Evaluation of an enteric-coated naproxen pellet formulation

Gellan gum macrobeads loaded with naproxen: The impact of various naturally derived polymers on pH-dependent behavior

Aims

After oral administration, naproxen generates several side-effects related to stomach malfunction. Undoubtedly, the enteric dosage forms with naproxen can be considered as safer. Moreover, since it has been evidenced that development and growth of colorectal cancer is related to the presence of cyclooxygenase, naproxen is investigated in terms of the tumor prevention. The aim of the present work was to formulate and evaluate the properties of novel naproxen-loaded macrobeads, made on the basis of low-acyl gellan gum and its blends with carrageenans, guar gum, cellulose sulfate, and dextran sulfates.

Method

Seven formulations were prepared by ionotropic gelation. The morphology of the dried beads was evaluated by scanning electron microscopy. The next step focused on Raman spectroscopy and thermal analysis of naproxen, polymers, and the beads. Next, the swelling behavior was examined in three acceptor fluids at pH = 1.2; 4.5, and 7.4. The beads were evaluated regarding naproxen content and encapsulation efficiency. The last stage of the work concerned the drug release studies.

Results

Addition of any other polysaccharide than gellan resulted in flattening of the beads upon drying. Differential scanning calorimetry confirmed the crystalline form of naproxen. Raman spectra showed that no apparent interactions occurred. In the acidic environment, all the beads revealed the tendency to absorb water. The beads swelled to the greatest extent at pH = 4.5. Naproxen was released from the beads at a varied rate. At pH = 7.4, the most prolonged release was observed for the beads containing carrageenans.

Conclusions

We have proved that blending of gellan with various polysaccharides can change the pH-dependent properties of the beads loaded with naproxen. We believe that the information enclosed in the paper will be of particular importance regarding the development and characteristics of novel oral dosage forms based on natural polymers.

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.

Gastric emptying of pellets under fasting conditions: a mathematical model

PURPOSE

To develop a mathematical model that would adequately describe human gastric emptying of pellets under fasting conditions of healthy subjects.

METHODS

Scintigraphic profiles representing the gastric emptying of pellets were obtained from the literature. Altogether 19 individual and three mean scintigraphic profiles were collected. Three mathematical models namely; the lag-time exponential (two parameters), the Weibull (two parameters), and the double Weibull (five parameters) model were proposed and fitted to the gastric emptying profiles.

RESULTS

Different patterns of gastric emptying (immediate and rapid, delayed but rapid, delayed and slow, and interruptive emptying) were observed, with the emptying time varied from approximately 15 min to more than 3 h. The best model for fitting to the individual profiles was the double Weibull model. This model also provided an insight into the mechanism of interruptive emptying of pellets, observed for some patients. In addition, mean gastric emptying of pellets was calculated using the Weibull model.

CONCLUSIONS

Mean gastric emptying of pellets was adequately described by the Weibull model (eta = 61.9 min, beta = 0.895), which could be applied in the design of in vitro dissolution experiments for pellet formulations with pH dependent dissolution.

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.

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.

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.

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).

Clinical pharmacokinetics of naproxen

Naproxen is a stereochemically pure nonsteroidal anti-inflammatory drug of the 2-arylpropionic acid class. The absorption of naproxen is rapid and complete when given orally. Naproxen binds extensively, in a concentration-dependent manner, to plasma albumin. The area under the plasma concentration-time curve (AUC) of naproxen is linearly proportional to the dose for oral doses up to a total dose of 500 mg. At doses greater than 500 mg there is an increase in the unbound fraction of drug, leading to an increased renal clearance of total naproxen while unbound renal clearance remains unchanged. Substantial concentrations of the drug are attained in synovial fluid, which is a proposed site of action for nonsteroidal anti-inflammatory drugs. Relationships between the total and unbound plasma concentration, unbound synovial fluid concentration and therapeutic effect have been established. Naproxen is eliminated following biotransformation to glucuroconjugated and sulphate metabolites which are excreted in urine, with only a small amount of the drug being eliminated unchanged. The excretion of the 6-O-desmethylnaproxen metabolite conjugate may be tied to renal function, as accumulation occurs in end-stage renal disease but does not appear to be influenced by age. Hepatic disease and rheumatoid arthritis can also significantly alter the disposition kinetics of naproxen. Although naproxen is excreted into breast milk the amount of drug transferred comprises only a small fraction of the maternal exposure. Significant drug interactions have been demonstrated for probenecid, lithium and methotrexate.

Evaluation of 153Sm-diethylenetriaminepentaacetic acid for radiolabelling of pharmaceutical dosage forms by neutron activation

153Sm-DTPA provides a suitable alternative to 99mTc-DTPA and 111In-DTPA as a water soluble tracer for the evaluation of pharmaceutical preparations. The chelate was handled biologically in a similar way to 99mTc-DTPA and 111In-DTPA. The chelate can be incorporated into the formulation as a non-radioactive excipient and the intact dosage form can then be neutron activated to produce 153Sm.

Localization of drug release sites from an oral sustained-release formulation of 5-ASA (Pentasa) in the gastrointestinal tract using gamma scintigraphy

Release of 5-ASA from a sustained release formulation (Pentasa, Ferring A/S, Copenhagen, Denmark) was monitored with plasma sampling for up to 24 hours in nine volunteers under both fasted and fed conditions. Drug absorption was correlated with location of the sustained-release microgranules in the gastrointestinal tract by gamma scintigraphy. Disintegration of the labeled tablet preparation occurred in the stomach within 20 minutes and acetylated 5-ASA was detectable in the plasma less than 60 minutes after ingestion. No significant differences were detected in either transit times through the small intestine, peak plasma acetylated 5-ASA concentration or lag time to absorption between fasted and fed individuals. Peak plasma concentration of acetylated 5-ASA usually occurred when the microgranules were present in the small intestine or ascending colon. The pharmacoscintigraphic study confirmed that 5-ASA release from the formulation occurred throughout the gastrointestinal tract, and that food effects on the in vivo behavior of the preparation were minimal.

Multiple-layer, direct-compression, controlled-release system: in vitro and in vivo evaluation

A new approach to achieve controlled drug delivery is demonstrated for a triple-layer tablet, which simultaneously combines the principles of diffusion and dissolution. Heckel's equation was used to characterize the compression behavior of formulation components. A balanced proportion of each component and a model drug (theophylline) were selected to avoid lamination after ejection and ensure coherent compaction. In vitro release profiles over a period of 10 h in different dissolution media and hydrodynamic conditions were similar and resulted in an n value of 0.786, signifying anomalous release kinetics. The n value is calculated from a curve fit to the empirical equation: Mt/Minfinity = Ktn, where Mt and Minfinity denote the amount of drug released at time t and at infinite time, respectively, K denotes the proportionality constant, and n characterizes the type of release mechanism operative during the dissolution process. In vivo study in human subjects after administration of the experimental triple-layer system exhibited a steady rise in plasma concentration up to 7 h. The actual amount of drug absorbed by the body was calculated by the Wagner-Nelson technique, and a linear relationship was observed between the percentage absorbed in vivo and the percentage dissolved in vitro. The proposed triple-layer model appears to provide good correlation between in vitro and in vivo results with maximum flexibility with respect of dose, duration range, and ease of production.

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.