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Unasyn Side Effects

Generic name: ampicillin / sulbactam

Medically reviewed by Last updated on Nov 26, 2022.

Note: This document contains side effect information about ampicillin / sulbactam. Some dosage forms listed on this page may not apply to the brand name Unasyn.

Applies to ampicillin / sulbactam: injection powder for solution.

Serious side effects of Unasyn

Along with its needed effects, ampicillin/sulbactam may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor or nurse immediately if any of the following side effects occur while taking ampicillin / sulbactam:

Less common

  • Changes in skin color
  • diarrhea
  • pain, tenderness, or swelling of the foot or leg


  • Bloody nose
  • burning while urinating
  • chest pain, discomfort, or pressure
  • chills
  • decrease in the frequency of urination
  • decrease in urine volume
  • difficulty in passing urine (dribbling)
  • flushing or redness of the skin
  • painful urination
  • swelling
  • swelling or puffiness of the face
  • tightness in the throat
  • unusually warm skin

Incidence not known

  • Abdominal or stomach cramps or tenderness
  • black, hairy tongue
  • blistering, peeling, or loosening of the skin
  • bloating
  • cough or hoarseness
  • cracks in the skin
  • diarrhea, watery and severe, which may also be bloody
  • fever
  • fever with or without chills
  • general feeling of tiredness or weakness
  • increased thirst
  • itching
  • joint or muscle pain
  • loss of heat from the body
  • lower back or side pain
  • nausea or vomiting
  • pain
  • red, irritated eyes
  • red, swollen skin
  • scaly skin
  • severe stomach pain
  • sore throat
  • sores, ulcers, or white spots on the lips or in the mouth
  • swelling or inflammation of the mouth
  • unusual bleeding or bruising
  • unusual tiredness or weakness
  • unusual weight loss
  • vomiting

Other side effects of Unasyn

Some side effects of ampicillin / sulbactam may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

  • Bleeding, blistering, burning, coldness, discoloration of the skin, feeling of pressure, hives, infection, inflammation, itching, lumps, numbness, pain, rash, redness, scarring, soreness, stinging, swelling, tenderness, tingling, ulceration, or warmth at the injection site


  • Excess air or gas in the stomach or intestines
  • full or bloated feeling
  • general feeling of discomfort or illness
  • headache
  • passing gas
  • pressure in the stomach
  • redness, swelling, or soreness of the tongue
  • swelling of the abdominal or stomach area
  • white patches in the mouth or throat or on the tongue
  • white patches with diaper rash

Incidence not known

For Healthcare Professionals

Applies to ampicillin / sulbactam: injectable powder for injection.


This drug was generally well-tolerated.[Ref]


Very common (10% or more): Pain at IM injection site (16%)

Common (1% to 10%): Pain at IV injection site, thrombophlebitis, phlebitis

Postmarketing reports: Injections site reaction[Ref]


Common (1% to 10%): Diarrhea

Uncommon (0.1% to 1%): Nausea, vomiting, flatulence, abdominal distension, glossitis

Frequency not reported: Pancreatitis, enterocolitis, pseudomembranous colitis

Postmarketing reports: Gastritis, stomatitis, black "hairy" tongue, Clostridium difficile associated diarrhea[Ref]


Frequency not reported: Hypersensitivity reactions to ampicillin (including urticarial rash, edema, hypotension, fever, eosinophilia, dyspnea, delayed hypersensitivity maculopapular rash, anaphylaxis, interstitial nephritis, Henoch-Schonlein purpura, focal glomerulonephritis, Stevens-Johnson syndrome)

Postmarketing reports: Serious and fatal hypersensitivity (anaphylactic) reactions[Ref]


Common (1% to 10%): Rash

Uncommon (0.1% to 1%): Itching, facial swelling, erythema

Frequency not reported: Ampicillin-associated bullous pemphigoid, linear IgA dermatosis, pseudoporphyria

Postmarketing reports: Erythema multiforme, toxic epidermal necrolysis, Stevens-Johnson syndrome, acute generalized exanthematous pustulosis, urticaria, exfoliative dermatitis[Ref]


Hemolytic anemia, thrombocytopenic purpura, and agranulocytosis were generally reversible when therapy was discontinued; may be hypersensitivity events.[Ref]

Frequency not reported: Decreased hemoglobin, decreased hematocrit, decreased red blood cells, decreased white blood cells, decreased neutrophils, decreased lymphocytes, decreased platelets, increased lymphocytes, increased monocytes, increased basophils, increased eosinophils, increased platelets, thrombocytopenia, leukopenia, red cell aplasia, anemia, atypical lymphocytosis

Postmarketing reports: Hemolytic anemia, thrombocytopenic purpura, agranulocytosis, positive direct Coombs test[Ref]

Nervous system

Seizures have been reported in very ill patients with high serum levels of ampicillin. High cerebral spinal fluid (CSF) levels of some penicillins are potentially neurotoxic; the CSF levels of ampicillin rise significantly in meningitis.[Ref]

Uncommon (0.1% to 1%): Headache

Frequency not reported: Seizures, neurotoxic potential, worsening myasthenia gravis symptoms

Postmarketing reports: Convulsion[Ref]


Frequency not reported: Increased AST, increased ALT, hepatitis, prolonged cholestasis

Postmarketing reports: Cholestatic hepatitis, cholestasis, hyperbilirubinemia, jaundice, abnormal hepatic function[Ref]


Frequency not reported: Increased alkaline phosphatase, increased lactate dehydrogenase, decreased serum albumin, decreased total protein[Ref]


Uncommon (0.1% to 1%): Urine retention, dysuria

Frequency not reported: Urinary red blood cells, urinary hyaline casts[Ref]


Frequency not reported: Increased BUN, increased creatinine

Postmarketing reports: Tubulointerstitial nephritis[Ref]


Uncommon (0.1% to 1%): Candidiasis, fatigue, malaise, chest pain, edema, chills, substernal pain, mucosal bleeding[Ref]


Uncommon (0.1% to 1%): Throat tightness, epistaxis


1. "Multum Information Services, Inc. Expert Review Panel"

2. "Product Information. Unasyn (ampicillin-sulbactam)." Roerig Division (2002):

3. Ramakrishnan K, Scheid DC "Diagnosis and management of acute pyelonephritis in adults." Am Fam Physician 71 (2005): 933-42

4. Ott SR, Allewelt M, Lorenz J, Reimnitz P, Lode H "Moxifloxacin vs ampicillin / sulbactam in aspiration pneumonia and primary lung abscess." Infection 36 (2008): 23-30

5. Poe RH, Condemi JJ, Weinstein SS, Schuster RJ "Adult respiratory distress syndrome related to ampicillin sensitivity." Chest 3 (1980): 449-51

6. Craig WA, Gerber AU "Worldwide experience with bacampicillin administered twice a day." Rev Infect Dis 3 (1981): 171-7

7. Beeching NJ, Gruer LD, Findlay CD, Geddes AM "A case of Henoch-Schonlein purpura syndrome following oral ampicillin." J Antimicrob Chemother 10 (1982): 479-82

8. Tagami H, Tatsuta K, Iwatski K, Yamada M "Delayed hypersensitivity in ampicillin-induced toxic epidermal necrolysis." Arch Dermatol 119 (1983): 910-3

9. Chan HL "Fixed drug eruption to bacampicillin (ampicillin)." Arch Dermatol 120 (1984): 542

10. Guinta JL, Fiumara N "Ampicillin allergy presenting as secondary syphilis." Oral Surg Oral Med Oral Patho 2 (1984): 152-4

11. Konstantinidis AB, Markopoulos A, Trigonides G "Ampicillin induced erythema multiforme." J Oral Med 40 (1985): 168-70

12. Mehta D, Warwick GL, Goldberg MJ "QT prolongation after ampicillin anaphylaxis." Br Heart J 55 (1986): 308-10

13. Dolovich J, Ruhno J, Sauder DN, Ahlstedt S, Hargreave FE "Isolated late cutaneous skin test response to ampicillin: a distinct entity." J Allergy Clin Immunol 82 (1988): 676-9

14. Hodak E, Ben-Shetrit A, Ingber A, Sandbank M "Bullous pemphigoid: an adverse effect of ampicillin." Clin Exp Dermatol 15 (1990): 50-2

15. Heim K, Alge A, Marth C "Anaphylactic reaction to ampicillin and severe complication in the fetus." Lancet 337 (1991): 859-60

16. Johnson JR, Lyons MF, Pearce W, et al. "Therapy for women hospitalized with acute pyelonephritis: a randomized trial of ampicillin versus trimethoprim-sulfamethoxasole for 14 days." J Infect Dis 163 (1991): 325-30

17. Cavanzo FJ, Garcia CF, Botero RC "Chronic cholestasis, paucity of bile ducts, red cell aplasia, and the Stevens-Johnson syndrome." Gastroenterology 99 (1990): 854-6

18. Blomqvist M, Hedtrom SA "The clinical efficacy and safety of bacampicillin twice daily in comparative studies." J Int Med Res 15 (1987): 32-43

19. Shimanovich I, Rose C, Sitaru C, Brocker EB, Zillikens D "Localized linear IgA disease induced by ampicillin / sulbactam." J Am Acad Dermatol 51(1 Pt 1) (2004): 95-8

20. Berliner S, Sidi Y, Shaklai M, Pinkhas J "Appearance of thrombocytopenia and benign monoclonal gammopathy following intake of drugs." Acta Haematol 67 (1982): 71-2

21. Hughes GS "Ampicillin and hematologic effects." Ann Intern Med 99 (1983): 573

22. Singh N, Yu VL, Mieles LA, Wagener MM "Beta-lactam antibiotic-induced leukopenia in severe hepatic dysfunction: risk factors and implications for dosing in patients with liver disease." Am J Med 94 (1993): 251-6

23. Hodgman T, Dasta JF, Armstrong DK, Visconti JA, Reilley TE "Ampicillin-associated seizures." South Med J 77 (1984): 1323-5

24. Argov Z, Brenner T, Abramsky O "Ampicillin may aggravate clinical and experimental myasthenia gravis." Arch Neurol 43 (1986): 255-6

25. Koklu S, Koksal AS, Asil M, Kiyici H, Coban S, Arhan M "Probable sulbactam/ampicillin-associated prolonged cholestasis." Ann Pharmacother 38 (2004): 2055-8

26. Moesch C, Rince M, Raby C, Denis F, Leroux-Robert C "Crystalluria following aminopenicillin therapy." Clin Nephrol 23 (1985): 318-9

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.