This drug is considered a "specialty drug".    Tell me why

This drug is considered a "specialty drug".  Specialty drugs are usually expensive, may need to be administered in a certain way, and often require ongoing assessments (appointments) to ensure the drug is working and to help manage side effects.
There may be other drugs that you can take first before taking this specialty drug.

Apo-Sildenafil R is used to treat  
Pulmonary Arterial Hypertension