.


          Ivermectin is a synthetic antiparasitic drug that lacks antibacterial properties (Dourmishev, Schwartz, 2005). This drug functions by binding to specific neurotransmitters in motor neurons of parasites in order to induce paralysis. Because of this characteristic, ivermectin has historically been used as a dewormer in small and large animal veterinary medicine (Papich, 2016) and has since been approved for human use in the treatment of various parasites including head lice, scabies, and river blindness (Ivermectin (systemic) monograph for professionals, 2022). More recent data, however, have found that ivermectin can act in an antiviral manner as well by inhibiting the function of membrane proteins, such as integrase and importin, which are necessary for the transport of viruses into host cells ( Carly et al., 2020; Kosyna et al., 2015). This function of ivermectin has been shown to be effective in the inhibition of HIV nuclear import of the virus itself and viral proteins (Wagstaff et al., 2011), as well as the inhibition of nuclear transport of some influenza viruses (Götz et al., 2016). When thinking about potential treatment options for COVID19, the previously stated antiviral effects led researchers to begin clinical trials in order to understand if ivermectin could potentially be used as a treatment, but much like hydroxychloroquine trials, ivermectin trials show mixed results in terms of treatment outcomes.

          Solo Treatment:

          One potential treatment option involving ivermectin included solo treatment plans, but there is some variation overall in the effectiveness of this treatment. One study found that ivermectin may be a successful treatment for COVID19 and included a study group only composed of patients that had been diagnosed with pneumonia as a side effect from COVID19 infection (Okumus et al., 2021). 200 mcg/kg/day of ivermectin for 5 days was administered to a study group of 36 patients, and overall, there was a higher level of clinical improvement seen in the study group as opposed to the control group. It was also found that the mortality rate of the study group was lower than that of the control group. Opposingly, there are many other clinical trials that have seen no significant effect between COVID19 patients treated with ivermectin versus those not treated with ivermectin. Namely, two studies recorded that there was no significant difference in regard to time of hospitalization or decrease in symptoms (Vallejos et al., 2021 & López-Medina et al., 2021). That being said, one of these studies only treated with ivermectin for 2 days (Vallejos et al., 2021) and consisted of a study group of 250 while the other study treated with a 5-day course of ivermectin 300 μg/kg per body weight with a study group of 238 (López-Medina et al., 2021). Both of these studies consisted of a much larger study group when compared with the study that found ivermectin to be effective. However, the variation in treatment length, dose, and analysis of clinical improvement makes it complicated to directly compare these trials.

          In Combination with Doxycycline and other Drugs:

          Other trials focused on the treatment of COVID19 with ivermectin in combination with other drugs. One of these such studies includes a clinical trial that paired ivermectin with doxycycline (Ahmed et al., 2021). This trial included three groups; an ivermectin alone group that received 12 mg of ivermectin once daily for 5 days, an ivermectin and doxycycline group that received 12 mg ivermectin in combination with a single dose of 200 mg doxycycline on day one, and then 100 mg of doxycycline every 12 hours for 4 days, and finally, a placebo group. All of these groups contained patients who presented with mild COVID19 symptoms. Results showed that ivermectin + doxycycline resulted in a greater viral clearance and a shorter duration of hospitalization than the control group. The most important result found from this study was that the treatment with ivermectin alone actually had the largest reduction in viral clearance and hospitalization length. Additionally, a second clinical trial that used ivermectin in combination with other drugs was performed by Elalfy et al., (2021). This study showed that a combination of ivermectin, nitazoxanide, and ribavirin resulted in a greater viral clearance over time in comparison to the control group. One important note is the patient sample sizes in each of these studies; the first study had 72 total patients, all dispersed throughout three groups (Ahmed et al., 2021), while the other study consisted of 113 total patients in the study, with 62 in the study group (Elalfy et al., 2021). Both of these studies had fairly small sample sizes, so little conclusive evidence can be drawn from these trials. With that in mind, both of these studies were able to show that ivermectin could potentially be a viable treatment option.

Meta-analyses of Hydroxychloroquine and Ivermectin:

In both the hydroxychloroquine solo treatment clinical trials and the trials done with a combination of azithromycin, there are no standards seen that allow for the head-to-head comparison of any trials. There were variations in dosage, treatment duration, sample size, and analyses. That being said, a meta analysis conducted by Ghazy et al. showed that there was no significant difference in mortality, duration of hospital stay, or virological cure rate between treatment groups and control groups (Ghazy et al., 2020).  This meta analysis included 14 articles after screening through an initial 4,730 articles. Many of these articles were not included due to replicants, publishing before 2019, retraction, and irrelevance. There were some forms of analyses, such as duration of symptoms, that were the basis of some of the clinical studies, but the ways in which this was measured was variable amongst different clinical trials to the point that no meta analysis could be conducted. Therefore, by looking at the different clinical studies presented here, it can be seen that the process of drug repurposing, although still quicker than the development of an entirely new drug, is still a long process that can often lead to differences in results based on a variety of factors. That being said, meta-analysis suggests that hydroxychloroquine alone or in combination with azithromycin does not appear to have any clinical benefits in regard to the treatment of COVID19.

          In regard to ivermectin, with the previous clinical trials in mind, a meta analysis is needed in order to truly understand the effectiveness of ivermectin for the treatment of COVID19. One specific analysis looked at various clinical trials and found that ivermectin may in fact have a positive impact on the treatment of COVID19 (Bryant et al., 2021). This meta analysis concluded with “moderate certainty” that treatment with ivermectin provided a survival benefit to individuals who had tested positive for COVID19. That being said, a second meta-analysis completed suggested that ivermectin does not, in fact, help with the length of hospital stay, mortality, or the viral clearance of COVID19 (Roman et al., 2021). With these two contradicting analyses, it is important to delve deeper to understand where these differences may have come from. The first issue with the Bryant et al. review is that it concludes with “moderate certainty”, which is not a term used in meta-analyses. Additionally, none of the results of Bryant’s paper reached statistical significance, which is another warning sign of the credibility of this paper. In terms of the Roman et al. meta-analysis, analysis found that there was no significance in terms of the treatment with ivermectin, but all of these results were shown to have a low quality of evidence. That being said, the strengths of this meta-analysis include that randomized clinical trials were the only trials included in analysis, offering a more standardized measurement than the previously mentioned analysis, and their inclusion-exclusion protocol was more streamlined as well. With these two conflicting analyses, it can be seen that with a novel virus, such as COVID19, more time needs to be put into different studies and treatment options in order to truly understand what effects certain drugs have.


          COVID19 has offered an invaluable opportunity to delve into the concepts of drug repurposing. COVID19 has affected hundreds of thousands of people, and with that the urgency for treatment has escalated dramatically. The effort that goes into repurposing offers a valuable chance to allow access of COVID19 treatment to a wider target population, as this reutilization can occur at a fraction of the cost. This is pertinent in the United States especially, as costs of medical care can play a large factor in treatment options. Repurposing allows for more readily available treatments, as it is much more cost effective to repurpose rather than synthesize a completely new drug.

More specifically, COVID19 has opened an opportunity to repurpose hydroxychloroquine and ivermectin, which have already been used for various treatments since they were first medically approved. In this review, although the results offered little clarity with regard to the effectiveness of these drugs, the research that has been done over the course of just 2 years shows how greatly the timeline of drug treatment is shortened by repurposing as opposed to the synthesis of entirely new drugs. There are some negatives that come from these rapid treatments, such as variable information and inconclusive results, but the benefits of repositioning a therapy outweighs the negatives substantially.

          Because the drugs being used in repurposing have already been approved and been found to be safe for patient consumption, new treatments everyday are able to be used in the attempt to lessen the impacts of this pandemic. It can clearly be seen that more research needs to be done in terms of hydroxychloroquine and ivermectin, as well as likely other drugs using this approach along the way. That being said, this process is potentially years faster than creating entirely new drugs, even with the trial and error time period that can be seen presented in this research.

          Although the results are mixed, the data suggest that hydroxychloroquine is ineffective for the treatment of COVID19 (Ghazy 2022, RECOVERY Collaborative Group, 2020, Boulware, 2020, Abd-Elsalam et al., 2020, Mitjà et al., 2020; Self et al., 2020). In terms of ivermectin, the same appears to generally hold true (Vallejos et al., 2021, López-Medina et al., 2021: Roman et al., 2021). More research must be done in order to establish reliable conclusions. These preliminary studies offer stable starting points for future research to come regarding these two drugs, which will likely lead to more standardized clinical trials in the future. Additionally, the trials previously mentioned can offer a jumping board for clinical trials with other drugs in the future as well. The COVID pandemic has opened a door into the already established world of repurposing and has certainly evolved the efficiency in which new potential treatments can be elevated in a fraction of the time that it would take novel drugs to be created.


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