In what situation should intranasal cromolyn NOT be used?

Intranasal cromolyn is primarily used to prevent or manage allergic rhinitis by stabilizing mast cells and preventing the release of mediators that cause allergic symptoms. Its effectiveness is maximized when used as a preventive measure rather than on an as-needed (PRN) basis.

Using it as needed may not provide the continuous therapeutic effect required to effectively manage allergic symptoms, which is why it is generally not recommended for PRN use. Instead, it is advised to use intranasal cromolyn regularly, particularly before exposure to known allergens, to gather the most benefit in reducing symptoms.

In contrast, the other options indicate scenarios where intranasal cromolyn is appropriate and can be effective. It is safe for prophylactic treatment because it helps reduce the onset of symptoms before they arise. Additionally, it can be used in children over 2 years old, making it a viable option in pediatrics. Pregnant women can also use it since it is classified as a category B medication and is considered safe during pregnancy when necessary.

Thus, the use of intranasal cromolyn on a PRN basis does not align with its intended use as a preventative treatment, highlighting why this situation should be avoided.