Pharmacokinetic-pharmacodynamic modeling of caffeine: tolerance to pressor effects

Coffee intake and hypertension in Korean adults: results from KNHANES 2012-2016

BACKGROUND

Coffee is the most popular and widely consumed drink in the world. Coffee consumption seems to have both benefits and risk with respect to hypertension; results from studies evaluating effect of frequency of coffee consumption on risk of hypertension are mixed and inconsistent. Hence, we investigated the association of coffee consumption and hypertension in Korean adults.

METHODS

Data from Korean National Health and Nutrition Examination Survey (KNHANES) 2012-2016 was obtained and 12,133 eligible participants were selected. The coffee consumption was attained using a food frequency questionnaire. Subsequently coffee intake was grouped into two categories: ≤2 and > 2 servings per day. Hypertension status was defined as systolic blood pressure ≥ 140 mmHg or diastolic blood pressure ≥ 90 mmHg, use of antihypertensive drug treatment, or both. Multivariable logistic regression analysis was used to examine the association of coffee consumption and hypertension.

RESULTS

Logistic regression analysis showed that consumption of more than two servings of coffee a day was inversely associated with hypertension with odds ratio (OR) 0.84 (95% confidence interval [CI], 0.73-0.99). Similar results were seen in the propensity score-matched analysis (OR, 0.83; 95% CI, 0.69-0.98). Adults having age more than median value (OR, 0.76; 95% CI, 0.65-0.89) and normal cholesterol (OR, 0.84; 95% CI, 0.70-0.99) had significantly inverse association with hypertension, when coffee consumption was more than two servings daily.

CONCLUSIONS

More than two servings of coffee intake per day was inversely associated with hypertension as compared to consumption of ≤ 2 servings coffee per day.

Coffee Intake and Risk of Hypertension: A Meta-Analysis of Cohort Studies

BACKGROUND

It remains unclear whether coffee intake is associated with the risk of hypertension. This study aimed to investigate the association between coffee intake and the risk of hypertension by using a meta-analysis of cohort studies.

METHODS

PubMed and Embase were searched using keywords in September 2022 to identify studies on coffee intake and the risk of hypertension.

RESULTS

We included a total of 13 longitudinal cohort studies, which involved a total of 64,650 incident cases of hypertension among 314,827 participants. In a random effects model meta-analysis of all the studies, coffee intake was not significantly associated with the risk of hypertension (relative risk [RR], 0.97; 95% confidence interval [CI], 0.90–1.05; I² = 58.0%; n = 13). In the subgroup meta-analysis, coffee intake was associated with a decreased risk of hypertension in studies conducted in America (RR, 0.93; 95% CI, 0.87-0.98; I² = 4.6%; n = 5) and in low-quality studies (RR, 0.92; 95% CI, 0.88-0.96; I² = 0.0%; n = 7). In the remaining subgroup meta-analyses by amount of coffee intake, gender, type of coffee (decaffeinated vs. caffeinated), smoking, and years of follow-up, coffee intake was not significantly associated with the risk of hypertension.

CONCLUSION

The current meta-analysis showed that coffee intake is not associated with the risk of hypertension.

How does caffeine influence memory? Drug, experimental, and demographic factors

Caffeine is a widely used nootropic drug, but its effects on memory in healthy participants have not been sufficiently evaluated. Here we review evidence of the effects of caffeine on different types of memory, and the associated drug, experimental, and demographical factors. There is limited evidence that caffeine affects performance in memory tasks beyond improved reaction times. For drug factors, a dose-response relationship may exist but findings are inconsistent. Moreover, there is evidence that the source of caffeine can modulate its effects on memory. For experimental factors, past studies often lacked a baseline control for diet and sleep and none discussed the possible reversal of withdrawal effect due to pre-experimental fasting. For demographic factors, caffeine may interact with sex and age, and the direction of the effect may depend on the dose, individual tolerance, and metabolism at baseline. Future studies should incorporate these considerations, as well as providing continued evidence on the effect of caffeine in visuospatial, prospective, and implicit memory measures.

Coffee consumption and risk of hypertension: A prospective analysis in the cohort study

BACKGROUND

Coffee is one of the most widely consumed beverages around the world. Dietary habits, specifically, coffee consumption has long been a suspected cause of hypertension. However, previous findings on coffee consumption and its association with the incidence of hypertension are not homogeneous and still inconsistent.

PURPOSE

To examine the association of habitual coffee consumption with the risk of developing hypertension in a middle-aged Brazilian cohort.

METHODS

Data were from the multicenter prospective cohort "Brazilian Longitudinal Study for Adult Health - ELSA-Brasil". The cohort comprises 15,105 civil servants, aged 35-74 years at baseline, who were sampled from universities located in six Brazilian cities. For the present study, we analyzed data from 8780 participants initially free of hypertension during a mean follow-up of 3.9 years. The consumption of coffee was obtained at baseline using a previously validated semi-quantitative food frequency questionnaire (FFQ). Subsequently coffee intake was categorized into four categories (cups/day): never/almost never, ≤1, 1-3, and >3. Hypertension status was defined as a systolic blood pressure ≥140 mmHg or a diastolic blood pressure ≥90 mmHg, use of antihypertensive drug treatment, or both. Poisson regression model with a robust variance was performed to estimate relative risk (RR) and confidence interval (95% CI) for hypertension according to baseline coffee consumption. The effect of interaction between coffee consumption and smoking status was assessed.

RESULTS

Most participants (90%) drank coffee, and the median total coffee intake was 150 mL/day. A total of 1285 participants developed hypertension. Compared to participants who never or almost never drink coffee, the risk of hypertension was lower for individuals consuming 1-3 cups/day (RR 0.82, 95% CI: 0.68-0.97) (P for interaction=0.018). After stratification by smoking status the analysis revealed a decreased risk of hypertension in never smokers drinking 1-3 cups of coffee per day (RR 0.79, 95% CI: 0.64-0.98), whereas the hypertension risk among former and current smokers was not associated with coffee consumption significantly. Moreover, upper category of coffee drinking (>3 cups/day) the association was not significant for risk of hypertension.

CONCLUSION

The association between coffee consumption and incidence of hypertension was related to smoking status. The beneficial effect of moderate coffee intake (1-3 cups/day) on risk of hypertension was observed only in never smokers.

Association between lifetime coffee consumption and late life cerebral white matter hyperintensities in cognitively normal elderly individuals

Coffee consumption is associated with cerebral hypoperfusion that may contribute to the development of cerebral white matter hyperintensities (WMH). We investigated the effect of lifetime coffee consumption on the volume of WMH (V_WMH) in late life, and compared the effect between men and women since caffeine clearance may be different between sexes. We enrolled 492 community-dwelling cognitively normal elderly individuals (73.4 ± 6.7 years old on average) from the Korean Longitudinal Study on Cognitive Aging and Dementia. We evaluated their patterns and amounts of coffee consumption using a study-specific standardized interview and estimated cerebral V_WMH by automatic segmentation of brain fluid-attenuated inversion recovery sequence magnetic resonance images. Higher cumulative lifetime coffee consumption was associated with higher logV_WMH in both sexes (p = 0.030). The participants who consumed more than 2 cups of coffee per day on average in their lifetime showed higher logV_WMH in late life than those who consumed less. When both sexes were analyzed separately, these coffee-logV_WMH associations were found only in women, although the volumes of brain and white matter of women were smaller than those of men. Our findings suggest that prolonged high coffee consumption may be associated with the risk of WMH in late life.

Caffeine Consumption through Coffee: Content in the Beverage, Metabolism, Health Benefits and Risks

Caffeine (1,3,7-trimethylxanthine) is the most consumed psychoactive substance in the world, acting by means of antagonism to adenosine receptors, mainly A1 and A2A. Coffee is the main natural source of the alkaloid which is quite soluble and well extracted during the brew’s preparation. After consumption, caffeine is almost completely absorbed and extensively metabolized in the liver by phase I (cytochrome P450) enzymes, mainly CYP1A2, which appears to be polymorphically distributed in human populations. Paraxanthine is the major caffeine metabolite in plasma, while methylated xanthines and methyluric acids are the main metabolites excreted in urine. In addition to stimulating the central nervous system, caffeine exerts positive effects in the body, often in association with other substances, contributing to prevention of several chronic diseases. The potential adverse effects of caffeine have also been extensively studied in animal species and in humans. These aspects will be approached in the present review.

A randomized controlled trial of a manual-only treatment for reduction and cessation of problematic caffeine use

BACKGROUND

Caffeine Use Disorder was added to DSM-5 as a diagnosis for further research, but few studies have been conducted to identify effective treatments. This randomized, controlled clinical trial examined the efficacy of a manual-only treatment program for caffeine cessation and reduction among individuals seeking treatment for problematic caffeine use.

METHODS

Individuals meeting at least two proposed DSM-5 diagnostic criteria for Caffeine Use Disorder were randomly assigned to receive either immediate treatment or treatment delayed by 7 weeks. The treatment consisted of a manual containing information about caffeine and instructions for gradually reducing caffeine consumption over a period of 6 weeks, with no counseling or additional support. Caffeine consumption and caffeine-related distress were assessed before treatment, 7 weeks after receiving the treatment manual (end-of-treatment), and 20 weeks post-treatment.

RESULTS

The manual-only treatment resulted in significant reductions in participants' self-reported caffeine consumption and caffeine-related distress at end-of-treatment that were sustained at 20-weeks post-treatment. Salivary caffeine levels and community observers corroborated the self-reported reductions in caffeine consumption. Comparisons between the immediate and delayed treatment groups suggest the reductions in caffeine consumption were attributable to the manualized treatment rather than spontaneous with the passage of time.

CONCLUSIONS

The present study provides evidence that a gradual caffeine reduction and cessation program may be successfully implemented using a manual-only approach. This time- and cost-effective intervention may be easily adopted by practitioners with limited time or experience with behavioral interventions who want to encourage their patients to reduce caffeine consumption.

Coffee consumption and risk of hypertension: a dose-response meta-analysis of prospective studies

PURPOSE

Recently, a large prospective study provided additional information concerning the debated possible association between habitual coffee consumption and risk of hypertension (HPT). Therefore, we updated the state of knowledge on this issue by carrying out a comprehensive new systematic review of the literature and a meta-analysis of the available relevant studies.

METHODS

We performed a systematic search for prospective studies on general population, published without language restrictions (1966-August 2017). A random-effects dose-response meta-analysis was conducted to combine study specific relative risks (RRs) and 95% confidence intervals. Potential non-linear relation was investigated using restricted cubic splines.

RESULTS

Four studies (196,256 participants, 41,184 diagnosis of HPT) met the inclusion criteria. Coffee intake was assessed by dietary questionnaire. Dose-response meta-analysis showed a non-linear relationship between coffee consumption and risk of HPT (p for non-linearity < 0.001). Whereas the habitual drinking of one or two cups of coffee per day, compared with non-drinking, was not associated with risk of HPT, a significantly protective effect of coffee consumption was found starting from the consumption of three cups of coffee per day (RR = 0.97, 95% CI = 0.94 to 0.99), and was confirmed for greater consumption.

CONCLUSIONS

The results of this analysis indicate that habitual moderate coffee intake is not associated with higher risk of HPT in the general population and that in fact a non-linear inverse dose-response relationship occurs between coffee consumption and risk of HPT.

Application of a Physiologically Based Pharmacokinetic Model to Study Theophylline Metabolism and Its Interactions With Ciprofloxacin and Caffeine

Theophylline is a commonly used bronchodilator. However, due to its narrow therapeutic range, moderate elevation of serum concentration can result in adverse drug reactions (ADRs). ADRs occur because of interhuman pharmacokinetic variability and interactions with coprescribed medicines. We developed a physiologically based pharmacokinetic (PBPK) model of theophylline, caffeine, and ciprofloxacin metabolisms to: examine theophylline pharmacokinetic variability, and predict population‐level outcomes of drug–drug interactions (DDIs). A simulation‐based equation for personalized dosing of theophylline was derived. Simulations of DDI show that calculated personalized doses are safe even after cotreatment with large doses of strong inhibitors. Simulations of adult populations indicate that the elderly are most susceptible to ADRs stemming from theophylline–ciprofloxacin and theophylline–caffeine interactions. Females, especially Asians, due to their smaller average size, are more susceptible to DDI‐induced ADRs following typical dosing practices. Our simulations also show that the higher adipose and lower muscle fractions in females significantly alter the pharmacokinetics of theophylline or ciprofloxacin.

Coffee consumption and risk of hypertension in the Polish arm of the HAPIEE cohort study

BACKGROUND/OBJECTIVES

Coffee consumption has been hypothesized to be associated with blood pressure (BP), but previous findings are not homogeneous. The aim of this study was to evaluate the association between coffee consumption and the risk of developing hypertension.

SUBJECTS/METHODS

Data on coffee consumption, BP and use of anti-hypertensive medicament were derived from 2725 participants of the Polish arm of the HAPIEE project (Health, Alcohol and Psychosocial factors In Eastern Europe) who were free of hypertension at baseline and followed up for an average of 5 years. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by multivariate logistic regression analyses and stratified for potential confounding factors.

RESULTS

Coffee consumption was related to decreased age, smoking status and total energy intake. Compared with persons who drink <1 cup coffee per day, systolic BP was significantly associated with coffee consumption and the risk of hypertension was lower for individuals consuming 3-4 cups per day. Despite the analysis stratified by gender showed that the protective effect of coffee consumption on hypertension was significant only in women, the analysis after stratification by smoking status revealed a decreased risk of hypertension in non-smokers drinking 3-4 cups of coffee per day in both sexes (OR 0.41, 95% CI: 0.21, 0.79 for men and OR 0.54, 95% CI: 0.29, 0.99 for women). Upper category coffee consumption (>4 cups per day) was not related to significant increased risk of hypertension.

CONCLUSIONS

Relation between coffee consumption and incidence of hypertension was related to smoking status. Consumption of 3-4 cups of coffee per day decreased the risk of hypertension in non-smoking men and women only.

Maternal Coffee Consumption During Pregnancy and Neural Tube Defects in Offspring: A Meta-Analysis

PURPOSE

To examine the association between maternal coffee consumption during pregnancy and the occurrence of neural tube defects (NTDs) in offspring.

METHODS

PubMed, Springer Link and Elsevier databases were searched up to August, 2014. Case-control and cohort studies published on the association between maternal coffee consumption during pregnancy and the occurrence of NTDs in offspring were included. Meta-analysis was applied to calculate the pooled effect estimates and their 95% confidence intervals (CIs) using a random-effects model.

RESULTS

A total of six case-control studies and one cohort study were included. The pooled effect estimate of maternal coffee consumption during pregnancy was 0.86 for total NTDs (95% CI: 0.51- 1.45) and 1.30 (95% CI: 0.67- 2.52) for NTDs subtype of spina bifida.

CONCLUSIONS

Our findings suggested that maternal coffee consumption during pregnancy was not significantly associated with the occurrence of total NTD or the spina bifida subtype of NTD.

A brief manualized treatment for problematic caffeine use: A randomized control trial

OBJECTIVE

The goal of the present investigation was to develop and test a brief therapist-guided manualized treatment for problematic caffeine use, including cognitive-behavioral strategies and 5 weeks of progressively decreased consumption.

METHOD

Individuals seeking treatment for problematic caffeine use (mean daily caffeine consumption of 666 mg at baseline) were randomized using a waitlist-control design to receive immediate treatment (N = 33) or delayed treatment (∼6 weeks later; N = 34). A 1-hr treatment session designed to help individuals quit or reduce caffeine consumption was provided by a trained counselor along with a take-home booklet. After the treatment session, participants completed daily diaries of caffeine consumption for 5 weeks. They returned for follow-up assessments at 6, 12, and 26 weeks and had a telephone interview at 52-weeks posttreatment.

RESULTS

Treatment resulted in a significant reduction in self-reported caffeine use and salivary caffeine levels. No significant posttreatment increases in caffeine use were observed for up to 1 year follow-up. Comparisons to the waitlist-control condition revealed that reductions in caffeine consumption were due to treatment and not the passing of time, with a treatment effect size of R² = .35 for the model.

CONCLUSION

A brief 1-session manualized intervention with follow-up was efficacious at reducing caffeine consumption. Future researchers should replicate and extend these findings, as well as consider factors affecting dissemination of treatment for problematic caffeine use to those in need.

Current and future directions in clinical fatigue management: An update for emergency medicine practitioners

Physicians worldwide are working round the clock to meet the demands of healthcare systems, especially in acute medical settings such as EDs. Demanding shift work schedules cause fatigue and thus deterioration in mood and motor performance. This article explores the effects of sleep deprivation, focusing on cognition, executive decision-making and the implications for clinical care. Humans are capable of functioning and even adapting to sleep restriction; however, clinicians should be aware of pitfalls and absolute minimums for sleep. Fatigue management training shows promise in enhancing safety in aviation and might have a role in medical shift work. Strategic napping improves performance during night shift in the ED, but does not fully negate fatigue. Drugs offer limited benefit for performance under sleep-deprived conditions, and whenever possible, sleep and/or strategic napping takes precedence.

Caffeine reduces myocardial blood flow during exercise

Caffeine consumption has been receiving increased interest from both the medical and lay press, especially given the increased amounts now available in energy products. Acute ingestion of caffeine usually increases cardiac work; however, caffeine impairs the expected proportional increase in myocardial blood flow to match this increased work of the heart, most notably during exercise. This appears to be mainly due to caffeine's effect on blocking adenosine-induced vasodilatation in the coronary arteries in normal healthy subjects. This review summarizes the available medical literature specifically relating to pure caffeine tablet ingestion and reduced exercise coronary blood flow, and suggests possible mechanisms. Further studies are needed to evaluate this effect for other common caffeine-delivery systems, including coffee, energy beverages, and energy gels, which are often used for exercise performance enhancement, especially in teenagers and young athletes.

Quantitative analysis of rate and extent of tolerance of biomarkers: application to nicotinic acid-induced changes in non-esterified fatty acids in rats

In this paper we quantitatively evaluate two feedback systems with a focus on rate and extent of tolerance and rebound development. In the two feedback systems, the regulation of turnover of response is governed by one or several moderators. In the basic system, one single moderator inhibits the formation of response. This system has been applied to cortisol secretion and serotonin reuptake inhibition. The basic system has been extended to adequately describe nicotinic acid (NiAc)-induced changes in non-esterified fatty acids (NEFA). In the extended system, the feedback is described by a cascade of moderators where the first inhibits formation of response and the last stimulates loss of response. The objectives of this paper were to analyze these systems from a mathematical/analytical and quantitative point of view and to present simulations with different parameter settings and dosing regimens in order to highlight the intrinsic behaviour of these systems and to present expressions and graphs that are applicable for quantification of rate and extent of tolerance and rebound. The dynamics of the moderators (k(tol)) compared to the dynamics of the response (k(out)), was shown to be important for the behaviour of both systems. For instance, slow dynamics of the moderator compared to the response (k(tol)<<k(out)), resulted in overshoot and pronounced rebound. The extent of tolerance was studied over time at a single constant drug concentration and at steady state for different drug concentrations and was found to be largest at drug concentrations close to IC(50). An upper limit for the response could be identified and included in the quantification of extent of rebound. Especially, for the extended system, the duration of exposure was an important factor affecting size of rebound. The rate of tolerance development was addressed by quantitatively estimating the time to steady state for the two systems, in which the value of k(tol) and the length of the cascade were critical.

Habitual coffee consumption and risk of hypertension: a systematic review and meta-analysis of prospective observational studies

BACKGROUND

In 2 meta-analyses of randomized controlled trials, increased coffee intake was associated with slightly higher blood pressure. However, these trials were short in duration (<85 d).

OBJECTIVE

We conducted a systematic review and meta-analyses of long-term prospective studies that examined the association of habitual coffee consumption with risk of hypertension.

DESIGN

We searched electronic databases (MEDLINE, EMBASE, Agricola, and Cochrane Library) through August 2009 with the use of a standardized protocol. Eligible studies were prospective cohort trials that examined the association of coffee consumption with incident hypertension or blood pressure.

RESULTS

From 6 prospective cohort studies, a total of 172,567 participants and 37,135 incident hypertension cases were included. Mean follow-up ranged from 6.4 to 33.0 y. Compared with the lowest consumption [<1 cup (≈237 mL)/d], the pooled relative risks (RRs) for hypertension were 1.09 (95% CI: 1.01, 1.18) for the next higher category (1-3 cups/d), 1.07 (95% CI: 0.96, 1.20) for the second highest category (3-5 cups/d), and 1.08 (95% CI: 0.96, 1.21) for the highest category (>5 cups/d). A dose-response meta-analysis showed an inverse "J-shaped" curve (P for quadratic term < 0.001) with hypertension risk increasing up to 3 cups/d (RR for comparison of 3 with 0 cups/d: 1.07; 95% CI: 0.97, 1.20) and decreasing with higher intakes (RR for comparison of 6 with 0 cups/d: 0.99; 95% CI: 0.89, 1.10).

CONCLUSION

The results suggest that habitual coffee consumption of >3 cups/d was not associated with an increased risk of hypertension compared with <1 cup/d; however, a slightly elevated risk appeared to be associated with light-to-moderate consumption of 1 to 3 cups/d.

Interrelations between plasma caffeine concentrations and neurobehavioural effects in healthy volunteers: model analysis using NONMEM

The objective was to develop a population pharmacokinetic-pharmacodynamic model of caffeine's psychomotor effects in healthy, non-habitual users of caffeine. Twenty Chinese males each received a single dose of 250 mg of caffeine orally. Plasma concentrations of caffeine were determined at various times within 24 h after dosing. The subjects' psychomotor performance was evaluated before and at various times after dosing by a test battery consisting of oculomotor assessment (saccadic velocity) as well as the computerised Swedish Performance Evaluation System. Nonlinear mixed-effects modelling to analyse the pharmacokinetic-pharmacodynamic relationships was performed using NONMEM. Model robustness was assessed by a nonparametric bootstrap. The results showed that caffeine caused significant improvements in psychomotor functioning. The time course of these effects was best described by pharmacokinetic/pharmacodynamic models involving an effect compartment. The transfer half-lives between plasma and effect site for different domains of psychomotor functioning were in the range 24.8-49.5 min. Evaluation of the final models showed close agreement between pairs of bootstrapped and final model parameter estimates (all differences<10%). These results provided the first suggestive evidence that caffeine effects on psychomotor performance occur after some time delay relative to changes in plasma caffeine concentration. The models for the neurobehavioural tests provided similar transfer half-lives between plasma and effect site.

Maternal caffeine consumption and risk of neural tube defects

BACKGROUND

Animal studies demonstrate teratogenic effects of caffeine, whereas human studies are inconclusive.

METHODS

Associations between maternal caffeine consumption and neural tube defects (NTDs) by type of NTD (anencephaly, spina bifida, or encephalocele) were examined using data from the National Birth Defects Prevention Study (NBDPS). Total average daily caffeine from coffee, tea, soda, and chocolate consumption during the year before pregnancy was estimated for 768 mothers of infants with NTDs and 4143 mothers of infants without birth defects who gave birth during 1997 through 2002. Periconceptional use of caffeine-containing medications was evaluated separately. Adjusted odds ratios (OR) and 95% confidence intervals (CI) associated with consumption of total caffeine and each caffeine source were estimated from logistic regression models.

RESULTS

Positive associations were observed between spina bifida and total caffeine consumption (OR 1.4; 95% CI: 1.1-1.9) and each caffeine source except caffeinated tea, which showed a negative association with spina bifida (OR 0.7; 95% CI: 0.6-0.9). Associations with modestly increased risk of NTDs and encephalocele were also observed. The association between caffeine consumption and anencephaly differed by maternal race/ethnicity. No dose effects were found.

CONCLUSIONS

Additional studies should confirm whether women who consume caffeine are at increased risk for pregnancies complicated by NTDs.

Relationship of blood pressure, behavioral mood state, and physical activity following caffeine ingestion in younger and older women

The purpose of this study was to examine the age-related differences in blood pressure, heart rate, and behavioral mood state after caffeine ingestion in younger and older women. Using a placebo-controlled, double-blind design, 10 younger (Y; 18-22 years) and 10 older (O; 50-67 years) healthy women who were moderate consumers of caffeine (self-reported mean intake: Y, 139 +/- 152 mg.day-1; O, 204 +/- 101 mg.day-1) were investigated. All volunteers were characterized for fasting plasma glucose, insulin, free-fatty acids and caffeine levels, body composition, cardiovascular fitness, physical activity, and energy intake. Before and after placebo and caffeine ingestion (5 mg.kg-1 fat-free mass; approximately 208-270 mg) test days, the following variables were measured in all subjects: plasma caffeine levels, heart rate, blood pressure, and behavioral mood state. Results showed that, following caffeine ingestion: (i) both systolic and diastolic blood pressure (SBP and DBP, respectively) increased significantly (p < 0.05) in the older women (SBP, 128.4 +/- 14.2 vs. 132.1 +/- 13.0 mm Hg (3%); DBP, 80.2 +/- 6.9 vs. 83.4 +/- 7.5 mm Hg (4%), whereas only DBP increased in the younger women (67.1 +/- 4.7 vs. 69.9 +/- 5.4 mm Hg (4.2%); p < 0.05); (ii) heart rate decreased significantly (Y, 59.2 +/- 8.7 to 53.9 +/- 10.6 beats.min-1 (p < 0.05); O, 61.9 +/- 9.2 to 59.2 +/- 8.4 beats.min-1 (p < 0.05)) in both groups; and (iii) self-reported feelings of tension and vigor increased and feelings of fatigue decreased (p < 0.05) in younger women, whereas depression decreased (p < or = 0.05) in older women. Self-reported level of physical activity was inversely related to change in DBP following caffeine ingestion in younger women. In conclusion, blood pressure response is augmented and subjective feelings of behavioral mood state are attenuated to a greater degree in older than in younger women following acute caffeine ingestion. Less physically active younger women are more vulnerable to the pressor response to caffeine than more active younger women. It should be noted that these findings are limited to moderate consumers of caffeine who abstained for 48 h prior to testing, and who ingested caffeine in pill form (approximately 240 mg).

Caffeine use in children: what we know, what we have left to learn, and why we should worry

Caffeine is a widely used psychoactive substance in both adults and children that is legal, easy to obtain, and socially acceptable to consume. Although once relatively restricted to use among adults, caffeine-containing drinks are now consumed regularly by children. In addition, some caffeine-containing beverages are specifically marketed to children as young as 4 years of age. Unfortunately, our knowledge of the effects of caffeine use on behavior and physiology of children remains understudied and poorly understood. The purpose of this article is to review what is known about caffeine use in children and adolescents, to discuss why children and adolescents may be particularly vulnerable to the negative effects of caffeine, and to propose how caffeine consumption within this population may potentiate the rewarding properties of other substances. The following topics are reviewed: (1) tolerance and addiction to caffeine, (2) sensitization and cross-sensitization to the effects of caffeine, (3) caffeine self-administration and reinforcing value, and (4) conditioning of preferences for caffeine-containing beverages in both adults and children.

Caffeine impairs myocardial blood flow response to physical exercise in patients with coronary artery disease as well as in age-matched controls

Background

Caffeine is one of the most widely consumed pharmacologically active substances. Its acute effect on myocardial blood flow is widely unknown. Our aim was to assess the acute effect of caffeine in a dose corresponding to two cups of coffee on myocardial blood flow (MBF) in coronary artery disease (CAD).

Methodology/Principal Findings

MBF was measured with ¹⁵O-labelled H2O and Positron Emission Tomography (PET) at rest and after supine bicycle exercise in controls (n = 15, mean age 58±13 years) and in CAD patients (n = 15, mean age 61±9 years). In the latter, regional MBF was assessed in segments subtended by stenotic and remote coronary arteries. All measurements were repeated fifty minutes after oral caffeine ingestion (200 mg). Myocardial perfusion reserve (MPR) was calculated as ratio of MBF during bicycle stress divided by MBF at rest. Resting MBF was not affected by caffeine in both groups. Exercise-induced MBF response decreased significantly after caffeine in controls (2.26±0.56 vs. 2.02±0.56, P<0.005), remote (2.40±0.70 vs. 1.78±0.46, P<0.001) and in stenotic segments (1.90±0.41 vs. 1.38±0.30, P<0.001). Caffeine decreased MPR significantly by 14% in controls (P<0.05 vs. baseline). In CAD patients MPR decreased by 18% (P<0.05 vs. baseline) in remote and by 25% in stenotic segments (P<0.01 vs. baseline).

Conclusions

We conclude that caffeine impairs exercise-induced hyperaemic MBF response in patients with CAD to a greater degree than age-matched controls.

Pharmacokinetic/pharmacodynamic modelling of venlafaxine: pupillary light reflex as a test system for noradrenergic effects

BACKGROUND AND OBJECTIVE

Venlafaxine and its major active metabolite O-desmethylvenlafaxine selectively inhibit serotonin and norepinephrine reuptake from the synaptic gap. The inhibition of norepinephrine uptake is assumed to enhance antidepressant efficacy when venlafaxine is given at higher therapeutic doses. Thus investigation of the concentration-response relationship of noradrenergic effects is of clinical interest. We used pupillography as a test system for the pharmacodynamic response to venlafaxine, since it had been shown to be useful for assessment of noradrenergic effects on the autonomous nervous system. The aim of the study was to develop a pharmacokinetic/pharmacodynamic model by means of nonlinear mixed-effects modelling in order to describe the time course of the noradrenergic response to venlafaxine.

SUBJECTS AND METHODS

Twelve healthy male subjects received venlafaxine 37.5 mg or placebo orally twice daily for 7 days and subsequently 75 mg or placebo twice daily for another 7 days. After a 14-day washout phase, the two groups were crossed over. After the last dose of venlafaxine or placebo on day 14, blood samples were drawn to determine venlafaxine and O-desmethylvenlafaxine concentrations and the amplitude and recovery time of the pupillary light reflex were measured. A pharmacokinetic/pharmacodynamic model was developed to describe the data using nonlinear mixed-effects modelling.

RESULTS

The pharmacokinetic part of the model could be simultaneously fitted to both venlafaxine and O-desmethylvenlafaxine data, yielding precise parameter estimates that were similar to published data. The model detected high variability of the intrinsic clearance of venlafaxine (94.8%), most likely due to cytochrome P450 2D6 polymorphism. Rapid development of tolerance of the pupillary light reflex parameters was seen and could be successfully accounted for in the pharmacodynamic part of the model. The half-life of development and regression of tolerance was estimated to be 30 minutes for the amplitude and 40 minutes for the recovery time.

CONCLUSION

The time course of the effect and the concentration-response relationship were successfully described by a pharmacokinetic/pharmacodynamic model that takes into account the rapid development of tolerance of pupillary light reflex parameters. This provides a basis for further investigations of the applicability of pupillography as a surrogate measurement of the effectivity of antidepressant drugs with norepinephrine reuptake-inhibiting properties.

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, diabetes, and weight control

Several prospective epidemiologic studies over the past 4 y concluded that ingestion of caffeinated and decaffeinated coffee can reduce the risk of diabetes. This finding is at odds with the results of trials in humans showing that glucose tolerance is reduced shortly after ingestion of caffeine or caffeinated coffee and suggesting that coffee consumption could increase the risk of diabetes. This review discusses epidemiologic and laboratory studies of the effects of coffee and its constituents, with a focus on diabetes risk. Weight loss may be an explanatory factor, because one prospective epidemiologic study found that consumption of coffee was followed by lower diabetes risk but only in participants who had lost weight. A second such study found that both caffeine and coffee intakes were modestly and inversely associated with weight gain. It is possible that caffeine and other constituents of coffee, such as chlorogenic acid and quinides, are involved in causing weight loss. Caffeine and caffeinated coffee have been shown to acutely increase blood pressure and thereby to pose a health threat to persons with cardiovascular disease risk. One short-term study found that ground decaffeinated coffee did not increase blood pressure. Decaffeinated coffee, therefore, may be the type of coffee that can safely help persons decrease diabetes risk. However, the ability of decaffeinated coffee to achieve these effects is based on a limited number of studies, and the underlying biological mechanisms have yet to be elucidated.

Pharmacokinetic-pharmacodynamic modelling: history and perspectives

A major goal in clinical pharmacology is the quantitative prediction of drug effects. The field of pharmacokinetic-pharmacodynamic (PK/PD) modelling has made many advances from the basic concept of the dose-response relationship to extended mechanism-based models. The purpose of this article is to review, from a historical perspective, the progression of the modelling of the concentration-response relationship from the first classic models developed in the mid-1960s to some of the more sophisticated current approaches. The emphasis is on general models describing key PD relationships, such as: simple models relating drug dose or concentration in plasma to effect, biophase distribution models and in particular effect compartment models, models for indirect mechanism of action that involve primarily the modulation of endogenous factors, models for cell trafficking and transduction systems. We show the evolution of tolerance and time-variant models, non- and semi-parametric models, and briefly discuss population PK/PD modelling, together with some example of more recent and complex pharmacodynamic models for control system and nonlinear HIV-1 dynamics. We also discuss some future possible directions for PK/PD modelling, report equations for general classes of novel semi-parametric models, as well as describing two new classes, additive or set-point, of regulatory, additive feedback models in their direct and indirect action variants.

Influences of caffeine, acetazolamide and cognitive stimulation on cerebral blood flow velocities

Assessment of cerebral blood flow velocities (CBFV) can be used as a non-invasive tool to evaluate specific drug effects, like caffeine (CAF), acetazolamide (AA) as well as cognition. Their influences on each others CBFV were evaluated in detail, using a randomized, double-blind, double-dummy, placebo-controlled three-fold cross-over study design in 18 right-handed healthy male volunteers. CBFV (maximal, mean, minimal) and pulsatility index of both middle cerebral arteries were recorded by transcranial Doppler ultrasound simultaneously, during a verbal memory test, oral CAF, intravenous AA or placebo. AA led to increase in CBFV of 25-32%. Caffeine resulted in decreased V(mean) and V(min) of 10-13%. Cognitive stimulation resulted in a slight increase of CBVF of about 4%, but was overruled by effects of AA and CAF. We conclude that pharmacological effects can easily be assessed by TCD during clinical pharmacological studies of vasoactive drugs. However intraindividual variability and effects of neuropsychological stimulation needs to be taken into account.

Modelling the cardiovascular effects of ephedrine

AIMS

Recent reports have called into question the safety of ephedra supplements especially with regards to their cardiovascular effects. The purpose of this analysis was to characterize, via pharmacokinetic/pharmacodynamic modelling, the cardiovascular effects of ephedrine, the main active ingredient of ephedra, in apparently healthy, overweight volunteers.

METHODS

In a randomized, double-blind, crossover, placebo-controlled study, eight subjects received either placebo, 0.25, 0.5 or 1.0 mg kg(-1) ephedrine sulphate by mouth with a 7-day washout between treatments. Plasma ephedrine concentrations, heart rate and blood pressure were determined for 8 h postdose.

RESULTS

The pharmacokinetics of ephedrine were best described by a one-compartment model with first-order absorption and elimination. The percentage change in heart rate was described by a linear model with a resulting slope of 0.14%.l microg(-1) (CV = 59%). The percentage change in systolic blood pressure demonstrated clockwise hysteresis, and a sigmoidal tolerance model was used to describe the data. The mean maximum predicted effect (Emax) was 53.7% (CV = 41%) with an EC50 of 107 microg.l(-1) (CV = 65%) and an inhibitory maximum (Imax) of 39.8% (CV = 60%). Tolerance developed with a mean half-life of 15 min (range 6-140 min).

CONCLUSIONS

This is the first study to apply a comprehensive pharmacokinetic/pharmacodynamic model to the cardiovascular effects of orally administered ephedrine. Although systolic blood pressure increases quickly after administration, the increase is nearly abolished by compensatory mechanisms.

Simultaneous vs. sequential analysis for population PK/PD data I: best-case performance

Dose [-concentration]-effect relationships can be obtained by fitting a predictive pharmacokinetic (PK)-pharmacodynamic (PD) model to both concentration and effect observations. Either a model can befit simultaneously to all the data ("simultaneous" method), or first a model can befit to the PK data and then a model can be fit to the PD data, conditioning in some way on the PK data or on the estimates of the PK parameters ("sequential" method). Using simulated data, we compare the performance of the simultaneous method with that of three sequential method variants with respect to computation time, estimation precision, and inference. Using NONMEM, under various study designs, observations of one type of PK and one type of PD response from different numbers of individuals were simulated according to a one-compartment PK model and direct Emax PD model, with parameters drawn from an appropriate population distribution. The same PK and PD models were fit to these observations using simultaneous and sequential methods. Performance measures include computation time,fraction of cases for which estimates are successfully obtained, precision of PD parameter estimates, precision of PD parameter standard error estimates, and type-I error rates of a likelihood ratio test. With the sequential method, computation time is less, and estimates are more likely to be obtained. Using the First Order Conditional Estimation (FOCE) method, a sequential approach that conditions on both population PK parameter estimates and PK data, estimates PD parameters and their standard errors about as well as the "gold standard" simultaneous method, and saves about 40% computation time. Type-I error rates of likelihood ratio test for both simultaneous and sequential approaches are close to the nominal rates.

Critical review of dietary caffeine and blood pressure: a relationship that should be taken more seriously

OBJECTIVE

This review aims to determine whether, and to what extent, dietary caffeine may be a risk to cardiovascular health.

METHODS

A critical review of the relevant experimental and epidemiologic literature was conducted, with particular reference to studies of caffeine and blood pressure (BP).

RESULTS

There is extensive evidence that caffeine at dietary doses increases BP. However, concern that the drug may contribute to cardiovascular disease appears to have been dampened by (1) the belief that habitual use leads to the development of tolerance, and (2) confusion regarding relevant epidemiologic findings. When considered comprehensively, findings from experimental and epidemiologic studies converge to show that BP remains reactive to the pressor effects of caffeine in the diet. Overall, the impact of dietary caffeine on population BP levels is likely to be modest, probably in the region of 4/2 mm Hg. At these levels, however, population studies of BP indicate that caffeine use could account for premature deaths in the region of 14% for coronary heart disease and 20% for stroke.

CONCLUSIONS

Current evidence supports the conclusion that the BP-elevating effects of dietary caffeine may be contributing appreciably to population levels of cardiovascular mortality and morbidity. Accordingly, strategies for encouraging reduced dietary levels of caffeine deserve serious consideration.

Caffeine use and dependence in adolescents: one-year follow-up

The objectives were to conduct a 1-year follow-up of daily caffeine-using adolescents to further describe caffeine dependence symptoms and to determine whether caffeine dependence is associated with other substance dependence disorders. Twenty-one of 36 (58.3%) adolescents who participated in a study of caffeine dependence returned for follow-up. The previous study was a case series of adolescents who consumed caffeine daily and met some Diagnostic and Statistical Manual of Mental Disorders (fourth edition) substance dependence criteria as applied to caffeine. At follow-up, caffeine consumption from beverages was 179.9 +/- 151.8 mg/day. Of the 21 teenagers, 23.8% (n = 5) met criteria for caffeine dependence. Four of these participants developed caffeine dependence during the follow-up period. Other substance dependence disorders were not overrepresented in the caffeine dependent group compared to the caffeine nondependent group. The most commonly reported withdrawal symptoms in dependent teenagers (at baseline and follow-up combined) were feeling drowsy/tired, fatigued, or sluggish/slowed down (83.3% each) and headache (75.0%). Caffeine dependence occurs in some adolescents who drink caffeine daily and is marked by symptoms similar to those found in adults.

Central and peripheral effects of sustained caffeine use: tolerance is incomplete

AIMS

It is widely held that tolerance develops to the effects of sustained caffeine consumption. This study was designed to investigate the effects of chronic, staggered caffeine ingestion on the responses of an acute caffeine challenge, during -euglycaemia.

METHODS

Twelve healthy volunteers were randomized using a double-blind, cross-over design to take either 200 mg caffeine (C-replete) or placebo (C-naïve) twice daily for 1 week. Following baseline measurements being made, the responses to 200 mg caffeine (blood-pressure, middle cerebral artery velocity, mood and cognitive performance) were examined over the subsequent 120 min. Blood glucose was not allowed to fall below 4.0 mmol l-1.

RESULTS

After the caffeine challenge, middle cerebral artery blood velocity decreased in both conditions but was greater in the C-naïve condition (-8.0 [-10.0, -6.1] cm s-1 vs -4.9 [-6.8, -2.9] cm s-1 C-replete, P < 0.02). Systolic blood pressure rise was not significantly different in C-naïve, although this rise was more sustained over time (P < 0.04). Mood was adversely affected by regular caffeine consumption with tense aspect of mood significantly higher at baseline in C-replete 11.6 +/- 0.6 C-naïve vs 16.3 +/- 1.6 C-replete, P < 0.01). Cognitive performance was not affected by previous caffeine exposure.

CONCLUSIONS

Overall these results suggest that tolerance is incomplete with respect to both peripheral or central effects of caffeine.

Caffeine and stress: implications for risk, assessment, and management of hypertension

Caffeine use is widespread, and its consumption increases during periods of stress. Caffeine raises blood pressure by elevating vascular resistance, and this effect is larger and more prolonged in hypertensive patients than in normotensive. The pressor response to caffeine occurs equally in persons at rest and under stress. The elevated baseline pressures of the hypertensive patient are therefore increased by both caffeine and stress, potentially leading to undesirably high pressures. Such combined effects on blood pressure may potentially confound the evaluation of hypertension, and possibly reduce the effectiveness of antihypertensive therapy. These effects are not abolished by pharmacologic tolerance to caffeine, as tolerance may not be complete with daily intake. The contribution of caffeine's effects to the development of hypertension warrants continued study, and caffeine use by patients merits consideration in terms of assessment and management of this disorder.

Pharmacokinetic-pharmacodynamic modeling of the antilipolytic effects of an adenosine receptor agonist in healthy volunteers

ARA is an adenosine receptor agonist with high affinity for A1 and A2 receptors, which are involved in regulation of free fatty acid (FFA) production. Two parallel groups of 13 healthy males were enrolled in a Phase I study to evaluate the pharmacokinetics of this compound and to characterize its effect on plasma FFA concentrations following administration of a single 6-hour intravenous infusion of ARA or placebo. ARA plasma concentrations were measured by a validated high-performance liquid chromatographic method (fluorescence detection). ARA is a highly cleared compound (Cl: 0.79 L/h/kg) with a modest volume of distribution (Vss: 0.91 L/kg) and short half-life (t1/2: approximately 1 hour). The mean percent change in plasma FFA concentrations relative to placebo was best described by an Emax-based tolerance model, in which a hypothetical metabolite/antagonist was used to describe the apparent development of tolerance to the suppressive effects of ARA on FFA levels. The EC50 values (%RSE of estimate) for ARA and the hypothetical antagonist were 17.0 (5.4) and 15.6 (12.8) ng/mL, respectively. The use of adenosine A1 agonists as antilipolytic drugs may be restricted due to the potential development of tolerance, and thus a period of abstinence from the agonist may be required before the response of FFA returns to pretolerant conditions. In the case of ARA, the value of 0.33 h-1 for Kant0 indicates that a period of approximately 11 hours should suffice. In agreement with preclinical data previously reported in literature, the present study provides evidence that desensitization of adenosine receptor-mediated inhibition of lipolysis may occur in humans. In conclusion, the ability of ARA to reduce circulating levels of FFA can be related to plasma ARA concentrations using a modified Emax-based tolerance model.

Clinically significant pharmacokinetic interactions between dietary caffeine and medications

Caffeine from dietary sources (mainly coffee, tea and soft drinks) is the most frequently and widely consumed CNS stimulant in the world today. Because of its enormous popularity, the consumption of caffeine is generally thought to be safe and long term caffeine intake may be disregarded as a medical problem. However, it is clear that this compound has many of the features usually associated with a drug of abuse. Furthermore, physicians should be aware of the possible contribution of dietary caffeine to the presenting signs and symptoms of patients. The toxic effects of caffeine are extensions of their pharmacological effects. The most serious caffeine-related CNS effects include seizures and delirium. Other symptoms affecting the cardiovascular system range from moderate increases in heart rate to more severe cardiac arrhythmia. Although tolerance develops to many of the pharmacological effects of caffeine, tolerance may be overwhelmed by the nonlinear accumulation of caffeine when its metabolism becomes saturated. This might occur with high levels of consumption or as the result of a pharmacokinetic interaction between caffeine and over-the-counter or prescription medications. The polycyclic aromatic hydrocarbon-inducible cytochrome P450 (CYP) 1A2 participates in the metabolism of caffeine as well as of a number of clinically important drugs. A number of drugs, including certain selective serotonin reuptake inhibitors (particularly fluvoxamine), antiarrhythmics (mexiletine), antipsychotics (clozapine), psoralens, idrocilamide and phenylpropanolamine, bronchodilators (furafylline and theophylline) and quinolones (enoxacin), have been reported to be potent inhibitors of this isoenzyme. This has important clinical implications, since drugs that are metabolised by, or bind to, the same CYP enzyme have a high potential for pharmacokinetic interactions due to inhibition of drug metabolism. Thus, pharmacokinetic interactions at the CYP1A2 enzyme level may cause toxic effects during concomitant administration of caffeine and certain drugs used for cardiovascular, CNS (an excessive dietary intake of caffeine has also been observed in psychiatric patients), gastrointestinal, infectious, respiratory and skin disorders. Unless a lack of interaction has already been demonstrated for the potentially interacting drug, dietary caffeine intake should be considered when planning, or assessing response to, drug therapy. Some of the reported interactions of caffeine, irrespective of clinical relevance, might inadvertently cause athletes to exceed the urinary caffeine concentration limit set by sports authorities at 12 mg/L. Finally, caffeine is a useful and reliable probe drug for the assessment of CYP1A2 activity, which is of considerable interest for metabolic studies in human populations.

Influence of age on the thermic response to caffeine in women

The purpose of this study was to examine age-related differences in the magnitude of caffeine-induced thermogenesis and the relationship of aerobic fitness, body composition, and hormone and substrate concentrations to the thermic effect of caffeine in younger and older women. Using a placebo-controlled, double-blind study design, 10 older (50 to 67 years) and 10 younger (21 to 31 years) healthy women who were moderate consumers of caffeine (self-reported intake: younger, 139 +/- 152 mg/d; older, 204 +/- 101 mg/d, NS, mean +/- SD) were characterized for fasting plasma glucose, insulin, free fatty acid (FFA), and caffeine levels, energy expenditure, body composition, anthropometry, aerobic fitness, physical activity, and energy intake. Before and after placebo and caffeine ingestion (5 mg/kg fat-free mass [FFM]), the following variables were measured: fasting plasma glucose, insulin, FFA, and energy expenditure, plasma glucose, insulin, and FFA, and energy expenditure in response to placebo and caffeine ingestion. Caffeine ingestion resulted in similar increases in younger and older women for plasma caffeine (younger, 80 +/- 34 to 5,604 +/- 528 ng/mL, P < .01; older, 154 +/- 134 to 5,971 +/- 867 ng/mL, P < .01) and fatty acids (younger, 294 +/- 118 to 798 +/- 248 micromol/L, P < .01; older, 360 +/- 180 to 727 +/- 310 micromol/L, P < .01), whereas plasma insulin and glucose levels remained unchanged from baseline. Energy expenditure increased following caffeine ingestion in both groups (younger, 15.4%, 1.09 +/- 0.14 to 1.24 +/- 0.13 kcal/min, P < .05; older, 7.8%, 0.98 +/- 0.14 to 1.06 +/- 0.12 kcal/min, P < .05), although there was a blunted thermic response in the older versus younger women (older, 6.9 +/- 5 kcal/90 min; younger, 15.5 +/- 7 kcal/90 min, P < .05). In younger women, the thermic response to caffeine was positively correlated with the waist circumference (r = .70, P < .05) and body weight (r = .91; P < .01), whereas aerobic fitness (r = .77; P < .05) was the only significant correlate in older women. In conclusion, older and younger women increase energy expenditure significantly following caffeine ingestion, but older women have a blunted thermic response compared with younger women. Second, the thermic response to caffeine is positively associated with the body weight and waist circumference in younger women, whereas a positive association with aerobic fitness was observed in older women. Thus, the physiologic determinants of the thermic response to caffeine differ among women of different age groups.

Population modelling in drug development

In this paper we discuss the vital role that population (hierarchical) modelling can play within the drug development process. Specifically, population pharmacokinetic/pharmacodynamic models can provide reliable predictions of an individualized dose-exposure-response relationship. A predictive model of this kind can be used to simulate and hence design clinical trials, find initial dosage regimens satisfying an optimality criterion on the population distribution of responses, and individualized regimens satisfying such a criterion conditional on individual features, such as sex, age, etc. Throughout we emphasize prediction and advocate mechanistic as opposed to empirical modelling, and argue that the Bayesian approach is particularly natural in this setting.

Are we dependent upon coffee and caffeine? A review on human and animal data

Caffeine is the most widely used psychoactive substance and has been considered occasionally as a drug of abuse. The present paper reviews available data on caffeine dependence, tolerance, reinforcement and withdrawal. After sudden caffeine cessation, withdrawal symptoms develop in a small portion of the population but are moderate and transient. Tolerance to caffeine-induced stimulation of locomotor activity has been shown in animals. In humans, tolerance to some subjective effects of caffeine seems to occur, but most of the time complete tolerance to many effects of caffeine on the central nervous system does not occur. In animals, caffeine can act as a reinforcer, but only in a more limited range of conditions than with classical drugs of dependence. In humans, the reinforcing stimuli functions of caffeine are limited to low or rather moderate doses while high doses are usually avoided. The classical drugs of abuse lead to quite specific increases in cerebral functional activity and dopamine release in the shell of the nucleus accumbens, the key structure for reward, motivation and addiction. However, caffeine doses that reflect the daily human consumption, do not induce a release of dopamine in the shell of the nucleus accumbens but lead to a release of dopamine in the prefrontal cortex, which is consistent with caffeine reinforcing properties. Moreover, caffeine increases glucose utilization in the shell of the nucleus accumbens only at rather high doses that stimulate most brain structures, non-specifically, and likely reflect the side effects linked to high caffeine ingestion. That dose is also 5-10-fold higher than the one necessary to stimulate the caudate nucleus, which mediates motor activity and the structures regulating the sleep-wake cycle, the two functions the most sensitive to caffeine. In conclusion, it appears that although caffeine fulfils some of the criteria for drug dependence and shares with amphetamines and cocaine a certain specificity of action on the cerebral dopaminergic system, the methylxanthine does not act on the dopaminergic structures related to reward, motivation and addiction.

Interchangeability and predictive performance of empirical tolerance models

Models of tolerance are commonly derived on empirical grounds, because of lack of knowledge about the mechanism of tolerance or because of the difficulty of appropriately simplifying complex physiological processes. The present study was performed to evaluate the interchangeability of tolerance models used in the literature and to address some determinants for selection of an appropriate design and data analysis strategy. Seven models were chosen (noncompetitive antagonist model, partial agonist model, reverse agonist model, direct moderator model, indirect moderator model, pool model and adaptive pool model) along with their corresponding parameter estimates, representing a wide range of empirical models. The performance of the models on various data sets was evaluated. Data were simulated from each original model and were further analysed by the other models. The effect-time course of each and every data set could be described well by at least 2 different empirical tolerance models, but no model could describe all the data sets adequately. However, all models could adequately describe at least 2 different data sets. This indicates that, without additional knowledge or assumptions, it is unlikely that reliable mechanistic information can be deduced from the mere fact that 1 (or more) of these models can describe the data. Generally, data expressing only limited tolerance can be described by a wide variety of models, whereas few models will be appropriate for data characterised by extensive tolerance. The models that gave an adequate description of a data set were selected for further study that investigated their predictive capacity based on the parameters previously determined. Predictions were made for 4 different administration schemes. The selected models gave similar predictions for the extended designs of 3 data sets for which the original study designs characterised tolerance well. For the other 4 data sets, the selected models gave disparate predictions, although the models described the original data set well. Thus, the predictive capability of a model was linked to the original study design, whereas the correlation between predictive performance and the type of model was weak or absent. Based on the results, factors of importance for the design and evaluation of studies of tolerance were identified and discussed.

Dose-dependence and repeated-dose studies for receptor/gene-mediated pharmacodynamics of methylprednisolone on glucocorticoid receptor down-regulation and tyrosine aminotransferase induction in rat liver

Dose-dependent and repeated-dose effects of methylprednisolone (MPL) on down-regulation of glucocorticoid receptor messenger RNA (GR mRNA) and GR density, as well as tyrosine aminotransferase (TAT) mRNA and TAT induction by receptor/gene-mediated mechanisms in rat liver were examined. A previously developed pharmacokinetic/pharmacodynamic (PK/PD) model was used to design these studies which sought to challenge the model. Three groups of male adrenalectomized Wistar rats received MPL by i.v. injection: low-dose (10 mg/kg at Time 0), high-dose (50 mg/kg at Time 0), and dual-dose (50 mg/kg at Time 0 and 24 hr). Plasma concentrations of MPL, and hepatic content of free GR, GR mRNA, TAT mRNA, and TAT activity were determined. The P-Pharm program was applied for population analysis of MPL PK revealing low interindividual variation in CL and Vc values (3-14%). Two indirect response models were applied to test two competing hypotheses for GR mRNA dynamics. Indirect Pharmacodynamic Response Model I (Model A) where the complex in the nucleus decreases the transcription rate of GR mRNA better described GR mRNA/GR down-regulation. Levels of TAT mRNA began to increase at 1-2 hr, reached a maximum at 5-6 hr, and declined to the baseline at 12-14 hr after MPL dosing. The induction of TAT activity followed a similar pattern with a delay of about 1-2 hr. The low-dose group had 50-60% of the TAT mRNA and TAT induction compared to the high-dose group. Since the GR density returned to about 70% of the baseline level before the second 50 mg/kg dose at 24 hr, tolerance was found for TAT mRNA/TAT induction where only 50-60% of the initial responses were produced. Our fourth-generation model describes the dose dependence and tolerance effects of TAT mRNA/TAT induction by MPL involving multiple-step signal transduction controlled by the steroid regimen, free GR density, and GR occupancy. This model may provide the foundation for studying other induced proteins or enzymes mediated by the similar receptor/nuclear events.

Expanding clinical applications of population pharmacodynamic modelling

Population pharmacokinetics or pharmacodynamics is the study of the variability in drug concentration or pharmacological effect between individuals when standard dosage regimens are administered. We provide an overview of pharmacokinetic models, pharmacodynamic models, population models and residual error models. We outline how population modelling approaches seek to explain interpatient variability with covariate analysis, and, in some approaches, to characterize the unexplained interindividual variability. The interpretation of the results of population modelling approaches is facilitated by shifting the emphasis from the perspective of the modeller to the perspective of the clinician. Both the explained and unexplained interpatient variability should be presented in terms of their impact on the dose-response relationship. Clinically relevant questions relating to the explained and unexplained variability in the population can be posed to the model, and confidence intervals can be obtained for the fraction of the population that is estimated to fall within a specific therapeutic range given a certain dosing regimen. Such forecasting can be used to develop optimal initial dosing guidelines. The development of population models (with random effects) permits the application of Bayes's formula to obtain improved estimates of an individual's pharmacokinetic and pharmacodynamic parameters in the light of observed responses. An important challenge to clinical pharmacology is to identify the drugs that might benefit from such adaptive-control-with-feedback dosing strategies. Drugs used for life threatening diseases with a proven pharmacokinetic-pharmacodynamic relationship, a small therapeutic range, large interindividual variability, small interoccasion variability and severe adverse effects are likely to be good candidates. Rapidly evolving changes in health care economics and consumer expectations make it unlikely that traditional drug development approaches will succeed in the future. A shift away from the narrow focus on rejecting the null hypothesis towards a broader focus on seeking to understand the factors that influence the dose-response relationship--together with the development of the next generation of software based on population models--should permit a more efficient and rational drug development programme.

Caffeine withdrawal in normal school-age children

OBJECTIVE

Caffeine is widely consumed by children around the world. The purpose of this study was to determine whether children manifest withdrawal effects after cessation of caffeine intake.

METHOD

Thirty normal children completed the single-blind, within-subjects, repeated-measures study with weekly sessions. Subjects were tested four times: (1) baseline (on regular caffeine diet); (2) on caffeine (approximately 120 to 145 mg/day); (3) during withdrawal (24 hours after discontinuation of caffeine taken for 13 consecutive days); and (4) at return to baseline. Subjects were evaluated with self-report measures of symptoms and objective measures of attention, motor performance, processing speed, and memory.

RESULTS

During caffeine withdrawal, there was a significant deterioration on response time of a visual continuous performance test of attention. This finding is consistent with caffeine withdrawal. The deterioration in response time appeared to persist for 1 week.

CONCLUSIONS

Twenty-four hours after children discontinued caffeine, there was a decrease in performance on reaction time of a task requiring sustained attention. Further work is indicated to determine whether children manifest caffeine withdrawal effects after cessation of caffeine intake.

Acute exercise reduces caffeine-induced anxiogenesis

PURPOSE

This experiment examined the influence of acute exercise on anxiety following caffeine-induced elevations in self-rated anxiety.

METHODS

Eleven physically active, moderately fit males aged 25.1 +/- 3.8 yr completed four conditions in a within-subject, counterbalanced design involving 60 min of (1) cycling at 60% VO2peak or (2) quiet rest following placebo consumption (800 mg of lactose), as well as (3) cycling at 60% VO2peak and (4) quiet rest following 800 mg of caffeine. State anxiety and blood pressure were assessed 10 min before and 10 and 20 min after the conditions.

RESULTS

A main effect for drug (caffeine vs placebo) determined by repeated measures ANOVA, (F(1,8) = 9.77; P = 0.01), indicated that state anxiety was elevated by caffeine. Drug effects were not obtained for blood pressure. Experimental hypotheses were tested by drug-by-condition (exercise vs quiet rest)-by-time (10 and 20 min postcondition) repeated measures ANOVA of change scores from the precondition baseline. A main effect for drug (F(1,8) = 5.81; P = 0.043) indicated that reductions in state anxiety were larger after caffeine ingestion. A condition-by-time effect (F(1,8) = 5.02; P = 0.055) indicated greater reductions in state anxiety 20 min after exercise compared with quiet rest. A condition effect for systolic blood pressure (F(1,10) = 4.56; P = 0.058) and condition-by-time interactions for diastolic (F(1,10) = 8.87; P = 0.014) and mean arterial blood pressures (F(1,10) = 8.46; P = 0.016) indicated reductions after exercise but not after quiet rest following both caffeine and placebo.

CONCLUSIONS

We conclude that exercise can reduce anxiety elevated by a high dose of caffeine.

Multiple-dose pharmacokinetics and pharmacodynamics of OROS and immediate-release amitriptyline hydrochloride formulations

The pharmacokinetics and pharmacodynamics of amitriptyline hydrochloride after oral administration of an OROS osmotic system, which provides controlled drug delivery, and an immediate-release (IR) tablet, were evaluated in 24 healthy volunteers after repeated administration for 14 days. Each morning, subjects received either 75 mg of the OROS (amitriptyline HCl) controlled-release formulation or the 75 mg IR amitriptyline tablet for 14 days on two separate occasions with a washout period of 21 days according to a randomly assigned sequence. Serial blood samples were collected for a period of 58 hours after the day 14 dose, then these samples were analyzed by the gas chromatography method for amitriptyline and nortriptyline. Subjective ratings of dry mouth and drowsiness were collected at specific times throughout each treatment period. Administration of the OROS formulation resulted in much more consistent plasma concentrations of the drug and metabolite compared with the IR formulation at steady state. The mean maximum concentration (Cmax) of amitriptyline was significantly lower after administration of OROS than the IR formulation. Mean values for area under the concentration--time curve (AUC0-24) for the OROS and IR formulations were 1,265 and 1,393 ng. hr/mL, respectively. The drug-to-metabolite ratio was found to be similar for both treatments, suggesting that there was no difference in metabolism between treatments. Incidence and severity of the anticholinergic effects were similar for the two treatments. A clockwise hysteresis between baseline-corrected drowsiness and drug concentration suggests development of tolerance of the anticholinergic effects after both treatments. Using a hypothetical anatagonist metabolite model to explain tolerance development, the shape of the hysteresis curves of the two treatments could be explained by differences in dosing frequency.

The impact of arteriovenous concentration differences on pharmacodynamic parameter estimates

In many pharmacodynamic investigations venous drug concentrations are measured and linked to effect-site concentrations by means of a traditional first-order effect-compartment model to estimate pharmacodynamic (PD) parameters. This analysis ignores the underlying physiology that arterial blood supplies both the venous sampling site and effect site. Recently, an extended effect-compartment model has been proposed that reflects physiology by postulating a first-order rate constant of equilibrium between arterial and effect-site concentrations (ke0) as well as first-order rate constant between arterial and venous concentrations (kv0). In the current paper, we evaluate the bias in PD parameter estimates if venous drug concentrations are measured and linked to effect-site concentrations by a traditional effect compartment as a function ke0, kv0, and the drug's elimination half-life (T1/2); we present an analytical solution to the differential equations characterizing the extended effect-compartment model; and we evaluate the performance of the extended effect-compartment model to estimate pharmacodynamic parameters on the basis of venous drug concentrations. Time profiles of venous drug concentrations and drug effect were simulated for a wide range of different values of the half-life of ke0 (T1/2,e0), the half-life of kv0 (T1/2,v0), and T1/2. The simulations showed that a significant bias (up to 90%) in PD parameter estimates occurred for certain values of T1/2,e0, T1/2,v0, and T1/2 if venous drug concentrations are linked to effect-site concentrations by a traditional effect-compartment model. This model misspecification is not apparent from the results of the fitting procedure. The extended effect-compartment model provided unbiased but imprecise PD parameter estimates. The extended effect-compartment model was also able to analyze instances in which the venous concentrations equilibrate slower with the arterial concentrations than the effect-site concentrations, and proteresis is observed in the concentration--effect relationship. It is concluded that if the apparent T1/2 of the drug in the time period in which the decline in pharmacological effect is most pronounced is greater than 5 times T1/2,e0 and T1/2,e0 is greater than T1/2,v0 there is no need to model the underlying arteriovenous equilibrium delay. Under these conditions a traditional first-order link between venous and effect-site concentrations will yield accurate and reliable (less than 10% bias) estimates of the PD parameters such as Emax, EC50 and N. If T1/2 is less than 5 times T1/2,e0 or if T1/2,v0 is greater than T1/2,e0, the underlying arteriovenous equilibration delay needs to be taken into account in the model to obtain unbiased estimates of the PD parameters. This applies for almost all values of T1/2.v0. Arteriovenous equilibration delay can be best taken into account by measuring arterial blood concentrations. If this is not possible, the extended effect-compartment link model can be used. However, a large number of effect measurements needs to be obtained to estimate the model parameters accurately.