Mahidol University Preclinical (Lab) Studies Indicate Potential of Ivermectin/Niclosamide Combination as Antiviral Targeting COVID-19

Recently, a team of scientists affiliated with Thailand-based academic medical centers, including Mahidol University’s Siriraj Hospital, investigated the use of repurposed antiparasitic drugs with in vitro anti-SARS-CoV-2 activity, as this continues to represent a promising approach for economical, available antiviral-like treatments targeting COVID-19. Of particular importance is the ability to alleviate stress on healthcare systems, especially in more vulnerable low-and middle-income countries (LMICs) such as Thailand. The recent study acknowledges the limitations of the global mass vaccination scheme as a strategy to eradicate COVID-19—the pathogen continues to spread whether in 100% vaccinated locations such as Gibraltar, to nearly universally vaccinated Singapore. Thus, the importance of utilizing safe and effective, not to mention economical antiviral-like treatments, as a public health strategy, as well as augmenting vaccination and other measures. Novel pharmaceutical products from companies such as Merk and Pfizer, while showing some promise, also present possible safety and cost issues. Thus, the team out of Mahidol University sought to test repurposed drugs in vitro, evaluating their anti-SARS-CoV-2 activity. They looked at combinations of Niclosamide, ivermectin, and Chloroquine. The results indicate that these combinations lead to over a 10-fold reduction in the half-maximal inhibitory concentration (IC50) as compared to the drugs by themselves. In the lab, combining Niclosamide and ivermectin produces a superior synergy score based on the synergy landscape analyses with a peak Loewe synergy score totaling over 20 with an average of 6.60 in Vero E6 cell and a peak Loewe synergy score equaling 13.2 and an associated average of 2.897 in Calu-3 cells. The authors suggest human clinical trials should look at combining ivermectin and Niclosamide. The study results are uploaded to a preprint server and thus haven’t been scientifically peer-reviewed yet.

Of course, TrialSite first reported on the phenomenal University of Monash-led in vitro study showing that ivermectin crushed SARS-CoV-2 in the cell culture, lab setting. Since then, 73 human studies have been conducted—the majority showing some positive data. TrialSite has been a leading media chronicling these studies. 

Some of the studies failed to produce solid enough findings, and one study was marred with allegations of data manipulation. At least one of the studies showing neutral to negative results had potential concerns, from conflict of interest to data issues.    

A majority of the human-based ivermectin studies were conducted in LMICs, and American and British health systems, for example, value those findings less than findings in wealthier, more advanced economic environments.  

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But Mahidol University remains a sophisticated place. The Thai authors point to the “promising results in many [ivermectin-based] clinical trials.” Of course, much hope was placed in chloroquine/hydroxychloroquine, but later human trials results were disappointing. Critics argued that some of these studies had design flaws—administering the medicine later in the disease life cycle rather than upfront, for example.

The authors point out that Niclosamide, another anti-parasitic medicine, shows good anti-SARS-CoV-2 activity with a high selective index. TrialSite has chronicled a handful of Niclosamide-based studies

Both drugs are widely available, inexpensive, and considered relatively safe for short-term usage. The Thai researchers emphasized the urgent need for repurposed medicines targeting COVID-19. Why not test an enhanced therapy combining some of these drugs? Thus, the basis of the study.

Study Data

Employing lab-based, in vitro studies, the Thai team isolated and cultivated the viruses in the cell-culture environment, employing various approaches and assays to determine select combinational anti-SARS-CoV-2 activity.

The table below reveals a single drug treatment against SARS-CoV-2 in vitro:

Drug CandidatesDrug ClassDrug IndicationCC50µMIC50µMPlaque AssayIC50µMqRT-PCRNiclosamideAnthelminthic Tapeworm, intestinal fluke infections0.290.0490.043IvermectinAntiparasiticonchocerciasis, and other worm infestations10.551.231.27ChloroquineAntiparasitic Treatment of malaria, rheumatic diseases and Zika virus infection118.200.830.89

The above table reveals the anti-SARS-CoV-2 activities and cytotoxicity of the generic, repurposed drugs in Vero E6 cells. The authors employed the plaque assay to evaluate viral production and it is measured as the percentage inhibition relative to the viral titer of DMSO-treated cells.

A one-step qRT-PCR reveals the viral RNA virus supernatants, expressed as the percent inhibition relative to the DMSO treated cells. IC50 values show a measure of dose-response based on the plaque assay for Niclosamide, ivermectin, and Chloroquine (see amounts in the table above). The data suggests viral RNA quantification via the one-step qRT-PCR precisely reveals the infectious virus output in the respective experiments. 

What about the combinations?

The Thailand-based study team reports they assessed two-drug combinations in vitro in Vero E6 cells by applying treatment scenarios across 16 various pairwise combinations of two drugs, including A) Niclosamide-ivermectin, B) Niclosamide-Chloroquine, and C) ivermectin-chloroquine.

Thereafter, the authors summarized the findings for each combination mentioned above. In table 2 and table 3 of the yet-to-be-reviewed manuscript, the authors reveal the antiviral activity for the two-drug combinations treatment against SARS-CoV-2 in Vero E6 cells.

What did they find?

In their discussion section, the authors declared, “Our study shows that the repurposed anti-parasitic drugs, Niclosamide, ivermectin, and Chloroquine possess high in vitro activity against SARS-CoV-2, as the IC50 values are in the low micromolar range.”

The authors note that their findings regarding the testing of single drug effectiveness against SARS-CoV-2 align with previous comparable preclinical lab-based investigations. The authors introduce that one reason why these drugs may show successful in vitro actions against SARS-CoV-2 yet not fare as well in human (in vivo) studies may be due to a lack of potency. 

Thus, the impetus to use various combinations to enhance potency. A key rationale underlying this preclinical, lab-based study was to better understand what proper combinations of these available, economically approved drugs could be synergistic with efficacious results.

And the results are positive from this Mahidol University-led study: the authors demonstrate the benefit of combining ivermectin, Niclosamide, and Chloroquine and their anti-SARS-CoV-2 activities in the cell culture environment. But what was the superior combination? Ivermectin and Niclosamide produce the best synergistic profile.

Study Support

The study was supported with funds and resources associated with the Thailand-based Chair Professor Program (P-20-52262), The National Science and Technology Development Agency (NSTDA). The study received additional support from the Faculty of Medicine Siriraj Hospital, Mahidol University in Thailand. 

TrialSite reminds us that this study hasn’t been peer-reviewed yet.

Mahidol University

This autonomous research center in Thailand originated with the establishment of the Siriraj Hospital back in 1888. The institution was known as the University of Medical Science by 1943, ultimately recognized as the Southeast Asian nation’s fourth public university. By 1969, it was named by King Bhumibol Adulyadej after his father—Prince Mahidol of Songkhla, who happens to also be the “Father of Modern Medicine and Public Health of Thailand,”  according to the most recent Wikipedia entry. By 2016, the acceptance rate into the school of medicine was 0.4%. 

Mahidol University remains a hub of medical-related research in Thailand. The academic medical center has been recognized by the United Nations’ World Health Organization and consequently, has been designated a WHO collaboration center. Much of the research here delves into major problems facing this Southeast Asian nation, from public health to other social and economic challenges. 

In the area of biomedical research, this university’s researchers have been at the forefront of important discoveries and breakthroughs in the following topics:

  • Better understanding of the molecular basis of thalassemia

  • Drug-resistance in malaria and avian influenza

  • Possible strategies and treatment and prevention including vaccine clinical trials

Lead Research/Investigator

Prasert Auewarakul, MD, Mahidol University Faculty of Medicine Siriraj Hospital. Dr. Prasert Auewarakul was educated in Germany.