Columbia subject headings:
Drugs--United States--Patents.
Patent extensions--United States.
Patent laws and legislation--United States.
Patent practice--United States.
Harvard subject headings:
Drugs--United States--Patents.
Patent extensions--United States.
Patent laws and legislation--United States.
Patent practice--United States.
Princeton subject headings:
Drugs--United States--Patents.
Patent extensions--United States.
Patent laws and legislation--United States.
Patent practice--United States.
Patents.