Gastrointestinal transit and disintegration of enteric coated magnetic tablets assessed by ac biosusceptometry

Dependence of Bioavailability on Mean Absorption Time: What Does It Tell Us?

The extent and rate of bioavailability are fundamental measures to characterize the pharmacokinetics of drugs after oral administration. Together with bioavailability (F), the mean absorption time (MAT) can be used to define the rate of bioavailability, i.e., the rate of drug absorption. Previous results suggest that F may depend on MAT. Estimates of F and MAT were obtained from the input function (sum of two inverse Gaussian functions) used to model the oral absorption process. The estimation was performed by population analysis (nonlinear mixed-effects modeling) based on data from bioavailability studies in healthy volunteers. For trospium and ketamine, F decreased significantly with increasing MAT, while for propiverine, a significant increase was observed. Thus, the interindividual variability in F could be largely attributed to the interindividual variability in MAT. For trospium and propiverine, the relative dispersion (normalized variance) of the absorption time distribution increased significantly with MAT. For trospium and propiverine, the plot of F versus MAT provides information about the effect of gastrointestinal transit on drug absorption. In contrast, an increase in hepatic extraction with increasing MAT is responsible for the dependence of F on MAT. The F versus MAT plot is suggested as a simple diagnostic tool in evaluating the results of bioavailability studies.

2D Quantitative Imaging of Magnetic Nanoparticles by an AC Biosusceptometry Based Scanning Approach and Inverse Problem

The use of magnetic nanoparticles (MNPs) in biomedical applications requires the quantitative knowledge of their quantitative distribution within the body. AC Biosusceptometry (ACB) is a biomagnetic technique recently employed to detect MNPs in vivo by measuring the MNPs response when exposed to an alternate magnetic field. The ACB technique presents some interesting characteristics: non-invasiveness, low operational cost, high portability, and no need for magnetic shielding. ACB conventional methods until now provided only qualitative information about the MNPs’ mapping in small animals. We present a theoretical model and experimentally demonstrate the feasibility of ACB reconstructing 2D quantitative images of MNPs’ distributions. We employed an ACB single-channel scanning approach, measuring at 361 sensor positions, to reconstruct MNPs’ spatial distributions. For this, we established a discrete forward problem and solved the ACB system’s inverse problem. Thus, we were able to determine the positions and quantities of MNPs in a field of view of 5×5×1 cm3 with good precision and accuracy. The results show the ACB system’s capabilities to reconstruct the quantitative spatial distribution of MNPs with a spatial resolution better than 1 cm, and a sensitivity of 1.17 mg of MNPs fixed in gypsum. These results show the system’s potential for biomedical application of MNPs in several studies, for example, electrochemical-functionalized MNPs for cancer cell targeting, quantitative sensing, and possibly in vivo imaging.

Pharmacomagnetography to evaluate the performance of magnetic enteric-coated tablets in the human gastrointestinal tract

A magnetic enteric-coated tablet containing diclofenac sodium was produced, and its performance under physiological and disturbed gastrointestinal motility was assessed through pharmacomagnetography analysis. In vitro studies were performed using conventional methods and in vivo studies were conducted on healthy volunteers before (control) and after domperidone administration. The magnetic tablet's gastrointestinal (GI) transit and disintegration process were monitored using the Alternating Current Biosusceptometry sensors combined with drug plasmatic concentration. The Gastric Residence Time, Colon Arrival Time, Small Bowel Transit Time, Disintegration Time and the pharmacokinetics parameters were calculated. The pH-dependent polymers used to coat the magnetic tablets were able to avoid the premature drug release on gastric or small intestine simulated medium. Gastric Residence Time was accelerated compared with the control group (p < 0.01). No significant differences were found regarding small bowel transit, colon arrival, disintegration process, or pharmacokinetics parameters. A strong correlation between magnetic monitoring and pharmacokinetics parameters analysis was determinant to evaluate the efficiency in the drug delivery at a specific site in the human gastrointestinal tract. In addition, a tablet with a damaged coating was used as a proof of concept to show the suitability of our methodology to evaluate the tablet. Our study showed that pharmacomagnetography is a multi-instrumental approach towards assessing drug delivery and bioavailability.

Gastro-retentive drug delivery systems: a recent update on clinical pertinence and drug delivery

Gastro-retentive drug delivery systems are some of the best technologies delivered through oral route. These mainly came into picture for their effective local action in the GI region, specifically for the drugs with narrow absorption window. In the recent decades, several technologies have evolved showing different mechanisms for retaining the drug in GI region for longer duration with increased bioavailability. Floatable, mucoadhesive, swelable, magnetic, nanofibrous, high-density, and expandable systems have been investigated extensively as the potential gastro-retentive strategies. The advances in the technologies studied, their clinical pertinence, and methods of drug delivery are described in this review with their immense future utilities. Their entry into the pharmaceutical market is a huge matter to look into as most of the studied strategies are facing problems and hence are underrated to overcome the clinical trials. Their success in the clinical trials are enormously required for gaining their access into the pharmaceutical market. Selection of the right technology for the right purpose through the right mechanism of action is to be done for obtaining the system with desired activity.

A Review of Disintegration Mechanisms and Measurement Techniques

Pharmaceutical solid dosage forms (tablets or capsules) are the predominant form to administer active pharmaceutical ingredients (APIs) to the patient. Tablets are typically powder compacts consisting of several different excipients in addition to the API. Excipients are added to a formulation in order to achieve the desired fill weight of a dosage form, to improve the processability or to affect the drug release behaviour in the body. These complex porous systems undergo different mechanisms when they come in contact with physiological fluids. The performance of a drug is primarily influenced by the disintegration and dissolution behaviour of the powder compact. The disintegration process is specifically critical for immediate-release dosage forms. Its mechanisms and the factors impacting disintegration are discussed and methods used to study the disintegration in-situ are presented. This review further summarises mathematical models used to simulate disintegration phenomena and to predict drug release kinetics.

Instrumentation of Flow-Through USP IV Dissolution Apparatus to Assess Poorly Soluble Basic Drug Products: a Technical Note

Supersaturation and precipitation are common limitations encountered especially with poorly soluble basic drugs. The aims of this work were to explore the pattern of dissolution and precipitation of poorly soluble basic drugs using a United States Pharmacopoeia (USP) IV dissolution apparatus and to compare it to the widely used USP II dissolution apparatus. In order to investigate the influence of gastric emptying time on bioavailability, tables of two model drugs (dipyridamole 100 mg and cinnarizine 15 mg) were investigated and pH change from 1.2 to 6.8 were achieved after 10, 20 or 30 min using USP II or USP IV dissolution apparatuses. Using USP II, dipyridamole and cinnarizine concentrations dropped instantly as a result of drug precipitation with drug crystals evident in the dissolution vessel. At pH change times of 10, 20 and 30 min, the total amount of dissolved drug was dependent on pH change time. Using USP IV, at a flow rate of 8 ml/min, it was possible to have comparable release to agitation at 50 rpm using USP II suggesting that comparable hydrodynamic forces are possible. No drop in drug percentage occurs as the dissolved fraction was readily emptied from the flow cell, preventing drug accumulation in the dissolution medium. However, a negligible percentage of drug release took place following pH change. In conclusion, the use of the flow-through cell dissolution provided laminar flow, use of realistic fluid volumes and avoided precipitation of dissolved drug fraction in the gastric phase as it is discharged before pH change.

Alternate current biosusceptometry for the assessment of gastric motility after proximal gastrectomy in rats: a feasibility study

BACKGROUND

This study proposes an experimental model to assess the consequences of gastric surgeries on gastric motility. We investigated the effects of proximal gastrectomy (PG) using a non-invasive technique (alternate current biosusceptometry [ACB]) on gastric contractility (GC), gastric emptying (GE), and orocecal transit (OCT) after the ingestion of liquids and solids in rats.

METHODS

Twenty-four male rats were subjected to gastric motility assessment before and after the PG procedure. The GE and OCT results are expressed as the mean time of gastric emptying (MGET) and cecum arrival (MCAT). The GC recordings are presented as the frequency and amplitude of contractions.

KEY RESULTS

Mean time of gastric emptying after solid meals were significantly different (p < 0.001) between control and PG (113 ± 5 to 99 ± 6 min). Mean time of cecum arrival ranged from 265 ± 9 to 223 ± 11 min (p < 0.001) and 164 ± 9 to 136 ± 17 min (p < 0.050) for solid and liquid meals, respectively. The assessment of GC showed that surgery decreased the phasic frequency (4.4 ± 0.4 to 3.0 ± 1.1 cpm, p < 0.050) and increased the amplitude of contractions (3.6 ± 2.7 to 7.2 ± 3.0 V/s, p < 0.050). No significant difference was found in tonic frequency.

CONCLUSIONS & INFERENCES

The ACB system was able to assess GE, OCT, and GC in gastrectomized rats. Overall, PG accelerated GE and gastrointestinal transit, likely due to the increase in both intragastric pressure and amplitude contraction. Our data presented an efficient model to investigate functional consequences from gastric surgeries that will allow further studies involving different procedures.

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.

A novel device with 36 channels for imaging and signal acquisition of the gastrointestinal tract based on AC biosusceptometry

The alternate current biosusceptometry (ACB) is a biomagnetic technique used to study some physiological parameters associated with gastrointestinal (GI) tract. For this purpose it applies an AC magnetic field and measures the response originating from magnetic marks or tracers. This paper presents an equipment based on the ACB which uses anisotropic magnetoresistive (AMR) sensors and an inexpensive electronic support. The ACB-AMR developed consists of a square array of 6×6 sensors arranged in a first-order gradiometer configuration with one reference sensor. The equipment was applied to capture magnetic images of different phantoms and to acquire gastric contraction activity of healthy rats. The results show a reasonable sensitivity and spatial-temporal resolution, so that it may be applied for imaging of phantoms and signal acquisition of the GI tract of small animals.

AC biosusceptometry technique to evaluate the gastrointestinal transit of pellets under influence of prandial state

Multiparticulate dosage forms have been proposed when distal regions of gastrointestinal tract are desirable as target of drugs. It is known that physiological parameters might interfere with the processes related to the drug delivery and absorption and therefore, it is essential to evaluate the behavior of such delivery systems in vivo. The aim of this study was to propose the AC Biosusceptometry technique as a noninvasive and radiation free device to evaluate the gastrointestinal transit of a magnetic multiparticulate dosage form in healthy volunteers under fasting and fed conditions. Magnetic pellets were prepared by the powder layering method of ferrite on nonpareils sugar beads and coated by using Eudragit. Our data showed that the AC Biosusceptometry technique was able to monitoring the gastrointestinal transit of pellets presenting similar profiles as demonstrated by standard techniques. Food intake has markedly influenced the gastric emptying as well as the colon arrival and the small intestine transit of magnetic pellets.

Pharmaceutical applications of AC biosusceptometry

AC Biosusceptometry offers an alternative to investigate noninvasively and without ionizing radiation the behavior of solid dosage forms in vitro and in the human gastrointestinal tract. This versatility allowed applying this technique in a wide field ranging from characterization of the disintegration process to elucidation of how the physiological parameters can interfere with pharmaceutical processes. It is increasingly important to understand how oral solid dosage forms behave in the human gastrointestinal tract. Once labelled, magnetic dosage forms provide an excellent opportunity to investigate complexes' interactions between dosage form and gastrointestinal physiology. In this paper, basic principles of this biomagnetic instrumentation and of the quantification based on magnetic images are reviewed. Also will be presented are some of the most recent applications of AC Biosusceptometry in the pharmaceutical research including oesophageal transit, gastric emptying and transit time of multiparticulate dosage forms, hydrophilic matrices and disintegration of tablets.

Magnetoresistive sensors in a new biomagnetic instrumentation for applications in gastroenterology

Anisotropic Magnetoresistive (AMR) sensors shows a new possibility to detect magnetic fields produced by magnetic particles present in the gastrointestinal (GI) tract. A system that uses excitation and detection of magnetic field was developed using AMR sensor. A magnetic flux concentrator was also studied to increase the sensitivity of AMR in this work.

A novel biomagnetic instrumentation with four magnetoresistive sensors to evaluate gastric motility

A novel instrumentation using anisotropic magnetoresistive (AMR) sensors associated with magnetic coils excitation was developed to evaluate gastrointestinal tract motility parameters. The susceptometer has four sensors that were used to measure the gastric activity contractions (GAC) in anaesthetized dogs, its performance was evaluated by manometry with good results.

A novel biomagnetic approach to study caecocolonic motility in humans

Motility patterns play a major role in human colonic functions; however, its physiological significance is poorly understood. Several studies have been introducing the Alternating Current Biosusceptometry (ACB) as a valuable tool in gastroenterology and pharmaceutical research. Using gold standard techniques, great effort has been made to validate ACB as a method for measuring gastrointestinal motility in humans and animals. The aim of this study was to evaluate caecocolonic motility and its response to a meal in healthy volunteers. The results showed a dominant frequency of 3.17 +/- 0.13 cycles per minute (mean +/- SD) that remained unchanged even after a standardized meal (P > 0.01). The colonic response to a meal was recorded as a considerable increase in amplitude, reflected by motility index (P < 0.01) and was observed for all the volunteers. The caecocolonic motility could be assessed by the ACB providing new insights into physiological patterns of motility. Moreover, the method is non-invasive, radiation-free, cost-effective and independent of bowel preparation.

Enteric Coated Magnetic HPMC Capsules Evaluated in Human Gastrointestinal Tract by AC Biosusceptometry

PURPOSE

To employ the AC Biosusceptometry (ACB) technique to evaluate in vitro and in vivo characteristics of enteric coated magnetic hydroxypropyl methylcellulose (HPMC) capsules and to image the disintegration process.

MATERIALS AND METHODS

HPMC capsules filled with ferrite (MnFe2O4) and coated with Eudragit were evaluated using USP XXII method and administered to fasted volunteers. Single and multisensor ACB systems were used to characterize the gastrointestinal (GI) motility and to determine gastric residence time (GRT), small intestinal transit time (SITT) and orocaecal transit time (OCTT). Mean disintegration time (t50) was quantified from 50% increase of pixels in the imaging area.

RESULTS

In vitro and in vivo performance of the magnetic HPMC capsules as well as the disintegration process were monitored using ACB systems. The mean disintegration time (t50) calculated for in vitro was 25+/-5 min and for in vivo was 13+/-5 min. In vivo also were determined mean values for GRT (55+/-19 min), SITT (185+/-82 min) and OCTT (240+/-88 min).

CONCLUSIONS

AC Biosusceptometry is a non-invasive technique originally proposed to monitoring pharmaceutical dosage forms orally administered and to image the disintegration process.