Dose-dependent pharmacokinetics of caffeine in humans: relevance as a test of quantitative liver function

Effect of caffeine and other xanthines on liver sinusoidal endothelial cell ultrastructure

Xanthines such as caffeine and theobromine are among the most consumed psychoactive stimulants in the world, either as natural components of coffee, tea and chocolate, or as added ingredients. The present study assessed if xanthines affect liver sinusoidal endothelial cells (LSEC). Cultured primary rat LSEC were challenged with xanthines at concentrations typically obtained from normal consumption of xanthine-containing beverages, food or medicines; and at higher concentrations below the in vitro toxic limit. The fenestrated morphology of LSEC were examined with scanning electron and structured illumination microscopy. All xanthine challenges had no toxic effects on LSEC ultrastructure as judged by LSEC fenestration morphology, or function as determined by endocytosis studies. All xanthines in high concentrations (150 μg/mL) increased fenestration frequency but at physiologically relevant concentrations, only theobromine (8 μg/mL) showed an effect. LSEC porosity was influenced only by high caffeine doses which also shifted the fenestration distribution towards smaller pores. Moreover, a dose-dependent increase in fenestration number was observed after caffeine treatment. If these compounds induce similar changes in vivo, age-related reduction of LSEC porosity can be reversed by oral treatment with theobromine or with other xanthines using targeted delivery.

Multiple comparisons of treatment against control under unequal variances using parametric bootstrap

In one-way analysis of variance models, performing simultaneous multiple comparisons of treatment groups with a control group may be of interest. Dunnett's test is used to test such differences and assumes equal variances of the response variable for each group. This assumption is not always met even after transformation. A parametric bootstrap (PB) method is developed here for comparing multiple treatment group means against the control group with unequal variances and unbalanced data. In simulation studies, the proposed method outperformed Dunnett's test in controlling the type I error under various settings, particularly when data have heteroscedastic variance and unbalanced design. Simulations show that power is often lower for the PB method than for Dunnett's test under equal variance, balanced data, or smaller sample size, but similar to or higher than for Dunnett's test with unequal variance, unbalanced data and larger sample size. The method is applied to a dataset concerning isotope levels found in elephant tusks from various geographical areas. These data have very unbalanced group sizes and unequal variances. This example illustrates that the PB method is easy to implement and avoids the need for transforming data to meet the equal variance assumption, simplifying interpretation of results.

Evaluation of CYP1A2 activity: Relationship between the endogenous urinary 6-hydroxymelatonin to melatonin ratio and paraxanthine to caffeine ratio in dried blood spots

The suitability of the endogenous 6‐hydroxymelatonin/melatonin urinary metabolic ratio as a surrogate for the paraxanthine/caffeine ratio to predict cytochrome P450 1A2 (CYP1A2) activity was assessed in this study. Twelve healthy volunteers completed four study sessions spread over 1 month (including overnight urine collection with first morning voids collected separately). Except for the third session, volunteers were asked to abstain from methylxanthine‐containing beverages and foods at least 24 h before urine collection. At the end of urine collection, subjects were given a caffeinated beverage and capillary blood samples were collected 2 h after the drink administration. A significant linear relationship between the 6‐hydroxymelatonin/melatonin ratios from 12‐h urine samples and first morning voids was observed (R² = 0.876, p < 0.0001). In contrast to the paraxanthine/caffeine ratio, consumption of methylxanthine‐containing beverages during session three did not significantly influence the 6‐hydroxymelatonin/melatonin ratios compared with the other sessions requiring abstinence from caffeine. A larger intra‐ and interindividual variability in the 6‐hydroxymelatonin/melatonin ratios compared with the paraxanthine/caffeine ratio was also observed. A very weak correlation was observed between the paraxanthine/caffeine ratio and both of the endogenous 6‐hydroxymelatonin/melatonin ratios (Pearson r < 0.35, p < 0.05). All these results question whether this endogenous metric could adequately reflect CYP1A2 activity or substitute for the probe caffeine. Additional studies with larger study samples are needed to examine this endogenous metric in more details.

Beyond AOPs: A Mechanistic Evaluation of NAMs in DART Testing

New Approach Methodologies (NAMs) promise to offer a unique opportunity to enable human-relevant safety decisions to be made without the need for animal testing in the context of exposure-driven Next Generation Risk Assessment (NGRA). Protecting human health against the potential effects a chemical may have on embryo-foetal development and/or aspects of reproductive biology using NGRA is particularly challenging. These are not single endpoint or health effects and risk assessments have traditionally relied on data from Developmental and Reproductive Toxicity (DART) tests in animals. There are numerous Adverse Outcome Pathways (AOPs) that can lead to DART, which means defining and developing strict testing strategies for every AOP, to predict apical outcomes, is neither a tenable goal nor a necessity to ensure NAM-based safety assessments are fit-for-purpose. Instead, a pragmatic approach is needed that uses the available knowledge and data to ensure NAM-based exposure-led safety assessments are sufficiently protective. To this end, the mechanistic and biological coverage of existing NAMs for DART were assessed and gaps to be addressed were identified, allowing the development of an approach that relies on generating data relevant to the overall mechanisms involved in human reproduction and embryo-foetal development. Using the knowledge of cellular processes and signalling pathways underlying the key stages in reproduction and development, we have developed a broad outline of endpoints informative of DART. When the existing NAMs were compared against this outline to determine whether they provide comprehensive coverage when integrated in a framework, we found them to generally cover the reproductive and developmental processes underlying the traditionally evaluated apical endpoint studies. The application of this safety assessment framework is illustrated using an exposure-led case study.

Pharmacokinetics of Caffeine: A Systematic Analysis of Reported Data for Application in Metabolic Phenotyping and Liver Function Testing

Caffeine is by far the most ubiquitous psychostimulant worldwide found in tea, coffee, cocoa, energy drinks, and many other beverages and food. Caffeine is almost exclusively metabolized in the liver by the cytochrome P-450 enzyme system to the main product paraxanthine and the additional products theobromine and theophylline. Besides its stimulating properties, two important applications of caffeine are metabolic phenotyping of cytochrome P450 1A2 (CYP1A2) and liver function testing. An open challenge in this context is to identify underlying causes of the large inter-individual variability in caffeine pharmacokinetics. Data is urgently needed to understand and quantify confounding factors such as lifestyle (e.g., smoking), the effects of drug-caffeine interactions (e.g., medication metabolized via CYP1A2), and the effect of disease. Here we report the first integrative and systematic analysis of data on caffeine pharmacokinetics from 141 publications and provide a comprehensive high-quality data set on the pharmacokinetics of caffeine, caffeine metabolites, and their metabolic ratios in human adults. The data set is enriched by meta-data on the characteristics of studied patient cohorts and subjects (e.g., age, body weight, smoking status, health status), the applied interventions (e.g., dosing, substance, route of application), measured pharmacokinetic time-courses, and pharmacokinetic parameters (e.g., clearance, half-life, area under the curve). We demonstrate via multiple applications how the data set can be used to solidify existing knowledge and gain new insights relevant for metabolic phenotyping and liver function testing based on caffeine. Specifically, we analyzed 1) the alteration of caffeine pharmacokinetics with smoking and use of oral contraceptives; 2) drug-drug interactions with caffeine as possible confounding factors of caffeine pharmacokinetics or source of adverse effects; 3) alteration of caffeine pharmacokinetics in disease; and 4) the applicability of caffeine as a salivary test substance by comparison of plasma and saliva data. In conclusion, our data set and analyses provide important resources which could enable more accurate caffeine-based metabolic phenotyping and liver function testing.

Physiologically Based Pharmacokinetic/Pharmacodynamic Model for Caffeine Disposition in Pregnancy

Caffeine is the most consumed active stimulant. About 80% of pregnant women consume caffeine orally on a daily basis. Many reports indicated consumption of >200 mg caffeine during pregnancy could increase the likelihood of miscarriage. In this article, we developed a pregnancy physiological-based pharmacokinetic/pharmacodynamic (PBPK/PD) model for caffeine to examine association between maternal caffeine consumption during pregnancy and caffeine plasma levels at doses lower and higher than 200 mg to predict changes in caffeine concentrations across the 3 trimesters, and to predict associated changes in caffeine PD parameters. Two models were successfully developed using GastroPlus software, a nonpregnant model for validation purposes and a pregnant model for validation and prediction of maternal caffeine plasma concentrations following single and multiple dosing. Using observed and predicted data, we were able to validate and simulate PK changes of caffeine in nonpregnant women and the PD effect of caffeine on certain enzymes and catecholamines associated with caffeine intake. Furthermore, the pregnancy PBPK model successfully predicted changes in caffeine PK across the three trimesters. Caffeine increased exposure during pregnancy was related to reduced activity of caffeine metabolizing enzyme CYP1A2. The model also predicted increased levels of caffeine in the fetoplacental compartment (FPC) due to increased maternal caffeine plasma concentrations. Increased caffeine levels in maternal blood was accompanied by greater inhibition of the phosphodiesterase enzyme, higher cyclic adenosine monophosphate, and greater increase of epinephrine levels, which could increase the risk of pregnancy loss. The application of the developed PBPK model to predict the PD effect could provide a useful tool to help define potential cut-offs for caffeine intake in various stages of pregnancy.

Potential nutraceutical and food additive properties and risks of coffee: a comprehensive overview

Coffee is a composite mixture of more than a thousand diverse phytochemicals like alkaloids, phenolic compounds, vitamins, carbohydrates, lipids, minerals and nitrogenous compounds. Coffee has multifunctional properties as a food additive and nutraceutical. As a nutraceutical, coffee has anti-inflammatory, anti-oxidant, antidyslipidemic, anti-obesity, type-2 diabetes mellitus (DM), and cardiovascular diseases (CVD), which can serve for the treatment and prevention of metabolic syndrome and associated disorders. On the other hand, as a food additive, coffee has antimicrobial activity against a wide range of microorganisms, inhibits lipid peroxidation (LPO), and can function as a prebiotic. The outcomes of different studies also revealed that coffee intake may reduce the incidence of numerous chronic diseases, like liver disease, mental health, and it also overcomes the all-cause mortality, and suicidal risks. In some studies, high intake of coffee is linked to increase CVD risk factors, like cholesterol, plasma homocysteine and blood pressure (BP). There is also a little evidence that associated the coffee consumption with increased risk of lung tumors in smokers. Among adults who consume the moderate amount of coffee, there is slight indication of health hazards with strong indicators of health benefits. Moreover, existing literature suggests that it may be cautious for pregnant women to eliminate the chances of miscarriages and impaired fetal growth. The primary purpose of this narrative review is to provide an overview of the findings of the positive impacts and risks of coffee consumption on human health. In conclusion, to date, the best available evidence from research indicates that drinking coffee up to 3-4 cups/day provides health benefits for most people.

Caffeine and the eye

Caffeine, a popular psychostimulant that acts as an adenosine receptor antagonist, is the most widely used drug in history, consumed daily by people worldwide. Knowledge of the physiological and pathological effects of caffeine is crucial in improving public health because of its widespread use. We provide a summary of the current evidence on the effect of caffeine on the eye. Most of the research conducted to date is in relation to cataract and glaucoma, two of the most common eye diseases among the elderly.

Interindividual Differences in Caffeine Metabolism and Factors Driving Caffeine Consumption

Most individuals adjust their caffeine intake according to the objective and subjective effects induced by the methylxanthine. However, to reach the desired effects, the quantity of caffeine consumed varies largely among individuals. It has been known for decades that the metabolism, clearance, and pharmacokinetics of caffeine is affected by many factors such as age, sex and hormones, liver disease, obesity, smoking, and diet. Caffeine also interacts with many medications. All these factors will be reviewed in the present document and discussed in light of the most recent data concerning the genetic variability affecting caffeine levels and effects at the pharmacokinetic and pharmacodynamic levels that both critically drive the level of caffeine consumption. The pharmacokinetics of caffeine are highly variable among individuals due to a polymorphism at the level of the CYP1A2 isoform of cytochrome P450, which metabolizes 95% of the caffeine ingested. Moreover there is a polymorphism at the level of another critical enzyme, N-acetyltransferase 2. At the pharmacodynamic level, there are several polymorphisms at the main brain target of caffeine, the adenosine A2A receptor or ADORA2. Genetic studies, including genome-wide association studies, identified several loci critically involved in caffeine consumption and its consequences on sleep, anxiety, and potentially in neurodegenerative and psychiatric diseases. We start reaching a better picture on how a multiplicity of biologic mechanisms seems to drive the levels of caffeine consumption, although much more knowledge is still required to understand caffeine consumption and effects on body functions.

A Randomized, Two-Way Crossover Study to Evaluate the Pharmacokinetics of Caffeine Delivered Using Caffeinated Chewing Gum Versus a Marketed Caffeinated Beverage in Healthy Adult Volunteers

Background: This study was conducted to compare the pharmacokinetics of caffeine delivered using caffeinated chewing gum to that delivered using a marketed caffeinated beverage (instant coffee) in 16 healthy adult volunteers. Materials and Methods: This was a controlled open-label, randomized, two-period crossover study. Caffeinated chewing gum and a serving of instant coffee, each containing ∼50 mg caffeine, were administered with blood samples collected before and up to 24 hours after administration starts. Plasma caffeine levels were analyzed using validated liquid chromatography coupled with tandem mass spectrometry methodology. Results: There were no statistical differences between the two caffeine products in tmax (p = 0.3308) and ka (p = 0.3894). Although formulated at ∼50 mg caffeine each, mean dose released from chewing gum was ∼18% less than beverage. Dose-normalized area under the concentration-time curve (AUC)0-t, AUC0-∞, and Cmax was similar between products. Although the criteria were not set a priori and the study was not powered for concluding bioequivalence, the 90% confidence intervals fell within the bioequivalence limit of 80% to 125%. Conclusions: Existing scientific literature on caffeine, based mostly on data from caffeinated beverages, can be leveraged to support the safety of caffeine delivered by chewing gum and current maximum safe caffeine dose advice should be applicable irrespective of delivery method.

Review of Caffeine-Related Fatalities along with Postmortem Blood Concentrations in 51 Poisoning Deaths

Publications reporting concentrations of caffeine in postmortem blood were reviewed if the cause of death was attributed to overdosing (poisoning) with drugs. Age and gender of the deceased, the manner of death (accident, suicide or undetermined) and types of co-ingested drugs were evaluated in relation to the concentrations of caffeine in blood (N = 51). The mean age (±SD) of the victims was 39 ± 17.8 years (range 18-84 years) and most were female (N = 31 or 61%). The difference in mean age of males (42 ± 17.2 years) and females (37 ± 18.3 years) was not statistically significant (t = 0.811, P = 0.421). The mean (±SD), median and range of caffeine concentrations in postmortem blood were 187 ± 96 mg/L (180 mg/L) and 33-567 mg/L, respectively. The median concentration of caffeine in males (161 mg/L) was not significantly different from that of females (182 mg/L), z = 1.18, P = 0.235. There was no correlation between the age of the deceased and the concentration of caffeine in postmortem blood (R2 = 0.026, P > 0.05). Manner of death was classified as suicide in 51% of cases (median blood-caffeine 185 mg/L), accidental in 16% (median 183 mg/L) or undetermined in 33% (median 113 mg/L). The median concentration of caffeine in blood was lower when manner of death was undetermined compared with suicide or accidental (P = 0.023). Although other drugs, including ethanol, antidepressants, antipsychotics, benzodiazepines and/or ephedrine, were often identified in postmortem blood, the predominant psychoactive substance was caffeine. The deceased had ingested caffeine in tablet or powder form and it does not seem likely that toxic concentrations of caffeine can be achieved from over-consumption of caffeinated beverages alone.

Effects of caffeine intake prior to stress cardiac magnetic resonance perfusion imaging on regadenoson- versus adenosine-induced hyperemia as measured by T1 mapping

The antagonistic effects of caffeine on adenosine receptors are a possible cause of false-negative stress perfusion imaging. The purpose of this study was to determine the effects of coffee intake <4 h prior to stress perfusion cardiac magnetic resonance imaging (CMR) in regadenoson- versus adenosine-induced hyperemia as measured with T1-mapping. 98 consecutive patients with suspected coronary artery disease referred for either adenosine or regadenoson perfusion CMR were included in this analysis. Twenty-four patients reported coffee consumption <4 h before CMR (15 patients with adenosine, and 9 patients with regadenoson); 74 patients reported no coffee intake (50 patients with adenosine, and 24 patients with regadenoson). T1 mapping was performed using a modified look-locker inversion recovery sequence. T1 reactivity was determined by subtracting T1_rest from T1_stress. T1_rest, T1_stress, and T1 reactivity in patients referred for regadenoson perfusion CMR were not significantly different when comparing patients with <4 h coffee intake and patients who reported no coffee intake (976 ± 4 ms, 1019 ± 48 ms, and 4.4 ± 3.2% vs 971 ± 33 ms, 1023 ± 43 ms, and 5.4 ± 2.4%) (p = 0.70, 0.79, and 0.40), and similar to values in patients without coffee intake undergoing adenosine CMR. In patients with <4 h coffee intake, T1_stress, and T1 reactivity were significantly lower for adenosine (898 ± 51 ms, and −7.8 ± 5.0%) compared to regadenoson perfusion CMR (p < 0.001). Coffee intake <4 h prior to regadenoson perfusion CMR has no effect on stress-induced hyperemia as measured with T1 mapping.

Dose-dependent model of caffeine effects on human vigilance during total sleep deprivation

Caffeine is the most widely consumed stimulant to counter sleep-loss effects. While the pharmacokinetics of caffeine in the body is well-understood, its alertness-restoring effects are still not well characterized. In fact, mathematical models capable of predicting the effects of varying doses of caffeine on objective measures of vigilance are not available. In this paper, we describe a phenomenological model of the dose-dependent effects of caffeine on psychomotor vigilance task (PVT) performance of sleep-deprived subjects. We used the two-process model of sleep regulation to quantify performance during sleep loss in the absence of caffeine and a dose-dependent multiplier factor derived from the Hill equation to model the effects of single and repeated caffeine doses. We developed and validated the model fits and predictions on PVT lapse (number of reaction times exceeding 500 ms) data from two separate laboratory studies. At the population-average level, the model captured the effects of a range of caffeine doses (50-300 mg), yielding up to a 90% improvement over the two-process model. Individual-specific caffeine models, on average, predicted the effects up to 23% better than population-average caffeine models. The proposed model serves as a useful tool for predicting the dose-dependent effects of caffeine on the PVT performance of sleep-deprived subjects and, therefore, can be used for determining caffeine doses that optimize the timing and duration of peak performance.

Effect of caffeine-containing beverage consumption on serum alanine aminotransferase levels in patients with chronic hepatitis C virus infection: a hospital-based cohort study

INTRODUCTION

To date, there have been no prospective studies examining the effect of coffee consumption on serum alanine aminotransferase (ALT) level among individuals infected with the hepatitis C virus (HCV). We conducted a hospital-based cohort study among patients with chronic HCV infection to assess an association between baseline coffee consumption and subsequent ALT levels for 12 months.

MATERIALS AND METHODS

From 1 August 2005 to 31 July 2006, total 376 HCV-RNA positive patients were recruited. A baseline questionnaire elicited information on the frequency of coffee consumption and other caffeine-containing beverages. ALT level as a study outcome was followed through the patients' medical records during 12 months. The association between baseline beverage consumption and subsequent ALT levels was evaluated separately among patients with baseline ALT levels within normal range (≤45 IU/L) and among those with higher ALT levels (>45 IU/L).

RESULTS

Among 229 patients with baseline ALT levels within normal range, 186 (81%) retained normal ALT levels at 12 months after recruitment. Daily drinkers of filtered coffee were three times more likely to preserve a normal ALT level than non-drinkers (OR=2.74; P=0.037). However, decaffeinated coffee drinkers had a somewhat inverse effect for sustained normal ALT levels, with marginal significance (OR=0.26; P=0.076). In addition, among 147 patients with higher baseline ALT levels, 39 patients (27%) had ALT reductions of ≥20 IU/L at 12 months after recruitment. Daily drinkers of filtered coffee had a significantly increased OR for ALT reduction (OR=3.79; P=0.034). However, in decaffeinated coffee drinkers, OR could not be calculated because no patients had ALT reduction.

CONCLUSION

Among patients with chronic HCV infection, daily consumption of filtered coffee may have a beneficial effect on the stabilization of ALT levels.

A pharmacometric approach to investigate the impact of methylxanthine abstinence and caffeine consumption on CYP1A2 activity

This study aimed to investigate the impact of methylxanthine abstinence (MA) periods on CYP1A2 activity in individuals with varying levels of caffeine consumption through development of a population pharmacokinetic model of caffeine and its major metabolite paraxanthine. This study developed and evaluated a mixed-effects pharmacokinetic model for caffeine and paraxanthine concentration-time data derived from a sequential single-dose cross-over study in healthy male volunteers (n = 30) who received oral 100 mg caffeine doses. Participants received caffeine with and without a MA period. Participants were classified as low (0-100 mg/d), medium (100-200 mg/d), or high (>200 mg/d) caffeine consumers (LCCs, MCCs, or HCCs, respectively). All caffeine and paraxanthine concentration-time data were simultaneously modeled. Caffeine pharmacokinetics was described by a two-compartment model with first-order absorption and two first-order elimination pathways. Paraxanthine was described by a one-compartment model with first-order absorption and elimination. Among LCCs (n = 16) and MCCs (n = 9), there was no difference in the mean (95% confidence interval) total apparent caffeine clearance (CL) between the MA period [LCCs: 6.88 (5.61-8.16 l/h); MCCs: 10.09 (7.57-12.60 l/h)] versus the no MA period [LCCs: 6.22 (4.97-7.46 l/h); MCCs: 9.68 (7.12-12.24 l/h)]. The mean CL among HCCs (n = 5) was considerably higher in the MA period [10.48 (5.62-15.33 l/h)] compared with the no MA period [6.30 (3.40-9.20 l/h)] (P < 0.05). The decrease in CL in the no MA period among HCC appears to be due to alternative caffeine elimination pathways, rather than CYP1A2.

Serum Metabolite/Caffeine Ratios as a Test for Liver Function

The aim of this study was to test the usefulness of the metabolite/caffeine ratio for the evaluation of hepatic dysfunction. Subjects with liver cirrhosis and chronic hepatitis, as well as healthy volunteers, were given the oral dose of 300 mg caffeine. Blood samples were collected after 4, 8, and 12 hours. Concentrations of caffeine (CA) and its three metabolites-paraxanthine (PX), theobromine (TB), and theophylline (TP)-were determined by high-performance liquid chromatography. Pharmacokinetic parameters of caffeine and PX/CA, TB/CA, and TP/CA ratios were calculated. Elimination of caffeine was decreased in cirrhotics in comparison with healthy volunteers, as proved by the values of clearance (0.035 vs. 0.094 L/h/kg), elimination coefficient (0.061 vs. 0.153 h(-1)), and half-life (11.4 vs. 4.3 h). Serum metabolite/caffeine ratios were significantly reduced in cirrhotic patients: PX/CA by more than 80%, TB/CA by 50% to 70%, and TP/CA by 40% to 70%. The reduction of the ratios in chronic hepatitis patients was lower and did not occur at all time points. A high correlation was found between caffeine clearance and metabolite/caffeine ratios. Metabolite/caffeine ratios calculated in a single blood sample collected 8 or 12 hours after caffeine administration could provide a practical assessment of hepatic function in cirrhotic patients. The value of the test for the chronic hepatitis patients is limited.

Pharmacokinetics of caffeine in plasma and saliva, and the influence of caffeine abstinence on CYP1A2 metrics

OBJECTIVES

To investigate the utility of metrics of CYP1A2 activity using caffeine as a probe, and saliva and plasma sampling with or without a 24-h caffeine abstinence.

METHODS

This was a cross-over pharmacokinetic study in 30 healthy male subjects who received a single oral 100mg caffeine dose after 24-h caffeine abstinence or after maintaining their regular caffeine intake (no caffeine abstinence). Serial blood and saliva samples were collected simultaneously over 24h. Caffeine and paraxanthine concentrations were measured using a validated HPLC assay.

KEY FINDINGS

There was a strong correlation between the paraxanthine/caffeine AUC(0-24) ratio (reference metric) and the paraxanthine/caffeine concentration (C(t) ) ratio at 4h (C(4) ) in both saliva and plasma (r≥0.75). The paraxanthine/caffeine AUC(0-24) ratio in plasma and saliva did not differ between the 24-h caffeine abstinence and the no abstinence period (P>0.05). The optimal paraxanthine/caffeine C(t) that correlated with the plasma paraxanthine/caffeine AUC(0-24) ratio in the 24-h abstinence period was 2 and 4h (r=0.88) in plasma, and 4 and 6h in saliva (r=0.70), while it was the saliva 4h time-point in the no abstinence period (r=0.78).

CONCLUSIONS

The saliva paraxanthine/caffeine concentration ratio at 4h was a suitable metric to assess CYP1A2 activity after oral administration of caffeine without the need for 24-h caffeine abstinence.

Pharmacokinetics and metabolism of natural methylxanthines in animal and man

Caffeine, theophylline, theobromine, and paraxanthine administered to animals and humans distribute in all body fluids and cross all biological membranes. They do not accumulate in organs or tissues and are extensively metabolized by the liver, with less than 2% of caffeine administered excreted unchanged in human urine. Dose-independent and dose-dependent pharmacokinetics of caffeine and other dimethylxanthines may be observed and explained by saturation of metabolic pathways and impaired elimination due to the immaturity of hepatic enzyme and liver diseases. While gender and menstrual cycle have little effect on their elimination, decreased clearance is seen in women using oral contraceptives and during pregnancy. Obesity, physical exercise, diseases, and particularly smoking and the interactions of drugs affect their elimination owing to either stimulation or inhibition of CYP1A2. Their metabolic pathways exhibit important quantitative and qualitative differences in animal species and man. Chronic ingestion or restriction of caffeine intake in man has a small effect on their disposition, but dietary constituents, including broccoli and herbal tea, as well as alcohol were shown to modify their plasma pharmacokinetics. Using molar ratios of metabolites in plasma and/or urine, phenotyping of various enzyme activities, such as cytochrome monooxygenases, N-acetylation, 8-hydroxylation, and xanthine oxidase, has become a valuable tool to identify polymorphisms and to understand individual variations and potential associations with health risks in epidemiological surveys.

Pharmacokinetics in special populations

Pharmacokinetics are typically dependent on a variety of physiological variables (e.g., age, ethnicity, or pregnancy) or pathological conditions (e.g., renal and hepatic insufficiency, cardiac dysfunction, obesity, etc.). The influence of some of these conditions has not always been thoroughly assessed in the clinical studies of antiallergic drugs. However, the knowledge of the physiological grounds of the pharmacokinetics can provide some insight for predicting the potential alterations and guiding the initial prescription strategies. It is important to recognize that both pharmacokinetic and pharmacodynamic differences between populations should be considered. The available information on drugs used for the therapy of allergic diseases is reviewed in this chapter.

Inverse association between coffee drinking and the risk of hepatocellular carcinoma: a case-control study in Japan

Coffee use has consistently been associated with lower serum liver enzyme levels and a reduced risk of liver cirrhosis. A limited number of cohort and case-control studies also suggest a decreased risk of hepatocellular carcinoma (HCC) among coffee drinkers, but mostly without consideration of hepatitis virus infection. In the present case-control study, we recruited 209 incident HCC cases and three different controls (1308 community controls, 275 hospital controls, and 381 patients with chronic liver disease [CLD] without HCC), all of whom were aged 40-79 years and residents of Saga Prefecture, Japan. A questionnaire survey elicited information on coffee use during the last 1-2 years and 10 years before, and plasma hepatitis B surface antigen and antibodies to hepatitis C virus were tested for all but community controls. After adjustment for sex, age, heavy alcohol use, smoking status and hepatitis virus markers (except for community controls), coffee use during the last 1-2 years was associated with a decreased risk against any control group. For coffee use 10 years before, comparison between HCC cases and either community controls or CLD patients revealed a decreased risk; adjusted odds ratios for occasional use, 1-2 cups/day and > or =3 cups/day compared with no use were 0.33, 0.27 and 0.22 (P trend < 0.001), respectively, against community controls, and 0.86, 0.62 and 0.53 (P trend = 0.05), respectively, against CLD patients. These results suggest that coffee may protect against the development of HCC, yet further elaborate studies (hopefully, intervention studies) are warranted to corroborate these findings.

Inhibitory Effects of Propafenone on the Pharmacokinetics of Caffeine in Humans

CYP1A2 is involved in the metabolism of both caffeine and propafenone, a class Ic antiarrhythmic agent. Despite the widespread consumption of caffeine, drug-drug interactions with this agent are often overlooked. This study investigated effects of propafenone on the pharmacokinetics of caffeine. Eight healthy volunteers were included in our study. A total of 300 mg of caffeine was given on 2 occasions, once alone and once during the coadministration of 300 mg propafenone. Serial blood samples were collected and pharmacokinetic parameters were estimated using a population pharmacokinetic approach. A one-compartment PK model with first-order absorption and elimination described plasma concentration profiles. Concomitant administration of propafenone decreased caffeine oral clearance from 8.3 +/- 0.9 L/h to 5.4 +/- 0.7 L/h (P < 0.05). Elimination half-life of caffeine was also increased 54% by propafenone. One of our volunteers was a poor metabolizer of CYP2D6. Concomitant administration of propafenone to this volunteer caused the greatest increase in caffeine plasma concentrations. These results support the concept of competitive inhibition between propafenone and caffeine. Our results suggest that propafenone causes significant inhibition of CYP1A2 activity leading to a decrease in the clearance of caffeine. Caffeine has intrinsic proarrhythmic effects; thus, its coadministration with an antiarrhythmic agent such as propafenone should be used with caution, especially in patients with poor CYP2D6 activity.

Coffee and health: a review of recent human research

Coffee is a complex mixture of chemicals that provides significant amounts of chlorogenic acid and caffeine. Unfiltered coffee is a significant source of cafestol and kahweol, which are diterpenes that have been implicated in the cholesterol-raising effects of coffee. The results of epidemiological research suggest that coffee consumption may help prevent several chronic diseases, including type 2 diabetes mellitus, Parkinson's disease and liver disease (cirrhosis and hepatocellular carcinoma). Most prospective cohort studies have not found coffee consumption to be associated with significantly increased cardiovascular disease risk. However, coffee consumption is associated with increases in several cardiovascular disease risk factors, including blood pressure and plasma homocysteine. At present, there is little evidence that coffee consumption increases the risk of cancer. For adults consuming moderate amounts of coffee (3-4 cups/d providing 300-400 mg/d of caffeine), there is little evidence of health risks and some evidence of health benefits. However, some groups, including people with hypertension, children, adolescents, and the elderly, may be more vulnerable to the adverse effects of caffeine. In addition, currently available evidence suggests that it may be prudent for pregnant women to limit coffee consumption to 3 cups/d providing no more than 300 mg/d of caffeine to exclude any increased probability of spontaneous abortion or impaired fetal growth.

Coffee and tea consumption are associated with a lower incidence of chronic liver disease in the United States

BACKGROUND & AIMS

Coffee drinking has been suggested to protect against liver injury, but it is uncertain whether this is of clinical significance. We examined the relationship of coffee and tea consumption with the incidence of hospitalization or death from chronic liver disease (CLD).

METHODS

Participants in the population-based, first National Health and Nutrition Examination Survey, 1971-1975, were asked about coffee and tea consumption, which was categorized as <1 cup (mean, 0.2 cups), 1 to 2 cups, and >2 cups per day (mean, 4.0 cups). A second analysis included persons who, in 1982-1984, were asked more detailed questions on coffee and tea drinking. Participants were followed through 1992-1993 for a hospital or death certificate diagnosis of CLD or cirrhosis (ICD-9-CM 571). Hazard rate ratios for CLD according to coffee and tea intake were calculated using Cox proportional hazards analysis.

RESULTS

Among 9849 persons followed for a median of 19.0 years (range, 0.02-22.1), the cumulative incidence of CLD was 1.4%. In multivariate analysis, participants who drank >2 cups per day had less than half the rate of CLD as those who drank <1 cup per day (hazard ratio, 0.43, 95% confidence interval: 0.24-0.78). Protection by coffee and tea was limited to persons at higher risk for liver diseases from heavier alcohol intake, overweight, diabetes, or high iron saturation. Among 9650 participants who provided detailed drink information in 1982-1984, intake of regular ground coffee and of caffeine was associated with lower incidence of CLD.

CONCLUSIONS

Coffee and tea drinking decreases the risk of clinically significant CLD.

Artemisinin and thiabendazole are potent inhibitors of cytochrome P450 1A2 (CYP1A2) activity in humans

OBJECTIVE

To investigate the likelihood of artemisinin and thiabendazole causing pharmacokinetic interactions involving cytochrome P450 (CYP1A2) in humans given their potent inhibitory effects on the isoform in vitro.

METHODS

Ten healthy volunteers received caffeine (136.5 mg), and after a washout period of 48 h, the volunteers were given a caffeine tablet (136.5 mg) together with thiabendazole (500 mg). After an additional 14 days, the volunteers received caffeine together with artemisinin (500 mg). After each treatment, plasma was obtained up to 24 h post-dose. The plasma concentrations of the drugs were measured by HPLC with UV and MS detection.

RESULTS

Using the ratio of paraxanthine to caffeine after 4 h as an indicator of CYP1A2 activity, thiabendazole and artemisinin inhibited 92 and 66%, respectively, of the enzyme activity in vivo. In addition, the pharmacokinetics of caffeine were altered in the presence of the drugs; increases in AUC(0-24) of 1.6-fold (P < 0.01) and 1.3-fold of caffeine in the presence of thiabendazole and artemisinin respectively were measured. The use of in vitro data to predict the effects of thiabendazole on the formation of paraxanthine yielded good results and underestimated the effects of artemisinin when total plasma concentrations were used. Corrections for protein binding resulted in underestimation of inhibitory effects on CYP1A2.

CONCLUSIONS

Co-administration of thiabendazole or artemisinin with CYP1A2 substrates could result in clinically significant effects. Our results highlight the validity of in vitro data in predicting in vivo CYP inhibition. The formation of paraxanthine seems to be a better indicator of in vivo CYP1A2 activity than caffeine levels.

Caffeine Use in Sports, Pharmacokinetics in Man, and Cellular Mechanisms of Action

Caffeine is the most widely consumed psychoactive 'drug' in the world and probably one of the most commonly used stimulants in sports. This is not surprising, since it is one of the few ergogenic aids with documented efficiency and minimal side effects. Caffeine is rapidly and completely absorbed by the gastrointestinal tract and is readily distributed throughout all tissues of the body. Peak plasma concentrations after normal consumption are usually around 50 microM, and half-lives for elimination range between 2.5-10 h. The parent compound is extensively metabolized in the liver microsomes to more than 25 derivatives, while considerably less than 5% of the ingested dose is excreted unchanged in the urine. There is, however, considerable inter-individual variability in the handling of caffeine by the body, due to both environmental and genetic factors. Evidence from in vitro studies provides a wealth of different cellular actions that could potentially contribute to the observed effects of caffeine in humans in vivo. These include potentiation of muscle contractility via induction of sarcoplasmic reticulum calcium release, inhibition of phosphodiesterase isoenzymes and concomitant cyclic monophosphate accumulation, inhibition of glycogen phosphorylase enzymes in liver and muscle, non-selective adenosine receptor antagonism, stimulation of the cellular membrane sodium/potassium pump, impairment of phosphoinositide metabolism, as well as other, less thoroughly characterized actions. Not all, however, seem to account for the observed effects in vivo, although a variable degree of contribution cannot be readily discounted on the basis of experimental data. The most physiologically relevant mechanism of action is probably the blockade of adenosine receptors, but evidence suggests that, at least under certain conditions, other biochemical mechanisms may also be operational.

Mechanistic pharmacokinetic modelling of ephedrine, norephedrine and caffeine in healthy subjects

AIM

The combination of ephedrine and caffeine has been used in herbal products for weight loss and athletic performance-enhancement, but the pharmacokinetic profiles of these compounds have not been well characterized. This study aimed to develop a mechanistic model describing ephedrine, norephedrine, and caffeine pharmacokinetics and their interactions in healthy subjects.

METHODS

The pharmacokinetic model was developed based on the simultaneous modelling using plasma samples gathered from two clinical trials. The treatments consisted of single-doses of pharmaceutical caffeine and ephedrine, given alone or together, and an herbal formulation containing both caffeine and ephedrine. We used a mixed-effect statistical model and the program NONMEM to take account of intersubject variability.

RESULTS

Three hundred and seventy-nine ephedrine, 352 norephedrine, 417 caffeine plasma concentrations and 40 ephedrine urine concentrations were obtained from 24 subjects. A one-compartment model with first-order absorption described the caffeine data. Caffeine clearance was 0.083 l min(-1) (CV 38%) and decreased to 0.038 l min(-1) in presence of oral contraceptive therapy, its volume of distribution was 38.6 l (CV 20%) and its absorption rate constant was 0.064 l min(-1) (CV 50%). A four-compartment model described the pharmocokinetics of ephedrine and norephedrine. Ephedrine was eliminated mostly renally, with a clearance of 0.34 l min(-1) (CV 11%), and a volume of distribution of 181 l (CV 19%). Nonlinearity in the conversion of ephedrine to norephedrine was observed. Different models showed that the simultaneous administration of caffeine, or the amount of caffeine in the absorption compartment, was associated with a slower rate of absorption of ephedrine. A 32% greater relative bioavailability of herbal compared with pharmaceutical ephedrine administration was observed.

CONCLUSIONS

We describe a mechanistic model for ephedrine, norephedrine and caffeine pharmacokinetics and their interactions. The relative bioavailability of ephedrine differed between the herbal supplement compared with the pharmaceutical formulation. Concomitant ingestion of caffeine slowed the absorption rate of ephedrine, which is mainly related to the amount of the former in the absorption compartment. A saturable process appears to be involved in the metabolism of ephedrine to norephedrine.

Coffee and caffeine consumption reduce the risk of elevated serum alanine aminotransferase activity in the United States

BACKGROUND & AIMS

Based on experimental and epidemiologic studies, we investigated whether coffee and caffeine consumption reduced the risk of elevated alanine aminotransferase (ALT) activity in persons at high risk for liver injury in a national, population-based study.

METHODS

Participants were 5944 adults in the Third US National Health and Nutrition Examination Survey, 1988-1994, with excessive alcohol consumption, viral hepatitis, iron overload, overweight, or impaired glucose metabolism. Liver injury was indicated by abnormal serum ALT activity (>43 U/L).

RESULTS

Elevated ALT activity was found in 8.7% of this high-risk population. In unadjusted analysis, lower ALT activity was associated with increasing consumption of coffee ( P = .001) and caffeine ( P = .001). Multivariate logistic regression analyses showed that the risk of elevated ALT activity declined with increasing intake of coffee ( P for trend = .034) and caffeine ( P < .001). Comparing persons who drank more than 2 cups per day with noncoffee drinkers, the odds ratio was .56 (95% confidence interval, .31-1.0). Comparing persons in the highest caffeine quintile with the lowest, the odds ratio was .31 (95% confidence interval, .16-.61). These relationships were consistent across subgroups at risk for liver injury and were relatively unchanged when analyses included the entire population or when limited to persons without impaired liver function or right upper quadrant pain. Fasting insulin concentrations did not mediate the effects.

CONCLUSIONS

In this large, national, population-based study, among persons at high risk for liver injury, consumption of coffee and especially caffeine was associated with lower risk of elevated ALT activity.

Improved cognitive performance in human volunteers following administration of guarana (Paullinia cupana) extract: comparison and interaction with Panax ginseng

Extracts from the plant guarana (Paullinia cupana) feature as putatively stimulating ingredients in a number of foods, drinks and dietary/herbal supplements. To date, little research in humans has examined the potential psychoactive effects of these extracts. Extracts of Panax ginseng, which are often sold in combination with guarana, contain similar potentially active components, and have been shown to modulate cognitive performance. In this double-blind, counterbalanced, placebo-controlled study, the cognitive and mood effects of separate single doses of: 75 mg of a dried ethanolic extract of guarana (approx 12% caffeine), 200 mg of Panax ginseng (G115), and their combination (75 mg/200 mg), were assessed in 28 healthy young (18-24) participants. On each day of the study (separated by a 7-day washout), cognitive performance and subjective mood were assessed pre-dose and at 1, 2.5, 4 and 6 h post-dose using the Cognitive Drug Research computerised assessment battery, Serial subtraction tasks and Bond-Lader mood scales. In comparison to placebo, all three treatments resulted in improved task performance throughout the day. In the case of guarana, improvements were seen across 'attention' tasks (but with some evidence of reduced accuracy), and on a sentence verification task. While also increasing the speed of attention task performance, both ginseng and the ginseng/guarana combination also enhanced the speed of memory task performance, with little evidence of modulated accuracy. Guarana and the combination, and to a lesser extent ginseng, also led to significant improvements in serial subtraction task performance. These results provide the first demonstration in humans of the psychoactive effects of guarana, and confirmation of the psychoactive properties of ginseng. Given the low caffeine content (9 mg) of this dose of guarana extract, the effects are unlikely to be attributable to its caffeine content.

Incorporating pharmacokinetic differences between children and adults in assessing children's risks to environmental toxicants

Children's risks from environmental toxicant exposure can be affected by pharmacokinetic factors that affect the internal dose of parent chemical or active metabolite. There are numerous physiologic differences between neonates and adults that affect pharmacokinetics including size of lipid, and tissue compartments, organ blood flows, protein binding capacity, and immature function of renal and hepatic systems. These factors combine to decrease the clearance of many therapeutic drugs, which can also be expected to occur with environmental toxicants in neonates. The net effect may be greater or lesser internal dose of active toxicant depending upon how the agent is distributed, metabolized, and eliminated. Child/adult pharmacokinetic differences decrease with increasing postnatal age, but these factors should still be considered in any children's age group, birth through adolescence, for which there is toxicant exposure. Physiologically based pharmacokinetic (PBPK) models can simulate the absorption, distribution, metabolism, and excretion of xenobiotics in both children and adults, allowing for a direct comparison of internal dose and risk across age groups. This review provides special focus on the development of hepatic cytochrome P-450 enzymes (CYPs) in early life and how this information, along with many factors unique to children, can be applied to PBPK models for this receptor population. This review describes a case study involving the development of neonatal PBPK models for the CYP1A2 substrates caffeine and theophylline. These models were calibrated with pharmacokinetic data in neonates and used to help understand key metabolic differences between neonates and adults across these two drugs.

Maternal Caffeine Consumption and Spontaneous Abortion

Since the 1980s, numerous studies have investigated whether caffeine intake during pregnancy affects the risk of spontaneous abortion. A clear consensus, however, has not been reached. Because of the public health importance of this question, we reviewed the results of 15 epidemiologic studies on this topic, with particular attention to the specific methodologic problems that would generate biased findings. These include selection and recall bias, confounding, several issues pertaining to exposure measurement, and the failure to account for fetal karyotype, caffeine metabolism, the timing of fetal demise, and the possibility that an effect of caffeine may be gestational age-specific. All of the studies reviewed suffer from important methodologic limitations that hinder both the interpretation of each study individually and the comparison of results across studies. Despite the fact that most epidemiologic studies have observed a positive association between maternal caffeine intake and the risk of spontaneous abortion, we conclude that the evidence must be considered to be equivocal, given the biases likely present and the fact that most of the potential biases would tend to overestimate any association. Until studies can overcome these limitations, evidence for a causal link between caffeine and spontaneous abortion will remain inconclusive.

Physiologically based pharmacokinetic (PBPK) modeling of caffeine and theophylline in neonates and adults: implications for assessing children's risks from environmental agents

Children's risks can differ from those in adults for numerous reasons, one being differences in the pharmacokinetic handling of chemicals. Immature metabolism and a variety of other factors in neonates can affect chemical disposition and clearance. These factors can be incorporated into physiologically based pharmacokinetic (PBPK) models that simulate the fate of environmental toxicants in both children and adults. PBPK models are most informative when supported by empirical data, but typically pediatric pharmacokinetic data for toxicants are not available. In contrast, pharmacokinetic data in children are readily available for therapeutic drugs. The current analysis utilizes data for caffeine and theophylline, closely related xanthines that are both cytochrome P-450 (CYP) 1A2 substrates, in developing PBPK models for neonates and adults. Model development involved scale-up of in vitro metabolic parameters to whole liver and adjusting metabolic function for the ontological pattern of CYP1A2 and other CYPs. Model runs were able to simulate the large differences in half-life and clearance between neonates and adults. Further, the models were able to reproduce the faster metabolic clearance of theophylline relative to caffeine in neonates. This differential between xanthines was found to be due primarily to an extra metabolic pathway available to theophylline, back-methylation to caffeine, that is not available to caffeine itself. This pathway is not observed in adults exemplifying the importance of secondary or novel routes of metabolism in the immature liver. Greater CYP2E1 metabolism of theophylline relative to caffeine in neonates also occurs. Neonatal PBPK models developed for these drugs may be adapted to other CYP1A2 substrates (e.g., arylamine toxicants). A stepwise approach for modeling environmental toxicants in children is proposed.

The effect of the CYP1A2 *1F mutation on CYP1A2 inducibility in pregnant women

AIMS

To investigate the influence of the CYP1A2*1F mutation on CYP1A2 activity in smoking and nonsmoking pregnant women.

METHODS

Pregnant women (n = 904) who served as control subjects in a case-control study of early fetal loss were investigated. They were phenotyped for CYP1A2 using dietary caffeine and the urinary ratio AFMU + 1X + 1 U/1,7 U. An assay for CYP1A2*1F using 5'-nuclease assay (Taqman) was developed to genotype the population.

RESULTS

The frequencies of *1 A and *1F alleles among Swedish women were 0.29 and 0.71, respectively. There was no statistically significant difference in CYP1A2 activity between the genotypes, although a trend towards enhanced activity was observed in *1F/*1F (log MRc 0.77) and *1F/*1 A (log MRc 0.82) genotypes compared with the *1 A/*1 A genotype (log MRc 0.71) (anovaP = 0.07). The mean difference between the *1 A homozygotes and the heterozygotes was 0.11 [95% confidence interval of the difference: (-0.21, -0.01)] and that between the *1 A and *1F homozygotes was 0.05 [95% confidence interval of the difference: (-0.13, 0.03)]. No significant effect (P = 0.22) of the *1F on CYP1A2 activity was observed in smokers, tested using an interaction term (smoking * genotype) in the anova model (*1F/*1F log MRc 0.79, *1F/*1 A log MRc 0.86, and *1 A/*1 A log MRc 0.73). In smokers, there was no difference in ratio between homozygotes for the *1 A and *1F alleles [mean difference -0.06; 95% confidence interval of the difference: -0.22, 0.11] or between *1 A/*1 A and *1 A/*1F genotypes [mean difference -0.13; 95% confidence interval of the difference: -0.29, 0.04].

CONCLUSIONS

The effect of the CYP1A2*1F mutation on CYP1A2 activity in smoking pregnant women could not be confirmed.

Effects of exercise and thermal stress on caffeine pharmacokinetics in men and eumenorrheic women

The influence of gender, exercise, and thermal stress on caffeine pharmacokinetics is unclear. We hypothesized that these factors would not have an effect on the metabolism of caffeine. Eight women participated in four 8-h trials and six men participated in two 8-h trials after the ingestion of 6 mg/kg caffeine. The women performed two resting trials (1 in the follicular phase and 1 in the luteal phase of the menstrual cycle) and two exercise trials (90 min of cycling exercise at 65% of maximal O(2) uptake, 1 h after caffeine ingestion) in the follicular phase (1 without and 1 with an additional thermal stress). The men performed one exercise and one resting trial. Menstrual cycle, gender, and exercise, with or without an additional thermal stress, had no effect on the pharmacokinetic measurements or urine caffeine. There was a trend for higher plasma caffeine and lower plasma paraxanthine concentrations in the women. These results confirm that gender, exercise, and thermal stress have no effect on caffeine pharmacokinetics in men and women.

Caffeine levels in saliva: associations with psychosocial factors and behavioural effects

The present study had two main aims. The first was to examine associations between psychosocial factors, health-related behaviours, regular level of caffeine consumption, time of day and levels of caffeine in saliva following acute caffeine challenges. The second aim was to determine whether individual differences in changes in performance following ingestion of caffeine were related to levels of caffeine in saliva. One hundred and forty-four young adults participated in the study. Questionnaires were administered prior to the study to measure psychosocial characteristics, health-related behaviours and habitual levels of caffeine consumption. Two double-blind acute caffeine challenges were then carried out 1 week apart. Volunteers were given either placebo or 1.5 or 3 mg/kg of caffeine on each occasion. The challenges were carried out at 8 : 00, 11 : 00, 14 : 00 or 18 : 00 h so that the impact of time of day could be assessed. In the week between the two challenges the volunteers consumed either caffeinated or decaffeinated products. This allowed investigation of the effects of caffeine withdrawal on caffeine metabolism. Prior to each caffeine challenge volunteers performed a range of tasks, and a baseline saliva sample was taken. The tasks were repeated 1 h after ingestion of the caffeine, with saliva samples being taken at the start and end of the 1 h test battery. The results showed that the level of caffeine in the saliva was a good indicator of the dose of caffeine consumed and of compliance with the withdrawal manipulation. Caffeine levels were not influenced by time of day, habitual caffeine consumption, psychosocial factors or health-related behaviours. Individual differences in caffeine levels in saliva were not related to the individual variation in the effects of caffeine on performance. Copyright 2001 John Wiley & Sons, Ltd.

Lifestyle and the development of increased serum gamma-glutamyltransferase in middle-aged Japanese men

To identify the lifestyle factors responsible for increases in serum gamma-glutamyltransferase (GGT), 1014 hepatobiliary dysfunction-free (no medication for and no past history of liver disease, < or = 39 U/L of serum aspartate and/or alanine aminotransferase, and < or = 59 U/L of serum GGT) Japanese male office workers aged 35-55 years were examined annually over five successive years (average period 4.5 years, SD 1.11 years). From the Cox proportional hazards model without serum GGT at entry, significant correlates with the incidence of increased (> or = 60 U/L) serum GGT levels were the slope of body mass index (BMI), alcohol intake, cigarette smoking and coffee drinking (negative). In the model including serum GGT at entry, the slope of BMI and coffee drinking (negative) remained as significant factors for the incidence of increased serum GGT levels. From stepwise regression analyses for the slope of log serum GGT at entry, not including serum GGT in the model, significant correlates with the slope of serum GGT were, in order of relative importance, the slope of BMI, alcohol intake and coffee drinking (negative). In the model with serum GGT at entry, the slope of BMI and coffee drinking (negative) remained as statistically significant. Our results indicate that an increase in body weight is the strongest determinant for increases in serum GGT and that coffee drinking may be associated with a reduced risk of the development of increased serum GGT levels.

Dose independent pharmacokinetics of caffeine after intravenous administration under a chronic food-limited regimen

Several studies have shown that caffeine follows non-linear pharmacokinetics in both rats and humans. Recent data have demonstrated that caffeine may following linear pharmacokinetics when administered orally and intraperitoneally to food-limited rats. In this study the pharmacokinetics of caffeine was analyzed following intravenous (i.v.) administration to rats under a food-limited regimen. Four rats were administered four doses of caffeine and a standard dose of the caffeine metabolites, paraxanthine, theobromine, and theophylline. Caffeine pharmacokinetic parameters were dose independent following intravenous doses ranging from 1 to 20 mg/kg. Furthermore, the caffeine area under the curve (AUC) increased linearly as a function of dose. The mean fraction of caffeine converted to paraxanthine, theobromine, and theophylline was 16%, 16%, and 7%, respectively. The linear pharmacokinetics demonstrated in the present study may be attributed to the induction of hepatic metabolism under a chronic food-limited regimen.

Cytochrome P450 and therapeutic drug monitoring with respect to clozapine

Clozapine is an atypical antipsychotic drug that is mainly used for the treatment of refractory schizophrenia. Clozapine is eliminated by oxidation in the liver, predominantly by cytochrome P4501A2 (CYP1A2). Due to the influence of inhibitors, inducers and genetic factors on CYP1A2-activity, several studies have reported a very large interindividual variability in clozapine plasma concentrations at a fixed dose. A number of methods have been published for the measurement of clozapine and metabolites in plasma. Plasma concentrations are most frequently measured by high-performance liquid chromatography. Most methods measure clozapine and the main metabolite, norclozapine, whereas two methods measure clozapine and two metabolites. Several studies suggest that a minimum effective clozapine plasma concentration of >350 microg/l must be achieved in order to ensure acceptable clinical response, whereas the upper limit of the therapeutic interval not yet has been clearly defined. The occurrence of agranulocytosis, the most serious side-effect of clozapine treatment does not seem to be dose-related and it is not possible to predict which patients are at risk of developing agranulocytosis. The risk of central nervous system side-effects seems to increase with concentrations above 1300 microg/l. Monitoring of clozapine plasma concentrations is recommended during concomitant use of other drugs that are known to interact with the oxidation of clozapine, such as carbamazepine (inducer) or fluvoxamine (inhibitor). Overall, it is concluded that therapeutic drug monitoring may be of value in the clinical management of clozapine.

Caffeine overdose in a premature infant: clinical course and pharmacokinetics

The elimination of caffeine was investigated in a 1860 g, 31 week gestation neonate, following the accidental administration of a 160 mg.kg-1 dose. The first serum concentration measured was 217.5 mg.l-1 at 36.5 h after dosing. Fitting of time-concentration data was performed using non-linear regression with MKMODEL. A first order elimination model was superior to a mixed order model. Parameter estimates were: clearance 0.01 l.h-1, volume of distribution 1.17 litres, elimination half-life 81 h. Toxic manifestations included hypertonia, sweating, tachycardia, cardiac failure, pulmonary oedema and metabolic disturbances (metabolic acidosis, hyperglycaemia and creatine kinase elevation). An unusual feature of this infant's illness course was gastric dilatation. These signs resolved by day 7 at a serum concentration of 60-70 mg.l-1. Caffeine clearance has traditionally been reported as either an absolute value or as directly proportional to body weight. The per kilogram model gives an erroneous impression that clearance is greatest in early childhood and then decreases with age until adult rates are reached in late adolescence. Age-related clearance values reported in the literature were reviewed using an allometric 3/4 power model. This size model demonstrates that clearance increases in infancy and reaches adult rates within the first three months of life.

Dietary caffeine as a probe agent for assessment of cytochrome P4501A2 activity in random urine samples

AIMS

To validate the use of randomly collected urine samples for assessment of cytochrome P4501A2 (CYP1A2) activity based on dietary caffeine (caffeine metabolic ratio, MRcaff ), and to relate the MRcaff to caffeine intake and smoking habits in a larger group of individuals.

METHODS

Nineteen healthy volunteers were included in the validation study. Caffeine (100 mg) was ingested and a urine sample was collected after 6 h. Within the following week a random urine sample was collected in the individuals without a preceding test dose of caffeine. Urine samples were analysed for caffeine and its metabolites by h.p.l.c. and the (AFMU+1U+1X)/1,7U metabolic ratio was used to reflect CYP1A2 activity. In an extended investigation of 522 healthy pregnant women the MRcaff was related to intake of caffeine from various sources, and to smoking.

RESULTS

The results from the random and standardised sampling methods correlate with each other (correlation coefficient of MRcaff was 0. 91). The MRcaff as assessed by the random sampling method in a larger population was not affected by source or amount of caffeine ingested. Significantly higher MRcaff was found in smokers compared to non-smokers. In the large group of individuals the random sampling method was possible to use in 80% of the cases. In the residual 20% one or several of the metabolite concentrations were too low or unmeasurable.

CONCLUSIONS

Our study demonstrates that the random urine caffeine phenotyping method is possible to use in as many as 80% of the individuals when based on dietary caffeine. Our approach should prove applicable in most countries with widely spread caffeine consumption. The method is useful in larger studies of drug metabolising enzyme activities and minimises the time consumption and costs.

Evaluation of pharmacokinetic methods used to estimate caffeine clearance and comparison with a Bayesian forecasting method

Simplified pharmacokinetic methods have been used to estimate caffeine clearance in subjects with liver disease. There is a need to have a reliable, easy to implement method for research and possible clinical use. This study evaluates the use of Bayesian pharmacokinetic forecasting techniques to estimate caffeine clearance and compares its performance to other published methods. Commonly used published methods include the two-concentration overnight salivary clearance method (Jost method) and a method that samples caffeine concentrations over a 4-hour time period (Nagel method). Both have been used in studies incorporating serial measurements of caffeine clearance to predict clinical outcomes in subjects with liver disease, but these approaches have not been proven useful. However, neither method has been formally evaluated for accuracy in estimating caffeine clearance in subjects with cirrhosis. The performance of the Jost, Nagel, and Bayesian methods was compared to a Gold Standard method that accurately measured caffeine clearance in healthy subjects and subjects with cirrhosis using an intravenous infusion of stable isotope-labeled caffeine. The Bayesian method, even when only one measured concentration of caffeine was used, was more accurate, better correlated to the Gold Standard method, and had less intraindividual variation than the two previously published methods. Before the idea of using serial measurements of caffeine clearance for clinical usefulness is rejected, a reevaluation using methods of estimating caffeine clearance that are more accurate than previous paradigms is needed.

Population pharmacokinetics of intravenous caffeine in neonates with apnea of prematurity

OBJECTIVE

The study the population pharmacokinetics of caffeine after intravenous administration to premature infants with apnea.

METHODS

A prospective, blinded parallel study in which daily caffeine citrate doses of 30, 15, and 3 mg/kg were administered over 7 days by intermittent intravenous infusion. Arterial blood samples (three to six per patient) were assayed for caffeine content by means of HPLC. Population pharmacokinetic modeling was performed with NONMEM.

RESULTS

Clearance (L/hr) = (0.00000399 . current weight [grams]) + (0.000128 . postnatal age [days]). For gestational age > 28 weeks, volume of distribution (L) = (0.000764 . weight [grams] + (0.0468 . postnatal age [days]); for gestational age < or = 28 weeks, volume of distribution (L) = (0.000755 . weight [grams]) + (0.0224. postnatal age [days]). Interpatient variability (coefficient of variation, in percent) was approximately 25% for clearance and approximately 11% for volume of distribution. Intrapatient error (standard deviation) was 3.9 mg/L. There was insignificant bias between observed and model-predicated serum caffeine concentrations in a separate group of 30 infants.

CONCLUSIONS

Caffeine was well tolerated at all doses. Clearance was markedly lower and volume of distribution was higher than the values reported previously for term infants and adults. Both parameters were significantly influenced by postnatal age and current body weight, whereas volume of distribution in infants > 28 weeks' gestational age was higher than that in more premature babies. The predictive performance and the clinical application of the derived population models was satisfactorily shown.

The effect of liver disease on urine caffeine metabolite ratios

OBJECTIVES

A number of caffeine metabolite ratios (CMRs) have been proposed to measure CYP1A2 activity in vivo. The effect of liver disease on these ratios is not clear. The objective of this study was to determine the influence of liver disease on caffeine metabolite ratios.

STUDY DESIGN

Two studies were performed. First, in healthy control subjects and in subjects with cirrhosis, caffeine clearance was measured by intravenous infusion of stable isotope-labeled caffeine while subjects consumed oral caffeine. Second, spot urine samples were collected from control subjects and from subjects with either chronic hepatitis or cirrhosis while they consumed caffeine.

RESULTS

In study 1, caffeine clearance was decreased in subjects with cirrhosis (control mean, 0.14 L/hr/kg; cirrhosis mean, 0.04 L/hr/kg; p = 0.003). CMRs were affected by liver disease (e.g., ratio characterizing paraxanthine demethylation [AAMU + 1X + 1U/17U], control median, 8.3; cirrhosis median, 6.2; p = 0.005). AAMU + 1X + 1U/17U correlated significantly with caffeine clearance in the control group (r2 = 0.68; p = 0.0001) and in subjects with cirrhosis (r2 = 0.41; p = 0.05). In study 2, there was a significant difference between control subjects and subjects with cirrhosis for AAMU + 1X + 1U/17U (median for control subjects, 6.2; median for subjects with cirrhosis, 4.3; p = 0.001) but not between control subjects and patients with chronic hepatitis.

CONCLUSIONS

We conclude that AAMU + 1X + 1U/17U is affected by liver disease and reflects the decrease in CYP1A2 activity in subjects with cirrhosis. AAMU + 1X + 1U/17U measured from a spot urine sample reflects caffeine clearance in subjects with cirrhosis and may be useful as a hepatic function test. Despite the large interindividual variation observed, the test can be repeated easily in the same patient and an individual patient's decline in CYP1A2 activity, such as in patients with progressively deteriorating liver function, can be monitored.

Validation of urine caffeine metabolite ratios with use of stable isotope-labeled caffeine clearance

OBJECTIVE

A number of caffeine metabolite ratios have been proposed to measure CYP1A2 activity in vivo. The data to validate these ratios are scanty. The objective of this study was to validate urine caffeine metabolite ratios versus stable isotope-labeled caffeine clearance under different caffeine dosing conditions.

STUDY DESIGN

Two experiments, one with nine nonsmoking subjects and the other with 12 cigarette smokers, were performed. We explored the relationship between caffeine clearance, measured by means of intravenous infusions of stable isotope-labeled caffeine, and a number of caffeine metabolite ratios during administration of different single or multiple doses of caffeine to smokers and nonsmokers on three different occasions over a 2-week period, using different durations of urine collections, including spot urines. The stable isotope technique allowed simultaneous oral dosing of caffeine and measurement of caffeine metabolite ratios and caffeine clearance, the latter reflecting CYP1A2 activity.

RESULTS

The caffeine metabolite ratio of AAMU + 1U +1X/17U (5-acetylamino-6-amino-3-methyluracil + 1-methyluric acid + 1 methylxanthine/1,7-dimethyluric acid) maintained a significant correlation with caffeine clearance for all the above conditions (gamma2 range, 0.4 to 0.9) except for dose. With high doses of caffeine (12 mg/kg), a significant relationship was not observed. AAMU + 1U + 1X/17U also correlated with the formation clearance of paraxanthine (gamma2 = 0.6, p = 0.002). Other reported caffeine metabolite ratios did not display the same robust correlation with caffeine clearance under all these different conditions.

CONCLUSIONS

We conclude that AAMU+1U+1X/17U measured from a single spot urine collection is a valid measure of CYP1A2 activity except at very high levels of caffeine dosing. The validity of the other proposed caffeine metabolite ratios is questionable.