Final answer:
Ibuprofen is the most appropriate initial medication for a 23-year-old female presenting with symptoms indicative of pericarditis, which include sharp chest pain worsened by inspiration and relieved by sitting up, accompanied by a pericardial friction rub.
Step-by-step explanation:
The most appropriate initial medication for a 23-year-old female presenting with sudden-onset sharp anterior chest pain, pain worsened with inspiration, relief upon sitting up, and a friction rub heard at the apex on auscultation would be Ibuprofen (D). This patient's symptoms are indicative of pericarditis— inflammation of the pericardium, often causing chest pain that changes in intensity when changing body positions and a distinctive pericardial friction rub can be heard on auscultation. Ibuprofen is typically used to reduce the inflammation and relieve the pain associated with pericarditis. Whereas, aspirin is often indicated for acute myocardial infarction (MI), and the role of aspirin in this scenario would be less specific as the patient's presenting symptoms do not align with those of an MI, such as angina pectoris. Angina, or chest pain caused by reduced blood flow to heart muscle cells, is a symptom shared by various cardiac conditions, but the sharp, positionally influenced pain points more toward pericarditis in this case.