Methylxanthines are plant-derived alkaloids that include caffeine (1,3,7 trimethylxanthine), theobromine (3,7-dimethylxanthine), and theophylline (1,3-dimethylxanthine). They are so named because they are methylated derivatives of xanthine. Members of this group have very similar pharmacologic properties and clinical effects. Methylxanthines are used ubiquitously throughout the world, most commonly in beverages imbibed for their stimulant, mood elevating, and fatigue abating effects. Coffea arabica and related species are used to make coffee, a beverage rich in caffeine. Cocoa and chocolate are derived from the seeds of Theobroma cacao, which contains theobromine and to a lesser extent caffeine. Thea sinensis, a bush native to China but now cultivated worldwide, produces leaves from which various teas, rich in caffeine and containing small amounts of theophylline and theobromine, are brewed. Paullinia spp, commonly known as guarana, is a South American plant that produces berries with a caffeine content much greater than that of coffee beans. Guarana is widely used as an additive in herbal energy drinks.
Selective β2 adrenergic agonists (β2AA) have been developed for the treatment of bronchoconstriction. Their selectivity has improved therapy for bronchoconstriction, allowing avoidance of the adverse effects of the previously used therapies: epinephrine, an α-and β-adrenergic agonist, as well as isoproterenol, a β1 and β2AA. All β2AAs have nearly identical clinical effects; the principal differences are their pharmacokinetics. This chapter does not examine each β2AA individually but instead discusses them as a class. The β2AAs include albuterol, bitolterol, formoterol, pirbuterol, salmeterol, terbutaline, and ritodrine. Clenbuterol, a long-acting agonist at β2 and β3 adrenergic receptors, used for the purpose of treating bronchoconstriction in countries outside the United States, has emerged as an abused anabolic xenobiotic in recent years.
The American Association of Poison Control Centers reported the following trends in methylxanthine exposures. Theophylline exposures decreased from 2609 involving 20 deaths in 1998 to 413 exposures and four deaths in 2006. Caffeine exposures decreased from 7390 exposures and no deaths in 1998 to 5696 exposures of pharmaceutical and herbal caffeine but involving seven deaths in 2006. The decrease in theophylline exposures presumably reflects continued decrease in use of theophylline in the treatment of patients with pulmonary disease. The number of caffeine exposures has essentially remained stable, reflecting steady use of caffeine, particularly caffeine in substances other than coffee, tea, and soft drinks.
There were 11,397 selective β2AA exposures and one death in 1998 and 9564 and one death in 2006. The number of selective β2AA exposures has remained relatively stable, presumably from consistent use of these agents, but death has remained uncommon. See Chap. 135 for a discussion of poison exposure data.
The overwhelming preponderance of caffeine consumed is in beverages, and a lesser portion is consumed in foods and tablets or capsules. Users typically seek the stimulant and psychoactive effects of caffeine. ...