ivermectin
Brand: Stromectol
Prototype Drug
Drug Class: macrocyclic lactone antiparasitic
Drug Family: antiparasitic
Subclass: avermectin antiparasitic agent
Organ Systems: infectious-disease
Mechanism of Action
Binds glutamate-gated chloride channels exclusive to invertebrate nervous systems; potentiates GABA at invertebrate neuromuscular junctions; causes hyperpolarization and paralysis of parasites; mammalian safety due to absence of GluCl channels and P-gp exclusion from CNS.
glutamate-gated chloride channels (GluCl) in invertebrate neurons and muscle cells
Indications
- onchocerciasis (river blindness) — microfilaricidal
- strongyloidiasis
- lymphatic filariasis (mass drug administration)
- scabies (including crusted/Norwegian scabies)
- pediculosis (lice) — for treatment-resistant cases
Contraindications
- ivermectin hypersensitivity
- Loa loa microfilaremia (>2500 mf/mL — encephalopathy risk)
- concurrent P-gp inhibitors in meningitis (theoretical BBB penetration)
Adverse Effects
Common
- Mazzotti reaction (fever, urticaria, edema, arthralgia from dying microfilariae)
- GI upset
- dizziness
Serious
- encephalopathy/neurotoxicity (in Loa loa coinfection or P-gp mutations that allow CNS entry)
- Mazzotti reaction with hypotension (in heavy infestations)
Pharmacokinetics (ADME)
| Absorption | high-fat meal increases absorption 2.5-fold; administration with food recommended |
| Distribution | large Vd; high lipophilicity; excluded from CNS in normal hosts by P-glycoprotein |
| Metabolism | hepatic CYP3A4 |
| Excretion | fecal (almost entirely); renal <1% |
| Half-life | 18 hours |
| Onset | 4 hours |
| Peak | 4 hours |
| Duration | variable; single dose for most indications |
| Protein Binding | 93% |
| Vd | large |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| warfarin | ivermectin may increase INR; monitor during and after therapy | moderate |
| P-gp inhibitors | may allow CNS penetration; theoretical neurotoxicity risk | moderate |
Nursing Considerations
- Administer with food or water; high-fat meal improves absorption for strongyloidiasis treatment.
- For scabies: after treatment, bedding, clothing, and towels must be washed in hot water; household contacts should be evaluated.
- Advise patients about Mazzotti reaction (flu-like symptoms after treatment of onchocerciasis) — this represents immune response to dying parasites and can be managed with antihistamines and antipyretics.
- Screen for Loa loa exposure in patients from endemic areas (Central Africa) before mass drug administration campaigns.
Clinical Pearls
- Ivermectin is one of the most transformative drugs in global health — its deployment for onchocerciasis and lymphatic filariasis elimination programs has dramatically reduced the burden of these tropical diseases; its discoverers received the 2015 Nobel Prize in Medicine.
- P-glycoprotein at the blood-brain barrier is essential for preventing ivermectin CNS entry in mammals; certain collies (MDR1/ABCB1 mutation) and humans with P-gp mutations lack this protection, resulting in ivermectin neurotoxicity at standard doses.
Safety Profile
Pregnancy avoid
Lactation use-with-caution
Renal Adjustment Not required
Hepatic Adjustment Required
TDM Not required
Concordance Terms
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