Determination Of Caffeine In Plasma Research Articles

Effect of Venlafaxine on CYP1A2‐Dependent Pharmacokinetics and Metabolism of Caffeine

Venlafaxine is a clinically effective antidepressant. Caffeine is a metabolic probe for the quantitative measurement of CYP1A2 activity in vivo. This open-label study evaluated the effect of steady-state venlafaxine on CYP1A2-dependent metabolism, as measured by the pharmacokinetic disposition of caffeine, and urinary caffeine metabolite ratios (CMRs). Sixteen healthy subjects received 200 mg of caffeine orally before (Day 1) and after (Day 8) venlafaxine was titrated to steady-state (37.5 mg every 12 hours on Days 2-4, then 75 mg every 12 hours on Days 5-8). Samples were collected before and for 24 hours after caffeine dosing for the determination of caffeine in plasma and 1,7-dimethylxanthine, 3,7-dimethylxanthine, 1,7-dimethyluric acid (17U), 1-methylxanthine (1X) and 1-methyluric acid (1U), and 5-acetylamino-6-amino-3-methyluracil (AAMU) in urine. Blood samples were obtained before venlafaxine doses on Days 7 and 8 (morning dose only) for the determination of trough venlafaxine and O-desmethylvenlafaxine levels. Venlafaxine did not significantly alter the pharmacokinetics of caffeine and its metabolites. Plasma caffeine AUC was unchanged and remained within the bioequivalence criteria (90% confidence interval: 87.9%-102%) in the presence of venlafaxine. Urine metabolite data showed variable increases and decreases in the CMR [(AAMU + 1U + 1X)/17U] for individual subjects. However, the mean CMR was altered by < 10% in the presence of venlafaxine. This in vivo study demonstrated that venlafaxine did not alter the pharmacokinetic profile of caffeine and confirms in vitro data that venlafaxine does not inhibit CYP1A2 metabolism. Therefore, venlafaxine appears to have a relatively low potential for drug interactions based on CYP1A2 inhibition.

Rapid and sensitive gas-chromatographic determination of caffeine in blood plasma, saliva, and xanthine beverages

A gas chromatographic procedure is reported for the determination of caffeine in plasma, saliva, and xanthine beverages. Using a 75 cm column packed with OV-17, nitrogen-sensitive detection, and 1 ml samples, a suitable limit of analysis (coefficient of variation (CV) = 10.2%) of 50 ng/ml was obtained in plasma. Within-day CVs at caffeine concentrations of 0.1-0.5-2.0-7.5-15.0 micrograms/ml in plasma were 7.7-5.6-4.8-3.8-3.4%, respectively. The limit of detection, defined as the injected quantity of caffeine giving rise to a signal to noise ratio of 2, is 40 pg, corresponding to a plasma concentration of 1 ng/ml. The procedure involves addition of the internal standard 7-pentyl theophylline and alkaline extraction of the sample with dichloromethane. The method described rivals any gaschromatographic assay published so far in rapidness and accuracy. Plasma and saliva caffeine concentrations were determined in a healthy male volunteer after swallowing 400 ml of coffee. The calculated pharmacokinetic parameters, assuming complete absorption of caffeine from the G.I. tract, agree well with previously published values.

Determination of Caffeine in Plasma by Gas Chromatography

A gas chromatographic method has been developed for the rapid, precise, and specific determination of caffeine in plasma. The method overcomes the major drawbacks of previous methods for the determination of caffeine in body fluids, which were: difficult isolation from interfering materials, a substantial blank error and low sensitivity. A standard response curve relating the signal-height ratio of caffeine to that of an internal standard, hexobarbital, permits quantitation of the amount of caffeine present. The method involves extraction of caffeine from plasma with chloroform, after the aqueous phase was adjusted to pH 11.5–12.0. The chloroform extract was evaporated to dryness and the sample was redissolved in carbon disulfide. Two milliliters of plasma was used and caffeine was determined at a concentration of 0.25 mcg./ml.