Ciprofloxacin, also known by the brand-name Cipro, is a strong, synthetic antibiotic from the fluoroquinolone family of drugs. Cipro is usually taken orally, and ingested Cipro dissolves in the stomach before being absorbed into the digestive system and circulated in the body.
The ciprofloxacin molecule, like other drugs in the fluoroquinolone family, naturally binds to elements including calcium. Because most soy milks contain calcium and other minerals, neither milk nor soy milk should be consumed close to a dose of Cipro.
Cipro was developed by the Bayer pharmaceutical company in the late 1980s. The medication is considered a member of the second generation of fluoroquinolone drugs, and was primarily developed to help patients with bacterial infections that had not been cured by other antibiotic therapies. It works by blocking effective DNA replication in bacteria.
Though initially seen as a "drug-of-last-resort," Cipro's potency against a wide range of infections was noted by doctors, and its use expanded concurrently with the development of other fluoroquinolones that could serve as Cipro alternatives. There are now over two dozen fluoroquinolone medications, along with low-cost generic versions of Cipro from many drug companies.
Fluoroquinolones and Digestive Binding
All fluoroquinolone molecules, including Cipro, have a natural binding affinity for calcium, zinc, iron, magnesium, aluminum and several other minerals and drugs. When these substances are present in the digestive system, ingested Cipro will bind to them, impeding the drug's absorption and nullifying its chemical activity against bacteria.
Foods and Drugs
Because they contain calcium, dairy products like milk, yogurt and cheese, or other foods containing a substantial amount of dairy ingredients, must be avoided in proximity to a dose of Cipro. Cipro must be taken at least six hours before or two hours after ingestion of products containing substantial calcium.
The same requirement applies to foods or supplements containing substantial amounts of the minerals listed above, as well as most antacids. Digestive-calming medications that contain bismuth, like Pepto-Bismol, are subject to the same restriction.
While soybeans don't naturally contain substantial calcium, most soy milk manufacturers enrich their products to contain almost as much calcium as a glass of regular dairy milk. The majority of soy milk brands contain 200-400 mg of calcium per cup, an amount that would strongly reduce the efficacy of a dose of Cipro if taken concurrently.
Due to enrichment, many soy milk brands also contain substantially more iron than the approximately null iron content of regular cow milk; another factor that would enable soy milk to reduce Cipro's effectiveness.
Extent of Effects
If bioavailability of Cipro is compromised, blood concentrations of Cipro may not rise high enough to defeat a bacterial infection. In addition to causing treatment failure, such an outcome increases the risk of making bacteria resistant to Cipro and other anti-microbial drugs.
Studies have documented the effects of calcium and other minerals' negative effects on Cipro bioavailability when the two are taken in proximity. A study by Frost, et al. in the early 1990s found that calcium tablets taken close to a Cipro dose reduced Cipro's bioavailability by 40 percent.
Calcium carbonate tablets taken two hours before Cipro were found to have little effect in one study, but researchers noted that following general calcium ingestion, "a large proportion of calcium remains in the gastrointestinal tract and may have a prolonged availability for potential interaction with quinolones."
Further studies have affirmed the negative interaction between calcium-containing drinks and Cipro when taken in proximity.
The simplest option for persons taking Cipro is to avoid soy milk within six hours before or two hours after a Cipro dose. If this would cause difficulty, you may want to look for a soy milk brand without calcium enrichment that contains very little calcium, iron or zinc.