High-performance liquid chromatographic determination of dimethylxanthine metabolites of caffeine in human plasma

Measurement of caffeine and its three primary metabolites in human plasma by HPLC-ESI-MS/MS and clinical application

Caffeine is a mild stimulant with significant potential for abuse, being consumed in larger doses with the widespread availability of energy drinks and by novel routes of administration such as inspired powder, oral sprays and electronic cigarettes. How these recent changes in caffeine consumption affecting caffeine disposition and abuse potential is of growing concern. In the study of caffeine disposition in humans, it is common to only measure the caffeine concentration; however, caffeine's three major metabolites (paraxanthine, theobromine and theophylline) retain central nervous system stimulant activity that may contribute to the overall pharmacological activity and toxicity. Therefore, it would be scientifically more rigorous to measure caffeine and its major metabolites in the evaluation of caffeine disposition in human subjects. Herein, we report a method for the simultaneous quantification of caffeine and its three major metabolites in human plasma by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry (HPLC-ESI-MS/MS). Human plasma samples were treated by simple protein precipitation and the analytes were separated using a 6 min gradient program. Precision and accuracy were well within in the 15% acceptance range. The simple sample preparation, short runtime, sensitivity and the inclusion of caffeine's major metabolites make this assay methodology optimal for the study of caffeine's pharmacokinetics and pharmacodynamics in human subjects.

Determination of urinary methylated purine pattern by high-performance liquid chromatography

We describe the group selective separation and quantification of unmodified and modified purines in human urine by high-performance reverse phase liquid chromatography. The pattern of oxypurines and methylated purines: hypoxanthine (Hx), xanthine (X), 1-methyl hypoxanthine (1-MHx), 1-methyl guanine (1-MG), 3-methyl guanine (3-MG), 7-methyl guanine (7-MG), 1-methyl xanthine (1-MX), 3-methyl xanthine (3-MX), 7-methyl xanthine (7-MX), 1,7-dimethyl guanine (1,7-dMG), 1,3-dimethyl xanthine (1,3-dMX), 1,7-dimethyl xanthine (3,7-dMX) and 1,3,7-trimethyl xanthine (1,3,7-tMX) were determined in a single run in urine of a healthy subject and a gout patient before and after treatment with allopurinol. This method may be useful to investigate the urinary pattern of methylated bases in diseases involving purine metabolism.

The confirmation and control of metabolic caffeine in standardbred horses after administration of theophylline

The origin of caffeine detections in equine serum and urine after theophylline administrations was examined. Three different preparations containing theophylline were administered to standardbred mares. Both blood and urine samples were collected. Caffeine was detected and quantified in theophylline administration samples by high performance liquid chromatography (HPLC) and liquid chromatography-tandem mass spectrometry (LC-MS-MS). Further in vitro analysis showed that caffeine metabolites were not detected when caffeine, or caffeine-containing products, were added to urine. Data derived from HPLC-UV and LC-MS-MS analysis of dosages of theophylline and caffeine are used to propose the establishment of a threshold limit to control and discern between metabolic and administered caffeine concentrations. A serum caffeine concentration of 250 ng/mL and a urine caffeine concentration of 1000 ng/mL are suggested. Based on the data supplied, these threshold concentrations could effectively control orally administered caffeine in racehorses, up to the dosage used in this work, up to 72 h before sampling time.

Different mass spectrometric approaches in the identification of endogenous methylated purine bases in urine extracts

A preliminary identification of endogenous and exogenous methylated purine bases in urinary extracts of healthy and tumor-bearing subjects has been performed using high performance liquid chromatography, and tandem mass spectrometry (MS/MS). MS/MS gave particularly fast and sensitive analyses, allowing the simultaneous and rapid determination of 26 different urinary methylated purines. Both sets of data confirm that tumor-bearing patients show changed levels of methylated purine bases.

Simultaneous determination of caffeine and its primary demethylated metabolites in human plasma by high-performance liquid chromatography

An improved high-performance liquid chromatographic method for the simultaneous determination of caffeine and its three primary metabolites (theophylline, theobromine and paraxanthine) in human plasma is described. The four substances were separated on a reversed-phase column (5 microns TSK gel ODS-80TM, 150 mm x 4.6 mm I.D.) by use of the mobile phase methanol-0.1 M NaH2PO4 (30:70, v/v) with a flow-rate of 0.8 ml/min. Absorbance was monitored at 274 nm. The detection limit was 5 ng/ml for theobromine and caffeine and 10 ng/ml for paraxanthine and theophylline. The linearity and reproducibility were sufficient for drug monitoring of caffeine and its primary methylxanthines.

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.

High performance liquid chromatographic determination of methylxanthines in canine serum, gastric and pancreatic juices

A convenient high performance liquid chromatographic method for the determination of methylxanthines in biological samples is described. Separation was achieved by reversed phase chromatography using a mobile phase consisting of tetrahydrofuran + methanol + 0.01M potassium dihydrogen phosphate, pH 3.5 (1:20:79, v/v/v), on a 7 microns C18 column and a C18 Lichrosorb precolumn at a flow rate of 0.8 mL/min. Levels varying from 0.25-16 mg/L could be detected by UV at 280 nm. In this range, standard curves were established for 4 methylxanthines: theobromine, paraxanthine, theophylline and caffeine in 4 media: mobile phase, serum, gastric and pancreatic juices, and were found to be linear (r greater than or equal to 0.9975). Overall characteristics of the method were determined as: percent recovery (89.54%), accuracy (greater than or equal to 99.4%) and reproducibility (greater than or equal to 95%). Retention times ranged from 4.21 +/- 0.01 (1-methyluric acid) to 10.8 +/- 0.03 min (caffeine). Animal experiments (5 and 10 mg/kg boluses) were used to determine caffeine half life in dog's blood (310 +/- 46 and 453 +/- 59 min, respectively) and its secretion into pentagastrin stimulated gastric juice (mean concentrations 2.51 and 6.04 mg/L; mean outputs 351 and 1206 micrograms/2.25 h; both statistically different at p less than 0.001 level).

Assessment of hepatic function. Comparison of caffeine clearance in serum and saliva during the day and at night

Hepatic microsomal function was assessed by a caffeine clearance test at night and during the day using saliva and serum samples obtained simultaneously. In 26 patients with cirrhosis, 21 patients with noncirrhotic liver disease and 15 control subjects caffeine elimination correlated well during the day and at night (r = 0.915 for serum and 0.917 for saliva). The correlation coefficients for caffeine clearance in saliva and serum were 0.940 during the day and 0.963 overnight. In the cirrhotic patients, clearance differed significantly from noncirrhotic liver disease and controls in saliva samples overnight: 0.51 +/- 0.45 ml/min per kg versus 0.91 +/- 0.44 and 1.41 +/- 0.56, respectively. Comparable results were obtained for serum clearance overnight and clearances during the day. Serum and saliva clearances at night correlated well with the aminopyrine breath test (rs = 0.884 and 0.907, respectively). Overnight caffeine clearance in saliva might be a simple useful method for assessing progression and prognosis of liver disease.

Methylxanthines: toxicity to humans. 2. Caffeine

While there are several comprehensive reviews on the toxic effects of methylxanthines in animals, data on the toxicity of these chemicals in humans has not been extensively reviewed in one document. In a previous paper (Stavric, Fd Chem. Toxic. 1988, 26, 541), the toxicity of theophylline was reviewed. This paper, the second of three, is intended to provide an overview of the human toxicity of caffeine. Only pertinent and recent information on caffeine toxicity is summarized. In addition, some information regarding the benefits of caffeine and the mechanism of its effects is also provided. The use, effects and toxicity of caffeine intake are reviewed separately for different segments of the population. Controversy concerning the possible association of caffeine with fibrocystic disease of the breast and over the behavioural effects of the drug is presented briefly.

Methylxanthines: toxicity to humans. 1. Theophylline

While there are several comprehensive reviews on the toxic effects of theophylline, caffeine and theobromine in animals, data on the toxicity of these methylxanthines in humans have not been extensively reviewed in one document. This question will be addressed in a series of three papers. This paper provides an overview of the human toxicity of theophylline. Only pertinent and recent information on theophylline toxicity is summarized. In addition, some information regarding the use and benefits of theophylline, the mechanism of its effects and factors that affect variability in its clearance and half-life is also provided. Some problems in the analytical methodology of theophylline, problems that may be responsible for the controversy in the reported dose-response effects, are critically reviewed.

Overnight salivary caffeine clearance: a liver function test suitable for routine use

The feasibility of measuring caffeine clearance from saliva (SCl) was assessed in ambulatory patients with liver disease and in a control group, and the results were compared with quantitative liver function tests. For this purpose, the subjects were given 280 mg caffeine p.o. in decaffeinated coffee powder between noon and 4 p.m., and caffeine concentrations were measured in saliva (using an enzyme immunoassay) before bedtime and upon arising. In the cirrhotics (n = 29), SCl was 0.58 +/- S.D. 0.45 ml per min X kg, thus being reduced to approximately one-third of drug-free, nonsmoking controls (1.53 +/- 0.46, n = 18); although patients with noncirrhotic liver disease showed intermediate values (0.95 +/- 0.47), their reduction in SCl was significant (p less than 0.001). SCl was correlated with indocyanine green fractional clearance, galactose elimination capacity and aminopyrine breath test; however, the closest relationship (Rs = 0.80) was observed with the aminopyrine breath test. It is suggested that the measurement of SCl represents a noninvasive and innocuous procedure for quantifying hepatic microsomal function, and is suitable for routine use. Since a.m. saliva concentrations of caffeine are highly correlated (Rs = -0.94) with SCl, further simplification of the test to a single-point measurement appears possible.

Fasting plasma caffeine concentration. A guide to the severity of chronic liver disease

Fasting plasma caffeine concentrations (FPCC) were measured in 86 outpatients being examined for suspected or known liver disease. Seven patients (8%) who avoided caffeine consumption had nonmeasurable FPCC; they were dropped from further consideration. The remaining 79 subjects were divided into 4 diagnostic groups: surgical shunt (n = 11); alcoholic, posthepatitic, or primary biliary cirrhosis (n = 29); miscellaneous liver disease (n = 23); and normal liver (n = 16). FPCC was highest (mean, 17.8 mumol/l) in the shunt group, followed by the cirrhosis (12.3), miscellaneous liver diseases (4.6), and normal liver (2.1) groups. FPCC seemed to reflect severity of functional impairment, further supported by highly significant correlations with quantitative liver function tests, such as aminopyrine breath test (Rs = -0.89; n = 66), indocyanine green disappearance (Rs = -0.85; n = 65), and galactose elimination capacity (Rs = -0.70; n = 75). A careful dietary history showed no significant difference in caffeine consumption among the groups. It is suggested that in regular coffee drinkers FPCC might serve as a simple and convenient guide to the severity of functional impairment in chronic liver disease.