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.

Note: Since sulfamethoxazole is often prescribed in combination with trimethoprim (e.g., Bactrim® or Septra®), it may be easy to associate this interaction with trimethoprim. However, this interaction is not known to occur with trimethoprim alone.

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.

Note: Since sulfamethoxazole is often prescribed in combination with trimethoprim (e.g., Bactrim® or Septra®), it may be easy to associate this interaction with trimethoprim. However, this interaction is not known to occur with trimethoprim alone.

The use of multivitamin supplements containing folic acid diminishes the occurrence of birth defects associated with trimethoprim. According to one study,³ pregnant women who took folic acid–containing multivitamin supplements in addition to their prescription drugs had fewer babies with heart defects and deformities of the upper lip and mouth.

TMP/SMX has been rarely associated with folic acid-deficiency anaemia.⁴ This action may be due to trimethoprim-induced folic acid depletion.⁵ Trimethoprim and TMP/SMX should be used with caution in patients with folic acid deficiency, for which blood tests are available. Folic acid replacement does not interfere with the antibacterial activity of trimethoprim⁶ or TMP/SMX.⁷

Potassium
TMP/SMX has been reported to elevate blood potassium and other constituents of blood (creatine and BUN).^{8 9} In particular, people with impaired kidney function should be closely monitored by their prescribing doctor for these changes. People taking trimethoprim or TMP/SMX should talk with the 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.¹⁰

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 boulardii¹¹ or Saccharomyces cerevisiae (baker’s or brewer’s yeast)¹² —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.¹³ 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.¹⁴

Vitamin K
A few cases of excessive bleeding have been reported in people who take antibiotics.^{15 16 17 18} 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.¹⁹ 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.