WASHINGTON (AP) — Federal health officials warned doctors Monday that a drug used in epilepsy patients can cause chemical imbalances in the blood, leading to heart problems and other serious complications. The Food and Drug Administration said recent data show patients taking the antiseizure pill Zonegran face higher risk of metabolic acidosis, which causes dangerously high levels of acid to accumulate in the blood. The imbalance can cause breathing difficulties, irregular heart rhythms and fatigue. Left untreated, the condition can do long-term damage to the kidneys and bones and slow growth in children. FDA advised physicians to monitor patient's blood serum levels while they are taking Zonegran, even if they don't have symptoms. The agency said it will work with drugmakers to add new warning information labels to the drug. Zonegran is sold by Woodcliff, N.J.-based Eisai Inc. "We've been in discussions with FDA regarding the issue and have submitted a proposed label change for the agency to review and approve," said company spokeswoman Judee Shuler. The drug is also available under its generic name zonisamide from various manufacturers. Data reviewed by the FDA showed patients taking higher doses of the drug were more likely to develop metabolism problems, though they were also seen at low doses. Patients with kidney disease, diarrhea and breathing problems are predisposed to suffer acid imbalances.