Gastrointestinal behavior of orally administered radiolabeled erythromycin pellets in man as determined by gamma scintigraphy

Fasting state is one of the factors associated with plasma levodopa fluctuations during levodopa‒carbidopa intestinal gel treatment

INTRODUCTION

Some patients with Parkinson's disease (PD) undergoing levodopa‒carbidopa intestinal gel (LCIG) treatment experience motor fluctuations in the afternoon. The migrating motor complex, a specific periodic migrating contraction pattern occurring in the stomach and small intestine during the fasting state, can affect drug absorption. We aimed to compare the pharmacokinetic parameters between two conditions (with and without lunch) and assessed the influence of the fasting state on the levodopa pharmacokinetics in LCIG treatment.

METHODS

We evaluated the levodopa pharmacokinetics from 12:00 p.m. to 6:00 p.m. in 10 LCIG-treated PD patients in the presence and absence of lunch.

RESULTS

The maintenance dose of LCIG correlated strongly with the mean plasma concentration of levodopa in the absence (r = 0.94, coefficient of determination (R²) = 0.89, p < 0.001) or presence of lunch (r = 0.96, R² = 0.93, p < 0.001). Comparison of the pharmacokinetic parameters revealed that the coefficient of variation was significantly greater in the condition without lunch than in the condition with lunch (p = 0.004): 16.73% (4.88%) without lunch and 9.22% (3.80%) with lunch. There were no significant differences in the mean plasma concentration of levodopa (p = 0.49) and area under the plasma concentration‒time curve (p = 0.27) between the two conditions.

CONCLUSIONS

Plasma concentrations of levodopa fluctuated more in patients undergoing LCIG treatment without than with lunch. Our results indicate that a small amount of food intake may be a better corrective approach for worsening of symptoms in the fasting state rather than additional levodopa.

Revising Pharmacokinetics of Oral Drug Absorption: I Models Based on Biopharmaceutical/Physiological and Finite Absorption Time Concepts

ABSRACT

PURPOSE: To demonstrate that oral drug absorption is terminated in finite time. To develop models based on biopharmaceutical/physiological and finite absorption time concepts.

METHODS

The models are based on i) the passive drug diffusion mechanism under the sink conditions principle ii) the rate limiting role of the drug's properties solubility and permeability and iii) the relevant restrictions associated with the gastrointestinal transit times of drug in the stomach, the small intestines and the colon. Two input functions of constant rate are considered for the absorption of drug from i) the stomach/small intestines with an upper limit of 5 h and ii) the colon with an upper limit of 30 h. Branched differential equations were written for the time course of drug in the body.

RESULTS

Simulations were performed using different scenarios, assuming a variety of drug properties and limited or non-existent absorption from the colon. Literature oral data of cephradine, ibuprofen, flurbiprofen and itraconazole were analyzed. For all drugs examined, nice fittings of the branched differential equations to the experimental data were observed.

CONCLUSIONS

For all drugs the absorption process was terminated in the small intestine. The meaning of partial AUCs, Cmax, tmax are questioned. Applications of these models to IVIVC are anticipated.

The mechanisms of pharmacokinetic food-drug interactions - A perspective from the UNGAP group

The simultaneous intake of food and drugs can have a strong impact on drug release, absorption, distribution, metabolism and/or elimination and consequently, on the efficacy and safety of pharmacotherapy. As such, food-drug interactions are one of the main challenges in oral drug administration. Whereas pharmacokinetic (PK) food-drug interactions can have a variety of causes, pharmacodynamic (PD) food-drug interactions occur due to specific pharmacological interactions between a drug and particular drinks or food. In recent years, extensive efforts were made to elucidate the mechanisms that drive pharmacokinetic food-drug interactions. Their occurrence depends mainly on the properties of the drug substance, the formulation and a multitude of physiological factors. Every intake of food or drink changes the physiological conditions in the human gastrointestinal tract. Therefore, a precise understanding of how different foods and drinks affect the processes of drug absorption, distribution, metabolism and/or elimination as well as formulation performance is important in order to be able to predict and avoid such interactions. Furthermore, it must be considered that beverages such as milk, grapefruit juice and alcohol can also lead to specific food-drug interactions. In this regard, the growing use of food supplements and functional food requires urgent attention in oral pharmacotherapy. Recently, a new consortium in Understanding Gastrointestinal Absorption-related Processes (UNGAP) was established through COST, a funding organisation of the European Union supporting translational research across Europe. In this review of the UNGAP Working group "Food-Drug Interface", the different mechanisms that can lead to pharmacokinetic food-drug interactions are discussed and summarised from different expert perspectives.

Challenges and innovations of drug delivery in older age

Both drug delivery performance and various age-related physical, mental and physiological changes can affect drug effectiveness and safety in elderly patients. The many drug delivery systems developed over the years include recent novel transdermal, nasal, pulmonary and orally disintegrating tablets that provide consistent, precise, timely and more targeted drug delivery. Certain drug delivery systems may be associated with suboptimal outcomes in the elderly because of the nature of drug present, a lack of appreciation of the impact of age-related changes in drug absorption, distribution and clearance, the limited availability of pharmacokinetic, safety and clinical data. Polypharmacy, patient morbidity and poor adherence can also contribute to sub-optimal drug delivery systems outcomes in the elderly. The development of drug delivery systems for the elderly is a poorly realised opportunity, with each system having specific advantages and limitations. A key challenge is to provide the innovation that best meets the specific physiological, psychological and multiple drug requirements of individual elderly patients.

Analysis of factors influencing gastric emptying of pellets in a fed state

OBJECTIVES

The aim of the present study is to evaluate the influence of factors such as biopharmaceutical properties and study protocol on the emptying of pellets from the human stomach in a fed state.

METHODS

A systematic literature search for data on human gastric emptying of pellets from a fed stomach state investigated by γ-scintigraphy was carried out. After selection of comparable data, a joint statistical analysis on the basis of multiple linear regression with 132 individual t50 values (time for 50% of the pellets to be emptied from the stomach) was performed. Parameters such as a second meal administration that can influence t50 values were also examined and included into the interpretation of the results.

RESULTS

The results showed that an increase in the caloric value of the meal in the interval between 1200 and 3600 kJ increased the mean t50 value. Pellets with a density of 2.8 g/cm(3) remained in the stomach longer than pellets of usual density with the same caloric value of the meal. Pellets incorporated in a tablet are emptied faster from the stomach than encapsulated pellets. A 45-min delay in the application of pellets after the start of the meal significantly diminished the mean t50 value, compared with application immediately after consuming the meal.

CONCLUSION

Thus, in the development of non-disintegrating pellets intended for fed-state application, all of these cited factors should be considered because of their potential influence on the gastric residence time.

Gastric emptying of multi-particulate dosage forms

The evidence in the literature for the concept that multi-particulate dosage forms below a specific size empty from the stomach as if they were liquids and hence have the potential to provide the best solution to the formulation of controlled release oral dosage forms, has been considered. There is some evidence that particles less than 1.0mm provide a more rapid response than larger size particles but there is also evidence that this is not always the case and that rapid and reproducible gastric emptying of small particles does not always occur when they are administered. There is strong evidence that food can delay the gastric emptying of multi-particulate systems. Some of the misconception for gastric emptying performance of multi-particulate system is shown to be related to the limitation of the study design and limitation of the way the data is processed. Nevertheless, there is clear evidence that multi-particulate systems can provide effective oral controlled release dosage forms. There is still some way to go with experimental techniques which would allow a definitive answer to the issue of how the variability of the gastric emptying of multi-particulate systems of less than 2.0mm arises.

The transit of dosage forms through the small intestine

The human small intestine, with its enormous absorptive surface area, is invariably the principal site of drug absorption. Hence, the residence time of a dosage form in this part of the gut can have a great influence on the absorption of the contained drug. Various methods have been employed to monitor the gastrointestinal transit of pharmaceutical dosage forms, but the use of gamma-scintigraphy has superceded all the other methods. However, careful consideration of the time interval for image acquisition and proper analysis of the scintigraphic data are important for obtaining reliable results. Most studies reported the mean small intestinal transit time of various dosage forms to be about 3-4h, being closely similar to that of food and water. The value does not appear to be influenced by their physical state nor the presence of food, but the timing of food intake following administration of the dosage forms can influence the small intestinal transit time. While the mean small intestinal transit time is quite consistent among dosage forms and studies, individual values can vary widely. There are differing opinions regarding the effect of density and size of dosage forms on their small intestinal transit properties. Some common excipients employed in pharmaceutical formulations can affect the small intestinal transit and drug absorption. There is currently a lack of studies regarding the effects of excipients, as well as the timing of food intake on the small intestinal transit of dosage forms and drug absorption.

Gastric emptying of pellets under fasting conditions: a mathematical model

PURPOSE

To develop a mathematical model that would adequately describe human gastric emptying of pellets under fasting conditions of healthy subjects.

METHODS

Scintigraphic profiles representing the gastric emptying of pellets were obtained from the literature. Altogether 19 individual and three mean scintigraphic profiles were collected. Three mathematical models namely; the lag-time exponential (two parameters), the Weibull (two parameters), and the double Weibull (five parameters) model were proposed and fitted to the gastric emptying profiles.

RESULTS

Different patterns of gastric emptying (immediate and rapid, delayed but rapid, delayed and slow, and interruptive emptying) were observed, with the emptying time varied from approximately 15 min to more than 3 h. The best model for fitting to the individual profiles was the double Weibull model. This model also provided an insight into the mechanism of interruptive emptying of pellets, observed for some patients. In addition, mean gastric emptying of pellets was calculated using the Weibull model.

CONCLUSIONS

Mean gastric emptying of pellets was adequately described by the Weibull model (eta = 61.9 min, beta = 0.895), which could be applied in the design of in vitro dissolution experiments for pellet formulations with pH dependent dissolution.

Review article: 5-aminosalicylate formulations for the treatment of ulcerative colitis--methods of comparing release rates and delivery of 5-aminosalicylate to the colonic mucosa

BACKGROUND

Many oral 5-aminosalicylic acid (5-ASA) formulations are designed to maximize 5-ASA release in the colon where it acts topically on the colonic mucosa. Delayed-release formulations and azo-prodrugs minimize 5-ASA absorption in the upper gastrointestinal (GI) tract.

AIMS

To review methods for assessing 5-ASA release and colonic distribution from oral formulations, and the potential use of this information for guiding clinical decisions.

METHODS

PubMed and recent conference abstracts were searched for articles describing techniques used to assess 5-ASA release from ulcerative colitis (UC) therapies.

RESULTS

In-vitro GI models, although unable to simulate more complex aspects of GI physiology, can provide useful data on 5-ASA release kinetics and bioaccessibility. Gamma-scintigraphy is useful for investigating GI disintegration of different formulations, but may not accurately reflect 5-ASA distribution. Plasma pharmacokinetic studies provide data on systemic exposure, but not on colonic distribution or mucosal uptake. Mucosal biopsies provide direct evidence of colonic distribution and may predict clinical efficacy, but must be interpreted cautiously because of considerable inter-subject variability and other confounding factors.

CONCLUSION

While assessment of 5-ASA release is important, limitations of individual measurement techniques mean that randomized clinical studies in UC patients remain the best guide for dosing and treatment regimen decisions.

A scintigraphic study to investigate the potential for altered gut distribution of loperamide from a loperamide-simethicone formulation in man

A loperamide simethicone combination formulation has recently been demonstrated to have significant clinical advantages compared to loperamide alone in the relief of diarrhoea and related symptoms. The product visualisation technique of gamma scintigraphy has been used to investigate the interaction of the formulation with the heterogenous environment of the human gut in a group of 12 healthy volunteers. The results suggest that changes in the intestinal kinetics of loperamide from the combination product, e.g. jejunal coating, could be contributing to the improved efficacy.

The role of gamma-scintigraphy in oral drug delivery

The gastrointestinal tract is usually the preferred site of absorption for most therapeutic agents, as seen from the standpoints of convenience of administration, patient compliance and cost. In recent years there has been a tendency to employ sophisticated systems that enable controlled or timed release of a drug, thereby providing a better dosing pattern and greater convenience to the patient. Although much about the performance of a system can be learned from in vitro release studies using conventional and modified dissolution methods, evaluation in vivo is essential in product development. The non-invasive technique of gamma-scintigraphy has been used to follow the gastrointestinal transit and release characteristics of a variety of pharmaceutical dosage forms. Such studies provide an insight into the fate of the delivery system and its integrity and enable the relationship between in vivo performance and resultant pharmacokinetics to be examined (pharmacoscintigraphy).

Bioequivalence study of stressed and nonstressed hard gelatin capsules using amoxicillin as a drug marker and gamma scintigraphy to confirm time and GI location of in vivo capsule rupture

PURPOSE

Evaluate if crosslinked hard gelatin capsules (HGCs) having different in vitro dissolution profiles changed in vivo release times or altered bioavailability of a drug marker; assess if a two-tier dissolution test (with and without enzyme) predicted in vivo performance.

METHODS

Two classifications of stressed HGCs were artificially produced by exposure to formaldehyde (HCHO). HGCs were categorized as, a) pass/pass (p/p) which met in vitro dissolution criterion (75% drug dissolution at 45 min), b) moderately crosslinked fail/pass (f/p) which failed dissolution criterion in the absence of enzymes and passed in the presence of enzymes, and c) severely crosslinked fail/fail (f/f) which failed in vitro standards with or without enzymes. A six-way, single dose bioequivalence study (n = 10) administered the three HGCs under the fasted and fed condition. In vivo capsule rupture and GI transit were monitored via gamma scintigraphy, and blood samples were collected through six hours.

RESULTS

Each crosslinked HGC was bioequivalent to the control p/p capsule when using AUC(0-infinity) and Cmax for comparison. Mean in vivo disintegration of the p/p capsule was 7 +/- 5 min for the fasted condition and 11 +/- 7 min for the fed condition. In vivo rupture for the f/p capsule was 22 +/- 12 min and 23 +/- 11 min for the fasted and fed studies, respectively, while the f/f HGC ruptured at 31 +/- 15 min and 71 +/- 19 min under the fasted and fed condition, respectively. Onset of amoxicillin absorption was dependent on in vivo HGC rupture and subsequent entry of the released radioactive marker into the small intestine. Consequently, fasted Tmax values were significantly later for the f/p HGC (1.62 +/- 0.53 hr) and f/f HGC (1.85 +/- 0.58 hr) as compared to the p/p HGC (1.17 +/- 0.30 hr). Fed Tmax values were statistically different only for the f/f capsule (2.55 +/- 0.44 hr) where Tmax values for the p/p and f/p HGCs under the fed condition were 1.50 +/- 0.47 hr and 1.60 +/- 0.46 hr, respectively.

CONCLUSIONS

A two-tier dissolution procedure that retested a crosslinked hard gelatin capsule with addition of gastric or intestinal enzymes provided an adequate in vitro indicator of the formulation's in vivo performance. The observed delays in the onset of amoxicillin absorption and Tmax for the severely crosslinked f/f HGC was attributed to delayed in vivo capsule rupture, however, this delay did not adversely change AUC(0-infinity) nor Cmax.

Different absorption profiles of deramciclane in man and in dog

We have studied the dog model for predicting the oral absorption of deramciclane, a novel anxiolytic compound, as a model acid-labile drug. The absorption profile of deramciclane was studied in man and beagle dogs after administration of conventional capsules and enteric coated tablets. Absorption in dogs pretreated with pentagastrin or saline was also studied after administration of conventional capsules. The in-vitro stability of deramciclane was determined over the pH range 1.2-6.0. The rate of degradation of deramciclane increased ten-fold as the pH was reduced from 2.1 to 1.2 (t 1/2 beta (elimination half-life) 9 h and 39 min, respectively). Deramciclane was stable at pH > or = 3. The two formulations were bioequivalent in dogs and there were no significant differences between pharmacokinetic parameters measured for dogs pretreated with pentagastrin or saline. In man the mean relative bioavailability and Cmax (peak plasma concentration) for the conventional capsules were approximately 75% and 83% of those for the enteric coated tablets (P = 0.0004 and P = 0.0031, respectively). This was probably because of degradation of deramciclane at lower pH of man's stomach compared with that of the dog. Pentagastrin was probably unsuccessful in reducing gastric pH and thus no change in absorption was observed. It is concluded that the absorption of deramciclane, and possibly other acid-labile drugs, cannot be predicted by use of the dog model.

In vivo evaluation of the absorption and gastrointestinal transit of avitriptan in fed and fasted subjects using gamma scintigraphy

The study was conducted to assess the bioavailability of avitriptan after a standard high fat meal, in relation to gastrointestinal transit. Six healthy male subjects were enrolled in a four-period study with a partial replicate design where each was administered 150-mg avitriptan capsule (i) after an overnight fast, (ii) 5 min after a standard high-fat breakfast, and (iii) 4 hr after a standard high fat breakfast. The treatment administered in Period 3 was repeated in Period 4 to assess intrasubject variations in pharmacokinetics and gastrointestinal (GI) transit. Avitriptan capsules were specially formulated with nonradioactive samarium chloride hexahydrate which was neutron-activated to gamma-emitting samarium before dosing. Serial blood samples were collected for analysis of avitriptan up to 24-hr postdose, and serial scintigraphic images were obtained to assess the plasma concentration-time profile in relation to the GI transit of the avitriptan capsule contents. Bioavailability of avitriptan was reduced when administered in the fed condition but only the decrease in AUC(INF) was statistically significant. Tmax was significantly delayed between the fed conditions and the fasted condition. Qualitative appearance of plasma concentration-time profiles for avitriptan could be related to the manner in which the drug emptied from the stomach. It was also apparent that avitriptan exerted a secondary pharmacologic effect that temporarily suspended gastric emptying in the fasted treatment. Thus, when gastric emptying was interrupted and then resumed, the net result was a double peak in some of the individual plasma concentration profiles. Scintigraphic analysis also demonstrated that upon emptying from the stomach, avitriptan was rapidly absorbed from the upper small intestine. In the fed state, gastric emptying was slow and continuous resulting in extended absorption and a lower occurrence of double peaks. Qualitatively, the intrasubject variability in Cmax and AUC could be explained by the intrasubject variability in gastric emptying in both fasted and fed conditions.

Explaining variable absorption of a hypolipidemic agent (CGP 43371) in healthy subjects by gamma scintigraphy and pharmacokinetics

The gastrointestinal absorption of a hypolipidemic agent (CGP 43371) was investigated using an external scintigraphy technique in six healthy men. After an overnight fast, subjects received a single 800-mg oral dose of CGP 43371 (4 capsules of 200 mg each) and one capsule of radioactive samarium-153 oxide (100-130 microCi) as a nonabsorbable marker of gastrointestinal transit and fecal recovery for CGP 43371. In vivo gastrointestinal transit of samarium-153 was monitored via gamma scintigraphy for 48 hours after administration to coincide with blood sampling. Samarium-153 content in whole fecal samples was determined by external gamma scintigraphy, and CGP 43371 content in both fecal and plasma samples was determined using high-performance liquid chromatography (HPLC). The results of fecal analysis indicated that transit of the two compounds in the gastrointestinal tract were similar, and bioavailability of CGP 43371 was calculated to be 9% based on the difference between the cumulative amounts of the nonabsorbable radioactive marker and CGP 43371 found in the feces. The onset of drug absorption occurred 4 hours after administration when radioactive samarium-153 was in the distal small bowel, and peak plasma drug level occurred 6 hours after administration, which corresponded with the arrival of samarium-153 in the terminal ileum and ileal/cecal junction. This observation supported the concept that primary absorption of this compound was in the distal to terminal portion of the ileum. Although the onset of drug absorption was delayed, it was curious that the rate of gastric emptying also affected the extent of absorption. A positive correlation (r = 0.91) between area under the drug curve (AUC) and area under the transit curve (AUTC) of the gastric emptying showed that longer gastric residence improved oral absorption of CGP 43371.

Gastric but not duodenal motor effects of oral erythromycin are dose related

There has been increasing interest in the potential use of erythromycin as a prokinetic agent, despite limited data on the effect of oral administration on gastrointestinal motility. We have now evaluated, in 15 conscious pigs fitted with strain gauges, the response of (i) basal gastric motility and (ii) gastric motility during inhibition with intraduodenal triglycerides infusion to increasing doses of oral erythromycin. In the basal state, erythromycin led to dose-dependent increases in both the amplitude (10-30 mg kg-1) and the frequency (10-55 mg kg-1) of gastric contractions. The corpus was more responsive than the antrum, with an increase in amplitude at lower doses. The amplitude of the duodenal contractions was also improved but not in a dose-dependent manner. Gastroduodenal coordination was unchanged regardless of the dose of erythromycin. Following inhibition of gastric motility, a dose of erythromycin below 45 mg kg-1 increased both the amplitude of gastric contractions and the gastroduodenal coordination, although individual doses produced smaller increases in amplitude than in the basal state. These results suggest that erythromycin has a different mechanism of action in the stomach compared with the duodenum. The reduced effectiveness of large doses of erythromycin has important therapeutic implications.

Variability in absorption lag time of pyridoxal phosphate under fasting and pre- and post-meal conditions

Inter-individual variations in the absorption lag time of pyridoxal phosphate were determined after administration of an enteric-coated tablet (EC) or a plain capsule (PC) to 113 healthy volunteers under fasting, pre-meal, and post-meal conditions. The absorption lag time of pyridoxal phosphate was assessed from the urinary excretion of 4-pyridoxic acid after administration of EC and PC. Significantly larger lag times after administration of both formulations were observed under post-meal conditions than under pre-meal conditions (0.477 +/- 0.315 h versus 0.081 +/- 0.086 h for PC and 1.995 +/- 1.345 h versus 1.064 +/- 1.327 h for EC), indicating that the mean gastric emptying rates of both a solution and a tablet were delayed after food intake. The lag time for PC showed little inter-individual variation with (0-1.2 h) or without food (0-0.25 h), whereas that for EC showed markedly large inter-individual variation, from 0.25 to 2.63 h (median, 1.5 h) in the fasting condition, from 0.25 to > 5.5 h (median 0.25 h) under pre-meal conditions, and from 0.25 to > 5.5 h (median 1.25 h) under post-meal conditions. The effect of food on the gastric emptying rate of a solution appears to be almost uniform, whereas that for a tablet is so unpredictable that a reliable absorption rate for an enteric-coated tablet cannot be expected, particularly under pre- and post-meal conditions.

Localization of drug release sites from an oral sustained-release formulation of 5-ASA (Pentasa) in the gastrointestinal tract using gamma scintigraphy

Release of 5-ASA from a sustained release formulation (Pentasa, Ferring A/S, Copenhagen, Denmark) was monitored with plasma sampling for up to 24 hours in nine volunteers under both fasted and fed conditions. Drug absorption was correlated with location of the sustained-release microgranules in the gastrointestinal tract by gamma scintigraphy. Disintegration of the labeled tablet preparation occurred in the stomach within 20 minutes and acetylated 5-ASA was detectable in the plasma less than 60 minutes after ingestion. No significant differences were detected in either transit times through the small intestine, peak plasma acetylated 5-ASA concentration or lag time to absorption between fasted and fed individuals. Peak plasma concentration of acetylated 5-ASA usually occurred when the microgranules were present in the small intestine or ascending colon. The pharmacoscintigraphic study confirmed that 5-ASA release from the formulation occurred throughout the gastrointestinal tract, and that food effects on the in vivo behavior of the preparation were minimal.

An in vitro/in vivo correlation for the disintegration and onset of drug release from enteric-coated pellets

An empirical mass-transfer model for enteric-coating dissolution that uses in vivo dissolution data to characterize the pH-dependent solubility properties of the polymer film and a mass-transfer coefficient determined from in vivo dissolution or disintegration studies is developed. Once the in vivo mass-transfer coefficient has been evaluated, it can be used in conjunction with in vitro dissolution data from other formulations to predict the in vivo time to disintegration and onset of drug release. Results of in vitro dissolution experiments using the USP basket dissolution apparatus and in vivo disintegration experiments using gamma scintigraphy with four enteric-coated pellet formulations are presented. The good agreement among the in vivo mass-transfer coefficients that were determined supports the validity of the model.

Gamma scintigraphy in the evaluation of pharmaceutical dosage forms

Gamma-scintigraphy is applied extensively in the development and evaluation of pharmaceutical drug delivery systems. It is used particularly for monitoring formulations in the gastrointestinal and respiratory tracts. The radiolabelling is generally achieved by the incorporation of an appropriate technetium-99m or indium-111 labelled radiopharmaceutical into the formulation. In the case of complex dosage forms, such as enteric-coated tablets, labelling is best undertaken by the addition of a non-radioactive tracer such as samarium-152 oxide or erbium-170 oxide followed by neutron activation of the final product. Systems investigated include tablets and multiparticulates for oral administration, enemas and suppositories, metered dose inhalers and nebulisers, and nasal sprays and drops. Gamma-scintigraphy provides information on the deposition, dispersion and movement of the formulation. The combination of such studies with the assay of drug levels in blood or urine specimens, pharmacoscintigraphy, provides information concerning the sites of drug release and absorption. Data acquired from the scintigraphic evaluation of pharmaceutical dosage forms are now being used increasingly at all stages of product development, from the assessment of prototype delivery systems to supporting the product licence application.

In vivo evaluation of enteric-coated naproxen tablets using gamma scintigraphy

Seven healthy, male volunteers were entered into a randomized, open crossover study of the gastrointestinal transit of two enteric-coated 500-mg naproxen tablets. Two radiolabeled tablets were given to each volunteer on two occasions separated by 7 days, once in the fasted state and once after breakfast. Radiolabeling of tablets was achieved by the incorporation of samarium-152 oxide during manufacture, followed by neutron activation of the tablet to produce the gamma-emitting isotope samarium-153. No loss of tablet integrity was seen in the stomach and all tablets disintegrated in the small intestine. Onset of tablet disintegration was controlled predominantly by gastric emptying. Time in the small intestine prior to tablet disintegration was independent of food intake. Naproxen blood levels with time were consistent with the delayed release of naproxen from the tablets. Overall, transit, disintegration, and absorption were as expected from an enteric-coated tablet.