Serotonin is a neurotransmitter—a brain chemical that carries nerve impulses from one nerve cell to another. Researchers think that depression and certain other mental disorders may be caused, in part, because there is not enough serotonin being released and transmitted in the brain. Like the other SSRI antidepressants, fluvoxamine (Luvox), sertraline (Zoloft), and paroxetine (Paxil), fluoxetine increases the level of brain serotonin (also known as 5-HT). Increased serotonin levels in the brain may be beneficial in patients with obsessive-compulsive dirder, alcoholism, certain types of headaches, post-traumatic stress disorder (PTSD), pre-menstrual tension and mood swings, and panic disorder.
Fluoxetine was the first of the class of antidepressants called selective serotonin reuptake inhibitors (SSRIs) to be approved for use in the United States. In 2000, fluoxetine was approved by the FDA for use in treating premenstrual dysphoric disorder.
The benefits of fluoxetine develop slowly over a period of several weeks. Patients should be aware of this and continue to take the drug as directed, even if they feel no immediate improvement.
Fluoxetine (marketed as Prozac) is available in 10-, 20-, and 40-mg capsules, 10-mg tablets, and in a liquid solution with 20 mg of active drug per 5 ml. Prozac Weekly capsules are a time-release formula containing 90 mg of active drug. Sarafem is available in 10- and 20-mg capsules.
Fluoxetine therapy in adults is started as a single 20-mg dose, initially taken in the morning. Depending on the patient's response after four to six weeks of therapy, this dose can be increased up to a total of 80 mg per day. Doses over 20 mg per day can be given as equally divided morning and afternoon doses.
Caution should also be exercised when prescribing fluoxetine to patients with impaired liver or kidney function, the elderly (over age 60) children, individuals with known manic-depressive disorder or a history of seizures, people with diabetes, and individuals expressing ideas of committing suicide.
Individuals should not take MAO inhibitors during fluoxetine therapy, for two weeks prior to beginning fluoxetine therapy, and for five weeks after stopping fluoxetine therapy.
People with diabetes should monitor their blood or urine sugar more carefully, since fluoxetine can affect blood sugar.
Until an individual understands the effects that fluoxetine may have, he or she should avoid driving, operating dangerous machinery, or participating in hazardous activities. Alcohol should not be used while taking fluoxetine.
More common side effects include decrease sexual drive, restlessness, difficulty sitting still, skin rash, hives, and itching.
Less common side effects include fever and/or chills, and pain in joints or muscles.
Rare side effects include pain or enlargement of breasts and/or abnormal milk production in women, seizures, fast heart rate, irregular heartbeats, red or purple spots on the skin, low blood sugar and its symptoms (anxiety, chills, cold sweats, confusion, difficulty concentrating, drowsiness, excess hunger, rapid heart rate, headache, shakiness or unsteadiness, severe fatigue), low blood sodium and its symptoms (including confusion, seizures, drowsiness, dry mouth, severe thirst, decreased energy), serotonin syndrome (usually at least three of the following: diarrhea, fever, sweatiness, mood or behavior changes, overactive reflexes, fast heart rate, restlessness, shivering or shaking), excitability, agitation, irritability, pressured talking, difficulty breathing, and odd body or facial movements.
Fluoxetine interacts with a long list of other medications. People starting this drug should review the other medications they are taking with their physician and pharmacist for possible interactions. Patients should always inform all of their health care providers, including dentists, that they are taking fluoxetine.
When taken with fluoxetine, blood levels of the following drugs may increase: benzodiazepines, beta blockers, carbamazepine, dextromethorphan, haloperidol,
The following drugs may increase the risk of serotonin syndrome: dexfenfluramine, fenfluramine, and tryptophan.
When buspirone is taken with fluoxetine, the therapeutic effect of buspirone may be impaired.
Low blood sodium may occur when fluoxetine is taken along with diuretics.
Severe, fatal reactions have occurred when fluoxetine is given along with MAO inhibitors.
Ellsworth, Allan J. Mosby's Medical Drug Reference. St. Louis, MO: Mosby Inc., 1999.
Mosby's Drug Consult. St. Louis, MO: Mosby, Inc., 2002.
Rosalyn Carson-DeWitt, M.D.