Final answer:
For a patient with persistent GERD symptoms after taking ranitidine, the next step is to refer to a gastroenterologist for an upper endoscopy/biopsy to rule out serious underlying conditions.
Step-by-step explanation:
The preferred next step for a 50-year-old male patient who has symptoms of GERD and continues to experience a sour sensation in his throat, despite taking ranitidine (Zantac), is d. Refer patient to GI for upper endoscopy/biopsy. Given the patient's age and the persistent symptoms after medication intervention, it's important to rule out more serious conditions that might be causing the GERD-like symptoms, such as esophageal strictures, Barrett's esophagus, or esophageal cancer. Consultation with a gastroenterologist for further diagnostic testing is warranted. Dietary and lifestyle modifications can also be considered to manage symptoms alongside pharmacologic treatment.