Between-subject and within-subject variations in the pharmacokinetics of ethanol

Fat-free mass accounts for most of the variance in alcohol elimination rate in women

BACKGROUND

Understanding how blood alcohol concentrations (BAC) achieved after drinking are determined is critical to predicting alcohol exposure to the brain and other organs and alcohol's effects. However, predicting end-organ exposures is challenging, as there is wide variation in BAC achieved after drinking a specified volume of alcohol. This variation is partly due to differences in body composition and alcohol elimination rates (AER), but there are limited data on how obesity affects AER. Here, we assess associations between obesity, fat-free mass (FFM), and AER in women and examine whether bariatric surgeries, which are linked to an increased risk of alcohol misuse, affect these associations.

METHODS

We analyzed data from three studies that used similar intravenous alcohol clamping procedures to estimate AER in 143 women (21 to 64 years old) with a wide range of body mass index (BMI; 18.5 to 48.4 kg/m2 ). Body composition was measured in a subgroup using dual-energy X-ray absorptiometry (n = 42) or Bioimpedance (n = 60), and 19 of the women underwent bariatric surgery 2.1 ± 0.3 years before participation. We analyzed data using multiple linear regression analyses.

RESULTS

Obesity and older age were associated with a faster AER (BMI: rs  = 0.70 and age: rs  = 0.61, both p < 0.001). Compared to women with normal weight, AER was 52% faster (95% Confidence Interval: 42% to 61%) in women with obesity. However, BMI lost predictive value when adding fat-free mass (FFM) to the regression model. Age, FFM, and its interaction explained 72% of individual variance in AER (F (4, 97) = 64.3, p < 0.001). AER was faster in women with higher FFM, particularly women in the top tertile of age. After controlling for FFM and age, bariatric surgery was not associated with differences in AER (p = 0.74).

CONCLUSIONS

Obesity is associated with a faster AER, but this association is mediated by an obesity-related increase in FFM, particularly in older women. Previous findings of a reduced alcohol clearance following bariatric surgery compared with prior to surgery are likely explained by a reduction in FFM post-surgery.

Development of a Physiologically Based Pharmacokinetic Model for Prediction of Ethanol Concentration-Time Profile in Different Organs

AIMS

A physiologically based pharmacokinetic (PBPK) modeling approach was used to simulate the concentration-time profile of ethanol (EtOH) in stomach, duodenum, plasma and other tissues upon consumption of beer and whiskey under fasted and fed conditions.

METHODS

A full PBPK model was developed for EtOH using the advanced dissolution, absorption and metabolism (ADAM) model fully integrated into the Simcyp Simulator® 15 (Simcyp Ltd., Sheffield, UK). The prediction performance of the developed model was verified and the EtOH concentration-time profile in different organs was predicted.

RESULTS

Simcyp simulation showed ≤ 2-fold difference in values of EtOH area under the concentration-time curve (AUC) in stomach and duodenum as compared to the observed values. Moreover, the simulated EtOH maximum concentration (Cmax), time to reach Cmax (Tmax) and AUC in plasma were comparable to the observed values. We showed that liver is exposed to the highest EtOH concentration, faster than other organs (Cmax = 839.50 mg/L and Tmax = 0.53 h), while brain exposure of EtOH (AUC = 1139.43 mg·h/L) is the highest among all other organs. Sensitivity analyses (SAs) showed direct proportion of EtOH rate and extent of absorption with administered EtOH dose and inverse relationship with gastric emptying time (GE) and steady-state volume of distribution (Vss).

CONCLUSIONS

The current PBPK model approach might help with designing in vitro experiments in the area of alcohol organ damage or alcohol-drug interaction studies.

Hip-flask defense: An experimental study in the Hungarian population

Toxicology tests and medical expert opinions are part of routine work in drunk driving cases in both domestic and international practice. The greatest challenge to forming an opinion is that the perpetrator claims to have consumed alcohol after the act of driving. To determine the time of consumption, it is essential to establish whether the alcohol in the body was in the absorption phase or in the elimination phase when the sample was collected. In domestic practice, breath alcohol content can be measured several times, two blood samples can be collected, and both blood and urine samples can be taken almost simultaneously. A recent Swedish study showed that taking a single blood sample and two urine samples allows for a more accurate examination of consumption after the fact. This study aimed to examine the applicability of such model to the domestic environment. We conducted a controlled drinking experiment involving 15 Hungarian casual drinker volunteers aged 18-25 years who consumed different amounts of alcohol at specified times while providing regular breath alcohol measurements as well as blood and urine samples. These measurement results provided accurate information about the changes in alcohol metabolism compared to the time of drinking and allowed us to draw the necessary conclusions, offering further evidence that alcohol metabolism can vary significantly between different ethnic groups. The results showed that the absorption and excretion of ethyl alcohol in the volunteers were much faster than those in the current Hungarian standards used in practice. In conclusion, the comparison of blood and urine samples collected between 60 min and 120 min cannot be considered suitable for establishing the fact of drinking after driving in Hungarian practice, and a local model is needed.

Effects of Consuming a Low Dose of Alcohol with Mixers Containing Carbohydrate or Artificial Sweetener on Simulated Driving Performance

The Australian National Drug and Alcohol Research Centre (NDARC) devised gender-based drinking recommendations to ensure blood or equivalized breath alcohol concentrations (BrAC) remain <0.050%. However, these may be inappropriate for individuals consuming alcohol without carbohydrate (CHO), which results in higher BrACs. This study investigated the effects of ingesting alcohol with and without CHO on BrACs and simulated driving performance. Thirty-two participants (16 males; age: 23 ± 6 years) completed two randomized single-blinded trials. Participants performed a baseline drive (Drive 1), then an experimental drive (Drive 2), following alcohol consumption (males: 20 g; females: 10 g). Alcoholic beverages contained either 25 g sucrose or aspartame (AS). Driving performance was assessed using lateral control (standard deviation of lane position [SDLP] and number of lane departures) and risk-taking (number of overtaking maneuvers and maximum overtaking speed). BrAC and subjective ratings (e.g., intoxication) were also assessed. BrAC was significantly lower as Drive 2 commenced with CHO compared to AS (0.022 ± 0.008% vs. 0.030 ± 0.011%). Two males provided BrACs >0.050% with AS. Neither beverage influenced changes to simulated driving performance. Ingesting alcohol in quantities advised by the NDARC results in no detectable simulated driving impairment. However, the likelihood of exceeding the legal drink-driving BrAC is increased when alcohol is consumed with artificially-sweetened mixers.

Effect of 8-weeks prebiotics/probiotics supplementation on alcohol metabolism and blood biomarkers of healthy adults: a pilot study

PURPOSE

Modulating gut bacteria via regular prebiotics/probiotics consumption may improve the metabolism of acute alcohol ingestion. This study investigated the impact of 8-weeks prebiotics/probiotics supplementation on microbiome changes and responses to acute alcohol consumption.

METHODS

38 participants (21 females, 23.6 ± 3.4 kg m^-2, mean ± SD) attended the laboratory on two occasions separated by an 8-week intervention period. On each of these visits, a dose of alcohol (0.40 ± 0.04 g kg^-1, Vodka + Soda-Water) was consumed over 10 min. Breath alcohol concentration was sampled over 5 h and alcohol pharmacokinetics was analysed using WinNonlin non-compartmental modelling (C _max, t _max, AUC_last). For the intervention, participants were randomised to receive Placebo + Placebo (PLA), Placebo + Prebiotics (PRE), Probiotics + Placebo (PRO), or Probiotics + Prebiotics (SYN) in a double-blinded manner. Probiotics were a commercially available source of Lactobacillus acidophilus (NCFM^®) and Bifidobacterium lactis (Bi-07). Prebiotics were a commercially available source of Larch Gum (from Larix occidentalis). Placebo was microcrystalline cellulose. Each visit, participants provided a stool sample, which was analysed to determine the presence of L. acidophilus and B. lactis. Differences between trials were analysed using paired samples t tests.

RESULTS

Increased counts for at least one bacterial strain (L. acidophilus or B. lactis) were observed for all participants on SYN (n = 10) and PRO (n = 10) trials. No difference in C _max or t _max was observed between trials when analysed by treatment condition or microbiome outcome. A significant decrease in AUC_last was observed between trials for PLA (p = 0.039) and PRE (p = 0.030) treatments, and when increases in at least one bacterial strain (p = 0.003) and no microbiome changes (p = 0.016) were observed.

CONCLUSION

Consumption of probiotics appears to alter faecal counts of supplemental bacterial strains in otherwise healthy individuals. However, translation to any possible beneficial impact on alcohol metabolism remains to be elucidated.

The Influence of Mixers Containing Artificial Sweetener or Different Doses of Carbohydrate on Breath Alcohol Responses in Females

BACKGROUND

Breath alcohol responses may be affected by the presence of carbohydrate (CHO) in a beverage. This study investigated the impact of consuming alcohol with mixers containing various doses of CHO or an artificial sweetener on breath alcohol concentration (BrAC), ratings of intoxication and impairment, and cognitive performance in females.

METHODS

Twenty-six females (age 25.1 ± 0.7 years, mean ± standard deviation) completed a crossover study involving 4 trials. A dose of alcohol was consumed in each trial mixed with water (W), artificial sweetener (150 ± 1 mg aspartame [AS]), or CHO (15 g sucrose [15CHO] and 50 g sucrose [50CHO]). BrAC was sampled for 210 minutes following beverage ingestion and analyzed for peak BrAC and other parameters using WinNonlin noncompartmental pharmacokinetic modeling (c_max , t_max , area under the curve to the last measured time point [AUC_last ]). An objective measure of cognitive performance was assessed using a 4-choice reaction time (CRT) task. Estimation of BrAC, self-reported ratings of intoxication, and willingness to drive were recorded.

RESULTS

Mean peak BrAC was reduced in a dose-response manner when alcohol was consumed with CHO compared to both W and AS treatments (W: 0.054 ± 0.015%, AS: 0.052 ± 0.011%, 15CHO: 0.049 ± 0.008%, 50CHO: 0.038 ± 0.007%). No difference in peak BrAC was observed between W and AS treatments. WinNonlin parameters revealed significant differences in c_max and AUC_last (W: 4.80 ± 1.12 g/dl/h, AS: 4.61 ± 0.92 g/dl/h, 15CHO: 4.10 ± 0.86 g/dl/h, 50CHO: 3.11 ± 0.58 g/dL/h) when CHO-containing beverages were consumed compared to W and AS treatments. No difference in t_max or CRT was observed between treatments. Participants were able to detect subtle differences in peak BrAC and reported greater ability to drive after consuming 50CHO compared to W. However, participant's willingness to drive and CRT did not differ between treatments.

CONCLUSIONS

Consuming alcohol with CHO-containing mixers attenuates peak BrAC and reduces total alcohol exposure in a dose-response manner compared to drinks containing artificial sweetener or no additives. The effect of adding CHO to alcoholic beverages may translate to reduced risk of alcohol-related harms.

Effects of idazoxan on alcohol pharmacokinetics and intoxication: a preliminary human laboratory study

BACKGROUND

Preliminary basic and human studies suggest that the α2 -adrenergic antagonist idazoxan may represent a novel medication for alcohol dependence. The goal of this study was to evaluate the safety and tolerability of the co-administration of idazoxan with alcohol and explore whether pharmacokinetics (PK) and biobehavioral mechanisms of idazoxan may alter alcohol's effects.

METHODS

This was a preliminary double-blind, single-dose, placebo-controlled, crossover, randomized human laboratory study. Ten social drinkers were dosed, in 2 different alcohol challenge studies (ACS), with a single oral dose of idazoxan (40 mg) or placebo, followed by a fixed alcohol dose 60 minutes later. Participants returned after a 1-week washout, and they were crossed over to the opposite medication condition.

RESULTS

There were no significant differences in adverse events between idazoxan and placebo. Moreover, during the ACS paradigm, 40 mg idazoxan was well tolerated with no significant autonomic effects compared to placebo; idazoxan reduced the peak blood alcohol level (p < 0.01) and time to peak (p < 0.05) compared to placebo. A PK/pharmacodynamic model aligned the biobehavioral effects, demonstrating that the co-administration of 40 mg idazoxan with alcohol decreased alcohol-related stimulation (p < 0.05) and increased alcohol-related sedation (p < 0.05).

CONCLUSIONS

This study supports the safety and tolerability of 40 mg idazoxan when co-administered with alcohol. Additionally, this study suggests that idazoxan may alter the biphasic effects of alcohol by decreasing stimulation and increasing sedation. These findings have implications for further investigation of using idazoxan as a probe to develop potential novel medications to treat alcoholic patients.

Alcohol pharmacokinetics and risk-taking behaviour following exercise-induced dehydration

This study investigated the influence of exercise-induced dehydration on alcohol pharmacokinetics, subjective ratings of impairment, and risk-taking behaviours. Twelve male volunteers participated in 3 experimental trials completed in a randomised cross over design separated by at least 7 days. In one trial, participants exercised to cause dehydration of ~2.5% body weight loss. For the other trials, participants were required to be in a rested and euhydrated state. A set volume of alcohol was then consumed in each trial and participants were monitored over a 4h period. Blood (BAC) and breath (BrAC) alcohol samples were collected throughout and analysed to calculate pharmacokinetic variables associated with the blood alcohol curve. Total urine production, estimates of BrAC, and subjective ratings of intoxication and impairment were also recorded throughout each trial. No difference was found in the pharmacokinetics of alcohol between any of the trial conditions. BrACs were higher than BACs for 2h following alcohol consumption, but lower at measures taken 3 and 4 h post ingestion. Participants' ratings of confusion and intoxication were significantly lower, and they were more willing to drive in the dehydration trial compared with one of the euhydration trials. These findings suggest that dehydration or other physiological changes associated with exercise may have an ability to influence the subjective effects of alcohol and increase the likelihood of risk-taking behaviours such as drink-driving. However, further research is required to examine the effects of alcohol under conditions of exercise-induced fluid loss in order to clarify these findings.

Alcohol induced region-dependent alterations of hemodynamic response: implications for the statistical interpretation of pharmacological fMRI studies

Worldwide, ethanol abuse causes thousands of fatal accidents annually as well as innumerable social dysfunctions and severe medical disorders. Yet, few studies have used the blood oxygenation level dependent functional magnetic resonance imaging method (BOLD fMRI) to map how alcohol alters brain functions, as fMRI relies on neurovascular coupling, which may change due to the vasoactive properties of alcohol. We monitored the hemodynamic response function (HRF) with a high temporal resolution. In both motor cortices and the visual cortex, alcohol prolonged the time course of the HRF, indicating an overall slow-down of neurovascular coupling rather than an isolated reduction in neuronal activity. However, in the supplementary motor area, alcohol-induced changes to the HRF suggest a reduced neuronal activation. This may explain why initiating and coordinating complex movements, including speech production, are often impaired earlier than executing basic motor patterns. Furthermore, the present study revealed a potential pitfall associated with the statistical interpretation of pharmacological fMRI studies based on the general linear model: if the functional form of the HRF is changed between the conditions data may be erroneously interpreted as increased or decreased neuronal activation. Thus, our study not only presents an additional key to how alcohol affects the network of brain functions but also implies that potential changes to neurovascular coupling have to be taken into account when interpreting BOLD fMRI. Therefore, measuring individual drug-induced HRF changes is recommended for pharmacological fMRI.

Age and gender differences in blood-alcohol concentration in apprehended drivers in relation to the amounts of alcohol consumed

This article reports the age, gender, and blood-alcohol concentration (BAC) of people apprehended in Sweden for driving under the influence of alcohol (DUIA) over an 8-year period (2000-2007). Duplicate determinations of ethanol were made in venous blood by headspace gas chromatography and results were reported positive at a cut-off concentration of 0.1 g/L (10 mg/100 ml or 0.01 g%). The mean, median and highest BAC was 1.74 g/L, 1.70 g/L and 5.18 g/L, respectively. The vast majority of offenders were men (89.5%) with a mean age of 39.0+/-14.6 y (+/-SD). The women (10.5%) were a few years older 41.8+/-13.6 y (p<0.001). The mean BAC in the men (1.73+/-0.85 g/L) did not differ significantly (p>0.05) from women (1.77+/-0.87 g/L). The youngest offenders aged 15-20 y (N=3513) had a mean BAC of 1.30+/-0.60 g/L (median 1.32), which was significantly less (p<0.001) than people aged 40-50 y (N=6644); mean 1.90 g/L (median 2.0 g/L). In 95 individuals (89 men and 6 women) the BAC exceeded 4.0 g/L, which is a level considered to cause death by acute alcohol poisoning. The Widmark formula was used to calculate that a man (80 kg) with a BAC of 1.7 g/L has 95 g ethanol (approximately 12 units of alcohol) in the body compared with 61 g (approximately 8 units) for a woman (60 kg). This study verifies that the average drunken driver in Sweden is typically a binge drinker and education programs and treatment for alcohol-use disorder might be a more appropriate sanction than the more conventional penalties for alcohol-impaired driving.

ADH single nucleotide polymorphism associations with alcohol metabolism in vivo

We have previously found that variation in alcohol metabolism in Europeans is linked to the chromosome 4q region containing the ADH gene family. We have now typed 103 single nucleotide polymorphisms (SNPs) across this region to test for allelic associations with variation in blood and breath alcohol concentrations after an alcohol challenge. In vivo alcohol metabolism was modelled with three parameters that identified the absorption and rise of alcohol concentration following ingestion, and the rate of elimination. Alleles of ADH7 SNPs were associated with the early stages of alcohol metabolism, with additional effects in the ADH1A, ADH1B and ADH4 regions. Rate of elimination was associated with SNPs in the intragenic region between ADH7 and ADH1C, and across ADH1C and ADH1B. SNPs affecting alcohol metabolism did not correspond to those reported to affect alcohol dependence or alcohol-related disease. The combined SNP associations with early- and late-stage metabolism only account for approximately 20% of the total genetic variance linked to the ADH region, and most of the variance for in vivo alcohol metabolism linked to this region is yet to be explained.

Inter- and intra-subject variability in ethanol pharmacokinetic parameters: Effects of testing interval and dose

Calculation of a blood alcohol concentration (BAC) at the time of an offence by forward or back-extrapolation, using population average values for ethanol pharmacokinetic parameters or a single estimate of individual specific parameters, ignores the possibility of inter- and intra-subject variability. In order to estimate inter- and intra-subject variability in the elimination rate and absorption rate, BAC was measured over time in 12 male volunteers on 4 occasions. Subjects received 0.44 g kg(-1) body weight of ethanol on the first study day, and 0.70 g kg(-1) body weight on subsequent study days 1, 11 and 12 weeks later, to enable comparisons in variability over short and long time periods and when the same or different doses were administered. Evidence of both inter- and intra-subject variability was found, with inter-subject variability substantially smaller than intra-subject variability when the dose varied. Forensically important differences in pharmacokinetic parameters were observed within individuals between occasions. These findings could have an important impact on medico-legal issues related to ethanol pharmacokinetics.

The relationship between alcohol elimination rate and increasing blood alcohol concentration—Calculated from two consecutive blood specimens

In the period 1991-2005, a blood-alcohol concentration (BAC) analysis was carried out at the Institute of forensic medicine in Novi Sad including 2023 two consecutive blood specimens using the Headspace Gas Chromatography method. Cases with no alcohol concentration values, as well as cases where blood samples were taken within 1 h after the criminal act, were not taken into consideration. Following this rule, 1198 cases were considered in this study and all samples were grouped in 29 ranges of BAC1 of delta(BAC) = 0.1 g/kg, starting from 0.1-0.19 g/kg to 2.9-2.99 g/kg of absolute alcohol. Gathered results and elimination curve differ from the zero-order model of elimination proposed by Widmark and point to an elimination process similar to a well-known Michaelis-Menten elimination kinetics model and its variants. Results reported in this study show dependence of alcohol elimination rate (beta-slope) and BAC value. The analysis of beta60-slope versus BAC shows that a correlation between beta60 (y) and BAC (x) has a logarithmic trend line. The value of alcohol elimination rate shows a slight increment with increase of BAC alcohol, with the mean value of beta60 = 0.221 +/- 0.075 g/kg. Differences in values of beta60 among consecutive intervals of delta(BAC) = 0.1 g/kg are not significant (p>0.05). When obtained samples were grouped into ranges of 0.5 g/kg each in these intervals beta60 had the following values by range: 0.1-0.49 g/kg = 0.139 g/kg +/- 0.035; 0.5-0.99 g/kg = 0.184 g/kg +/- 0.043; 1-1.49 g/kg = 0.213 g/kg +/- 0.052; 1.5-1.99 g/kg = 0.239 g/kg +/- 0.058; 2-2.49 g/kg = 0.265 g/kg +/- 0.073; 2.5-2.99 g/kg = 0.306 g/kg +/- 0.096. Differences in values of beta slope among consecutive intervals of delta(BAC) = 0.5 g/kg are significant (p<0.01). The elimination curve in the BAC interval 0.5-2.5 g/kg has a linear trend, while beta-slope (y)/BAC (x) correlation is given as beta60 = 0.15 g/kg + (0.05 g/kg x BAC). Retrograde calculation of the blood alcohol concentration in tempore criminis (BAC(tc)) based on the determined alcohol concentration in the blood specimen (BAC(t)) shows a statistically significant difference between BAC(tc) calculated using a standard zero-order model versus corrected methodology. The higher the BAC(t) and the longer the calculation time, the greater and statistically more significant (p<0.01) is the difference between the calculated values of BAC(tc).

Alcohol levels in Chinese lactating mothers after consumption of alcoholic diet during postpartum "doing-the-month" ritual

This study examined the effects of exposure to ethanol through cultural practices by lactating mothers. Specifically, the pharmacokinetics of alcohol in Chinese lactating mothers was investigated after they consumed chicken soup flavored with sesame oil and rice wine (CSSR), a typically prescribed diet during the postpartum "doing-the-month" period. Experimental findings were employed to estimate the potential ethanol dose to neonates and determine associated health risks. Twenty-three lactating mothers were examined. Informed consent was obtained from each subject. The target alcohol dosage was 0.3g/kg. Milk and blood samples were collected at fixed time intervals from each subject following exposure to CSSR, and alcohol levels were determined. Acute health risks to infants were estimated by comparing the potential infant dosage to an established criterion dose. Blood alcohol level peaked at 20 min after exposure to CSSR and decreased almost linearly thereafter. Alcohol in milk reached a plateau roughly at 20-40 min after exposure to CSSR and then decreased. Alcohol pharmacokinetics among subjects varied widely. The coefficients of variation in subject alcohol concentrations were 16.5-46.2% (mean, 30.0%) for blood and 32.8-57.6% (mean, 44.4%) for milk. Mean maximal alcohol concentration in blood (30.2+/-5.0 mg/dl) was achieved at 23.5+/-7.6 min and in milk (31.6+/-10.3 mg/dl) at 31.7+/-12.7 min. Potential infant doses were 3.0-58.8 mg (mean, 13.4 mg), and the predicted time required for milk alcohol level to return to zero level was 175 min. The acute health risks for infants exposed to alcohol through their mothers' milk under the current exposure scenario are low (hazard index<0.2). Nursing infants at least 3h after ingesting a diet containing alcohol would further reduce potential health risks.

Human variability for metabolic pathways with limited data (CYP2A6, CYP2C9, CYP2E1, ADH, esterases, glycine and sulphate conjugation)

Human variability in the kinetics of a number of phase I (CYP2A6, CYP2C9, CYP2E1, alcohol dehydrogenase and hydrolysis) and phase II enzymes (glycine and sulphate conjugation) was analysed using probe substrates metabolised extensively (>60%) by these routes. Published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and available data on subgroups of the population (effects of ethnicity, age and disease) were abstracted using parameters relating primarily to chronic exposure [metabolic and total clearances, area under the plasma concentration time-curve (AUC)] and acute exposure (C(max)). Interindividual differences in kinetics for all these pathways were low in healthy adults ranging from 21 to 34%. Pathway-related uncertainty factors to cover the 95th, 97.5th and 99th centiles of healthy adults were derived for each metabolic route and were all below the 3.16 kinetic default uncertainty factor in healthy adults, with the possible exception of CYP2C9*3/*3 poor metabolisers (based on a very limited number of subjects). Previous analyses of other pathways have shown that neonates represent the most susceptible subgroup and this was true also for glycine conjugation for which an uncertainty factor of 29 would be required to cover 99% of this subgroup. Neonatal data were not available for any other pathway analysed.

Role of variability in explaining ethanol pharmacokinetics: research and forensic applications

Variability in the rate and extent of absorption, distribution and elimination of ethanol has important ramifications in clinical and legal medicine. The speed of absorption of ethanol from the gut depends on time of day, drinking pattern, dosage form, concentration of ethanol in the beverage, and particularly the fed or fasting state of the individual. During the absorption phase, a concentration gradient exists between the stomach, portal vein and the peripheral venous circulation. First-pass metabolism and bioavailability are difficult to assess because of dose-, time- and flow-dependent kinetics. Ethanol is transported by the bloodstream to all parts of the body. The rate of equilibration is governed by the ratio of blood flow to tissue mass. Arterial and venous concentrations differ as a function of time after drinking. Ethanol has low solubility in lipids and does not bind to plasma proteins, so volume of distribution is closely related to the amount of water in the body, contributing to sex- and age-related differences in disposition. The bulk of ethanol ingested (95-98%) is metabolised and the remainder is excreted in breath, urine and sweat. The rate-limiting step in oxidation is conversion of ethanol into acetaldehyde by cytosolic alcohol dehydrogenase (ADH), which has a low Michaelis-Menten constant (Km) of 0.05-0.1 g/L. Moreover, this enzyme displays polymorphism, which accounts for racial and ethnic variations in pharmacokinetics. When a moderate dose is ingested, zero-order elimination operates for a large part of the blood-concentration time course, since ADH quickly becomes saturated. Another ethanol-metabolising enzyme, cytochrome P450 2E1, has a higher Km (0.5-0.8 g/L) and is also inducible, so that the clearance of ethanol is increased in heavy drinkers. Study design influences variability in blood ethanol pharmacokinetics. Oral or intravenous administration, or fed or fasted state, might require different pharmacokinetic models. Recent work supports the need for multicompartment models to describe the disposition of ethanol instead of the traditional one-compartment model with zero-order elimination. Moreover, appropriate statistical analysis is needed to isolate between- and within-subject components of variation. Samples at low blood ethanol concentrations improve the estimation of parameters and reduce variability. Variability in ethanol pharmacokinetics stems from a combination of both genetic and environmental factors, and also from the nonlinear nature of ethanol disposition, experimental design, subject selection strategy and dose dependency. More work is needed to document variability in ethanol pharmacokinetics in real-world situations.

Evaluating alleged drinking after driving--the hip-flask defence. Part 1. Double blood samples and urine-to-blood alcohol relationship

This two-part article examines the strengths and weaknesses of various ways of investigating claims of drinking alcohol after driving, commonly known as the hip-flask or glove-compartment defence. In many countries the onus of proof in hip-flask cases rests on the prosecution. With good co-operation from the police and timely sampling of body fluids, such as blood and urine for forensic analysis of ethanol, useful evidence can be mustered to support or challenge the truthfulness of alleged drinking after driving. The person's blood-alcohol concentration (BAC) can be compared with values expected on the basis of the amount of alcohol consumed after driving, according to theoretical Widmark calculations. The actual BAC measured is then adjusted for the additional amount of alcohol consumed in the after-drink. Double blood samples, that is, taking two specimens of venous blood about 30-60 minutes apart and looking at the magnitude and direction of change in BAC provides little or no more information than a single blood specimen. However, the relationship between alcohol in blood and urine is very useful in hip-flask cases whereby the concentration expected in the primary urine is compared with the concentration in the bladder urine voided. The concentration of alcohol determined in a second urine sample collected 30-60 min later gives supporting evidence in hip-flask cases. A graphical method, which entails plotting ethanol concentrations in blood and urine as a function of time provides a robust and practical way to investigate hip-flask defences. In the second part of the review, congener analysis is presented, which entails comparing the concentrations of n-propanol, isobutanol and occasionally other congeners in the alcoholic beverage allegedly consumed after driving with the volatiles present in the suspect's blood and urine determined by headspace gas chromatography.

Within- and between-subject variations in pharmacokinetic parameters of ethanol by analysis of breath, venous blood and urine

AIMS

To evaluate the prerequisites for using ethanol dilution to estimate total body water, we studied the within- and between-subject variation in the parameter estimates of a two-compartment model for ethanol pharmacokinetics with parallel Michaelis-Menten and first-order renal elimination. Because sampling of breath might be preferable in some clinical situations the parameter estimates derived from breath and venous blood were compared.

METHODS

On two occasions, ethanol 0.4 g kg-1 was given by intravenous infusion to 16 volunteers after they had fasted overnight. The proposed model was fitted by means of nonlinear regression to concentration-time data measured in the breath, venous blood and urine during 360 min. The model contained six parameters: Vmax and Km (Michaelis-Menten elimination constants), CLd (intercompartmental distribution parameter), VC and VT (volumes of the central and tissue compartment, respectively) and CLR (renal clearance). The volume of distribution, Vss, was calculated as the sum of VC and VT.

RESULTS

The mean +/- total s.d. of the parameter estimates derived from blood data were Vmax 95 +/- 25 mg min-1, Km 27 +/- 19 mg l-1, CLd 809 +/- 232 ml min-1, VC 14.5 +/- 4.3 l, VT 21. 2 +/- 4.4 l, CLR 3.6 +/- 2.0 ml min-1 and Vss 35.8 +/- 4.3 l. The variation within subjects amounted to 3%, 9%, 21%, 21%, 17%, 26% and 2%, respectively, of the total variation. Breath samples were associated with a similar or lower variation than blood, both within and between subjects. About 1.5% of the infused ethanol was recovered in the urine.

CONCLUSIONS

The low within-subject variation of the key parameter Vss (only 2%) suggests that ethanol dilution analysed by the pharmacokinetic model applied here may be used as an index of the total body water. Breath samples yielded at least as good reproducibility in the model parameters as venous blood.

Is there an interaction between H2-antagonists and alcohol?

H2-antagonists are commonly prescribed drugs and alcohol use is widespread in the community. Any possible interaction may be important because of the frequent co-administration of both drugs and the potential for unexpected impairment of pyschomotor function, in particular, driving skills. Hepatic ADH is the major site of alcohol metabolism. ADH is also found in the stomach, but it is uncertain whether gastric ADH is able to metabolise a significant amount of alcohol in vivo. Significant first-pass metabolism can be demonstrated at lower doses of alcohol, and if alcohol is given after meals. Varying degrees of extraction of alcohol from the portal circulation probably explains the data regarding first pass metabolism rather than gastric metabolism by gastric ADH. H2-receptor antagonists inhibit gastric ADH activity to a variable extent. If gastric metabolism of alcohol is negligible then this inhibition has no relevance. Given the uncertainty regarding a mechanism of interaction, only carefully conducted studies in controlled environments will answer the question. The large inter-subject variability of alcohol absorption means that any study which seeks to determine the effect of an H2-receptor antagonist on ethanol metabolism must have sufficient numbers. A cross-over design, with each subject acting as his own control, is preferable to avoid ascribing an effect to treatment rather than to chance. The alcohol dosing studies are reviewed and the results summarised according to dose of alcohol given. At a dose of 0.15 g/kg of alcohol, four commonly used H2-antagonists may cause a small increase in blood alcohol concentrations in certain conditions. This absolute increase is very small. The magnitude of effect is far less than the effect of taking a meal before alcohol. At doses of 0.3 g/kg and above the majority of evidence favours no interaction between H2-antagonists and alcohol. There is no interaction at doses that would be expected to impair psychomotor skills (above 25 mg/dl). There remains a question regarding the cumulative effect of repeated small doses of alcohol and further studies are required. The relationship between ethanol absorption and gastric emptying raises the possibility that the effects of H2-receptor antagonists observed at very low doses of alcohol may be due to the acceleration of gastric emptying by these drugs. This is an attractive hypothesis that explains many aspects of the debate, but studies of the effect of H2-antagonists on gastric emptying have been conflicting.

Reduction in BOLD fMRI response to primary visual stimulation following alcohol ingestion

The physiology of alcohol's effects on brain function is poorly understood. Emission tomographic imaging has revealed both acute and chronic alterations in resting cerebral hemodynamics and metabolism following alcohol ingestion. However, cerebral functional integrity under these conditions has received less attention. Functional magnetic resonance imaging (fMRI) offers a non-invasive method for assessing brain functional activation. In order to assess its utility for studying the effect of alcohol on brain function, we performed fMRI with photic stimulation before and after administration of either 0.7 mg/kg alcohol (N = 12) or placebo (N = 5), resulting in peak breath alcohol levels averaging 0.069 g/dl. We found that the amplitude of visual cortical activation in response to photic stimulation was significantly reduced by approximately 33% following alcohol administration (4.0 +/- 1.7% vs. 2.7 +/- 1.3%, P = 0.02), but not following placebo (4.2 +/- 1.5% vs. 4.1 +/- 1.4%, P = 0.7). The results also suggest that the baseline right hemispheric predominance of activation in response to photic stimulation may be reduced following alcohol, suggesting a greater effect on the right hemisphere, consistent with previous studies and alcohol's known effects on visuospatial processing. In addition, through the course of each activation session, there was a progressive reduction in response following alcohol. These data demonstrate that the cerebral effects of alcohol intoxication can be studied with fMRI, and that the effects on brain function of even moderate alcohol intoxication may be widespread, may be lateralized, and may include the visual system.

Pharmacokinetic interactions between alcohol and other drugs

The frequent use of alcohol (ethanol) together with prescription drugs gives any described pharmacokinetic interaction significant clinical implications. The issue is both the effect of alcohol on the pharmacokinetics of various drugs and also the effect of those drugs on the pharmacokinetics of alcohol. This review discusses these pharmacokinetic interactions but also briefly describes some other effects of alcohol that are clinically relevant to drug prescribing. The use of several different study designs may be required before we can confidently state the presence or absence of any alcohol-drug interaction. Short term administration of alcohol in volunteers is the most common study design but studies of social drinking and prolonged moderate alcohol intake can be important in some situations. Community-based studies may illustrate the clinical relevance of any interaction. Alcohol can affect the pharmacokinetics of drugs by altering gastric emptying or liver metabolism (by inducing cytochrome P450 2E1). Drugs may affect the pharmacokinetics of alcohol by altering gastric emptying and inhibiting gastric alcohol dehydrogenase. The role of gastric alcohol dehydrogenase in the first-pass metabolism of alcohol is reviewed in this article and the arguments for and against any potential interaction between alcohol and H2 receptor antagonists are also discussed. The inhibition of the metabolism of acetaldehyde may cause disulfiram-like reactions. Pharmacodynamic interactions between alcohol and prescription drugs are common, particularly the additive sedative effects with benzodiazepines and also with some of the antihistamine drugs; other interactions may occur with tricyclic antidepressants. Alcohol intake may be a contributing factor to the disease state which is being treated and may complicate treatment because of various pathophysiological effects (e.g. impairment of gluconeogenesis and the risk of hypoglycaemia with oral hypoglycaemic agents). The combination of nonsteroidal anti-inflammatory drugs and alcohol intake increases the risk of gastrointestinal haemorrhage.

Disposition and first-pass metabolism of ethanol in humans: is it gastric or hepatic and does it depend on gender?

OBJECTIVE

To assess the extent and site of the first-pass metabolism of ethanol and to examine whether first-pass metabolism and disposition of ethanol are dependent on gender.

METHODS

After a standardized lunch, healthy subjects (six women and six men) received on two separate occasions a 60-minute intravenous infusion of ethanol (0.3 gm/kg) and concomitantly an equimolar dose of d3-ethanol/kg either orally (over 20 minutes) or intraduodenally (infused over 30 minutes). Blood levels, urinary excretion of d0- and d3-ethanol, and sedative effects were monitored for 6 hours. Disposition and first-pass metabolism of ethanol were evaluated by applying an open two-compartment model with Michaelis-Menten elimination.

RESULTS

Comparison of the corresponding intravenous/oral versus intravenous/intraduodenal data of each individual revealed that total first-pass metabolism (gastric plus hepatic) was not pronounced in either males (9.1% +/- 4.0%; mean +/- SD) or females (8.4% +/- 3.1%) and that this first-pass metabolism was partly of gastric origin. Dose-corrected values for area under blood concentration-time curve were on average 28% higher (p < 0.0001) in the women than in the men. Mean total blood ethanol disappearance rate was higher (p < 0.001) in women (3.92 +/- 0.40 mmol/L . hr) than in men (3.19 +/- 0.48 mmol/L . hr). Renal clearance was gender-independent and negligible. A linear relationship (p < 0.001) could be found between the blood levels of ethanol and sedation index. Because the slope was steeper in women (1.04) than in men (0.42) a higher central nervous system sensitivity to the sedative effects of ethanol in women can be assumed.

CONCLUSIONS

Under realistic life conditions (social drinking of moderate doses of ethanol after a light lunch) only a minor, gender-independent first-pass metabolism is observed that is partly of gastric origin.

Inter-individual and intra-individual variability of ethanol concentration-time profiles: comparison of ethanol ingestion before or after an evening meal

1. The magnitude of the variability of ethanol absorption is an important factor for studies that seek to determine the significance of potential interactions between ethanol and drugs. The aim of this study was to determine the extent of inter- and intra-individual variability of ethanol concentration-time profiles in fasted and fed subjects. 2. Twenty-four healthy male subjects were randomized to receive ethanol 0.3 g kg-1 before an evening meal on two study days and ethanol 0.3 g kg-1 after an evening meal on two study days. Plasma ethanol concentrations were measured at intervals from 0-240 min. 3. There were significant differences in the mean area under the ethanol concentration-time curve (AUC), the mean peak ethanol concentration (Cmax), the mean ethanol elimination slope and the time to peak ethanol concentration between the fed and fasted subjects. There were no significant differences between the first and second study days for either fed or fasting subjects for all parameters. 4. There was no statistically significant difference in inter- or intra-subject variance between fed and fasted studies although the coefficients of variation (standard deviation expressed as a percentage of the mean) for the differences between the first and second study day were higher for fed studies. 5. The large inter- and intra-individual variability of alcohol absorption for both fasted and fed subjects must be considered in the design of alcohol-drug interaction studies.