The equivalent content of anhydrous theophylline is the active ingredient that determines blood concentration and clinical response. If a change in theophylline product is made and it involves a change in anhydrous theophylline equivalence, the dose should be adjusted accordingly. This should be taken into consideration when interpreting biochemistry tests. When plasma levels of theophylline are measured by spectrophotometric methods, coffee, tea, cola beverages, chocolate and acetaminophen contribute to falsely high values. The influence of the type and amount of other foods, as well as time interval between drug and food has not been studied.
Theophylline crosses the placental barrier, it also passes into breast milk.
Safe use of theophylline in pregnancy and in lactation has not been established. The risk of uncontrolled asthma should be balanced against potential effects on the fetus or on the nursing newborn. These are usually early signs of toxicity. However, with high doses ventricular arrhythmias or seizures may be the first signs to appear. Sensory disturbances such as tinnitus or flashes of light are common.