theophylline
Meaning of theophylline: The gap between a helpful amount and a harmful one is narrow, which is why blood levels are checked during treatment.
Definition of theophylline
Theophylline is a medication that widens narrowed airways by relaxing the muscle in their walls, easing the airflow obstruction of asthma and chronic obstructive pulmonary disease. It belongs to the methylxanthines, the same chemical family as caffeine, and is taken by mouth or given into a vein. Once a mainstay of lung treatment, it now has a limited role.
Why are blood levels measured?
Most medicines have a wide margin between the amount that helps and the amount that causes trouble. Theophylline does not. Too little achieves nothing, while a modest excess brings nausea, vomiting, headache, tremor, restlessness and a racing or irregular heartbeat, and a larger excess can provoke seizures. The margin is narrow enough that ordinary changes in how fast the body clears the drug can push a settled dose out of range without anything else changing. Measuring the level in blood turns that guesswork into a number, which is why testing continues through treatment rather than stopping once a dose is established.
What shifts the level?
| Direction | Examples |
|---|---|
| Pushes the level up | Some antibiotics, including ciprofloxacin and erythromycin; fever; liver disease; heart failure; giving up smoking |
| Pulls the level down | Tobacco smoke, which speeds the liver enzyme that clears the drug; rifampin and certain anticonvulsants |
Smoking deserves the attention it gets, because the effect runs both ways. A smoker clears theophylline faster and needs more of it, so stopping can lift the level into the range where side effect trouble begins, even though nothing about the prescription has changed. Diet has a smaller effect in the same direction. The practical consequence is that the dose belongs to a person's current circumstances rather than to the person permanently.
Why is it used less than it once was?
Inhaled treatments overtook it. A bronchodilator breathed straight into the airway acts where it is needed and reaches the rest of the body only in small amounts, while theophylline is swallowed and circulates everywhere, so its unwanted effects arrive along with the intended one. It survives as an added option in chronic lung disease when inhaled treatment is not controlling symptoms, and it remains widely used where inhalers are hard to obtain. A closely related soluble form, aminophylline, is given into a vein when treatment is needed quickly.
Used in a sentence
Theophylline levels were checked as part of routine monitoring for the patient's chronic lung disease.
Good to know
Because theophylline's effective dose is close to a level associated with side effects, blood levels are monitored periodically to keep the amount within a safe and effective range.
Word origin
Where “theophylline” comes from
Formed from thea, referring to the tea plant, and Greek phyllon, meaning leaf, since the compound was first isolated from tea leaves.