Moxidectin

Moxidectin is an antiparasitic drug approved for one specific infection:

• Onchocerciasis (river blindness) — an infection caused by the parasitic worm Onchocerca volvulus, approved for adults and pediatric patients aged 4 years and older weighing at least 13 kg. Moxidectin Tablets treat the larval stage of the parasite (microfilariae) but do not kill adult worms. Follow-up is advised after treatment. Repeat dosing for this infection has not been studied.

Moxidectin is a macrocyclic lactone — a class of antiparasitic agents. It works by interfering with the nervous system of the immature parasitic larvae (Onchocerca volvulus microfilariae), impairing their ability to survive. This reduces the larvae circulating in the body, which helps control the infection and its complications. It does not affect the adult worms, which is why ongoing medical follow-up after treatment is necessary.

Moxidectin is taken by mouth as a single dose — you don't take it daily or on a continuing schedule. The number of tablets depends on body weight, especially for children. It can be taken with or without food, though eating a high-fat meal alongside it does increase how much of the drug your body absorbs. Always follow your prescriber's exact instructions. Because this is a one-time dose, there is no missed-dose routine — contact your prescriber if you have questions about timing.

Most side effects after Moxidectin are tied to the Mazzotti reaction — your body's immune response to dying parasite larvae — and typically appear and resolve within the first week after treatment:

Serious reactions — including an inability to stand due to blood pressure drops, significant liver enzyme elevations, or neurological symptoms — require prompt medical attention. See the warnings section for details.

• Mazzotti reaction: As the parasite larvae die off, your immune system may trigger skin, eye, and body-wide reactions including itching, rash, fever, low blood pressure, rapid heartbeat, and eye discomfort. These typically resolve within a week. Patients with higher parasite loads may have more intense reactions.
• Orthostatic hypotension (dizziness on standing): About 5% of patients experience significant drops in blood pressure when standing up, sometimes to the point of being unable to stand. If this happens, lie down until it passes. This most commonly occurs on Days 1 and 2 after treatment.
• Loa loa co-infection — serious brain risk: People infected with both O. volvulus and Loa loa (a different parasite found in parts of Africa) may develop serious or fatal brain swelling (encephalopathy) after treatment. Screening for Loa loa before treatment is strongly recommended for anyone who has traveled or lived in Loa loa-endemic areas.
• Severe skin swelling (sowda): Patients with hyper-reactive onchodermatitis (sowda) are at higher risk of severe swelling and worsening skin disease after treatment.
• Liver changes: Elevated liver enzymes and bilirubin (a marker of liver function) occurred more often in moxidectin-treated patients than in comparison groups. These were mostly temporary, but monitoring may be appropriate.

Based on clinical and laboratory studies, Moxidectin has a low potential for drug interactions:

• CYP3A4 substrates (a broad class of common drugs): A clinical study showed moxidectin does not meaningfully affect the levels of midazolam, a representative CYP3A4 drug — so co-administration with CYP3A4 substrates is considered acceptable.
• CYP enzymes and other drug-processing pathways: Lab studies show moxidectin is not broken down by CYP enzymes, does not inhibit them, and is not a substrate for UGT enzymes or P-glycoprotein — meaning it is unlikely to cause significant interactions through these common pathways.

Not a complete list. The label covers the interactions the manufacturer studied or reported, and our own interaction database does not cover every medicine either. Bring your full medication list, including vitamins and herbal products, to your pharmacist.

• Loa loa exposure: If you have lived in or traveled to areas where Loa loa is endemic (parts of Central and West Africa), tell your doctor before taking moxidectin — you should be screened for that infection first due to the risk of serious brain complications.
• Sowda (hyper-reactive skin disease): Let your doctor know if you have this severe form of onchocerciasis-related skin disease, as you may be at higher risk of severe swelling and skin worsening.
• Pregnancy: There are insufficient human data to confirm safety in pregnancy. Animal studies showed developmental effects at high doses, and effects on nursing offspring were seen at doses close to the human dose. Discuss the risks with your doctor.
• Breastfeeding: Moxidectin passes into breast milk. Because of serious harm seen in nursing animal offspring, breastfeeding is not recommended during treatment or for 7 days after the dose.
• Children under 4 or weighing less than 13 kg: Safety and effectiveness have not been established in this group.
• Severe kidney disease: The safety of moxidectin in patients with severe renal impairment or end-stage kidney disease is unknown. Mild-to-moderate kidney disease does not appear to significantly affect drug levels.
• Liver disease: How liver impairment affects moxidectin processing in the body is unknown — discuss this with your doctor if applicable.
• Older adults (65+): Clinical studies included patients over 65 with no notable differences in safety or effectiveness, though individual sensitivity cannot be completely ruled out.

There is no specific antidote if too much moxidectin is taken. If an overdose occurs, medical providers will monitor for signs of toxicity and provide supportive care — this may include fluids, monitoring vital signs, respiratory support, and treatment for low blood pressure if needed. Contact a poison control center or seek emergency care right away.

At doses well above the approved level (4.5 times the recommended dose), moxidectin does not cause a meaningful prolongation of the QT interval — the heart's electrical reset time — meaning it does not appear to carry significant heart rhythm risk at therapeutic doses. Its main measurable effects in the body are immune and inflammatory reactions driven by the death of parasite larvae (the Mazzotti reaction), including changes in blood cell counts, blood pressure, and heart rate, which typically resolve within the first week after treatment.

After a single oral dose, moxidectin is absorbed and reaches peak blood levels in about 4 hours. Eating a high-fat meal increases the amount absorbed by roughly one-third compared to taking it on an empty stomach. Moxidectin has an exceptionally long half-life — about 23 days in patients with onchocerciasis — meaning it stays in the body for a prolonged period after a single dose. It is highly bound to proteins in the blood (nearly 100%) and is widely distributed throughout the body. The drug is only minimally metabolized by the liver, and very little is eliminated unchanged through the kidneys or feces, with renal elimination being negligible.

Store below 30°C (86°F). Protect from light.