Final answer:
The nurse should identify a rash as a manifestation of an allergic reaction to guaifenesin.
Step-by-step explanation:
The nurse should identify a rash as a manifestation of an allergic reaction to guaifenesin. Allergies are a hypersensitivity reaction of the immune system to typically harmless substances in the environment. In the case of an allergic reaction to guaifenesin, the immune system may release histamines which can cause skin reactions like hives or rashes.