Which drug is commonly associated with high protein binding alongside diazepam?

Propranolol, like diazepam, is known for its significant protein binding properties. In pharmacokinetics, a drug's degree of protein binding is crucial because it affects the drug's distribution, free drug concentration, and ultimately its therapeutic effect. Propranolol, a beta-blocker widely used for the treatment of hypertension and anxiety, binds extensively to plasma proteins, particularly albumin. This high protein binding is a key factor to consider when assessing the drug's pharmacokinetic profile and potential interactions with other medications.

In contrast, while other drugs listed may have varying degrees of protein binding, they do not share the same high binding characteristics as propranolol and diazepam. For example, fentanyl also has significant protein binding, but it is not as commonly associated with diazepam in clinical practice in the context of high protein binding. The other two options, morphine and propranolol, do have notable protein binding, but propranolol's association with diazepam in this context reinforces its selection as the answer. This association is essential when considering drug interactions and the overall management of patients on multiple medications.