Which of the following is a requirement for a written prescription for a medicinal drug?

A written prescription for a medicinal drug must include the name of the prescribing practitioner. This requirement is essential as it identifies the licensed professional authorized to prescribe the medication, ensuring the prescription is valid and can be trusted. The inclusion of the prescribing practitioner's name not only helps in the verification of the credentialed individual responsible for the patient's treatment but also provides a clear line of accountability in case there are questions regarding the medication prescribed.

Other elements such as pharmacy details and proof of payment, while relevant in the context of filling a prescription or managing a patient's financial responsibilities, do not directly relate to the essential components needed for the legality and safety of the prescription itself. Additionally, the patient's signature is not typically required on a prescription; rather, it is the practitioner's signature that legitimizes the prescription.