6136-37-4Relevant articles and documents
Metabolism of theophylline and its inhibition by fluoroquinolones in rat hepatic microsomes
Davis,Aarons,Houston
, p. 563 - 573 (1995)
1. The effects of β-naphthoflavone, dexamethasone, phenobarbitone and isosafrole on the metabolism of theophylline by rat liver microsomes have been studied. Only β-naphthoflavone, a known P4501A inducer, increased the rate of 1-methylxanthine formation (3-fold), whereas all the inducers studied increased the rate of 1,3-dimethyluric acid production (2.5-3-fold). 2. To study the effects of a range of fluoroquinolones on theophylline metabolism, β-naphthoflavone-induced microsomes mere used, as the ratio for metabolite production rates was similar to that of untreated microsomes (4:1,3-dimethyluric acid: 1-methylxanthine at 2 mM theophylline). High concentrations of fluoroquinolones (0.5-1.5 mM) were required to affect microsomal theophylline metabolism. 1-Methylxanthine was more sensitive to fluoroquinolone inhibition by enoxacin, ciprofloxacin, norfloxacin and pipemidic acid than 1,3-dimethyluric acid; CP67015, had a significant effect on 1,3-dimethyluric acid production only; binfloxacin had no effect on either pathway. 3. Ethoxycoumarin, a rapidly metabolized substrate, was also investigated as a surrogate for theophylline in in vitro experiments. Fluoroquinolone inhibition of ethoxycoumarin O-de-ethylation in β-naphthoflavone-induced microsomes was quantitatively greater but qualitatively similar to theophylline metabolism (IC(50s) 440-870 μM at 2 μM 7-ethoxycoumarin). 4. These data are comparable with previous rat experiments in vivo, indicating that enoxacin, ciprofloxacin and norfloxacin have similar intrinsic activity in the inhibition of theophylline metabolism.
Characterization of Human Cytochromes P450 Involved in Theophylline 8-Hydroxylation
Zhang, Zhi-Yi,Kaminsky, Laurence S.
, p. 205 - 212 (2007/10/03)
Studies were undertaken to determine which human P450 enzymes catalyze the metabolism of theophylline to 1,3-dimethyluric acid (1,3-DU), to facilitate predictions of theophylline drug-drug interactions, and to develop a noninvasive test for human P4501A2. Microsomes from a human cell line transfected individually with human P450 cDNAs for P4501A1, 1A2, 2A6, 2B6, 2C9, 2D6, 2E1, or 3A4 were used to demonstrate that only P4501A2 exhibited catalytic activity for theophylline metabolism to 1,3-DU with high affinity and low capacity (Km = 0.6 mM, Vmax = 37.8, pmol/min/mg), while P4502D6, 2E1, and 3A4 (Km = 14.4, 19.9, and 25.1 mM, respectively, and Vmax = 219.8, 646.4, and 20.8 pmol/min/mg, respectively) exhibited activities with low affinity and variable capacities. Correlations of rates of theophylline 8-hydroxylation to 1,3-DU with other P450 form-specific activities, in a series of ten human liver microsomal preparations, at 5 and 40 mM theophylline concentrations, revealed that at low concentrations the metabolism was catalyzed primarily by P4501A2, while at high substrate concentrations P4502E1 was primarily responsible for catalysis. The results with individually expressed P450s and hepatic microsomal preparations were consistent, indicating that the former system provides a qualitatively accurate reflection of the function of the heterogeneously expressed liver P450s. At pharmacologic theophylline concentrations achieved in vivo, its metabolism must thus be catalyzed primarily by P4501A2.
General synthesis and properties of 1-monosubstituted xanthines
Muller
, p. 125 - 128 (2007/10/02)
A general convenient synthesis of 1-monosubstituted xanthines (7H-imidazo[4,5-d]pyrimidine-2,6(1H,3H)-diones), starting from 3-substituted 6-aminouracils, is described. After conversion of the 6-aminouracils to the corresponding 5,6-diaminouracils, reaction with formic acid, or with triethyl orthoformate, leads to the novel xanthines in good to excellent yields, while ring closure in alkaline medium, which is commonly used in xanthine synthesis, is not successful.
