The influence of posture on the gastric emptying of antacids

Analyzing parametric influences driving age-associated changes in absorption using a PBPK-GSA approach

The advanced age population may be susceptible to an increased risk of adverse effects due to increased drug exposure after oral dosing. Factors such as high-interindividual variability and lack of data has led to poor characterization of absorption's role in pharmacokinetic changes in this population. Physiologically based pharmacokinetic (PBPK) models are increasingly being used during the drug development process, as their unique qualities are advantageous in atypical scenarios such as drug-drug interactions or special populations such as older people. Along with relying on various sources of data, auxiliary tools including parameter estimation and sensitivity analysis techniques are employed to support model development and other applications. However, sensitivity analyses have mostly been limited to localized techniques in the majority of reported PBPK models using them. This is disadvantageous, since local sensitivity analyses are unsuitable for risk analysis, which require assessment of parametric interactions and proper coverage of the input space to better estimate and subsequently mitigate the effects of the phenomenon of interest. For this reason, this study seeks to integrate a global sensitivity analysis screening method with PBPK models based in PK-Sim® to characterize the consequences of potential changes in absorption that are often associated with advanced age. The Elementary Effects (Morris) method and visualization of the results are implemented in R and three model drugs representing Biopharmaceutical Classification System classes I-III that are expected to exhibit some sensitivity to three age-associated hypotheses were successfully tested.

Integration of advanced methods and models to study drug absorption and related processes: An UNGAP perspective

This collection of contributions from the European Network on Understanding Gastrointestinal Absorption-related Processes (UNGAP) community assembly aims to provide information on some of the current and newer methods employed to study the behaviour of medicines. It is the product of interactions in the immediate pre-Covid period when UNGAP members were able to meet and set up workshops and to discuss progress across the disciplines. UNGAP activities are divided into work packages that cover special treatment populations, absorption processes in different regions of the gut, the development of advanced formulations and the integration of food and pharmaceutical scientists in the food-drug interface. This involves both new and established technical approaches in which we have attempted to define best practice and highlight areas where further research is needed. Over the last months we have been able to reflect on some of the key innovative approaches which we were tasked with mapping, including theoretical, in silico, in vitro, in vivo and ex vivo, preclinical and clinical approaches. This is the product of some of us in a snapshot of where UNGAP has travelled and what aspects of innovative technologies are important. It is not a comprehensive review of all methods used in research to study drug dissolution and absorption, but provides an ample panorama of current and advanced methods generally and potentially useful in this area. This collection starts from a consideration of advances in a priori approaches: an understanding of the molecular properties of the compound to predict biological characteristics relevant to absorption. The next four sections discuss a major activity in the UNGAP initiative, the pursuit of more representative conditions to study lumenal dissolution of drug formulations developed independently by academic teams. They are important because they illustrate examples of in vitro simulation systems that have begun to provide a useful understanding of formulation behaviour in the upper GI tract for industry. The Leuven team highlights the importance of the physiology of the digestive tract, as they describe the relevance of gastric and intestinal fluids on the behaviour of drugs along the tract. This provides the introduction to microdosing as an early tool to study drug disposition. Microdosing in oncology is starting to use gamma-emitting tracers, which provides a link through SPECT to the next section on nuclear medicine. The last two papers link the modelling approaches used by the pharmaceutical industry, in silico to Pop-PK linking to Darwich and Aarons, who provide discussion on pharmacometric modelling, completing the loop of molecule to man.

Development of a furosemide-containing expandable system for gastric retention

More than 50 years ago, the first gastroretentive dosage forms came up. Since then, no practical and at the same time reliable gastroretentive system is available on market. A major obstacle in the development of novel gastroretentive systems is the lack of proper predictive test methods. In the present work, we aimed at developing and fully characterizing an expandable gastroretentive system containing furosemide as model drug. On the one hand, we used well-established in vitro tests for drug dissolution and gastroretentive properties (paddle apparatus, swelling characteristics). On the other hand, we used two novel models (dissolution stress test device, mechanical antrum model) to assess these properties under biorelevant conditions. Moreover, we performed an in vivo study under fed and fasted conditions that combined blood sampling and a high-resolution imaging technique (magnetic marker monitoring) to determine gastrointestinal location with the assessment of a pharmacodynamic endpoint (urinary sodium excretion). In vitro dissolution tests confirmed prolonged drug release over more than 8 h independent from pH and with slight pressure sensitivity. Swelling studies indicated good swelling behavior within 4 h along with medium gastroretentive properties as determined with the mechanical antrum model. In vivo imaging showed prolonged gastric residence time after fed compared to fasted administration (481 min vs 38 min). Comparison of geometric means of AUC_o-tlast of the model drug confirmed this observation with 10 times higher value after fed administration. Urinary excretion of sodium well reflected the increased sodium-reuptake inhibition due to higher furosemide exposure under fed conditions. However, the poor performance after fasted intake of the system is in line with data from several other gastroretentive formulations. The present study highlighted the value of novel test methods during the development of gastroretentive formulations. Yet, a system with reproducible gastroretentive properties especially under fasted conditions has to be designed.

In Vitro and In Vivo Test Methods for the Evaluation of Gastroretentive Dosage Forms

More than 50 years ago, the first concepts for gastroretentive drug delivery systems were developed. Despite extensive research in this field, there is no single formulation concept for which reliable gastroretention has been demonstrated under different prandial conditions. Thus, gastroretention remains the holy grail of oral drug delivery. One of the major reasons for the various setbacks in this field is the lack of predictive in vitro and in vivo test methods used during preclinical development. In most cases, human gastrointestinal physiology is not properly considered, which leads to the application of inappropriate in vitro and animal models. Moreover, conditions in the stomach are often not fully understood. Important aspects such as the kinetics of fluid volumes, gastric pH or mechanical stresses have to be considered in a realistic manner, otherwise, the gastroretentive potential as well as drug release of novel formulations cannot be assessed correctly in preclinical studies. This review, therefore, highlights the most important aspects of human gastrointestinal physiology and discusses their potential implications for the evaluation of gastroretentive drug delivery systems.

The Effect of Omeprazole Pre-treatment on Rafts Formed by Reflux Suppressant Tablets Containing Alginate

Alginate-based reflux suppressant preparations provide symptom relief by forming a physical barrier on top of the stomach contents in the form of a neutral floating gel or raft. This study investigated whether reduced acidity in the stomach brought about by omeprazole pre-treatment affected the formation and gastric residence time of alginate rafts. It was a balanced, cross-over study in 12 healthy non-patient volunteers following a single dose of two indium-111-labelled alginate tablets in the presence or absence of 3 days' pre-treatment with omeprazole. Raft formation and gastric residence, in the presence of a technetium-99m-labelled meal, were assessed by gamma scintigraphy for 3 h after alginate tablet administration. The relative raft-forming ability of alginate tablets after omeprazole compared with alginate tablets alone was 0.950 with 95% confidence intervals of 0.882 and 1.018. Pre-treatment and co-administration with omeprazole has no significant effect on the raft-forming ability of alginate tablets.

Advances in gastro retentive drug-delivery systems

INTRODUCTION

In recent years, various technological improvements have been achieved and new concepts have been developed, in the area of controlled release solid oral dosage forms, especially for products where an extended time of release is associated with an extended gastric retention time. These Gastro Retentive Systems have been quite investigated because they can improve the in-vivo performance of many drugs.

AREAS COVERED

This paper summarizes current approaches in the research and development of gastro retentive dosage forms from recent literature. Apart from the numerous mechanisms of action involved, a short review of different key parameters is proposed, taking into account the stomach physiology. Most of the current technologies published, patented or marketed are presented. Promising drugs to develop in the near future are mentioned, and the importance of such systems in fixed Dose Combinations is also discussed. The importance of food effect is mentioned, and the impact of the multiple unit systems versus monolithic approach is discussed, especially regarding the dose intake.

EXPERT OPINION

In conclusion, numerous mechanisms like floating, sinking, effervescence, swelling, bioadhesion, magnetic, etc. have been proposed over the years. While most of the proposed systems show promising dissolution profiles and in-vitro retention, only few of them have also shown success in-vivo. Currently, the polymeric swelling monolithic systems are the most prominent marketed forms. The possibility to combine different mechanisms in order to ensure true gastric retention even in the fasted state should be further investigated.

Gastroretentive drug delivery systems

A controlled drug delivery system with prolonged residence time in the stomach is of particular interest for drugs that i) are locally active in the stomach, ii) have an absorption window in the stomach or in the upper small intestine, iii) are unstable in the intestinal or colonic environment, or iv) exhibit low solubility at high pH values. This article gives an overview of the parameters affecting gastric emptying in humans as well as on the main concepts used to design pharmaceutical dosage forms with prolonged gastric residence times. In particular, bioadhesive, size-increasing and floating drug delivery systems are presented and their major advantages and shortcomings are discussed. Both single- and multiple-unit dosage forms are reviewed and, if available, results from in vivo trials are reported.

Rapid onset of effect of sodium alginate on gastro-oesophageal reflux compared with ranitidine and omeprazole, and relationship between symptoms and reflux episodes

The objective of the open, randomised, four-period crossover study was to compare the time of onset of effect of sodium alginate (SA), omeprazole, ranitidine and control, based on oesophageal and intragastric pH and to determine any correlation between reflux symptoms and episodes in volunteers suffering from occasional gastro-oesophageal reflux. SA showed extensive prevention of acid exposure in the oesophagus compared with other treatments during the first hour. Overall, SA was more effective than control or omeprazole and comparable with ranitidine. There was little evidence of association between 'oesophageal' symptoms and reflux episodes, but associations between 'gastric' symptoms and acidity in the oesophagus, fundus and corpus were apparent. For an immediate reduction in gastro-oesophageal reflux into the oesophagus and gastric acidity during the first hour, SA was significantly superior to control, ranitidine and omeprazole. Ranitidine showed a superior effect from 2 h, consistent with its pharmacological mode of action.

The use of citric acid to prolong the in vivo gastro-retention of a floating dosage form in the fasted state

Gastro-retentive dosage forms have the potential to improve local therapy and decrease the variation in bioavailability that is observed with a number of commercially available immediate and modified release preparations. In this study, a dosage form has been developed, utilising freeze-dried calcium alginate beads, designed to float on the surface of the stomach contents thus prolonging the retention time. The aim of the study was to also assess the in vivo behaviour of the radio-labelled calcium alginate beads when they were administered under fasting conditions with either water or an aqueous solution of citric acid, a potential gut transit delaying substance. The study was performed in healthy male volunteers who swallowed the radio-labelled calcium alginate beads after a 10h overnight fast. Gamma scintigraphy was selected as the method to monitor the movement of the calcium alginate beads. The volunteers consumed no further food or drink until gastric emptying of the calcium alginate beads was complete. The results indicated that prolonged gastric retention was achieved when the dosage form was administered with the citric acid solution when compared to retention in the absence of citric acid. Citric acid, therefore, has the potential to delay the gastric emptying of the calcium alginate beads when administered to fasted volunteers.

Gastric emptying of two radiolabelled antacids with simultaneous monitoring of gastric pH

The aim of this study was to assess the gastric emptying rate of two antacids using an scintigraphic technique and simultaneous monitoring of gastric pH in 16 healthy male volunteers. Ten ml of Talcid (hydrotalcite 1 g) and Maalox (Mg-Al-hydroxide), with a similar neutralization capacity, were labelled with technetium-99m using a pyrophosphate bridge. Labelled antacids were given on separate days (within 2 weeks), 1 h after a standard meal. Intragastric pH was measured for at least 4 h, using ambulatory pH-metry with a dual-crystant antimony catheter. Continuous monitoring was started 1 h prior to the meal (baseline) and lasted 3 h (post-prandial, post-antacid and final periods). The antacid capacity of labelled and unlabelled antacids was similar. The mean percentages of antacids retained in the stomach fitted a linear model. The mean half-emptying time of Talcid was 63.9 +/- 27.9 min, while that of Maalox was 57.3 +/- 23.9 min (P = NS). The recordings of gastric pH (mean values of pH for each period) showed a similar profile for both antacids. The mean pH (Maalox vs Talcid) was 1.69 vs 2.07 in the baseline period, 1.95 vs 1.93 in the post-prandial period, 1.79 vs 1.15 in the post-antacid period (P = NS) and 0.4 vs 0.52 in the final period (P < 0.05 vs prior periods). In conclusion, the gastric emptying of Talcid and Maalox was similar and pH profiles were parallel and remained unchanged for the two antacids within the first hour of intake. A significant decrease in pH was observed 1 h after intake of the antacids, suggesting a possible rebound effect.

An investigation into the effect of cimetidine pre-treatment on raft formation of an anti-reflux agent

It is now becoming common practice to co-administer H2-receptor antagonists and anti-reflux agents in the treatment of reflux oesophagitis. The mechanism by which anti-reflux agents achieve flotation requires a small amount of gastric acid to be present in the stomach. This study investigated whether an anti-reflux agent would remain effective after the decrease in acid secretion produced by a typical clinical dosage regimen of cimetidine (400 mg q.d.s., 7 days). Gastric distribution and residence of a meal and an anti-reflux agent were assessed in 12 normal subjects using gamma scintigraphy. The area under the gastric and fundal emptying curves demonstrated that Liquid Gaviscon (sodium alginate compound) had a significantly greater gastric residence than the meal, both during the control period and after cimetidine pretreatment, and that the majority of the Gaviscon was located in the fundus. The distribution of Gaviscon into the fundus was not affected by cimetidine pretreatment. Cimetidine pre-treatment slightly, but not significantly, increased the time for half the meal and the Gaviscon to empty from the stomach. The results suggest that the mechanism of action of Liquid Gaviscon is not compromised by concurrent H2-antagonist therapy.

A comparison of gastro-oesophageal reflux in volunteers assessed by ambulatory pH and gamma monitoring after treatment with either Liquid Gaviscon or Algicon Suspension

This study was designed to compare the effectiveness of single doses of either Liquid Gaviscon or Algicon Suspension in the suppression of food and acid reflux into the oesophagus after a test meal in volunteers. After the pH electrode and gamma detector were positioned 5 cm above the cardia, the volunteers received a refluxogenic radiolabelled meal. The subjects then remained untreated, or thirty minutes later they were given a dose of unlabelled Algicon Suspension, or Liquid Gaviscon and a recording was made for a minimum of 3 hours. Allocation to the treatment group was randomized with the cross-overs performed 1 week apart. Liquid Gaviscon suppressed gastro-oesophageal reflux of both food and acid whereas only an insignificant reduction in reflux was seen after Algicon Suspension. The oesophageal pH remained below 4 for 3.21 +/- 0.92% (S.E.M.) of the recording period in the control study, 0.88 +/- 0.33 after Gaviscon and 2.91 +/- 0.68 after Algicon. The reflux of food was reduced from 17,070 x 10(3) +/- 4713 x 10(3) counts in the control study to 224 x 10(3) +/- 93 x 10(3) counts after the Gaviscon and 16,080 x 10(3) +/- 7131 x 10(3) counts after Algicon. The suppression of reflux by Liquid Gaviscon was significantly better than that produced by Algicon Suspension.

Effect of time of dosing relative to a meal on the raft formation of an anti-reflux agent

Gamma scintigraphy was used in twelve healthy volunteers to establish whether the time of dosing of Liquid Gaviscon relative to a meal influenced its therapeutic action. Indium-113m labelled Liquid Gaviscon was administered to fasted subjects, 30 min after a technetium-99m labelled meal or immediately before ingestion of the meal. The time for 50% of the Gaviscon to empty from the stomach was 0.36 +/- 0.13 h, 3.10 +/- 0.31 h and 0.68 +/- 0.04 h (s.e.m.), respectively. The preparation was found to empty rapidly from the fasted stomach and could not be floated on a meal consumed subsequently. For raft formation to occur, Liquid Gaviscon should be taken 30 min after a meal.

Drug delivery to the proximal colon

The transits of a capsule and a multiparticulate pellet system have been monitored through the gastrointestinal tract in six healthy volunteers. Both preparations moved together through the stomach and small intestine, reaching the colon, on average, 4 h after dosing. Within the colon the pellets dispersed and moved at a slower rate than the capsule. There was considerable intersubject variability in the large bowel transit times. The findings are discussed in terms of drug delivery to the colon.