1,3,7-Trimethylxanthine C8H10N4O2, M 194,19 g/mol
Caffeine, 1820 isolated by RUNGE for the first time, is one of the most important alkaloids, which is contained in luxuries such as coffee (up to 2.5 percent in the coffee beans) and tea (up to 5 percent in tea sheets), refreshment beverages (Cola, 65-250 mg/l) and energy drinks (approx. 50 mg/250 ml). The highest content of caffeine is found in the Guarana seeds, which contain the caffeine however bound at Catechine tan agents. caffeine is offered also in tablet form (100-200 mg), is a component of pain-relieving combination preparations and in illegal drugs as stretching agents.
Caffeine is absorbed after oral admission rapidly within approx. 30 minutes from the gastro-intestinal tract and distributed in the entire body. It is provable also over the mother's milk in the blood of unborn children. The effect of caffeine is based in an excitation of the central and vegetative nervous system. As phosphodiesterase inhibitor the transformation from cyclo AMP to AMP is slowed down. The main effect is based after newer investigations however as adenosine antagonist: The adenosine receptors in the brain are occupied by caffeine, so that the binding with adenosine is blocked. Adenosine acts presynaptically to inhibit the release of glutamate and dopamine.Therefore caffeine reduces fatigue symptoms. The blood pressure is increased, the heart vessels are extended. In case of overdosing it can come to sleep disturbances (fewer deep sleep phases). caffeine leads to a strengthened diurea (increased urine urge). The excitation of the breath center in the brain stem is used therapeutically for the treatment of respiratory embarrassments of earlyborn children. Caffeine energizes the fat dismantling and supports the entire metabolism. Therefore caffeine - apart from the increase in performance - is used also as doping agent. The cerebral vessels are narrowed, on which probably also the analgetic effect of caffeine is based.
With long-term admission of more than 500 mg caffeine per day anxieties, sleep disturbances, blood high pressure as well as stomach intestine complaints can occur. In the case of overdosing it comes to the excitation of the breath center, heartbeat disturbances and trembling.
The half-life time of the blood concentration is normally from 3 to 5 hr., however by combination effect - in particular together with alcohol - from 5 to 7 hr. Therapeutic blood plasma concedntrations are about 2-10 µg/ml, toxic > 15 µg/ml. The outer divorce is clearly slower with children, pregnant women and older persons.
Caffeine as a component of pain-relieving combination preparations stood in the suspicion to produce dependence and causing the analgesic headache. Newer studies occupy however, caffeine possess analgetic effect and work synergistically with other analgesics. By small caffeine doses physical withdrawal syndromes does not arise. With longer analgesic use generally headache arises,independently of the fact whether it concerns preparations with or without caffeine.