Circadian rhythms and drug delivery

Circadian hormone control in a human-on-a-chip: In vitro biology's ignored component?

Organs-on-Chips (OoCs) are poised to reshape dramatically the study of biology by replicating in vivo the function of individual and coupled human organs. Such microphysiological systems (MPS) have already recreated complex physiological responses necessary to simulate human organ function not evident in two-dimensional in vitro biological experiments. OoC researchers hope to streamline pharmaceutical development, accelerate toxicology studies, limit animal testing, and provide new insights beyond the capability of current biological models. However, to develop a physiologically accurate Human-on-a-Chip, i.e., an MPS homunculus that functions as an interconnected, whole-body, model organ system, one must couple individual OoCs with proper fluidic and metabolic scaling. This will enable the study of the effects of organ-organ interactions on the metabolism of drugs and toxins. Critical to these efforts will be the recapitulation of the complex physiological signals that regulate the endocrine, metabolic, and digestive systems. To date, with the exception of research focused on reproductive organs on chips, most OoC research ignores homuncular endocrine regulation, in particular the circadian rhythms that modulate the function of all organ systems. We outline the importance of cyclic endocrine regulation and the role that it may play in the development of MPS homunculi for the pharmacology, toxicology, and systems biology communities. Moreover, we discuss the critical end-organ hormone interactions that are most relevant for a typical coupled-OoC system, and the possible research applications of a missing endocrine system MicroFormulator (MES-µF) that could impose biological rhythms on in vitro models. By linking OoCs together through chemical messenger systems, advanced physiological phenomena relevant to pharmacokinetics and pharmacodynamics studies can be replicated. The concept of a MES-µF could be applied to other standard cell-culture systems such as well plates, thereby extending the concept of circadian hormonal regulation to much of in vitro biology. Impact statement Historically, cyclic endocrine modulation has been largely ignored within in vitro cell culture, in part because cultured cells typically have their media changed every day or two, precluding hourly adjustment of hormone concentrations to simulate circadian rhythms. As the Organ-on-Chip (OoC) community strives for greater physiological realism, the contribution of hormonal oscillations toward regulation of organ systems has been examined only in the context of reproductive organs, and circadian variation of the breadth of other hormones on most organs remains unaddressed. We illustrate the importance of cyclic endocrine modulation and the role that it plays within individual organ systems. The study of cyclic endocrine modulation within OoC systems will help advance OoC research to the point where it can reliably replicate in vitro key regulatory components of human physiology. This will help translate OoC work into pharmaceutical applications and connect the OoC community with the greater pharmacology and physiology communities.

A time-adjustable pulsatile release system for ketoprofen: In vitro and in vivo investigation in a pharmacokinetic study and an IVIVC evaluation

A time-adjustable pulsatile release system (TAPS) containing ketoprofen (KF) as an active pharmaceutical agent was developed having been designed for bedtime dosing and releasing drug in the early morning to control the symptoms of rheumatoid arthritis (RA). The formulation involved a tablet core (KF) and a control-release layer, and the coating membrane was composed of EC and Eudragit L100. A single-factor study, a central composite design and a response surface method were selected to optimize the formula and the optimum prescription was as follows: tablet core (KF 50mg, MCC 70mg, lactose 40mg, L-HPC 38mg), and film (EC 7.8g, Eudragit L100 4.2g, PEG 6000 1.8g in 95% alcohol each 200ml). The in vivo release behavior of the tablets was evaluated in Beagle dogs after a parallel oral administration of KF TAPS tablets and commercial KF capsules, when it was found that the KF TAPS tablets released the drug after a lag-time of 3.458h and the T_max was 5.833h. The relative bioavailability was 85.01%, and the two formulations were bioequivalent in terms of C_max and AUC_0-t and the in vitro- in vivo correlations indicated that test formulation had a good in vivo-in vitro correlation (r=0.9703). These results show that the novel drug delivery system (TAPS) has the potential to be used as a KF preparation with chronophamacokinetics characteristics.

A systems theoretic approach to analysis and control of mammalian circadian dynamics

The mammalian circadian clock is a complex multi-scale, multivariable biological control system. In the past two decades, methods from systems engineering have led to numerous insights into the architecture and functionality of this system. In this review, we examine the mammalian circadian system through a process systems lens. We present a mathematical framework for examining the cellular circadian oscillator, and show recent extensions for understanding population-scale dynamics. We provide an overview of the routes by which the circadian system can be systemically manipulated, and present in silico proof of concept results for phase resetting of the clock via model predictive control.

Artificia Therio-Responsive Membrane Able to Control On-Off Switching Drug Release through Nude Mice Skin without Interference from Skin-Penetrating Enhancers

The influence of skin-penetrating enhancers such as Azone, ethanol and propylene glycol (PG) on the on-off switching penetration behavior of salbutamol sulfate through the thermo-responsive cholesteryl oleoyl carbonate (COC)-embedded membrane with or without application to the excised nude mice skin was examined. Without the nude mice skin, gel formulations without any enhancer and with Azone showed higher drug penetration across the COC-embedded membrane than those with ethanol and propylene glycol (PG). Moreover, the on-off switching function of COC-embedded membrane still existed. These results indicate that Azone did not alter the thermo-responsive property of COC-embedded membrane. A lower penetration behavior associated with ethanol or PG was probably due to the increased solubility of salbutamol sulfate in each gel formulation and improved drug-carbopol gel interaction. The application of COC-embedded membrane to excised nude mice skin resulted in a similar on-off switching penetration behavior to the gel, but the penetration was significantly weakened compared to the gel formulation that only penetrated through the COC-embedded membrane. However, passage of salbutamol sulfate across the COC-embedded membrane applied to the excised nude mice skin was severely restricted when an enhancer was absent from the gel. Obviously, the excised skin was the predominant barrier to drug penetration. The present study suggests that skin-penetrating enhancer does not alter the structure of the COC embedded in membrane to change the thermo-responsive on-off switching penetration behavior of salbutamol sulfate from gel formulas through COC-embedded membrane.

Timing of Administration: For Commonly-Prescribed Medicines in Australia

Chronotherapy involves the administration of medication in coordination with the body's circadian rhythms to maximise therapeutic effectiveness and minimise/avoid adverse effects. The aim of this study is to investigate the "time of administration" recommendations on chronotherapy for commonly-prescribed medicines in Australia. This study also aimed to explore the quality of information on the timing of administration presented in drug information sources, such as consumer medicine information (CMI) and approved product information (PI). Databases were searched for original research studies reporting on the impact of "time of administration" of the 30 most commonly-prescribed medicines in Australia for 2014. Further, time of administration recommendations from drug information sources were compared to the evidence from chronotherapy trials. Our search revealed 27 research studies, matching the inclusion and exclusion criteria. In 56% (n = 15) of the research studies, the therapeutic effect of the medicine varied with the time of administration, i.e., supported chronotherapy. For some medicines (e.g., simvastatin), circadian-based optimal administration time was evident in the information sources. Overall, dedicated studies on the timing of administration of medicines are sparse, and more studies are required. As it stands, information provision to consumers and health professionals about the optimal "time" to take medications lags behind emerging evidence.

Time controlled pulsatile transdermal delivery of nicotine: A phase I feasibility trial in male smokers

Nicotine substitution is a mainstay component in smoking cessation schemes. Current products including patches are poorly effective mainly because they do not give smokers the same pharmacokinetic profile of nicotine as cigarette consumption. This work evaluates a new computer operated delivery system for time controlled pulsatile transdermal administration of nicotine in a phase I clinical trial with twelve heavy smoking male volunteers. The device was affixed to the ventral side of the leading lower arm of the subjects and was programmed to deliver two pulses of drug within 16h with three delivery rates in a consecutive dose escalation study. Tolerability of the three increasing doses of nicotine was established. Plasma concentration of nicotine exhibited two peaks and one trough and reached therapeutically effective levels that behaved linearly with the drug load concentration of the device. In vivo input rate, delivered amount and elimination kinetics were deduced by pharmacokinetic modeling to analyze device performance. Timing, dose and duration of delivery were controlled by system operation parameters. Hence, feasibility of controlled pulsatile delivery of nicotine at predetermined intervals was demonstrated. After additional optimization, preprogrammed or on demand administration to meet individualized and circadian replacement needs should improve smoking cessation efficacy.

Application of design of experiment for polyox and xanthan gum coated floating pulsatile delivery of sumatriptan succinate in migraine treatment

Migraine follows circadian rhythm in which headache is more painful at the awakening time. This needs administration of dosage form at night time to release drug after lag period when pain gets worse. Sumatriptan succinate is a drug of choice for migraine. Sumatriptan succinate has bitter taste, low oral bioavailability, and shorter half-life. Present work deals with application of design of experiment for polyox and xanthan gum in development of press coated floating pulsatile tablet. Floating pulsatile concept was applied to increase gastric residence of the dosage form. Burst release was achieved through immediate release tablet using crospovidone as superdisintegrant (10%). Pulse lag time was achieved using swellable polymer polyox WSR 205 and xanthan gum. 3² experimental design was applied. Optimized formulation was evaluated for physical characteristics and in-vitro and in-vivo study. From results, it can be concluded that optimized batch F8 containing polyox WSR205 (72.72%) and xanthan gum (27.27%) of total weight of polymer has shown floating lag time of 55 ± 2 sec, drug content of 100.35 ± 0.4%, hardness of 6 ± 0.1 Kg/cm², and 98.69 ± 2% drug release in pulse manner with lag time of 7 ± 0.1 h. Optimized batch showed prolong gastric residence which was confirmed by in-vivo X-ray study.

Design and optimization of self-microemulsifying drug delivery system (SMEDDS) of felodipine for chronotherapeutic application

The objective of this research work was to design, develop and optimize the self micro-emulsifying drug delivery system (SMEDDS) of Felodipine (FL) filled in hard gelatine capsule coated with polymer in order to achieve rapid drug release after a desired time lag in the management of hypertension. Microemulsion is composed of a FL, Lauroglycol FCC, Transcutol P and Cremophor EL. The optimum surfactant to co-surfactant ratio was found to be 2:1. The resultant microemulsions have a particle size in the range of 65-85 nm and zeta potential value of -13.71 mV. FL release was adequately adjusted by using pH independent polymer i.e. ethyl cellulose along with dibutyl phthalate as plasticizer. Influence of formulation variables like viscosity of polymer, type of plasticizer and percent coating weight gain was investigated to characterize the time lag. The developed formulation of FL SMEDDS capsules coated with ethyl cellulose showed time lag of 5-7 h which is desirable for chronotherapeutic application.

A novel multilayered multidisk oral tablet for chronotherapeutic drug delivery

A Multilayered Multidisk Tablet (MLMDT) comprising two drug-loaded disks enveloped by three drug-free barrier layers was developed for use in chronotherapeutic disorders, employing two model drugs, theophylline and diltiazem HCl. The MLMDT was designed to achieve two pulses of drug release separated by a lag phase. The polymer disk comprised hydroxyethylcellulose (HEC) and ethylcellulose (EC) granulated using an aqueous dispersion of EC. The polymeric barrier layers constituted a combination of pectin/Avicel (PBL) (1st barrier layer) and hydroxypropylmethylcellulose (HPMC) (HBL1 and HBL2) as the 2nd and 3rd barrier layers, respectively. Sodium bicarbonate was incorporated into the diltiazem-containing formulation for delayed drug release. Erosion and swelling studies confirmed the manner in which the drug was released with theophylline formulations exhibiting a maximum swelling of 97% and diltiazem containing formulations with a maximum swelling of 119%. FTIR spectra displayed no interactions between drugs and polymers. Molecular mechanics simulations were undertaken to predict the possible orientation of the polymer morphologies most likely affecting the MLMDT performance. The MLMDT provided two pulses of drug release, separated by a lag phase, and additionally it displayed desirable friability, hardness, and uniformity of mass indicating a stable formulation that may be a desirable candidate for chronotherapeutic drug delivery.

Timing is important in medication administration: a timely review of chronotherapy research

BACKGROUND

Chronotherapy involves altering the timing of medication administration to improve the overall control of a disease and to minimise treatment side-effects, and is an emerging concept in the field of therapeutics.

AIM

The aim of this review is to conduct an in-depth analysis of the recent literature in order to identify and evaluate the evidence base for drug chronotherapy.

METHOD

A literature search was conducted in three databases (Medline, Embase, International Pharmaceutical Abstracts) using the search terms "Chronotherapy", "Chronopharmacology", "Chronopharmacokinetics", "Chronopharmacodynamics", "Chronoefficacy", "Chronoformulation", "Morning and Evening", "Morning and Bedtime" and their combinations. The selection criteria for the inclusion of articles in the review included currency (years 2008-Aug 2011), publication in English language, studies done in Humans and non-review articles that pertained to 'drug' therapy.

RESULTS

Our search revealed a total of 192 journal articles, of which 41 articles were selected for review. The specific hypothesis for the effectiveness of chronotherapy that was tested in these 41 studies was chronoeffectiveness (n = 34), followed by chronopharmacokinetics (n = 5), chronomodulation (n = 3) and chronopharmacodynamics (n = 2). The findings from two-thirds (n = 27) of the reviewed studies, support the notion of chronotherapy.

CONCLUSION

The review presents the scope of chronotherapy in drug utilization. We believe that the knowledge of chronotherapy is growing and the current research for chronotherapy is promisingly in the conceptualization or early experimental phase. Going forward, chronotherapy studies should also explore genetic, gender and age related differences. Preliminary screening of new drugs for chronotherapeutic potential may be a way of enhancing quality use of medicines.

Programmed delivery of verapamil hydrochloride from tablet in a capsule device

The aim of the present work was to develop a programmed drug delivery system which would be able to release the drug after 6 h of lag time by use of hydrophilic polymers. The capsule body was made impermeable by use of formaldehyde vapor treatment, while the cap was untreated. The capsule was filled with two layered tablets (tablet-in-capsule), followed by a sodium bicarbonate:citric acid mixture (SBCM) and lactose as bulking agent. Sodium alginate, chitosan, HPMC K15 and chitosan:sodium alginate complex (CSAC) were used as the rate modulating layer. Through combined use of HPMC K15 and adjusting the ratio of CSAC, the desired lag time of 6 h was obtained. The effect of the bulking agents on the lag time were also studied and it was found that the lag time was decreased with higher amounts of lactose, and delayed dissolution and decreased lag time was observed at higher amount of effervescent mixture.

A new pressure-controlled colon delivery capsule for chronotherapeutic treatment of nocturnal asthma

The purpose of this study was to prepare a pressure-controlled colon delivery capsule (PCDC) containing theophylline (TPH) dispersion in a lipid matrix as a chronotherapeutic drug delivery system for the treatment of nocturnal asthma. The system was made by film coating using Eudragit S100- based formula over the sealed-hard gelatin capsules containing the drug-lipid dispersion. The lipid formula was composed mainly of Gelucire 33/01 (G33) with different ratios of surfactants (1-10%). The efficiency of the prepared system was evaluated in vitro for its ability to withstand both the gastric and intestinal medium. In addition, the drug plasma concentrations were monitored after single administration to Beagle dogs and compared to that obtained after administration of a reference marketed, generic, sustained-release TPH tablets, Avolen(®) SR. It was found that the optimum lipid formula was GL2 containing 90% G33 and 10% Labrasol. The film-coated capsules showed complete resistance to both the acidic environment (pH 1.2) for 2 hours and phosphate buffer pH 6.8 for 3 hours at 37°C. In vivo evaluation of the TPH-based PCDCs showed longer lag time compared TO the marketed formula followed by sudden increase in TPH blood levels, which recommends the high potential of this system as a chronotherapeutic drug delivery for nocturnal asthma. The prepared PCDCs exhibited a significantly higher C(max) and T(max) and a nonsignificantly different AUC compared with Avolen(®) SR. Higher TPH blood levels from 1 to 8 hours postadministration was detected in the case of the prepared PCDCs.

Statistical optimization of ranitidine HCl floating pulsatile delivery system for chronotherapy of nocturnal acid breakthrough

Present work conceptualizes a specific technology, based on combining floating and pulsatile principles to develop drug delivery system, intended for chronotherapy in nocturnal acid breakthrough. This approach will be achieved by using a programmed delivery of ranitidine hydrochloride from a floating tablet with time-lagged coating. In this study, investigation of the functionality of the outer polymer coating to predict lag time and drug release was statistically analyzed using the response surface methodology (RSM). RSM was employed for designing of the experiment, generation of mathematical models and optimization study. The chosen independent variables, i.e. percentage weight ratios of ethyl cellulose to hydroxypropyl methyl cellulose in the coating formulation and coating level (% weight gain) were optimized with a 3(2) full factorial design. Lag time prior to drug release and cumulative percentage drug release in 7h were selected as responses. Results revealed that both, the coating composition and coating level, are significant factors affecting drug release profile. A second-order polynomial equation fitted to the data was used to predict the responses in the optimal region. The optimized formulation prepared according to computer-determined levels provided a release profile, which was close to the predicted values. The proposed mathematical model is found to be robust and accurate for optimization of time-lagged coating formulations for programmable pulsatile release of ranitidine hydrochloride, consistent with the demands of nocturnal acid breakthrough.

Top-down and bottom-up fabrication techniques for hydrogel based sensing and hormone delivery microdevices

We review a set of studies dealing with molecular (glucose) sensing and hormone delivery, in which the swelling and shrinking of a hydrogel as a function of glucose concentration play a central role. Confining hydrogels in microfabricated structures permits transduction of their chemomechanical behaviors. Prototype microdevices for wireless glucose sensing and closed loop insulin delivery control have been designed using hydrogels containing phenylboronic acid sidechains. While these devices exhibit desired responses, improved response time is needed, warranting further miniaturization. In a separate application, geometric confinement of glucose oxidase by a pH-sensitive hydrogel membrane sets up a nonlinear feedback loop which enables rhythmic swell/shrink cycles when the system is exposed to a constant glucose concentration. The latter system may be applied to delivery of gonadotropin release hormone, for which rhythmicity of secretion is essential for therapeutic function.

Erosion Characteristics of an Erodible Tablet Incorporated in a Time-Delayed Capsule Device

A time-delayed oral drug delivery device was investigated in which an erodible tablet (ET), sealing the mouth of an insoluble capsule, controlled the lag-time prior to drug release. The time-delayed capsule (TDC) lag-time may be altered by manipulation of the excipients used in the preparation of the ET. Erosion rates and drug release profiles from TDCs were investigated with four different excipient admixtures with lactose: calcium sulphate dihydrate (CSD), dicalcium phosphate (DCP), hydroxypropylmethyl cellulose (HPMC; Methocel K100LV grade) and silicified microcrystalline cellulose (SMCC; Prosolv 90 grade). Additionally, the compressibility of different insoluble coated capsules was tested at different moisture levels to determine their overall integrity and suitability for oral delivery. Erosion rates of CSD, DCP, and SMCC displayed a nonlinear relationship to their concentration, while HPMC indicated rapid first-order erosion followed by zero-order erosion, the onset of which was dependent on the HPMC concentration. Capsule integrity was confirmed to be most suitable for oral delivery when the insoluble ethyl cellulose coat was applied to a hard gelatin capsule using an organic spray coating process. T50% drug release times varied between 245 (+/-33.4) and 393 (+/-40.8) minutes for 8% and 20% DCP, respectively, T50% release times of 91 (+/-22.1) and 167 (+/-34.6) were observed for 8% and 20% CSD; both formulations showed incidence of premature drug release. The SMCC formulations showed high variability due to lamination effects. The HPMC formulations had T50% release times of 69 (+/-13.9), 213 (+/-25.4), and 325 (+/-30.3) minutes for 15%, 24%, and 30% HPMC concentrations respectively, with no premature drug release. In conclusion, HPMC showed the highest reproducibility for a range of time-delayed drug release from the assembled capsule formulation. The method of capsule coating was confirmed to be important by investigation of the overall capsule integrity at elevated humidity levels. The erosion characteristics of ETs containing HPMC may be described by gravimetric loss. The novel time-delayed capsule device presented in this study may be assembled to include an erodible tablet with a known concentration of HPMC. A variety of suitable drugs for targeted chronopharmaceutical therapy can be incorporated into such a device, ultimately improving drug efficacy and patient compliance, and reducing harmful side effects.

Miscibility Behavior and Formation Mechanism of Stabilized Felodipine-Polyvinylpyrrolidone Amorphous Solid Dispersions

In the present study, solid dispersion systems of felodipine (FEL) with polyvinylpyrrolidone (PVP) were developed, in order to enhance solid state stability and release kinetics. The prepared systems were characterized by using Differential Scanning Calorimetry, X-Ray Diffraction, and Scanning Electron Microscopy techniques, while the interactions which take place were identified by using Fourier Transformation-Infrared Spectroscopy. Due to the formation of hydrogen bonds between the carbonyl group of PVP and the amino groups of FEL, transition of FEL from crystalline to amorphous state was achieved. The dispersion of FEL was found to be in nano-scale particle sizes and dependent on the FEL/PVP ratio. This modification leads to partial miscibility of the two components, as it was verified by DSC and optimal glass dispersion of FEL into the polymer matrix since no crystalline structure was detected with XRD. The above deformation has a significant effect on the dissolution enhancement and the release kinetics of FEL, as it causes the pattern to change from linear to logarithmic. An impressive optimization of the dissolution profile is observed corresponding to a rapid release of FEL in the system containing 10% w/w of FEL, releasing 100% in approximately 20 min. The particle size of dispersed FEL into PVP matrix could be classified as the main parameter affecting dissolution optimization. The mechanism of such enhancement consists of the lower energy required for the dissolution due to the amorphous transition and the fine dispersion, which leads to an optimal contact surface of the drug substance with the dissolution media. The prepared systems are stable during storage at 40 +/- 1 degrees C and relative humidity of 75 +/- 5%. Addition of sodium docusate as surfactant does not affect the release kinetics, but only the initial burst due to its effect on the surface tension and wettability of the systems.

In Vitro and In Vivo Performance of a Multiparticulate Pulsatile Drug Delivery System

The objective of this study was to investigate the in vitro and in vivo drug release performance of a rupturable multiparticulate pulsatile system, coated with aqueous polymer dispersion Aquacoat ECD. Acetaminophen was used as a model drug, because in vivo performance can be monitored by measuring its concentration in saliva. Drug release was typical pulsatile, characterized by lag time, followed by fast drug release. Increasing the coating level of outer membrane lag time was clearly delayed. In vitro the lag time in 0.1 N HCl was longer, compared to phosphate buffer pH 7.4 because of ionisable ingredients present in the formulation (crosscarmelose sodium and sodium dodecyl sulphate). In vitro release was also longer in medium with higher ion concentration (0.9% NaCl solution compared to purified water); but independent of paddle rotation speed (50 vs.100 rpm). Macroscopically observation of the pellets during release experiment confirms that the rupturing of outer membrane was the main trigger for the onset of release. At the end of release outer membrane of all pellets was destructed and the content completely released. However, pellets with higher coating level and correspondingly longer lag time showed decreased bioavailability of acetaminophen. This phenomenon was described previously and explained by decreased liquid flow in the lower part of intestine. This disadvantage can be considered as a limitation for drugs (like acetaminophen) with high dose and moderate solubility; however, it should not diminish performance of the investigated system in principle.

Oral pulsatile delivery systems based on swellable hydrophilic polymers

Upon contact with aqueous fluids, swellable hydrophilic polymers undergo typical chain relaxation phenomena that coincide with a glassy-rubbery transition. In the rubbery phase, these polymers may be subject to swelling, dissolution and erosion processes or, alternatively, form an enduring gel barrier when cross-linked networks (hydrogels) are dealt with. Because of the peculiar hydration and biocompatibility properties, such materials are widely exploited in the pharmaceutical field, particularly as far as hydrophilic cellulose derivatives are concerned. In oral delivery, they have for long been employed in the manufacturing of prolonged release matrices and, more recently, for pulsatile (delayed) release devices as well. Pulsatile delivery, which is meant as the liberation of drugs following programmed lag phases, has drawn increasing interest especially in view of emerging chronotherapeutic approaches. In pursuit of pulsatile release, various design strategies have been proposed, chiefly including reservoir, capsular and osmotic formulations. In most cases, water-swellable polymers play a key role in the overall delivery mechanism after being activated by physiological media. Based on these premises, the aim of the present review is to survey the main oral pulsatile delivery systems, for which swelling, dissolution and/or erosion of hydrophilic polymers are primarily involved in the control of release.

Development of hollow/porous calcium pectinate beads for floating-pulsatile drug delivery

The purpose of this work was to develop hollow calcium pectinate beads for floating-pulsatile release of diclofenac sodium intended for chronopharmacotherapy. Floating pulsatile concept was applied to increase the gastric residence of the dosage form having lag phase followed by a burst release. To overcome limitations of various approaches for imparting buoyancy, hollow/porous beads were prepared by simple process of acid-base reaction during ionotropic crosslinking. The floating beads obtained were porous (34% porosity), hollow with bulk density<1 and had Ft50% of 14-24 h. In vivo studies by gamma scintigraphy determined on rabbits showed gastroretention of beads up to 5 h. The floating beads provided expected two-phase release pattern with initial lag time during floating in acidic medium followed by rapid pulse release in phosphate buffer. This approach suggested the use of hollow calcium pectinate microparticles as promising floating-pulsatile drug delivery system for site- and time-specific release of drugs acting as per chronotherapy of diseases.

Performance comparison of neural network training algorithms in modeling of bimodal drug delivery

The major aim of this study was to model the effect of two causal factors, i.e. coating weight gain and amount of pectin-chitosan in the coating solution on the in vitro release profile of theophylline for bimodal drug delivery. Artificial neural network (ANN) as a multilayer perceptron feedforward network was incorporated for developing a predictive model of the formulations. Five different training algorithms belonging to three classes: gradient descent, quasi-Newton (Levenberg-Marquardt, LM) and genetic algorithm (GA) were used to train ANN containing a single hidden layer of four nodes. The next objective of the current study was to compare the performance of aforementioned algorithms with regard to predicting ability. The ANNs were trained with those algorithms using the available experimental data as the training set. The divergence of the RMSE between the output and target values of test set was monitored and used as a criterion to stop training. Two versions of gradient descent backpropagation algorithms, i.e. incremental backpropagation (IBP) and batch backpropagation (BBP) outperformed the others. No significant differences were found between the predictive abilities of IBP and BBP, although, the convergence speed of BBP is three- to four-fold higher than IBP. Although, both gradient descent backpropagation and LM methodologies gave comparable results for the data modeling, training of ANNs with genetic algorithm was erratic. The precision of predictive ability was measured for each training algorithm and their performances were in the order of: IBP, BBP>LM>QP (quick propagation)>GA. According to BBP-ANN implementation, an increase in coating levels and a decrease in the amount of pectin-chitosan generally retarded the drug release. Moreover, the latter causal factor namely the amount of pectin-chitosan played slightly more dominant role in determination of the dissolution profiles.

Sigmoidal release of indomethacin from pectin matrix tablets: Effect of in situ crosslinking by calcium cations

Sigmoidal release pattern is therapeutically beneficial for timed release and colonic drug delivery, and is always observed in coated systems. In this study, sigmoidal release from pectin matrix tablets with indomethacin as a model drug was investigated. The underlying mechanisms are calcium cation-induced in situ crosslinking that retard the initial drug release to a limited percentage. Power law equation n values were estimated for sigmoidal release profiles. Results indicated that calcium chloride incorporated in pectin matrix functioned as retarding mechanisms on drug release. Larger amount of calcium chloride led to slower drug release and matrix erosion. Even at extremely high levels, retarding on drug release and matrix erosion rate was obvious, which highlighted the effect of calcium-induced in situ crosslinking as calcium chloride was a freely water-soluble salt. The sigmoidal release profiles were characterized by power law equation with high correlation coefficients of about 0.99 or over. Power law n values increased up to as high as 1.20 when calcium chloride content kept increasing. Erosion correlated well with release in almost all pectin matrix tablets indicating erosion-controlled mechanisms. It is concluded that large amount of calcium induces in situ crosslinking of pectin matrix and leads to sigmoidal release of indomethacin, and power law n values, sometimes larger than 1.0, are suitable to be used to describe sigmoidal release profiles.

Circadian variations in the pharmacokinetics, tissue distribution and urinary excretion of nifedipine after a single oral administration to rats

Circadian variations in the pharmacokinetics, tissue distribution and urinary excretion of nifedipine were examined in fasted rats after administering a single oral dose at three different dosing times (08:00 am, 16:00 pm, 00:00 am). The plasma concentrations, the areas under the plasma concentration-time curve from zero to 6 h (AUC(0-6 h)) and the peak plasma concentration (C(max)) were significantly higher in the rats dosed at 08:00 am (immediately inactive), and was lower at 16:00 pm (most inactive) and 00:00 am (most active). The time to reach the C(max) (T(max)) was the shortest in the rats dosed at 08:00 am. It was very interesting to observe the double peak phenomena in the plasma concentration profiles, showing a larger peak followed by a smaller peak. There was a dosing time dependency on the tissue distribution 30 min after administration, showing a similar tendency to the pharmacokinetic behavior. However, there was no distinct dosing time dependency observed at 2 h after administration due to the extensive disposition. The cumulative urine excretion of nifedipine in the rats dosed at 08:00 am was significantly higher (about two-fold) than in those dosed at 16:00 pm and 00:00 am. The pharmacokinetics of nifedipine in the rats was consistent with that observed in human subjects in terms of the day-night clock time but the biological time was the opposite, as marked by the rest-activity cycles. These results may help to explain the circadian time-dependency of nifedipine pharmacokinetics.

Design and evaluation of a dry coated drug delivery system with an impermeable cup, swellable top layer and pulsatile release

In this investigation a novel oral pulsatile drug delivery system based on a core-in-cup dry coated tablet, where the core tablet surrounded on the bottom and circumference wall with inactive material, is proposed. The system consists of three different parts, a core tablet, containing the active ingredient, an impermeable outer shell and a top cover layer-barrier of a soluble polymer. The core contained either diclofenac sodium or ketoprofen as model drugs. The impermeable coating cup consisted of cellulose acetate propionate and the top cover layer of hydrophilic swellable materials, such as polyethylene oxide, sodium alginate or sodium carboxymethyl cellulose. The effect of the core, the polymer characteristics and quantity at the top cover layer, on the lag time and drug release was investigated. The results show that the system release of the drug after a certain lag time generally due to the erosion of the top cover layer. The quantity of the material, its characteristics (viscosity, swelling, gel layer thickness) and the drug solubility was found to modify lag time and drug release. The lag time increased when the quantity of top layer increased, whereas drug release decreased. The use of sodium carboxymethyl cellulose resulted in the greatest swelling, gel thickness and lag time, but the lowest drug release from the system. Polyethylene oxide showed an intermediate behaviour while, the sodium alginate exhibited the smallest swelling, gel thickness and the shortest lag time, but the fastest release. These findings suggest that drug delivery can be controlled by manipulation of these formulations.

Oral pulsatile drug delivery systems

In the field of modified release, there has been a growing interest in pulsatile delivery, which generally refers to the liberation of drugs following a programmable lag phase from the time of administration. In particular, the recent literature reports on a variety of pulsatile release systems intended for the oral route, which have been recognised as potentially beneficial to the chronotherapy of widespread diseases, such as bronchial asthma or angina pectoris, with mainly night or early morning symptoms. In addition, time-dependent colon delivery may also represent an appealing related application. The delayed liberation of orally administered drugs has been achieved through a range of formulation approaches, including single- or multiple-unit systems provided with release-controlling coatings, capsular devices and osmotic pumps. Based on these premises, the aim of this review is to outline the rational and prominent design strategies behind oral pulsatile delivery.

Rheological characterization and turbidity of riboflavin-photosensitized changes in alginate/GDL systems

Riboflavin (RF) in combination with light, in the wavelength range of 310-800 nm, is used to induce degradation of alginic acid gels. Light irradiation of alginate solutions in the presence of RF under aerobic conditions causes scission of the polymer chains. In the development process of a new drug delivery system, RF photosensitized degradation of alginic acid gels is studied by monitoring changes in the turbidity and rheological parameters of alginate/glucono-delta-lactone (GDL) systems with different concentrations of GDL. Addition of GDL induces gel formation of the samples by gradually lowering the pH-value of the system. The turbidity is measured and the cloud point determined. The turbidity starts to increase after shorter times with enhanced concentration of GDL. Enhanced viscoelasticity is detected with increasing GDL concentration in the post-gel regime, but small differences are detected at the gel point. The incipient gel is 'soft' and has an open structure independent on the GDL concentration. In the post-gel regime solid-like behavior is observed, this is more distinct for the systems with high GDL concentrations. The effect of photosensitized RF on alginate/GDL systems decreases with increasing amount of GDL in the system. The same trend is detected whether the systems are irradiated in the pre-gel or in the post-gel regime.

Time-release compression-coated core tablet containing nifedipine for chronopharmacotherapy

Compression-coated time-release tablets (CC tablets) containing nifedipine, dihydropyridine Ca channel blocker, in the core tablet were prepared by dry coating with different polyethylene oxide-polyethylene glycol mixtures. Each formulation showed a clear lag period before nifedipine release initiation, followed by sustained drug release lasting up to 24 h. The lag time of nifedipine release increased as the amount of polyethylene oxide in the outer layer increased. To investigate the applicability of such CC-tablets for chronopharmacotherapy, the pharmacokinetics of CC-1 and CC-2 tablets, with different in vitro lag times before drug release, were compared with the pharmacokinetics of a sustained-release (SR) tablet in dogs. The times of first nifedipine appearance (TFA) in plasma were 0.7 +/- 0.3 h for SR, 2.5 +/- 1.2 h for CC-1, and 5.3 +/- 1.0 h for CC-2. These data show a significant difference in in vivo lag time (P < 0.01) among the three formulations that correlates with the in vitro lag times. Thus, the in vivo lag time could be predicted from the in vitro lag time. Additionally, higher plasma nifedipine concentrations were observed at 8 h after administration of the CC-2 than that observed for the SR-tablet. These results indicate that a CC-tablet with a lag time before drug release is a potentially useful formulation for chronopharmacotherapy that can control the time and duration of plasma drug concentration better than existing SR technologies.

Different HPMC viscosity grades as coating agents for an oral time and/or site-controlled delivery system: a study on process parameters and in vitro performances

Currently, delayed/pulsatile release and colon delivery represent topics of remarkable interest. The present paper deals with the study and development of an oral dosage form devised to release drugs following a programmed time period after administration or, when opportune design modifications are introduced, to target the colon. The system is composed of a drug-containing core and a hydrophilic swellable polymeric coating capable of delaying drug release through slow interaction with aqueous fluids. An optional external gastroresistant film is applied to overcome gastric emptying variability, thus allowing colon delivery to be pursued according to the time-dependent approach. The aim of this work was to evaluate different hydroxypropyl methylcellulose (HPMC) viscosity grades as possible materials for the attainment of the system retarding hydrophilic layer. Both the relevant suitability for application onto tablet cores by aqueous spray-coating in fluid bed and capability of delaying drug release for a programmable period were explored and compared. Methocel E50 was found to afford the best balance among different important items, i.e. process time, retarding ability, dimensions of the coated units and possibility of finely tuning the delay duration. Further results pointed out the robustness of Methocel E50-based systems, which have shown to be practically unaffected by the concentration of the employed coating solution and the pH of the release medium, as well as only poorly influenced by ionic strength, at least with regard to values encompassed in the physiological range for gastrointestinal fluids.

The effect of wet granulation on the erosion behaviour of an HPMC–lactose tablet, used as a rate-controlling component in a pulsatile drug delivery capsule formulation

The purpose of this study was to investigate the variability in the performance of a pulsatile capsule delivery system induced by wet granulation of an erodible HPMC tablet, used to seal the contents within an insoluble capsule body. Erodible tablets containing HPMC and lactose were prepared by direct compression (DC) and wet granulation (WG) techniques and used to seal the model drug propranolol inside an insoluble capsule body. Dissolution testing of capsules was performed. Physical characterisation of the tablets and powder blends used to form the tablets was undertaken using a range of experimental techniques. The wet granulations were also examined using the novel technique of microwave dielectric analysis (MDA). WG tablets eroded slower and produced longer lag-times than those prepared by DC, the greatest difference was observed with low concentrations of HPMC. No anomalous physical characteristics were detected with either the tablets or powder blends. MDA indicated water-dipole relaxation times of 2.9, 5.4 and 7.7x10(-8)ms for 15, 24 and 30% HPMC concentrations, respectively, confirming that less free water was available for chain disentanglement at high concentrations. In conclusion, at low HPMC concentrations water mobility is at its greatest during the granulation process, such formulations are therefore more sensitive to processing techniques. Microwave dielectric analysis can be used to predict the degree of polymer spreading in an aqueous system, by determination of the water-dipole relaxation time.

A pulsatile drug delivery system based on rupturable coated hard gelatin capsules

The objective of this study was to develop and evaluate a pulsatile drug delivery system based on drug-containing hard gelatin capsules, which were coated with a swelling layer and an outer insoluble, water-permeable polymeric coating. An inner pressure developed by the swelling layer resulted in the rupture of the outer coating. Preliminary studies with a simulated rupture test demonstrated the dependence of the lag time prior to rupture on the properties of the coating, such as its water permeability and mechanical strength. The lag time increased with a higher coating level, but decreased with the addition of the hydrophilic pore former, hydroxypropyl methylcellulose. Increasing the amount of the swelling layer decreased the lag time. The coated capsules took up release medium at a nearly constant rate until a critical maximum was reached, where the swelling pressure was sufficient to rupture the outer coating. The rate of medium uptake decreased with increasing coating level, while the extent of medium uptake was almost the same for the different coating levels. A hydrophobic particulate material, magnesium stearate, was added to the coating layer to reduce the mechanical strength and therefore the lag time. The test conditions, such as surfactant addition to the release medium or floating vs. complete immersion of capsules in the medium, affected the lag time.

Formulation parameters affecting the performance of coated gelatin capsules with pulsatile release profiles

The objective of this study was to develop and evaluate a rupturable pulsatile drug delivery system based on soft gelatin capsules with or without a swelling layer and an external water-insoluble but -permeable polymer coating, which released the drug after a lag time (rupturing of the external polymer coating). The swelling of the gelatin capsule itself was insufficient to rupture the external polymer coating, an additional swelling layer was applied between the capsule and the polymer coating. Croscarmellose sodium (Ac-Di-Sol) was more effective as a swelling agent than low and high molecular weight hydroxypropylmethyl cellulose (HPMC; E5 or K100M). Brittle polymers, such as ethyl cellulose (EC) and cellulose acetate propionate (CAPr), led to a better rupturing and therefore more complete drug release than the flexible polymer coating, Eudragit RS. The lag time of the release system increased with higher polymer coating levels and decreased with the addition of a hydrophilic pore-former, HPMC E5 and also with an increasing amount of the intermediate swelling layer. The water uptake of the capsules was linear until rupture and was higher with CAPr than with EC. Soft gelatin capsule-based systems showed shorter lag times compared to hard gelatin capsules because of the higher hardness/filling state of the soft gelatin capsules. The swelling pressure was therefore more directed to the external polymer coating with the soft gelatin capsules. Typical pulsatile drug release profiles were obtained at lower polymer coating levels, while the release was slower and incomplete at the higher coating levels. CAPr-coated capsules resulted in a more complete release than EC-coated capsules.

Biphasic drug release from film-coated tablets

A study was carried out into the biphasic drug release properties of film-coated paracetamol tablets. The tablet cores were formulated without a disintegrant and film-coated with a coating formulation consisting of pectin, chitosan and hydroxypropylmethylcellulose in a ratio of 6:1:0.37. The tablet cores and the film-coated tablets with coat weight gains (CWGs) of 6, 9 and 13% were evaluated for their water absorption (swelling) and drug release properties. All the tablets absorbed water from pH 6.0 Sorensen's phosphate buffer and the amount of water absorbed increased with an increase in tablet CWG. The addition of 100 microl/50 ml pectinolytic enzymes to the medium resulted in at least a 40% reduction in the amount of water absorption by the tablets, as compared to the medium without enzymes. When the enzyme concentration was increased to 200 microl/50 ml, there was a further reduction ( approximately 8% w/w) in the amount of water absorbed by the tablets. Drug release was controlled in upper gastrointestinal fluids and decreased with an increase in tablet CWG. Drug release was, however, accelerated in the presence of pectinolytic enzymes, consistent with the entry of the tablets in the colon. An evaluation of the drug release data by the Korsmeyer-Peppas equation showed the involvement of molecular diffusion and other factors such as film/tablet erosion and drug dissolution in drug release.

Ionizable drugs and pH oscillators: buffering effects

It has been proposed that chemical pH oscillators may form a basis for periodic, pulsed drug delivery of weak acids and bases across lipophilic membranes. However, drugs have been shown to interfere with the ability of the chemical systems to oscillate, and rhythmic delivery of drugs by this means has been demonstrated only under constrained circumstances. Herein, we provide evidence that low concentrations of acidic drugs can attenuate and ultimately quench chemical pH oscillators, by a simple buffering mechanism. A model system consisting of the bromate-sulfite-marble pH oscillator in a continuous stirred tank reactor is used, along with acidic drugs of varying concentration and acid dissociation constant, pK(D). A published kinetic model for this oscillator is modified to account for the presence of acidic drug, and the results of this model are in qualitative agreement with the experimental results.

Transience in polyion complexation between nicotinamide-modified dextran and carboxymethyl dextran during enzymatic degradation of dextran

A self-regulated degradation system using polyion complexation through oxidation reaction from degradation products was preliminarily studied. 1,4-Dihydronicotinamide-modified dextran (NAH-Dex) with different molecular weights was prepared, and NAH moiety in NAH-Dex was oxidized by H2O2 to the dehydrated form (NA+-Dex). The dependence of stoichiometry, concentration, and molecular weight on polyion complexation with carboxymethyl dextran (CMD) were examined. NA+-Dex with a molecular weight above 40000 formed an insoluble complex with CMD, and the complexation was found to proceed stoichiometrically. The extent of polyion complexation was dependent on the concentration of NA+-Dex and CMD, whereas the time to reach complexation was dependent on H2O2 concentration. When H2O2 and dextranase were added to the solution containing NAH-Dex, CMD, and dextran, transmittance dropped and then increased again. From these results, the addition of dextran into the system of H2O2, NAH-Dex, CMD, and dextranase can regulate formation and dissociation of the polyion complex between NA+-Dex and CMD. The antagonistical inhibition of the degradation of the polyion complex is a key parameter of the self-regulated degradation system.

Biphasic drug release: the permeability of films containing pectin, chitosan and HPMC

The permeabilities of mixed films of pectin/chitosan/HPMC have been studied to assess their value in producing a dosage form with biphasic drug release characteristics. The inclusion of chitosan enhanced the properties of the films, rendering them stable at all physiological pH values. Pectin/HPMC films were soluble at pH values above 3.0. All pectin/chitosan/HPMC films were permeable to a model drug, paracetamol. HPMC initially increased the permeability of the films and subsequently reduced it at higher concentrations. The minimum permeability was obtained at pH 3 and at an HPMC level of 5% where the potential for polyelectrolyte complex formation between pectin and chitosan exists. The permeabilities of the films increased when they were exposed to pectinolytic enzymes, a system designed to mimic conditions in the colon. The film formulation thus show the potential for biphasic delivery with an initial, controllable slow phase that can be manipulated by changes in the formulation followed by a faster phase under conditions pertaining in the colon.

In vitro and in vivo evaluation of an oral system for time and/or site-specific drug delivery

Aim of this work was the evaluation of an oral system (Chronotopic) designed to achieve time and/or site-specific release. The system consists in a drug-containing core, coated by a hydrophilic swellable polymer which is responsible for a lag phase in the onset of release. In addition, through the application of an outer gastroresistant film, the variability in gastric emptying time can be overcome and a colon-specific release can be sought relying on the relative reproducibility of small intestinal transit time. For this study, cores containing antipyrine as the model drug were prepared by tableting and both the retarding and enteric coatings were applied in fluid bed. The release tests were carried out in a USP 24 paddle apparatus. The in vivo testing, performed on healthy volunteers, envisaged the HPLC determination of antipyrine salivary concentration and a gamma-scintigraphic investigation. The in vitro release curves presented a lag phase preceding drug release and the in vivo pharmacokinetic data showed a lag time prior to the detection of model drug in saliva. Both in vitro and in vivo lag times correlate well with the applied amount of the hydrophilic retarding polymer. The gamma-scintigraphic study pointed out that the break-up of the units occurred in the colon. The obtained results showed the capability of the system in delaying drug release for a programmable period of time and the possibility of exploiting such delay to attain colon-targeted delivery according to a time-dependent approach.

Self-complex formation of nicotinamide-modified dextran with carboxymethyl dextran using their degradation products

A pseudo-metabolic cycle as a self-degradation system was designed: enzymatic degradation products from a polysaccharide generate oxidants which introduce a cationic charge into the polysaccharide chains, and can form a polyion complex with an anionic polysaccharide. As a component of such a system, dextran, with various degrees of nicotinamide substitution, was prepared. Its degradation by dextranase, redox reaction via glucose oxidase-catalysis, and polyion complex formation with carboxymetyl dextran (CMD) were examined. Nicotinamide-modified dextran (NA-Dex) with nine nicotinamide moieties per 100 glucose units was soluble in PBS and completely oxidized by > 100 mM H2O2. The oxidized type of NA-Dex was found to form a 1:1 complex with CMD. By the addition of dextranase, isomaltase, and glucose oxidase (GOD) to phosphate buffer solution of the reduced type of NA-Dex and CMD, the transmittance of the solution dropped, suggesting polyion complex formation via the oxidation of 1,4-dihydronicotinamide in NA-Dex by H2O2 generated from GOD-catalytic reaction. These findings are of great importance for designing a self-complex formation system aimed at biodegradable and osillative drug release.

Chronopharmaceutical drug delivery from a pulsatile capsule device based on programmable erosion

We report the development of a chronopharmaceutical capsule drug delivery system capable of releasing drug after pre-determined time delays. The drug formulation is sealed inside the insoluble capsule body by an erodible tablet (ET). The release time is determined by ET erosion rate and increases as the content of an insoluble excipient (dibasic calcium phosphate) and of gel-forming excipient (hydroxypropylmethylcellulose; HPMC) increases. The time-delayed release of a model drug (propranolol HCI) was investigated by dissolution testing (USP XXIII paddle method). Both composition and weight of ET influence the time of drug release. Moreover it was found that drug release was controlled by the quantity of HPMC, irrespective of lactose content within the tablet weight range 80-160 mg, when above a threshold concentration of 20% HPMC. Programmable pulsatile release has been achieved from a capsule device over a 2-12-h period, consistent with the demands of chronotherapeutic drug delivery. The time of drug release can be controlled by manipulation of tablet formulation.