Twenty-one deaths have been reported among children under age 2 who took carbinoxamine products, the Food and Drug Administration said.
"While it is not clear that the carbinoxamine caused these deaths, FDA is concerned about the risks of these unapproved products," an agency statement said.
Many unapproved prescription carbinoxamine products are sold illegally for treating cough and cold symptoms even though the drug has not been found safe and effective for that use, the FDA said. Some companies sell drops and syrups labeled for use in children as young as one month old.
The FDA said it was told of 120 unapproved carbinoxamine products that were being sold. Doctors likely are prescribing the medicines without knowing they lack FDA clearance, officials said.
Companies that keep selling unapproved carbinoxamine after the deadline could receive FDA warning letters or face other action, the agency said. The manufacturers can apply for FDA approval if they supply evidence of safety and effectiveness.
The FDA said two unapproved carbinoxamine products were sold under the brand names Cardec and Rondec.
Maker Alliant Pharmaceuticals reformulated Rondec in December 2004 and it no longer contains carbinoxamine, company spokeswoman Sharon Kraun said.
One company, Mikart Inc., has FDA approval to sell carbinoxamine products for treating allergy symptoms.
The FDA said the carbinoxamine action was part of a renewed effort to crack down on unapproved prescription drugs that are on the market. Less than 2 percent of prescribed drugs contain unapproved ingredients, the agency said.