Cefdinir is a third-generation cephalosporin antibiotic. It’s taken by mouth (unlike some other third-generation cephalosporins that require injection) and is commonly prescribed for respiratory infections, ear infections, and skin infections in both adults and children.
What Third-Generation Means
Cephalosporin antibiotics are grouped into generations based on when they were developed and, more importantly, which bacteria they can kill. Each successive generation generally gained broader coverage against a different set of bacteria. First-generation cephalosporins work best against common skin and soft-tissue bacteria. Second-generation drugs expanded that range somewhat. Third-generation cephalosporins, including cefdinir, cover a wider variety of bacteria while also resisting breakdown by certain bacterial defense enzymes called beta-lactamases, which older generations couldn’t survive as well.
Like all cephalosporins, cefdinir kills bacteria by blocking the final step of cell wall construction. Without an intact wall, the bacterial cell bursts. Cefdinir specifically targets two key proteins bacteria need to build that wall, which gives it reliable activity against many of the organisms responsible for common outpatient infections.
What Cefdinir Treats
Cefdinir is FDA-approved for mild to moderate infections. In adults and adolescents, that includes community-acquired pneumonia, flare-ups of chronic bronchitis, acute sinus infections, strep throat and tonsillitis, and uncomplicated skin infections. In children (six months and older), it covers ear infections, strep throat, and skin infections. It is not used for severe or hospital-acquired infections, where injectable third-generation cephalosporins or newer drugs are preferred.
How It Compares to Other Generations
A practical way to think about the generations: first-generation cephalosporins (like cephalexin) are the go-to for simple skin infections and urinary tract infections. Second-generation options broadened coverage. Third-generation drugs like cefdinir, cefixime, and ceftriaxone shifted the balance further, gaining stronger activity against harder-to-treat bacteria while keeping reasonable coverage of common ones. Fourth- and fifth-generation cephalosporins exist too, reserved for more serious or resistant infections in hospital settings.
One advantage cefdinir has over ceftriaxone, probably the most well-known third-generation cephalosporin, is that cefdinir comes as a capsule or liquid suspension. Ceftriaxone requires an injection, making cefdinir a convenient option when oral treatment is appropriate.
The Iron Interaction Worth Knowing
Cefdinir has a notable interaction with iron. When taken at the same time as an iron supplement, cefdinir forms a chemical complex with the iron that almost completely blocks absorption. In one study, taking cefdinir with iron reduced the amount of drug absorbed by more than 90% compared to taking cefdinir alone. Even spacing the iron three hours after the antibiotic still reduced later absorption by about 40%. If you take iron supplements or an iron-containing multivitamin, separate them from your cefdinir dose by at least two hours before or after.
This iron interaction also produces a harmless but alarming side effect: reddish or rust-colored stools. The cefdinir-iron complex creates a colored precipitate in the gut. It looks startling, but tests confirm there’s no blood involved, and it causes no digestive symptoms. This can happen with iron-fortified infant formula too, which is why parents of young children on cefdinir sometimes call their pediatrician in a panic.
Penicillin Allergy and Cross-Reactivity
Because cephalosporins share a structural backbone with penicillin, people with penicillin allergies sometimes wonder if cefdinir is safe. Third-generation cephalosporins have a cross-reactivity rate below 1% in people with confirmed immune-mediated penicillin allergies. That’s considerably lower than the 1% to 8% range seen with first- and second-generation cephalosporins. Your prescriber will weigh the severity of your penicillin allergy history when deciding whether cefdinir is appropriate.
How the Body Processes Cefdinir
Cefdinir’s oral bioavailability is around 25%, meaning a quarter of the dose reaches the bloodstream. That’s relatively low, but it still reaches effective concentrations at common infection sites. The drug has a short half-life of about 1.7 hours and leaves the body primarily through the kidneys. Because of that kidney-dependent clearance, people with significantly reduced kidney function need a lower dose, typically once daily instead of twice.
For children, dosing is weight-based at 14 mg per kg per day, split into one or two doses. Kids weighing 43 kg (about 95 pounds) or more receive the standard adult maximum of 600 mg per day.