A nurse is providing discharge instructions to a client who has asthma and is about to start taking theophylline (Theo-24). The nurse should tell the client that this medication might cause which of the following adverse effects?

A. Constipation: Theophylline does not typically affect gastrointestinal motility, so constipation is not a common adverse effect. Monitoring bowel habits is not a primary concern with this medication. B. Tachycardia: Theophylline is a methylxanthine that stimulates the heart and central nervous system, which can lead to increased heart rate. Patients may also experience palpitations or nervousness, making cardiovascular monitoring important during therapy. C. Drowsiness: Theophylline is a stimulant rather than a sedative, so drowsiness is uncommon. Patients are more likely to experience insomnia or restlessness instead. D. Oliguria: Theophylline does not significantly affect renal function to cause decreased urine output. Monitoring for this is not a routine concern when administering the medication.