Generic name: Ampicillin.

Other brand names: D-Amp, Polycillin, Principen, Totacillin.

Omnipen is a penicillin antibiotic. Antibiotics inhibit the growth of bacteria.

Quick Facts About Omnipen


Used to treat a wide variety of infections, including gonorrhea and other genital and urinary infections, and gastrointestinal infections.

Omnipen Dosage

Capsules to be taken with a full glass of water 1/2 hour before or 2 hours after a meal. Shake oral suspension well before use. Take exactly as prescribed; try not to miss doses. For best results must maintain a constant level in the body. Must take entire amount prescribed (especially in the case of strep throat); otherwise you may get other infections, such as kidney infection or rheumatic fever.

  • Usual adult dose: for infections of genital, urinary, or gastrointestinal tracts — 500 milligrams taken 4 times per day. For gonorrhea — 3.5 grams in a single oral dose, with 1 gram of probenecid. For respiratory tract infections — 250 milligrams taken 4 times per day.
  • Usual child dose: for children weighing over 44 pounds — follow adult schedule. For children weighing under 44 pounds — Infections of genital, urinary or gastrointestinal tracts — 100 milligrams for each 2.2 pounds of body weight divided into 4 doses for capsules and 3 to 4 doses for suspension. Respiratory tract infections — 50 milligrams for each 2.2 pounds of body weight per day, divided into 3 to 4 doses.
  • Missed dose: If taking 2 doses per day — take as soor as possible; take next dose 5 to 6 hours later. Then go back to regular schedule. If taking 3 or more doses per day — take as soon as possible; take next dose 2 to 4 hours later. Then go back to regular schedule. Do not double doses.

Omnipen Side Effects

Overdose symptoms:

no specific information available. If you suspect an overdose, immediately seek medical attention.

Side effects: anemia; colitis (inflammation of the bowel); diarrhea; fever; hives; itching; nausea; rash; skin redness, peeling or flaking; sore or inflamed tongue or mouth; vomiting.

No known less common or rare Omnipen side effects.


Inform your doctor before combining Omnipen with:

allopurinol (Zyloprim); atenolol (Tenormin); chloroquine (Aralen); mefloquine (Lariam); other antibiotics such as chloramphenicol, tetracycline, erythromycin, and sulfonamides; oral contraceptives; probenecid (Benemid). Oral contraceptives may have a reduced effect with Omnipen.

No known food/other substance interactions.

Special Cautions

If you become pregnant during Omnipen therapy, inform your doctor immediately. Appears in breast milk; could affect a nursing infant.

No special precautions apply to seniors.

Follow doctor’s instructions carefully for children.

  • Inform your doctor before taking Omnipen if you are allergic to penicillin or cephalosporin antibiotics in any form; may cause extremely severe reaction.
  • Stop taking medication and immediately contact your doctor if you feel signs of allergic reaction.
  • Secondary infection not treatable by this medication (superinfection) may occur if taking Omnipen for an extended period.
  • Can cause diarrhea; consult your doctor before taking a diarrhea medication.
  • Has caused false positive urine glucose tests in diabetics.

Note: provides accurate and independent information prescription pills, over-the-counter medicines and natural products. This material is provided for educational purposes only and is not intended for medical advice, diagnosis or treatment. If you have questions about  dosage, or Omnipen side effects, please contact your healthcare provider