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.
Caffeine (1,3,7-trimethylxanthine), a structural analog of adenosine, is found with varying amounts in beverages and “energy-enhanced” foods, such as candy bars, potato chips, and oatmeal (Table 192-1).3 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.4 Other uses for caffeine include apnea of prematurity, analgesic adjuncts, postdural puncture headache, appetite suppression for weight loss, sleep prevention, and diuresis.
TABLE 192-1Caffeine Content of Various Products ||Download (.pdf) TABLE 192-1 Caffeine Content of Various Products
|Source ||Caffeine Content (milligrams) |
|Coffee (8 oz or 240 mL, brewed) ||60–120 |
|Tea (8 oz or 240 mL, brewed) ||20–90 |
|Colas, caffeinated (8 oz or 240 mL) ||20–40 |
|Dark chocolate (1 oz or 30 mL) ||5–35 |
|“Higher caffeine energy drinks” (8–24 oz) ||70–505 |
|Acetaminophen-aspirin-caffeine tablet ||65 |
|Nonprescription antidrowsiness tablet ||200 |
|Caffeine powder (via online sources) ||Varies; up to 1700 per 5 mL |
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.
Theobromine (3,7-dimethylxanthine) is found in the seeds of Theobroma cacao, from which chocolate and cocoa are derived, and Camellia 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.5
Caffeine is most commonly consumed orally; however, it can be administered rectally or parenterally. Theophylline is usually taken orally as an elixir or as an extended-release or controlled-release tablet, although its absorption may be affected by food. Controlled-release tablets can result in erratic or delayed absorption. Theophylline can also be administered IV as aminophylline.
All methylxanthines are rapidly absorbed with early peak levels, cross the blood–brain barrier and placenta, and are excreted in breast milk (Table 192-2). Half-lives are only accurate at therapeutic concentrations and vary according to drug level, age extremes, smoking, organ system dysfunction (e.g., cirrhosis), infection, and cytochrome P450 inhibition (Table 192-3).