The influence of food on the gastric emptying of multiparticulate dosage forms

On the processes limiting oral drug absorption when amorphous solid dispersions are administered after a high-calorie, high-fat meal: Sporanox® pellets

OBJECTIVES

1) Identify processes limiting the arrival of itraconazole at the intestinal epithelium when Sporanox® amorphous solid dispersion (ASD) pellets are transferred from the stomach through the upper small intestine, after a high-calorie, high-fat meal. 2) Evaluate whether itraconazole concentrations in the colloidal phase of aqueous contents of the upper small intestine are useful for the assessment of dose effects in the fed state and food effects on plasma levels.

METHODS

Itraconazole concentrations, apparent viscosity, and solubilization capacity were measured in aspirates from the upper gastrointestinal lumen collected during a recently performed clinical study in healthy adults. Published itraconazole concentrations in plasma, after a high-calorie high-fat meal and Sporanox® ASD pellets, and in contents of the upper small intestine of healthy adults, after administration of Sporanox® ASD pellets in the fasted state, were used to achieve the second objective.

RESULTS

When Sporanox® ASD pellets (up to 200 mg) are transferred from the stomach through the upper small intestine, after a high-calorie, high-fat meal, itraconazole concentrations in the colloidal phase or the micellar phase of aqueous contents of the upper small intestine are unsaturated, in most cases. During the first 3 h post-dosing after a high-calorie, high-fat meal, the impact of dose (200 mg vs. 100 mg) on itraconazole concentrations in the colloidal phase of aqueous contents of the upper small intestine seems to underestimate the impact of dose on plasma levels. When Sporanox® ASD pellets are administered after a high-calorie, high-fat meal at the 200 mg dose level, itraconazole concentrations in the colloidal phase of aqueous contents of the upper small intestine are, on average, lower than those achieved in fasted state.

CONCLUSIONS

When Sporanox® ASD pellets are transferred from the stomach to the upper small intestine after a high-calorie, high-fat meal, itraconazole's arrival at the intestinal epithelium seems to be limited by its arrival at the colloidal phase of aqueous contents of the upper small intestine. The impact of dose (100 mg vs. 200 mg) on plasma levels after a high-calorie, high-fat meal and during the gastrointestinal transfer of Sporanox® pellets requires consideration of pre-systemic itraconazole metabolism. At the 200 mg dose level, after taking into consideration differences in the volume of the contents of the upper small intestine between the fasted and the fed state during the gastrointestinal transfer of Sporanox® ASD pellets, itraconazole concentrations in the colloidal phase of aqueous contents of the upper small intestine suggest a mild negative food effect on average plasma levels; published clinical data are inconclusive.

Understanding the Conditions Under Which Drugs are Transferred from the Stomach Through the Upper Small Intestine After a High-Calorie, High-Fat Meal

Information on the conditions under which drugs are transferred from the stomach through the upper small intestine after a high-calorie, high-fat meal is very limited. To simulate the drug presence after disintegration and arrival in the antral region, paracetamol solution and Sporanox® amorphous solid dispersion pellets at two dose levels were administered to the antrum of 8 healthy adults 30 min after administration of a high-calorie, high-fat meal on a crossover basis. The overall median buffer capacity of antral contents was estimated to be 18.0 and 24.0 mmol/ml/ΔpH when titrating with NaOH and HCl, respectively. The corresponding values for the contents of upper the small intestine were 14.0 and 16.8 mmol/ml/ΔpH, respectively. The drug transfer process from the antrum through the upper small intestine occurred with apparent first-order kinetics. The best estimate for the antral emptying half-life was 39min and 45min for paracetamol and itraconazole, respectively, the apparent volume of contents of the upper small intestine was more than double compared with previously reported values in the fasted state, the half-life of drug elimination from the upper small intestine was similar to recent estimates for highly permeable drugs in the fasted state, and the apparent volume of antral contents during the first couple of hours post drug administration was 303mL. Information collected in this study could increase the reliability of in silico and/or in vitro modelling approaches applied in clinical drug development.

Physiological Considerations and In Vitro Strategies for Evaluating the Influence of Food on Drug Release from Extended-Release Formulations

Food effects on oral drug bioavailability are a consequence of the complex interplay between drug, formulation and human gastrointestinal (GI) physiology. Accordingly, the prediction of the direction and the extent of food effects is often difficult. With respect to novel formulations, biorelevant in vitro methods can be extremely powerful tools to simulate the effect of food-induced changes on the physiological GI conditions on drug release and absorption. However, the selection of suitable in vitro methods should be based on a thorough understanding not only of human GI physiology but also of the drug and formulation properties. This review focuses on in vitro methods that can be applied to evaluate the effect of food intake on drug release from extended release (ER) products during preclinical formulation development. With the aid of different examples, it will be demonstrated that the combined and targeted use of various biorelevant in vitro methods can be extremely useful for understanding drug release from ER products in the fed state and to be able to forecast formulation-associated risks such as dose dumping in early stages of formulation development.

The gut in the beaker: Missing the surfactants?

Gastrointestinal drug administration is the preferred route for the majority of drugs however, the natural physiology and physicochemistry of the gastrointestinal tract is critical to absorption but complex and influenced by factors such as diet or disease. The pharmaceutical sciences drive for product consistency has led to the development of in vitro product performance tests whose utility and interpretation is hindered by the complexity, variability and a lack of understanding. This article explores some of these issues with respect to the drug, formulation and the presence of surfactant excipients and how these interact with the natural bile salt surfactants. Interactions start in the mouth and during swallowing but the stomach and small intestine present the major challenges related to drug dissolution, solubility, the impact of surfactants and supersaturation along with precipitation. The behaviour of lipid based formulations and the influence of surfactant excipients is explored along with the difficulties of translating in vitro results to in vivo performance. Possible future research areas are highlighted with the conclusion that, "a great deal of work using modern methods is still required to clarify the situation".

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

Decades of research in drug targeting to the upper gastrointestinal tract using gastroretention technologies: where do we stand?

A major constraint in oral controlled release drug delivery is that not all the drug candidates are absorbed uniformly throughout the gastrointestinal tract (GIT). Drugs having "absorption window" are absorbed in a particular portion of GIT only or are absorbed to a different extent in various segments of the GIT. Thus, only the drug released in the region preceding and in close vicinity to the absorption window is available for absorption. The drug must be released from the dosage form in solution form; otherwise, it is generally not absorbed. Hence, much research has been dedicated to the development of gastroretentive drug delivery systems that may optimize the bioavailability and subsequent therapeutic efficacy of such drugs, as these systems have unique properties to bypass the gastric emptying process. These systems show excellent in vitro results but fail to give desirable in vivo performance. During the last 2-3 decades, researchers from the academia and industries are giving considerable importance in this field. Unfortunately, till date, few so-called gastroretentive dosage forms have been brought to the market in spite of numerous academic publications. The manuscript considers strategies that are commonly used in the development of gastroretentive drug delivery systems with a special attention on various parameters, which needs to be monitored during formulation development.

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.

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.

Gastric emptying of multi-particulate dosage forms

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

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.

Pharmacokinetic Modeling and Simulation of Gastrointestinal Transit Effects on Plasma Concentrations of Drugs from Mixed Immediate-Release and Enteric-Coated Pellet Formulations

Effects of gastrointestinal transit on plasma concentrations of drugs from mixed immediate-release and enteric-coated pellet formulation were simulated with models developed by including gastric emptying time and lag time of emptying. Models were evaluated by comparing simulated plasma concentrations of amphetamine from Monte Carlo simulations to available published data of a commercial mixed pellet formulation (Adderall XR). Results show that the plasma profile from the mixed pellet formulation does not mimic that from two immediate-release doses administered at different times. Instead, the plasma profile from the mixed pellets of amphetamine is similar to a typical sustained-release formulation. The pharmacokinetic models presented herein describe plasma concentrations of amphetamine from mixed pellet formulation quite well. The models and assumptions are general and can be applied to other drugs in similar mixed pellet dosage forms.

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.

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).

Influence of pluronic F-68 on dissolution and bioavailability characteristics of multiple-layer pellets of nifedipine for controlled release delivery

A multiple-layer design of pellets for nifedipine was developed using pluronic F-68 to enhance dissolution rate. The influence of ratios of nifedipine in the inner layer to that in the outer layer, the ratios of pluronic F-68 to nifedipine in the solid dispersion, and the thickness of the control membrane on dissolution characteristics were investigated. With an increasing ratio of pluronic F-68 to nifedipine, the dissolution rate of nifedipine was gradually promoted and the extent of release was enhanced as well. DSC thermograms illustrate the gradual disappearance or broadening of the nifedipine melting peak with the presence of pluronic F-68. The decrease of the nifedipine ratio in the inner layer and the increase of the ratio of pluronic F-68 to nifedipine in the outer layer can enhance the release of nifedipine. With a fixed nifedipine ratio of 1.5 between the inner layer and the outer layer, increasing the ratio of pluronic F-68 to nifedipine in the outer layer significantly increased the initial release rate of nifedipine. By increasing the nifedipine ratio of the inner layer to the outer layer to 1:1, the increase of coating percentage referenced to the total weight decreased the release rate of nifedipine from the inner layer. The pharmacokinetic bioequivalence between the test product (Cardilate, N-6) and Coracten was found with a multiple-dose oral administration of 20 mg in 12 healthy, normal Chinese male volunteers.

Lack of bioequivalence between disulfiram formulations. Exemplified by a tablet/effervescent tablet study

A comparison of the bioavailability of disulfiram (DSF) after administration of non-effervescent Antabuse tablets (CP Pharmaceuticals, UK) and Antabuse effervescent tablets Antabuse (A/S Dumex, DK) has been made in two cross-over studies. The first study included 6 volunteers who were given 400 mg DSF after an overnight fast. The bioavailability of DSF after administration of non-effervescent was found to be only 27% of that achieved with effervescent tablets. The second study included 24 volunteers who were given 800 mg DSF after a light standardized meal. The relative bioavailability of DSF after administration of non-effervescent compared with effervescent tablets was found to be only 34%. In addition to the difference in bioavailability of DSF after administration of the two preparations, a considerable difference was seen between the two studies. A light meal seems both to increase the bioavailability of DSF and to reduce the interindividual variation. A two to threefold increase in the bioavailability of DSF was found. Thus, the bioavailability of DSF appears to depend on both the formulation (preparation) and the mode of administration. A lack of bioequivalence between the two investigated DSF preparations was found.

Novel drug-delivery systems for hypertension

Although novel controlled-release drug-delivery systems have been used in other areas of medicine, their application in the treatment of hypertension has been relatively recent. Biotechnical use of chemical-dispensing systems has been applied to propranolol, clonidine (the transdermal therapeutic system), nifedipine (the gastrointestinal therapeutic system), verapamil (the sodium alginate and spheroidal oral-delivery absorption system), felodipine (the hydrophilic gel principle), metoprolol succinate (the multiple-unit pellet system), and diltiazem (one system comprising sustained-release beads and the other utilizing the patented Geomatrix extended-release system). Oral drug-delivery systems allow antihypertensive agents that previously had to be administered two to four times daily to be administered once each day. Potential disadvantages of the oral controlled-release products include delayed attainment of pharmacodynamic effect, unpredictable or reduced bioavailability, enhanced first-pass hepatic metabolism, dose dumping, sustained toxicity, dosing inflexibility, and increased cost. Potential advantages include reduced dosing frequency, enhanced compliance and convenience, reduced toxicity, stable drug levels, uniform drug effect, and decreased total dose. Although skin reactions are common, the transdermal drug delivery of clonidine provides another innovative approach to supplying transcutaneous, controlled, continuous delivery of drug for 7 days. It is possible that future research will prove that the agents that provide complete 24-hour control may reduce the cardiovascular events associated with the early-morning blood pressure surge. This evolution in antihypertensive therapy to achieve once-daily dosing may prove to be of great value to both physicians and patients in the 1990s.

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.

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

The behavior of single 250-mg doses of a multiparticulate form of erythromycin base (ERYC(R)), each including five pellets radiolabeled with neutron-activated samarium-153, was observed by gamma scintigraphy in seven male subjects under fasting and nonfasting conditions. The residence time and locus of radiolabeled pellets within regions of the gastrointestinal tract were determined and were correlated with plasma concentrations of erythromycin at coincident time points. Administration of food 30 minutes postdosing reduced fasting plasma erythromycin Cmax and area under the plasma erythromycin versus time curve (AUC) values by 43% and 54%, respectively. Mean peak plasma concentration of erythromycin (Cmax) in the fasting state was 1.64 micrograms/mL versus 0.94 micrograms/mL in the nonfasting state. Total oral bioavailability, as determined by mean AUC (0-infinity) of the plasma erythromycin concentration versus time curve, was 7.6 hr/micrograms/mL in the fasted state, versus 3.5 hr/micrograms/mL in the nonfasting state. Mean time to peak plasma erythromycin concentration (tmax) in the fasting state was 3.3 hours, versus 2.3 hours in the nonfasting state. Plasma concentrations of erythromycin in both fasting and nonfasting states were within acceptable therapeutic ranges. Evidence provided by this study: 1) indicates that pellet erosion and absorption of active erythromycin base begins when the enteric-coated pellets reach the highly vascular mucosa of the jejunum and proximal ileum, and is essentially completed within the ileum, with a significant portion absorbed in the medial-to-distal ileum; 2) confirms that acceptable therapeutic plasma levels of erythromycin are attained in nonfasting subjects (Cmax = 0.94 microgram/mL) and that superior plasma erythromycin concentrations (Cmax = 1.64 micrograms/mL) are achieved by administration of the dose on an empty stomach 1 to 2 hours before or after meals; 3) corroborates other comparative studies reporting greater fasting bioavailability with this multiparticulate dosage form of erythromycin base than with reference single tablet or particle-in-tablet formulations; and 4) indicates that neutron activation of stable isotopes incorporated as a normal excipient in industrially-produced formulations provides an effective means for in vivo evaluation of dosage forms through gamma scintigraphy.

What happens to tablets and capsules in the stomach: endoscopic comparison of disintegration and dispersion characteristics of two microencapsulated potassium formulations

Previously we investigated gastric emptying and distribution of a capsule formulation of microencapsulated KCl and found the drug was usually present in clumps of KCl crystals held in place by gastric mucus. We therefore investigated whether a tablet formulation of microencapsulated KCl would have improved dispersion. We characterized the intragastric disintegration of capsules and tablets of microencapsulated KCl in 12 subjects. The capsule formulation floated in the gastric pool; one end would adhere to the gastric mucosa and the motion of the tethered capsule would pull the end of the capsule off. The KCl crystals would then be deposited in a mass. In contrast, the tablet formulation sank to the anatomically most dependent portion of the stomach. The tablet rapidly became soft and fragile but, if allowed to remain in one place and minimally disturbed, required a median of 12 min to lose its shape. If allowed to reach the gastric antrum, the tablet was quickly ground by the antro-pyloric pump and widely dispersed. Once liberated in the stomach, the microencapsulated KCl crystals were bound into a more-or-less cohesive mass. The differences between KCl formulations, once the crystals were released, was minimal although the larger crystals from the tablet formulation appeared less adherent and cohesive; they dispersed more in a reticulated pattern when the stomach was distended. We conclude that formulation of a drug in a microencapsulated multiple-unit dosage form does not guarantee wide dispersion nor absence of high local concentration of drug.

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.

The effect of food on the movement of pellets in the gastro-intestinal tract

The effect of food on the movement of pellets in the gastro-intestinal tract was investigated in seven volunteers, either by means of X-rays taken after oral administration of barium sulfate pellets or by means of saliva concentration profiles of lithium obtained after oral administration of lithium sulfate controlled-release pellets. The X-ray studies showed that food had an effect on the time required for the pellets to leave the stomach and on their degree of dispersion in the small intestine, but not on other parameters. The studies with the lithium sulfate controlled-release pellets showed that food had a significant effect only in one in three subjects.

Oral absorption profile of nitrendipine in healthy subjects: a kinetic and dynamic study

1. In nine healthy male subjects the kinetics of nitrendipine were assessed after i.v. administration and its absorption profile was studied when given by a tablet formulation and by an osmotic pumping device (Osmet) with a zero-order in vitro release of 2.62 +/- 0.19 mg h-1 for 13 h. 2. Plasma concentrations of nitrendipine and its pyridine metabolite, heart rate and blood pressure were determined at regular intervals after drug administration. 3. After i.v. nitrendipine, the plasma concentration declined triexponentially with a mean terminal elimination half-life of 11.7 +/- 5.4 h. The mean systemic plasma clearance was 1.47 +/- 0.22 l min-1. 4. Administration of the Osmet resulted in a relatively smooth plasma concentration-time profile in comparison with the tablet. The mean plateau concentration was 2.63 +/- 1.31 ng ml-1 and the duration of this plateau was 10.7 +/- 3.2 h. The intake of food gave rise to a transient increase of the plasma concentration of both nitrendipine and its pyridine metabolite. 5. The mean bioavailability of nitrendipine from the Osmet (8.2 +/- 1.6%) was lower than from the tablet (11.1 +/- 4.5%), which is probably due to release of nitrendipine in lower parts of the G.I. tract where absorption is not or less possible. 6. Intravenous administration caused a transient decrease in DBP of 26 +/- 4%, accompanied by a maximal reflex tachycardia of 46 +/- 17%. No clear haemodynamic effects were observed after oral administration. The Osmet produced less side-effects (headache) than the tablet.

Oral naproxen formulations

The absorption of naproxen is dependent on the gastric emptying and the dissolution of the drug product in the small intestine. Enteric-coated granules designed to dissolve at pH 5.5 have a delayed absorption profile when given orally. Delivered directly into the duodenum, however, rapid absorption is obtained, indicating that the gastric emptying is the rate-limiting step. By varying the coating layer, it is possible to monitor the dissolution of enteric-coated products within a pH range from 4.5 to 7.0. The onset of absorption can be delayed by increasing the pH resistance of the coating, without affecting the extent of absorption.