Why do you keep saying 'annual count' if I only feel itchy?
The annual count writes the 3 mg chip number
Start with the parasite load, not the coupon. The 3 mg chip is a counting tool.
Skin snips and nodule maps still decide whether a person swallows anything. Onchocerciasis is a blackfly disease. The adult worms live in fibrous nodules for years. Ivermectin knocks down the microfilariae that scar skin and the anterior chamber; it does not reliably kill the adults. That is why mass programmes often space rounds about twelve months apart, and why an individual patient can be retreated as soon as three months if the larvae rebound.
Label arithmetic for river blindness is blunt. The target is about 150 mcg/kg as a single oral dose of 3 mg tablets, empty stomach, water only. From 15 to 25 kg that is one chip. From 26 to 44 kg, two. From 45 to 64 kg, three. From 65 to 84 kg, four. At 85 kg and above the prescriber calculates 150 mcg/kg instead of guessing a round number. Eight 3 mg chips is a commercial pack size, not a slogan dose.
Strongyloides uses a different target on the same chip. Uncomplicated intestinal infection is dosed near 200 mcg/kg once, then stool checks three to four weeks later. Many clinicians add a second swallow around two weeks because autoinfection can restock the gut. Same 3 mg tablet. Different mcg/kg. Different follow-up. Mixing those two schedules is how a desk gets the count wrong.
Why the US tablet is a 3 mg chip
Merck scored the human tablet at 3 mg so a clinic can add whole chips instead of cutting paste. The molecule is a semi-synthetic avermectin, two closely related B1 derivatives, made more stable than the raw soil product. That stability is why a single swallow can hold a skin-microfilaria drop for months. It is also why a farm tube marked for a 500 kg animal is not a home substitute.
Absorption jumps if the swallow meets a fatty meal. Peak plasma for the major component sits near four hours in fasting adults after a 12 mg study dose. The US label therefore keeps the tablet on an empty stomach with water, the same condition used in the onchocerciasis and strongyloidiasis files. Doubling exposure on purpose is not a clever hack. It is an unstudied shove toward the brain barrier.
A topical ivermectin cream for rosacea or lice is a different product. Do not swap that tube for the 3 mg oral chip, and do not treat a named worm with a face cream. The oral remit on the US label is intestinal strongyloidiasis and onchocerciasis due to Onchocerca volvulus. Everything else a clinic uses it for is either off-label here or licensed somewhere else. The discovery note at how the soil sample became a tablet keeps that origin separate from the dose card.
From a golf-course scoop to a donated round
1970s
Omura isolates Streptomyces avermitilis from Japanese soil and sends cultures to Merck.
1975
Campbell's group marks avermectin activity in animal worm models.
1981
Ivermectin launches for veterinary use as a refined, more selective derivative.
1987
Merck commits to donate Mectizan for river-blindness control for as long as needed.
1990s-2000s
Annual mass rounds drive several African and Latin American foci toward elimination.
2015
Omura and Campbell share the Nobel Prize for the discovery.
Satoshi Omura collected soil near a golf course southwest of Tokyo in the 1970s and shipped an unnamed Streptomyces to William Campbell at Merck. The broth killed worms in animals. Chemists saturated one double bond and got a cleaner, more selective molecule. Veterinary launch landed around 1981. Human onchocerciasis work followed once the team saw what the drug did to a related filaria.
Merck pledged Mectizan free of charge in 1987 for as long as river blindness needed it. That donation, not a weekend forum, is why whole river valleys could run annual rounds. WHO still lists the molecule among essential medicines. Omura and Campbell shared the 2015 Nobel Prize in Physiology or Medicine for the discovery. The prize is a field record, not a license to treat a cough.
US clinics see imported onchocerciasis and, more often, Strongyloides that has sat quiet for decades until steroids or chemotherapy wake it. The cheap 3 mg chip in a grocery pharmacy is the same molecule the campaigns use. The logistics are not. A donated community round is organised, screened, and repeated. A one-off internet swallow with no weight and no travel history is how people get hurt.
Open chloride channels in the worm, not in your cortex
Glutamate-gated chloride channels sit in invertebrate nerve and muscle. Ivermectin holds those channels open. Chloride pours in. The membrane hyperpolarises. The larva goes flaccid and cannot feed, mate, or stay put. Host immunity and gut motility then clear what the drug has stunned. That is a paralysis story, not an 'immune boost' story.
Human peripheral nerves do not carry those glutamate-gated channels. Related GABA channels that the drug could bother sit behind the blood-brain barrier, and P-glycoprotein pumps the molecule back out at ordinary doses. The safety margin is that pump plus that anatomy. Overwhelm either with a massive veterinary load, or inherit a pump defect, and sedation, tremor, ataxia, and coma become the file.
Adult Onchocerca in nodules mostly survive. That is the operational limit. You suppress larvae on a calendar; you do not 'cure the river' with one cheap strip. Tapeworms and flukes use other machinery and do not fall. Viruses were never the target. Early dish work on SARS-CoV-2 needed concentrations no safe human swallow can reach. Large randomised trials later found no meaningful drop in hospitalisation or death. The evidence note at what the trial signals actually moved keeps those files apart.
What the 1278-patient onchocerciasis file actually moved
| Setting | Approx target | Clock |
|---|---|---|
| Onchocerciasis (US label) | ~150 mcg/kg as 3 mg chips | Often yearly; individual repeat from 3 months |
| Strongyloidiasis (US label) | ~200 mcg/kg once | Stool check at 3-4 weeks; many repeat ~2 weeks |
| Scabies (off-label US) | ~200 mcg/kg | Repeat at 1-2 weeks; treat contacts |
| Crusted scabies | ~200 mcg/kg, several swallows | Plus topical therapy; specialist follow-up |
DailyMed still cites 1278 patients in the onchocerciasis evaluation. In a double-blind, placebo-controlled adult study of moderate to severe infection, a single 150 mcg/kg swallow cut the geometric-mean skin microfilaria count by 83.2% at day 3 and 99.5% at three months. A drop above 90% held for up to twelve months. That is the annual-count rationale in one table.
Eye larvae can rise in the anterior chamber at day 3, then fall by months 3 and 6 more often than on placebo. Clinics watch ocular disease after a round for that reason. Mazzotti features - itch, rash, tender nodes, fever, joint pain - are the corpse signal, not proof the tablet was 'too strong.' Burden predicts intensity. Supportive care handles most of it. Collapse or confusion is a different page.
Strongyloides head-to-heads used stool-larva absence at three to four weeks as the cure mark. A single 170-200 mcg/kg swallow beat albendazole 200 mg twice daily for three days and matched thiabendazole 25 mg/kg twice daily for three days with fewer gut complaints. Scabies comparisons against permethrin are off-label in the US and generally close on clearance, with the oral route winning in outbreaks where cream technique fails. The working card at 3 mg counts versus mcg/kg keeps those schedules from collapsing into one row.
A high Loa loa load stops the round
West and Central African rainforest history is not small talk. People with a very high Loa loa microfilaria density can develop encephalopathy, coma, or death after a microfilaricide, ivermectin included. Programmes in those belts screen before a community round. A travel clinic in Edinburgh does the same with a smear and a specialist call, not with a coupon app.
Neurotoxicity has also been reported without Loa, including altered consciousness, confusion, and rare deaths, generally after supportive care and stopping the drug. Those reports cluster with overdose and with veterinary product. They do not make a correct 150-200 mcg/kg human tablet 'the same as horse paste.' They make the barrier story real.
Pregnancy has no adequate controlled human file. Animal work showed cleft palate and, in rabbits, clubbed forepaws at or near maternotoxic doses. The label says do not use in pregnancy because safety is not established. Below about 15 kg, paediatric safety is not established. Breast milk carries a little drug; that decision is case by case. Immunocompromised Strongyloides can hyperinfect - repeat courses and tight stool follow-up, not a single cheap chip and a hope.
Itch after the swallow is often the larvae dying
| Ping | Trace | Flag |
|---|---|---|
| Central-Africa years | Loa loa smear / specialist | Hold the round if the load is high |
| Steroids or chemo | Strongyloides risk | Treat and re-check stools; watch hyperinfection |
| Chronic azole or macrolide | CYP3A4 traffic | Keep to the studied mcg/kg; do not 'boost' with food |
| Warfarin | INR a few days later | Adjust the anticoagulant, not the worm dose, if it moves |
Onchocerciasis trials in 963 adults logged Mazzotti worsening in the first four days: pruritus in 27.5%, skin edema or rash in 22.7%, fever in 22.6%, inguinal node tenderness in 13.9%. Facial or peripheral edema, orthostatic hypotension, and tachycardia showed up as drug-related in a few percent. Headache and myalgia were common overall even when not attributed to the tablet.
Strongyloides files in 109 people given one or two 170-200 mcg/kg swallows were quieter: brief dizziness, nausea, diarrhoea, itch. Lab noise included ALT/AST bumps in 2% and a leukocyte dip in 3%. That gentler profile is why a single supervised chip is usually uneventful in an otherwise well gut infection. It is not a reason to skip the Loa question in someone who lived along the Congo basin.
Warfarin has scattered INR-shift reports. Checking the INR a few days after a dose is cheap. Strong CYP3A4 inhibitors - some azoles, some macrolides - can raise exposure. P-glycoprotein blockers are a theoretical CNS nudge. Grapefruit is the same family of caution. None of these replace the Loa screen. They sit on the medication list after the parasite has a name.
How a single swallow parks for a day
Absorption
Oral, fasting with water. Peak near 4 hours. A fatty meal can roughly double absorption, so the label keeps food off the swallow.
Distribution
Wide tissue spread, high protein binding. P-glycoprotein limits CNS entry at ordinary 150-200 mcg/kg counts.
Metabolism
Mainly CYP3A4; minor CYP2D6 and CYP2E1 in vitro. Strong 3A4 inhibitors can lift levels.
Excretion
Almost entirely faecal over ~12 days; <1% renal. Parent half-life about 18 hours.
Plasma tracks dose in a rough line. After 12 mg fasting, mean peak of the major component sat around 31-47 ng/mL at about four hours, with a wide person-to-person spread. The drug is lipophilic and highly protein-bound, which is why tissue - where the worms live - sees it, and why a fatty meal can roughly double the amount that lands in blood.
Hepatic CYP3A4 does most of the work; CYP2D6 and CYP2E1 are minor in vitro extras. Parent half-life in people is about 18 hours. Metabolites linger longer. Almost all of the dose leaves in faeces over roughly twelve days. Less than 1% hits urine. Kidney impairment is therefore not the first worry. Marked liver disease is a thinner file, so we stay conservative there.
P-glycoprotein at the blood-brain barrier is the quiet partner. At the 3 mg chip counts in the label tables, that pump plus the missing peripheral glutamate channels keep the cortex mostly out of the story. Saturate the pump with a veterinary load and the story changes in an hour. That is the whole overdose file in one sentence.
Who does not swallow the chip this week
Do not treat a rumour. Confirm the worm or mite, ideally with stool larvae, a skin snip, or a scabies exam, before anyone counts 3 mg chips. Do not treat a virus. Do not treat a tapeworm. Do not hand a child under 15 kg a fraction of a tablet 'to be safe.' Do not use the drug in pregnancy unless an infectious-disease desk has weighed a severe infection against an empty human file.
Do not use animal ivermectin paste, drench, or 'horse gel.' Concentration, excipients, and the dosing marks on those tubes were built for livestock. People have reached coma that way. The human 3 mg chip is inexpensive once a real prescription exists. Saving a clinic visit by raiding a tack shop is how this molecule earned a toxicology chapter it did not need.
Compare the specialist lane with a fluoroquinolone such as ciprofloxacin and the contrast is the point of this desk: one drug is a narrow antiparasitic with a Loa hold, the other is a broad antibacterial with a tendon hold. Neither is a general 'infection pill.' CDC parasite pages and the Stromectol label on DailyMed are the files we trace, not a social post.
Eight 3 mg chips at four grocery counters
| Counter | Pack this desk priced | Cash band (qualitative) | Official pharmacy page |
|---|---|---|---|
| Kroger Pharmacy | Ivermectin 3 mg × 8 | Coupon-low vs mid retail | Prescription fill only |
| Publix Pharmacy | Ivermectin 3 mg × 8 | Grocery-mid cash | Prescription fill only |
| Meijer Pharmacy | Ivermectin 3 mg × 8 | Coupon-low | Prescription fill only |
| Safeway Pharmacy | Ivermectin 3 mg × 8 | Mid-to-higher cash | Prescription fill only |
Once the annual count and the mcg/kg card are written, a US cash patient may still need eight 3 mg tablets - a heavier adult, a planned repeat, or a household scabies plan a clinician actually signed. This desk does not sell. A prescription is required. The bands below are qualitative cash pictures from public GoodRx and SingleCare tools, not a price tag we invented, and they move by zip code.
Grocery counters often undercut big-box drug chains on this generic. Coupon-low at Kroger or Meijer is a different band from mid-to-higher cash at some Safeway counters. Publix sits in a grocery-mid pocket in the snapshots we checked. None of those numbers replace insurance, a 340B clinic, or donated Mectizan in an endemic programme. If a site offers 3 mg chips with no clinician and no weight, treat that as a counterfeit ping, not a bargain.
Post the count, not the rumour
Used on its real targets, the 3 mg chip is one of the better public-health tools of the last forty years. River blindness campaigns turned on that annual arithmetic. Strongyloides still yields to a weight-based swallow plus stool proof. The molecule earned a Nobel because field counts moved, not because a forum liked the name.
The flags that matter on this desk are a named parasite, a weight, an empty stomach, a Loa history when the map says so, and a hard no on veterinary paste. Price the grocery pack after those holds. Bring the travel story and the medication list to your own clinician before anyone changes a dose. This page teaches. It does not prescribe.
Onchocerciasis and Strongyloides still land on my list in an Edinburgh ID week. The questions below are the ones families actually ask after I write a 3 mg chip count.
Because the adults keep living in nodules after one swallow. Ivermectin clears the larvae that drive itch and eye injury, then those adults stock the skin again. Campaigns often wait about a year; I can retreat an individual from three months if the snips rebound. Itch alone is not a count. I want a travel map, an exam, and, when we can get them, snips or a specialist read before I write 3 mg chips. The cheap pack is the last line on that card, not the first.
I weigh 78 kg. How many 3 mg tablets is a river-blindness swallow?
On the US onchocerciasis table you sit in the 65-84 kg band, which is four 3 mg tablets, aimed at about 150 mcg/kg, fasting, water only. I do not 'round up to eight' because a coupon pack is eight. Eight chips would overshoot that band unless I have a separate reason - a planned repeat, a different indication, or a much heavier body. Strongyloides at 200 mcg/kg would be a different chip count on the same 3 mg tablet. Tell me which parasite we are treating before we count. Bring a recent weight, not a guess from last year.
Can I take the tablets after a cooked breakfast so they 'absorb better'?
Please don't. Fat can roughly double how much reaches the blood. The label studied fasting swallows with water, and that is how the 150 and 200 mcg/kg files were built. Extra exposure is not extra worm-kill we can promise. It is extra traffic at the brain barrier we did not study. Take the chips on an empty stomach, then eat. If nausea is the fear, we talk about timing, not about buttering the dose.
I grew up in Cameroon. Does that change the tablet?
It can change whether you get a tablet this week at all. Loa loa lives in parts of West and Central Africa. A very high load plus ivermectin can trigger encephalopathy. Before I treat onchocerciasis in anyone with that map, I ask, and I often need a blood smear and an ID colleague. CDC loiasis pages are the public file I point families to. A grocery coupon does not screen Loa. We do.
My cousin used horse paste during the pandemic. Same drug?
Same INN on the tube, different product. Livestock paste is concentrated for a large animal and may carry excipients never cleared for people. Overdose looks like confusion, tremor, ataxia, seizures, coma. The human 3 mg chip dosed to weight is the medicine with a trial file. I will not bless a tack-shop swallow, and I will not treat a virus with this molecule. Large randomised COVID trials did not move hospitalisation or death at safe doses.
I felt feverish and my glands swelled the night after treatment. Did I overdose?
More often that is a Mazzotti reaction: larvae dying in bulk, itch, rash, tender nodes, fever, aches. Trials saw those features in a large share of onchocerciasis patients in the first four days. It usually settles. What I do not call expected is fainting, severe breathlessness, or a sudden change in thinking. Those get urgent care. Burden predicts how loud the reaction is. We treat through mild cases with fluids and rest, not with a second unplanned chip.
I'm 11 weeks pregnant and someone suggested ivermectin for a possible worm.
I hold the tablet. Safety in pregnancy is not established on the US label, and animal studies showed palate and limb defects at or near doses that also harmed the mother. Unless an infection is severe enough that an ID desk judges treatment safer than waiting, we pick another path or we wait. Bring the stool result and the obstetrician into the same conversation. Do not start a 3 mg strip from a leftover bottle.
Our flat all have scabies. Do the children swallow the same chips?
Household treatment on the same days is the right idea, including people not yet itching, plus hot-wash of bedding. Oral ivermectin for scabies is off-label in the US and usually 200 mcg/kg, repeated at one to two weeks because eggs survive the first swallow. Safety is not established under about 15 kg, so small children often get a topical plan instead of a fraction of a 3 mg chip. I want ages and weights before anyone shares an adult pack.
I take warfarin and an azole for a nail infection. Still a simple one-off?
Not simple. Ivermectin runs through CYP3A4, and a chronic azole can lift levels. Warfarin has scattered INR-shift reports, so I recheck INR a few days after the swallow. For a single labelled dose these collisions are usually manageable, but I want the full list, including grapefruit habits. We do not 'skip the worm' because of warfarin. We watch the INR and we keep the mcg/kg on the label card.
Do I need another stool test if I already feel better?
For Strongyloides, yes more often than not. One stool pass misses light infection. I repeat studies a few weeks out and I retreat if larvae persist or symptoms hang on. Feeling better is welcome and not proof of clearance. Onchocerciasis is a longer calendar because adults survive, so we plan the next count rather than calling one swallow a cure. If you are on steroids or chemo, the follow-up is tighter because hyperinfection moves fast.
Why is a 3 mg chip cheap at a grocery counter but 'priceless' in a campaign?
Different logistics, same molecule. Mectizan donation made annual rounds possible in endemic river valleys. A US grocery fill is a cash generic after a clinician writes a weight-based prescription, often for Strongyloides or an imported case. Cheap is good once the holds are clear. 'Priceless' in a campaign means supply, screening, and repeat rounds, not a mystical tablet. I still want the Loa map and the empty-stomach instruction either way.
Can I drink after the dose?
A modest drink is not a named clash on the label the way fat is. The interaction that changes the number is the meal, not a glass of wine. I still ask people not to treat the evening like a holiday if they already feel lightheaded from a Mazzotti reaction. Skip the greasy takeaway that night. Keep the chips fasting. If you are on warfarin, alcohol is a separate INR problem and we talk about that on its own.
Where should I read the official onchocerciasis table?
The Stromectol 3 mg weight bands live on the US label, which DailyMed carries, and MedlinePlus translates the same idea into plainer language. I also walk people through the working card on 3 mg versus mcg/kg so the annual oncho count does not get mixed with the 200 mcg/kg Strongyloides swallow. Read those, then bring questions back. Do not invent a chip count from a forum screenshot.
General education from a clinician, not personal medical advice. Bring your own history to your own prescriber.
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