The Official Statements About Ivermectin

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The multinational pharmaceutical company Merc, headquartered in the US, known as MSD outside the US and Canada, recently clarified its view of the use of ivermectin in combating COVID-19. Overall, the summary of the company’s findings is as follows:

  • at the moment, within the framework of the conducted clinical studies, no serious scientific grounds have been identified that would determine the
  • manifestation of a tangible and measurable potential therapeutic effect of ivermectin on the course of COVID-19 disease in research participants;
  • most of the current clinical studies do not provide any convincing data on the safety of ivermectin use in patients with COVID-19;
  • there is no significant evidence of clinical activity and/or clinical efficacy of ivermectin in patients with COVID-19.

The multinational pharmaceutical company Merc, headquartered in the US, known as MSD outside the US and Canada, recently clarified its view of the use of ivermectin in combating COVID-19. Overall, the summary of the company’s findings is as follows:

Indications for the Use of Ivermectin (Trade Name Stromectol)

Ivermectin is the main active ingredient of a drug registered in the United States under the trade name Stromectol. The main indication for the use of this drug is the therapy of intestinal strongyloidosis (not disseminated) caused by the nematode parasite Strongyloides stercoralis. In addition, Stromectol is indicated for the treatment of onchocerciasis caused by the nematode parasite Onchocerca volvulus. An important fact to note is that Stromectol shows no effect against adult parasites Onchocerca volvulus, it annihilates only newly hatched nematodes. In this regard, the process of treatment of onchocerciasis with Stromectol can be quite long.

Stromectol: Basic Information on the Safety of Use

Absolute and Relative Contraindications

The main contraindication to the use of Stromectol is hypersensitivity to any of the components that make up this medication. With caution, Stromectol should be prescribed to patients suffering from bronchial asthma and hepatitis. If the patient is pregnant or breastfeeding, it is necessary to carefully assess the ratio of the potential benefit to the risk of using Stromectol for the fetus/child. According to a number of studies, the presence of a patient’s co-infection with Loa loa (a nematode parasite) can lead to the development of severe or even fatal encephalopathy during or after treatment with Stromectol. In this regard, before prescribing Stromectol, patients from West and Central Africa are recommended to be additionally examined for the presence of loiasis.

Warnings and Precautions

Patients who have been prescribed Stromectol against onchocerciasis may demonstrate adverse reactions of varying severity. These may include skin, ophthalmic and systemic reactions. The most serious among the latter is the so-called Mazzotti reaction. Its occurrence is caused by the death of microfilariae under the action of the drug and the release of the corresponding antigens. As a rule, the severity of the Mazzotti reaction is in direct proportion to the degree of infection of the patient’s body with microfilariae. Typical manifestations of the Mazzotti reaction include fever, chills, urticaria, enlarged lymph nodes and soreness, tachycardia, hypotension, arthralgia, edema, and abdominal pain. In severe cases, the Mazzotti reaction can be life-threatening for the patient. Side effects such as severe edema and exacerbation of onchodermatitis are often observed in patients with hyperreactive onchodermatitis.

Patients infected with Loa loa, when treated with Stromectol, in addition to encephalopathy, may experience reactions such as neck and back pain, redness of the eyes and hemorrhage in the conjunctiva, shortness of breath, in severe cases, urinary and/or fecal incontinence, difficulty standing and/or walking, changes in normal mental status, confusion, lethargy, stupor, seizures, or coma.

Administration of Stromectol

In all cases, Stromectol should be taken on an empty stomach with enough water. When treating strongyloidosis with Stromectol, the patient must undergo at least two repeated stool examinations to confirm the complete disappearance of Strongyloides stercoralis infection from the body.

When treating onchocerciasis, it should be borne in mind that Stromectol does not kill adult Onchocerca nematodes, affecting only young ones. For this reason, one course of treatment is almost never sufficient to get rid of onchocerciasis. In most cases, long-term observation and repeated courses or courses of treatment with Ivermectin or other antiparasitic drugs are required.

Side effects of Stromectol

The side effects that patients experience when taking Stromectol often differ depending on which disease is being treated.

Thus, in the case of the treatment of strongyloidiasis, clinical studies show that in patients receiving one or two doses of 170 to 200 μg/kg of Stromectol, the following side effects were noted:

  • on the part of the body as a whole: asthenia, fatigue, abdominal pain (all with a probability of about 1%);
  • from the gastrointestinal tract: anorexia (1%), constipation (1%), diarrhea (2%), nausea (2%), vomiting (1%);
  • from the nervous system and psychiatry: dizziness (3%), drowsiness (1%), tremor of the extremities (1%);
  • on the part of the skin: itching (3%), rash (1%) and urticaria (1%).


In the case of the treatment of onchocerciasis in 1000 patients who took Stromectol at a dosage of 100 to 200 μg/kg and demonstrated the development of the Mazzotti reaction, this reaction worsened within 4 days after manifestation. Adverse reactions included:

  • arthralgia and synovitis (9.5%);
  • an increase and soreness of the axillary lymph nodes (11% and 4.5%, respectively);
  • an increase and soreness of the cervical lymph nodes (5.5% and 1%, respectively);
  • an increase and soreness of the inguinal lymph nodes (12.5% ​​and 14%, respectively);
  • enlargement and soreness of lymph nodes of other localization (3.0% and 2%, respectively);
  • itchy skin (27.5%);
  • skin lesions, including edema, papular and pustular or overt urticaria (23%);
  • fever (23%).

In most clinical studies, ophthalmic reactions associated with Stromectol are studied before starting therapy, on the third day, and also 3 and 6 months after treatment with Stromectol at a dosage of 100 to 200 μg / kg. In a number of cases, changes in the course of ophthalmic reactions when measured 3 and 6 months after treatment were worse compared to the level before the start of treatment and three days after the start of treatment. In most cases, however, negative ophthalmic reactions either returned to pretreatment conditions or improved from baseline severity. The main ophthalmic reactions studied include limbit and punctate opacity.

Ophthalmic side effects such as abnormal sensations in the eyes, eyelid edema, anterior uveitis, conjunctivitis, limbit, keratitis, chorioretinitis, and choroiditis usually arise directly from onchocerciasis itself. With Stromectol therapy, they can increase, but are rarely severe and usually do not require serious treatment, for example, with the use of corticosteroids. In the vast majority of cases, they do not lead to loss or tangible deterioration of vision.

Clinical studies of the use of Stromectol in humans show that approximately 1% of patients experience side effects such as facial edema, 3% – peripheral edema, 1% – orthostatic hypotension, 4% – tachycardia. Less than 1% of patients experience headache and muscle pain.

Interaction of Stromectol with Other Drugs

Ivermectin should be used with caution in combination with a number of other medicines.


Taking ivermectin together with anti-nausea and vomiting medicines such as aprepitant and its derivative fosaprepitant can cause severe side effects similar to those caused by ivermectin. In most cases, these side effects worsen a few days after you start taking aprepitant. This situation is due to the fact that ivermectin is a substrate of cytochrome CYP3A4. Aprepitant, when taken orally for 3 days, acts on the human body as a moderate inhibitor and inducer of CYP3A4, which, as a rule, increases the concentration of ivermectin in the blood plasma. There is an increase in the bioavailability of ivermectin and the effect of the increased dosage, even if the ivermectin is taken at a sufficiently low dosage. Aprepitant has the same effect on other CYP3A4 substrates, such as midazolam (an agent for increasing the sedative effect of anesthetics, treating seizures and mild insomnia). With a single use of this drug, the area under the pharmacokinetic curve describing the concentration/time dependence (AUC) of midazolam increases by about 1.5 times. When aprepitant is taken for five days, the AUC of midazolam increases already by 3 times. After administration, fosaprepitant quickly converts to aprepitant and has many drug interactions similar to this substance. It should be noted that less than a 2-fold increase in the AUC of midazolam while taking aprepitant is not considered clinically important and rarely has a significant effect on the patient’s body.


Boceprevir is a protease inhibitor used in the treatment of hepatitis caused by hepatitis C virus genotype 1. When using ivermectin with boceprevir, it is recommended to carefully monitor the patient’s condition due to the increased risk of moderate to severe side effects associated with ivermectin. If it is necessary to take ivermectin together with boceprevir, it is advised to reduce the dose of ivermectin; at the end of taking boceprevir, it can be increased. At the moment, there is a need for a more careful study of the interaction of ivermectin and boceprevir, since the main recommendations regarding their interaction are related to theoretical conclusions based on the study of the metabolic pathway of ivermectin. The use of ivermectin in combination with boceprevir may cause an increase in the concentration of ivermectin in the blood plasma because of the fact that ivermectin is partially metabolized by the hepatic isoenzyme CYP3A4, while boceprevir inhibits this isoenzyme.


Idelalisib (a medicine used in the treatment of chronic lymphocytic leukemia, follicular B-cell non-Hodgkin lymphoma and small lymphocytic lymphoma) strongly (more than 5 times) increases the AUC of ivermetkin, which leads to a significant increase in the toxicity of the latter. It is not recommended to take these medicines together in order to avoid the development of serious adverse reactions up to the life-threatening of the patient.


Mirabegron is a moderate CYP2D6 inhibitor used to treat overactive bladder. Ivermectin also metabolizes cytochrome CYP2D6, therefore, in order to prevent the development of severe side effects caused by ivermectin, it is desirable to reduce the dosage of ivermectin and monitor the patient’s condition.


Mitotane is a steroidogenesis inhibitor and cytostatic anticancer drug used to treat adrenocortical carcinoma and Cushing’s syndrome. Since mitotane is a strong inducer of CYP3A4, and ivermectin is a substrate of CYP3A4, their combined use may lead to a decrease in the concentration of ivermectin in blood plasma and the need to increase the dosage.


The simultaneous use of an antimycotic drug posaconazole and ivermectin is fraught with an increased possibility of side effects associated with ivermectin, since posaconazole is an inhibitor of the CYP3A4 enzyme, which is partially involved in the metabolism of ivermectin.


Telaprevir (a drug for the treatment of hepatitis C), when used with ivermectin, increases the side effects of the latter. Ivermectin is partially metabolized by the hepatic isoenzyme CYP3A4, while telaprevir inhibits it. Because of this, the combined use of these drugs can lead to an increase in the concentration of ivermectin in the blood plasma.


An indirect anticoagulant, warfarin, according to some clinical studies, in combination with ivermectin, causes an increase in prothrombin time, but at the moment there is insufficient data on this issue.

Use in Certain Populations

The safety of using ivermectin during pregnancy has not yet been proven, and the use in this case is not recommended.

When breastfeeding, the use of ivermectin is justified only in cases where the lack of treatment is more dangerous than the risk to the newborn.

The use of ivermectin in children weighing less than 15 mg is not recommended due to its unidentified safety and efficacy.

To date, no studies have been conducted to clarify the need for ivermectin dosage adjustments in elderly patients.

Patients with HIV in most cases require longer courses or repeated treatment with ivermectin.

About Merck

Merck has been active in the international pharmaceutical market for 130 years, inventing numerous medicines and vaccines. Our mission is to save people and improve their quality of life. Our core values ​​are protecting public health and expanding access to health care through forward-looking policies, programs and collaboration. In the third decade of the 21st century, Merck remains one of the leading research companies in the prevention and treatment of diseases that threaten humans and animals, including cancer, infectious diseases and emerging animal diseases. Our goal is to become the world’s leading research biopharmaceutical company. You can find out more about us at and on our Twitter, Facebook, Instagram, YouTube and LinkedIn pages.

Forward-Looking Statement for Merck & Co., Inc., Headquartered in Kenilworth, NJ, USA

This press release from Merck & Co., Inc., Kenilworth, NJ, USA (the “company”) includes “forward-looking statements” within the meaning of “safe harbor” of US Private Securities Litigation Reform Act 1995. The statements are based on the current beliefs and expectations of the company’s management and are subject to significant risks and uncertainties. The company’s position may change over time and under the influence of certain circumstances or data. In the event that the company’s key assumptions prove to be inaccurate, risks or uncertainties arise, or the situation changes, the bottom line could differ materially from those projected by the company.

Risks and uncertainties include, but are not limited to, general industry conditions and competition; general economic factors; the impact of the global outbreak of the novel coronavirus disease (COVID-19); the impact of pharmaceutical industry regulation and healthcare legislation in the United States and around the world; global trends towards containment of health care costs; technical progress, products and patents obtained by competitors; problems associated with the development of new products; production difficulties or delays; financial instability of the global economy and sovereign risk; dependence on the effectiveness of the company’s patents and other means of protecting innovative products; and exposure to litigation or regulation.