What serious risk is associated with the use of promethazine in children under the age of 2?

Promethazine is an antihistamine with antiemetic and sedative properties, commonly used to treat nausea and motion sickness. However, its use in children, particularly those under the age of 2, poses a significant risk of respiratory depression. In this age group, the central nervous system effects of promethazine can lead to severe respiratory complications, which may result in fatal outcomes.

Young children are particularly vulnerable because their respiratory systems are still developing, and they may not tolerate the sedative effects of anticholinergic medications well. The risk of respiratory depression is heightened due to the potential for increased sensitivity to the drug's effects, which can lead to inadequate ventilation and a life-threatening situation.

Other risks associated with promethazine, such as allergic reactions or cardiac issues, are present but are not as directly correlated with its use in this specific population as respiratory depression. Thus, the serious risk of fatal respiratory depression in young children stands out as the most critical concern when considering the safety of promethazine in this age group.