Serum Caffeine Concentrations Research Articles

Development of a simple estimation method of serum caffeine concentration using a point-of-care test kit for urinary caffeine.

Serum caffeine concentration is an indicator of caffeine intoxication; however, it is difficult to measure it in most emergency departments. We developed a simple estimation method using a point-of-care test kit for urinary caffeine. Caffeine-spiked human serum (100, 50, 25, and 10µg/mL) was diluted 10-, 20-, 50-, and 100-fold with phosphate-buffered saline and applied to the kit. After 5min incubation, the kit was scanned by a flatbed scanner and the membrane image was processed with ImageJ. When the 20-fold diluted serum was applied, serum samples with initial caffeine concentration ≤ 25 and ≥ 50µg/mL were caffeine-negative and -positive, respectively. When the 100-fold diluted serum was applied, none of the caffeine-spiked serum samples gave positive results. Therefore, we proposed the following test procedure: (i) 20-fold diluted serum was initially tested and (ii) 100-fold diluted serum was additionally tested when the initial result was caffeine positive. Using this procedure, caffeine concentration is expected to be classified into three levels: ≤ 25, > 25- ≤ 100, and > 100µg/mL, which almost correspond to no or mild, severe, and potentially fatal intoxication, respectively. The test procedure was validated using postmortem heart blood from two cases of fatal caffeine intoxication (caffeine concentration: 276 and 175µg/mL) and two cases of other intoxication. Our developed method using point-of-care urinary caffeine test kits enabled simple estimation of serum caffeine concentration.

Interaction of a caffeine overdose with clinical doses of contraceptive ethinyl estradiol in a young woman.

The overdose of caffeine, a cytochrome P450 1A2 probe, in young women has become a problem. The aim of this study was to evaluate possible drug interactions between intentionally overdosed caffeine (12 g) and oral contraceptive doses of ethinyl estradiol prescribed to a young woman in a suicide attempt. The serum concentrations of caffeine in the patient and the time-dependent ethinyl estradiol inhibition of caffeine oxidation invitro were evaluated. The serum concentration of caffeine 4 h after overdose was 136 μg/mL; from the data obtained between 4 and 28 h after overdose, the half-life was estimated to be 33 h, which is many times larger than the normal value. Prescribed ethinyl estradiol prolonged caffeine elimination invivo and inhibited paraxanthine formation, as evidenced by the low serum concentrations. In human liver microsomes, ethinyl estradiol (50 nM) inhibited half of caffeine N 3 -demethylation. Pre-incubation of human liver microsomes with ethinyl estradiol resulted in a powerful time-dependent inhibitory effect on caffeine N 3 -demethylation in human liver microsomes. These results suggest that a prescription history of contraceptives at clinical doses may have a strong effect on the pharmacokinetics of overdosed caffeine in young women, resulting in dangerous drug interactions.

Serum Caffeine Concentration at the Time of Traumatic Brain Injury and Its Long-Term Clinical Outcomes.

Caffeine is one of the most widely consumed psychoactive drugs in the general population. It has a neuroprotective effect in degenerative neurological disorders; however, the association between caffeine and traumatic brain injury (TBI) outcomes is contradictory. The objective of this study was to evaluate the association between serum caffeine concentration at the time of injury and long-term functional outcomes of patients with TBI visiting the emergency department (ED). This was a prospective multi-center cohort study including adult patients with intracranial injury confirmed by radiological examination, who visited five participating EDs within 72 h after TBI. The main exposure was the serum caffeine level within 4 h after injury, and the study outcome was a favorable functional recovery at 6 months after injury. Multi-variable logistic regression analysis adjusted for potential confounders was performed to calculate adjusted odds ratios (AORs) with 95% confidence intervals (CIs). Among the 334 study participants, caffeine was not detected in 102 patients (30.5 %). In patients with identifiable caffeine level, serum caffeine level was categorized into tercile groups; low (0.01-0.58 μg/mL), intermediate (0.59-1.66 μg/mL), and high (1.67-10.00 μg/mL). The proportions of patients with a 6-month favorable functional recovery were 56.9% in the no-caffeine group, 79.2% in the low-caffeine group, 75.3% in the intermediate-caffeine group, and 66.7% in the high-caffeine group (p = 0.006). In multi-variable logistic regression analysis, the low- and intermediate-caffeine groups were significantly associated with a higher probability of 6-month favorable functional recovery compared with the no-caffeine group [AORs (95% CI): 2.82 (1.32-6.02) and 2.18 (1.06-4.47], respectively. This study showed a significant association between a serum caffeine concentration of 0.01 to 1.66 μg/mL and good functional recovery at 6 months after injury compared with the no-caffeine group of patients with TBI with intracranial injury. These results suggest the possibility of using serum caffeine level as a potential biomarker for TBI outcome prediction and of using caffeine as a therapeutic agent in the clinical care of patients with TBI.

Elimination of 1,3,7-trimethyl-xanthine in laboratory animals during induction of toxic hepatitis

Liver pathologies have a significant impact on caffeine clearance, which deserves serious attention and research. In the case of liver pathologies, the processes of caffeine metabolism are significantly modified; however, according to the scientific literature, the vector of such transformations for specific pathologies has not been determined. This is due to the fact that hepatopathy reduces the activity of enzymes responsible for caffeine metabolism. In some cases, an increase in caffeine clearance may occur, which is associated with a temporary compensatory activation of certain enzymes that may be involved in caffeine metabolism. Also, the clearance of caffeine may be reduced due to a decrease in the metabolic activity of the liver, which will significantly slow down its final excretion. To determine changes in the clearance of 1,3,7-trimethylxanthine, the most appropriate is to study its pharmacokinetic parameters, in particular, to compare its concentration in the blood serum in the phases of initial growth, plateau and decline with further construction of graphs - “caffeine curves”. The purpose of the study was to determine changes in serum caffeine levels during the induction of toxic hepatitis. The studies were carried out in the vivarium of the Department of Pharmacology and Toxicology of the Federal State Budgetary Educational Institution of Higher Education of St. Petersburg State University of Medicine. In order to simulate toxic hepatitis, experimental animals were intragastrically injected with a 35% oil solution of carbon tetrachloride (CCl4) daily for 5 days at a dosage of 1.5 ml/kg. Upon completion of induction, toxic hepatitis was confirmed based on clinical and biochemical signs. A day after the completion of the modeling of toxic hepatitis, the levels of caffeine in the blood serum were determined in the experimental animals in full accordance with the previous series of experiments. As a result of the study, “caffeine” curves were constructed, indicating increased caffeine concentrations in serum, increased elimination time, as well as an extremely long plateau in the concentration of caffeine in the blood serum during toxic liver damage.

Serum caffeine concentrations in preterm infants: a retrospective study

Therapeutic drug monitoring is generally unnecessary in caffeine treatment for apnea of prematurity, as serum caffeine concentrations in preterm infants are normally markedly lower than those at which caffeine intoxication occurs. However, several studies have reported preterm infants having developed toxicity. This retrospective observational study, conducted at a tertiary center in Kagawa, Japan, aimed to evaluate the correlation between the maintenance dose and serum caffeine concentrations and determine the maintenance dose leading to suggested toxic caffeine levels. We included 24 preterm infants (gestational age, 27 ± 2.9 weeks; body weight, 991 ± 297 g) who were treated with caffeine citrate for apnea of prematurity between 2018 and 2021, and 272 samples were analyzed. Our primary outcome measure was the maintenance dose leading to suggested toxic caffeine levels. We found a positive correlation between caffeine dose and serum caffeine concentrations (p < 0.05, r = 0.72). At doses of ≥ 8 mg/kg/day, 15% (16/109) of patients had serum caffeine concentrations above the suggested toxic levels. Patients who receive doses ≥ 8 mg/kg/day risk reaching the suggested toxic serum caffeine levels. It remains unclear whether suggested toxic caffeine concentrations are detrimental to neurological prognosis. Further investigation is required to understand the clinical effects/outcomes of high serum levels of caffeine and to obtain long-term neurodevelopmental follow-up data.

Test-retest reproducibility of cerebral adenosine A2A receptor quantification using [11C]preladenant.

To evaluate the reproducibility of cerebral adenosine A2A receptor (A2AR) quantification using [11C]preladenant ([11C]PLN) and PET in a test-retest study. Eight healthy male volunteers were enrolled. Dynamic 90min PET scans were performed twice at the same time of the day to avoid the effect of diurnal variation. Subjects refrained from caffeine from 12h prior to scanning, and serum caffeine was measured before radioligand injection. Arterial blood was sampled repeatedly during scanning and the fraction of the parent compound in plasma was determined. Total distribution volume (VT) was estimated using 1- and 2-tissue compartment models (1-TCM and 2-TCM, respectively) and Logan graphical analysis (Logan plot) (t* = 30min). Plasma-free fraction (fP) of [11C]PLN was measured and used for correction of VT values. Distribution volume ratio (DVR) was calculated from VT of target and reference regions and obtained by noninvasive Logan graphical reference tissue model (LGAR) (t* = 30min). Absolute test-retest variability (aTRV), and intra-class correlation coefficient (ICC) of VT and DVR were calculated as indexes of repeatability. Correlation between DVR and serum concentration of caffeine (a nonselective A2AR blocker) was analyzed by Pearson's correlation analysis. Regional time-activity curves were well described by 2-TCM models. Estimation of VT by 2-TCM produced some erroneous values; therefore, the more robust Logan plot was selected as the appropriate model. Global mean aTRV was 20% for VT and 14% for VT/fP (ICC, 0.72 for VT and 0.87 for VT/fP). Global mean aTRV of DVR was 13% for Logan plot and 10% for LGAR (ICC, 0.70 for Logan plot and 0.81 for LGAR). DVR estimates using LGAR and Logan plot were in good agreement (r2 = 0.96). Coefficients of variation for VT, VT/fP, DVR (Logan plot), and DVR (LGAR) were 47%, 47%, 27%, and 18%, respectively. Despite low serum caffeine levels, significant concentration-dependent effects on [11C]PLN binding to target regions were observed (p < 0.01). In this study, moderate test-retest reproducibility and large inter-subject differences were observed with [11C]PLN PET, possibly attributable to competition by baseline amount of caffeine. Analysis of plasma caffeine concentration is recommended during [11C]PLN PET studies. UMIN000030040.

Influence of nanocrystal size on the in vivo absorption kinetics of caffeine after topical application

The absorption of topically applied substances is challenging due to the effective skin barrier. Encapsulation of substances into nanoparticles was expected to be promising to increase the bioavailability of topically applied products. Since nanoparticles cannot traverse the intact skin barrier, but penetrate into the hair follicles, they could be used to deliver substances via hair follicles, where the active is released and can translocate independently transfollicularly into the viable epidermis.In the present in vivo study, this effect was investigated for caffeine. Caffeine nanocrystals of two sizes, 206 nm and 694 nm, with equal amounts of caffeine were used to study caffeine serum concentration kinetics after topical application on 5 human volunteers.The study demonstrated that at early time points, the smaller nanocrystals were more effective in increasing the bioavailability of caffeine, whereas after 20 min, the serum concentration of caffeine was higher when caffeine was applied by larger nanocrystals. Caffeine was still detectable after 5 days. The area under the curve could be increased by 82% when the 694 nm nanocrystals were applied.Especially larger sized nanocrystals seem to be a promising type of nanoparticulate preparation to increase the bioavailability of topically applied drugs via the transfollicular penetration pathway.

Rapid measurement of serum caffeine concentrations in acuteclinical settings

The number of acute caffeine poisoning cases have increased in Japan. We can use serum caffeine concentrations to evaluate the severity of caffeine poisoning and determine whether or not we should perform hemodialysis. In this study, we sought to develop a rapid method for measuring serum caffeine concentrations. We used liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the new method. We chose caffeine-d9 as the internal standard, and we used the standard addition method to quantify caffeine concentrations. We collected six blood samples from three patients with acute caffeine poisoning to measure serum caffeine concentrations. In our method, retention time for caffeine was 0.4 min, and the time required for the total LC-MS/MS analysis was 1 min per sample. We obtained accurate serum caffeine concentrations 7 min after injection into the LC-MS/MS instrument. Further, time-consuming sample pretreatment was not required because each sample was diluted 10,000-fold. As a result, we could obtain serum caffeine concentrations for each patient in a total of 40 min. Our findings suggest that rapid, accurate measurement of serum caffeine concentrations by LC-MS/MS could contribute to real-time evaluation of poisoning severity and determination of appropriate therapeutic strategies in acute clinical settings.

Criterion for initiating hemodialysis based on serum caffeine concentration in treating severe caffeine poisoning.

Criterion for initiating hemodialysis based on serum caffeine concentration in treating severe caffeine poisoning.

Pharmacokinetic Variability of Caffeine in Routinely Treated Preterm Infants: Preliminary Considerations on Developmental Changes of Systemic Clearance.

The purpose of this study was to clarify the variability of serum concentrations of caffeine (CAF) in preterm infants, and to deliberate on a better explanation for developmental changes of systemic clearance during the neonatal period. Forty-nine serum samples were obtained from 23 preterm neonates (age, 34.1 ± 18.8 d), and additive blood sampling was conducted periodically for 10 of the 23 patients after discontinuation of CAF treatment. The concentrations of CAF and its major metabolites were determined by liquid chromatography-tandem mass spectrometory. The serum concentrations of CAF were within therapeutic levels (5-25 µg/mL) in 37 samples and exceeded 25 µg/mL in the rest of the 12 samples, although no sample was in the toxic range (> 50 µg/mL). The inter- and intra-individual variability of the concentration to dose (C/D) ratio corrected for body surface area (BSA) was more negatively associated with postmenstrual age (PMA) rather than postnatal age (PNA). The serum concentrations of major metabolites were much smaller than those of CAF throughout the study, suggesting that the contribution of hepatic metabolism to drug elimination was small in the preterm infants under 241 d of PMA. The mean values for elimination half-life and oral clearance estimated in the 10 patients were 124.6 ± 44.6 h and 2.26 ± 0.73 mL/min/1.73 m2, respectively. Consequently, we confirmed that the exposure to CAF was considerably variable and provided additive insight that the C/D ratio corrected for patient's BSA and PMA are promising for describing and understanding the developmental change of clearance in preterm infants.

Quantification of Blood Caffeine Levels in Patients With Parkinson's Disease and Multiple System Atrophy by Caffeine ELISA.

Caffeine is considered to be a neuroprotective agent against Parkinson's disease (PD) and is expected to offer a blood-based biomarker for the disease. We herein investigated the ability of this biomarker to discriminate between PD and neurodegenerative diseases. To quantify caffeine concentrations in serum and plasma, we developed a specific competitive enzyme-linked immunosorbent assay (ELISA). To validate the diagnostic performance of the assay, we conducted a case control-study of two independent cohorts among controls and patients with PD and multiple system atrophy (MSA). Parallelism, recovery rate, and intra- and inter-assay precision of our assay were within the standard of acceptance. In the first cohort of 31 PD patients, 18 MSA patients and 33 age-matched controls, serum caffeine levels were significantly lower in PD patients than in Controls (p = 0.018). A similar trend was also observed in the MSA group, but did not reach the level of significance. In the second cohort of 50 PD patients, 50 MSA patients and 45 age-matched controls, plasma caffeine levels were significantly decreased in both PD and MSA groups compared to Controls (p < 0.001). This originally developed ELISA offered sufficient sensitivity to detect caffeine in human serum and plasma. We reproducibly confirmed decreased blood concentrations of caffeine in PD compared to controls using this ELISA. A similar trend was observed in the MSA group, despite a lack of consistent significant differences across cohorts.

Stopping caffeine in premature neonates: how long does it take for the level of caffeine to fall below the therapeutic range?

Background Caffeine is routinely used in preterm infants for apnea of prematurity. Preterm infants are usually monitored for 5 days after discontinuation of caffeine to assess for possible recurrence of apnea. Our objective was to determine if the serum concentration of caffeine decreases to a subtherapeutic level 5 days after its discontinuation. Methods This is a retrospective analysis of caffeine levels after the drug was discontinued in preterm neonates (birth weight ≤1500 g) born between January 2010 and June 2017. The primary outcome was the proportion of infants with therapeutic levels of caffeine 5 days after the drug was stopped. Results Caffeine levels were measured in 353 samples from 280 infants (birth weight 1246 ± 390 g and gestational age 29.2 ± 2.4 weeks) after discontinuation of the drug. Five and more days after discontinuation of caffeine, 29.3% (82/280) of the infants had caffeine levels ≥5 mg/L. Approximately 41% (75/181) of the caffeine levels measured between 5 and 7 days and 18% (17/95) between 8 and 10 days were ≥5 mg/L. A caffeine dose of >5 mg/kg/day when discontinued was associated with the caffeine level of ≥5 mg/L (OR 2.3, 95% CI 1.28–4.13, p = .005). Conclusions Preterm infants treated with caffeine frequently had therapeutic levels of caffeine 5–10 days after discontinuation of the drug. The infants receiving higher doses were more likely to have a therapeutic level of caffeine 5 days after stopping the medication. Preterm infants should be monitored for recurrence of apnea for more than 5 days after stopping caffeine or levels should be monitored prior to discharge.

Caffeine Uptake into the Vitreous after Peroral Coffee Consumption

Introduction: Caffeine and its metabolites have antioxidant activity, scavenging reactive oxygen species. The aim of our study was to measure caffeine concentrations in vitreous samples after peroral caffeine intake. Methods: This prospective study included patients scheduled for 23-G pars plana vitrectomy with membrane peeling due to epiretinal membranes. The study was performed in two parts: in the first part, patients were recruited into three different groups: group A consisted of habitual coffee drinkers who agreed to drink coffee containing 180 mg caffeine 1 h before surgery (n = 10), group B consisted of habitual coffee drinkers who were not offered coffee before surgery (n = 5), and group C consisted of non-habitual coffee drinkers, forming the control group (n = 5). In the second part (group D) patients (habitual coffee drinkers) agreed to give additional blood serum samples for measurement of caffeine concentration. Harvested samples of vitreous (groups A–D), epiretinal membranes (groups A–C), and blood serum samples (group D) were examined for concentrations of caffeine with gas chromatography-mass spectrometry. Results: Samples of 40 eyes of 40 patients were harvested. The concentrations of caffeine in the vitreous samples were 1,998 ± 967 ng/mL in group A and 1,108 ± 874 ng/mL in group B. In group C, caffeine concentrations were below 176 ng/mL in all vitreous samples. Both groups A and B had significantly higher concentrations of caffeine in the vitreous samples than group C (p < 0.002, p < 0.01, Mann-Whitney U test). Caffeine concentrations in epiretinal membranes were below the limits of detection. Correlation of caffeine concentrations between blood serum samples and vitreous samples in group D was high, with significantly higher caffeine concentrations in the blood serum. Conclusion: Coffee consumption leads to significant caffeine levels in the vitreous compared to patients in the control group, and caffeine concentrations in the vitreous showed a high correlation to blood serum concentrations of caffeine after peroral coffee consumption.

Administration of Micronized Caffeine Using a Novel Oral Delivery Film Results in Rapid Absorption and Electroencephalogram Suppression.

Route of administration is well-known to impact factors ranging from absorption and distribution, up through the subjective effects of active ingredients. Different routes of administration confer specific advantages, such as more rapid absorption resulting from intravenous injection, or increased convenience with oral administration, but a combination of both rapid and convenient delivery is highly desirable. QuickStrip™ was designed as a rapidly dissolving thin film matrix that contains active ingredients, which may be promising for rapid and convenient delivery via the oral mucosa. To assess the delivery of QuickStrip™, we administered the well-characterized active ingredient caffeine to mice and compared QuickStrip™ to standard oral gavage delivery at an equivalent dose of 20 mg kg-1. Using HPLC assessment of serum concentrations of caffeine, we found that QuickStrip™ delivery resulted in higher serum levels of caffeine at 1, 10, and 30 min following administration compared to gavage. QuickStrip™ also produced greater bioavailability compared to gavage, as demonstrated by area under the curve analysis. Caffeine delivered by QuickStrip™ produced robust behavioral activation of locomotion, consistent with gavage caffeine. Electroencephalographic (EEG) assessment of central nervous system effects demonstrated that both gavage and QuickStrip™ caffeine produced suppression of delta and theta, consistent with prior literature on the effects of caffeine. In addition, QuickStrip™ produced a more rapid onset of EEG suppression, supporting the more rapid absorption demonstrated in the serum studies. Collectively, these studies suggest that QuickStrip™ may provide a balance between convenience and rapid onset, offering new options for delivery of therapeutics.

Effects of Caffeine on Myocardial Blood Flow: A Systematic Review.

Background. Caffeine is one of the most widely consumed stimulants worldwide. It is a well-recognized antagonist of adenosine and a potential cause of false-negative functional measurements during vasodilator myocardial perfusion. The aim of this systematic review is to summarize the evidence regarding the effects of caffeine intake on functional measurements of myocardial perfusion in patients with suspected coronary artery disease. Pubmed, Web of Science, and Embase were searched using a predefined electronic search strategy. Participants—healthy subjects or patients with known or suspected CAD. Comparisons—recent caffeine intake versus no caffeine intake. Outcomes—measurements of functional myocardial perfusion. Study design—observational. Fourteen studies were deemed eligible for this systematic review. There was a wide range of variability in study design with varying imaging modalities, vasodilator agents, serum concentrations of caffeine, and primary outcome measurements. The available data indicate a significant influence of recent caffeine intake on cardiac perfusion measurements during adenosine and dipyridamole induced hyperemia. These effects have the potential to affect the clinical decision making by re-classification to different risk-categories.

Caffeine inhibits STAT1 signaling and downregulates inflammatory pathways involved in autoimmunity

Caffeine is a widely consumed pharmacologically active product. We focused on characterizing immunomodulatory effects of caffeine on peripheral blood mononuclear cells. Caffeine at high doses showed a robust downregulatory effect on cytokine activity and genes related to several autoimmune diseases including lupus and rheumatoid arthritis. Dose-dependent validation experiments showed downregulation at the mRNA levels of key inflammation-related genes including STAT1, TNF, IFNG, and PPARG. TNF and PPARG were suppressed even with the lowest caffeine dose tested, which corresponds to the serum concentration of caffeine after administration of one cup of coffee. Cytokine levels of IL-8, MIP-1β, IL-6, IFN-γ, GM-CSF, TNF, IL-2, IL-4, MCP-1, and IL-10 were decreased significantly with caffeine treatment. Upstream regulator analysis suggests that caffeine inhibits STAT1 signaling, which was confirmed by showing reduced phosphorylated STAT1 after caffeine treatment. Further studies exploring disease-modulating potential of caffeine in autoimmune diseases and further exploring the mechanisms involved are warranted.

Abstract B73: The association of caffeine, trigonelline, and chlorogenic acid, active components from coffee, enhances caffeine-induced cytotoxicity in hepatocellular carcinoma cells

Abstract Background: A cup of traditional coffee is a complex mixture of biologically active components, including caffeine (CAF), trigonelline (TRI), chlorogenic acid (CGA), and many others (1). Daily coffee consumption reduces by ~40% the risk of fibrosis/cirrhosis and hepatocellular carcinoma (HCC) in humans while, in general, decaffeinated coffee consumption does not (2-4). However, it is not clear whether this beneficial effect is attributed to the CAF alone or its association with other coffee constituents. Aim: This work evaluated the modifying effects of CAF alone or associated to CGA and/or TRI in human HCC and hepatic stellate cells (HSC). Experimental Procedures: Human C3A (clonal derivative of HepG2 cells) and LX2 (HSC) cells were grown in Eagle's Minimum Essential Medium supplemented with 10% fetal bovine serum (FBS), 100 U/ml penicillin, and 100 μg/ml streptomycin in a humidified atmosphere of 5% CO2 at 37oC. C3A and LX2 cells were seeded in 96-well plates at a density of 7 x 104 and 1 x 105 cells/mL, respectively, and treated with CAF alone (20, 40, 80, or 160 μM) or combined to TRI (10, 20, 40, or 80 μM) and/or CGA (10, 20, 40, or 80 μM) for 24 and 48 h. To select the CAF concentration, we considered the human serum peak (~35 µM) after the ingestion of ~450 mg of CAF, corresponding to 2-3 cups of coffee, and the toxic limit established for plasma concentration in humans (~400 μM) (5,6). For CGA and TRI, abundant in coffee beverages, we considered the 1:2 proportion (CGA or TRI:CAF) found in traditional coffee (1). We evaluated the cell viability (MTT assay) of LX2 and the cytotoxicity (lactate dehydrogenase [LDH] assay) of C3A cells. Results: All tested CAF concentrations significantly increased cytotoxicity in C3A cells at 48 h compared to untreated cells (p&amp;lt;0.001). The CAF+TRI+CGA combinations (20, 10, and 10 µM and 40, 20, and 20 µM, respectively) enhanced cytotoxicity at 24 and 48 h when compared to the control, CAF alone, and other associations (p&amp;lt;0.001). Notably, these combinations enhanced caffeine-induced cytotoxicity at 48 h (p&amp;lt;0.001). All treatments did not alter the viability of LX2 cells at both 24 and 48 h. Conclusion: In general, the combination of CAF with other common compounds found in filtered and espresso coffee, TRI and CGA, enhanced CAF-mediated cytotoxicity on HCC cells at physiologically applicable concentrations. These findings suggest a synergistic effect of coffee compounds in exerting a chemopreventive effect and reducing the risk for HCC. The potential mechanisms related to these modifying effects will be further evaluated. Financial support: CNPq (140251/2016-2) and FAPESP (16/14420-0).

Therapeutic drug monitoring of caffeine in preterm infants: Could saliva be an alternative to serum?

Evaluate whether saliva could be a useful alternative to serum for routine therapeutic drug monitoring of caffeine in preterm infants using the enzyme multiplied immunoassay technique (EMIT) assay. We conducted a prospective study including preterm infants (less than 34 weeks' amenorrhea) admitted to the intensive care and neonatal medicine department. All infants received 5, 10, 15, 20 and 25mg/kg/day of citrate caffeine intravenously from the first to the fifth day of birth, respectively. For each patient, two concomitant blood and saliva samples corresponding to the trough concentrations were collected 24hours after each caffeine dose. The caffeine concentrations were determined using the EMIT®2000 caffeine assay. Thirteen preterm infants were included. The saliva and the serum caffeine concentration increased proportionally to the administered dose. Saliva and serum kinetics were comparable and the saliva caffeine concentrations were correlated to the serum ones (r2=0.76). Saliva caffeine monitoring by EMIT is a valid, useful and safe alternative to serum in preterm infants.

Serum caffeine and paraxanthine concentrations and menstrual cycle function: correlations with beverage intakes and associations with race, reproductive hormones, and anovulation in the BioCycle Study

Clinicians often recommend limiting caffeine intake while attempting to conceive; however, few studies have evaluated the associations between caffeine exposure and menstrual cycle function, and we are aware of no previous studies assessing biological dose via well-timed serum measurements. We assessed the relation between caffeine and its metabolites and reproductive hormones in a healthy premenopausal cohort and evaluated potential effect modification by race. Participants (n = 259) were followed for ≤2 menstrual cycles and provided fasting blood specimens ≤8 times/cycle. Linear mixed models were used to estimate associations between serum caffeine biomarkers and geometric mean reproductive hormones, whereas Poisson regression was used to assess risk of sporadic anovulation. The highest compared with the lowest serum caffeine tertile was associated with lower total testosterone [27.9 ng/dL (95% CI: 26.7, 29.0 ng/dL) compared with 29.1 ng/dL (95% CI: 27.9, 30.3 ng/dL), respectively] and free testosterone [0.178 ng/mL (95% CI: 0.171, 0.185 ng/dL) compared with 0.186 ng/mL (95% CI: 0.179, 0.194 ng/dL), respectively] after adjustment for age, race, percentage of body fat, daily vigorous exercise, perceived stress, depression, dietary factors, and alcohol intake. The highest tertiles compared with the lowest tertiles of caffeine and paraxanthine were also associated with reduced risk of anovulation [adjusted RRs (aRRs): 0.39 (95% CI: 0.18, 0.87) and 0.40 (95% CI: 0.18, 0.87), respectively]. Additional adjustment for self-reported coffee intake did not alter the reproductive hormone findings and only slightly attenuated the results for serum caffeine and paraxanthine and anovulation. Although reductions in the concentrations of total testosterone and free testosterone and decreased risk of anovulation were greatest in Asian women, there was no indication of effect modification by race. Caffeine intake, irrespective of the beverage source, may be associated with reduced testosterone and improved menstrual cycle function in healthy premenopausal women.

Apnea of prematurity and caffeine pharmacokinetics: potential impact on hospital discharge.

To determine the half-life of serum caffeine concentrations and its relation to apnea of prematurity (AOP) after caffeine is discontinued in preparation for hospital discharge. Prospective cohort study involving preterm infants with gestational ages ⩽33 weeks at birth. After caffeine was discontinued, serum caffeine concentrations and electronic detection of pathologic apnea, defined a priori, were obtained at 24 and 168 h, respectively. Caffeine levels decreased from 13.3±3.8 to 4.3±2 mg l(-1) (n=50, mean±s.d.) at 24 and 168 h, respectively (P<0.01). The mean caffeine half-life was 87±25 h at 35±1 weeks postmenstrual age. Seven days after discontinuation of caffeine, 64% of the infants had pathologic apnea. Hospital discharge planning for preterm infants with a history of AOP should be carefully considered after discontinuing caffeine. This study showed that caffeine may not reach subtherapeutic levels until around 11-12 days.