This article is for information only and is not medical advice. If you think your child may be bleeding, stop reading and call your doctor or seek urgent care.
Reddish or maroon stool during a course of cefdinir is usually not blood. The FDA label explains it as "a nonabsorbable complex between cefdinir or its breakdown products and iron in the gastrointestinal tract." It is a pigment passing through. Some red stool is real bleeding, though, so the warning signs come first.
When red stool is not the iron complex
Call your doctor or get urgent care rather than waiting this out if any of these are true:
- Blood that looks bright red and streaky, or stool that is black and tarry
- Blood in vomit, or vomit that looks like coffee grounds
- Watery, frequent, or severe diarrhea, especially with cramping or fever. The cefdinir label warns that "Clostridium difficile associated diarrhea (CDAD) has been reported with use of nearly all antibacterial agents, including cefdinir, and may range in severity from mild diarrhea to fatal colitis"
- Your child is unusually sleepy, floppy, pale, or hard to rouse
- Belly pain that keeps getting worse
- Fewer wet diapers, no tears when crying, or other signs of dehydration
- Anything that simply frightens you and is not settling
None of that describes most cefdinir red stool. But you should rule it out first, and a phone call is cheaper than a night of worrying.
What the red actually is
Cefdinir is a cephalosporin antibiotic, sold as Omnicef among other names, and it is prescribed for common bacterial infections such as ear, sinus, and throat infections. In the United States it accounts for roughly 8.2 million prescriptions a year across about 6.0 million people, according to the ClinCalc DrugStats database built on the federal Medical Expenditure Panel Survey.
The mechanism is simple and it is printed in the label. Cefdinir, or one of its breakdown products, binds to iron in the gut. That pairing forms a complex your body cannot absorb, so it travels the length of the intestine and leaves in the stool, carrying its color with it.
Doctors who have written this up describe the same thing. In a 2008 report in the Journal of the American Board of Family Medicine, Graves and Weaver documented a 7-month-old girl with maroon stools while taking cefdinir alongside iron, and relayed the manufacturer's explanation that "cefdinir or its metabolites combine with iron and form a precipitate which gives a characteristic discoloration to stool." The authors add that "the complex has no known adverse effects."
The published cases describe the color as maroon rather than bright red. That is a hint, not a test. No color chart can rule out bleeding from a photo or a description, which is why the list above routes anything ambiguous to your doctor rather than to your own judgment.
Timing can be fast. In a 2020 case report in the Journal of Family Medicine and Primary Care, Bahkali and colleagues described a 6-month-old boy whose stool turned red after the very first dose of cefdinir suspension while he was taking iron-fortified formula. A clinical pharmacist recognized the interaction and reassured the family. The discoloration resolved when the antibiotic finished. The authors call it "a mild and benign interaction."
How common is it?
Honestly, nobody knows precisely, and the published range is wide. The 2008 report notes a small tolerability study in which red discoloration appeared in about 10% of treated children, 4 of 39, while the Sanford Guide puts the figure at 1%.
The more telling number in that paper is a different one. The authors found only three cases previously reported in the medical literature, even though the effect is described in the package insert and parents were already discussing it widely online. So if you searched this at 11pm and found forum threads instead of a clear answer, that gap is real and it is not your imagination.
Formula is not the same as an iron supplement
This is the part that general advice usually gets wrong, and it changes what you actually do tonight.
There are two separate questions hiding inside "cefdinir and iron." One is cosmetic: will the stool change color. The other is about whether the antibiotic still works. The label answers them differently depending on how much iron is involved.
| Iron source | Effect on cefdinir absorption | What the label says to do |
|---|---|---|
| Therapeutic iron supplement (60 mg elemental iron) | Absorption reduced by 80% | Separate cefdinir by at least 2 hours |
| Vitamin with 10 mg elemental iron | Absorption reduced by 31% | Separate cefdinir by at least 2 hours |
| Iron-fortified infant formula (2.2 mg per 6 oz) | No significant effect | No separation needed |
| Antacid such as Maalox | Rate and extent reduced by about 40% | Separate by 2 hours |
Figures quoted from the FDA cefdinir oral suspension and capsule labels.
Read the third row again, because it is the one parents need. The FDA label for cefdinir oral suspension states plainly: "Iron-fortified infant formula does not significantly interfere with the absorption of cefdinir." At formula-level iron, roughly 2.2 mg per 6 ounces, the label reports "no significant effect on cefdinir pharmacokinetics."
So both things are true at once. Formula iron can be enough to tint the stool, and it is not enough to compromise the antibiotic. You do not need to switch formulas or start juggling feeds around doses. That 2-hour spacing rule belongs to therapeutic iron supplements and multivitamins, which carry far more iron than a bottle does.
If your child is on an actual iron supplement, that is where the timing work lives. Our guide to iron supplement timing covers the other side of that gap, and medications you need to take hours apart explains which spacing rules do real work and which do not.
Finishing the course still matters
The reassurance here is about the color. It is not a reason to relax about the antibiotic itself.
Cefdinir is usually prescribed for a set number of days, and the point of that schedule is to clear the infection completely. A red diaper is not a reason to stop early or to start skipping doses while you decide. If a dose does get missed, our guides to a missed antibiotic dose for a child and missed antibiotic doses generally walk through the timing.
Two other questions come up constantly during a course like this. Whether milk matters depends entirely on which antibiotic you were given, and we sort that out in antibiotics and dairy and why milk blocks certain antibiotics. Ask your pharmacist about cefdinir specifically rather than applying another antibiotic's rule to it. And if your child accidentally gets an extra dose, that is a different situation with its own answer, similar to a double dose of amoxicillin.
Keeping a short antibiotic course on track
The scheduling work in a cefdinir course is real but modest: doses spaced through the day, for a set number of days, at a time when a sick child has upended the household routine. Add an iron supplement to separate by two hours and it gets fiddly.
Pillo's alarms keep going until you mark the dose given, so a dose that got interrupted by a crying toddler does not quietly become a skipped one. If you manage medications for more than one person, each dependent gets their own schedule in the app. How long antibiotics stay in your system explains why finishing the course matters more than any single dose.
FAQ
Is red stool from cefdinir dangerous?
The reddish stool itself is generally described as harmless. The FDA label attributes it to a nonabsorbable complex between cefdinir and iron in the gut, and the 2008 JABFM report notes the complex "has no known adverse effects." What matters is confirming it is the complex and not bleeding, so check for bright red streaks, black tarry stool, blood in vomit, severe diarrhea, fever, or lethargy, and call your doctor if any are present.
Do I need to stop iron-fortified formula while my baby is on cefdinir?
The label says no. The cefdinir oral suspension label states that "iron-fortified infant formula does not significantly interfere with the absorption of cefdinir," and reports no significant pharmacokinetic effect at 2.2 mg of elemental iron per 6 ounces. The stool may still change color, but the antibiotic is still being absorbed. Confirm with your pediatrician or pharmacist before changing how you feed your baby.
How long does the red stool last after stopping cefdinir?
In the published case reports the discoloration resolved once the antibiotic was finished or stopped. The 2020 case report describes it clearing after discontinuation. If red stool continues well after the course ends, that is worth a call, because at that point the cefdinir explanation no longer applies.
How common is red stool with cefdinir?
Published figures disagree. A small tolerability study cited in the 2008 JABFM report found red discoloration in about 10% of treated children, 4 of 39, while the Sanford Guide reports 1%. The true rate is unknown, partly because only three cases had been formally written up in the literature as of that report despite widespread reports from parents.
Can adults get red stool from cefdinir too?
Yes. The label describes the interaction generally rather than as a pediatric-only effect, and it depends on iron being present in the gut rather than on age. Adults taking cefdinir alongside an iron supplement or an iron-containing multivitamin can see the same discoloration, and the same 2-hour separation applies to those supplements.
This article provides general information about medication management and is not a substitute for professional medical advice. Always consult your doctor or pharmacist for advice specific to your medications before making changes to your medication schedule.
