A 45-year-old woman presents in your pharmacy not feeling very well. She has a past medical history of asthma. She tells you she has recently been started on a new medication for her asthma. She has been vomiting, is restless and has sinus tachycardia. Which of the options is a likely causative agent?

• A. Salbutamol
• B. Theophylline 200mg MR tablets BD - Signs of Theophylline toxicity
• C. Montelukast
• D. Budesonide

Answer: (B)

The important idea is recognizing drugs with a very narrow therapeutic window and how toxicity presents. Theophylline, once a mainstay for asthma, has a small margin between effective and toxic levels. When levels rise, you typically see gastrointestinal symptoms like vomiting, along with central nervous system effects such as restlessness or agitation, and cardiovascular signs like sinus tachycardia.

In this scenario, the patient is already on a sustained-release theophylline regimen, and she is experiencing vomiting, restlessness, and a fast heart rate. Those symptoms fit the pattern of theophylline toxicity much more than the typical side effects of other asthma medications listed. Salbutamol can cause tachycardia and tremor due to beta-agonism, but vomiting and marked restlessness point toward theophylline toxicity. Montelukast and budesonide do not usually produce this combination of acute systemic symptoms.

So, the drug most likely responsible for her presentation is theophylline.