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Bactrim vs. Cefdinir: What’s the Difference Between Antibiotics?

What’s the Difference Between Bactrim and Cefdinir?

  • Bactrim and cefdinir are antibiotics used to treat a variety of infections.
  • Bactrim and cefdinir belong to different antibiotic drug classes. Bactrim is a combination of an anti-bacterial sulfonamide (a "sulfa" drug) and a folic acid inhibitor. Cefdinir is a cephalosporin antibiotic
  • The brand name for cefdinir called Omnicef is discontinued in the U.S.
  • Side effects of Bactrim and cefdinir that are similar include headache, diarrhea, nausea, vomiting, and skin rash.
  • Side effects of Bactrim that are different from cefdinir include dizziness, lethargy, and loss of appetite.
  • Side effects of cefdinir that are different from Bactrim include vaginal yeast infection, abdominal pain, vaginitis, and rarely, abnormal liver tests. Cefdinir may cause a condition called pseudomembranous colitis (Clostridium difficile colitis), a potentially serious bacterial infection of the colon.
  • Persons allergic to penicillin-type antibiotics may also be allergic to cefdinir. Serious and rare allergic reactions include severe allergic reactions (anaphylaxis), seizures, and low platelet or red blood cell count.

What Are Bactrim and Cefdinir?

Bactrim (sulfamethoxazole and trimethoprim) is a combination of two antibiotics both of which reduce the ability of some bacteria to utilize folic acid for growing. Sulfamethoxazole is an anti-bacterial sulfonamide (a "sulfa" drug) and trimethoprim is a folic acid inhibitor. The combination is more effective than either drug alone. Bactrim is used to treat infections due to susceptible bacteria such as urinary tract infections, bronchits, middle ear infections, to prevent infections due to pneumococcus in organ transplant recipients, to treat or prevent or Pneumocystis carinii pneumonia, chancroid, and to prevent toxoplasma encephalitis in patients with AIDS.

Cefdinir is a cephalosporin antibiotic used against susceptible bacteria that can cause infections of the middle ear (otitis media), tonsils (tonsillitis), throat (strep throat), larynx (laryngitis), sinuses (sinusitis), bronchi (bronchitis), lungs (pneumonia), and skin and other soft tissues. Other cephalosporin antibiotics include cephalexin (Keflex), cefaclor (Ceclor), cefuroxime (Zinacef), cefpodoxime (Vantin), cefixime (Suprax), and cefprozil (Cefzil).

What Are the Side Effects of Bactrim and Cefdinir?


Common side effects of sulfamethoxazole/trimethoprim are:

Other side effects include:


Cefdinir generally is well tolerated. The most common side effects are:

Rare side effects include:

Cefdinir may cause false test results with some tests for sugar in the urine.

Like most antibiotics, cefdinir may cause a condition called pseudomembranous colitis (Clostridium difficile colitis), a potentially serious bacterial infection of the colon. Patients who develop signs of pseudomembranous colitis after starting cefdinir (diarrhea, fever, abdominal pain, and possibly shock) should contact their doctor immediately.

People who are allergic to the penicillin class of antibiotics, for example, amoxicillin, amoxicillin and clavulanic acid (Augmentin), which are related to cephalosporins, may or may not be allergic to cephalosporins.

What Is the Dosage of Bactrim vs. Cefdinir?


  • The recommended adult dose for urinary tract infections is one double strength tablet (Bactrim DS, Septra DS) or two single strength tablets every 12 hours for 10 to 14 days.
  • Flares of chronic bronchitis are treated with a similar regimen for 14 days.
  • Sulfamethoxazole/trimethoprim should be taken with 6 to 8 ounces of liquid to prevent crystals from forming in the urine. Persons with advanced kidney disease may require lower doses.


  • Cefdinir is taken once or twice daily, depending on the type and severity of the infection.
  • The capsules or suspension can be taken with or without food.
  • Patients with advanced kidney disease may need to take lower doses to prevent accumulation of cefdinir since it is eliminated from the body by the kidneys.
  • For adult infections the usual dose is 300 mg every 12 hours or 600 mg per day for 5-10 days depending on the nature and severity of the infection.
  • The recommended dose for children 6 months to 12 years of age is 7 mg/kg every 12 hours or 14 mg/kg per day for 5-10 days depending on the type of infection.
  • For most infections, once daily dosing is as effective as twice daily dosing, although once daily dosing has not been evaluated for the treatment of skin infections or pneumonia.


Bowel regularity means a bowel movement every day.
See Answer

What Drugs Interact with Bactrim and Cefdinir?


Sulfamethoxazole/trimethoprim can enhance the blood-thinning effects of warfarin (Coumadin), possibly leading to bleeding. Sulfonamides such as sulfamethoxazole can increase the metabolism (break-down and elimination) of cyclosporine (causing loss of effectiveness of cyclosporine), and can add to the kidney damage caused by cyclosporine.

All sulfonamides can crystallize in urine when the urine is acidic. Since methenamine (Hiprex, Urex, Mandelamine) causes acidic urine, it should not be used with sulfonamides.

Blood levels of phenytoin (Dilantin) may be increased by treatment with sulfamethoxazole/trimethoprim. This may lead to side effects associated with phenytoin (Dilantin, Dilantin-125) such as dizziness, and reduced attention.

Sulfamethoxazole/trimethoprim also may increase blood levels of digoxin (Lanoxin) and possibly lead to serious toxic effects. Anemia, due to a reduction in folic acid, can occur in persons receiving sulfamethoxazole/trimethoprim in combination with:

Increased blood levels of potassium may occur when sulfamethoxazole/trimethoprim is combined with ACE inhibitors.


  • Aluminum or magnesium containing antacids reduce the absorption of cefdinir from the intestine. Separating the administration of cefdinir and such antacids by two hours prevents this interaction.
  • Iron supplements also reduce the absorption of cefdinir. Separating the administration of cefdinir and iron supplements by two hours prevents this interaction. There have been reports of reddish stool in patients who have received cefdinir. This could be due to the formation of a chemical complex between cefdinir and iron in the stomach.

Are Bactrim and Cefdinir Safe to Take While Pregnant or Breastfeeding?


Use of sulfonamides may cause bilirubin to be displaced from proteins in the infant's blood. Displacement of bilirubin can lead to jaundice and a dangerous condition called kernicterus in the infant. For this reason, sulfamethoxazole/trimethoprim should not be used near term (late in pregnancy) among women.

Sulfamethoxazole/trimethoprim should not be used by nursing mothers because sulfamethoxazole is excreted in milk and can cause kernicterus.


There are no adequate studies of cefdinir in pregnant women; however, studies in animals suggest no important effects on the fetus. Cefdinir is not secreted in human milk.


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