(1) A person is guilty of forgery of a prescription when, with intent to defraud, deceive, or injure another, he falsely makes, completes, or alters a written instrument which is or purports to be or which is calculated to become or to represent a prescription for a legend drug when completed.
(2) Forgery of a prescription is:
(a) For a first offense, a Class D felony.
(b) For a second or subsequent offense, a Class C felony.