Serum Caffeine Research Articles

High-throughput determination of theophylline and caffeine in human serum by conventional liquid chromatography-mass spectrometry

Automated high-performance liquid chromatography/mass spectrometry (HPLC-MS) with backflush column-switching was established for ultra-fast determination of theophylline and caffeine. A 400-μl portion of serum sample diluted with ultrapure water was injected and transferred to an Oasis HLB cartridge used as a precolumn for extraction. After switching the valves, the analytes trapped in the precolumn were eluted in the backflush mode and separated with a Chromolith Performance RP-18e column (C18-bonded monolithic silica); the compounds in column effluents were then detected by atmospheric pressure chemical ionization (APCI)-MS. The present method successfully provided high-throughput determination of theophylline and caffeine within 2 min. Satisfactory linearity, reproducibility, and sensitivity could be obtained for analysis of therapeutic and toxic levels of both compounds. Because of the very simple procedure and high throughput using the conventional HPLC system, the present method seems to have high potential in the fields of forensic toxicology and emergency medicine.

Caffeine Citrate Treatment for Extremely Premature Infants With Apnea: Population Pharmacokinetics, Absolute Bioavailability, and Implications for Therapeutic Drug Monitoring

The objective of this study was to develop a population model of the pharmacokinetics (PK) of caffeine after orogastric or intravenous administration to extremely premature neonates with apnea of prematurity who were to undergo extubation from ventilation. Infants of gestational age <30 weeks were randomly allocated to receive maintenance caffeine citrate dosing of either 5 or 20 mg/kg/d. Four blood samples were drawn at prerandomized times from each infant during caffeine treatment. Serum caffeine was assayed by enzyme-multiplied immunoassay technique. Concentration data (431 samples, median: 4 per subject) were obtained from 110 (52 male) infants of mean birth weight of 1009 g, current mean weight (WT) of 992 g, mean gestational age of 27.6 weeks, and mean postnatal age (PNA) of 12 days. Of 1022 doses given, 145 were orogastric, permitting estimation of absolute bioavailability. A 1-compartment model with first-order absorption was fitted to the data in NONMEM. Patient characteristics were screened (P < 0.01) in nested models for pharmacokinetic influence. Model stability was assessed by nonparametric bootstrapping. Clearance (CL) increased nonlinearly with increasing PNA, whereas volume of distribution (Vd) increased linearly with WT, according to the following allometric models: CL (L/h) = 0.167 (WT/70) (PNA/12); Vd (L) = 58.7 (WT/70). The mean elimination half-life was 101. Interindividual variability (IIV) of CL and Vd was 18.8 % and 22.3 %, respectively. Interoccasion variability (IOV) of CL and Vd was 35.1% and 11.1%, respectively. This study established that the elimination of caffeine was severely depressed in extremely premature infants but increased nonlinearly after birth up to age 6 weeks. Caffeine was completely absorbed, which has favorable implications for switching between intravenous and orogastric routes. The interoccasion variability about CL was twice the interindividual variability, which, among other factors, indicates that routine serum concentration monitoring of caffeine in these patients is not warranted.

The effect of caffeine ingestion on human neutrophil oxidative burst responses following time-trial cycling

Following fixed-duration exercise of submaximal intensity, caffeine ingestion is associated with an attenuation of the exercise-induced decline in N-formyl-methionyl-phenyl-alanine (f-MLP) stimulated neutrophil oxidative burst. However, the response following high-intensity exhaustive exercise is unknown. Nine endurance-trained male cyclists ingested 6 mg caffeine or placebo per kilogram of body mass 60 min before cycling for 90 min at 70% of maximal oxygen consumption ([Vdot]O2max) and then performing a time-trial requiring an energy expenditure equivalent to 30 min cycling at 70% maximum power output. Time-trial performance was 4% faster in the caffeine than in the placebo trial (P = 0.043). Caffeine was associated with an increased plasma adrenaline concentration after 90 min of exercise (P = 0.046) and immediately after the time-trial (P = 0.02). Caffeine was also associated with an increased serum caffeine concentration (P < 0.01) after 90 min of exercise and immediately after the time-trial, as well as 1 h after the time-trial. However, the f-MLP-stimulated neutrophil oxidative burst response fell after exercise in both trials (P = 0.002). There was no effect of caffeine on circulating leukocyte or neutrophil counts, but the lymphocyte count was significantly lower on caffeine (20%) after the time-trial (P = 0.003). Our results suggest that high-intensity exhaustive exercise negates the attenuation of the exercise-induced decrease in neutrophil oxidative burst responses previously observed when caffeine is ingested before exercise of fixed duration and intensity. This may be associated with the greater increase in adrenaline concentration observed in the present study.

Modest maternal caffeine exposure affects developing embryonic cardiovascular function and growth

Caffeine consumption during pregnancy is reported to increase the risk of in utero growth restriction and spontaneous abortion. In the present study, we tested the hypothesis that modest maternal caffeine exposure affects in utero developing embryonic cardiovascular (CV) function and growth without altering maternal hemodynamics. Caffeine (10 mg.kg(-1).day(-1) subcutaneous) was administered daily to pregnant CD-1 mice from embryonic days (EDs) 9.5 to 18.5 of a 21-day gestation. We assessed maternal and embryonic CV function at baseline and at peak maternal serum caffeine concentration using high-resolution echocardiography on EDs 9.5, 11.5, 13.5, and 18.5. Maternal caffeine exposure did not influence maternal body weight gain, maternal CV function, or embryo resorption. However, crown-rump length and body weight were reduced in maternal caffeine treated embryos by ED 18.5 (P < 0.05). At peak maternal serum caffeine concentration, embryonic carotid artery, dorsal aorta, and umbilical artery flows transiently decreased from baseline at ED 11.5 (P < 0.05). By ED 13.5, embryonic aortic and umbilical artery flows were insensitive to the peak maternal caffeine concentration; however, the carotid artery flow remained affected. By ED 18.5, baseline embryonic carotid artery flow increased and descending aortic flow decreased versus non-caffeine-exposed embryos. Maternal treatment with the adenosine A(2A) receptor inhibitor reproduced the embryonic hemodynamic effects of maternal caffeine exposure. Adenosine A(2A) receptor gene expression levels of ED 11.5 embryo and ED 18.5 uterus were decreased. Results suggest that modest maternal caffeine exposure has adverse effects on developing embryonic CV function and growth, possibly mediated via adenosine A(2A) receptor blockade.

Modulation of Adenosine-Induced Responses in the Guinea-Pig Trachea During Long-Term Caffeine Treatment: Possible Role of Epithelium

The responses to adenosine were studied on isolated, methacholine-precontracted tracheal strips of guinea pigs in the course of long-term caffeine or solvent treatment. Guinea pigs were fed caffeine for 10 weeks (average serum caffeine concentration: 39.1 ± 3.9 µM). In epithelium-intact tracheal preparations (EITPs), sensititization to adenosine-induced relaxation (AIR) developed. It attained a maximum in week 1 of caffeine treatment, and then its level diminished and disappeared completely by weeks 4 – 6. In epithelium-denuded tracheal preparations (EDTPs), an increase in the sensitivity to adenosine was observed from week 1 to week 10 (a 4 – 6-fold reduction in EC50). Use of a coaxial bioassay system confirmed the role of epithelium in this process. The enhancement of the AIR of the EITPs was not modified by inhibitors of cyclooxygenase and lipoxygenase. Following depletion of the neuropeptides by acute capsaicin pretreatment, the AIR of the EITPs was strongly enhanced after caffeine treatment for 6 weeks. In chronically caffeine-treated EITPs, the inhibition of neutral endopeptidase led to dramatic reduction of the AIR. On the basis of the results by inhibiting nitric oxide synthase, it can be supposed that nitric oxide released from EITPs of long-lasting caffeine-treated animals operated as a constrictor agent. Our results show that chronic caffeine treatment gives rise to an initial sensitization to adenosine of the EITPs, this being followed by the development of a specific adaptive process in the epithelial cells, which counterbalances the increased tracheal sensitivity to adenosine.

Serum Caffeine Concentrations in Preterm Neonates

Caffeine therapy reduces apnea of prematurity, promotes successful extubation from invasive positive-pressure ventilation, and decreases the incidence of bronchopulmonary dysplasia. The recommended dosing for caffeine is a loading dose of 20 mg/kg followed by a 5 mg/kg/d maintenance dose. However, controversy exists about the optimal dosing regimen and data on serum caffeine concentrations in extremely immature infants are scant. We determined serum caffeine concentrations approximately 7 days after starting therapy with a 20 or 25 mg/kg loading dose and a 6 mg/kg/d maintenance dose in 154 infants with a mean gestational age of 29 weeks. The 25th to 75th percentile range for the serum caffeine concentrations with the two dosing regimens was equivalent, approximately 18 to 23 mg/L. Within the first 14 postnatal days, the serum caffeine concentrations were not dependent on postmenstrual age, weight, or postnatal age, and were in a range that is safe and therapeutic. This latter observation remained valid over the ranges of clinical and laboratory assessments of renal and hepatic functions that are usually found in practice. Routine measurement of steady-state serum caffeine concentrations in infants 24 to 35 weeks gestational age is not required in the absence of ongoing apnea/hypopnea or signs compatible with toxicity.

Association of serum caffeine concentrations with serum glucose levels in caffeine-drug users and non-users ? results of German National Health Surveys

The purpose of this study was to explore the association of serum caffeine concentrations with serum glucose levels in caffeine-drug users and non-users, aiming at the chronic effects of caffeine on glucose metabolism in comparison with known acute effects of caffeine. Eight hundred and fourteen caffeine-drug users and 623 non-users were identified from German National Health Surveys. Their serum caffeine concentrations and glucose levels were measured. The associations of caffeine concentrations with glucose levels were established by correlation analysis and multivariable regression analysis in caffeine-drug users and non-users separately. Antidiabetic therapy was considered. Caffeine concentrations were closely positively correlated to serum glucose levels in caffeine-drug users (Spearman r = 0.117, p = 0.001; partial r = 0.102, p = 0.020) particularly in women (Spearman r = 0.155, p < 0.001; partial r = 0.150, p = 0.005) although the correlation was weak as shown by multivariable regression analysis. The serum glucose levels were significantly higher (5.403 +/- 0.033 vs. 5.306 +/- 0.037 mmol/l) whereas the magnesium level was significantly lower (0.8941 +/- 0.0026 vs. 0.9024 +/- 0.0030 mmol/l) in caffeine-drug users than in non-users. No associations of caffeine concentrations with serum glucose levels were found in any groups of caffeine-drug non-users in our study. Whereas acute intake of caffeine-drugs may impair glucose metabolism, chronic intake of caffeine exclusively from diet has little effects on glucose metabolism and therefore may not contribute to the risk reduction of type 2 diabetes that was found in recent coffee consumption studies.

Does caffeine modify corticomotor excitability?

Aims To test the influence of caffeine on the lower and upper motor neuron excitability. Methods In Experiment A, 18 healthy subjects received 200 mg of caffeine or placebo, in a randomized, double-blind, placebo-controlled design protocol. Mean F-waves amplitude, amplitude of the motor response evoked by magnetic stimulation (MEP), MEP duration, cortical silent period (CSP), central conduction time, and cortical threshold were evaluated. In Experiment B, 6 healthy controls received 400 mg of caffeine, the peripheral silent period (PSP) and CSP were evaluated. CSP was recorded bilaterally in biceps brachii (intensity 10% above threshold) and abductor digiti minimi (ADM) (intensity at 10% and 50% above threshold). Muscle contraction was above 50% of the maximum force in both experiments. Latencies were defined by a technician who was not aware of this investigation. Serum caffeine level was evaluated. Results In Experiment A, only the CSP, recorded in both ADM with intensity at 10% above threshold showed a significant change after caffeine (decrease of 17.1 ± 34.0 ms, about 12% reduction). In Experiment B, PSP did not change, but CSP tested with intensities 10% above threshold was significantly decreased by 20.8 ± 34.4 ms in ADM and 13.5 ± 13.8 ms in biceps (about 13 and 16%, respectively). Serum caffeine level clearly increased after consumption but no correlation could be found between these levels and CSP reduction. Conclusions In our investigation, caffeine elicited a consistent decrease of the CSP, suggesting that caffeine increases cortical neuronal excitability.

Effect of caffeine supplementation on the extracellular heat shock protein 72 response to exercise

The stimulus for the release of 72-kDa heat shock protein (HSP72) during exercise in humans is currently unclear. Recent evidence in an animal model is suggestive of an involvement of catecholamines. The present study, therefore, investigated the effect of caffeine supplementation, a known stimulator of sympathetic activity, on the extracellular (e)HSP72 response to prolonged exercise. Ten healthy male endurance-trained cyclists were recruited (age: 21 +/- 1 yr, maximum O(2) uptake 61.1 +/- 1.7 ml x kg(-1) x min(-1), mean +/- SE). Each subject was randomly assigned to ingest either 6 mg/kg body mass of caffeine (Caff) or placebo (Pla) 60 min before one of two 90-min bouts of cycling at 74 +/- 1% maximum O(2) uptake. Trials were performed at least 7 days apart in a counterbalanced design. Venous blood samples were collected by venepuncture at pretreatment, preexercise, postexercise, and 1 h postexercise. Serum caffeine and plasma catecholamines were determined using a spectrophotometric assay and high-performance liquid chromatography, respectively. Plasma HSP72 and cortisol were determined by ELISA. Serum caffeine concentrations were significantly increased throughout Caff, while no increases were detected in Pla. Caffeine supplementation and exercise was associated with a greater eHSP72 response than exercise alone (postexercise Caff 8.6 +/- 1.3 ng/ml; Pla 5.9 +/- 0.9 ng/ml). This greater eHSP72 response was associated with a greater epinephrine response to exercise in Caff. There was a significant increase in norepinephrine and cortisol, with no intertrial differences. The present data suggest that, in humans, catecholamines may be an important mediator of the exercise-induced increase in eHSP72 concentration.

Salivary IgA Responses to Prolonged Intensive Exercise following Caffeine Ingestion

Prolonged, intensive exercise is associated with a reduction in concentration and secretion of salivary IgA (s-IgA). Saliva composition and secretion are under autonomic nervous system control, and caffeine ingestion, a widespread practice among athletes for its ergogenic properties, is associated with increased sympathetic nervous system activation. Therefore, this study investigated the influence of caffeine ingestion on s-IgA responses to prolonged, intensive exercise. In a randomized crossover design, 11 endurance-trained males cycled for 90 min at 70% VO2peak on two occasions, having ingested 6 mg x kg(-1) body mass of caffeine (CAF) or placebo (PLA) 1 h before exercise. Whole, unstimulated saliva samples were collected before treatment (baseline), preexercise, after 45 min of exercise (midexercise), immediately postexercise, and 1 h postexercise. Venous blood samples were collected from a subset of six of these subjects at baseline, preexercise, postexercise, and 1 h postexercise. An initial pilot study found that caffeine ingestion had no effect on s-IgA concentration, secretion rate, or saliva flow rate at rest. Serum caffeine concentration was higher on CAF than PLA at preexercise, postexercise, and 1 h postexercise (P < 0.001). Plasma epinephrine concentration was higher on CAF than PLA at pre- and postexercise (P < 0.05). s-IgA concentration was higher on CAF than PLA at mid- and postexercise (P < 0.01), and s-IgA secretion rate was higher on CAF than PLA at midexercise only (P < 0.02). Caffeine ingestion did not affect saliva flow rate. Saliva alpha-amylase activity and secretion rate were higher on CAF than PLA (main effect for trial, P < 0.05). These findings suggest that caffeine ingestion before intensive exercise is associated with elevated s-IgA responses during exercise, which may be related to increases in sympathetic activation.

The Effect of Caffeine Ingestion on Neutrophil Oxidative Burst Responses Following Prolonged Cycling

This study investigated the effect of caffeine ingestion on neutrophil oxidative burst responses to prolonged cycling. In a two part study, 19 endurance trained male cyclists (Part A--11; Part B--8) performed 90 min of exercise at 70% VO2max 1 h after ingesting 6 mg/kg body mass of caffeine (CAF) or placebo (PLA). CAF ingestion had no effect on the PMA-stimulated oxidative burst response (Part A), yet it attenuated the exercise-induced decline in f-MLP stimulated response that occurred with PLA (Part B). CAF ingestion significantly increased serum caffeine concentration and plasma adrenaline concentration following exercise. In addition, circulating lymphocyte count was increased following CAF ingestion whereas there was no effect on neutrophil number. Therefore, although CAF ingestion was associated with an increase in adrenaline, this was not associated with an expected decrease in neutrophil function. This suggests that in the present study, CAF ingestion influenced neutrophil function via alternative mechanisms.

5 Effect of Diet on the Ontongeny of Drug Biotransformation in Healthy Infants.

Drug biotransformation can be altered by diet in adults resulting in drug accumulation and toxicity, or in some cases, enhanced elimination. The cytochrome P450 enzymes (CYPs) are a super family of heme-containing phase I enzymes responsible for biotransformation of a significant number of commonly used pharmacologic agents and a large array of endogenous substrates. Previous studies suggest that drug metabolism by CYPs differs between breast-fed and formula-fed infants. The effect of infant diet on the development of functional CYP activity is assessed in this report. Oral doses of caffeine and dextromethorphan were used as pharmacologic probes to track CYP enzyme activity in neonates seen at 6 visits over their first 6 months of life. The caffeine elimination rate constant (ke) was determined from serum caffeine levels obtained on alternating visits. At all visits, levels of caffeine, dextromethorphan, and their respective metabolites were determined by HPLC in urine samples collected over a 24 hr post-dose period. The serum caffeine ke of infants at their first study visit (2 weeks post-natal age) was unrelated to post-conceptional age. Caffeine elimination was low in infants at this first visit and displayed a significant positive linear correlation with increasing post-natal age (ke = .004 (Age [weeks]) + .001; p<0.001). Caffeine ke increased faster in formula-fed infants (slope = .005 95%CI: 0.004, 0.006) than in breast-fed infants (slope = .002 95%CI: 0.001, 0.002) (p<0.001) concomitant with increased conversion of caffeine to 3-demethylated metabolites. In contrast, breast feeding significantly increased the urinary fractional molar recovery of 3-methylxanthine (fr3X) [(fr3X) = .004 Age [weeks] + .016; p< 0.01] suggesting that this feeding modality produces a relative shunt in metabolism towards 7-demethylated metabolites. Dextromethorphan metabolism, assessed as the fractional molar recovery of 3-hydroxymorphinan (fr3HM), showed a similar marked increase with postnatal age [(fr3HM) = .014 Age [weeks] + .203; p< 0.001] that did not differ between diets. The maturation of caffeine elimination does not appear to begin until after birth. Formula feeding appears to accelerate the development of caffeine metabolism but not dextromethorphan. There may be specific ligand(s) unique to infant formula or human breastmilk that modify the developmental regulation of CYP1A gene expression and/or activity. Dietary modification of CYP activity may alter drug bioavailability and increase exposure to modified xenobiotics or endogenous metabolites from a very early age.

Separation of caffeine and theophylline in poly(dimethylsiloxane) microchannel electrophoresis with electrochemical detection

A method for the rapid separation and sensitive determination of caffeine and theophylline was presented in poly(dimethylsiloxane) (PDMS) microchannel electrophoresis integrated with electrochemical detection. By using methanol as an additive, the peak shape and resolution were essentially improved. The analytes were well separated within only 40 s in the running buffer of 5.0 mM borate solution (pH 9.2) containing 10% (v/v) methanol. The linear ranges were from 6 μM to 0.6 mM and the detection limits were 4 μM for caffeine and theophylline, respectively. The proposed method has been successfully applied to determine caffeine and theophylline in rat serum and urine.

Association of caffeine metabolites in umbilical cord blood with IUGR and preterm delivery: A prospective cohort study of 1609 pregnancies

To examine the association between IUGR and preterm delivery (PTD) and fetal caffeine exposure when estimated by serum caffeine and paraxanthine in umbilical cord. Prospective cohort study conducted in Connecticut and Massachusetts specifically testing the relation of caffeine and its metabolites, measured in cord blood (ng/ml) to IUGR (N = 1606) and PTD (N = 1609). Important covariates were controlled for in logistic regression models. Ridge regression for generalized linear models was used to control for collinearity among metabolites. All metabolite analyses were done blind to consumption data and reproductive outcomes. We observed a 24% increase in risk for IUGR per paraxanthine quartile change (Ridge adjusted OR 1.24; 95% CI 1.10, 1.39), while caffeine was protective for IUGR: Ridge adjusted OR 0.87 (95% CI 0.78, 0.97) per quartile change. When the ratio of paraxanthine:caffeine was modeled, there was a 6-fold increase in risk for IUGR for every one-unit increase in the ratio (MLE adjusted OR 6.03; 95% CI 2.14, 17.03). There was an 18% increase in risk for preterm delivery per paraxanthine quartile change (Ridge adjusted OR 1.18; 95% CI 1.05, 1.33). Caffeine was not associated with PTD nor was the paraxanthine:caffeine ratio. Maternal self-reported caffeine consumption during the third trimester was not associated with either outcome. Paraxanthine, rather than caffeine, may increase risk for IUGR and PTD. These findings may explain the equivocal literature evaluating reported consumption only. More research to replicate and extend these findings which have relevance to other health outcomes is warranted.

Relationship of Coffee Consumption with Risk Factors of Atherosclerosis in Rats

Aims: In experimental animals we investigated the relationship of coffee consumption with risk factors of atherosclerosis such as cholesterol, homocysteine, oxidative stress and inflammatory cytokines. Methods: Forty-eight male Wistar rats were assigned to 3 treatment groups (a control diet group, 0.62% coffee diet group, and 1.36% coffee diet group), and animals were maintained on the experimental diets for 140 days. Results: Coffee diets led to an increase in the caffeine concentration to 0.53 ± 0.11 and 1.77 ± 0.22 µg/ml, respectively, although caffeine in serum was not detected in rats fed the control diet. It also led to slightly increased total serum levels of homocysteine and cholesterol, but no significant differences were found between the control and coffee diet groups. Coffee intake did not affect the production of IL-6 and TNF-α induced by LPS, which contributes to the atheroma-promoting effect of recurrent bacterial infection. Regarding the biomarkers of oxidative stress, the serum level of 15-isoprostane F_2t, which was significantly increased by LPS injection, was not altered by coffee intake. In contrast, urinary 8-hydroxy-2-deoxyguanosine was significantly increased in the coffee diet groups (p < 0.05). On the other hand, serum glutathione peroxidase (GPx) activity tended to decrease in the coffee groups compared with the control group, but no significant difference was found between the control and coffee diet groups. Interestingly, a significant negative correlation was observed between GPx activity and homocysteine levels in the sera from control and coffee diet groups (r = –0.403, p < 0.05). Conclusions: This report is the first animal study on the relationship of coffee consumption with risk factors for atherosclerosis. From these results, we conclude that moderate coffee intake is not a risk factor for atherogenesis.

Association of serum caffeine concentrations with blood lipids in caffeine-drug users and nonusers – Results of German National Health Surveys from 1984 to 1999

Previous studies regarding effects of caffeine on lipids focused mainly on coffee consumption, the real association of serum caffeine concentrations with blood lipids is unclear. 814 caffeine-drug users who had taken any caffeine/caffeine-containing pharmaceutical products and 623 nonusers without any drug use in the last seven days before the medical interview were identified from German National Health Surveys from 1984 to 1999. Serum caffeine concentrations were measured by using EIA for caffeine-drug users and nonusers in the same laboratory. Blood lipids were measured routinely for all survey participants. The association of caffeine concentrations with blood lipids was established by means of partial correlation analysis and regression analysis. After controlling for influence factors, caffeine concentrations were closely positively related to triglycerides in caffeine-drug users (male: r = 0.245, p < 0.001; female: r = 0.117, p = 0.018) and related to HDL-C in female nonusers (r = 0.245, p < 0.001). No associations were found between caffeine concentrations and total cholesterol and LDL-C levels in any groups of our study. Acute intake of caffeine might increase triglycerides levels especially in men while chronic intake of caffeine might be weakly but positively associated with HDL-C concentrations in women. The effects of caffeine on the pathogenesis of cardiovascular diseases should be further confirmed through epidemiological studies.

Determination of myoglobin based on its enzymatic activity by stopped-flow spectrophotometry

A new method has been developed for the determination of myoglobin (Mb) based on its enzymatic activity for the oxidation of o-phenylenediamine (OPDA) with hydrogen peroxide. Stopped-flow spectrophotometry was used to study the kinetic behavior of the oxidation reaction. The catalytic activity of Mb was compared to other three kinds of catalyst. The time dependent absorbance of the reaction product, 2,3-diamimophenazine (DAPN), at a wavelength of 426 nm was recorded. The initial reaction rate obtained at 40 °C was found to be proportional to the concentration of Mb in the range of 1.0 × 10 −6 to 4.0 × 10 −9 mol L −1. The detection limit of Mb was found to be 9.93 × 10 −10 mol L −1. The relative standard deviations were within 5% for the determination of different concentrations of Mb. Excess of bovine serum albumin (BSA), Ca(II), Mg(II), Cu(II), glucose, caffeine, lactose and uric acid did not interfere.

Stimulant and relaxant drugs combined with stimulant and relaxant information: a study of active placebo

The active placebo hypothesis states that placebo effects are potentiated when an active drug is administered. This hypothesis was tested in an experiment where information about the effect of a drug was combined with administration of an active drug or placebo. Information that a drug acted as a relaxant, a stimulant, or as a placebo was crossed with oral administration of a relaxant drug (700 mg carisoprodol), a stimulant drug (400 mg caffeine) or placebo (lactose) in healthy volunteers ( n=94). Dependent variables were subjective and physiological measures of arousal, as well as serum carisoprodol and caffeine levels. Data were collected from 15 to 280 min after administration of drug or placebo. Caffeine increased alertness, systolic and diastolic blood pressure, startle blink reflexes, and skin conductance responses. Subjects were calmer after carisoprodol, and heart rate was increased. There was a positive correlation between increased arousal and carisoprodol levels when stimulant information had been provided. However, this was only seen when carisoprodol levels were very low. There was no evidence that caffeine modulated the placebo response. Active placebo responses were seen only transiently when carisoprodol levels were low, and only in the subjective arousal data. Caffeine did not support active placebo responses. The overall findings did not favour the active placebo hypothesis.

Effect of diet on caffeine elimination in healthy infants

This study was designed to assess the impact of infant diet on the acquisition of CYP1A2 activity in healthy infants as measured by caffeine (CAF) elimination. Methods: Neonates were seen at 2 wk, 1, 2, 3, 4 and 6 mo where they received oral CAF (7 mg/kg). Serum CAF concentrations were assessed on alternating visits for estimation of CAF elimination rate constant (ke). Urine was collected for 24 hr following dosing for metabolite determination. Results: To date, 33 infants have been enrolled with18 having completed all 6 study visits. Substantial inter-individual variation in CAF ke was observed at 2 wks (0.013±0.009 hr−1) that appeared unrelated to post-conceptional age, diet, gender, or tobacco smoke exposure. A marked increase in CAF ke was observed between 2 wks (0.011 hr−1 95%CI [0.009,0.014]) and 8 wks (0.027 hr−1 [0.018,0.040]) postnatal age (P<0.001) and continued to increase at subsequent visits. CAF ke was not different between breast- (BF) and formula-fed (FF) infants at their first study visit but was significantly greater in FF infants (0.038 hr−1 [0.027,0.054]) vs BF (0.013 hr−1 [0.007,0.029]) infants at 8 weeks postnatal age (p = .011). Conclusions: 1) The form of infant feeding appears to alter the developmental profile for CYP1A2 expression (as reflected by CAF elimination). 2) Accelerated caffeine elimination in FF as opposed to BF infants supports a role for dietary modulation of CYP1A2 activity in healthy infants. Clinical Pharmacology & Therapeutics (2004) 75, P50–P50; doi: 10.1016/j.clpt.2003.11.188

Effect of Caffeine‐Containing versus Decaffeinated Coffee on Serum Clozapine Concentrations in Hospitalised Patients

Clozapine and caffeine are metabolised mainly by the cytochrome P4501A2 (CYP1A2) enzyme. Studies suggest that caffeine in coffee inhibits clozapine metabolism and increases serum clozapine concentrations. Our objective was to study whether coffee in the amounts usually consumed has an effect on steady-state serum clozapine concentrations. A randomised placebo-controlled cross-over design with two phases was used. Twelve hospitalised clozapine-using patients volunteered in the study where, after one-week run-in period, either caffeine-containing or decaffeinated instant coffee was available ad libitum for seven days. Serum concentrations of clozapine, N-desmethylclozapine, clozapine-N-oxide, caffeine, paraxanthine and C-reactive protein were measured after run-in period and on days 4 and 8 of the following study phases. Two patients were excluded from the statistical analysis because of non-compliance based on serum caffeine and paraxanthine determinations. In six fully compliant patients caffeine-containing coffee increased the mean serum trough concentration of clozapine by 26% (non-significant (NS), 95% CI -3% to +54%, P=0.07), N-desmethylclozapine by 6% (95% CI 1% to 12%, P=0.03), and clozapine-N-oxide by 7% (NS, 95% CI -6% to +20%, P=0.22). The ratio of N-desmethylclozapine/clozapine decreased by 13% (NS, 95% CI -1% to +27%, P=0.06) and that of clozapine-N-oxide/clozapine by 7% (NS, 95% CI -5% to +17%, P=0.19). In the analysis of combined data (including day 4 data of the four patients compliant up to that point) serum trough concentration of clozapine was 20% (95% CI 3% to 37% to P=0.03) higher, and that of N-desmethylclozapine 7% (95% CI 2% to 13%, P=0.02) higher during the caffeine phase than during the decaffeinated phase. We conclude that the effect of instant coffee drinking on serum clozapine concentrations is of minor clinical relevance in most of the patients, but some individuals may be more sensitive to this interaction due e.g. to genetic factors. The increase in serum clozapine concentration was most likely due to the inhibition of the CYP1A2 enzyme by caffeine.