Gastrointestinal transit of an enteric-coated delayed-release 5-aminosalicylic acid tablet

Budding Multi-matrix Technology-a Retrospective Approach, Deep Insights, and Future Perspectives

The human race is consistently striving for achieving good health and eliminate disease-causing factors. For the last few decades, scientists have been endeavoring to invent and innovate technologies that can substitute the conventional dosage forms and enable targeted and prolonged drug release at a particular site. The novel multi-matrix technology is a type of matrix formulation where the formulation is embraced to have a matrix system with multiple number of matrices. The MMX technology embraces with a combination of outer hydrophilic layer and amphiphilic/lipophilic core layer, within which drug is encapsulated followed by enteric coating for extended/targeted release at the required site. In comparison to conventional oral drug delivery systems and other drug delivery systems, multi-matrix (MMX) technology formulations afford many advantages. Additionally, it attributes for targeting strategy aimed at the colon and offers modified prolonged drug release. Thus, it has emerged rapidly as a potential alternative option in targeted oral drug delivery. However, the development of this MMX technology formulations is a exigent task and also has its own set of limitations. Due to its promising advantages and colon targeting strategy over the other colon targeted drug delivery systems, premier global companies are exploiting its potential. This article review deep insights into the formulation procedures, drug delivery mechanism, advantages, limitations, safety and efficacy studies of various marketed drug formulations of MMX technology including regulatory perspectives and future perspectives.

pH-dependent ileocolonic drug delivery, part I: in vitro and clinical evaluation of novel systems

After the pH dependency of novel pH-dependent ileocolonic drug delivery systems is confirmed in vitro, their performance should be evaluated in human volunteers.

Analysis of small intestinal transit and colon arrival times of non-disintegrating tablets administered in the fasted state

In this study individual data on tablet gastrointestinal transit times (i.e. gastric emptying, small intestinal transit, ileocecal junction residence, and colon arrival times) were obtained from literature in order to present and analyze their distributions and relationships. The influence of the time of food intake after tablet administration in fasted state on gastrointestinal transit times was additionally evaluated. There were 114 measurements from subjects who received the first meal at 4h after tablet administration. Approximately 32% of the tablets arrived into the colon before the meal intake at 4h. An evident increase in the frequency of colon arrival of tablets within 40min after the meal intake at 4h post-dose was observed, where approximately 39% of all tablets arrived into the colon. This is in accordance with findings described in literature where a meal ingested several hours post-dose accelerates tablet transit through the terminal ileum and shortens the transit through the small intestine. The median (min, max) of gastric emptying, small intestinal transit, and colon arrival times in the group where the first meal intake was at 4h post-dose is 35 (0,192), 215 (60,544), and 254 (117,604) minutes, respectively. The dependence of colon arrival times on gastric emptying times was described by the nonparametric regression curve, and compared with the presumed interval of colon arrival times, calculated by summation of observed gastric emptying times and frequently cited small intestinal transit time interval, i.e. 3-4h. For shorter gastric emptying times the trend of colon arrival times was within the presumed interval. At short gastric emptying times many observation points are also within the presumed interval since this interval coincides with short period after meal intake at 4h post-dose. Additionally, in numerous occasions relatively long ileocecal junction residence times were obtained, which may be important information from the point of view of drug absorption. The findings of gastrointestinal transit times are important and should be taken into consideration when predicting the in vivo performance of dosage forms after oral administration.

Absolute bioavailability and regional absorption of ticagrelor in healthy volunteers

Objective

Ticagrelor is a direct-acting, reversibly-binding, oral P2Y₁₂ receptor antagonist. It demonstrates predictable, linear pharmacokinetics. Two studies were undertaken to further elucidate the absolute bioavailability of ticagrelor and its regional absorption in the gastrointestinal (GI) tract.

Design and methods

In two open-label, randomized, cross-over studies, 12 volunteers received a single dose of ticagrelor: oral 90 mg and 15 mg IV (Study 1); or 100 mg oral suspension vs 100 mg immediate release (IR) tablet (Study 2). After the initial cross-over period in Study 2, patients received 100 mg suspension delivered to specific sites in the GI tract using an Enterion capsule. In both studies, plasma concentrations of ticagrelor and AR-C124910XX were measured following administration of each formulation.

Results

The mean absolute bioavailability of ticagrelor was 36% (95% confidence interval = 30–42%). Metabolite:parent ratios were higher after oral administration, compared with IV administration (maximum plasma concentration [C_max] = 0.356 and 0.037; area under the plasma concentration-time curves [AUC] = 0.530 and 0.173, respectively). Following oral administration of the 100 mg IR tablet, the AUC and C_max of ticagrelor were 78% and 58%, respectively, of those following oral administration of the 100 mg suspension. Exposure to ticagrelor decreased the further down the GI tract it was released: mean C_max for ticagrelor was 91%, 68%, and 13% that for the oral suspension when released in the proximal small bowel, distal small bowel and ascending colon, respectively; mean AUCs were 89%, 73%, and 32%, respectively.

Conclusion

The mean absolute bioavailability of ticagrelor was 36% and the proportion of ticagrelor absorbed decreased the further down the GI tract it was released: the mean AUC for ticagrelor was 89% (proximal small bowel), 73% (distal small bowel), and 32% (ascending colon) that of the mean AUC for the orally administered suspension.

Assessment of levetiracetam bioavailability from targeted sites in the human intestine using remotely activated capsules and gamma scintigraphy: Open-label, single-dose, randomized, four-way crossover study in healthy male volunteers

BACKGROUND

Levetiracetam is a broad-spectrum antiepileptic drug that binds to synaptic vesicle protein SV2A. Levetiracetam is indicated in the adjunctive treatment of partial-onset seizures, myoclonic seizures, and generalized tonic-clonic seizures. It is also approved in Europe as monotherapy for newly diagnosed partial-onset seizures. A Phase I clinical pharmacology trial was conducted during preregistration clinical development to better understand the regional gastrointestinal (GI) absorption of levetiracetam.

OBJECTIVE

This study evaluated the relative bioavailability of levetiracetam in various regions of the GI tract using a noninvasive, remote-controlled capsule device providing targeted drug delivery, relative to that after oral administration, and explored the drug's absorption characteristics in healthy volunteers.

METHODS

Pharmacokinetic data were obtained from healthy men aged 18 to 65 years in an open-label, single-dose, randomized, 4-way crossover study. Treatments included levetiracetam 250 mg administered as an immediate-release tablet and capsule delivery of 250 mg drug substance (levetiracetam powder without excipients) to the proximal small bowel, distal small bowel, and ascending colon. The location of the capsule in the GI tract was monitored using γ-scintigraphic imaging. Blood samples for plasma levetiracetam concentration were collected before dosing; at 10, 20, 30, and 45 minutes; and at 1, 1.5, 2, 3, 6, 9, 12, 16, 20, and 24 hours after tablet intake or after capsule activation. Pharmacokinetic parameters C(max), T(max), AUC₀₋(last), AUC₀₋(∞) and t(½) were calculated using noncompartmental methods. Tolerability was determined using clinical assessment, monitoring of vital signs, laboratory analysis, and interviews with the volunteers regarding adverse events.

RESULTS

Nine healthy men, 7 whites and 2 Asians, were enrolled (mean [SD] age, 31 [14] years; weight, 77 [5] kg; height, 176 [6] cm). Six volunteers completed all 4 treatments. Seven adverse events (headache [3], lethargy [2], tachycardia [1], and contusion [1]) were reported in 5 volunteers, but only 2 (headache and lethargy) were judged by the investigator to be possibly drug related. The geometric mean (%CV) AUC(0-last) values of levetiracetam delivered in the proximal small bowel, distal small bowel, ascending colon, and stomach (oral tablet) were 58.2 (9.3%), 59.6 (8.9%), 51.5 (12.0%), and 59.0 (7.4%) μg · h/mL, respectively. Values for bioavailability in the proximal small bowel, distal small bowel, and ascending colon relative to the tablet were 98.5% (95% CI, 89.7%-108.2%), 100.8% (95% CI, 91.4%-111.1%), and 87.1% (95% CI, 77.9%-97.5%).

CONCLUSION

After delivery in the proximal small bowel, distal small bowel, or ascending colon, the systemic bioavailability of levetiracetam (AUC), but not C(max) and T(max), appeared comparable to that after oral administration and thus appeared site independent in this small group of healthy fasting men.

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.

Colonic treatments and targets: issues and opportunities

The colon provides a plethora of therapeutic opportunities. There are multiple disease targets, drug molecules, and colon-specific delivery systems to be explored. Clinical studies highlight the potential for systemic delivery via the colon, and the emerging data on the levels of cell membrane transporters and metabolic enzymes along the gut could prove advantageous for this. Often efflux transporters and metabolic enzyme levels are lower in the colon, suggesting a potential for improved bioavailability of drug substrates at this site. The locoregional distribution of multiple metabolic enzymes (including cytochromes), efflux transporters (including P-glycoprotein and breast cancer resistance proteins), and influx transporters (including the solute carrier family) along the intestine is summarized. Local delivery to the colonic mucosa remains a valuable therapeutic option. New therapies that target inflammatory mediators could improve the treatment of inflammatory bowel disease, and old and new anticancer molecules could, when delivered topically, prove to be beneficial adjuncts to the current systemic or surgical treatments. New issues such as pharmacogenomics, chronotherapeutics, and the delivery of prebiotics and probiotics are also discussed in this review. Targeting drugs to the colon utilizes various strategies, each with their advantages and flaws. The most promising systems are considered in the light of the physiological data which influence their in vivo behavior.

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.

Release of 5-aminosalicylate from an MMX mesalamine tablet during transit through a simulated gastrointestinal tract system

5-Aminosalicylate (5-ASA; mesalamine) is the current first-line treatment for mild to moderate ulcerative colitis, a chronic inflammatory condition that most commonly affects the distal part of the colon. MMXtrade mark mesalamine (Lialdatrade mark [US]; Mezavanttrade mark XL [UK and Ireland]; Mezavanttrade mark [elsewhere]; Shire Pharmaceuticals Inc., Wayne, Pa, under license from Giuliani SpA, Milan, Italy) was created to be a novel, once-daily 5-ASA formulation. MMX mesalamine in tablet form has a pH-dependent, gastroresistant coating and is designed to delay the release of 5-ASA during transit through the upper gastrointestinal tract; it consists of hydrophilic and lipophilic excipients that are designed to prolong the release of 5-ASA throughout the colon. The release kinetics of 5-ASA from an MMX mesalamine tablet were assessed with the use of a dynamic in vitro gastrointestinal tract system (TNO GastroIntestinal Model) that simulates physiologic conditions in the adult human gastrointestinal tract under standardized fed and fasted conditions. This system incorporates removal of released drug via dialysis and automated sampling taken at various sections of the system. Less than 1% of 5-ASA was found to be released from the tablet in the simulated stomach and small intestine (before introduction into the simulated colon). Most of the 5-ASA within each tablet was released in the simulated colon (fasted state conditions: 78.0%; fed state conditions: 68.5%). Substantial quantities were released during the 8- to 18-hour sampling period (49.6 mg/h[fasted] and 40.7 mg/h [fed]). In conclusion, with the use of an in vitro system, the investigators showed that 5-ASA release from an MMX mesalamine tablet was delayed until the tablet reached the simulated colon. Throughout the simulated colon, release of 5-ASA from an MMX mesalamine tablet was prolonged.

In vivo drug release from hydrophilic dextran tablets capable of forming polyion complex

The aim of this comparative study was to investigate the in vivo drug release property of hydrophilic dextran tablets with or without swelling in the upper gastrointestinal tract (GIT) in humans. Two kinds of theophylline (TH) tablets were prepared by direct compression from a mixture of carboxymethyldextran and [2-(diethylamino)ethyl]dextran as a matrix capable of forming polyion complex (PIC-tablet), and a mixture of low and medium molecular weight hydroxypropylcellulose as a representative hydrophilic matrix (HPC-tablet). In these tablets, in vitro drug release behaviors and saliva TH level profiles after oral administration to humans were similar to each other, indicating equivalent AUC value. The tablets were then coated with Eudragit S100, enteric-coating polymer, by a dipping method in order to reveal drug release without full swelling in the upper GIT. Although the two enteric-coated tablets showed a similar in vitro release pattern, saliva level profiles were quite different as reflected in AUC values of 16.4 and 4.68 microg h/ml for enteric-coated PIC- and enteric-coated HPC-tablet, respectively. These results demonstrated that HPC-tablet could not release sufficiently without swelling in the upper GIT. In contrast, enteric-coated PIC-tablet showed an equivalent AUC value to PIC-tablet, indicating that TH was released well even in the lower GIT.

Gastrointestinal transit and release of 5-aminosalicylic acid from 153Sm-labelled mesalazine pellets vs. tablets in male healthy volunteers

BACKGROUND

Mesalazine (5-aminosalicylic acid)-containing formulations, designed to optimize drug delivery to the ileo-caecal region, represent a cornerstone in the treatment of inflammatory bowel diseases.

AIM

: To test, by means of pharmaco-scintigraphy, whether novel mesalazine-containing pellets release 5-aminosalicylic acid in the same target region as mesalazine tablets (Salofalk).

METHODS

Fourteen healthy male volunteers received a single dose of either pellets or tablets containing 500 mg of mesalazine and 2 mg of 152Sm2O3 with a 1-week washout period. The gastrointestinal transit of 153Sm, incorporated into the formulations, was followed by gamma-scintigraphy. Mesalazine release was verified by assessing 5-aminosalicylic acid plasma pharmacokinetics.

RESULTS

The formulations reached the ileo-caecal target region almost at the same time (3.3 +/- 1 and 3.8 +/- 1 h for pellets and tablets, respectively). Plasma 5-aminosalicylic acid tmax values were comparable and corresponded to the time during which the formulations were located in the target region. Plasma AUC values were significantly lower for pellets, which might be explained by a more prolonged release of 5-aminosalicylic acid.

CONCLUSIONS

Novel mesalazine pellets and Salofalk tablets release active 5-aminosalicylic acid in the same target region and pass through the gastrointestinal tract under fasting conditions in healthy volunteers in a comparable time. From a comparison of in vitro dissolution and plasma concentration data, a slower and more prolonged release of 5-aminosalicylic acid from pellets is suggested.

Bioequivalence testing for locally acting gastrointestinal products: what role for gamma scintigraphy?

Bioequivalence testing for locally acting gastrointestinal products is a challenging issue for both the pharmaceutical industry and the global regulatory authorities. It is widely accepted that for medicinal products not intended to be delivered into the systemic circulation, pharmacokinetic bioavailability cannot be used. However, it is becoming increasingly accepted that local availability may be assessed, where appropriate, by approaches that qualitatively reflect the presence of the active substance at the site of action. These methods must be specifically chosen for that combination of active substance and route of drug delivery. This paper argues for the use of gamma scintigraphy as a validated measure of local availability and bioequivalence for topically acting products administered to the gastrointestinal tract by the oral and rectal route.

Enteric coated HPMC capsules designed to achieve intestinal targeting

The enteric coating of HPMC capsules containing paracetamol was investigated. Two enteric polymers, Eudragit L 30 D-55 and Eudragit FS 30 D were studied, which are designed to achieve enteric properties and colonic release, respectively. The capsules were coated in an Accela Cota 10, and, as shown by optical microscopy, resulted in capsules with a uniform coating. Scanning electron microscopy of the surface of the capsules illustrate that, in contrast to gelatin, HPMC has a rough surface, which provides for good adhesion to the coating. Dissolution studies demonstrated that capsules coated with Eudragit L 30 D-55 were gastro resistant for 2 h at pH 1.2 and capsules coated with Eudragit FS 30 D were resistant for a further 1 h at pH 6.8. The product visualisation technique of gamma scintigraphy was used to establish the in vivo disintegration properties of capsules coated with 8 mg cm(-2) Eudragit L 30 D-55 and 6 mg cm(-2) Eudragit FS 30 D. For HPMC units coated with Eudragit L 30 D-55, complete disintegration occurred predominately in the small bowel in an average time of 2.4 h post dose. For HPMC capsules coated with Eudragit FS 30 D, complete disintegration did not occur until the distal small intestine and proximal colon in an average time of 6.9 h post dose.

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).

Delivery systems for penetration enhancement of peptide and protein drugs: design considerations

This paper discusses the challenges to be met in designing delivery systems that maximize the absorption of peptide and protein drugs from the gastrointestinal and respiratory tracts. The ideal delivery system for either route of administration is one that will release its contents only at a favorable region of absorption, where the delivery system attaches by virtue of specific interaction with surface determinants unique to that region and where the delivery system travels at a rate independent of the transitory constraints inherent of the route of administration. Such a delivery system, which is as yet unavailable, will benefit not only peptide and protein drugs, but other poorly absorbed drugs.

[Pharmacokinetic data for different 5-aminosalicylic acid and budesonide preparations]

Different orally and rectally applicable forms of 5-ASA and budesonide have been developed to achieve sufficient high concentrations of the active moieties at the site of inflammation (small and/or large bowel) and to limit the systemic action of the drugs. This concept of drug targeting could be accomplished by both special galenic formulations and by utilizing the pharmacokinetic properties of the agents especially their high intestinal and hepatic presystemic elimination. Thus, 5-ASA and budesonide represent drugs of first choice in the treatment of Crohn's disease and ulcerative colitis. This review describes the various pharmacokinetic and (patho)physiologic factors and their impact on drug delivery and biological availability of the different 5-ASA and budesonide preparations.

Review article: Targeted drug delivery in treatment of intestinal diseases

Topical therapy within the treatment of intestinal diseases presents realistic formulation challenges for targeted drug delivery. Some relevant oral formulation concepts are reviewed. The basic principles employed are based mainly on differences in pH and metabolic activity between the different parts of the gastrointestinal tract. A successful example of targeted drug delivery within the treatment of Crohn's disease is presented. Topical therapy for the treatment of ulcerative colitis is also discussed. Physiological variations and influence of the disease and disease status present major challenges when deciding upon a suitable formulation principle.

Delivery and fate of oral mesalamine microgranules within the human small intestine

BACKGROUND/AIMS

Oral use of mesalamine in inflammatory bowel disease requires slow-release preparations to prevent premature absorption and inactivation. Resulting luminal concentrations within the human small intestine are unknown. The aim of this study was to determine human intestinal delivery patterns of mesalamine from a microgranule preparation (Pentasa; Ferring Arzeimittel, Kiel, Germany) effective in Crohn's disease with small bowel involvement.

METHODS

A multilumen tube for duodenal, jejunal, and ileal aspiration and marker perfusion was placed in 6 normal subjects. Levels of luminal, plasma, and urinary mesalamine and its main metabolite, acetyl mesalamine, were measured for 7 hours after ingestion of mesalamine (500 mg) with a labeled meal.

RESULTS

Gastric emptying of mesalamine paralleled the meal, and its release occurred throughout the small intestine (cumulative, 20% of dose). For 4 hours, mean luminal mesalamine and acetyl mesalamine concentrations were 52 and 38 micrograms/mL (duodenum), 59 and 82 micrograms/mL (jejunum), and 64 and 104 micrograms/mL (ileum). Cumulative colonic delivery was 82% (7% dissolved, 75% in microgranules), and urinary excretion was 3.5%.

CONCLUSIONS

Although the major part of continuous-release mesalamine is delivered to the colon, large proportions are liberated and available at high concentrations within the small intestinal lumen, thus explaining its therapeutic efficacy in small intestinal Crohn's disease.

Colonic spreading of a non-chlorofluorocarbon mesalazine rectal foam enema in patients with quiescent ulcerative colitis

BACKGROUND

Rectal foam enemas provide for drug delivery to the distal colon for treatment of left sided ulcerative colitis. However, currently available formulations contain chlorofluorocarbons which are due to be phased out in the near future. The objective of this study was therefore to determine the degree of dispersion of a newly developed non-chlorofluorocarbon rectal foam preparation in ulcerative colitis patients.

METHODS

This was an open label non-controlled study of a single administration of a mesalazine foam enema (two actuations containing 2 g of mesalazine in approximately 120 mL foam) in 10 patients with quiescent ulcerative colitis. Spreading of the 99mTc-labelled foam enema was assessed over a 4-h period by the non-invasive technique of gamma scintigraphy.

RESULTS

All patients retained the enema for the full 4-h imaging period. In nine out of the 10 patients, the enema was observed to spread as far as the descending colon and on average 23% of the dose was present in the descending colon at 4 h post-dose.

CONCLUSIONS

The extent of spreading observed in the study supports the use of the formulation in the treatment of left sided ulcerative colitis.

Targeting of drugs and vaccines to the gut

Targeted delivery to the gastrointestinal tract requires a multi-disciplinary approach to research involving contributions from polymer and material scientists, gastroenterologists, pharmaceutical scientists and technologists. Intestinal delivery is important not only for drugs that act locally, but also for those with systemic activity. In particular, there is considerable interest in the oral delivery of peptides and it is felt that the colon may provide an advantageous absorption site for such molecules. The different targeting mechanisms available to the pharmaceutical scientist to provide site-specific delivery in the gastrointestinal tract will be critically assessed. Delivery systems and targeting agents, which are being developed for the delivery of drugs, may also be exploited for the delivery of vaccines, since many of the delivery problems are common to both areas. Recent developments in the design of oral antigen formulations will be discussed in this review.

Targeting drugs to the colon: delivery systems for oral administration

The oral delivery of drugs to the colon has applications in a variety of therapeutic areas. This review is concerned with the approaches taken to achieve a universal system for delivery. The design of such a system requires the identification and exploitation of a unique feature of the colonic environment. The use of transit times, pH and bacterial enzymes are critically assessed. In addition, the system must provide protection for the drug during transit to the colon. Upper gastro-intestinal physiology and the transit of pharmaceuticals through these regions are reviewed with reference to their relevance in achieving site specificity.

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.

Prandial and diurnal effects on the absorption of orally administered enteric coated 5-aminosalicylic acid (5-ASA)

Plasma and urine concentrations of 5-ASA and its N-acetyl metabolite 5-AcASA were measured over 48 h in 12 young healthy male subjects, who received three doses of three times enteric coated 500 mg 5-ASA tablets at 7 h interval, on two occasions 14 days apart. On one occasion the doses were given after standard meals; on the other occasion, they were given 1 h before meals. Administration of the tablets after meals delayed systemic drug absorption but did not affect the extent of absorption. There was a sharp rise in the plasma concentrations of 5-ASA and 5-AcASA in the early morning (i.e. circa 24 h after administration of the 1st dose) independent of when the tablets were taken with respect to the meals. This suggests that tablets or tablet fragments remained in the stomach until the later part of the night. Thus, diurnal effects may be more important than prandial effects in the evaluation of the kinetics of 5-ASA and its metabolites after peroral administration of enteric coated tablets.

Steady-state pharmacokinetics of enteric coated 5-amino-salicylic acid tablets in healthy volunteers and in patients with Crohn's disease or ulcerative colitis

An Eudragit-L coated oral 5-aminosalicylic acid (5-ASA; mesalazine) product (Mesasal), has been formulated to deliver 5-ASA to the distal small bowel and colon for the treatment of inflammatory bowel disease. The purpose of this study was to compare the pharmacokinetic profile of this product at steady-state between healthy volunteers and two different patient groups with inflammation of either the small or the large bowel. Two carefully selected groups of patients, nine with Crohn's disease restricted to the small intestine and ten with total ulcerative colitis and one group of ten healthy volunteers received two 250 mg Mesasal tablets three times daily for 10 days to reach steady-state. Plasma 5-ASA and acetyl-5-ASA concentrations were followed for 48 h and urinary excretion for 72 h. There was a great variation in most pharmacokinetic parameters within each group and no significant differences were noticed between the groups. The location of the inflammatory process probably does not influence the pharmacokinetics of 5-ASA in any significant way in patients with either Crohn's disease in the small bowel or total ulcerative colitis.

Evaluation of an enteric-coated naproxen pellet formulation

An enteric-coated, pellet formulation of naproxen has been evaluated in eight healthy subjects. Each volunteer was dosed with 153Sm-labelled, enteric-coated pellets on two occasions, once whilst fasted and once after breakfast. Gastrointestinal transit was followed using gamma scintigraphy and drug absorption compared with that from uncoated naproxen pellets dosed on a separate occasion. The pH in the stomach and intestines was monitored using radiotelemetry capsules. Gastric emptying was delayed by dosing after breakfast, but small intestinal transit of the enteric-coated formulation was the same on both occasions. The highest pH recorded from the stomach was 4.0 and in all subjects the pH rose to at least 7.3 in the small intestine. The onset of drug absorption was fastest from the uncoated formulation and slowest from the coated pellets taken after breakfast. The total amount of drug absorbed was the same on all three occasions.

Gastric emptying of indigestible tablets in relation to composition and time of ingestion of meals studied by metal detector

Enteric-coated tablets leave the stomach mainly during the interdigestive phase. Composition as well as time of ingestion of meals may influence their gastric emptying considerably. In 12 normal volunteers gastric emptying of a plastic tablet with a metal core was followed by a metal detector in relation to different compositions and various times of ingestion of meals. With an empty stomach and after ingestion of 250 ml water, the mean time for gastric emptying of the tablet was 38 +/- 11 min (mean +/- SEM) and 38 +/- 8 min. Two hundred fifty milliliters of milk (652 kJ) and a formula diet (1000 kJ) delayed gastric emptying time to 128 +/- 14 and 152 +/- 6 min, respectively (P less than 0.05). Breakfast (2200 kJ) further retarded gastric emptying compared with both liquids to 249 +/- 24 min (P less than 0.05). There was a close correlation between nutritive density and gastric emptying of the tablet (r = 0.92; P less than 0.001). Main meals also delayed gastric emptying of tablets when compared to empty stomach (P less than 0.05). A snack after breakfast further delayed gastric emptying from 201 +/- 10 to 278 +/- 19 min (P less than 0.05). The largest delay was observed following ingestion of breakfast, lunch, dinner, and additional snacks (509 +/- 220 min). We conclude that the delay of gastric emptying of enteric-coated tablets by food is related to its nutritive density and eating habits. The gastric emptying of an enteric coated tablet that is ingested early in the morning may be delayed until late at night when several meals and snacks are ingested during the day, leading to unwanted alterations in bioavailability and to possible adverse effects.

Pharmacokinetics of a 5-aminosalicylic acid enteric-coated tablet in patients with Crohn's disease or ulcerative colitis and in healthy volunteers

An Eudragit-L coated oral 5-aminosalicylic acid (5-ASA; mesalazine) product (Mesasal), has been formulated to deliver 5-ASA to the distal small bowel and colon for the treatment of inflammatory bowel disease. The purpose of this study was to compare the pharmacokinetic profile of this drug between two patient groups, with either inflamed small or large bowel and with volunteers. Two carefully selected patient groups (one with nine patients suffering from Crohn's disease restricted to the small intestine, and one with ten patients suffering from total ulcerative colitis) and a group of ten volunteers received two 250 mg Mesasal tablets in the morning, on a fasting stomach. Plasma 5-ASA and acetyl-5-ASA concentrations were followed for 48 h, and urine and faecal excretion for 72 h. There was a great variation in most pharmacokinetic parameters within each group. Numerically, however, the data suggests a somewhat higher systemic absorption in patients with Crohn's disease than in healthy volunteers or patients with ulcerative colitis. The location of the inflammatory process might have some influence on the pharmacokinetics of 5-ASA in inflammatory bowel disease.

Absorption of oral mesalazine-containing preparations and the influence of famotidine on the absorption

The mesalazine-containing preparations Asacol, Pentasa, and Salofalk (=Claversal) are frequently used in the treatment of inflammatory bowel disease. The release patterns of these formulations are time- and/or pH-dependent. The aim of this study was to investigate the patterns of absorption of these preparations and the influence of raised intragastric pH on absorption. Gastric pH was raised by simultaneous administration of famotidine. Absorption was determined by assaying with a high-performance liquid chromatography method the urinary excretion of acetylmesalazine, the major metabolite of mesalazine. A large intra- and inter-individual variability in absorption was found for all three formulations, both with and without concomitant famotidine administration. Asacol and Pentasa were significantly less absorbed than Salofalk. A significant lower absorption of mesalazine was seen when Asacol was combined with famotidine. Variations in gastric pH have negligible effect on the bioavailability of mesalazine in vivo.

Gastrointestinal transit and release of mesalazine tablets in patients with inflammatory bowel disease

Gastrointestinal transit and release of a delayed-release, enteric-coated tablet of mesalazine (Claversal) were studied in 13 patients with Crohn's disease and ulcerative colitis. The tablets disintegrated a mean of 3.2 h after leaving the stomach, resulting in drug dispersion in the distal small intestine or proximal colon. Tablet disintegration closely correlated with onset of drug absorption. Peak mean concentrations of mesalazine and its main metabolite, Ac-5-ASA, were 0.5 microgram/ml and 1.0 microgram/ml, respectively, and occurred 3 to 4 h after gastric emptying. The plasma levels correlated with scintigraph images of tablet disintegration. It is concluded that the tablets effectively deliver mesalazine to the terminal ileum and proximal colon in patients with inflammatory bowel disease.

Pharmacokinetics of a 5-aminosalicylic acid enteric-coated tablet and suppository dosage form

An Eudragit-L coated oral 5-aminosalicylic acid (5-ASA; mesalazine) product (Mesasal), has been formulated to deliver 5-ASA to the distal small intestine and colon for the treatment of inflammatory bowel disease. The purpose of this study was to compare the pharmacokinetic profile of this product to sulphasalazine (SASP; Salazopyrin) and to assess the pharmacokinetics of a suppository 5-ASA dosage form. Twelve healthy volunteers randomly received four single doses of 5-ASA delivering formulations not less than 1 week apart. (a) Mesasal tablets, 2 x 250 mg, fasting; (b) Mesasal tablets, 2 x 250 mg, fed; (c) Salazopyrin tablets, 3 x 500 mg (corresponding to 576 mg 5-ASA), fasting; and (d) Mesasal suppository, 1 x 500 mg, fasting. Plasma 5-ASA and acetyl-5-ASA (Ac-5-ASA) concentrations were followed for 48 h and urine and faecal concentrations for 72 h. Mesasal tablets (fasting) produced a greater area under the concentration-time curve (AUC), peak and time to peak for both plasma 5-ASA and Ac-5-ASA than Salazopyrin. Median urinary recovery values were 21.7% for Salazopyrin and 35.5% for Mesasal (fasting) (P less than 0.01). This means that the systemic absorption was higher after Mesasal than after Salazopyrin. The total faecal recovery values were 38.3 and 26.5%, respectively (NS). Except for a delay of 1.5-.3 h in the time to peak of 5-ASA and Ac-5-ASA plasma levels, the pharmacokinetics of Mesasal tablets were essentially the same in fasting or fed subjects. Suppository administration of 5-ASA resulted in a low median urinary recovery of 10.8%.

The effect of capsule size and density on transit through the proximal colon

Colonic transit of radiolabelled capsules has been monitored in 18 healthy subjects using gamma scintigraphy. The capsules ranged in volume from 0.3-1.8 cm3 and in density from 0.7-1.5 gcm-3. The capsules were administered after an overnight fast and entered the colon, on average, 5 h after dosing. Transit rates through the proximal colon were independent of capsule density. Any effect due to capsule volume was small when compared with intersubject variations in transit rates. Within 10 h of entering the colon 80% of the units had reached the splenic flexure. These findings have implications in the design of non-disintegrating, sustained release dosage forms.