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Pronunciation: am-pih-SILL-in
Class: Aminopenicillin

Trade Names

- Capsules 250 mg (as trihydrate)
- Capsules 500 mg (as trihydrate)
- Powder for oral suspension 125 mg/5 mL (as trihydrate) when reconstituted
- Powder for oral suspension 250 mg/5 mL (as trihydrate) when reconstituted

Ampicillin Sodium
- Powder for injection 250 mg
- Powder for injection 500 mg
- Powder for injection 1 g
- Powder for injection 2 g

Novo-Ampicillin (Canada)


Inhibits bacterial cell wall mucopeptide synthesis.

Slideshow: When Harmless Bacteria Turn Bad: Group B Strep



Well absorbed from GI tract. C max is approximately 3 mcg/mL (500 mg capsules) and 3.4 mcg/mL (500 mg oral suspension). Food affects absorption; take on empty stomach.


Diffuses readily into most body tissues and fluids; penetrates into the CSF and brain only when meninges are inflamed. Approximately 20% protein bound; excreted in breast milk.


Excreted largely unchanged in the urine.

Special Populations

Renal Function Impairment

T 1/2 may be prolonged. Dosing interval adjustments may be necessary.

Indications and Usage

Treatment of respiratory, GI, and GU tract and soft tissue infections, bacterial meningitis and enterococcal endocarditis, septicemia and gonococcal infections caused by susceptible microorganisms.

Unlabeled Uses

Prophylaxis in Cesarean section in certain high risk patients.


Hypersensitivity to penicillins, cephalosporins or imipenem. Oral form not used to treat severe pneumonia, empyema, bacteremia, pericarditis, meningitis, and purulent or septic arthritis during acute stage.

Dosage and Administration

Enterococcal Endocarditis

IV 12 g/day either continuously or in equally divided doses every 4 h plus mg/kg IM or IV gentamicin every 8 h for 4 to 6 wk.

Respiratory Tract and Soft Tissue Infections
Adults and children (at least 40 kg)

IV / IM 250 to 500 mg every 6 h.

Children (less than 40 kg)

IV / IM 25 to 50 mg/kg/day in equally divided doses every 6 to 8 h.

Adults and children (more than 20 kg)

PO 250 mg every 6 h.

Children (20 kg or less)

PO 50 mg/kg/day in equally divided dose every 6 to 8 h.

Bacterial Meningitis
Adults and children

Initial treatment is usually IV followed by IM 150 to 200 mg/kg/day in equally divided doses every 3 to 4 h.

Adults and children

IV 150 to 200 mg/kg/day for at least 3 days followed by IM every 3 to 4 h.

GI and GU Infections (Other Than N. gonorrhea )
Adults and children (more than 20 kg)

PO 500 mg every 6 h; use larger doses for severe or chronic infections, if needed.

Children (20 kg or less)

PO 100 mg/kg/day in equally divided doses every 6 h.

GI and GU infections ( N. gonorrhea )

PO 3.5 g administered simultaneously with 1 g probenecid.

Adults and children (at least 40 kg)

IV / IM 500 mg every 6 h.

Children (less than 40 kg)

IV / IM 50 mg/kg/day in equally divided doses every 6 to 8 h.

Urethritis caused by N. gonorrhea
Adult males

IV / IM Two 500 mg doses at an interval of 8 to 12 h. Dose may be repeated if necessary. In complicated gonorrheal urethritis, intensive therapy is recommended.

Drug Interactions


Increases potential for ampicillin-induced skin rash.


Antihypertensive and antianginal effects may be impaired.

Contraceptives, oral

May reduce efficacy of oral contraceptives.


May impair bactericidal effects of ampicillin.


Do not mix with aminoglycosides (eg, gentamicin).

Laboratory Test Interactions

May cause false-positive urine glucose test results with Benedict solution, Fehling solution, or Clinitest tablets (enzyme-based tests, eg, Clinistix , Tes-tape , are recommended); false-positive direct Coombs test result in certain patient groups; false-positive protein reactions with sulfosalicylic acid and boiling test, acetic acid test, biuret reaction and nitric acid test (the bromphenol blue test, Multistix , is recommended).

Adverse Reactions


Thrombophlebitis at injection site.


Dizziness; fatigue; insomnia; reversible hyperactivity; neurotoxicity (eg, lethargy, neuromuscular irritability, hallucinations, convulsions, seizures).


Urticaria; maculopapular to exfoliative dermatitis; vesicular eruptions; erythema multiforme; skin rashes.


Itchy eyes; laryngospasm; laryngeal edema.


Diarrhea; pseudomembranous colitis.


Interstitial nephritis (eg, oliguria, proteinuria, hematuria, hyaline casts, pyuria); nephropathy; increased BUN and creatinine; vaginitis.


Decreased Hgb, Hct, RBC, WBC, neutrophils, lymphocytes, platelets; increased lymphocytes, monocytes, basophils, eosinophils, and platelets.


Elevated serum alkaline phosphatase, glutamic oxaloacetic transaminase, ALT, AST, and LDH; reduced serum albumin and total proteins.


Pain at injection site; hyperthermia.



Category B .


Excreted in breast milk.


Reactions range from mild to life threatening. Use cautiously in cephalosporin-sensitive patients because of possible cross-allergenicity.

Renal Function

Use cautiously with altered dosing interval.


May result in overgrowth of nonsusceptible bacterial or fungal organisms.



Hyperexcitability, convulsive seizures.

Patient Information

  • Instruct patient to time the doses evenly over a 24-h period.
  • Inform patient that medication works best on an empty stomach, but may be taken with food if there is GI upset.
  • Tell patient to increase fluid intake to 2,000 to 3,000 mL/day, unless contraindicated.
  • Advise patient to refrigerate oral liquid preparations, and to discard unrefrigerated preparations that are more than 7 days old.
  • Inform patient to notify health care provider immediately if rash develops or if having difficulty breathing.
  • Warn diabetic patient that product may cause false-positive glucose urine test results, and identify alternative tests.
  • If therapy is changed because of allergic reaction, explain the significance of penicillin allergy and inform of potential sensitivity to cephalosporins.

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