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Methylxanthines include caffeine, theophylline, theobromine, and nicotine. These agents are plant-derived alkaloids with ubiquitous use in beverages (caffeine in coffee and soda), foods (theobromine in chocolate), tobacco products (nicotine), and medications (theophylline and caffeine). Newer methylxanthine derivatives include pentoxifylline (improves peripheral blood flow) and doxofylline (a bronchodilator).1,2 All methylxanthines have shared pharmacologic properties and very similar pharmacodynamic effects.

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Epidemiology

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Caffeine (1,3,7-trimethylxanthine), a methylxanthine and structural analog of adenosine, is the most commonly used psychoactive drug in the world and the only one that can be legally purchased by children. It is found in varying amounts in beverages and "energy-enhanced" foods, such as candy bars, potato chips, and oatmeal (Table 186–1).3 Nearly 6 billion caffeinated "energy drinks" were purchased in the United States in 2012.4 Many "energy drinks" contain guarana, a plant whose seeds contain high concentrations of caffeine and other methylxanthines. Drinks with guarana may not list caffeine as an ingredient.5 Other uses for caffeine include apnea of prematurity, analgesic adjuncts, appetite suppression for weight loss, sleep prevention, and diuresis.

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Table 186–1 Caffeine Content of Various Products
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Theophylline (1,3-dimethylxanthine) and its water-soluble salt, aminophylline, were used extensively in the past for the treatment of asthma and chronic obstructive pulmonary disease. However, theophylline's use has declined due to its narrow therapeutic window and the development of safer agents. Theophylline is still used in patients with debilitating bronchospastic disease, particularly outside the United States, and has been studied for the treatment of other diseases, including acute mountain sickness and contrast-induced nephropathy.6,7

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Theobromine (3,7-dimethylxanthine) is found in the seeds of Theobroma cacao, from which chocolate and cocoa are derived; and Commelia thea, from which teas are steeped; and is an ingredient in numerous "energy drinks" in addition to caffeine. There are very few cases of human toxicity, but theobromine has been associated with atrial fibrillation.8

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Pharmacology

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Caffeine is most commonly consumed orally; however, it can be administered rectally or parenterally. Theophylline is usually taken orally, although its absorption may be affected by food. It is available as an elixir or as extended-release and controlled-release tablets. Controlled-release tablets can result in erratic or rapid absorption. Theophylline can also be administered IV as aminophylline.

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All methylxanthines are rapidly absorbed with early peak levels; they cross the blood–brain barrier and placenta and are excreted in breast milk (...

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