What symptom indicates a possibly serious adverse reaction after administering penicillin IV?

Laryngeal edema is a critical symptom to recognize as a possible serious adverse reaction after administering penicillin IV. This type of swelling in the throat can obstruct the airway and lead to significant respiratory distress, which requires immediate medical attention. Laryngeal edema may indicate anaphylaxis, a severe allergic reaction that can occur with penicillin and other antibiotics. The presence of this symptom suggests that the patient may be experiencing a life-threatening event requiring urgent intervention, such as epinephrine administration and airway management.

While itchy skin, tachycardia, and diarrhea can occur with various adverse reactions, they are not as immediately life-threatening as laryngeal edema. Itchy skin may suggest a mild allergic reaction, tachycardia can be a non-specific response to various stimuli including anxiety or fever, and diarrhea often indicates gastrointestinal intolerance or infection but does not directly threaten airway safety. Therefore, laryngeal edema is a clear indicator of a potentially severe reaction necessitating prompt medical evaluation.