Inter- and intrasubject variability of gastric emptying in healthy volunteers measured by scintigraphy and paracetamol absorption

Mechanistic evaluation of the inhibitory effect of four SGLT-2 inhibitors on SGLT 1 and SGLT 2 using physiologically based pharmacokinetic (PBPK) modeling approaches

Sodium-glucose co-transporter type 2 (SGLT 2, gliflozins) inhibitors are potent orally active drugs approved for managing type 2 diabetes. SGLT 2 inhibitors exert a glucose-lowering effect by suppressing sodium-glucose co-transporters 1 and 2 in the intestinal and kidney proximal tubules. In this study, we developed a physiologically based pharmacokinetic (PBPK) model and simulated the concentrations of ertugliflozin, empagliflozin, henagliflozin, and sotagliflozin in target tissues. We used the perfusion-limited model to illustrate the disposition of SGLT 2 inhibitors in vivo. The modeling parameters were obtained from the references. Simulated steady-state plasma concentration-time curves of the ertugliflozin, empagliflozin, henagliflozin, and sotagliflozin are similar to the clinically observed curves. The 90% prediction interval of simulated excretion of drugs in urine captured the observed data well. Furthermore, all corresponding model-predicted pharmacokinetic parameters fell within a 2-fold prediction error. At the approved doses, we estimated the effective concentrations in intestinal and kidney proximal tubules and calculated the inhibition ratio of SGLT transporters to differentiate the relative inhibition capacities of SGLT1 and 2 in each gliflozin. According to simulation results, four SGLT 2 inhibitors can nearly completely inhibit SGLT 2 transporter at the approved dosages. Sotagliflozin exhibited the highest inhibition activity on SGLT1, followed by ertugliflozin, empagliflozin, and henagliflozin, which showed a lower SGLT 1 inhibitory effect. The PBPK model successfully simulates the specific target tissue concentration that cannot be measured directly and quantifies the relative contribution toward SGLT 1 and 2 for each gliflozin.

Comparing Salivary Caffeine Kinetics of 13C and 12C Caffeine for Gastric Emptying of 50 mL Water

Gastric water emptying as a critical parameter for oral drug absorption can be investigated by several imaging techniques or by the interpretation of pharmacokinetics of appropriate substances. Recently introduced salivary caffeine kinetics is a valuable tool, but the required caffeine abstinence limits its applicability. To avoid the caffeine abstinence, stable isotope-labeled caffeine might be used, but the representability and transferability of kinetics for evaluation of gastric emptying must be demonstrated. Thus, salivary caffeine pharmacokinetics were compared for naturally occurring ¹²C-caffeine and ¹³C₃-caffeine after the administration of water under fasting conditions in six healthy young subjects. For this purpose, an ice capsule containing the two caffeine species was administered with 50 mL tap water. Gastric water emptying was simultaneously quantified using magnetic resonance imaging (MRI). Gastric emptying of 50 mL of water could be successfully evaluated. The salivary caffeine kinetics of ¹³C₃- and ¹²C-caffeine were nearly congruent and showed good linear correlations in all subjects, with a mean correlation coefficient of 0.96 in pooled data. Thus, the substitution of natural ¹²C caffeine with stable isotope-labeled ¹³C₃-caffeine offers the opportunity for broader application of the salivary caffeine gastric emptying technique and increases the robustness of the method against environmental contamination with caffeine.

Comparison of the Status of Interstitial Cells of Cajal in the Smooth Muscle of the Antrum and Pylorus in Diabetic Male and Female Patients with Severe Gastroparesis

Females dominate in the area of gastroparesis (GP), making up to 70–80% of these patients. One attractive hypothesis is that females have less smooth muscle reserve and thus less resilience to recover from an insult. Our aim was to investigate if there are gender differences in the number of interstitial cells of Cajal (ICC) in the antral and pyloric smooth muscle of diabetic (DM) patients with severe gastroparesis refractory to standard medical management. Full thickness antral and pyloric biopsies were obtained during surgery to implant a gastric electrical stimulation system and perform a pyloroplasty. Thirty-eight DM patients (66% females, n = 25; mean age 44) who failed medical therapies provided antral biopsies. Pyloric tissue samples were also collected from 29 of these patients (65% females, n = 19). Tissues were stained with H&E and c-Kit for the presence of ICC. ICC depletion was defined as less than 10 cells/HPF. In the antrum, 40% of females had significant ICC depletion, similar to 38% in males. In the pylorus, 68% of females had depletion of ICC, compared to 80% depletion in males. When combining both antral and pyloric smooth muscle regions, ICC depletion was similar in males (40%) when compared to females (38%). In diabetic patients with severe GP, females and males showed similar degrees of reduction in antral ICC, while more males had depletion of pyloric smooth muscle ICC compared to their female counterparts. Future larger studies should focus on whether differences in other smooth muscle biomarkers can be identified between males and females.

Radiologic assessment of gastric emptying of water-soluble contrast media: New data security from a longitudinal study

BACKGROUND AND OBJECTIVES

Practice guidelines for preoperative fasting have not clearly established the fasting time needed after oral administration of water-soluble contrast media. The aim of this study was to determine the time required for the gastric emptying during the water-soluble contrast media in patients with acute abdominal pain.

METHODS

This prospective longitudinal study included sixty-eight patients older than 18 years of age with acute abdominal pain, who required a water-soluble contrast media enhanced abdominal computed tomography study. Plain radiographs were obtained hourly until complete the gastric emptying. Patients with probable bowel obstruction were not included in the study.

RESULTS

A total of 31 (45,6%), 54 (79,4%), and 64 (94,1%) patients achieved a complete gastric clearance of barium in 1, 2 and 3 hours, respectively. All patients achieved complete emptying of water-soluble contrast media within 6 hours. Gastric emptying time was not associated with gender (P=0,44), body mass index (P=.35), fasting time prior to water-soluble contrast media intake (P=0,12), administration of opioids in the emergency room (P=0,7), and the presence of comorbidities (P=0,36).

CONCLUSION

Ninety-four percent of the patients with acute abdominal pain achieved complete gastric emptying within 3hours after the administration of water-soluble contrast media. All of them achieved complete gastric emptying within 6hours. The results suggested 6hours after oral intake of the contrast media is enough to complete transit of water-soluble contrast media through the stomach and avoid unnecessary risks.

Interindividual and intraindividual variability of fasted state gastric fluid volume and gastric emptying of water

The amount and composition of gastrointestinal media are crucial parameters in oral drug delivery. In fasted state, variable residual gastric volumes and gastric emptying behavior often cause variable drug release and absorption from oral drug products. Unfortunately, interindividual and intraindividual variability of the gastric conditions in fasted state are currently insufficiently mapped. In this work, datasets from 5 MRI studies with 16 treatments in total were pooled. The interindividual and intraindividual variability of residual gastric volumes after 10 h overnight fasting and the subsequent emptying of 240 mL of water were compared in healthy human subjects under conditions mimicking clinical studies. This work shows that even under standardized clinical conditions, residual gastric volumes and water emptying are highly variable. Interestingly, interindividual and intraindividual variabilities of both parameters were comparable, suggesting that the variability within the studies was mainly resulting from intraindividual day-to-day variations. The mean resting volumes in all conducted investigations amounted to 25 ± 18 mL (n = 120). Furthermore, 85 ± 13% (n = 22) of initially available gastric volume (resting volume plus 240 mL) was emptied after 30 min. The findings of this work will hopefully contribute to a better comprehension of the variability of oral drug release and absorption.

Acetaminophen absorption kinetics in altered gastric emptying: establishing a relevant pharmacokinetic surrogate using published data

Acetaminophen has been used as a tool for clinical and nonclinical experimental designs that evaluate gastric emptying because acetaminophen is not absorbed in stomach but efficiently absorbed from the small intestine. Published pharmacokinetic data of acetaminophen in subjects with normal gastric emptying vs. impaired gastric emptying (i.e., morphine treatment) were evaluated to select a key surrogate. Using Caverage (average concentration), computed from the exposure within the first hour, individual rank distribution was plotted across different studies. Caverage was highly correlated with Cmax (maximum concentration) in subjects with normal gastric emptying (R(2) = .7532) but not in those where gastric emptying was impaired (R(2) = .0213). The 50th percentile value of the distribution pattern of 1/Caverage in acetaminophen+morphine-treated group (coincided with the first shift in the slope) was considered as the cutoff point to figure out the impaired gastric emptying. The individual rank distribution plots for 1/Caverage across different studies supported similar trends in subjects with normal gastric emptying but showed a distinct distribution pattern in the cohort of impaired gastric emptying. Caverage, calculated within the first hour of dosing of acetaminophen (average concentration at 0-1 hour, C0-1havg), can be used as a key surrogate to distinguish the effects of gastric emptying on the absorption of acetaminophen. A 4 μg/mL C0-1havg of acetaminophen (dose: 1.5 g) may be used as cutoff point in future clinical investigations of acetaminophen to clarify the role of gastric emptying.

Utilizing in vitro and PBPK tools to link ADME characteristics to plasma profiles: case example nifedipine immediate release formulation

One of the most prominent food-drug interactions is the inhibition of intestinal cytochrome P450 (CYP) 3A enzymes by grapefruit juice ingredients, and, as many drugs are metabolized via CYP 3A, this interaction can be of clinical importance. Calcium channel-blocking agents of the dihydropyridine type, such as felodipine and nifedipine, are subject to extensive intestinal first pass metabolism via CYP 3A, thus resulting in significantly enhanced in vivo exposure of the drug when administered together with grapefruit juice. Physiologically based pharmacokinetic (PBPK) modeling was used to simulate pharmacokinetics of a nifedipine immediate release formulation following concomitant grapefruit juice ingestion, that is, after inhibition of small intestinal CYP 3A enzymes. For this purpose, detailed data about CYP 3A levels were collected from the literature and implemented into commercial PBPK software. As literature reports show that grapefruit juice (i) leads to a marked delay in gastric emptying, and (ii) rapidly lowers the levels of intestinal CYP 3A enzymes, inhibition of intestinal first pass metabolism following ingestion of grapefruit juice was simulated by altering the intestinal CYP 3A enzyme levels and simultaneously decelerating the gastric emptying rate. To estimate the in vivo dispersion and dissolution behavior of the formulation, dissolution tests in several media simulating both the fasted and fed state stomach and small intestine were conducted, and the results from the in vitro dissolution tests were used as input function to describe the in vivo dissolution of the drug. Plasma concentration-time profiles of the nifedipine immediate release formulation both with and without simultaneous CYP 3A inhibition were simulated, and the results were compared with data gathered from the literature. Using this approach, nifedipine plasma profiles could be simulated well both with and without enzyme inhibition. A reduction in small intestinal CYP 3A levels by 60% was found to yield the best results, with simulated nifedipine concentration-time profiles within 20% of the in vivo observed results. By additionally varying the dissolution input of the PBPK model, a link between the dissolution characteristics of the formulation and its in vivo performance could be established.

Simulation of the pharmacokinetics of bisoprolol in healthy adults and patients with impaired renal function using whole-body physiologically based pharmacokinetic modeling

AIM

To develop and evaluate a whole-body physiologically based pharmacokinetic (WB-PBPK) model of bisoprolol and to simulate its exposure and disposition in healthy adults and patients with renal function impairment.

METHODS

Bisoprolol dispositions in 14 tissue compartments were described by perfusion-limited compartments. Based the tissue composition equations and drug-specific properties such as log P, permeability, and plasma protein binding published in literatures, the absorption and whole-body distribution of bisoprolol was predicted using the 'Advanced Compartmental Absorption Transit' (ACAT) model and the whole-body disposition model, respectively. Renal and hepatic clearances were simulated using empirical scaling methods followed by incorporation into the WB-PBPK model. Model refinements were conducted after a comparison of the simulated concentration-time profiles and pharmacokinetic parameters with the observed data in healthy adults following intravenous and oral administration. Finally, the WB-PBPK model coupled with a Monte Carlo simulation was employed to predict the mean and variability of bisoprolol pharmacokinetics in virtual healthy subjects and patients.

RESULTS

The simulated and observed data after both intravenous and oral dosing showed good agreement for all of the dose levels in the reported normal adult population groups. The predicted pharmacokinetic parameters (AUC, C(max), and T(max)) were reasonably consistent (<1.3-fold error) with the observed values after single oral administration of doses ranging from of 5 to 20 mg using the refined WB-PBPK model. The simulated plasma profiles after multiple oral administration of bisoprolol in healthy adults and patient with renal impairment matched well with the observed profiles.

CONCLUSION

The WB-PBPK model successfully predicts the intravenous and oral pharmacokinetics of bisoprolol across multiple dose levels in diverse normal adult human populations and patients with renal insufficiency.

Retention of acetaminophen in an in vitro model of solid-phase gastric emptying of animals

OBJECTIVE

To apply an in vitro model for assessment of the solid-phase binding capacity of acetaminophen and thus assess the reliability of this marker for evaluation of solid-phase gastric emptying in vivo in animals.

SAMPLE POPULATION

4 test meals.

PROCEDURES

A spectrophotometric method for detection of acetaminophen was validated and applied for assessment of the percentage retention of acetaminophen in the solid phase of 4 test meals. The gastric milieu was simulated by incubating each meal in artificial gastric juice for 2 hours in a shaking water bath maintained at 37 degrees C. Solid-phase retention was then assessed 3 times by measuring the amount of acetaminophen that had leached into the liquid phase.

RESULTS

Acetaminophen was poorly retained in the solid phase of all the test meals examined in the study. There was also a large degree of variability in the percentage retention for each meal when the experiment was repeated 3 times.

CONCLUSIONS AND CLINICAL RELEVANCE

Analysis of the results of this in vitro study confirmed that acetaminophen may not be an appropriate marker of solid-phase gastric emptying. The acetaminophen gastric emptying test should be applied only for the assessment of liquid-phase emptying in animals.

Determinants of symptom pattern in idiopathic severely delayed gastric emptying: gastric emptying rate or proximal stomach dysfunction?

BACKGROUND

Idiopathic gastroparesis is a syndrome characterised by severely delayed gastric emptying of solids without an obvious underlying organic cause. Although delayed gastric emptying is traditionally considered the mechanism underlying the symptoms in these patients, poor correlations with symptom severity have been reported.

AIMS

To investigate proximal stomach function and to study the correlation of delayed gastric emptying and proximal stomach dysfunction with symptom pattern and severity in idiopathic gastroparesis.

METHODS

58 consecutive patients (19 men, mean (standard deviation) age 41 (2) years) with severely delayed solid gastric emptying (gastric half-emptying time (t(1/2))>109 min) without an organic cause were recruited. They filled out a symptom-severity questionnaire and underwent a gastric barostat study for assessment of gastric sensitivity and accommodation. Correlation of these mechanisms with symptom pattern and overall symptom severity (sum of individual symptoms) was analysed.

RESULTS

At two different cut-off levels for gastric emptying (upper limit of normal t(1/2) up to 1.5 and 2 times), no significant change in symptom pattern occurred. 25 (43%) patients had impaired accommodation, and this was associated with higher prevalence of early satiety (p<0.005) and weight loss (p = 0.009). 17 (29%) patients had hypersensitivity to gastric distension, and this was associated with higher prevalences of epigastric pain (p = 0.005), early satiety (p = 0.04) and weight loss (p<0.005). Overall symptom severity was not correlated with gastric emptying or accommodation, but only with sensitivity to gastric distension (R = -0.3898, p = 0.003) and body weight (R = -0.4233, p = 0.001).

CONCLUSIONS

In patients with idiopathic gastroparesis, the symptom pattern is determined by proximal stomach dysfunction rather than by the severity of delayed emptying.

Influence of simulated weightlessness on the intramuscular and oral pharmacokinetics of promethazine in 12 human volunteers

The National Aeronautics and Space Administration (NASA) recommends using promethazine to prevent and treat space motion sickness, but pharmacologic responses in space and on Earth are different. Twelve volunteers were given 50 mg promethazine orally or intramuscularly before and after 48 hours of bed rest to simulate weightlessness. The maximum measured plasma concentration (C(max)), time to C(max) (t(max)), and area under plasma concentration versus time curve from 0 to infinity (AUC(inf)) were determined, and the bioequivalence was tested between bed-rest and ambulatory status for the intramuscular and oral routes as well as between both routes for bed-rest and ambulatory position. Simulated weightlessness did not influence the ratio AUC(bed rest)/AUC(ambulatory) after intramuscular injection, whereas a significant increase (26%) in the ratio was seen after oral administration, probably because of a prolonged contact time between promethazine and the intestinal wall associated with an increase in the intestinal transit time. The AUC was 3-fold higher when the drug was administered by the intramuscular route during both positions. Thus, intramuscular administration could be a good alternative to the oral route.

The influence of weightlessness on pharmacokinetics

The primary hostile factor during a spaceflight is the lack of gravity, which can induce space motion sickness and act on bones, muscles and the cardiovascular system. These physiological effects may modify the pharmacokinetics of the drugs administered during the flight producing reduced pharmacological activity or appearance of adverse effects. Given the small number of spaceflights and the difficulties of conducting experiments during missions, pharmacokinetic data obtained in flight are insufficient to determine if drug monitoring is necessary for the drugs present in the onboard medical kit. Therefore, validated earthbound models like tail-suspension performed with animals and long-term bedrest performed with human volunteers are used to simulate weightlessness and to study the pharmacokinetic variations of either absorption, distribution, or elimination of drugs. As a result of these studies, it is possible to make some dosing recommendations but more information is necessary to predict with precision all of the pharmacokinetic variations occurring in spaceflight. To collect more pharmacokinetic information, head-down bedrest studies are still the best solution and as saliva is an appropriate substitution for plasma for some drugs, salivary sampling can be planned during flights.

Effect of an indwelling nasogastric tube on gastric emptying rates of liquids in horses

OBJECTIVE

To evaluate the effect of an indwelling nasogastric tube on gastric emptying of liquids in horses.

ANIMALS

9 healthy adult horses.

PROCEDURE

A randomized block crossover design was used. For treatment group horses, a nasogastric tube was placed and 18 hours later, acetaminophen was administered; the nasogastric tube remained in place until the experiment was complete. For control group horses, a nasogastric tube was passed into t stomach, acetaminophen was administered, and the nasogastric tube was removed immediately. Serial blood samples were collected 15 minutes before and after administration of acetaminophen. Serum concentration of acetaminophen was determined by use of fluorescence polarization immunoassay. The variables, time to maximum acetaminophen concentration (Tmax) and the appearance constant for acetaminophen (Kapp), were determined. The values for Kapp and Tmax in horses with and without prolonged nasogastric tube placement were compared.

RESULTS

No significant difference was found in Kapp between horses with and without prolonged nasogastric tube placement; the median difference in Kapp was 0.01 min(-1) (range, -0.48 to 0.80 min(-1). No significant difference was found in Tmax between horses with and without prolonged nasogastric tube placement; the median difference in Tmax was 5 minutes (range, -30 to 50 minutes). Reanalysis of data following the removal of possible outlier values from 1 horse resulted in a significant difference in Tmax between horses with and without prolonged nasogastric tube placement.

CONCLUSIONS AND CLINICAL RELEVANCE

Although no clinically important impact of 18 hours of nasogastric intubation was found on gastric emptying in healthy was found among horses.

Determination of abomasal emptying rate in suckling calves by use of nuclear scintigraphy and acetaminophen absorption

OBJECTIVE

To develop nuclear scintigraphic and acetaminophen absorption methods for measuring abomasal emptying rate in suckling calves.

ANIMALS

9 male Holstein-Friesian calves < 30 days old.

PROCEDURE

Calves were fed 2 L of milk replacer, fresh cow's milk, or an isoosmotic (150mM) solution of NaCl, NaHCO3, or sodium acetate containing technetium TC 99m-diethylenetriamine-pentaacetic acid (370 MBq) and acetaminophen (50 mg/kg). Right lateral scintigraphic images and venous blood samples were obtained periodically after feeding. Two power exponential equations were fitted to the scintigraphic data, and 3 pharmacokinetic models were fitted to the acetaminophen concentration-time data.

RESULTS

Data from 32 feedings were analyzed, with half emptying time for scintigraphic evaluation ranging from 29 to 202 minutes. Siegel's modified power exponential equation provided a better description of the scintigraphic data than did Elashoff's power exponential equation. The first derivative of Siegel's modified power exponential formula provided the best pharmacokinetic model for the acetaminophen absorption data. Time to maximal acetaminophen concentration (Tmax) provided the most accurate index of abomasal emptying rate from the acetaminophen concentration-time data.

CONCLUSIONS AND CLINICAL RELEVANCE

Abomasal emptying rate is best determined in healthy suckling calves by use of Siegel's modified power exponential equation to model the scintigraphic data. Pharmacokinetic calculation of Tmax from the acetaminophen absorption curve provides an alternative method for determining abomasal emptying rate in healthy suckling calves that is accurate, inexpensive, practical, and safe. However, it is unclear whether diarrhea would alter the acetaminophen absorption curve in calves.

Influence of simulated weightlessness on the oral pharmacokinetics of acetaminophen as a gastric emptying probe in man: a plasma and a saliva study

This study evaluated the effect of simulated weightlessness on gastric emptying, using acetaminophen as a probe and -6 degrees head-down bed rest to simulate zero gravity. Eighteen volunteers were given 1 g of acetaminophen orally before the bed rest and at days 1, 18, and 80. Cmax, tmax, AUC0- infinity, AUC0-t, and t1/2 were calculated for plasma and saliva. The plasma Cmax showed a significant increase (10.43 microg/mL [day 1] to 14.74 microg/mL [day 80]), while tmax significantly decreased (1.41 h [day 1] to 0.91 h [day 80]). Similar results were obtained with saliva, and there were significant increases in the AUCs. The good correlation between the plasma and saliva data suggests that saliva sampling can be valid for acetaminophen pharmacokinetics. The changes in Cmax and tmax indicated more rapid drug absorption, which could have been as a result of faster gastric emptying or an increased blood flow to the intestine.

Erythromycin accelerates gastric emptying in a dose-response manner in healthy subjects

STUDY OBJECTIVES

To evaluate whether a dose-response curve exists for erythromycin, determine the lowest effective dose of erythromycin needed to improve gastric motility, and compare erythromycin's effectiveness with that of metoclopramide in improving gastric emptying.

DESIGN

Randomized, crossover, multiintervention trial.

SETTING

Inpatient clinical research center.

SUBJECTS

Ten healthy volunteers (four men, six women) from the general population.

INTERVENTION

On each study day, the subjects were infused with erythromycin 0.75 mg/kg, 1.5 mg/kg, or 3.0 mg/kg; metoclopramide 10 mg; or placebo, in random order. Subjects then drank Ensure 200 ml mixed with acetaminophen 1.5 g. Gastric emptying was estimated by comparing the area under the curve after 60 minutes for acetaminophen absorption using four timed blood draws.

MEASUREMENTS AND MAIN RESULTS

Erythromycin increased gastric emptying in a dose-response manner. Erythromycin 3.0 mg/kg and metoclopramide 10 mg were associated with statistically significant increases in liquid gastric emptying compared with placebo. During infusion, nausea and stomach cramping were associated with the 3.0-mg/kg dose of erythromycin; drowsiness was associated with metoclopramide.

CONCLUSION

In patients requiring intravenous erythromycin for gastric motility, the 3.0-mg/kg dose seems the most effective, with a reasonable side effect profile.

Infrared spectrometry based 13C-octanoic acid breath test in measuring human solid gastric emptying

BACKGROUND AND AIMS

Because of the convenience of non-dispersive infrared spectrometry (NDIRS), we attempted to validate the usefulness of NDIRS compared with scintigraphy in human solid gastric emptying (GE) measurement, and tried to establish the normal range of solid GE based on NDIRS.

METHODS

Twelve healthy volunteers (three men, nine women) were recruited for simultaneous scintigraphy and 13C-octanoic acid breath test (13C-OABT) studies. Stomach half-emptying time (t1/2) and lag phase (tlag) were the two main GE parameters measured and correlated. The breath samples were analyzed using NDIRS every 10-15 min for a total of 6 h, while scintigraphy was taken minute by minute for the first 30 min, then hourly for 4 h. Another 32 healthy volunteers (19 men, 13 women) received only the 13C-OABT to measure their solid GE.

RESULTS

A significant correlation for t1/2 was found between the breath test and scintigraphy (r = 0.85, P = 0.001), while tlag was also positively correlated (r = 0.73, P = 0.007). The reference range of t1/2B based on all 44 subjects was 89.4-185.1 min (135.9 +/- 21.1 min (mean +/- SD)), while the range for tlagB was 37.1-117.8 min (81.9 +/- 17.4 min). No demographic characteristics were found to influence the GE parameters.

CONCLUSIONS

13C-octanoic acid breath test determined by NDIRS is a simple, non-invasive and reliable measurement, which may provide an 'office-based' tool to detect solid GE.

Performance characteristics of scintigraphic transit measurements for studies of experimental therapies

BACKGROUND

The intra- and inter-individual reproducibility of gastrointestinal and colonic transit tests require full characterization.

AIMS

(i) To characterize the normal values and reproducibility effects of age and gender on the scintigraphic transit of solids in health. (ii) To compare scintigraphic and radio-opaque marker measurements of colonic transit. (iii) To estimate demonstrable effect sizes for different transit end-points based on observed variations.

METHODS

A scintigraphic gastrointestinal and colonic transit study and the mean colonic transit time were measured using radio-opaque markers in 37 healthy volunteers; 21 subjects had a repeat scintigraphic test 3 weeks later.

RESULTS

Gastric emptying at 4 h was highly reproducible (coefficient of variation, 4%) on repeat testing. The colonic measurement varied by more than 1 geometric centre unit in 37% of subjects at 24 h and in 26% of subjects at 48 h. There were no age- or gender-related differences in transit. Effect sizes demonstrable with 14 subjects per group were in the range previously shown to be clinically relevant: 25% change in gastric emptying at 4 h; 1.5 geometric centre unit change in colonic transit at 48 h.

CONCLUSIONS

These data demonstrate the reproducibility and performance to be expected of transit measurements and are essential for designing studies in experimental therapeutics.

How useful is paracetamol absorption as a marker of gastric emptying? A systematic literature study

Functional dyspepsia is a common disorder in primary care and gastroenterology units; however, the pathophysiology is poorly understood. Delayed gastric emptying is present in nearly 40% of patients. We evaluated the validity of the paracetamol absorption test in comparison with scintigraphy for gastric emptying assessment. Studies comparing scintigraphy with paracetamol absorption were selected through a structured Medline search. A correlation coefficient between scintigraphy and paracetamol absorption over 0.6 was considered good, between 0.45 and 0.6 intermediate, and below 0.45 poor. Feasibility was assessed by studying the administration of paracetamol, frequency of blood sampling, duration of the test period, and parameters used in the analysis. Thirteen studies were identified, eight (127 subjects) found a good correlation between scintigraphy and paracetamol absorption, two studies (28 subjects) found a moderate correlation, and three (25 subjects) found no correlation. Parameters used were area under the curve (N = 9), fixed-time concentrations (N = 6), concentration-max (N = 4) and time-to-concentration-max (N = 5). Repetitive blood samples ranged from 6 to 20 samples. The durations were 1.5-8 h. In conclusion, the paracetamol absorption technique generally correlates well to scintigraphy of liquid phase gastric emptying. The execution and outcome parameters however need further standardization to optimize its' value for clinical use and research purposes.

Gastric emptying characteristics of a novel (13)C-octanoate-labeled muffin meal

GOALS

Determine the gastric emptying characteristics of a novel, 350-kcal test meal consisting of two muffins, using scintigraphy and the 13C-octanoate breath test (OBT).

STUDY

Healthy volunteers underwent three studies on separate days within a 1-week period. On day 1, we measured emptying of the 350-kcal muffin test meal labeled simultaneously with 99mTc sulfur colloid and 13C-octanoate. On day 2, reproducibility of the OBT using a single-labeled 350-kcal test meal was assessed. On day 3, the effect of erythromycin on the 350-kcal OBT was determined.

RESULTS

The mean (+/-SD) half-emptying time (T1/2) as measured by scintigraphy was 104 +/- 24 minutes, versus 212 +/- 52 minutes by OBT. There was a strong correlation between T1/2 determined by scintigraphy and the breath test (r = 0.83). Multiple linear regression analysis identified a significant relationship between T1/2 determined by scintigraphy and the 90-and 180-minute breath samples. There was a strong correlation (r = 0.830, slope = 0.732 +/- 0.120 [SE], intercept = 26.4 +/- 12.7) between the T1/2 obtained using the regression equation and the actual T1/2 obtained by scintigraphy. The mean T1/2 (+/-SD) for replicate determinations using the OBT was 209 +/- 52 minutes, compared with 196 +/- 42 minutes on days 1 and 2, respectively (not significant, p = 0.28, paired Student t test). Treatment with erythromycin on day 3 produced a significant decrease in T1/2 (155 +/- 49 minutes, p = 0.002).

CONCLUSIONS

The 350-kcal muffin meal OBT provides a convenient, nonscintigraphic way of measuring solid-phase gastric emptying. Multiple linear regression appears promising as a method of analyzing OBT data and may allow for an abbreviated breath test protocol.

Comparison of nuclear scintigraphy and acetaminophen absorption as a means of studying gastric emptying in horses

OBJECTIVE

To evaluate the correlation between halftime of liquid-phase gastric emptying (T50), determined with nuclear scintigraphy using technetium Tc 99m pentetate, and absorption variables of orally administered acetaminophen.

ANIMALS

6 mature horses.

PROCEDURE

Technetium Tc 99m pentetate (10 mCi) and acetaminophen (20 mg/kg of body weight) were administered simultaneously in 200 ml of water. Serial left and right lateral images of the stomach region were obtained with a gamma camera, and T50 determined separately for counts obtained from the left side, the right side and the geometric mean. Power exponential curves were used for estimation of T50 and modified R2 values for estimation of goodness of fit of the data. Serial serum samples were taken, and acetaminophen concentration was determined, using fluorescence polarization immunoassay. Maximum serum concentration (Cmax), time to reach maximum serum concentration (Tmax), area under the curve for 240 minutes and the absorption constant (Ka) were determined, using a parameter estimation program. Correlations were calculated, using the Spearman rank correlation coefficient.

RESULTS

Correlations between T50 and Tmax and between T50 and Ka were significant.

CONCLUSIONS AND CLINICAL RELEVANCE

Tmax and Ka are valuable variables in the assessment of liquid-phase gastric emptying using acetaminophen absorption. Acetaminophen absorption may be a valuable alternative to nuclear scintigraphy in the determination of gastric emptying rates in equine patients with normally functioning small intestine.

The diagnosis and work-up of the patient with gastroparesis

Gastroparesis-or delayed gastric emptying--is associated with upper gastrointestinal symptoms that include early satiety, nausea, vomiting, regurgitation, fullness, and bloating. Gastroparesis should be considered in the diagnosis of a patient with these symptoms after mechanical and structural lesions have been ruled out. This review briefly summarizes gastric motor physiology and discusses the etiology and diagnostic approach to the treatment of a patient with possible gastroparesis. We highlight the methods available to measure gastric motility and describe their relative advantages and disadvantages.

Potato-lactulose breath hydrogen testing as a function of gastric motility in diabetes mellitus

OBJECTIVE

Scintigraphic determination of gastric emptying is the current standard for the assessment of gastric motility and the diagnosis of diabetic gastroparesis. However, such studies are expensive, inconvenient, and involve exposure to radiation. Because the time course of breath hydrogen (H2) excretion after ingestion of lactulose correlates with upper gastrointestinal transit time, we hypothesized that patients with diabetic gastroparesis would exhibit prolonged breath H2 excretion after ingestion of a test meal containing complex carbohydrate and lactulose compared to subjects without diabetes and subjects with diabetes but without gastroparesis.

RESEARCH DESIGN AND METHODS

Ten healthy subjects without diabetes, 10 subjects with diabetes but without gastroparesis (gastric emptying T1/2,T1/2 < 90 minutes), and 10 subjects with diabetes and previously diagnosed gastroparesis (T1/2 > 90 minutes) were admitted for a single 24-hour study. Gastric motility agents were withheld 24 hours prior to the study. Euglycemia was established and maintained overnight in subjects with diabetes with continuous intravenous insulin infusion. At 6:00 AM, all subjects ingested a breakfast containing 100 g of cooked potato starch and 20 g lactulose. Breath H2 excretion was monitored at baseline and every 30 minutes for 12 hours after ingestion of the test meal.

RESULTS

Twelve hours after ingestion of the test meal, raw and baseline adjusted breath H2 excretion was significantly elevated in the gastroparesis group compared to the unaffected group with diabetes and the group without diabetes (p < 0.001). The baseline and 12-hour data points were adequate to discriminate between normal and delayed gastric emptying.

CONCLUSIONS

We conclude that patients with previously diagnosed gastroparesis exhibit prolonged breath H2 excretion after ingestion of a test meal. This test may prove to be a safe, reliable, and affordable outpatient screening test for diabetic gastroparesis.

Is the 13C-acetate breath test a valid procedure to analyse gastric emptying in children?

BACKGROUND/PURPOSE

Scintigraphy is regarded as the "gold standard" procedure in measuring gastric emptying (GE) rates. 13C-acetate breath test (ABT), which already has been validated in adults, is a noninvasive and nonradioactive alternative method. The aim of the current study was to validate ABT against technetium Tc 99m scintigraphy in children affected by delayed GE.

METHODS

Sixty children were recruited and divided into 2 groups: group A, 30 healthy controls; group B, 30 patients with gastroesophageal reflux, and scintigraphy-documented DGE (15 neurologically impaired). After an overnight fast, all of them underwent ABT using 25 to 150 mg 13C-acetate. Breath samples were obtained at baseline and then every 10 minutes for 2 hours. The 13CO2 to 12CO2 ratio in breath samples was analysed by isotope ratio mass spectrometry. Data are expressed as follows: time of peak 13C exhalation (tP13CO2b) and half emptying time in ABT (t(1/2b)), and scintigraphy half emptying time (t(1/2s)).

RESULTS

In controls tP13CO2b was 37 +/- 13 minutes and t(1/2b) 74 +/- 12 minutes. In patients tP13CO2b and t(1/2b) were, respectively, 65 +/- 26 minutes and 104 +/- 18 minutes t(1/2s) was 91 +/- 21 minutes. In group B tP13CO2b and t(1/2b) were delayed significantly compared with controls, respectively, P < .03 and P < .01. In group B significant correlation between t(1/2s) and t(1/2b) was noted (r1 = 0.97). A close correlation was also observed between t(1/2s) and tP13CO2b (r2 = 0.95).

CONCLUSION

The 13C ABT is an easy, reliable, and less expensive procedure for measuring GE, and its results closely correlate with those of scintigraphy in a paediatric population.

Are there changes in gastric emptying during the menstrual cycle?

BACKGROUND

The questions of whether gastric emptying of solids and liquids differs in men and women and whether emptying is influenced by the action of sex hormones on gastric smooth muscle remain unresolved.

METHODS

We analysed the gastric emptying of digestible solids (GES), liquids (GEL), and radiopaque indigestible solids (GER) in three groups of healthy volunteers: 50 women in the follicular phase of the menstrual cycle, 50 women in the luteal phase, and 100 men. [99mTc]-labelled diethylenetriamine pentaacetic acid (DTPA) was used as the radioactive marker for digestible solids, and [111In]DTPA was used as the marker for liquids, to time gastric motility after a solid and a liquid meal. GER was evaluated on a different day in abdominal roentgenograms.

RESULTS

GES and GEL were slower in women than in men (P < 0.05), but GER was similar in the two sexes. However, there were no significant differences in GES, GEL, or GER between women in the follicular and those in the luteal phase, between plasma concentrations of oestradiol and progesterone and the variables used to characterize gastric emptying.

CONCLUSIONS

Evidence of postprandial 'physiologic gastroparesis' was found in women, although no differences were found between men and women in gastric motility during fasting. The rate of emptying was not related to changes in plasma concentrations of sex hormones during the menstrual cycle.

Delayed postoperative gastric emptying following intrathecal morphine and intrathecal bupivacaine

PURPOSE

A decrease in the rate of gastric emptying can delay resumption of enteral feeding, alter bioavailability of orally administered drugs, and result in larger residual gastric volumes, increasing the risk of nausea and vomiting. We compared the effects of 1) intrathecal bupivacaine (17.5 mg) and 2) the combination of intrathecal morphine (0.6 mg) and intrathecal bupivacaine (17.5 mg) on the rate of gastric emptying in patients undergoing elective hip arthroplasty.

METHODS

Twenty four fasting ASA 1-3 patients were randomly assigned, in a double blind manner, to receive intrathecal hyperbaric bupivacaine (17.5 mg), either alone (group 1), or followed by intrathecal morphine (0.6 mg) (group 2). Gastric emptying was measured (using an acetaminophen absorption technique), twice in each patient; preoperatively, and approximately one hour postoperatively. Gastric emptying parameters are: AUC (area under the plasma acetaminophen concentration time curve), maximum plasma acetaminophen concentration (Cmax), and time to Cmax (tCmax), analyzed using paired Student's t tests.

RESULTS

Gastric emptying rates were reduced in both group 1 (AUC = 14.98 (3.8) and 11.05 (4.6) pre- and postoperatively, respectively) and group 2 (AUC = 13.93 (3.59) and 6.4 (3.42) pre- and postoperatively, respectively); the magnitude of the reduction was greater in group 2 [AUC (P = 0.04), Cmax (P = 0.05), tCmax (P = 0.13)].

CONCLUSION

The combination of intrathecal morphine (0.6 mg) and intrathecal bupivacaine (17.5 mg) delays gastric emptying postoperatively.

The effect of octreotide on gastric emptying at a dosage used to prevent complications after pancreatic surgery: a randomised, placebo controlled study in volunteers

BACKGROUND

Octreotide is used in many centres to prevent complications after pancreatic surgery. Delayed gastric emptying is a another complication occurring in around 30% of patients after pancreatoduodenectomy (PD) and causes prolonged hospital stay. The influence of octreotide on this complication is doubtful.

AIMS

To assess the effect of octreotide, at the clinical dosage used after pancreatic surgery, on gastric emptying in healthy volunteers.

SUBJECTS AND METHODS

Eight healthy male volunteers (mean age 22.5 years) participated in this double blind, placebo controlled study. On day 1 subjects received 100 micrograms of octreotide or placebo subcutaneously, three times daily and on day 2, one hour after the fourth injection, gastric emptying, postprandial cholecystokinin (CCK) release, and mouth to caecum transit time (MCTT) were measured. This protocol was repeated after one week, in a crossover design. On the test day subjects received a liquid test meal (1.57 MJ/300 ml) and gastric emptying measurements were performed with applied potential tomography, an non-invasive, validated technique which measures gastric emptying through impedance differences. From the gastric emptying curves, lag time, t50, and postlag emptying rate were measured. MCTT was measured using the hydrogen breath test.

RESULTS

Lag time decreased from 29.6 (6.3) (mean (SEM)) to 12.2 (4.6) minutes (p < 0.05) during octretide treatment; t50 decreased from 87.8 (12.0) to 47.5 (8.2) minutes (p < 0.02) and there was a trend towards an increased postlag emptying rate (0.8 to 1.6% per minute; p = 0.07). MCTT increased from 150 (12.7) to 229 (17.9) minutes during octreotide treatment (p < 0.01). Octreotide suppressed postprandial CCK release (p < 0.05).

CONCLUSIONS

MCTT was delayed by octreotide, suggesting impairment of small bowl treatment. Octreotide administered at the clinical dosage for pancreatic surgery accelerates gastric emptying, mainly by shortening the lag time. Suppression of postprandial CCK release may be involved in this process. Octreotide administration is therefore not a contributing factor in the pathogenesis of delayed postoperative gastric emptying after PD and might even play a role in preventing this complication.

Long-term control of erythropoietin secretion by doxycycline in mice transplanted with engineered primary myoblasts

We investigated tetracycline regulation of gene expression in an experimental model relevant to gene therapy. Mouse primary myogenic cells were engineered for doxycycline-inducible and skeletal muscle-specific expression of the mouse erythropoietin (Epo) cDNA by using two retrovirus vectors. Gene expression increased 200 fold in response to both myogenic cell differentiation and doxycycline stimulation. After transplantation of transduced cells into mouse skeletal muscles, Epo secretion could be iteratively switched on and off over a five-month period, depending on the presence or the absence of doxycycline in the drinking water. We conclude that tetracycline regulation provides a suitable control system for adjusting the delivery of therapeutic proteins from engineered tissues over long periods of time.

Modulation of erythropoietin delivery from engineered muscles in mice

In most relevant diseases, the permanent systemic delivery of a therapeutic protein from engineered cells might be proposed only if secretion levels can be regulated. The tetracycline resistance operon of Escherichia coli provides a transcriptional regulatory system effective in mammalian cells, which could be used for that purpose. A chimeric transactivator (tTA) consisting of the tetracycline repressor fused to the transactivation domain of the herpes simplex virus VP16 protein stimulates transcription by binding a minimal cytomegalovirus (CMV) promoter containing repeats of the tetracycline operator (tetO-CMV). Binding is abolished by tetracycline, thus impairing promoter activation. We have transduced C2.7 myoblasts with two U3-deleted retroviral vectors containing these regulatory elements. The tetP-Epo vector expressed the murine erythropoietin (Epo) cDNA under the control of the tetO-CMV promoter. The D-De-tTA vector expressed tTA under the control of the muscle-specific human desmin enhancer-promoter. Northern blot analysis showed background Epo mRNA expression in myoblasts. Myotubes differentiation induced tTA expression, leading to a 28-fold increase of Epo mRNAs, which was suppressed by tetracycline. Basal Epo secretion in myoblasts increased 23- to 41-fold during the formation of multinucleated myotubes, and turned back close to myoblast level when tetracycline was added. Myoblasts transduced with both vectors and treated with mitomycin with the aim to prevent tumor formation were engrafted in skeletal muscles of syngeneic C3H mice. Hematocrit levels were significantly higher in animals bearing cells transduced with both vectors than in control animals grafted with cells transduced with the Epo vector only. This difference was abolished when tetracycline was given to mice. These data indicate that the tetracycline regulatory elements can modulate transcription in the context of retroviral vector genomes, and that this system can be used to control the in vivo delivery of a therapeutic protein from genetically modified muscles.

Impaired gastric emptying in mechanically ventilated, critically ill patients

OBJECTIVE

To measure gastric emptying in critically ill patients using an acetaminophen absorption model and determine which variables are associated with impaired gastric emptying.

DESIGN

A prospective, cohort study.

SETTING

A medical/surgical ICU at a tertiary care hospital: Hamilton General Hospital, Hamilton, Ontario.

PATIENTS AND PARTICIPANTS

We recruited 72 mechanically ventilated patients expected to remain in the ICU for more than 48 h. Our results were compared to those in healthy volunteers.

INTERVENTION

Within 48 h of admission to the ICU, 1.6 g acetaminophen suspension were administered via a nasogastric tube into the stomach. Blood samples were drawn a t = 0, 30, 60, 90, and 120 min for measurement of plasma acetaminophen levels determined by the enzymatic degradation method.

MEASUREMENTS AND RESULTS

Maximal concentration of acetaminophen was 94.1 (75.3) mumol/l compared to 208.4 (33.1) mumol/l in a control population (p < 0.0001). The time to reach the maximal concentration was 105 min (60-180) compared to 30 min (15-90) in controls (p < 0.0001). The area under the time-acetaminophen concentration curve t = 120 was 9301 (7343) mumol/min per l compared to 11644 (1336) mumol/min per l in the controls (p = 0.28). The variables associated with delayed gastric emptying were age, sex and use of opioids for analgesia and sedation.

CONCLUSIONS

Gastric emptying is delayed in critically ill patients. The important consequences of this phenomenon include intolerance to enteral nutrition and gastric colonization. Strategies to minimize the use of narcotics may improve gastric emptying. Studies to examine the effect of gastrointestinal prokinetic agents on gastric emptying are needed.

Gastric emptying of a light hospital breakfast. A study using real time ultrasonography

While intake of clear fluids 2-3 h before surgery is considered safe as it does not influence gastric content, it is not known if the same applies to a light breakfast meal. We therefore studied gastric emptying of a light breakfast in healthy, female volunteers without evidence of gastrointestinal motility disorders. The test meal consisted of one slice of buttered toast with jam, one cup of coffee without milk or sugar and one glass of pulp-free orange juice taken together with a paracetamol mixture. Using gastric ultrasonography, the stomach was identified without problems in all subjects, and gastric emptying curves using changes in gastric antral area and serum-paracetamol were obtained. Emptying of the fluid phase started immediately after intake of the meal. All subjects had solid particles in the stomach 120 min after the meal, 3 patients were considered empty after 180 min, 6 after 210 min and all after 240 min. The gastric antral area returned to fasting value significantly faster than the disappearance of solid particles; median 150 min versus 210 min; P = 0.01. Our results show that in healthy subjects the stomach cannot be considered empty for solid particles the first 4 h after a light breakfast meal. To secure some safety limits, we suggest a 6-h mandatory preoperative fast after a light breakfast.

Adding fentanyl 0.0002% to epidural bupivacaine 0.125% does not delay gastric emptying in laboring parturients

Previous studies have shown that bolus doses of fentanyl (50 and 100 micrograms) with epidural bupivacaine delay gastric emptying by up to 45 min. We studied the effect of the addition of small-dose fentanyl to epidural bupivacaine infusions on gastric emptying during labor. The acetaminophen absorption technique was used to infer gastric emptying. Twenty-eight patients in established labor consented to participate in the study. They were randomized to receive either 1) 10 mL bupivacaine 0.125% followed by an infusion of 0.125% bupivacaine at 10 mL/h or 2) 10 mL bupivacaine 0.125% with 50 micrograms fentanyl followed by an infusion of 0.125% bupivacaine and 0.0002% fentanyl at 10 mL/h. Two hours after initiation of epidural analgesia, each patient ingested 20 mg/kg acetaminophen in a suspension of 150 mL water. Venous blood samples were drawn for a baseline and then every 15 min for 2 1/2 h. There were no significant demographic differences between the groups. There were no differences detected between groups in the peak plasma concentrations of acetaminophen, the time to achieve the peak plasma concentrations, or the area under the curve at 45 and 90 min. Our results indicate that epidural infusions for labor analgesia using 0.125% bupivacaine and 0.0002% fentanyl do not delay gastric emptying compared to infusions of bupivacaine 0.125% alone.

The migrating motor complex modulates intestinal motility response and rate of gastric emptying of caloric meals

The present study elucidates whether the phase of the migrating motor complex (MMC) present at the moment of food intake modulates postprandial motor response and rate of gastric emptying of caloric meals. Eight healthy male volunteers with a mean age of 26 years were examined twice. During water-perfused gastroduodenal manometry, a liquid meal with paracetamol added as a marker was orally administered during phase I and late phase II. Paracetamol appeared in serum 14.1 +/- 3.8 min and 9.1 +/- 4.0 (mean +/- SD) min, respectively, after intake of the meal (P < 0.02). The area under the curve of s-paracetamol until 25 min after intake was 232 +/- 169 mumol l-1 min and 362 +/- 130 (P < 0.05), respectively. When taken during late phase II, a phase III-like activity occurred within 2.1 +/- 1.3 min in the duodenum, and was succeeded by quiescence. During phase I, the meal invariably initiated irregular contractions within 4 min. The phase of MMC during which a caloric meal is ingested modulates duodenal motor response and rate of gastric emptying during the initial postprandial period. Initial postprandial motor activity thus represents the combined effect of nutrient stimulation and the underlying enteric biorhythm as reflected by phase of MMC.

Sulfamethizole absorption test for the assessment of gastric emptying. Comparison with scintigraphic method

BACKGROUND

To investigate whether the sulfamethizole absorption test can be applied for the assessment of gastric emptying, we measured comparatively plasma sulfamethizole concentration and gastric emptying as determined by scintigraphy in 15 subjects.

METHODS

After the ingestion of a solid-liquid meal that contained sulfamethizole and radioisotope (technetium-99m-labeled diethylenetriaminepentaacetic acid), the plasma sulfamethizole concentrations were measured every 15 to 60 min up to 180 min. The initial emptying time (duration after ingestion until 10% reduction in radioactivity of the stomach) and the exponential curve in the cumulative reduction of radioactivity were used as indicators of gastric emptying.

RESULTS

The initial emptying time was significantly correlated with the sulfamethizole concentration at 15 min after ingestion (r = -0.64, p < 0.05). A close correlation was observed between the rate of decrease in radioactivity and sulfamethizole concentration at 60 min after ingestion (r = 0.80, p < 0.001).

CONCLUSIONS

The sulfamethizole absorption test can be used for the evaluation of gastric motility. Two points of measurement, 15 and 60 min after ingestion, are sufficient to demonstrate the initial and subsequent gastric emptying.

Relationship between fractional calcium absorption and gastric emptying

The relationship between calcium absorption and gastric emptying and the precision of measurement of fractional calcium absorption using a single isotope technique were evaluated in 14 normal postmenopausal women (age range 61-72 years). On two occasions separated by between 5 and 15 days, each subject was given 250 mL water containing 0.2 MBq of 45Ca in 20 mg of calcium carrier as the chloride, 20 mg kg-1 paracetamol and 9 MBq of 99mTc sulphur colloid. Venous blood samples were taken at -2, 15, 30, 45, 60, 90, 120, 150 and 180 min after consumption of the drink, and gastric emptying (GE) was monitored with a gamma camera. Fractional calcium absorption in the first hour (alpha 6) was calculated from the blood samples obtained at 15, 30, 45, 60, 90 and 120 min. An absorption rate was also derived from the 60 min sample using only a calibration curve (alpha 1). There were close correlations between radiocalcium absorption on the two study days (r = 0.89, P < 0.001 for both alpha 1 and alpha 6) and between alpha 1 and alpha 6 (r = 0.93, P < 0.001). Plasma paracetamol concentrations at 15 min were directly related to the early phase of GE (r = 0.42, P < 0.05). In contrast, calcium absorption was inversely related to GE (r = 0.45, P < 0.05). We conclude that radiocalcium absorption is not greatly influenced by gastric emptying rate and that the single blood sample procedure has similar precision to the six-blood sample test.

Pharmacokinetic considerations in gastrointestinal motor disorders

Although it has been recognised that alterations in gastrointestinal motility, whether induced by physiological or pathological processes, have significant effects on the pharmacokinetics of orally administered drugs, this subject has received inappropriately little attention. Studies relating to this topic have focused on healthy volunteers and animals and have largely been confined to the effects of single drug doses. There is limited information about the effects of disease on pharmacokinetics under steady-state conditions. Changes in gastrointestinal motility may affect the pharmacokinetics of orally administered drugs by altering the rate of delivery, bioavailability or mucosal absorption of the drug. In general the rate of absorption and time taken to achieve maximal plasma concentrations for well absorbed drugs may be modified by changes in gastrointestinal motility, but overall bioavailability is not usually affected. In these cases the therapeutic and clinical effects of the alteration in pharmacokinetics will, therefore, depend on which parameters are important for the action of the drug. For poorly absorbed drugs both the rate of absorption and bioavailability are likely to be altered by changes in gastrointestinal motility. However, the complex effects of food and disease, as well as the properties and formulation of any drug (solubility, ease of dispersion, delayed release formulation) often make the prediction of the magnitude, or even the direction, of any effect difficult to predict. Drugs with direct effects on gastrointestinal motility may influence their own patterns of absorption. In patients with gastrointestinal motility disorders, drugs administered in a controlled release formulation, or those with poor bioavailability, are most likely to have a poorly predictable therapeutic effect. Care should be taken to ensure that the formulation of the drug, its timing of administration in relation to meals and the use of coadministered drugs optimise, or at least ensure consistent absorption.

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

1. Twelve healthy men drank 0.80 g ethanol kg-1 body weight on four occasions spread over several weeks. Ethanol was given as 96% v/v solvent which was diluted with orange juice to make a cocktail (20-25% v/v). This drink was ingested in exactly 30 min at 08.00 h after an overnight (10 h) fast. 2. Samples of venous blood were obtained at exactly timed intervals of 0, 10, 20, 30, 45, 60, 90, 120, 150, 180, 240, 300, and 360 min after the start of drinking. The concentrations of ethanol in whole blood were determined by headspace gas chromatography. 3. Summary measures were used to evaluate the concentration-time profiles of ethanol for each subject. The between-subject and within-subject components of variation for the pharmacokinetics of ethanol were derived by one-way analysis of variance (ANOVA). 4. The variation between different subjects dominated the total variance for all of the pharmacokinetic parameters studied except the rate of disappearance of ethanol from blood (ko). For this latter parameter, 42% and 58% of the total variation arose from variations between- and within-subjects respectively. These results might be important to consider when experiments on the clinical pharmacokinetics of ethanol are being planned.

Measurement of gastric emptying rate of solids by means of a carbon-labeled octanoic acid breath test

BACKGROUND

The aim of the present study was to develop a breath test for measuring gastric emptying rate of solids that would induce less radiation exposure than radioscintigraphy and would be applicable to field testing.

METHODS

A test meal was used in which [14C]-octanoic acid was mixed with egg yolk and prepared as a scrambled egg. The test meal was labeled with a second marker, 99mTc-albumin colloid, and simultaneous radioscintigraphic and breath test measurements were performed in 36 subjects, 16 normal controls, and 20 patients with dyspeptic symptoms. Mathematical analysis of the excretion rate of labeled CO2 resulted in the definition of three parameters, i.e., gastric emptying coefficient, gastric half-emptying time, and lag phase.

RESULTS

There was an excellent correlation between the gastric emptying coefficient and the scintigraphic half-emptying time (r = -0.88); between the half-emptying time determined by the breath test and the scintigraphic half-emptying time (r = 0.89); and between the lag phases determined by scintigraphy and those determined by breath test (r = 0.92). 14C can be replaced by 13C for labeling the octanoic acid used in the breath test.

CONCLUSIONS

It is concluded that the octanoic acid breath test is a reliable noninvasive test to measure gastric emptying rate of solids.

Voluntary suppression of defecation delays gastric emptying

We wished to test the hypothesis that colonic loading with fecal material leads to delayed gastric emptying. Twelve healthy male volunteers were studied. Each of these subjects went through two randomized study periods of four days. In one of these, the subjects defecated upon urge, in the other period defecation was voluntarily suppressed. Gastric emptying of a semisolid meal (mashed potatoes) was measured with the noninvasive applied potential tomography technique. On day 3 no significant changes in gastric emptying were found, but on day 4 the emptying rate had decreased from 85.8 +/- 11.0%/hr (mean +/- SEM) to 70.3 +/- 10.9%/hr (P < 0.05) and the T50 had increased from 38.5 +/- 3.4 min to 46.2 +/- 4.0 min (P < 0.025). The duration of the lag phase (4.1 +/- 1.5 min) was not significantly altered by suppression of defecation. Our conclusion is that voluntary suppression of defecation delays gastric emptying in normal subjects. This "cologastric brake" may be involved in the pathogenesis of upper abdominal symptoms in constipated patients.

Experimental ischaemic tourniquet pain delays gastric emptying of semi-solids in healthy volunteers

The effect of controlled, experimental ischaemic pain, induced by tourniquet, on gastric emptying of a semi-solid meal of Tc-99m labelled Chelex-100 resin oatmeal was assessed in seven healthy volunteers, each acting as his/her own control. In the pain study, the submaximal effort tourniquet test was applied immediately, 30 min and 45 min after beginning of the study. Pain intensity was rated during the procedure using a linear visual analogue scale (VAS). All subjects participating in the study assessed their pain as close to maximal tolerance after 2-4 min. The pain stimulus caused an immediate acceleration, followed by a reproducible, significant delay in gastric emptying relative to the control situation. The median reduction in meal emptied after 60 min in the pain study was 15% P = 0.035). There was no difference in the duration of the lag period between the groups.