I was treated for scabies and I am still itching two weeks later. Another round?
A cheap 3 mg chip is a unit, not a flat adult dose
Feeds treat 'a tablet' as the plan. The label treats body weight as the plan and the 3 mg chip as the unit you round to.
| Body weight | Strongyloides ~200 mcg/kg | 3 mg chips |
|---|---|---|
| 15-24 kg | 3 mg | 1 |
| 25-35 kg | 6 mg | 2 |
| 36-50 kg | 9 mg | 3 |
| 51-65 kg | 12 mg | 4 |
| 66-79 kg | 15 mg | 5 |
| 80 kg and up | 0.2 mg/kg | calculate |
Most adult Strongyloides work anchors near 200 micrograms per kilogram as a single oral dose. Onchocerciasis anchors near 150. A 60 kg person and a 95 kg person do not leave with the same stack. Absolute milligrams stay small, which is why the profile is gentle when the arithmetic is honest - and why a guessed stack is a bad idea.
Stromectol weight bands exist so a prescriber can turn mcg/kg into whole chips without a calculator argument at the counter. For Strongyloides, the labeled bands run 15-24 kg = 1 chip, 25-35 kg = 2, 36-50 kg = 3, 51-65 kg = 4, 66-79 kg = 5, then calculate at 0.2 mg/kg above that. Onchocerciasis uses a different band set because the mcg/kg target is lower. Same 3 mg unit. Different count.
Claim: cheap means you can eyeball it. Label: chips follow kilograms. Strike the flat-adult habit. File the band that matches the named infection. Trial backing for why those infections are on the card at all is in the trial review, not here.
Two labeled targets: 200 mcg/kg is not 150 mcg/kg
| Job | Target | Clock |
|---|---|---|
| Strongyloidiasis | ~200 mcg/kg | One dose; stool check; many repeat ~2 weeks |
| Onchocerciasis | ~150 mcg/kg | Yearly in MDA; as soon as 3 months individually |
| Scabies (off-label) | ~200 mcg/kg | Two doses, 1-2 weeks apart |
| Crusted scabies | ~200 mcg/kg | Multiple doses plus topical |
| Larva migrans | ~200 mcg/kg | Often one dose |
Intestinal strongyloidiasis: one oral dose designed to deliver about 200 mcg/kg, empty stomach, water. Extra doses are not routine on the label, but follow-up stool is. Many teams still plan a second pass around two weeks later because autoinfection can restock the gut. Immunocompromised hosts are not a one-chip story.
Onchocerciasis: one oral dose designed to deliver about 150 mcg/kg. Mass campaigns often repeat yearly. Individual care may repeat as soon as three months. Adults live in nodules for years; the tablet clears larvae and quiets output, then you come back. Treating a river-blindness patient on a Strongyloides chip count is the wrong target. Treating a Strongyloides patient on the lower onchocerciasis count is an underdose.
Scabies, off-label in the US, usually borrows the 200 mcg/kg figure and adds a second dose at 1-2 weeks because eggs hatch after the first pass. Crusted disease needs multiple rounds plus a topical. Cutaneous larva migrans often finishes in one weight-based dose. Head lice, when oral drug is used at all, follows a hatch-repeat logic and often stays behind a topical. Match the clock to the life cycle or 'did it work?' becomes guesswork.
Water on an empty stomach is part of the dose
Labels call for an empty stomach with water, at least an hour before food. That is how the microgram targets were studied, so that is the exposure the bands assume. At these amounts there is little room to 'make it easier' with breakfast and still claim you gave the studied dose.
A fatty meal can raise absorption, sometimes roughly doubling it. A few clinicians use that on purpose for a stubborn, supervised case. That is a deliberate exposure change, not a licence to swallow chips with dinner because you forgot. Unless the prescriber writes a fed plan, fasted dosing is the file.
Peak levels land around four hours. Parent half-life sits near 18 hours; most of the drug leaves in stool over days, not in urine. Those numbers explain why a single well-timed dose can cover a simple course - and why stacking extra chips 'to be sure' is not a harmless habit. CYP3A4 inhibitors and a theoretical P-glycoprotein issue belong on the med list you bring, not on a guess.
Repeat clocks follow eggs, adults, and autoinfection
One swallow finishes some jobs. Others fail on purpose if you skip the second date. The clock is biology, not a upsell.
Eggs and hatching mites are why scabies and some lice plans book a return. Adult Onchocerca worms are why river-blindness plans book a year. Autoinfection is why Strongyloides follow-up stool - and often a second dose - exists. If itch lasts two to four weeks after scabies treatment, that is often dead-mite debris, not proof you need an emergency third round. Fresh burrows are a different story.
Households and institutions fail when only the itchiest person is dosed. Treat contacts together. Hot-wash bedding on treatment days. Crusted disease is a specialist card: huge loads, longer courses, topical plus oral. Do not copy that card onto an ordinary case, and do not copy an ordinary two-dose card onto a crusted case.
Children under about 15 kg sit outside the usual labeled bands. Safety is not established the way it is above that weight. Pregnancy is a pause unless infection severity forces a shared decision. Those are hold marks on the card, not fine print you skip because the chip is cheap.
Mazzotti, Loa loa, and when geography holds the pen
At correct weight-based doses for a real parasite, most people feel little: mild dizziness, nausea, a day of ache. A heavy Onchocerca load can throw a Mazzotti reaction - itch, rash, tender nodes, fever, sometimes a blood-pressure drop - because larvae are dying, not because the tablet 'failed.' Ocular inflammation can follow larval death in the eye. Heavier loads mean fiercer flares.
In parts of Central and West Africa, Loa loa can circulate at high density. Ivermectin there can trigger a severe die-off with dangerous swelling and, rarely, encephalopathy. Programs count larvae in blood before mass rounds. Outside those zones, a scabies or Strongyloides patient rarely needs that workup. Lived or travelled extensively in the belt? Say so before anyone counts chips.
That exception does not make the tablet unsafe on a Manchester street. It makes geography part of the prescription. How the molecule reached campaign scale is a history file - the Kawana trail - not a dosing trick. This card only needs you to name the countries before the count.
Paste math fails a human kilogram on purpose
Horse and cattle products are built for animals that weigh hundreds of kilograms. A fingertip of paste can hold several safe human doses, plus excipients never studied as a human tablet. Eyeballing a syringe mark is not a conversion. Emergency departments saw the overdoses when viral posts treated livestock paste as a cheap 3 mg substitute. Confusion, vomiting, hypotension, seizures - that is barrier overflow, not a mystery toxin.
Human tablets, matched to weight, for a confirmed parasite: that is the safe line. No parasite, no upside. Veterinary paste, no conversion that a fact line will file. FDA language on livestock products at fda.gov is blunt because the arithmetic is blunt. Why COVID use failed the endpoint test is already in the trial review. This card only needs the product name to be Stromectol or a human generic, not a farm tube.
A Manchester card you can take to clinic
| Keep | Strike |
|---|---|
| Named parasite first | Chips 'just in case' |
| kg times 200 or 150 mcg | One chip for every adult |
| Empty stomach, water | A greasy meal as a default |
| Human 3 mg tablets | Horse or cattle paste |
| West/Central Africa history named | Skipping a Loa loa question |
Short checklist for the visit: name the parasite, weigh the person, pick 200 or 150 mcg/kg, convert to 3 mg chips on the matching band, take it fasted with water, book the repeat if eggs or adults demand it, flag Central or West African time if Loa loa is possible, and expect scabies itch to outlast the mites.
The two self-inflicted failures are livestock formulations and swallowing chips without a parasite on the card. Both add risk without a measured gain. Human tablets at the right weight, geography named, clocks booked - the tablet then does what decades of labeled use show. Discuss any change with your own clinician or pharmacist before you alter a dose. This desk files teaching lines, not a personal plan.
Reader mail
Reader questions on this article
Answered by Dr. Marcus Bellinger, MD · Internal medicine & infectious disease
Working-card mail from named readers. Kilograms first, then the strike. Not a refill.
Probably not yet. Dead mites leave debris that keeps skin angry for two to four weeks, so itch outlasts the infestation. That is healing, not automatic relapse. Night antihistamines and a plain moisturiser help. Worry if you see fresh burrows or new tracks - those mean live mites and may mean the planned second dose was missed. Treat everyone in the home together and hot-wash bedding. CDC steps at cdc.gov walk through the sequence. I file lingering itch as expected unless new tracks appear.
Do I really have to take it on an empty stomach? I forget every time.
Fasted dosing is how the microgram targets were studied. Water, at least an hour before food, keeps the exposure the weight bands assume. Fatty meals can raise uptake, sometimes roughly doubling it. A few clinicians use that on purpose for a tough, supervised case. That is a written plan, not a snack hack. If mornings are easier, dose before breakfast and keep the habit there. I do not file 'food never matters' on this card.
How dangerous is the horse paste a relative keeps recommending?
Dangerous enough to stop today. Paste is built for animals of hundreds of kilograms and is far more concentrated than a 3 mg human chip. A dab has no reliable conversion; overdoses bring confusion, vomiting, collapse, and seizures, and emergency rooms have seen the pattern. With no confirmed parasite there is zero upside. Human tablets calculated for your weight on a real diagnosis are the only line I will file. FDA warnings at fda.gov are blunt because the arithmetic is blunt.
I lived in West Africa for years. What do I tell a doctor before chips are counted?
Say the countries and the years, every time. In parts of Central and West Africa, heavy Loa loa loads can trigger dangerous swelling or, rarely, brain inflammation when ivermectin kills larvae suddenly. A blood check may come first. That does not ban the tablet. It makes the count careful. Outside the belt the issue rarely applies. Geography holds the pen on this line of the card. Do not let a relative's 'I took it fine' override a travel history.
How do I turn micrograms per kilogram into a chip count without guessing?
Kilograms times 200 mcg for Strongyloides, or times 150 mcg for onchocerciasis, then divide by 3 mg and round on the labeled band. Roughly, at 200 mcg/kg, one 3 mg chip covers about 15 kg: four chips near 60 kg, five near 70 kg. Your prescriber uses the official band so two people of similar size can still leave with different stacks. Never back-calculate a human dose from a paste concentration. Let a clinician do the math on a labeled human product.
Can I give a child a smaller piece of an adult tablet?
Only with a clinician and a confirmed indication. Above about 15 kg, children use the same mcg/kg targets and the labeled bands. Below that weight, safety is not established the way the bands assume - specialist input or another agent, not a snapped adult chip. Do not use animal products at any age. Confirm the parasite first. MedlinePlus at medlineplus.gov is a useful read before that visit.
I felt worse for a day after the dose - itchy, achy. Did it fail?
Often that means a load is dying. A brief immune flare - itch, rash, mild fever, aches, swollen nodes - tracks with burden and usually fades. Onchocerciasis has a name for a fiercer version: Mazzotti. Seek urgent care for severe swelling, breathing trouble, fainting, or confusion, especially if Loa loa exposure is possible. A rough day afterward commonly signals dying parasites, not a failed course. A new burrow two weeks after scabies is a different file.
Why are there two mcg/kg numbers? My friend took a different stack.
Because the labeled jobs are not the same target. Strongyloides uses about 200 mcg/kg. Onchocerciasis uses about 150 mcg/kg and a different chip table. Scabies, when a clinician uses oral drug, usually borrows the 200 figure and adds a hatch repeat. Your friend's stack is not a template. The organism and the kilograms are. Mixing the two targets is how a course underdoses one infection or overshoots another. Ask which job is on the prescription before you compare chip counts.
What should I actually carry into the appointment from this card?
A named parasite if you have one, a recent weight, a travel list that includes Central or West Africa if that applies, the full med list (azoles, some macrolides, warfarin), and a question about the repeat clock. Do not carry a farm syringe or a screenshot that treats 3 mg as a flat adult dose. This desk files teaching lines. Your own clinician files the plan. Read the Stromectol reference if you want the channel and the hold marks in one place.
General education from a clinician, not personal medical advice. Bring your own history to your own prescriber.
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