Interactions with Dietary Supplements

Bromelain
When taken with amoxicillin, bromelain was shown to increase absorption of amoxicillin in humans.¹ When 80 mg of bromelain was taken together with amoxicillin and tetracycline, blood levels of both drugs increased, though how bromelain acts on drug metabolism remains unknown.² An older report found bromelain also increased the actions of other antibiotics, including penicillin, chloramphenicol, and erythromycin, in treating a variety of infections. In that trial, 22 out of 23 people who had previously not responded to these antibiotics did so after adding bromelain taken four times per day.³

Doctors will sometimes prescribe enough bromelain to equal 2,400 gelatine dissolving units (listed as GDU on labels) per day. This amount would equal approximately 3,600 MCU (milk clotting units), another common measure of bromelain activity.

Probiotics
A common side effect of antibiotics is diarrhoea, which may be caused by the elimination of beneficial bacteria normally found in the colon. A nonpathogenic yeast known as Saccharomyces boulardii has been shown in two double-blind studies to decrease frequency of diarrhoea in people taking amoxicillin as well as other penicillin-type drugs compared to placebo.^{4 5} There were overall few people in these studies using amoxicillin specifically, so there is no definitive proof that Saccharomyces boulardii will be beneficial for everyone when it is combined with amoxicillin. The studies used 1 gram of Saccharomyces boulardii per day.

A separate double-blind study found that taking a combination of Lactobacillus acidophilus and Lactobacillus bulgaricus, two normal gut bacteria, with amoxicillin did not protect children from developing diarrhoea.⁶ The authors of the study point out some problems such as the parents’ inability to consistently define diarrhoea. However, at this time, it is unknown if lactobacillus products will reduce diarrhoea due to amoxicillin.

Controlled studies have shown that taking other probiotic microorganisms—such as Lactobacillus casei or Bifidobacterium longum—also helps prevent antibiotic-induced diarrhoea.⁷

The diarrhoea 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 boulardii⁸ or Saccharomyces cerevisiae (baker’s or brewer’s yeast)⁹ —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.¹⁰ Therefore, people taking antibiotics who later develop diarrhoea 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.¹¹

Vitamin K
A few cases of excessive bleeding have been reported in people who take antibiotics.^{12 13 14 15} 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.¹⁶ A few 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.