Ciprofloxacin - Interactions

Interactions

Ciprofloxacin interacts with other drugs, herbal and natural supplements, a characteristic it shares with other widely used antibacterial drugs such as amoxicillin, trimethoprim, azithromycin, cephalexin, and doxycycline.

Concurrent administration of ciprofloxacin with magnesium or aluminium antacids, sucralfate or products containing calcium, iron, or zinc (including multivitamins or other dietary supplements) may substantially decrease the absorption of ciprofloxacin, resulting in serum and urine levels considerably lower than desired.

The toxicity of drugs that are metabolised by the cytochrome P450 system is enhanced by concomitant use of some quinolones. Coadministration may dangerously increase Coumadin (warfarin) activity; INR should be monitored closely. They may also interact with the GABA A receptor and cause neurological symptoms; this effect is augmented by certain nonsteroidal anti-inflammatory drugs. Quercetin, a flavonol, occasionally used as a dietary supplement, may interact with fluoroquinolones, as quercetin competitively binds to bacterial DNA gyrase. Some foods, such as garlic and apples, contain high levels of quercetin; whether this inhibits or enhances the effect of fluoroquinolones is not entirely clear. Ciprofloxacin can reduce phenytoin plasma levels, which may, in some cases, result in seizures. Ciprofloxacin may interfere with the levels of thyroid medications resulting in hypothyroidism.

The Committee on the Safety of Medicines and the FDA warn that central nervous system adverse effects, including seizure risk, may be increased when NSAIDs are combined with quinolones. The interaction between quinolones and NSAIDs is important, because it has the potential for considerable CNS toxicity. The mechanism for this interaction is believed to be due to a synergistic increased antagonism of GABA neurotransmission.

Ciprofloxacin's renal clearance may affect other drugs subject to renal clearance or otherwise affecting the kidney. The use of ciprofloxacin concomitantly with cyclosporine has also been associated with transient elevations in serum creatinine. Renal tubular transport of methotrexate may be inhibited by concomitant administration of ciprofloxacin, potentially leading to increased plasma levels of methotrexate and risk of methotrexate toxicity. Probenecid interferes with renal tubular secretion of ciprofloxacin and produces an increase in the level of ciprofloxacin in serum.

Some quinolones, including ciprofloxacin, exert an inhibitory effect on the cytochrome P-450 enzyme CYP1A2, thereby reducing clearance, and thus increasing blood levels of tizanidine and methylxanthines (for example, theophylline and caffeine). The quinolones have also been reported to enhance the effects of warfarin or its derivatives. Such interactions can augment the effects of the co-administered drug, including adverse effects. Ciprofloxacin can reduce effects of other drugs; for example, it has been shown to interact with thyroid medications (levothyroxine), resulting in unexplained hypothyroidism. Altered serum levels of phenytoin and carbamazepine (increased and decreased) have been reported in patients receiving concomitant ciprofloxacin.

Current or past treatment with oral corticosteroids is associated with an increased risk of achilles tendon rupture, especially in elderly patients who are also taking the fluoroquinolones. This is the subject of Black box warnings in FDA and BNF labeling for quinolones.