Biopharmaceutic and pharmacokinetic aspects in the design of controlled release peroral drug delivery systems

Osmotic pellet system comprising osmotic core and in-process amorphized drug in polymer-surfactant layer for controlled delivery of poorly water-soluble drug

The aim of the present investigation was to develop controlled porosity osmotic system for poorly water-soluble drug based on drug in polymer-surfactant layer technology. A poorly water-soluble drug, glipizide (GZ), was selected as the model drug. The technology involved core of the pellets containing osmotic agent coated with drug dispersed in polymer and surfactant layer, finally coated with release-retardant layer with pore former. The optimized drug-layer-coated pellets were evaluated for solubility of GZ at different pH conditions and characterized for amorphous nature of the drug by differential scanning calorimetry and X-ray powder diffractometry. The optimized release-retardant layer pellets were evaluated for in vitro drug release at different pH, hydrodynamic, and osmolality conditions. The optimized drug layer showed improvement in solubility (10 times in pH 1.2, 11 times in pH 4.5, and 21 times in pH 6.8), whereas pellets coated with cellulose acetate (15.0%, w/w, weight gain) with pore former triethyl citrate (10.0%, w/w, of polymer) demonstrated zero-order drug release for 24 h at different pH conditions; moreover, retardation of drug release was observed with increment of osmolality. This system could be a platform technology for controlled delivery of poorly water-soluble drugs.

Formulation and optimization of sustained release Stavudine microspheres using response surface methodology

The aim of the current study was to formulate and optimize the formulation on the basis of in vitro performance of microsphere. A 3² full factorial design was employed to study the effect of independent variables, polymer-to-drug ratio (X₁) and stirring speed (X₂), on dependent variables, encapsulation efficiency, particle size, and time to 80% drug release. The best batch exhibited a high entrapment efficiency of 70% and mean particle size 290 μm. The drug release was also sustained for more than 12 hours. The study helped in finding the optimum formulation with excellent sustained drug release.

Novel microparticle drug delivery systems based on chitosan and Eudragit® RSPM to enhance diltiazem hydrochloride release property

The aim of this study was to enhance the release properties of diltiazem hydrochloride (diltiazem HCl) by using microparticle system. For this reason, microparticle drug delivery systems based on chitosan and Eudragit(®)RSPM were developed. The microparticles were prepared by using double-emulsion solvent extraction method and the mean sizes of microparticles were less than 120 µm. The in vitro drug release from microparticles was studied in simulated gastric (pH 1.2) and intestinal media (pH 7.4) than the results were evaluated by kinetically. In vitro diltiazem HCl release from microparticles showed good zero order kinetic. For the microparticles with chitosan, the release of diltiazem HCl at pH 1.2 could be effectively sustained, while the release of diltiazem HCl increased at pH 7.4 when compared to Eudragit(®)RSPM microparticles. The highest release percent obtained was 1:1 ratio of drug: polymer at pH 1.2 and 7.4. All results clearly suggest that the release properties of diltiazem HCl were improved by using microparticle systems especially which contain chitosan.

Development and evaluation of controlled porosity osmotic pump for nifedipine and metoprolol combination

Background

A system that can deliver multi-drug at a prolonged rate is very important for the treatment of various chronic diseases such as diabetes, asthma and heart disease. Controlled porosity osmotic pump tablet (CPOP) system was designed to deliver Nifedipine (NP) and Metoprolol (MP) in a controlled manner up to 12 h. It was prepared by incorporating drugs in the core and coated with various types (PVP, PEG-400 and HPMC) and levels (30, 40 and 50% w/w of polymer) of pore former at a weight gain of 8, 12 & 15%.

Results

Formulation variables like type and level of pore former and percent weight gain of membrane was found to affect the drug release from the developed formulations. Drug release was inversely proportional to the membrane weight but directly related to the level of pore former. Burst strength of the exhausted shell was inversely proportional to the level of pore former, but directly affected by the membrane weight. Results of scanning electron microscopy (SEM) studies showed the formation of pores in the membrane from where the drug release occurred. Dissolution models were applied to drug release data in order to establish the mechanism of drug release kinetics. In vitro release kinetics was subjected to superposition method to predict in vivo performance of the developed formulation.

Conclusion

The developed osmotic system is effective in the multi-drug therapy of hypertension by delivering both drugs in a controlled manner.

Design, in vitro and in vivo evaluation of glipizide Eudragit microparticles

Glipizide microparticles made with Eudragit (RS 100 and RL 100), prepared by emulsion solvent evaporation technique were evaluated for various in-vitro properties viz. encapsulation efficiency, particle size and surface morphology, drug release pattern and in-vivo hypoglycaemic activity. The optimized formulation parameters were used to prepare smooth and spherical microparticles (2-32 microm) with higher entrapment efficiency (67-89%). Drug release patterns of glipizide microparticles of Eudragit RS 100 and Eudragit RL 100 with drug-to-polymer ratio of 1 : 4 (i.e. EGM14 and ELGM14) have shown gradual and extended release for 24 h with cumulative release of glipizide to the extent of 72.3% and 83.9%, respectively. However, EGM14 showed a significant in-vivo hypoglycaemic effect up to 12 h in rabbits while ELGM14 showed for 9 h. Hence, glipizide microparticles of Eudragit RS 100 (glipizide: polymer 1 : 4) is better suited for oral sustained release formulation.

Simultaneous delivery of Nifedipine and Metoprolol tartarate using sandwiched osmotic pump tablet system

The sandwiched osmotic tablet system that could deliver Nifedipine and Metoprolol tartarate simultaneously for extended period of time was developed in order to reduce the problems associated with multidrug therapy of hypertension. This system composed of a middle push layer and attached drug layers of Nifedipine and Metoprolol. The advantage of the sandwiched osmotic tablet system over the commercialized push-pull osmotic tablet system is its simplicity of preparation, as the surface identification was avoided. Polyethylene oxide 600,000 and 8,000,000 g/mole were used as thickening agent of drug layer and the expandable hydrogel of push layer, respectively. It has been observed that amount of polyethylene oxide (PEO) and KCL of the drug and push layer had profound influence on Nifedipine and Metoprolol release. Further, the release of drugs was optimized by the size of the delivery orifice, level of plasticizer and membrane thickness. The optimal osmotic pump tablet was found to deliver both drugs at a rate of approximately zero order for up to 16 h independent of pH and agitational intensity, but dependent on the osmotic pressure of the release media. The formulations were found to be stable after 3 months of accelerated stability studies. Prediction of steady-state levels showed the plasma concentrations of Nifedipine and Metoprolol to be within the desired range. Further sandwiched system had a good sustained effect in comparison with the conventional product. Hence the prototype design of the system could be applied to other combinations of drugs used for cardiovascular diseases, diabetes, etc.

Preparation and In Vitro/In Vivo Evaluation of Gliclazide Loaded Eudragit Nanoparticles as a Sustained Release Carriers

The aim of this study was to formulate and optimize gliclazide-loaded Eudragit nanoparticles (Eudragit L100 and Eudragit RS) as a sustained release carrier with enhanced efficacy. Eudragit L 100 nanoparticles (ELNP) were prepared by controlled precipitation method whereas Eudragit RSPO nanoparticles (ERSNP) were prepared by solvent evaporation method. The influence of various formulation factors (stirring speed, drug:polymer ratio, homogenization, and addition of surfactants) on particle size, drug loading, and encapsulation efficiency were investigated. The developed Eudragit nanoparticles (L100 and RS) showed high drug loading and encapsulation efficiencies with nanosize. Mean particle size altered by changing the drug:polymer ratio and stirring speed. Addition of surfactants showed a promise to increase drug loading, encapsulation efficiency, and decreased particle size of ELNP as well as ERSNP. Dissolution study revealed sustained release of gliclazide from Eudragit L100 as well as Eudragit RSPO NP. SEM study revealed spherical morphology of the developed Eudragit (L100 and RS) NP. FT-IR and DSC studies showed no interaction of gliclazide with polymers. Stability studies revealed that the gliclazide-loaded nanoparticles were stable at the end of 6 months. Developed Eudragit NPs revealed a decreased t(min) (ELNP), and enhanced bioavailability and sustained activity (ELNP and ERSNP) and hence superior activity as compared to plain gliclazide in streptozotocin induced diabetic rat model and glucose-loaded diabetic rat model. The developed Eudragit (L100 and RSPO) NP could reduce dose frequency, decrease side effects, and improve patient compliance.

Studies on dissolution enhancement and mathematical modeling of drug release of a poorly water-soluble drug using water-soluble carriers

Role of various water-soluble carriers was studied for dissolution enhancement of a poorly soluble model drug, rofecoxib, using solid dispersion approach. Diverse carriers viz. polyethylene glycols (PEG 4000 and 6000), polyglycolized fatty acid ester (Gelucire 44/14), polyvinylpyrollidone K25 (PVP), poloxamers (Lutrol F127 and F68), polyols (mannitol, sorbitol), organic acid (citric acid) and hydrotropes (urea, nicotinamide) were investigated for the purpose. Phase-solubility studies revealed AL type of curves for each carrier, indicating linear increase in drug solubility with carrier concentration. The sign and magnitude of the thermodynamic parameter, Gibbs free energy of transfer, indicated spontaneity of solubilization process. All the solid dispersions showed dissolution improvement vis-à-vis pure drug to varying degrees, with citric acid, PVP and poloxamers as the most promising carriers. Mathematical modeling of in vitro dissolution data indicated the best fitting with Korsemeyer-Peppas model and the drug release kinetics primarily as Fickian diffusion. Solid state characterization of the drug-poloxamer binary system using XRD, FTIR, DSC and SEM techniques revealed distinct loss of drug crystallinity in the formulation, ostensibly accounting for enhancement in dissolution rate.

Preclinical Assessment of the Feasibility of Applying Controlled Release Oral Drug Delivery to a Lead Series of Atypical Antipsychotics

In this paper, we present a preclinical approach for evaluating the feasibility of applying controlled-release (CR) oral drug delivery to increase the duration of exposure and lower the C(max) of compounds in a lead series of short half-life atypical antipsychotics. Three lead compounds in the series had demonstrated potential pharmacological benefits for the treatment of psychosis, in preclinical studies. However, the compounds showed evidence of insufficient half-lives to enable a once-a-day (QD) product using immediate-release (IR) oral delivery. To evaluate and compare the potential for oral CR delivery to extend the duration of action and thereby enable QD administration, the in vitro solubility and permeability, and the duodenal and colonic absorption of three compounds in the series were measured. Based on the results, one candidate was selected for advancement that showed moderate in vitro solubility, but had the highest in vitro permeability and ratio of colonic to duodenal bioavailability (0.9) in the rat. The results from this study provided evidence that a CR drug delivery system could be used to extend the duration of exposure of the compounds in the series and a scientific basis for selecting one of the three compounds as a candidate.

Development and evaluation of osmotically controlled oral drug delivery system of glipizide

Extended release formulation of glipizide based on osmotic technology was developed and evaluated. The effect of different formulation variables, namely, level of solubility modifier in the core, membrane weight gain, and level of pore former in the membrane, were studied. Drug release was found to be affected by the level of solubility modifier in the core formulation. Glipizide release was inversely proportional to the membrane weight but directly related to the initial level of pore former (PVP) in the membrane. Burst strength of the exhausted shells increased with the weight gain of the membrane. On the other hand, burst strength decreased with an increase in the level of pore former in the membrane. Drug release from the developed formulations was independent of pH and agitational intensity, but dependent on the osmotic pressure of the release media. Results of SEM studies showed the formation of pores in the membrane from where the drug release occurred. The numbers of pores were directly proportional to the initial level of pore former in the membrane. The manufacturing procedure was found to be reproducible and formulations were stable after 3 months of accelerated stability studies.

In Vitro–In Vivo Characterization of Release Modifying Agents for Parenteral Sustained‐Release Ketorolac Formulation

One of the prerequisites for a parenteral preparation is that the excipients incorporated are biocompatible and biodegradable. In the present study hydrophilic and hydrophobic excipients were investigated for developing an intramuscular sustained-release formulation of ketorolac. Kollidon 17 PF, Peceol (glyceryl monooleate), and castor oil were chosen as the potential release-retarding agents, each with a distinct mechanism of action. They were evaluated by in vitro drug-release profiles and in vivo pharmacodynamic and pharmacokinetic study in mice. Cumulative drug release was determined for standard and test formulations in modified Franz diffusion cell. Pharmacodynamic parameter, T = 70% response of peak analgesic response, was used to compare the performance of test formulations. Based on pharmacodynamic/pharmacokinetic correlation in the animal studies, Css(max) and Css(min) of 51.39 and 30.0 microg/mL, respectively, were determined and considered as performance markers for pharmacokinetic evaluation of test formulations. The study suggested that the sustained-release capability of glyceryl monooleate was maximum followed by that of castor oil and Kollidon 17 PF, when compared to conventional ketorolac tromethamine formulation. It was inferred that water soluble excipient, though, showed release retarding property in vitro but could not maintain it in the in vivo environment. Glyceryl monooloeate-based formulation produced the most favorable drug blood concentration vs. time profile.

Preparation and in vitro evaluation of Eudragit microspheres containing acetazolamide

The aim of this study was to prepare and evaluate Eudragit (RS and RL) microspheres containing acetazolamide. Microspheres were prepared by solvent evaporation method using acetone/liquid paraffin system. The influence of formulation factors (stirring speed, polymer:drug ratio, type of polymer, ratio of the combination of polymers) on particle size, encapsulation efficiency and in vitro release characteristics of the microspheres were investigated. The yields of preparation and the encapsulation efficiencies were high for all formulations the microspheres were obtained. Mean particle size changed by changing the polymer:drug ratio or the stirring speed of the system. Although acetazolamide release rates from Eudragit RS microspheres were very slow and incomplete for all formulations, they were fast from Eudragit RL microspheres. When Eudragit RS was added to Eudragit RL microsphere formulations, release rates slowed down and achieved the release profile suitable for peroral administration.

Pharmacokinetic evaluation of an azithromycin controlled release dosage form in healthy human volunteers: a single dose study

Azithromycin (AZI) follows a two-compartment model pharmacokinetically. The purpose of this study was to evaluate the in vivo performance of a controlled release (CR) formulation of AZI, which would eliminate the risk of high peak plasma concentrations obtained within 2-3 h after peroral administration of immediate release (IR) products. The study was conducted in twelve healthy male human volunteers to compare an experimental NIPER product (CR tablets) with Vicon (IR tablets) at the same dose level as a single-dose, randomized, one-period, two-treatment, and parallel-study. Concentrations of AZI in serum samples were assessed using the validated HPLC method. From the serum concentration-time profiles various pharmacokinetic parameters (AUC(0-96), AUC(0-inf), C(max) and T(max)) were calculated for both products. Results showed that the high peak concentration obtained by administration of a conventional IR formulation were eliminated with the CR product. A mean dosage form index (DI) of 1.17 with fluctuations of 7.57% was obtained with the CR product at steady state level, indicating reduced fluctuations at the steady state serum concentrations. Elimination of the pronounced peak as well as fluctuations reduced or minimized AZI adverse effects associated with the IR product.

Design of controlled release delivery systems using a modified pharmacokinetic approach: a case study for drugs having a short elimination half-life and a narrow therapeutic index

The objectives of peroral controlled release drug delivery systems (CRDDS) are to maintain therapeutically effective plasma drug concentration levels for a longer duration thereby reducing the dosing frequency and to minimise the plasma drug concentration fluctuations at steady state by delivering drug in a controlled and a reproducible manner. Drug delivery rate, duration of delivery and the dosing interval are the target features for any temporal CRDDS. The classical pharmacokinetic model for designing CRDDS [Drug Dev. Ind. Pharm. 15 (1989) 1073] assumes the time of drug delivery (t(del)) to be less than the dosing interval. However, termination of drug release from such a CRDDS at t(del) and/or a declining drug input function towards the terminal phase of t(del) from a first order kinetic CRDDS can have severe implications on plasma drug concentration and steady state fluctuations for a drug with very short half-life. A case study is presented in this paper, wherein by means of theoretical calculations using a classical pharmacokinetic approach, it is shown that a first order kinetic CRDDS for hypothetical drugs with short elimination half-life and different pharmacokinetic conditions would result in sub-therapeutic plasma concentrations at least for some time during the dosing interval at steady state. In order to avoid sub-therapeutic plasma drug concentrations a modification in classical pharmacokinetic model is proposed and discussed through theoretical calculations for different hypothetical pharmacokinetic situations and a practical single dose pharmacokinetic study with a first order kinetic CRDDS for nifedipine (a short half-life drug; about 2h). It is shown that improved therapeutic efficacy could be expected from a CRDDS developed based on proposed modification in the classical pharmacokinetic model.

In vitro release of metoclopramide from hydrophobic matrix tablets. influence of hydrodynamic conditions on kinetic release parameters

There has been growing interest in the subject of drug delivery and the design and evaluation of controlled-release systems. The simplest way to control the release of an active agent is to disperse it in an inert polymeric matrix. Controlled-release systems are of interest because they are technologically simple, relatively cheap, and practically unaffected by physiological changes. In this study, a new matrix system was formed by an active principle, metoclopramide hydrochloride, scattered into a biocompatible hydrophobic polymerical mesh, polyamide 12, to achieve sustained and controlled delivery of metoclopramide hydrochloride. This research was conducted to investigate the in vitro drug release behavior from these new inert polymeric matrix tablets. The drug release process was investigated both experimentally and by means of mathematical models. Different models were applied for the evaluation of drug release data. On the basis of our results, a biexponential equation was proposed, Q=Qfast(1)(1 - e(-Kfast t)) + Qslow(2)(1 - e(-Kslow t)), in an attempt to explain the mechanism responsible for the release process. Additionally, the influence of the experimental conditions of the dissolution devices, such as rate of flow and pH of dissolution medium, on the parameters that characterize the release mechanism was studied, and it was found that the main factor was the hydrodynamic condition of rate of flow.

Drug delivery: an odyssey of 100 years

Drug delivery has metamorphosed from the concept of a pill to molecular medicine in the past 100 years. Better appreciation and integration of pharmacokinetic and pharmacodynamic principles in design of drug delivery systems has led to improved therapeutic efficacy. A greater understanding of the molecular transport in relation to physico-chemical properties has led to the evolution of a biopharmaceutics classification system, which should be a future road map, governing drug design, development and delivery. While drugs belonging to class I and II will be delivered by established platform technologies, novel delivery strategies will evolve and mature to realize the potential of 'new generation' biotech and non biotech drugs belonging to class III and IV, respectively.

A biopharmaceutic approach in designing a controlled release tablet of sodium monofluorophosphate: 1. In vitro and in vivo studies in beagle dogs

The purpose of this study was to develop a controlled release tablet (CRT) of sodium monofluorophosphate (NaMFP) based on biopharmaceutic and pharmacokinetic principles. NaMFP was introduced in the early eighties to treat osteoporosis. The required dose size (200 mg of NaMFP) and time of drug delivery (8.3 h) were theoretically determined based on the pharmacokinetic parameters of fluoride (F-). A CRT was formulated with ethyl cellulose (EC) by the direct compression method. The ratio of drug to polymer was adjusted 1:1, after studying the in vitro release profiles. The release mechanism from the developed dosage form followed the square root of time relationship. This dosage form was evaluated for its in vivo performance in dogs. The pharmacokinetics of F-, after the IV and PO administration of NaMFP, was determined to standardize the animal model. F- followed a two-compartment model and no significant differences were found between the two routes of administration. The bioavailability in dogs was only 60%. The reason for this poor bioavailability was postulated to be the delivery of drug extended beyond the principal sites of absorption of the gastrointestinal tract. Hence, we decided to characterize the absorption sites of NaMFP and to modify the CRT.