Theophylline and Caffeine

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Also known as: Aminophylline, Nuelin, Phyllocontin, Slo-Phyllin, Uniphyllin
Formal name: Theophylline and Caffeine

At a Glance

Why Get Tested?

To measure the amount of theophylline or caffeine in the blood, to establish an appropriate dose and to maintain an appropriate level

When to Get Tested?

At the start of drug therapy and at regular intervals to monitor the drug’s levels; when indicated, to detect low or possible toxic concentrations

Sample Required?

A blood sample taken from a vein in your arm or from pricking an infant’s heel

Test Preparation Needed?

No specific test preparation is needed.

The Test Sample

What is being tested?

Theophylline and caffeine are methylxanthines – drugs that ease and stimulate breathing. These tests measure the amount of theophylline or caffeine in the blood to help establish an appropriate dose and maintain the right level. Theophylline is one of several medicines that may be taken by children and adults who have asthma and by adults who have chronic obstructive pulmonary disease (COPD). It is a bronchodilator with a narrow therapeutic window – too little theophylline will not work and too much can cause toxicity. Chronic theophylline toxicity is associated with an increased risk of seizures. Both short and long term toxicity can be life-threatening.

Theophylline may also be prescribed to treat apnoea in premature babies, but caffeine citrate is the preferred medicine. Apnoea reduces the amount of oxygen available to the body. It is a common and serious condition in premature babies that must be promptly treated and closely monitored. While both theophylline and caffeine can reduce episodes of apnoea, caffeine has fewer side effects and, thus, a lower risk of toxicity. At very high doses, symptoms similar to those found with theophylline toxicity may be seen.

Establishing and maintaining therapeutic doses can be a challenge. Both theophylline and caffeine levels may need to be monitored because the range of concentrations in which the drugs are effective, but not toxic, is narrow and in some cases the dose given does not correlate well with concentrations in the blood. The rate at which the drugs are metabolized will vary from person to person and is decreased in both the very young and the elderly. The drug levels may also be affected by other conditions such as liver disease, hypothyroidism, and by short term infections or illnesses. Many drugs interact and interfere with the metabolism of theophylline. They may increase or decrease its rate of metabolism.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.  In infants, blood may be collected by pricking a heel.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No specific test preparation is needed.

The Test

Common Questions

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.