Pharmacokinetics of theophyline metabolites in 8 Chinese patients

目的：研究病人常规剂量茶碱治疗后代谢物的动力学．方法：病人静滴茶碱（６６μｍｏｌ·ｋｇ－１）．ＨＰＬＣ法测定给药前后２４ｈ茶碱及其代谢物：１，３二甲基尿酸（ＤＭＵＡ），３甲基黄嘌呤（３ＭＸ），１甲基尿酸（ＭＵＡ），中间代谢产物１甲基黄嘌呤（１ＭＸ）的浓度．结果：ＤＭＵＡ是代谢物中浓度最高的．３ＭＸ的清除速率最低．１ＭＸ很快转化成ＭＵＡ，体内浓度很低，但是，翌晨，１ＭＸ又回升到一个较高的浓度（从００４μｍｏｌ·Ｌ－１上升到１０５μｍｏｌ·Ｌ－１）．结论：ＤＭＵＡ是茶碱的主要代谢产物；在夜间１ＭＸ浓度积蓄，这是茶碱在夜间消除率下降的原因之一．     

应用咖啡因作为探针研究中国人N——乙酰化酶多态性

本研究探讨了咖啡因代谢物在Ｎ－乙酰化酶活怀评价中的意义。用ＨＰＬＣ法测定咖啡因代谢物，所有代谢物均能良好分离。以５－乙酰胺基－６－甲酰胺基－３－甲基尿嘧啶（ＡＦＭＵ）和１－甲基黄嘌呤（１Ｘ０摩尔浓度幽会作为评价Ｎ－乙酰化酶的代谢指标。对１２０名志愿者进行了Ｎ－乙酰化酶多态性分析，受试者可明显划分为快乙酰化和慢乙酰化者，快、慢、乙酰化表型之比为１００：２０。与同时用磺胺二甲嘧作为探针进行乙酰化乙型的     

汉族儿童N—乙酰化代谢表型分布及其与21—三体综合征和假肥大性肌营养不良症相关性研究

目的 以咖啡因为代谢探针，研究汉族儿童Ｎ－乙酰化代谢表型分布规律及其与２１－三体综合征（ＤＳ）和假肥大性肌营养不良症（ＤＭＤ）相关性。方法 根据参试者尿中咖啡因代谢物５－乙酰氨基－６－甲酰氨基－３－甲基尿嘧啶（ＡＦＭＵ）和甲磺嘌呤（１Ｘ）峰高比的对数值（１ｇＡＦＭＵ／１Ｘ）绘制频率分布直方图，寻找区分快、慢乙酰化代谢表型的截点，确定患儿和健康儿童的Ｎ－乙酰化代谢表型分布。结果 正常儿童乙酰化代谢表型分布直方图呈双态性，截点明显，为 ０．２５（ｌｇＡＦＭＵ／１Ｘ），慢乙酰化代谢表型个体为１６．９％，而 ＤＳ和ＤＭＤ患儿则分别为４１．９％和５０％（ｘ２分别为８．２８７和１１．３８７，Ｐ＜０．０５）。男、女和＞６岁与≤６岁儿童快、慢乙酰化代谢表型分布差异无显著性。结论 汉族儿童乙酰化代谢表型分布呈多态性，与成人相似。年龄和性别对结果无显著影响。     

4,5—二氢—6—[（苯乙酰基—哌嗪基）苯基]—5—甲基—3（2H）—哒…

４，５－二氢－６－［（苯乙酰基－哌嗪基）苯基］－５－甲基－３（２Ｈ）－达嗪酮（ＳＭⅡ４）０．１－２．５μｍｏｌ．Ｌ＾－＾１能使血小板激活因子（ＰＡＦ）及血栓素Ａ２类似物Ｕ４６６１９诱导的兔血小板聚集剂量一效应曲线左移且最大反应降低。其ｐＤ２分别为６．０±ｓ０．４及６．１±ｓ０．３．ＳＭⅡ４还能抑制ＡＤＰ，花生四烯酸（ＡＡ）及Ｕ４６６１９诱导的人血小板聚集，其ＩＣ５０分别是１．２，１．３及１．６．．     

ND－60 氨氯地平马来酸盐

ＮＤ－６０氨氯地平马来酸盐（ＡｍｌｏｄｉｐｉｎｅＭａｌｅａｔｅ）２－［（２－氨基乙氧基）甲基］－３－乙氧羰基－４－（２－氯苯基）－５－甲氧羰基－６－甲基－１，４－二氢吡啶马来酸盐ＥｕｒＰａｔＡＰＰｌ１９８３：８９１６７（ＵＳ１９８６：４５７２９０９）...     

Modulation of cyclothiazide on the glutamate receptor/NO/cyclic GMP pathway in the hippocampus of freely-moving rats

通过活体微透析的方法研究了环噻嗪对大鼠海马谷氨酸受体／ＮＯ／ｃＧＭＰ通路的影响．局部灌流α－氨基羟甲基异唑丙酸（ＡＭＰＡ）受体脱敏阻断剂环噻嗪能引起细胞外ｃＧＭＰ水平的提高．环噻嗪的这种作用能够被ＮＯ合酶抑制剂Ｎ－硝基－Ｌ－精氨酸（Ｌ－ＮＮＡ）或选择性的可溶性鸟苷酸环化酶抑制剂１Ｈ－［１，２，４］二唑［４，３－ａ］喹喔啉－１－酮（ＯＤＱ）所阻断．在环噻嗪灌流过程中，大鼠呈现明显的痉挛前的行为变化湿狗样反应（ＷＤＳ）．由环噻嗪引起的ｃＧＭＰ增加和ＷＤＳ反应能够被Ｎ－甲基－Ｄ－天冬氨酸（ＮＭＤＡ）受体通道阻断剂甲基二苯并环庚烯亚胺（ＭＫ－８０１）或镁离子所阻断．ＡＭＰＡ受体拮抗剂６，７－二硝基喹喔啉－２，３－二酮（ＤＮＱＸ）和２，３－二羟基－６－硝基－７－氨磺酰基－苯并（ｆ）－喹喔啉（ＮＢＱＸ）可拮抗ＷＤＳ反应，但不能阻断环噻嗪引起的ｃＧＭＰ反应．这种结果表明：（１）在海马内与ＮＯ－ｃＧＭＰ通路有关的ＡＭＰＡ受体由于内源性谷氨酸的存在保持部分脱敏状态．（２）环噻嗪对ＡＭＰＡ受体脱敏的阻断作用可导致内源性ＮＭＤＡ受体的激活．     

4，5－二氢－6－［（苯乙酰基－哌嗪基）苯基］－5－甲基－3（2H）－哒嗪酮对血小板聚集，花生四烯酸代谢及cAMP含量的影响

４，５－二氢－６－［（苯乙酰基－哌嗪基）苯基］－５－甲基－３（２Ｈ）－达嗪酮（ＳＭＤ。）０．１一２．５ｐｍｏｌ·Ｌ能使血小板激活因子（ＰＡｎ及血栓素Ａ，类似物Ｕ４６６１９诱导的兔血小板聚集剂量一效应曲线不移且最大反应降低。其ｐＤ２分别为６．０±ｓ０．４及６．１±ｓ０．３ＳＭⅡ４还能抑制ＡＤＬ花生四烯酸（ＡＡ）及Ｕ４６６１９诱导的人血小板聚集，其ＩＣ（５０）分别是１２，１３及１．６μｍｏｌ．Ｌ．用放射性薄层层折及放射免疫测定法分别检测血小板ＡＡ代谢产物及ｃＡＭＰ含量表明，ＳＭⅡ４对血小板ＡＡ代谢没有显著影响，但能剂量依赖性地升高血小板内ｃＡＭＰ含量，ＰＡＦμｍｏｌ·Ｌ不能改变此作用     

2－甲基－5－巯基－1，3，4－噻二唑的合成

２－甲基－５－巯基－１，３，４－噻二唑的合成李敬芬，王旭，黄剑（佳木斯医学院药学系黑龙江１５４００２）ＳＹＮＴＨＥＳＩＳＯＦ２－ＭＥＴＨＹＬ－５－ＭＥＲＣＡＰＴＯ－１，３，４－ＴＨＩＡＤＩＡＺＯＬＥ￥ＬＩＪｉｎｇ－Ｆｅｎ；ＷＡＮＧＸｕ；ＨＵＡＮＧＪｉ...     

阿片类药物在豚鼠离体回肠中的交互依赖性和交互耐受性

研究了阿片类药物在豚鼠离体回肠中的交互依赖性和交互耐受性．豚鼠回肠分别与羟甲芬太尼（ＯＭＦ１ｎｍｏｌ·Ｌ－１），Ｄ－Ａｌａ２，Ｄ－Ｌｅｕ５－脑啡肽（ＤＡＤＬＥ，０．３μｍｏｌ·Ｌ－１）或Ｕ５０４８８Ｈ（５０ｎｍｏｌ·Ｌ－１）在３７℃温育４ｈ，它们相互及自身均能抑制纳洛酮（０．１μｍｏｌ·Ｌ－１）或Ｍｒ２２６６（０．１μｍｏｌ·Ｌ－１）引起的戒断性收缩．它们也能自身预先阻断戒断性收缩的产生．Ｕ５０４８８Ｈ能预先阻断ＯＭＦ，ＤＡＤＬＥ温育后纳洛酮所产生的戒断性收缩，但后两者不能预先阻断Ｕ５０４８８Ｈ温育后由Ｍｒ２２６６所产生的戒断性收缩，并且ＯＭＦ和ＤＡＤＬＥ之间也不能相互阻断．豚鼠回肠分别与ＯＭＦ（１ｎｍｏｌ·Ｌ－１），ＤＡＤＬＥ（０．３μｍｏｌ·Ｌ－１）在３７℃温育２ｈ后，对去甲吗啡（ＮＭ），ＯＭＦ，ＤＡＤＬＥ的敏感性明显下降，浓度反应曲线右移，但对Ｕ５０４８８Ｈ不产生耐受．在Ｕ５０４８８Ｈ（１０ｎｍｏｌ·Ｌ－１）中温育１ｈ的回肠，对Ｕ５０４８８Ｈ的敏感性下降，浓度反应曲线右移，但对ＯＭＦ，ＮＭ，ＤＡＤＬＥ的敏感性不变．这些结果表明豚鼠回肠中μ，κ阿片受体是分离的．     

O^6—苄基鸟嘌呤增强BCNU体积小和体内抗肿瘤作用的研究

探讨Ｏ＾６－苄基鸟嘌呤（Ｏ＾６－ＢＧ）对Ｏ＾６－烷基鸟嘌呤－ＤＮＡ烷基转移酶（Ｏ＾６－ＡＧＴ）阳性（或ｍｅｒ＋）的人胃癌细胞ＢＧＣ－８２３和人肝癌细胞ＳＭＭＣ－７７２１对ＢＣＮＵ细胞毒作用敏感性的影响及其与ＢＣＮＵ合用治疗移植瘤的协同效果。方法：应用ＭＴＴ试验检测Ｏ＾６－ＢＧ与ＢＣＮＵ合用的细胞毒作用，转移酶活性用从＾３Ｈ－甲基ＤＮＡ底物转移的Ｏ＾６－［＾３Ｈ］甲基鸟嘌呤数表示。结果：１．５￣６．     

Nonlinear metabolic disposition of theophylline

Eleven healthy volunteers were given maintenance treatment with oral theophylline in increasing doses (210-1,260 mg/day). Seven subjects took four different doses, three subjects took three doses and one subject discontinued treatment after only two doses. Plasma and urine were collected during a dose interval at steady state. Theophylline in plasma and urine and metabolites in urine (1-methyluric acid, 1-MU; 3-methylxanthine, 3-MX; 1,3-dimethyluric acid, DMU) were determined by high-performance liquid chromatography. Total clearance of theophylline as well as clearances to all three metabolic products (but not theophylline renal clearance) decreased with increasing dose. The individual Michaelis-Menten parameters Km and Vmax could be estimated for six subjects who took all four doses. Considerable interindividual variability in these parameters and particularly Km:s was found. The Km for overall elimination averaged 133 mumol/L (range 55-213 mumol/L) and the Vmax 611 mumol/h (2,640 mg/day; range 452-813 mumol/h). With regard to individual metabolic routes, the Km for theophylline metabolism to 1-MU was 88 +/- 41 (mean +/- SD) mumol/L and the Vmax was 110 +/- 15 mumol/h; the Km for metabolism to 3-MX was 90 +/- 37 mumol/L and the Vmax was 78 +/- 13 mumol/h; the Km for metabolism to DMU was 179 +/- 92 mumol/L and the Vmax was 357 +/- 122 mumol/h. The Km values for the N-demethylation pathways (1-MU and 3-MX) were significantly correlated (r = 0.95; p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of decursinol angelate on the pharmacokinetics of theophylline and its metabolites in rats

Herb-drug interactions represent a serious problem as herbal medicine is used extensively in the modern world. This study investigated the effects of decursinol angelate on the pharmacokinetics of theophylline, a typical substrate of the cytochrome P450 1A2 enzyme, in rats. After 3 days of decursinol angelate pretreatment, on the fourth day, rats were administered decursinol angelate and theophylline concomitantly. Blood theophylline and its major metabolite [1-methylxanthine (1-MX), 3-methylxanthine (3-MX), 1-methyluric acid (1-MU), and 1,3-dimethyluric acid (1,3-DMU)] levels were monitored by liquid chromatography-tandem mass spectroscopy. The results indicated that theophylline clearance significantly decreased and the area under the concentration–time curve (AUC) increased in decursinol angelate (25 mg/kg)-pretreated rats administered theophylline (10 mg/kg). The elimination half-life (t1/2) of theophylline was increased by 20%. In the presence of decursinol angelate (25 mg/kg), the pharmacokinetic parameters of three metabolites (1-MX, 1,3-DMU, and 1-MU) were significantly altered (half-life for 1-MU, and AUC24 h for 1-MX, 1,3-DMU, and 1-MU). Our results suggest that patients receiving CYP1A2-metabolized drugs, such as caffeine and theophylline, should be advised of the potential herb-drug interaction to reduce the risk of therapeutic failure or increased toxicity of conventional drug therapy.     

Theophylline metabolism by human, rabbit and rat liver microsomes and by purified forms of cytochrome P450

The capacity of human, rabbit and rat liver microsomes and purified isozymes of cytochrome P450 to metabolize theophylline has been assessed. In all three species the 8-hydroxylation of theophylline to 1,3-dimethyluric acid (1,3-DMU) was the major pathway. In human, control rabbit and rat liver microsomes this metabolite accounted for 59, 77 and 94%, respectively, of the total metabolites formed. In both human and control rabbit liver microsomes the N-demethylation of theophylline to 1-methylxanthine (1-MX) accounted for 20% of the total metabolites formed. N-demethylation of theophylline to 3-methylxanthine (3-MX) accounted for 21% of theophylline metabolism in human microsomes but was a minor pathway in control rabbit and rat microsomes. Acetone and phenobarbitone pretreatment markedly increased the formation of 1,3-DMU by rabbit liver microsomes. Rifampicin and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) administration caused a slight but significant increase in this pathway. In general the N-demethylation pathways in rabbit liver microsomes were refractory to induction. In the rat, the metabolism of theophylline to 1-MX, 3-MX and 1,3-DMU were all significantly increased in Aroclor 1254, dexamethasone, phenobarbitone and 3-methylcholanthrene-treated microsomes. In reconstitution experiments the polycyclic hydrocarbon inducible rabbit cytochrome P450 Forms 4 and 6 and the constitutive Form 3b all metabolized theophylline to its three metabolites. In human liver microsomes from four subjects anti-rabbit cytochrome P450 Form 4 IgG inhibited the metabolism of theophylline to 1-MX, 3-MX and 1,3-DMU by approximately 30%. These data indicate that theophylline is metabolized by multiple forms of cytochrome P450 in human, rabbit and rat liver microsomes.     

Dose dependent pharmacokinetics of theophylline: Michaelis-Menten parameters for its major metabolic pathways.

Dose Dependency for pharmacokinetics of theophylline and the formation of its major metabolites, 3-methylxanthine (3-MX); 1-methyluric acid (1-MU); 1,3-dimethyluric acid (DMU), were examined by administering three single oral doses (250, 375, 500 mg) of theophylline to six healthy adult volunteers. The serum and urine concentrations of theophylline and the metabolites in serum and urine were determined by high-performance liquid chromatography. Total clearance of theophylline decreased and its half life increased over the range of doses administered (p<0.01). There was a significant dose related decrease in the fractional recovery of 3-MX and 1-MU (p<0.001) and a dose related increase in fractional excretion of DMU and unchanged theophylline (p<0.01 and p<0.001 respectively). No significant dose related changes were observed in the renal clearance of 3-MX, 1-MU and DMU, indicating linear urinary excretion kinetics of the metabolites. Theophylline metabolic clearance to 3-MX as well as to 1-MU decreased with increasing dose but clearance to DMU remained unnaffected by the size of dose. The individual Michaelis-Menten parameters Km and Vmax were estimated for six subjects receiving three different single doses. The Km values for theophylline metabolism to 3-MX, 1-MU and DMU were 2.4+/-0.6, 5.1+/-1.8+/- and 112.3+/-36.8 mg/L respectively and the Vmax values were 3.5+/-0.7, 7.5+/-2.6 and 112.3+/-36.8 mg/hr respectively. The Km values for the N-demethylation pathways (3MX and 1-MU) were lower corresponding to therapeutic serum concentrations of drug. These results suggest that the elimination kinetics of theophylline is nonlinear in the human in the therapeutic range of serum concenntrations and can be explained by saturable formation kinetics of 3-MX and 1-MU. In contrast to previous studies we didn't find obvious indication for nonlinear formation of DMU at therapeutic concentration range.     

反相HPLC法同时测定人尿中茶碱及其两种代谢产物

目的:建立一种同时测定人尿中茶碱及其1,3-二甲基尿酸(1,3-DMU)和3-甲基噻嗪(3-MX)代谢产物的HPLC方法.方法:尿样用异丙醇/二氯甲烷(2/8)混合液提取,有机相在空气吹干,用流动相复溶后进行HPLC分析.色谱柱为Diamonsil ODS C_(18)5 μm,150 mm×4.6 mm I.D),流动相由0.1%甲酸液和乙腈(95:5)组成,流速1.0 mL/min,测定波长280 nm.测定12名受试者单剂量和多剂量口服茶碱后24 h内尿中茶碱及其代谢物累计排泄量.结果:尿中茶碱及其代谢物1,3 DMU和3-MX的线性范围分别为0.312～40.0、0.156～20.0、0.078～10.μg/mL,最低可定量浓度分别为0.312、0.156、0.078μg/mL.批间和批内的变异小于15%,回收率大于70%.结论:该方法的特异性、灵敏度能够满足临床上对人尿中茶碱及其代谢产物同时测定的要求.     

Cytochrome P450 isoform selectivity in human hepatic theobromine metabolism

AIMS: The plasma clearance of theobromine (TB; 3,7-dimethylxanthine) is known to be induced in cigarette smokers. To determine whether TB may serve as a model substrate for cytochrome P450 (CYP) 1A2, or possibly other isoforms, studies were undertaken to identify the individual human liver microsomal CYP isoforms responsible for the conversion of TB to its primary metabolites. METHODS: The kinetics of formation of the primary TB metabolites 3-methylxanthine (3-MX), 7-methylxanthine (7-MX) and 3,7-dimethyluric acid (3,7-DMU) by human liver microsomes were characterized using a specific hplc procedure. Effects of CYP isoform-selective xenobiotic inhibitor/substrate probes on each pathway were determined and confirmatory studies with recombinant enzymes were performed to define the contribution of individual isoforms to 3-MX, 7-MX and 3,7-DMU formation. RESULTS: The CYP1A2 inhibitor furafylline variably inhibited (0-65%) 7-MX formation, but had no effect on other pathways. Diethyldithiocarbamate and 4-nitrophenol, probes for CYP2E1, inhibited the formation of 3-MX, 7-MX and 3,7-DMU by approximately 55-60%, 35-55% and 85%, respectively. Consistent with the microsomal studies, recombinant CYP1A2 and CYP2E1 exhibited similar apparent Km values for 7-MX formation and CYP2E1 was further shown to have the capacity to convert TB to both 3-MX and 3,7-DMU. CONCLUSIONS: Given the contribution of multiple isoforms to 3-MX and 7-MX formation and the negligible formation of 3,7-DMU in vivo, TB is of little value as a CYP isoform-selective substrate in humans.     

Effects of lansoprazole on pharmacokinetics and metabolism of theophylline

The effect of the new substituted benzimidazole proton pump inhibitor, lansoprazole, on pharmacokinetics and metabolism of theophylline has been studied in healthy adults given oral lansoprazole 30 mg once daily for 11 days. On Days 4 and 11 of 300 mg aminophylline was simultaneously administered orally and blood samples for theophylline analysis were taken over 24 h. Urine samples were collected for up to 24 h and were assayed for theophylline and its major metabolites 1,3-dimethyluric acid (1,3-DMU), 1-methyluric acid (1-MU) and 3-methylxanthine (3-MX). The pharmacokinetic parameters of theophylline were determined, and the urinary recovery of unchanged theophylline and its major metabolites were calculated.After administration of lansoprazole for 4 days, no significant alteration in the terminal elimination half-life (t _1/2) or the mean residence time (MRT) was detected. However, there was a significant decrease of about 13% in the area under the plasma concentration-time curve (AUC) and a significant increase of about 19% in the apparent clearance (CL_app). Lansoprazole treatment for 11 days caused a significant decrease of approximately 12% in t _1/2 and about 10% in the MRT of theophylline, although neither AUC nor CL_app showed a significant alteration. The excretion of 3-MX in the urine was significantly increased by about 20% after lansoprazole treatment for 4 and 11 days, although there was no significant alteration in the excretion of unchanged theophylline, 1,3-DMU or 1-MU.The results indicate that repeated administration of lansoprazole to humans induces the hepatic microsomal P-450-dependent drug oxidation system that mediates N-1-demethylation of theophylline, consequently increasing its metabolism.     

Characterization of human liver cytochromes P-450 involved in theophylline metabolism.

Theophylline is metabolized in the liver by one or more cytochrome P-450 enzymes. To assess the amounts and types of these human cytochromes P-450, we incubated theophylline with microsomes prepared from 22 different human livers in the presence of NADPH, and measured simultaneous rates of 1- and 3-N-demethylations to 3-methylxanthine (3-MX) and 1-methylxanthine (1-MX), respectively; and 8-hydroxylation to 1,3-dimethyluric acid (1,3-DMU). Under optimal conditions, 3-MX, 1-MX, and 1,3-DMU formation proceeded with mean Km values of 2.05, 1.93, and 5.34 mM and Vmax values of 2.28, 2.48, and 23.4 pmol/mg/min, respectively. Formation of 3-MX and 1-MX correlated best with amounts of the immunoreactive protein HLd (P-450IA2) (p less than 0.05), whereas formation of 1,3-DMU correlated with the microsomal content of HLp (P-450IIIA3) and HLj (P-450IIE1). In immunoinhibition experiments, incubations conducted with a polyclonal anti-rat P-450c/d antibody, the formation of all the three theophylline metabolites (p less than 0.05) was significantly inhibited. However, addition of isoform-specific anti-rat-P-450d antibodies to the microsomal mixture significantly inhibited 1-N-demethylation, selectively, with little (if any) inhibition of 3-N-demethylation or 8-hydroxylation. Nonspecific cytochrome P-450 inhibition was ruled out by showing that erythromycin N-demethylation, an activity catalyzed by HLp, was unaffected by either anti-P-450c/d (P-450IA1/IA2) or anti-P-450d. Anti-rat-P-450p antibodies failed to block formation of theophylline metabolism, but did inhibit erythromycin N-demethylase.(ABSTRACT TRUNCATED AT 250 WORDS)     

Renal clearance of theophylline and its major metabolites: Age and urine flow dependency in paediatric patients

Summary The renal clearance of theophylline (TH) and its metabolites 1,3-dimethyluric acid (1,3-DMU), 3-methylxanthine (3-MX), and 1-methyluric acid (1-MU) has been studied in 10 children aged 8 months to 14 years. Individual renal clearances were calculated from serum levels and amounts excreted in urine after i.v. administration of the parent drug. The clearance of 1,3-DMU was found to depend both upon urine flow rate and age, which are interrelated. An effect of urinary pH was expected, but was not studied. Consistent age-dependent changes in the relative quantities of metabolites excreted were not observed.     

Theophylline steady state pharmacokinetics is not altered by omeprazole

Summary The effect of omeprazole treatment on theophylline pharmacokinetics was studied in eight, non-smoking healthy male volunteers during repeated administration of a slow release formulation of theophylline. In a randomized double-blind cross-over study, the subjects received theophylline 5 mg·kg^–1 per day with omeprazole 20 mg per day or identical placebo during two periods, each of 7 days, separated by a washout period of 7 days.The oral clearance of theophylline remained unchanged whether it was administered alone or with omeprazole (54.2 ml·min^–1). The average urinary excretion of theophylline and its metabolites, 1,3 dimethyluric acid (1,3-DMU), 3-methylxanthine (3-MX), 1-methyluric acid (1-MU) amounted to 9%, 32%, 12% and 22% of the administered dose, respectively, and no significant change occured during concomitant treatment with omeprazole.Thus, the formation and clearance of the metabolites was not altered by omeprazole. Consequently, omeprazole in the recommended dose of 20 mg daily can safely be administered to patients on theophylline therapy.