In this investigator-initiated, triple-blind, randomized, placebo-controlled trial, we examined the efficacy and safety of Ivermectin at two doses (24 mg and 12 mg) in the management of non-severe COVID-19. Patients in the Ivermectin 24 mg arm demonstrated a numerically higher rate of conversion to negative RT-PCR at day 5 compared to the placebo arm overall and also separately in the mild and moderate subgroups; however, this did not reach statistical significance (Figure 2). Further, the decline in viral load at day 5 in all groups was similar.
The interest in Ivermectin in the treatment of COVID-19 was sparked by an in-vitro study by Caly et al, wherein they had demonstrated in Vero/hSLAM cells, that a single application of Ivermectin to achieve concentrations of 2-2.5 µg/mL enable a 5000-fold reduction in the viral load within 48 hours(6). Ivermectin has a plausible broad spectrum anti-viral action by inhibiting the importin α/β protein of the host(3). The inhibition of this protein blocks the entry of the viral nucleocapsid into host nucleus for subsequent replication. Previously, in a phase III clinical trial, Ivermectin increased rate of viral clearance of dengue virus compared with placebo without any demonstrable clinical benefit (14).
However, the micromolar doses described in the in-vitro study by Caly et al are difficult to achieve in vivo with the FDA-approved dose (200 µg/kg) of Ivermectin(15). Although Ivermectin is usually administered in tablet form, its bioavailability may increase upto 2.5-fold when given alongwith a fat-rich meal or in an alcohol-based formulation(10,16). Furthermore, Ivermectin may preferentially distribute into the tissues, including the lung(12). Hence, we included a higher dose (400 µg/kg) of Ivermectin in an alcohol-based elixir given after breakfast. Nonetheless, even higher doses may be required to achieve optimal therapeutic doses against SARS-CoV-2. Indeed, doses up to 1-2 g/kg have been found to be safe and may be explored further(9,10). Furthermore, Ivermectin may have immunomodulatory actions at nanomolar doses by inhibiting the nicotinic acetylcholine receptor (nAChR). The nAChR may act as a receptor for SARS-CoV-2 and drive dysregulated cytokine release (IL1, IL6, TNF and IL18) from macrophages(17,18).
In our study subjects, Ivermectin did not improve the time to symptom recovery, clinical status at day 14, or hospital-free days at day 28 after drug administration. Similar results were observed in the only other randomized-trial of Ivermectin (12 µg/kg) in predominantly mild COVID-19 patients (n=62) in Bangladesh, wherein Podder et al(19) found that Ivermectin failed to hasten the resolution of symptoms compared to usual care. The same investigators repeated RT-PCR only once on day 10 and found that most patients had attained a negative result(19). In contrast, we performed RT-PCR at days 3, 5 and 7 to serially evaluate decline in viral load with Ivermectin. Our rationale was that faster viral load decline may enable the non-severe COVID-19 patient to become non-infectious sooner, thereby limiting the contagion. Indeed, it has been shown that at a lower viral load (CT > 24), infectivity declines with lower viral culture positivity(20). Hence the trend towards increased viral negativity at day 5 with ivermectin 24 mg in our trial, particularly among mildly ill patients, encourages further exploration in this regard.
In a retrospective study of hospitalized patients in Florida(21), patients who received Ivermectin were found to have a significantly lower mortality that those who did not (15% versus 25%). The mortality benefit remained significant after propensity-matched analysis and adjusting for confounders. However, they included patients with greater illness severity than our study population, illustrated by lack of mortality in our trial. Furthermore, the greater use of concurrent therapies and retrospective design preclude drawing definitive conclusions from their data. Nonetheless, we did find a 56.2-61.5% RT-PCR negativity among moderately ill patients who received Ivermectin at day 5 of enrolment. The immunomodulatory rather than antiviral effect of Ivermectin may be hypothetically more important in moderate and severe COVID-19(22).
There were no serious adverse events in our trial. Since we have used a novel elixir-based formulation with an aim to maximize plasma bioavailability of Ivermectin, this reassures us regarding its safety for further study. The frequency of mild adverse events was similar with ivermectin at either dose or placebo. Other studies of Ivermectin in COVID-19 have also found a low rate of adverse events(19,23). The predominant adverse event in our study was transient burning sensation in the epigastrium which could be attributed to the alcohol-based elixir preparation.
The major limitation of our study was that it was conducted at a single centre with a relatively small sample size. Most of our patient population was male and relatively young (mean age, 35.3 years) with few comorbidities which reflects the demographics of the catchment area of our centre. Such a patient population is likely to have an uncomplicated disease course(24,25). Furthermore, in the absence of previous clinical trials and considering the urgency of the research question, our sample size was exploratory. Hence, we cannot exclude the possibility that a similarly conducted study in a larger and more diverse population could have uncovered clinical efficacy of Ivermectin, if such benefit indeed exists. Furthermore, the favourable safety profile is encouraging for the conduct of larger trials to further clarify the role of ivermectin in COVID-19.
Secondly, the elixir formulation of ivermectin used by us is not yet commercially available. Although our Ivermectin formulation and dosing strategy was determined by a simulation study to attain an adequate drug concentration in the lung, further pharmacokinetic studies are necessary to define the optimal therapeutic dosing of Ivermectin in COVID-19. Furthermore, Ivermectin has a plasma half-life of 18 hours and does not accumulate on repeat dosing(10). Whether multiple doses of Ivermectin in this disease may be superior to a single dose strategy is currently unknown. Hence, the translation of our findings to the use of Ivermectin tablet at various dosing strengths and frequencies in clinical practice requires caution.
Finally, in our study we have recruited patients irrespective of the duration of illness prior to enrolment. The median duration of symptoms at randomization was 5 days in the three arms. Hence, a significant number of patients had a negative RT-PCR result at baseline and were excluded from the modified intention-to-treat analysis. The recruitment of mild patients at a later stage of illness could also have contributed to high rates of RT-PCR negativity in the placebo arm at day 5 of enrolment (31.1%). In a previous study, over 90% of patients with mild COVID-19 have been found to have negative RT-PCR at day 10 of onset of illness(26). Furthermore, antiviral benefits of Ivermectin are postulated to be maximal early in disease course, while hypothetical immunomodulatory benefits may occur later in the illness. Hence, a better understanding of the cellular actions of ivermectin is necessary to define target populations precisely for future trials.