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Ivermectin

Ivermectin: Generic Medication Overview

Ivermectin is an antiparasitic medication belonging to the macrocyclic lactone class. It is marketed as oral tablets (pill) in strengths of 3 mg, 6 mg, and 12 mg. In Hong Kong the drug is prescription-only and is regulated by the Department of Health. Ivermectin is approved for the treatment of a range of parasitic infections; it has also been studied off-label for potential support in COVID-19, a use that is not endorsed by regulatory agencies.

How Ivermectin Works in the Body

Ivermectin binds with high affinity to glutamate-gated chloride channels that are present in the nerve and muscle cells of many invertebrates. This binding increases the permeability of the cell membrane to chloride ions, leading to hyperpolarization, paralysis, and death of the parasite. In mammals, these channels are absent in the central nervous system, which limits the drug’s toxic effect on human nerve cells.

• Onset of action: Parasites are immobilized within a few hours after absorption.
• Peak plasma concentration: Typically occurs 4-5 hours after oral ingestion.
• Duration: Therapeutic concentrations persist for about 24 hours, allowing single-dose regimens for many indications.

Conditions Treated by Ivermectin

Ivermectin’s approved indications (as listed by the Hong Kong Department of Health) include:

• Onchocerciasis (river blindness) - a single oral dose of 150 µg/kg.
• Strongyloidiasis - a single dose of 200 µg/kg; repeat dosing may be required in disseminated disease.
• Pediculosis capitis and corporis (head and body lice) - a single dose of 200 µg/kg.
• Scabies - a single dose of 200 µg/kg, sometimes followed by a second dose after 1-2 weeks for severe infestations.

These uses target adult parasites and, in some cases, the larval stages that cause disease.

Evidence-Based Off-Label Uses

Off-Label Use for COVID-19

Several laboratory studies have shown that ivermectin can inhibit replication of SARS-CoV-2 in cell culture at concentrations far above those achieved with standard oral dosing. Clinical trials conducted worldwide have produced mixed results, and meta-analyses have highlighted methodological limitations, heterogeneity, and potential bias.

• Regulatory status: Ivermectin is not approved by the Hong Kong Department of Health, the U.S. FDA, the European EMA, or any other major agency for the prevention or treatment of COVID-19.
• Disclaimer: Off-label use of ivermectin for COVID-19 should only be considered under the direct supervision of a qualified healthcare professional, with a clear assessment of potential benefits, risks, and alternative evidence-based therapies.

Who Should and Should Not Use Ivermectin?

Absolute Contraindications

• Known hypersensitivity to ivermectin or any excipients in the tablet.
• Concurrent use of strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole) in patients with a history of severe reactions to ivermectin.

Relative Contraindications

• Pregnancy and lactation: Animal studies suggest a risk of fetal harm; use only if the benefit outweighs potential risk and no safer alternatives exist.
• Severe hepatic impairment: Reduced metabolism may increase plasma levels, requiring dose adjustment or avoidance.
• Neurological disorders: Patients with a history of seizures should be monitored closely, as high plasma concentrations can cross the blood-brain barrier in rare cases.

Special Populations

• Children: Ivermectin is approved for use in children weighing 15 kg or more; dosing must be weight-based.
• Elderly: No dose reduction is required solely based on age, but renal or hepatic function should be evaluated.

Safety Profile: Side Effects and Interactions

Common Side Effects

• Gastrointestinal upset: nausea, abdominal pain, or diarrhea (usually mild and self-limiting).
• Skin reactions: mild rash or pruritus at the site of parasite die-off.
• Dizziness or headache: transient and uncommon.

Serious Adverse Events

• Neurological toxicity: rare cases of ataxia, seizures, or coma, typically associated with overdose or compromised blood-brain barrier.
• Hypersensitivity reactions: urticaria, angioedema, or anaphylaxis require immediate medical attention.

Drug Interactions

• CYP3A4 inhibitors (e.g., ritonavir, clarithromycin) can raise ivermectin concentrations; dose adjustment or alternative therapy should be considered.
• P-glycoprotein substrates (e.g., digoxin) may have altered absorption when co-administered; monitor therapeutic levels.
• Anticoagulants: No clinically significant interaction has been documented, but routine monitoring is advisable.

Food and Lifestyle Interactions

• Ivermectin may be taken with or without food; a fatty meal can modestly increase absorption, which is not clinically relevant for most indications.
• Alcohol does not have a known interaction, but excessive intake may exacerbate gastrointestinal irritation.
• No restriction on operating machinery; however, if dizziness occurs, patients should avoid hazardous activities until it resolves.

How to Take Ivermectin

• Standard dosing for parasitic infections: 150-200 µg per kilogram of body weight, administered as a single oral tablet. The exact tablet strength (3 mg, 6 mg, or 12 mg) is selected to approximate the calculated dose as closely as possible.
• Example: A 70 kg adult requiring 200 µg/kg would need 14 mg total. This can be achieved with one 12 mg tablet plus half of a 6 mg tablet (or the nearest practical combination).
• Frequency: Most approved indications require a single dose; scabies and severe strongyloidiasis may need a repeat dose after 1-2 weeks.
• Administration: Swallow tablets whole with a glass of water. Do not crush or chew unless specifically instructed by a pharmacist.
• Missed dose: If the scheduled time is missed and the next dose is more than 12 hours away, take the missed dose; otherwise skip it and continue with the regular schedule. Do not double the dose.
• Overdose: Symptoms may include vomiting, ataxia, seizures, or coma. Seek emergency medical care; supportive care and, if available, activated charcoal are the primary treatments.
• Discontinuation: No tapering is required for short-course therapy. For prolonged use (e.g., repeat dosing in severe strongyloidiasis), follow the prescriber’s guidance.

All dosing decisions must be individualized by a qualified healthcare provider, taking into account weight, comorbidities, and concomitant medications.

Monitoring and Follow-Up

• Baseline assessment: Verify weight, liver function tests (ALT, AST) for patients with known hepatic disease, and assess for signs of active infection.
• Post-treatment review: For onchocerciasis and strongyloidiasis, repeat stool or skin snip examinations 2-4 weeks after therapy to confirm eradication.
• Adverse-event surveillance: Patients should be instructed to report neurological symptoms, severe rash, or persistent gastrointestinal distress promptly.

Storage and Handling

• Store tablets at room temperature (20-25 °C) away from excess heat, moisture, and direct sunlight.
• Keep the container tightly closed and out of reach of children.
• Do not use tablets that are discoloured, cracked, or past the printed expiration date.
• Dispose of unused medication according to local pharmacy-take-back programs or the instructions on the medication label.

Medication-Specific Glossary

Glutamate-gated chloride channel

A protein channel in invertebrate nerve and muscle cells that, when opened by ivermectin, allows chloride ions to flow into the cell, causing paralysis of the parasite.

Microfilariae

The early, circulating larval form of certain filarial worms (e.g., Onchocerca volvulus) that are targeted by ivermectin.

Pharmacokinetic half-life

The time required for the plasma concentration of a drug to reduce by half; ivermectin’s half-life is approximately 12-36 hours, depending on individual metabolism.

Weight-based dosing

Calculation of drug amount based on a patient’s body weight (µg/kg), a standard approach for ivermectin to ensure therapeutic exposure while minimizing toxicity.

Off-label use

Prescription of a medication for an indication, route, or patient group that is not approved by the relevant regulatory authority.

Medical Disclaimer

This article provides educational information about ivermectin and is not a substitute for professional medical advice. Treatment decisions, including use for unapproved indications, must be made under the guidance of a qualified healthcare provider. The content is intended for informational purposes and does not constitute medical recommendations. Always consult a physician before starting, stopping, or changing any medication regimen.