Cefdinir is an oral antibiotic used to treat mild to moderate bacterial infections of the ears, sinuses, throat, lungs, and skin. It belongs to the cephalosporin family, a class of antibiotics closely related to penicillin, and works by breaking down the walls of bacterial cells so they can’t survive and multiply. It comes in capsule form for adults and a liquid suspension for children.
Infections Cefdinir Treats in Adults
The FDA has approved cefdinir for five types of infections in adults and adolescents:
- Community-acquired pneumonia: lung infections picked up in everyday life, not in a hospital setting
- Acute flare-ups of chronic bronchitis: worsening bacterial infections in people who already have ongoing bronchitis
- Acute sinus infections: bacterial sinusitis affecting the maxillary sinuses (the ones behind your cheekbones)
- Strep throat and tonsillitis: throat and tonsil infections caused by group A strep bacteria
- Uncomplicated skin infections: bacterial skin infections caused by staph or strep bacteria
Cefdinir is not the strongest antibiotic available. It’s designed for infections that are mild to moderate in severity. For community-acquired pneumonia specifically, clinical guidelines position it as an alternative option rather than a first-line choice, meaning your doctor may reach for it when other antibiotics aren’t suitable.
Infections Cefdinir Treats in Children
Cefdinir is approved for children as young as 6 months old. One of its most common pediatric uses is acute bacterial ear infections (otitis media), which is one of the top reasons children are prescribed antibiotics in general. Beyond ear infections, children can also receive cefdinir for sinus infections, strep throat, tonsillitis, and uncomplicated skin infections.
The liquid suspension form makes dosing easier for young children. It’s dosed based on body weight, with a total daily dose of 14 mg per kilogram, up to a maximum of 600 mg per day. Depending on the infection, treatment courses last anywhere from 5 to 10 days. Once mixed, the liquid suspension needs to be stored at room temperature, shaken well before each dose, and discarded after 10 days.
How Cefdinir Works
Like all cephalosporins, cefdinir targets the structure that holds bacterial cells together. Bacteria build and maintain a rigid cell wall to survive, and cefdinir interferes with that construction process. Without an intact wall, bacteria swell, rupture, and die. Human cells don’t have this type of wall, which is why the drug can kill bacteria without damaging your own tissue.
Cefdinir is effective against a range of common bacteria on both sides of the gram-positive and gram-negative divide. It handles staph and strep species well, along with respiratory bacteria like Haemophilus influenzae and Moraxella catarrhalis. Notably, it works against many strains that produce an enzyme called beta-lactamase, which is a defense mechanism some bacteria use to break down older antibiotics like amoxicillin. This gives cefdinir an edge in infections where those resistant strains are involved.
Common Side Effects
Diarrhea is the most frequently reported side effect of cefdinir. This is true of many antibiotics, since they disrupt the balance of normal bacteria in the gut along with the harmful ones. The diarrhea is typically mild and resolves once the course of treatment ends. In rare cases, it can become severe and watery. If diarrhea is persistent or contains blood, that warrants a call to your prescriber, as it could signal a secondary infection in the colon.
Other possible side effects include nausea, headache, and vaginal yeast infections. These are generally mild and manageable.
Why Cefdinir Can Turn Stools Red
One side effect catches people off guard: reddish or rust-colored stools. This happens when cefdinir or its breakdown products combine with iron in the digestive tract, forming a reddish compound. It’s harmless but alarming, especially in infants and toddlers, because it can look like blood. A case report in the Journal of the American Board of Family Medicine documented this in an infant, confirming the discoloration was simply a chemical reaction between the drug and iron, not actual bleeding.
This reaction is most likely if you or your child are also taking an iron supplement or an iron-fortified formula. If you’re taking both, separating the doses by at least two hours can help reduce this effect. The same timing advice applies to antacids containing aluminum or magnesium, which can interfere with how well your body absorbs cefdinir.
Cefdinir and Penicillin Allergy
Because cephalosporins and penicillins share a similar chemical structure, people with penicillin allergies sometimes worry about taking cefdinir. The actual cross-reactivity risk is low. According to the CDC, third-generation cephalosporins like cefdinir have less than a 1% rate of cross-reactivity in people with confirmed penicillin allergies. That’s significantly lower than the 1% to 8% range seen with first- and second-generation cephalosporins. Still, if you’ve ever had a severe allergic reaction to penicillin, such as throat swelling or anaphylaxis, your doctor will weigh the risks carefully before prescribing cefdinir.
What Cefdinir Does Not Treat
Cefdinir only works against bacteria. It has no effect on viral infections, including the common cold, the flu, or most cases of bronchitis that aren’t tied to an underlying chronic condition. Taking an antibiotic for a viral illness won’t speed up recovery and contributes to antibiotic resistance. If your symptoms point to a virus rather than a bacterial infection, your doctor will likely recommend supportive care instead.
Cefdinir also isn’t the right choice for more serious or complicated infections. It’s designed for outpatient treatment of mild to moderate illness. Deeper infections, hospital-acquired infections, or bacteria with certain resistance patterns call for different antibiotics entirely.