Optimization of release from magnetically controlled polymeric drug release devices

Release rates from drug:polymer matrices embedded with small magnets increase in the presence of oscillating magnetic fields. Previous studies of these systems have defined those parameters that determine the extent of the increase in release, and implied that not only was the force generated within the matrix an important determinant of the extent of modulation but also that the greater the amount of matrix actually displaced, the greater the observed modulation. We investigated this possibility in the magnetic system and developed a model taking into account the intersection of the volume of a cylindrical polymer-drug magnet embedded matrix with an imaginary sphere representing the upper limit of matrix deformation by the magnet. The intersection correlated in a linear fashion with the increase in release (slope = 1.16 +/- 0.26, R = 0.864, P = 0.003, s.e.e. = 1.38). Magnet orientation alone was insufficient to explain the data. It appears that a modulated system is optimized when the modulating force overlaps precisely with the maximum amount of matrix drug that can be released. If the size of the matrix, position of the magnet, force generated on the matrix by the magnet, viscoelastic properties of the matrix, etc. are not matched then modulation is inefficient. These results should provide further insight into and a means of optimization for externally regulated controlled release systems.     

Swelling of and drug release from monoglyceride-based drug delivery systems

Sudden sensorineural hearing loss (SNHL) is a well-recognized phenomenon that is attributed to a variety of etiologies. Sudden SNHL after cardiopulmonary bypass surgery has been well reported and is thought to be due to microemboli. However, a review of the English literature revealed only 15 cases of SNHL after general anesthesia for nonotologic surgery. Several etiologies for this loss have been suggested, but no proven pathogenesis is yet available. This report adds to the literature three additional cases of sudden SNHL after general anesthesia for nonotologic surgery. The literature is reviewed and proposed mechanisms of injury are discussed.     

Formulation of controlled release drug preparations with antacid effect

Opportunities for the formulation of long-acting antacid preparations were demonstrated summarizing the results of pharmaceutical technological experiments. The telemetric intragastric data were in correlation with the in vitro measurements and demonstrated the significantly higher bioavailability of long-acting antacid preparations.     

Effects of drug solubility, drug loading, and polymer molecular weight on drug release from Polyox tablets

BACKGROUND: This study augments a randomized controlled trial to analyze the cost-effectiveness of 2 standardized treatments for major depression relative to each other and to the "usual care" provided by primary care physicians. METHODS: A randomized controlled trial was conducted in which primary care patients meeting DSM-III-R criteria for current major depression were assigned to pharmacotherapy (where nortriptyline hydrochloride was given) or interpersonal psychotherapy provided in a standardized framework or a primary physician's usual care. Two outcome measures, depression-free days and quality-adjusted days, were developed using information on depressive symptoms over time. The costs of care were calculated. Cost-effectiveness ratios comparing the incremental outcomes with the incremental costs for the different treatments were estimated. Sensitivity analyses were performed. RESULTS: In terms of both economic costs and quality-of-life outcomes, patients assigned to the pharmacotherapy group did slightly better than those assigned to interpersonal psychotherapy. Both standardized therapies provided better outcomes than primary physician's usual care, but each consumed more resources. No meaningful cost-offsets were found. The incremental direct cost per additional depression-free day for pharmacotherapy relative to usual care ranges from $12.66 to $16.87 which translates to direct cost per quality-adjusted year gained from $11270 to $19510. CONCLUSIONS: Standardized treatments for depression lead to better outcomes than usual care but also lead to higher costs. However, the estimates of the cost per quality-of-life year gained for standardized pharmacotherapy are comparable with those found for other treatments provided in routine practice.     

PLGA nanoparticles prepared by nanoprecipitation: drug loading and release studies of a water soluble drug

The nanoprecipitation technique for preparation of nanoparticles suffers the drawback of poor incorporation of water soluble drugs. The aim of this study was therefore to assess various formulation parameters to enhance the incorporation of a water soluble drug (procaine hydrochloride) into poly(dl-lactide-co-glycolide) (PLGA) nanoparticles prepared by this technique. Approaches investigated for drug incorporation efficiency enhancement included the influence of aqueous phase pH, replacement of procaine hydrochloride with procaine dihydrate and the inclusion of excipients: poly(dl-lactide) (PLA) oligomers, poly(methyl methacrylate-co-methacrylic acid) (PMMA-MA) or fatty acids into the formulation. The nanoparticles produced were submicron size (<210 nm) and of low polydispersity. It was found that an aqueous phase pH of 9.3, replacement of procaine hydrochloride with procaine dihydrate and the incorporation of PMMA-MA, lauric and caprylic acid into the formulation could enhance drug incorporation efficiency without the size, morphology and nanoparticle recovery being adversely influenced. For instance changing the aqueous phase pH from 5.8 to 9.3 increased nanoparticle recovery from 65.1 to 93.4%, drug content from 0.3 to 1.3% w/w and drug entrapment from 11.0 to 58.2%. However, the presence of high ratios of lauric acid and procaine dihydrate in the formulation adversely affected the morphology and size of the nanoparticles. Also, PLA oligomers were not considered a feasible approach since it decreased drug entrapment from 11.0 to 8.4% and nanoparticle recovery from 65.1 to 19.6%. Drug release from nanoparticles appears to consist of two components with an initial rapid release followed by a slower exponential stage. This study has demonstrated that formulation variables can be exploited in order to enhance the incorporation of a water soluble drug into PLGA nanoparticles by the nanoprecipitation technique.     

T4 and T3 release from the perfused canine thyroid isolated in situ

A method for once-through perfusion of the canine thyroid isolated in situ is described. The perfusion medium was a modified Krebs Ringer buffer with 4% dextran added. In 4 control experiments of the T4 and T3 concentratios in effluent were stable or slightly falling during 3 h perfusion. There were no significant alterations in the T4/T3 ratio in the effluent during these experiments. A 10-min infusion of bovine TSH (1 mU/ml) caused an increase in the release of T4 and T3 after 15-25 min. The T4/T3 ration in the effluent was significantly reduced after TSH stimulation. However, the ratio returned to pre-stimulation values while the hormone release was still very high. T4 and T3 content of the contralateral thyroid was determatio in the homogenate was twice as high as the T4(3 ratio in the effluent during control perfusion. Thus there was a preferential secretion of T3 from the perfused canine thyroid and this was increased after TSH stimulation.     

The antinarcoleptic drug modafinil increases glutamate release in thalamic areas and hippocampus

The antinarcoleptic drug modafinil [(diphenyl-methyl)-sulfinyl-2-acetamide; Modiodal] dose-dependently inhibits the activity of GABA neurons in the cerebral cortex and in the nucleus accumbens, as well as in sleep-related brain areas such as the medial preoptic area and the posterior hypothalamus. This study examined the effects of modafinil (30-300 mg/kg, i.p.) on dialysate glutamate and GABA levels in the ventromedial (VMT) and ventrolateral (VLT) thalamus and hippocampal formation (Hip) of the awake rat. The results show a maximal increase in glutamate release in these brain regions at the 100 mg/kg dose, associated with a lack of effect on GABA release. Thus modafinil may increase excitatory glutamatergic transmission in these regions, altering the balance between glutamate and GABA transmission.     

Simple methods for determination of the release limits for drug products

Gradients of cellular activities are ubiquitous in embryonic development. It is widely believed that the inhomogeneous spatial distribution of a morphogen would be able to set up such gradients. But how then does the morphogen propagate in the first place? Straightforward molecular diffusion is often proposed as a possible mechanism. We first show that, surprisingly, the mere binding of the diffusing morphogen to its membrane receptors suffices to prevent the establishment of a concentration-based positional signalling system. Instead, a flat, saturated distribution of receptor-bound morphogen builds up. Because the distribution spreads gradually from the morphogen source, however, cells may still know their position if they are able to integrate the morphogen signal in time. The irregularities of diffusion in the complex extracellular medium would in fact be partially compensated for by such time summation. Another, non-exclusive possibility is that morphogen transport does not occur by simple diffusion only. We put forth a novel model of receptor-aided, directed diffusion that achieves a spatial distribution of morphogen. Our model is based, as an illustration, on the properties of members of the TGFbeta family of molecules. We show that two simple hypotheses regarding the kinetics of TGBbeta binding to its receptors suffice to establish a remarkable transfer mechanism whereby a morphogen such as activin could be both propagated along cell membranes, and transferred between cells that are in contact. The model predicts that morphogen propagation properties depend strongly on the closeness of cell-cell appositions, does not necessitate protein synthesis, accumulation or slow degradation (in contrast to the diffusion/time integration model), and that the morphogen is localised mostly on or close to cell membranes.     

Evaluation of solubilizers in the drug release testing of hydrophilic matrix extended-release tablets of felodipine

The drug release of felodipine, a water-insoluble drug, was tested by using sodium lauryl sulphate (SLS), polyoxyethylene 20 sorbitan monooleate (Tween) or cetyltrimethylammonium bromide (CTAB) in the test medium as solubilizers. Three slightly different felodipine extended-release (ER) tablets 10 mg based on the gel matrix principle were evaluated under different solubilizer concentrations, agitation intensities and pH. These tablets were also tested in a bioavailability study together with an oral solution. All three solubilizers substantially enhanced the drug solubility and sink conditions were obtained. The choice of solubilizer affected the drug release rate. This is most probably due to physico-chemical interactions between the gel-forming agent and the solubilizers. All in vitro test conditions provided a good correlation (r2 = 0.94-0.97) to in vivo dissolution, as determined by moment analysis. However, a much steeper in vitro/in vivo relationship was obtained for SLS compared to Tween and CTAB reflecting an inferior discrimination between the tablets by use of this anionic solubilizer.     

A two-phase model for controlled drug release from biphasic polymer hydrogels

A comprehensive two phase model is developed to describe the sustained release of a solute or drug from a biphasic hydrogel substrate. Such a material consists of a continuous hydrophilic phase (polymer backbone in water) and a dispersion of spherical microdomains made of the hydrophobic side chains of the polymer organised in a micelle like fashion. The solute or drug is assumed to be encapsulated within the dispersed microdomains, and to diffuse from the interior to the surface of the microdomain where it exchanges following a Langmuir isotherm. Mass transfer to the bulk phase occurs by desorption of the drug from the surface through a driving force that is proportional to the difference of surface and bulk concentration. Accordingly the drug is released to the surroundings by diffusion through the bulk. Depending on the values of the Langmuir constant and assuming well stirred behaviour in the interior of the microdomain, the present model results in either of the two asymptotic models developed in previous studies. The results of a parametric study show that the desired steady state flux of a specific drug to the surroundings may be obtained given appropriate values of structural properties of the material. This conclusion is further supported when using this model to simulate earlier experimental results. The polymer structural properties can be manipulated easily during the fabrication of dispersed-phase networks, as indicated by preliminary experiments.     

Effects of the antiparkinsonian drug budipine on neurotransmitter release in central nervous system tissue in vitro

The effects of the antiparkinsonian drugs budipine and biperiden on spontaneous and electrically evoked release of dopamine (DA), acetylcholine (ACh), GABA or noradrenaline (NA) were studied in caudate nucleus or cortex slices, respectively, of the rabbit brain. Whereas both drugs (1-10 microM) strongly increased spontaneous [3H]outflow in caudate nucleus slices preincubated with [3H]DA, budipine inhibited but biperiden facilitated the evoked DA release. In the presence of the DA-reuptake inhibitor nomifensine, a significant part of the budipine-induced basal [3H] outflow consisted of unmetabolized DA. Synaptosomal high-affinity uptake of [3H]DA was only weakly affected by budipine and biperiden (IC50 values, 11 and 9 microM, respectively). Budipine enhanced also basal [3H]outflow from cortex slices prelabeled with [3H]NA, however this outflow consisted mainly of NA metabolites even in the presence of cocaine. The evoked release of [3H]ACh in rabbit caudate nucleus slices preincubated with [3H] choline was almost unaffected by budipine but enhanced by biperiden in the absence of further drugs. In the presence of nomifensine, however, budipine inhibited, but biperiden still enhanced, the evoked ACh release. Moreover, both drugs showed antimuscarinic properties in the presence of the ACh esterase inhibitor physostigmine, i.e., they facilitated the evoked ACh release, exhibiting pA2 values of about 6.9 (budipine) and 8.3 (biperiden). Addition of the D2 receptor antagonist domperidone diminished all inhibitory effects of budipine on the evoked ACh release. The evoked overflow of [3H] in caudate nucleus slices preincubated with [3H]GABA was reduced by both budipine and biperiden. It is concluded that both anticholinergic and indirect dopaminomimetic properties contribute to the antiparkinsonian effects of budipine, whereas biperiden exhibits mainly anticholinergic effects. Moreover, both drugs might disinhibit GABA controlled neurons in the central nervous system.     

Synthesis of antibiotic-loaded interporous hydroxyapatite blocks by vacuum method and in vitro drug release testing

Interporous hydroxyapatite ceramic (Ca10(PO4)6(OH)2) has excellent bio-compatibility and interlinked pore structure, antibiotics could be loaded into pores in vacuum system. To confirm penetration of the agent to the HAb (2 cm3 cubic block), the aminoglycoside antibiotic (Isepamicin Sulfate; ISP) dissolved in eosin dye at various vacuum pressures. In ISP slow release study, the blocks were placed in 5 ml of PBS at a temperature of 37 degrees C. The PBS was replaced every 48 h and samples containing released ISP were stored until assay. All were found to release the drug maintaining a mean concentration of 0.41 microg ml(-1) even after 18 days of nine exchanges. This concentration of antibiotic exceeded the minimum inhibitory concentration against the common causative organisms of osteomyelitis. The results suggest that HAb impregnated with antibiotics using a simple vacuum system may serve as a valuable new method of administering local chemotherapy, primarily when used as a strut graft for bone defects.     

Oral solid controlled release dosage forms: role of GI-mechanical destructive forces and colonic release in drug absorption under fasted and fed conditions in humans

PURPOSE: This study was undertaken to examine the effects of mechanical destructive forces on drug release from controlled release (CR) dosage forms in vitro and in vivo and their colonic release, using two CR tablets of acetaminophen A and B, showing slower and faster erosion rates, respectively. METHODS: In vitro release rates were determined by several official methods. Tablets were administered to healthy volunteers under fasting and fed conditions. RESULTS: Both tablets showed similar release rates under mild destructive conditions (e.g., paddle method at 10 rpm) but CR-B showed faster release under highly destructive conditions (e.g., rotating basket method at 150 rpm), where the tablet was eroded. The in vivo release from CR-B was faster than from CR-A, possibly because of enhanced erosion. The variable in vivo release from CR-B indicated large inter-subject differences in destructive GI forces. The fastest in vivo release from CR-B among individuals was approximated by the in vitro dissolution determined by destructive methods such as the rotating basket at 150 rpm. The slowest in vivo release from tablets A and B was lower than the dissolution by the paddle method at 10 rpm. The release from both tablets was markedly reduced at 3-4 hrs after dosing irrespective of feeding conditions which can be attributed to release inhibition in the colon. CONCLUSIONS: Effects of GI destructive forces on the tablet erosion and the release inhibition in the colon must be considered in the development of CR dosage forms.     

Mathematical modelling of the release of drug from porous, nonswelling transdermal drug-delivery devices

A general model is presented for the release of drug from porous nonswelling, transdermal drug-delivery devices and it is shown to reduce to previously proposed models in suitable limits. The processes which govern the release of drug are considered to be diffusion of dissolved drug and dissolution of dispersed drug, both in the body of the device and in the device pores, and transfer of drug between the two domains. In the classical limit of large dissolution rates, the problem reduces to one of the moving-boundary type, and solution of this problem in the case where the initial drug loading is much greater than the drug solubility in the device yields expressions for the flux of drug to a perfect sink (modelling in vitro conditions). It is shown that behaviour greatly differing from the classical first-order drug delivery (alpha t 1/2) may be exhibited, depending upon the parameter regime. In some situations the dissolution rates may not be so large and solutions of the general model are derived in the case where the dispersed drug is considered to be undepleted and the diffusivity in the solvent-filled pores is much larger than in the body of the delivery device. Numerical studies are undertaken, and the coupling of delivery device and skin-diffusion models (in order to model the complete transdermal drug-delivery process) is also considered.     

Effect of temperature on bleeding and drug release from a liquid droplet dispersion ointment

A liquid droplet dispersion ointment, LDDS, a formulation containing a drug solution as droplets in an oily vehicle, is excellent for percutaneous drug absorption. Bleeding of LDDS and in vitro drug release from LDDS were found to be enhanced by temperature increase. The influence of temperature on the physical properties of LDDS was studied using differential scanning calorimetry and X-ray diffraction spectroscopy. The liquid component content, possibly a hydrocarbon in the vehicle, increased with temperature; this may have been due to melting of the vehicle. In this liquid component, the drug concentration measured by HPLC increased with temperature. This change in the drug concentration may cause an increase in drug release, leading to the conclusion that, compared with conventional ointments, temperature has much greater effect on drug release from LDDS.