Officials at the US Food and Drug Administration are clarifying dosing and warning recommendations for the drug Celexa, or citalopram hydrobromide. \"There is the possibility that high doses of the antidepressant can cause dangerous abnormalities in the electrical activity of the heart,\" the FDA said in a statement. The drug\'s label has been changed to describe the caution that needs to be taken when citalopram is used in patients with certain underlying heart conditions, and those who are predisposed to having low levels of potassium and magnesium in the blood. The revised drug label also describes lower doses that should be used in patients age 60 and older, officials said. \"Changes in the electrical activity of the heart can lead to the risk of fatal abnormal heart rhythm; because of this risk in certain circumstances -- health care providers might need to regularly monitor the heart, or check blood levels of potassium and magnesium -- in patients that must use Celexa,\" the statement said. \"The maximum recommended dose of Celexa is 20 milligrams per day for patients age 60 and older.\" The FDA said: Do not stop taking Celexa or change your dose without talking to your healthcare professional. Stopping Celexa suddenly can cause withdrawal effects. If currently taking a Celexa dose greater than 40 mg per day, talk to your healthcare professional. Seek immediate care if you experience an irregular heartbeat, shortness of breath, dizziness or fainting while taking Celexa. If you are taking Celexa, your healthcare professional may occasionally order an electrocardiogram to monitor your heart rate and rhythm.