The minerals calcium, iron, magnesium, and zinc can interfere with the absorption of fluoroquinolones (and vice versa). Therefore, if you take supplements of these minerals, you should take them at least 2 hours before or after your fluoroquinolone dose.1,2

The herb fennel appears to reduce blood levels of ciprofloxacin, possibly impairing its effectiveness.3 This finding comes from a placebo-controlled study in rats. Fennel might be expected to interfere similarly with other fluoroquinolone antibiotics.

Allowing 2 hours between taking ciprofloxacin and fennel should reduce the potential for an interaction, but may not eliminate it. For this reason, it may be advisable to avoid fennel supplementation during therapy with ciprofloxacin or other antibiotics in this family.

Fluoroquinolone antibiotics have been reported to cause increased sensitivity to the sun, amplifying the risk of sunburn or skin rash. Because St. John's wort and dong quai may also cause this problem, taking these herbal supplements during treatment with fluoroquinolone drugs might add to the risk.

It may be a good idea to wear a sunscreen or protective clothing during sun exposure if you take one of these herbs with a fluoroquinolone antibiotic.