Yesair D W, Branfman A R, Callahan M M
Prog Clin Biol Res. 1984;158:215-33.
The human disposition of caffeine, theophylline, and theobromine is essentially characterized by rapid and complete gastrointestinal absorption; minimal first pass metabolism; distribution throughout the total body water; extensive and, in the case of caffeine almost complete, biotransformation in the liver; and elimination of metabolites from the body via the kidneys. Methylxanthine metabolism is affected by such factors as diet, smoking, pregnancy, use of oral contraceptives, age, and disease state. These factors have been studied extensively in relationship to caffeine disposition, less so for theophylline, and minimally for theobromine as well as the metabolites of these compounds, in particular paraxanthine and the diaminouracils. The facts that the loss of the 3-methyl group from caffeine to form 1,7-dimethylxanthine (paraxanthine) is the preferential path of metabolism in humans and that an acetylated diaminouracil is one of the major end-products of caffeine metabolism would indicate the need for additional studies of these compounds. The variability often associated with caffeine disposition may be in part genetic in origin since the population is generally biomodally distributed in its ability to acetylate molecules possessing an amino functional group. In addition, caffeine metabolism may be useful as a diagnostic tool to determine an individual's ability to acetylate and thus eliminate potentially harmful compounds from the body, as well as a measure of liver function in terms of enzymatic metabolizing ability.
咖啡因、茶碱和可可碱在人体内的代谢特点主要包括：胃肠道吸收迅速且完全；首过代谢极小；分布于全身水分中；在肝脏中广泛进行生物转化，咖啡因几乎完全转化；通过肾脏从体内清除代谢产物。甲基黄嘌呤的代谢受饮食、吸烟、妊娠、口服避孕药的使用、年龄和疾病状态等因素影响。这些因素与咖啡因代谢的关系已得到广泛研究，对茶碱的研究较少，对可可碱及其这些化合物的代谢产物，特别是对黄嘌呤和二氨基尿嘧啶的研究更少。咖啡因失去3 - 甲基形成1,7 - 二甲基黄嘌呤（对黄嘌呤）是人体内优先的代谢途径，且乙酰化二氨基尿嘧啶是咖啡因代谢的主要终产物之一，这些事实表明需要对这些化合物进行更多研究。与咖啡因代谢相关的变异性可能部分源于遗传，因为人群在乙酰化具有氨基官能团分子的能力上通常呈双峰分布。此外，咖啡因代谢可作为一种诊断工具，用于确定个体乙酰化并从而从体内清除潜在有害化合物的能力，以及作为衡量肝脏酶促代谢能力的肝功能指标。
