Reinout C. A. Schellekens

Pulsatile drug delivery to ileo-colonic segments by structured incorporation of disintegrants in pH-responsive polymer coatings.

Conventional pH-responsive coatings used for oral drug delivery to the lower parts of the gastro-intestinal tract often show a poor performance. A new system for site-specific pulsatile delivery in the ileo-colonic regions is described. The system is based on the non-percolating incorporation of disintegrants in a coating which consists further of a continuous matrix of pH-responsive polymer (Eudragit S). Extensive in vitro release studies were performed in which coatings with different concentrations and disintegrants were studied and compared to non-disintegrant containing coatings. In vitro data show that the incorporation of swelling agents in an Eudragit S-coating still allows delayed release in the simulated terminal ileum. The pulse time and the robustness could be improved compared to conventional Eudragit S-coatings. The augmented pH-responsiveness of the new coating was related to the swelling index of the applied disintegrant. Based on the in vitro data comparing different swelling agents, Ac-di-sol appears to be the best performing swelling agent. A proof-of-concept study in human subjects was performed to investigate the performance of the new system in vivo. Coated capsules containing the stable isotope (13)C(6)-glucose as the test compound were administered and the occurrence of (13)CO(2) in the breath of the subjects was measured. It could be shown that the coating is able to resist the environmental conditions in the stomach and duodenum and delay release until deeper parts of the intestines are reached. Furthermore, the capsule is able to maintain a pulsatile release profile. It is concluded that the structured incorporation of swelling agents in pH-responsive polymers improves the delayed, pulsatile release kinetics of coated capsules. In a proof-of-concept in vivo study it was shown that the newly developed coating enables pulsatile delivery of the content to the lower parts of the intestines.

Applications of stable isotopes in clinical pharmacology

This review aims to present an overview of the application of stable isotope technology in clinical pharmacology. Three main categories of stable isotope technology can be distinguished in clinical pharmacology. Firstly, it is applied in the assessment of drug pharmacology to determine the pharmacokinetic profile or mode of action of a drug substance. Secondly, stable isotopes may be used for the assessment of drug products or drug delivery systems by determination of parameters such as the bioavailability or the release profile. Thirdly, patients may be assessed in relation to patient-specific drug treatment; this concept is often called personalized medicine. In this article, the application of stable isotope technology in the aforementioned three areas is reviewed, with emphasis on developments over the past 25 years. The applications are illustrated with examples from clinical studies in humans.

Oral ileocolonic drug delivery by the colopulse-system : A bioavailability study in healthy volunteers

The release profile of a novel oral ileocolonic drug delivery technology (ColoPulse-technology) was assessed by a combination of conventional kinetics of a marker substance in blood and site-specific signaling by stable isotope technology. Since ileocolonic delivery involves the drug release in a region in which bacteria are highly present, a prolonged lag time should coincide with proven bacterial enzyme activity. The latter can be tested using 13C-urea as the marker substance. The study was designed as a two period (uncoated versus coated capsule) crossover single dose bioavailability study in healthy subjects. The 13C-recovery data after oral administration of 13C-urea using the ColoPulse delivery system showed a delayed sigmoid release in all subjects with a lag time of > 3h (median: 330 min). Release was achieved in a urease-containing intestinal segment in all healthy subjects. Complete release in the ileocolonic region was achieved in 10 of 11 subjects. The ColoPulse-technology therefore enables specific and reliable drug delivery in the ileocolonic region in healthy volunteers.

Gastrointestinal pH and Transit Time Profiling in Healthy Volunteers Using the IntelliCap System Confirms Ileo-Colonic Release of ColoPulse Tablets

Introduction ColoPulse tablets are an innovative development in the field of oral dosage forms characterized by a distal ileum and colon-specific release. Previous studies in humans showed release in the ileo-colonic region, but the relationship between gastrointestinal pH and release was not experimentally proven in vivo. This information will complete the in vivo release-profile of ColoPulse tablets. Materials and Methods Release from ColoPulse tablets was studied in 16 healthy volunteers using the dual label isotope strategy. To determine gastrointestinal pH profiles and transit times the IntelliCap system was used. A ColoPulse tablet containing 13C-urea and an uncoated, immediate release tablet containing 15N2-urea were taken simultaneously followed by a standardized breakfast after three hours. Five minutes after intake of the tablets the IntelliCap capsule was swallowed and pH was measured until excretion in the feces. Breath and urine samples were collected for isotope analysis. Results Full analysis could be performed in 12 subjects. Median bioavailability of 13C -urea was 82% (95% CI 74–94%, range 61–114%). The median lag time (5% release of 13C) was 5:42 h (95% CI 5:18–6:18 h, range 2:36–6:36 h,) There was no statistically significant difference between lag time based on isotope signal and colon arrival time (CAT) based on pH (median 5:42 vs 5:31 h p = 0.903). In all subjects an intestinal pH value of 7.0 was reached before release of 13C from the ColoPulse tablet occurred. Discussion and Conclusions From the combined data from the IntelliCap system and the 13C -isotope signal it can be concluded that release from a ColoPulse tablet in vivo is not related to transit times but occurs in the ileo-colonic region after pH 7.0 is reached. This supports our earlier findings and confirms that the ColoPulse system is a promising delivery system for targeting the distal ileum and colon. Trial Registration ISRCTN Registry 18301880

Proof-of-concept study on the suitability of 13C-urea as a marker substance for assessment of in vivo behaviour of oral colon-targeted dosage forms

Background and purpose:  13C‐urea may be a suitable marker to assess the in vivo fate of colon‐targeted dosage forms given by mouth. We postulated that release in the colon (urease‐rich segment) of 13C‐urea from colon‐targeted capsules would lead to fermentation of 13C‐urea by bacterial ureases into 13CO2. Subsequent absorption into the blood and circulation would lead to detectable 13C (as 13CO2) in breath. If, however, release of 13C‐urea occurred in the small intestine (urease‐poor segment), we expected detectable 13C (as 13C‐urea) in blood but no breath 13C (as 13CO2). The differential kinetics of 13C‐urea could thus potentially describe both release kinetics and indicate the gastrointestinal segment of release.

Film coated tablets (ColoPulse technology) for targeted delivery in the lower intestinal tract: Influence of the core composition on release characteristics

The design of a film coating technology which allows a tablet to deliver the drug in the ileocolonic segment would offer new treatment possibilities. The objective is to develop a platform technology that is suitable for a broad range of drug compounds. We developed a coated tablet with a delayed, pulsatile release profile based on a pH-sensitive coating technology (ColoPulse). The production process was validated, and the effect of core composition on the in vitro release and water uptake investigated. The release profile of the standard tablet core composition, based on the use of cellulose as a filler, was independent of the coat thickness in a range of 9.0–13.2 mg/cm2. The release profile of a coated tablet was strongly influenced when cellulose was partly replaced by the model substance glucose (loss of sigmoidal release), citric acid (stabilization), sodium bicarbonate (destabilization) or sodium benzoate (destabilization). The film coating takes up water when below the pH-threshold. However, this did not cause early disintegration of the coating. The ColoPulse technology is successfully applied on tablets. The in vitro release characteristics of the coated tablets are influenced by the composition of the core.

Preparation and physicochemical evaluation of a new tacrolimus tablet formulation for sublingual administration.

The aim of this study was to develop a new fast-disintegrating tablet formulation containing 1 mg tacrolimus for sublingual application. First, solid dispersions containing tacrolimus (2.5%, 5% and 10% w/w) incorporated in Ac-Di-Sol® and carriers (inulin 1.8 kDa and 4 kDa, and polyvinylpyrrolidone (PVP) K30) were prepared by freeze drying. Subsequently, a tablet formulation composed of a mixture of the solid dispersions, Ac-Di-Sol®, mannitol, Avicel® PH-101 and sodium stearyl fumarate was optimized concerning drug load in the solid dispersions and the type of carrier. Tablet weight was kept constant at 75 mg by adjusting the amount of Avicel® PH-101. Differential scanning calorimetry (DSC) and X-ray powder diffraction (XRPD) results indicated the absence of the drug in the crystalline state, which was confirmed by the scanning electron microscopy (SEM). These results suggest that tacrolimus incorporated in all of the solid dispersions was fully amorphous. Dissolution of the tablets containing solid dispersions with a low drug load highly depends on the type of carrier and increased in the order: PVP K30 < inulin 4 kDa < inulin 1.8 kDa. Solid dispersions with a drug load of 10% w/w incorporated in the carriers yielded optimal formulations. In addition, the physicochemical characteristics and the dissolution behavior of the tablet formulation containing inulin 1.8 kDa-based solid dispersions with a drug load of 10% w/w did not change after storage at 20°C/45%RH for 6 months indicating excellent storage stability.

ColoPulse tablets perform comparably in healthy volunteers and Crohn's patients and show no influence of food and time of food intake on bioavailability

ColoPulse tablets are an innovative development in the field of oral drug delivery and are characterized by a colon-specific release. Until now ColoPulse dosage forms (only capsules) have been studied in healthy volunteers having a standardized breakfast three hours after administration but not in specific patient groups and not with a shorter interval between administration and breakfast. Information on bioavailability and release characteristics of ColoPulse tablets in Crohns patients and the influence of food and time of food intake is a prerequisite to properly design future clinical studies with active substances in these patients. In the current cross-over study bioavailability and drug release characteristics of ColoPulse tablets were compared in healthy volunteers and in Crohns patients in remission. Furthermore the influence of food and time of food intake on the in vivo drug release behavior of ColoPulse tablets was investigated. In this study the dual label isotope strategy was used which means that a ColoPulse tablet containing (13)C-urea and an uncoated, immediate release tablet containing (15)N2-urea were taken simultaneously. Breath and urine samples were collected during the test day for isotope analysis. The appearance of the stable isotopes in breath and/or urine provides information on the site of release from the dosage form, release characteristics and bioavailability. Both tablets were administered on two different days in a cross-over design: the first day with a breakfast (non-standardized) one hour after administration and the second day with a standardized breakfast three hours after administration of the tablets. There was no difference in instructions for administration between both days. Results of 16 healthy volunteers and 14 Crohns patients were evaluated. At least 86% (51 out of 59) of all ColoPulse tablets administered in this study released their contents at the desired intestinal region. There was no significant difference in bioavailability between healthy volunteers and Crohns patients on both days (day 1 75.8% vs 90.2%, p=0.070 and day 2 83.4% vs 91.4%, p=0.265). There was also no significant influence of food and time of food intake on bioavailability in healthy volunteers (75.8% and 83.4%, p=0.077) and in Crohns patients (90.2% and 91.4%, p=0.618) when day 1 and day 2 were compared. Release characteristics did not significantly differ between healthy volunteers and Crohns patients. However, food and time of food intake had some, clinically non-relevant, influence on the release characteristics within both groups which is in line with the fact that food affects gastro-intestinal transit times. This study shows that ColoPulse tablets enable the site-specific delivery of drugs or other compounds (e.g. diagnostics) deep in the ileo-colonic region of the intestine of Crohns patients in a comparable amount and rate as in healthy volunteers. Food and time of food intake had no relevant influence on bioavailability. In conclusion ColoPulse delivery systems are promising and deserve further research for local therapy with immunosuppressive drugs in Crohns patients in the near future.

Development and potential application of an oral ColoPulse infliximab tablet with colon specific release : A feasibility study

The monoclonal antibody infliximab is one of the cornerstones in the treatment of Crohns disease. Local delivery of infliximab would be an alternative to overcome the inherent disadvantages of intravenous therapy. For this purpose 5mg infliximab tablets were developed. To stabilize the antibody during production and storage it was incorporated in a sugar glass containing the oligosaccharide inulin. To obtain colon-specific release a ColoPulse coating was applied. The tablets were stored for 16 months under different conditions based on ICH climatic zone I.

Isotope-labelled urea to test colon drug delivery devices in vivo: principles, calculations and interpretations

This paper describes various methodological aspects that were encountered during the development of a system to monitor the in vivo behaviour of a newly developed colon delivery device that enables oral drug treatment of inflammatory bowel diseases. [13C]urea was chosen as the marker substance. Release of [13C]urea in the ileocolonic region is proven by the exhalation of 13CO2 in breath due to bacterial fermentation of [13C]urea. The 13CO2 exhalation kinetics allows the calculation of a lag time as marker for delay of release, a pulse time as marker for the speed of drug release and the fraction of the dose that is fermented. To determine the total bioavailability, also the fraction of the dose absorbed from the intestine must be quantified. Initially, this was done by calculating the time-dependent [13C]urea appearance in the body urea pool via measurement of 13C abundance and concentration of plasma urea. Thereafter, a new methodology was successfully developed to obtain the bioavailability data by measurement of the urinary excretion rate of [13C]urea. These techniques required two experimental days, one to test the coated device, another to test the uncoated device to obtain reference values for the situation that 100 % of [13C]urea is absorbed. This is hampered by large day-to-day variations in urea metabolism. Finally, a completely non-invasive, one-day test was worked out based on a dual isotope approach applying a simultaneous administration of [13C]urea in a coated device and [15N2]urea in an uncoated device. All aspects of isotope-related analytical methodologies and required calculation and correction systems are described.