Interactions with Dietary Supplements

Calcium, Magnesium, Vitamin B12
Sulfonamides, including sulfamethoxazole, can decrease absorption of calcium, magnesium, and vitamin B12.¹ This is generally not a problem when taking sulfamethoxazole for two weeks or less. People taking sulfamethoxazole for longer than two weeks should ask their doctor about nutrient monitoring and supplementation.

Folic acid, Vitamin B6, Vitamin K
Sulfonamides, including sulfamethoxazole, can interfere with the activity of folic acid, vitamin B6, and vitamin K.² This is generally not a problem when taking sulfamethoxazole for two weeks or less. People taking sulfamethoxazole for longer than two weeks should ask their doctor about nutrient monitoring and supplementation.

PABA (para-aminobenzoic acid)
PABA may interfere with the activity of sulfamethoxazole. PABA should not be taken with this drug until more is known.

Potassium
TMP/SMX has been reported to elevate potassium and other constituents of blood (creatinine and BUN).³ In particular, people with impaired kidney function should be closely monitored by their prescribing doctor for these changes. People taking sulfamethoxazole or TMP/SMX should talk with their prescribing doctor before taking any potassium supplements or potassium-containing products, such as No Salt®, Salt Substitute®, Lite Salt®, and even 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.⁴

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 boulardii⁵ or Saccharomyces cerevisiae (baker’s or brewer’s yeast)⁶ —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.⁷ 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.⁸

Vitamin K
Several cases of excessive bleeding have been reported in people who take antibiotics.^{9 10 11 12} 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.¹³ 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.