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Also indexed as: Amficot, Omnipen, Principen, Totacillin


Ampicillin is used to treat diseases caused by bacterial infections; it is a type of antibiotic called an aminopenicillin.

Summary of Interactions with Vitamins, Herbs, and Foods
In some cases, an herb or supplement may appear in more than one category, which may seem contradictory. For clarification, read the full article for details about the summarized interactions.

Beneficial May Be Beneficial: Depletion or interference—The medication may deplete or interfere with the absorption or function of the nutrient. Taking these nutrients may help replenish them.

Vitamin C*

Vitamin K*

Beneficial May Be Beneficial: Side effect reduction/prevention—Taking these supplements may help reduce the likelihood and/or severity of a potential side effect caused by the medication.

Bifidobacterium longum*

Lactobacillus acidophilus*

Lactobacillus casei*


Saccharomyces boulardii*

Saccharomyces cerevisiae*

Vitamin K*

Beneficial May Be Beneficial: Supportive interaction—Taking these supplements may support or otherwise help your medication work better.

Saccharomyces boulardii*

Avoid Avoid: Reduced drug absorption/bioavailability—Avoid these supplements when taking this medication since the supplement may decrease the absorption and/or activity of the medication in the body.


Adverse interaction

None known

An asterisk (*) next to an item in the summary indicates that the interaction is supported only by weak, fragmentary, and/or contradictory scientific evidence.

Interactions with Dietary Supplements

Vitamin C
Test tube studies show that ampicillin significantly reduces the amount of vitamin C in the blood.1 Controlled research is needed to determine whether individuals might benefit from supplementing vitamin C while taking ampicillin.

A common side effect of antibiotics is diarrhea, which may be caused by the elimination of beneficial bacteria normally found in the colon. Controlled studies have shown that taking probiotic microorganisms—such as Lactobacillus casei, Lactobacillus acidophilus, Bifidobacterium longum, or Saccharomyces boulardii—helps prevent antibiotic-induced diarrhea.2

The diarrhea experienced by some people who take antibiotics also might be due to an overgrowth of the bacterium Clostridium difficile, which causes a disease known as pseudomembranous colitis. Controlled studies have shown that supplementation with harmless yeast—such as Saccharomyces boulardii3 or Saccharomyces cerevisiae (baker’s or brewer’s yeast)4 —helps prevent recurrence of this infection. In one study, taking 500 mg of Saccharomyces boulardii twice daily enhanced the effectiveness of the antibiotic vancomycin in preventing recurrent clostridium infection.5 Therefore, people taking antibiotics who later develop diarrhea might benefit from supplementing with saccharomyces organisms.

Treatment with antibiotics also commonly leads to an overgrowth of yeast (Candida albicans) in the vagina (candida vaginitis) and the intestines (sometimes referred to as “dysbiosis”). Controlled studies have shown that Lactobacillus acidophilus might prevent candida vaginitis.6

Vitamin K
Several cases of excessive bleeding have been reported in people who take antibiotics.7 8 9 10 This side effect may be the result of reduced vitamin K activity and/or reduced vitamin K production by bacteria in the colon. One study showed that people who had taken broad-spectrum antibiotics had lower liver concentrations of vitamin K2 (menaquinone), though vitamin K1 (phylloquinone) levels remained normal.11 Several antibiotics appear to exert a strong effect on vitamin K activity, while others may not have any effect. Therefore, one should refer to a specific antibiotic for information on whether it interacts with vitamin K. Doctors of natural medicine sometimes recommend vitamin K supplementation to people taking antibiotics. Additional research is needed to determine whether the amount of vitamin K1 found in some multivitamins is sufficient to prevent antibiotic-induced bleeding. Moreover, most multivitamins do not contain vitamin K.

Interactions with Herbs

Khat (Catha edulis)
Khat is an herb found in East Africa and Yemen that has recently been imported into the United States. Studies have shown that chewing khat significantly reduces the absorption of ampicillin,12 which might reduce the effectiveness of the antibiotic. Therefore, people taking ampicillin should avoid herbal products that contain khat.

Interactions with Foods and Other Compounds

Taking ampicillin with food reduces the amount of drug that is absorbed regardless of the type of meal eaten.13 Therefore, ampicillin should be taken an hour before or two hours after a meal.

Normally, bacteria in the intestines help break down indigestible carbohydrates into useable forms. Ampicillin blocks this process, which may result in increased undigested carbohydrates in the intestine, increased water in the stool, and diarrhea.14 Consequently, people taking ampicillin might experience fewer episodes of diarrhea if they eat a diet low in indigestible carbohydrate during the treatment period. Consult a health practitioner to learn about sources of indigestible carbohydrate.

Dietary Fiber
Controlled studies with amoxicillin, an antibiotic similar to ampicillin, have shown that a diet low in fiber (7 g/day) increases the absorption of the drug when compared to a high-fiber diet (36 g/day).15 However, further research is needed to determine whether different amounts of dietary fiber exert the same effect on ampicillin. Until more information is available, people taking ampicillin might benefit more from eating a low-fiber diet during the treatment period.

Normally, the body converts alcohol to acetaldehyde, which test tube studies show blocks the action of ampicillin.16 Whether drinking alcoholic beverages affects the activity of ampicillin in the body is unknown; therefore, until more information is available, people taking ampicillin should avoid alcohol.


1. Alabi ZO, Thomas KD, Ogunbona O, Elegbe IA. The effect of antibacterial agents on plasma vitamin C levels. Afr J Med Med 1994;23:143–6.

2. Elmer GW, Surawicz CM, McFarland LV. Biotherapeutic agents. A neglected modality for the treatment and prevention of selected intestinal and vaginal infections. JAMA 1996;275:870–6 [review].

3. Elmer GW, Surawicz CM, McFarland LV. Biotherapeutic agents. A neglected modality for the treatment and prevention of selected intestinal and vaginal infections. JAMA 1996;275:870–6 [review].

4. Schellenberg D, Bonington A, Champion CM, et al. Treatment of Clostridium difficile diarrhoea with brewer’s yeast. Lancet 1994;343:171–2.

5. Surawicz CM, Elmer GW, Speelman P, et al. Prevention of antibiotic-associated diarrhea by Saccharomyces boulardii: A prospective study. Gastroenterol 1989;96:981–8.

6. Elmer GW, Surawicz CM, McFarland LV. Biotherapeutic agents. A neglected modality for the treatment and prevention of selected intestinal and vaginal infections. JAMA 1996;275:870–6 [review].

7. Suzuki K, Fukushima T, Meguro K, et al. Intracranial hemorrhage in an infant owing to vitamin K deficiency despite prophylaxis. Childs Nerv Syst 1999;15:292–4.

8. Huilgol VR, Markus SL, Vakil NB. Antibiotic-induced iatrogenic hemobilia. Am J Gastroenterol 1997;92:706–7.

9. Bandrowsky T, Vorono AA, Borris TJ, Marcantoni HW. Amoxicllin-related postextraction bleeding in an anticoagulated patient with tranexamic acid rinses. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1996;82:610–2.

10. Kaiser CW, McAuliffe JD, Barth RJ, Lynch JA. Hypoprothrombinemia and hemorrhage in a surgical patient treated with cefotetan. Arch Surg 1991;126:524–5.

11. Conly J, Stein K. Reduction of vitamin K2 concentration in human liver associated with the use of broad spectrum antimicrobials. Clin Invest Med 1994;17:531–9.

12. Attel OA, Ali AA, Ali HM. Effect of khat chewing on the bioavailability of ampicillin and amoxicillin. J Antimicrob Chemother 1997;39:523–5.

13. Hamid S, Beg AE. Influence of ethnic diets on ampicillin bioavailability and pharmacokinetics in healthy Pakistani subjects. Pol J Pharmacol Pharm 1987;39:337–42.

14. Rao SS, Edwards CA, Austen CJ, et al. Impaired colonic fermentation of carbohydrate after ampicillin. Gastroenterology 1988;94:928–32.

15. Lutz M, Espinoza J, Arancibia A. Effect of structured dietary fiber on bioavailability of amoxicillin. Clin Pharmacol Ther 1987;42:220–4.

16. Nunez-Vergara LJ, Yudelevich J, Squella JA, Speisky H. Drug-acetaldehyde interactions during ethanol metabolism in vitro. Alcohol Alcohol 1991;26:139–46.

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