Effects of dietary components on GI absorption of acetaminophen tablets in man

Do Thickening Agents Used in Dysphagia Diet Affect Drug Bioavailability?

Swallowing oral solid dosage forms is challenging in patients with dysphagia who are at risk of aspiration or choking. The most common method to facilitate drug administration in dysphagia patients is to mix the powdered drug with a small amount of thickened water, however little is known about the effects of this method on in vivo bioavailability of drugs. This study aimed to evaluate the impact of thickened liquids on dissolution rate and bioavailability of levetiracetam as a model drug. Powdered commercial tablets of levetiracetam, carbamazepine, atenolol and cefixime were mixed with water thickened with two commercial thickeners, modified maize starch (MS) and xanthan gam (XG), at three thickness levels: nectar, honey and pudding in test groups, and mixed with only water in the control group. At the first stage, the effects of thickened water on in vitro drug release of 4 drugs (levetiracetam, carbamazepine, atenolol and cefixime) were tested by using dialysis membrane method. Addition of both thickeners significantly reduced the release of three drugs compared to the control group, except carbamazepine. Levetiracetam which had the highest solubility was chosen as the model drug for in vivo experiments. In the second stage, New Zealand albino female rabbits (n=24) were divided into two groups as: control group (water+drug, n=6) and test group (thickened water+drug, n=18). Powdered levetiracetam tablets were mixed with water thickened with XG (n=9, 1.2 %, 2.4 %, 3.6 %) and MS (n=9, 4 %, 6%, 8 %) at three thickness levels and administered to the rabbits by intragastric gavage. Blood samples were collected at 9 time points following administration. After two-weeks of wash-out, test groups were crossed over and sample collection was repeated. Blood samples were analysed using liquid chromatography with tandem mass spectrometry (LC-MS/MS). An in vitro-in vivo correlation (IVIVC) model was developed using in vitro drug dissolution (%) and in vivo plasma concentrations of levetiracetam for control group and test groups. The peak plasma concentration (C_max) was lower and time to reach C_max (t_max) was relatively higher in test groups compared to control group. The lowest C_max was detected at the highest thickness level, however, the differences between groups were not statistically significant (p=0.117 and p=0.495 for C_max and t_max, respectively). No significant difference in total amount of levetiracetam absorbed (AUC) was found between groups (p=0.215 and p=0.183 for AUC_infinity and AUC_last, respectively). The comparisons according to the type of thickener also revealed that pharmacokinetic parameters did not significantly differ between groups, except for a significantly lower C_max when drug was mixed with MS-thickened water at nectar consistency (1.2 %) compared to drug mixed with XG (4 %) at the same thickness level (p=0.038). A good correlation was observed between in vitro and in vivo data, which was characterized by higher r² values as the concentration of the thickening agents was increased, but not for all thickness levels studied, indicating an inability of this in vitro model to fully predict the in vivo response. These results suggest that regardless of the thickness level, the administration of levetiracetam with two commercial thickening agents commonly used in dysphagia for safe swallowing, do not affect the pharmacokinetic efficiency and thus, the bioavailability of the drug.

Effects of food and exercise on the absorption of effervescent aspirin

1 The absorption of effervescent aspirin was studied in normal volunteers of both sexes under varied conditions of activity in both fasting and non-fasting states. 2 Moderate activity resulted in no significant changes in absorption compared with that at rest. 3 In non-fasting subjects the absorption was reduced but this reduction was attenuated with time until after 60 min the plasma levels were similar. 4 There was no interaction between the resting/non-resting and fasting/non-fasting absorption.

Pharmacokinetics of an oral drug (acetaminophen) administered at various times relative to subcutaneous injection of pramlintide in subjects with type 2 diabetes

Pramlintide, an adjunct treatment to mealtime insulin for patients with type 2 and type 1 diabetes, aids glycemic control by suppressing postprandial glucagon secretion, slowing gastric emptying, and enhancing satiety. Because gastric emptying affects oral medication absorption, this placebo-controlled, single-blind, crossover study examined the absorption of 1000 mg of acetaminophen elixir administered -2, -1, 0, +1, and +2 hours relative to pramlintide (120 microg) or 0 hours relative to placebo in 24 patients with type 2 diabetes. When acetaminophen administration occurred 0, +1, or +2 hours relative to pramlintide, the maximum observed plasma concentration of acetaminophen decreased 14% to 29%, and time to maximum observed plasma concentration increased by 0.8 to 1.2 hours compared with administration 0 hours relative to placebo. Pramlintide treatment slowed but did not alter the extent of acetaminophen absorption (area under the concentration-time curve). No serious adverse events or withdrawals were reported. Oral agents should be administered at least 1 hour before or 2 hours after pramlintide injection if rapid onset of action is required for efficacy.

A dynamic artificial gastrointestinal system for studying the behavior of orally administered drug dosage forms under various physiological conditions

PURPOSE

The purpose of this study was to demonstrate the potential of a dynamic, multicompartmental in vitro system simulating the human stomach and small intestine (TIM-1) for studying the behavior of oral drug dosage forms under various physiological gastrointestinal conditions.

METHODS

Two model drug compounds were studied in TIM-1: a lyophilized Lactobacillus strain and paracetamol (acetaminophen). The Lactobacillus survival rate was determined by bacterial counting in the gastric and ileal effluents while simulating the conditions of the gastrointestinal tract of infants or adults. The availability for absorption of paracetamol from two oral dosage forms was investigated by measuring the drug concentration in jejunal dialysis fluid. The effect of gastrointestinal passage time and food intake on paracetamol absorption was also studied.

RESULTS

The Lactobacillus survival rate in both gastric and ileal effluents was higher during simulation of the infant compared to adult conditions. We also showed that (i) paracetamol absorption was faster when it was administered as a free powder than in sustained-release tablet form, (ii) a slow passage time resulted in a delay in the absorption of paracetamol, and (iii) there was a lower rate of absorption when paracetamol was ingested with a standard breakfast as opposed to water. The in vitro results were consistent with in vivo data, showing the predictive value of TIM-1.

CONCLUSIONS

TIM-1 is a powerful tool for supplying valuable information about the effects of various gastrointestinal conditions on biopharmaceutical behavior and efficacy of drug delivery systems in the development of oral formulations.

Effect of a high-fat meal on thalidomide pharmacokinetics and the relative bioavailability of oral formulations in healthy men and women

The effect of food on the oral pharmacokinetics of thalidomide and the relative bioavailability of two oral thalidomide formulations were determined in an open label, single dose, randomized, three-way crossover study. Five male and eight female healthy volunteers received a single oral dose of 200 mg Celgene thalidomide capsules under fasted and non-fasted conditions, and a single dose of 200 mg tablets of Serral thalidomide under fasted conditions. The high-fat meal resulted in a 0.5-1.5 h absorption lag time, an increased mean C(max), a decreased mean AUC and a delay in mean T(max). The Serral tablet formulation resulted in a lower mean C(max), and slower terminal decline in plasma thalidomide concentrations compared with both Celgene treatments. Mean C(max) concentrations were 1.99+/-0.41 microg/mL (range 1.28-2.76) within 4.00+/-1.13 h (2-5) for the Celgene formulation fasted, 2.17+/-0.51 microg/mL (1.43-3.01) within 6.08+/-2.33 h (3-12) for the Celgene formulation with food, and 1. 05+/-0.31 microg/mL (0.62-1.65) within 6.23+/-1.88 h (5-10) for the Serral formulation fasted. Mean terminal half-lives were 13.50+/-6. 77 h for the Serral product, compared with 5.80+/-1.72 h and 5. 09+/-1.03 h for Celgene fasted and fed, respectively. Celgene's formulation exhibited slightly greater bioavailability than Serral's formulation, with mean ratios of 122% and 110% for Ln-transformed AUC(0-t) and AUC(0-infinity), respectively. The mean C(max) for the Celgene formulation was approximately two times greater than Serral's. Food delayed the onset of absorption of by 0.5-1.5 h, but had little effect on the extent of absorption from the Celgene capsule. Under fasted conditions, the Celgene thalidomide resulted in a two-fold greater C(max) and 10% greater AUC(0-infinity) than the Serral formulation.

Critical dissolution tests of oral systems based on statistically designed experiments. III. In vitro/in vivo correlation for multiple-unit capsules of paracetamol based on PLS modeling

The main aims of the present study were to establish an in vitro/in vivo correlation for multiple-unit capsules of paracetamol by means of statistical prediction models and to investigate the effect of a number of in vitro variables on the discussion rate of paracetamol from the formulation. A fractional factorial screening design was used to investigate the effects of the variables agitation, pH, osmolality, viscosity, and the presence of bile salt on the dissolution rate of paracetamol. The effects were evaluated in two separate partial least-squares models, in which the responses were expressed as the cumulative percentage of paracetamol dissolved at specified time-points (model I) and as the shape (beta) and scale (eta) parameters according to the Weibull function (model II). It was concluded that agitation and viscosity had significant effects on the dissolution rate of paracetamol. Statistical models based on the responses from models I and II were then used to predict the in vitro conditions most closely correlated with the in vitro dissolution of paracetamol after administration of the formulation to 10 healthy volunteers. The predicted optimal in vitro conditions were similar for the two models and not too far from what is expected from the gastrointestinal tract. The experimental verification of the in vitro conditions showed that both models were equally good, and contributed to high degrees of correlation with the in vivo dissolution behavior of the formulation during 9 hr. The relationships obtained when plotting the percentage dissolved in vitro versus in vivo were y = 1.1x (r2 = 0.98) and y = 1.1x (r2 = 0.94) for models I and II, respectively. Based on these results, it is difficult to state a preference for one of the models. Finally, the use of statistical prediction models to develop critical in vitro tests is a successful approach in the establishment of associations between dissolution behavior in vitro and in vivo for oral extended-release systems.

Effect of diet on the single- and multiple-dose pharmacokinetics of sustained-release ketoprofen

The indirect effect of diet on the single- and multiple-dose pharmacokinetics of sustained-release ketoprofen was studied in 16 healthy male volunteers. In an open, cross-over design, 200 mg ketoprofen was administered as a gastric-juice-resistant, sustained-release tablet once daily during two periods of 5 days. A low-calorie/low-fat diet (LCFD) was given in the first period and a high-calorie/high-fat diet (HCFD) in the second period. The first meal on each day was given 4 h after drug intake. Ketoprofen plasma concentrations were measured over 24 h after the first dose on day 1 and over 36 h after the final dose on day 5 of each period. On average, plasma concentrations of ketoprofen were higher with the LCFD than with the HCFD. With the HCFD there was a tendency to longer absorption-lag times on day 5. The maximum concentration and the area under the curve over one 24-h dosage period (AUC0-24) were significantly higher with the LCFD, both on day 1 and on day 5. For AUC0-24 the differences were on average 15% (day 1) and 24% (day 5). The same tendency was observed for the amount excreted in urine over 24 h (Ae), but the difference was only significant on day 1 (14%). The elimination rate constant (K beta) and the mean residence time were similar for the two diets, both on day 1 and on day 5. From these results, we conclude that there was an acute indirect effect of diet when a meal was had 4 h after intake of the medication.(ABSTRACT TRUNCATED AT 250 WORDS)

Impaired absorption of paracetamol in vegetarians

1. The absorption and disposition of paracetamol was investigated in 10 healthy male Thai vegetarians and 10 similar non-vegetarians following an oral dose of 20 mg kg-1. 2. The absorption rate of paracetamol was significantly impaired in the vegetarians compared with the non-vegetarians as shown by a lower mean Cmax (11.7 +/- 1.4 vs 15.6 +/- 1.6 mg l-1; 95% confidence interval of the difference 2.49 to 5.36), increased tmax (median 1.75, range 0.75 to 3 h compared with 0.75 and 0.25 to 2 h) and an increase in the time for input of 50% of the total amount absorbed (0.54 +/- 0.38 compared with 0.20 +/- 0.10 h; 95% confidence interval of the difference 0.063 to 0.61). 3. A significantly lower total 24 h urinary recovery of paracetamol and metabolites (72.1 +/- 5.4 vs 86.4 +/- 5.4% of the dose; 95% confidence interval of the difference 8.0 to 20.6) indicated a decrease in the extent of absorption in the vegetarians also, although the total AUC values did not differ significantly between the two groups. 4. The plasma paracetamol half-life, partial metabolic clearances and fractional urinary excretion of the glucuronide, sulphate, cysteine and mercapturic acid conjugates of paracetamol were similar in the vegetarians and non-vegetarians.

Influence of food on the pharmacokinetics of dipyrone

Twelve healthy volunteers were given a single oral dose of dipyrone 1 g, once while fasting and once after a standard breakfast. Plasma levels of the active dipyrone metabolite-Methylaminoantipyrine (MAA) were measured and the calculated pharmacokinetic parameters were compared. Taking dipyrone with food resulted in a small delay in the mean time to peak from 1.5 h to 1.9 h (p less than 0.01). However, there was no significant difference in AUC, Cmax or K(elim) between fasting and nonfasting conditions. The rate of absorption, expressed as the mean K(abs), was somewhat slower in the nonfasting state, but not significantly so. It is suggested that dipyrone may be taken regardless of the times of eating.

The effect of food on ciramadol bioavailability in normal subjects

Eleven healthy volunteers completed a study to compare the relative bioavailability to orally administered ciramadol in a fasting versus postprandial state. A single oral dose of 30 mg of ciramadol was administered on two separate occasions, 2 weeks apart, in a randomized crossover study. A mono- or biexponential pharmacokinetic equation with first-order absorption was applied to analyse the serum data for each subject. Significant differences were found in peak time (tmax) and absorption time (tabs) whereas the mean AUCs for the two modes of administration were not significantly different. The relative bioavailability (F) of the drug when administered in the postprandial state with respect to the fasting state was 96 per cent. It is thus concluded that ingestion of food has no effect on the extent of absorption of ciramadol; however, food may alter its rate of absorption.

Temporal variations in paracetamol absorption and metabolism in man

When paracetamol (1.5 g) was administered orally to non-fasted healthy subjects, statistically significantly more paracetamol glucuronide was detected in 0-4 h urine when the drug was given at 8.00 a.m. as compared to other times of the day. Compared to administration at 8.00 pm, the urine contained almost twice as much glucuronide. However, there was apparently no temporal variation in the excretion of intact drug and its other metabolites. Marked differences were observed in salivary concentrations of paracetamol during the first 90 min following oral administration at 8.00 a.m. and 8.00 p.m. These data were consistent with a decreased rate of absorption of paracetamol at 8.00 p.m. Paracetamol clearance, elimination half-life and volume of distribution did not differ when the drug was administered by intravenous infusion at 8.00 a.m. and 8.00 p.m. There was also no change in the amounts of paracetamol and metabolites excreted in the urine. There appears to be a temporal variation in the elimination of paracetamol glucuronide following oral administration of paracetamol, which is probably related to a variation in absorption.

Effect of migraine attacks on paracetamol absorption

The absorption of effervescent paracetamol (1000 mg) was investigated in nine female patients during a migraine attack and in the same patients when headache free. Migraine attack decreased (P less than 0.05) the areas under the serum paracetamol concentration-time curves (AUC) of 0-2 h, 0-4 h and 0-6 h and the peak serum concentration. The severity of nausea correlated significantly with the decrease in the AUC values. Our results support findings of delayed gastric emptying in migraine attacks. Both a delay and an impairment of drug absorption may follow.

Interactions affecting drug absorption

The influence of drug-drug and drug-food interactions affecting the absorption of orally administered medication is reviewed. Drug-drug interactions can be classified in terms of indirect effects by one drug on gastrointestinal tract physiology influencing the absorption of other drugs, or direct interactions involving altered pH, adsorption, absorption, or chelation. Most, but not all, drug-drug interactions result in reduced or delayed systemic drug availability. Drug-food interactions may result in reduced, delayed, or increased systemic drug availability. The absorption of only a small number of drugs is unaffected by concomitant food intake. The degree of interaction and whether it positively or negatively affects drug absorption depends on a number of factors including the physical and chemical nature of the drug, the formulation, the type of meal, and the time interval between eating and dosing. Mechanisms of drug-food interactions are not well characterised. They clearly involve both direct and indirect factors in a similar fashion to drug-drug interactions, but indirect factors probably predominate. Reduced or delayed drug absorption is generally attributed, at least in part, to delayed stomach-emptying due to food. Increased absorption may also result from delayed stomach-emptying facilitating greater drug dissolution before it passes from the stomach into the small intestine. Increased bioavailability of some drugs, e.g. propranolol, metoprolol and labetalol, may be related to reduced presystemic clearance. The potential clinical implications of drug-drug and drug-food interactions must be taken into account with oral medications in order to minimise variations in systemic drug availability and hence in clinical efficacy.

Interactions of analgesics with other drugs

Antipyretic analgesics, such as salicylates, acetaminophen, and pyrazolones, are often given concomitantly with a variety of other drugs. Drug interactions that occur at the receptors are known as pharmacodynamic interactions; alterations in absorption (bioavailability), distribution (plasma protein-binding), and elimination (renal excretion, hepatic metabolism) are termed pharmacokinetic interactions. For example, antacids and food both delay the absorption of analgesics. Highly protein-bound drugs (such as phenylbutazone, phenytoin, or warfarin) can compete with the common binding sites of salicylates. Hepatic elimination of salicylates can be influenced by drugs such as beta-blockers and cimetidine. Clinically important interactions involving salicylates, acetaminophen, and other antipyretic analgesics are discussed.

Clinical pharmacokinetics of paracetamol

In therapeutic doses paracetamol is a safe analgesic, but in overdosage it can cause severe hepatic necrosis. Following oral administration it is rapidly absorbed from the gastrointestinal tract, its systemic bioavailability being dose-dependent and ranging from 70 to 90%. Its rate of oral absorption is predominantly dependent on the rate of gastric emptying, being delayed by food, propantheline, pethidine and diamorphine and enhanced by metoclopramide. Paracetamol is also well absorbed from the rectum. It distributes rapidly and evenly throughout most tissues and fluids and has a volume of distribution of approximately 0.9L/kg. 10 to 20% of the drug is bound to red blood cells. Paracetamol is extensively metabolised (predominantly in the liver), the major metabolites being the sulphate and glucuronide conjugates. A minor fraction of drug is converted to a highly reactive alkylating metabolite which is inactivated with reduced glutathione and excreted in the urine as cysteine and mercapturic acid conjugates. Large doses of paracetamol (overdoses) cause acute hepatic necrosis as a result of depletion of glutathione and of binding of the excess reactive metabolite to vital cell constituents. This damage can be prevented by the early administration of sulfhydryl compounds such as methionine and N-acetylcysteine. In healthy subjects 85 to 95% of a therapeutic dose is excreted in the urine within 24 hours with about 4, 55, 30, 4 and 4% appearing as unchanged paracetamol and its glucuronide, sulphate, mercapturic acid and cysteine conjugates, respectively. The plasma half-life in such subjects ranges from 1.9 to 2.5 hours and the total body clearance from 4.5 to 5.5 ml/kg/min. Age has little effect on the plasma half-life, which is shortened in patients taking anticonvulsants. The plasma half-life is usually normal in patients with mild chronic liver disease, but its prolonged in those with decompensated liver disease.

The effect of wheat bran and pectin on paracetamol absorption in the rat

1. The absorption of an oral dose of paracetamol was measured in rats given either a basal fibre-free diet, or the basal diet with either pectin or bran added. 2. Urinary excretion of the oral dose was significantly greater during the first 8 h in the pectin-fed rats compared with those on basal diet, though cumulative excretion after 72 h was the same. 3. Free paracetamol levels in the plasma were significantly higher in the pectin-fed rats compared with those on basal diet at 30, 60, 90 and 120 min after the oral dose. 4. The plasma half-life of intravenously-injected paracetamol was shorter in the pectin-fed rats than in those on basal diet alone, but the antipyrine half-lives were not significantly different. 5. Pectin feeding had no effect on either the apparent volume of distribution of paracetamol and antipyrine, or on the rate of gastric empyting. 6. Perfusion of the whole length of the small bowel showed a significantly greater capacity for paracetamol absorption in the pectin-fed rats. 7. Bran had no effect on paracetamol absorption. 8. It was concluded that dietary fibre intake affects drug absorption and that the effect varies with the type of fibre. Unexpectedly pectin accelerates rather than retards absorption of paracetamol, though the mechansim of this effect is unknown.

The gastrointestinal absorption of paracetamol in the rat

The absorption of [3H]paracetamol by rat small intestine, colon and stomach was studied in vivo and in vitro. Small intestinal in vivo studies, using a wide range of drug concentrations, showed that absorption was efficient and uniform throughout the small bowel, no site showing preferential absorption. Double reciprocal and direct plots indicated first order kinetics. The pattern was not observed when uptake was occurring from high concentrations of paracetamol in suspension. Gastric and colonic in vivo studies showed that there was appreciable absorption of [3H]paracetamol from these sites. In vitro studies using everted intestinal sacs showed no effect on paracetamol transfer when the incubation temperature was lowered to 10 degrees C or when iodoacetate (5 X 10(-2)M) and 2.4 dinitrophenol (5 X 10(-4)M) was added to the incubation medium. There was, however, a significant reduction in transfer of paracetamol against a concentration gradient of 10:1 applied across the mucosa. These data suggest that the uptake of paracetamol is by a passive transport process and confirm the efficiency of paracetamol absorption observed indirectly by others.

Reduction of absorption of paracetamol by activated charcoal and cholestyramine: a possible therapeutic measure

The absorption of an oral 2-g dose of paracetamol was markedly reduced by the simultaneous oral administration of either activated charcoal or cholestyramine but was only slightly reduced when the adsorbents were given 60 minutes after the paracetamol. Since the absorption of a larger dose of the drug will probably be slow, the administration of adsorbents may be of value even when delayed several hours.