timing
10 interactions related to timing
methotrexate + folate
Methotrexate works by inhibiting dihydrofolate reductase, depleting active folate and causing GI, mucosal, and hepatic side effects. Folic acid supplementation reduces those side effects by 26-77% without compromising efficacy, but must be timed correctly to avoid blunting the drug's action.
levothyroxine + soy
Soy protein and isoflavones can bind to levothyroxine in the gut and reduce its absorption, sometimes increasing dose requirements in hypothyroid patients. Case reports and systematic reviews describe rising TSH and unstable thyroid levels in patients consuming soy products close to their dose.
liothyronine + calcium
Calcium salts (carbonate, citrate, acetate) can bind thyroid hormone in the gastrointestinal tract and reduce absorption of liothyronine (T3) much as they do with levothyroxine. This can blunt the effect of the dose and lead to suboptimal thyroid replacement.
liothyronine + iron
Iron salts (ferrous sulfate, fumarate, gluconate, bisglycinate) can chelate thyroid hormone in the gut and reduce absorption of liothyronine, similar to the established interaction with levothyroxine. Concurrent dosing can cause inadequate T3 effect and elevated TSH.
yogurt + antibiotics
Yogurt's calcium content can reduce the absorption of tetracycline and fluoroquinolone antibiotics through chelation, and antibiotics may also kill the live probiotic bacteria in yogurt. Taking yogurt and antibiotics simultaneously reduces the effectiveness of both.
kefir + antibiotics
Antibiotics can kill the live Lactobacillus and yeast cultures in kefir if both are consumed at the same time, reducing the probiotic benefit. Spacing kefir 2-3 hours away from the antibiotic dose preserves the live cultures and helps replenish gut microbes during and after the course.
levothyroxine + fiber
Dietary and supplemental fiber can adsorb levothyroxine in the gut and reduce its bioavailability, leading to higher TSH and unstable dosing when fiber intake is high or variable. The effect has been demonstrated with high-fiber diets and pharmaceutical fiber supplements such as psyllium.
levothyroxine + coffee
Coffee, including espresso and instant coffee, can reduce levothyroxine absorption by roughly 25 to 55 percent when consumed at the same time as the tablet. Chlorogenic acids and tannins in coffee appear to bind levothyroxine and the acidic environment may also alter dissolution and gastric emptying.
phenytoin + calcium
Phenytoin reduces calcium absorption by accelerating vitamin D catabolism and by directly inhibiting active transcellular calcium transport in intestinal enterocytes; separately, calcium-containing antacids and supplements can chelate phenytoin in the gut and lower its absorption when taken simultaneously.
coffee + iron
Coffee contains chlorogenic acid and other polyphenols with galloyl groups that chelate non-heme iron in the gut lumen, forming insoluble complexes. A cup of coffee taken with a meal can reduce non-heme iron absorption by roughly 39% to 60%.