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Posted on 11.29.01
Ciprofloxacin: Potential for Harmful Drug Interactions
By Sally Yasuda, PharmD
Medicines often are broken down (metabolized) by enzymes in the liver for removal from the body. When another drug interferes with this process, harmful effects can result from the interaction of the drugs.
Ciprofloxacin (Cipro®, Bayer), one of the drugs approved by the U.S. Food and Drug Administration (FDA) for use after exposure to inhaled anthrax, can block one of the pathways that the body uses eliminate other medicines. Ciprofloxacin is among the top-selling prescription drugs in the U.S. and is used to treat various other infections, including urinary-tract infections, skin infections, and pneumonia.
The pathway that can be affected by Cipro works through an enzyme in the liver known as cytochrome P450 1A2. This pathway also is called CYP1A2. Some of the drugs that are removed by this pathway are listed in the table (for a more detailed list, click here). If the pathway is blocked, and the dose of drug is not reduced, the medicine can accumulate in the body to levels that could cause harmful drug reactions.
Ciprofloxacin can block the metabolism of the drugs listed in the table, and these interactions can cause adverse reactions. For example, ciprofloxacin reduces the elimination of theophylline, and seizures have been reported when the two drugs have been taken together. To prevent this, the dose of theophylline should be reduced, and its level in the blood checked, if the patient also begins taking ciprofloxacin.
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Table
1. Drugs Metabolized by CYP1A2
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Medication
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Brand
Name(s)
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Common
Uses
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| Clozapine | Clozaril | Schizophrenia |
| Cyclobenzaprine | Flexeril | Skeletal muscle relaxationt |
| Imipramine | Tofranil | Depression, bedwetting |
| Olanzapine | Zyprexa | Schizophrenia |
| Propanolol | Inderal | High blood pressure, heart attack |
| Tacrine | Cognex | Alzheimer disease |
| Theophylline | Theo-Dur, Slo-bid, Theolair, and others | Asthma |
Note: Drug names are linked to references in PubMed.
Ciprofloxacin also can be involved in other types of drug interactions. For example, because ciprofloxacin can have harmful effects in the brain, including seizures, it should be used cautiously with other drugs that can have similar effects. Antacids, sulcralfate (an anti-ulcer drug), and products containing calcium, iron, or zinc (such as vitamin supplements) can interfere with the absorption of oral ciprofloxacin when taken together, resulting in "therapeutic failure" of ciprofloxacin. Therefore, these products should be taken either 6 hours before or 2 hours after the dose of ciprofloxacin.
Before a patient begins taking ciprofloxacin for any reason, the patient's doctor and pharmacist should have a complete list of medicines that the patient is taking or recently stopped taking. The list should include prescription drugs, over-the-counter medicines, and natural products such as herbal therapies or supplements.
Patients can use a form to keep track of their medicines by visiting http://www.arizonacert.org/consumers/med-record.htm. They should show the form to their healthcare provider at each visit. With careful review of the medicine record, many drug interactions can be prevented.