Interactions with Dietary Supplements

Folic acid
TMP/SMX has, on rare occasions, been associated with anaemia due to folic acid deficiency.¹ This effect may be due to trimethoprim.² TMP/SMX should be used with caution in patients with folic acid deficiency, for which a blood test is available. Folic acid replacement does not interfere with the antibacterial activity of TMP/SMX.³ People with AIDS-related pneumonia given TMP/SMX had a worse survival rate when folinic acid, an activated form of folic acid, was added.⁴

PABA (para-aminobenzoic acid)
PABA may interfere with the action of sulfamethoxazole. It should not be taken together with trimethoprim/sulfamethoxazole.

Potassium
TMP/SMX has been reported to increase blood potassium to levels above the normal range in some patients, particularly those with impaired kidney function.⁵ People who have been prescribed TMP/SMX should ask their doctor whether they should avoid potassium supplements, potassium-containing salt substitutes (No Salt®, Morton Salt Substitute®, and others), and high-potassium foods (primarily fruit).

Probiotics
A common side effect of antibiotics is diarrhoea, 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 diarrhoea.⁶

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 boulardii⁷ or Saccharomyces cerevisiae (baker’s or brewer’s yeast)⁸ —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.⁹ 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.¹⁰

Vitamin K
A few cases of excessive bleeding have been reported in people who take antibiotics.^{11 12 13 14} 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.¹⁵ 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.