Final answer:
Patients taking oral theophylline should avoid consuming caffeine to prevent complications.
Step-by-step explanation:
The substance that the patient should avoid using to prevent complications while taking oral theophylline is caffeine. Both caffeine and theophylline are methyxanthines that share similar pharmacological actions. This means that caffeine can interact with theophylline, potentially leading to increased side effects such as nervousness, tremors, and heart palpitations. Therefore, it is recommended for the patient to avoid consuming caffeine-containing products like coffee, tea, energy drinks, and chocolate.
The patient taking oral theophylline for maintenance therapy of stable asthma should avoid excessive consumption of caffeine-containing substances. Caffeine can increase the risk of theophylline toxicity.