Citalopram is a prescription drug used for the treatment of depression. Other uses of citalopram include treatment of dementia, smoking cessation, alcohol abuse, obsessive compulsive disorder in children and diabetic neuropathy; these indications have not been approved by the FDA yet. Its breakdown -- how it is metabolized -- may cause drug interactions that affect how citalopram functions in your body.
Action of Citalopram
Citalopram belongs to the class of antidepressants called selective serotonin reuptake inhibitors, or SSRIs. It works by blocking the absorption of serotonin in the brain. This increases the amount of serotonin in the brain, which improves the symptoms of depression.
Liver
The liver has a high concentration of a group of enzymes known as the cytochrome P450 system, which is involved in metabolizing drugs into less toxic substances that are easily released from the body. Each enzyme has its own name; citalopram is primarily broken down by the enzymes cytochrome P450 3A4, or CYP3A4, and cytochrome P450 2C19, or CYP2C19. The cytochrome P450 2D6 enzyme, or CYP2D6, plays a minor role in citalopram breakdown, as well.
Drug Interactions
Citalopram may interact with medications that affect the CYP enzymes. Some medications inhibit, or block, the actions of the enzymes, while others induce, or enhance, them. Inhibitors may increase the levels or effects of citalopram when administered together, explains the "Drug Information Handbook." Common CYP 3A4 inhibitors include verapamil, quinidine, nicardipine, nefazodone, clarithromycin, diclofenac, doxycycline, protease inhibitors and azole antifungals. Examples of CYP 2C19 inhibitors include omeprazole, gemfibrozil, fluvoxamine, fluconazole, isoniazid, delavirdine and ticlopidine. Inducers of these enzymes may decrease the effects of citalopram. Examples of CYP 3A4 inducers are aminoglutethimide, carbamazepine, nafcillin, nevirapine, phenobarbital, phenytoin and rifamycins. Aminoglutethimide, carbamazepine, phenytoin and rifampin are also inducers of CYP 2C19. CYP 2D6 plays a minimal role and has no interactions with other drugs.
Prevention and Monitoring
You should inform your physician of all the medications you take, including over-the-counter medications, to make sure there are no drug interactions. You should also go to the doctor regularly to make sure the medication is working properly. Monitoring parameters include improvement of symptoms and evaluation of mental status for suicidal ideation, anxiety, social functioning, panic attacks and mania. If there is no improvement, you may need a higher dosage. On the other hand, if you develop symptoms of overdose or toxicity, you may need a lower dosage. RxList.com states that these symptoms include dizziness, nausea, vomiting, sweating, shakiness, sleepiness and heart palpitations; seek medical help if you develop any of these.
References
- "Drug Information Handbook"; Charles F. Lacy, et al.; 2009
- RxList.com: Celexa
- "Pharmacotherapy: A Pathophysiologic Approach"; Josep T. Dipiro, et al.; 2008
- National Cancer Institute: Cytochrome P450 Enzyme System
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