An asthma drug first pulled from tea leaves is a cousin of caffeine
Theophylline was extracted from tea leaves around 1888, and its name joins the old genus name for tea with the Greek word for leaf. Chemically it is a close relative of caffeine and theobromine, and it has long been used for asthma and COPD, but the gap between a useful dose and a toxic one is unusually narrow.
The German biologist Albrecht Kossel identified the compound around 1888. Seven years later Emil Fischer and Lorenz Ach described a way to synthesise it from 1,3-dimethyluric acid, and in 1900 Wilhelm Traube introduced an alternative route. Doctors first used it in 1902 as a diuretic, and roughly two decades passed before anyone reported it as an asthma treatment. Syrups called Theostat 20 and Theostat 80 were prescribed up to the 1970s, followed by a Quibron tablet in the early 1980s.
It works in two main ways. It blocks adenosine receptors, all three main subtypes about equally, which accounts for much of its effect on the heart, and it inhibits phosphodiesterase enzymes, raising levels of the signalling molecules cAMP and cGMP and damping inflammation. The result widens airways, strengthens and speeds heartbeats and stimulates the brain's breathing centre; athletes have used methylxanthines for the same alertness and bronchodilation.
The catch is a therapeutic window below 20 micrograms per millilitre, so blood levels are monitored directly. Because liver metabolism can saturate even within the normal range, a small dose increase can push concentrations up disproportionately. Overdose can bring nausea, fast or abnormal heart rhythms and, in severe cases, seizures, and antibiotics such as erythromycin and ciprofloxacin raise the risk. Smoking tobacco or marijuana speeds its clearance.
How long it lingers varies enormously: its half-life is about 30 hours in premature newborns, 3.5 hours in children aged 1 to 9, 8 hours in adult non-smokers and 5 in adult smokers. In food it appears only in traces. Brewed tea supplies about 1 milligram per litre, far below a medical dose, though Criollo cocoa beans have been measured at up to 3.7 milligrams per gram.
Source: Theophylline
