Caly et al. at Monash University in Australia recently published a paper in Antiviral
Research, reporting that ivermectin, a medication widely used for the treatment of
certain parasitic diseases in humans and livestock animals, inhibits the replication
of SARS-CoV-2 in cell culture (Caly et al., 2020). Despite the authors' cautious conclusion
that ivermectin "warrants further investigation for possible benefits in humans,"
the paper has excited widespread interest on medical and veterinary websites, which
often incorrectly describe the drug as a treatment or cure for COVID-19. These inappropriate
statements led to a warning by the US FDA, that ivermectin in veterinary products
should not be used for human therapy,
https://www.fda.gov/animal-veterinary/product-safety-information/fda-letter-stakeholders-do-not-use-ivermectin-intended-animals-treatment-covid-19-humans.
The FDA message also explains that in vitro studies such as the report in AVR are
"commonly used in the early stages of drug development."
The paper by Caly et al. has also elicited two letters to the editor, which are printed
below, followed by the authors' response to both letters. Readers should be aware
that neither the letters nor the response has been peer-reviewed, so appropriate caution
should be used in quoting or citing them.
Mike Bray, MD, Editor-in-chief
Antiviral Research
Caly L, Druce JD, Catton MG, Jans DA, Wagstaff KM, 2020. The FDA-approved Drug Ivermectin
inhibits the replication of SARS-CoV-2 in vitro. Antiviral Res. Apr 3:104787..
Rayner
Craig R.
PharmD
craig.rayner@certara.com
Certara, Inc, 100 Overlook Center, Princeton, NJ, USA, 08540
To the Editor,
Recently Caly et al. reported in vitro activity of ivermectin against SARS-CoV-2 following
a single addition to Vero-hSLAM cells, and suggest that these data “demonstrate that
ivermectin is worthy of further consideration as a possible SARS-CoV-2 antiviral”
[1]. In isolation, these in vitro data are robust and encouraging but the report does
not include a correlation of the in vitro findings with clinically achievable plasma
and, more relevantly, lung concentrations that would permit the determination of whether
the macrocyclic lactones (and specifically in this case ivermectin) are genuine therapeutic
options.
Caly et al bathed Vero-hSLAM cells with ivermectin at a concentration of 5μM from
2 hours post-infection SARS-CoV-2 isolate Australia/VIC01/2020 until the conclusion
of the experiment. SARS-CoV-2 RNA was determined by RT-PCR at Days 0 to 3 in both
supernatant and cell pellet experiments. The authors noted 93 to 99.8% reduction in
viral RNA for ivermectin versus DMSO control at 24h in supernatant (released virions)
and cell associated viral RNA (total virus) respectively. They also describe by 48
hours a ∼5000-fold reduction of viral RNA and maintenance of effect at 72 hours. Additional
experiments were conducted with serial dilutions of ivermectin to establish the concentration-response
profile, and the authors describe ivermectin as a potent inhibitor of SARS-CoV-2,
with an IC50 determined to be approximately 2 μM under these conditions.
We sought to examine the clinical relevance of the concentrations evaluated in these
in vitro experiments to those that may be achieved with ivermectin dosing in practice,
in order to assist in prioritizing ongoing efforts with finding therapeutics that
may be effective in COVID-19.
Ivermectin is one of humanity’s most important medicines [2] and is extensively used
for 5 neglected tropical diseases at single oral doses of 150 to 200 μg/kg, resulting
in the mean peak plasma concentrations of approximately 30 to 47 ng/mL [3]. In Phase
I studies, doses up to 2000 μg/kg [4] have been administered in a fasted state or
up to 600 μg/kg following a standard high-fat meal. Smit et al [5] report that ivermectin
600 μg/kg administered orally resulted in a maximum median concentrations (Cmax) in
plasma of 118.9 ng/mL (p5-p95: 45.2–455.1ng/mL), with relatively rapid clearance and
a half-life of approximately 3 to 5 hours.
Similar to Yao et al. who proposed the potential for hydroxychloroquine for treating
COVID-19,[6] we applied a physiologic-based pharmacokinetic (PBPK) model of ivermectin
using the Simcyp platform to explore the plasma and lung concentrations relative to
the IC50 values against SARS-CoV-2 determined in vitro. The ivermectin PBPK model
was initially developed to facilitate drug development for parasitic diseases including
onchocerciasis and is a full model that allows prediction of tissue drug concentrations.
The model has been independently verified. The predicted versus observed plasma profiles
for ivermectin across clinical studies in the Mectizan NDA were well aligned, [7]
indicating the base model is well defined. Furthermore, the PBPK model was able to
predict ivermectin exposures in plasma, adipose and skin to within 1.3-fold of observed
data in patients infected with Onchocerca volvulus [8]
Simulations were performed using the Simcyp Simulator Version 19 Release 1. Ten virtual
trials of 10 subjects aged 18-75 years (50 % female) were simulated using the Sim-NEurCaucasion
population. In the simulation, high dose ivermectin (600 μg/kg) was administered orally,
daily for 3 days and the virtual study carried on to 9 days. Dosing was in the Fed
state and fraction unbound was 0.07 (plasma) and 0.13 (lung). Simulations for mean
systemic plasma and lung tissue concentrations are shown in Figure 1.
Figure 1
Simulated mean concentration-time profile of ivermectin in plasma (black line) and
lung tissue (blue line) following 600 μg/kg dose daily for 3 days. The 5th and 95th
percentiles are also shown. The red-line is the IC50 (2μM) against SARS-CoV-2 determined
in vitro by Caly et al. [1].
Figure 1
Pharmacodynamic response is generally achieved by ensuring an appropriate duration
of exposure above the minimum therapeutic concentration at the site of action. Even
with most generous assumptions for clinical translation, the in vitro IC50 is >9-fold
and >21-fold higher than the day 3 plasma and lung tissue simulated Cmax respectively,
following a high dose ivermectin regimen of 600 μg/kg dose daily for 3 days. [5] This
dose scenario, which ignores consistent exposure, exceeds the highest regulatory approved
dose of ivermectin, being a 200 μg/kg single dose for the treatment of Strongyloidiasis.[3].
Caly et al. cite the importance of regulatory approval of ivermectin as a key part
of the rationale for further evaluation against SARS-CoV-2. However, the rigorous
data review and reassurance of a stringent regulatory authority review only applies
to currently approved doses – clinical pharmacology and toxicology margins (including
pre-and post-natal and carcinogenicity studies) would, therefore, need to be recalculated.
In reality, the resultant unravelling of the supporting package of data could result
in lengthy delays while supporting data are revised and re-run.
It is understandable that, faced with a devastating pandemic and a medical and societal
imperative, there is great enthusiasm for promising news of treatments. Picking and
supporting the best therapies and preventions to tackle the COVID-19 pandemic head
on is one of the scientific community’s most urgent priorities. To assist this process,
the clinical pharmacological relevance of in vitro or in vivo findings should be included.
In vitro promise leads to clinical failure in the vast majority of cases, and in the
volatile environment of the current pandemic, it is critical that we are sensitive
to the implications of our communication and apply our resources to compounds most
likely to succeed. A small window exists for the current data to have relevance for
humans: we need to confirm the effective concentrations, assess if the class of macrocyclic
lactones has similar target interactions, and understand the relevance of the concentrations
used in vitro against SARS-CoV-2 to those likely to be achieved at the site of action,
within a dose range considered to be well tolerated. Alternative routes could also
be considered, although these present new formulation and safety challenges. Modelling
and simulation approaches integrate in vitro findings with the in vivo situation and
may serve to prioritize existing drugs that are candidates for repurposing.
Co-authors: Karen Yeo PhD, David Wesche MD, PhD, Lisa Almond PhD, Michael Dodds, PhD,
Patrick F Smith PharmD, Mark Sullivan BSc.
Declaration of Competing Interest
KY, DW, LA, MD, PS and CR work for Certara, a consulting firm in integrated drug development
and have directly consulted with a variety of not-for-profit global health organizations,
biotechnology and pharmaceutical companies and governments with an interest in medical
countermeasures against respiratory virus infections. MS works for Medicines Development
for Global Health and the Kirby Institute and has no conflicts of interest to declare.
Funding information
No funding was provided to write this short communication.
References
1
Caly
L.
The FDA-approved drug ivermectin inhibits the replication of SARS-CoV-2 in vitro
Antiviral research
2020
10.1016/j.antiviral.2020.104787
2
Crump
A.
Omura
S.
Ivermectin, 'wonder drug' from Japan: the human use perspective
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Merck, Stromectol USPI. https://www.accessdata.fda.gov/drugsatfda_docs/label/2009/050742s026lbl.pdf,
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4
Guzzo
C.A.
Safety, tolerability, and pharmacokinetics of escalating high doses of ivermectin
in healthy adult subjects
J Clin Pharmacol
42
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5
Smit
M.R.
Pharmacokinetics-Pharmacodynamics of High-Dose Ivermectin with Dihydroartemisinin-Piperaquine
on Mosquitocidal Activity and QT-Prolongation (IVERMAL)
Clin Pharmacol Ther
105
2
2019
388
401
30125353
6
Yao
X.
In Vitro Antiviral Activity and Projection of Optimized Dosing Design of Hydroxychloroquine
for the Treatment of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)
Clin Infect Dis
2020
7
Merck, Mectizan NDA 050742. 1996.
8
Baraka
O.Z.
Ivermectin distribution in the plasma and tissues of patients infected with Onchocerca
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Noël
François
PhD
fnoel@pharma.ufrj.br
Laboratory of Biochemical and Molecular Pharmacology, Institute of Biomedical Sciences,
Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
To the Editor:
In the context of repositioning/repurposing strategy for urgent unmet medical needs,
various drugs are being proposed for the treatment of COVID-19, the pandemic disease
caused by SARS-CoV-2 (Noël and Lima, 2020). This is the case for the broad-spectrum
macrocyclic lactone ivermectin, as reported by Caly et al. (2020) based on their data
showing that ivermectin inhibits the replication of SARS-CoV-2 in vitro. However,
this in vitro activity occurred at much higher concentrations (IC50 ≈ 2-3 μM) than
the very low (nanomolar) concentrations effective against many nematode species (Geary,
2005), obtained after a usual dose of 200 μg/kg. This micromolar concentration is
also higher than the therapeutic peak plasma concentration (about 40 nM) measured
in humans treated for onchocerciasis control with a standard dose of 150 μg/kg (Apud
Shu et al. 2000) and even after a high daily dose (600 μg/kg) where Cmax of 105-119
ng/ml (0.12-0.14 μM) has been obtained by PK/PD modeling (Smit et al., 2019).
As we previously showed (Pimenta et al., 2010) that ivermectin is a nonselective inhibitor
of three important mammalian P-type ATPases (SERCA, Na+/K+-ATPase and H+/K+-ATPase)
at similar micromolar concentrations (IC50 ≈ 6-17 μM), we have to be concerned with
putative important adverse effects that this drug could produce at the higher than
usual doses that would be necessary for treating COVID-19 patients. As a result, a
phase 1 study is absolutely needed before using ivermectin since a recent meta-analysis
concluded that there are not enough data to support a recommendation for its use in
higher-than-approved doses (Navarro et al., 2020).
Declaration of Competing Interest
No conflict.
References
Caly
L.
Druce
J.D.
Catton
M.G.
Jans
D.A.
Wagstaff
K.M.
The FDA-approved Drug Ivermectin inhibits the replication of SARS-CoV-2 in vitro
Antiviral Res
2020
10.1016/j.antiviral.2020.104787
Navarro
M.
Camprubí
D.
Requena-Méndez
A.
Buonfrate
D.
Giorli
G.
Kamgno
J.
Safety of high-dose ivermectin: a systematic review and meta-analysis
J Antimicrob Chemother
75
4
2020
827
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31960060
Noël
F.
Lima
J.
Pharmacological aspects and clues for the rationale use of Chloroquine/Hydroxychloroquine
facing the therapeutic challenges of COVID-19 pandemic
Lat Am J Clin Sci Med Technol
2
2020
28
34
Pimenta
P.H.C.
Silva
C.L.M.
Noël
F.
Ivermectin is a nonselective inhibitor of mammalian P-type ATPases
Naunyn-Schmied Arch Pharmacol
381
2010
147
152
Smit
M.R.
Ochomo
E.O.
Waterhouse
D.
Kwambai
T.K.
Abong´o
B.O.
Bousema
T.
Pharmacokinetics-Pharmacodynamics of High dose Ivermectin with Dihydroartemisinin-piperaquine
on Mosquitocidal Activity and QT-Prolongation (IVERMAL)
Clin Pharmacol Ther
105
2
2019
388
401
30125353
Jans
David A.
Prof.
David.Jans@monash.edu
Wagstaff
Kylie. M.
Dr.
Nuclear Signalling Laboratory, Monash Biomedicine Discovery Institute and Department
of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, 3800,
Australia
Response of the authors.
To the Editor,
Yeo et al. and Noël aptly point out that published studies show that blood levels
of ivermectin achieved during standard therapy are much lower than the concentrations
we reported as inhibitory for SARS-CoV-2 in cell culture (Caly et al., 2020). Yeo
et al. (2020) further explore the question via pharmacokinetic modeling (from Certara
Inc.), while Noel (2020) voices concern that if high concentrations of ivermectin
could be achieved, this would likely be toxic. These points are well made, and we
are in agreement, but they do not address the reported mechanism of action of ivermectin
(Yang et al., 2020), and thereby fail to highlight a further vitally important reason
to be very cautious in considering ivermectin as a therapeutic for viral infection
in human patients.
Ivermectin’s key direct target in mammalian cells is a not a viral component, but
a host protein important in intracellular transport (Yang et al., 2020); the fact
that it is a host-directed agent (HDA) is almost certainly the basis of its broad-spectrum
activity against a number of different RNA viruses in vitro (Tay et al., 2013; Yang
et al., 2020). The way a HDA can reduce viral load is by inhibiting a key cellular
process that the virus hijacks to enhance infection by suppressing the host antiviral
response. Reducing viral load by even a modest amount by using a HDA at low dose early
in infection can be the key to enabling the body’s immune system to begin to mount
the full antiviral response before the infection takes control.
Pharmaceutical research efforts are currently underway to refine liquid formulations
for intravenous administration of long-acting ivermectin, develop aerosol administration,
and consider using ivermectin in combination with other agents to enhance efficacy
at low doses. However, it is important to urge great caution in approaching the use
of ivermectin in this simplistic way, precisely because ivermectin is a HDA. Because
it targets a host component, it cannot be assumed that even doses lower than those
discussed by Yeo et al. (2020) and Noel (2020) are safe in the context of a burgeoning
viral infection, where a measured immune response is key to recovery. Clinical testing
of ivermectin at any dose in the fight against viral infection must include intensive
monitoring of patient well-being, to pre-empt any immunosuppressive or other adverse
reactions as early as possible.
Finally, it is critically important to remember that ivermectin as an antiviral is
in a very early phase – under no circumstances should self-medication be considered
without the guidance of a qualified physician, and especially not using therapeutics
designed for veterinary purposes!
Declaration of Competing Interest
Authors have no conflict of interest, with no link to any pharma company.
Funding information
No funding supported this letter to the editor.
References
Caly
L.
Druce
J.D.
Catton
M.G.
Jans
D.A.
Wagstaff
K.M.
The FDA-approved Drug Ivermectin inhibits the replication of SARS-CoV-2 in vitro
Antiviral Res
2020
104787
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Antiviral Res
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Uncited
Smit et al., 2020, Caly et al., 2020.