International Journal of Pharmaceutics (v.317, #2)

Limitations of the Heckel equation in characterizing material compression behavior have been well reported. In this work, the Gurnham equation, which was first introduced in chemical engineering, is proposed as an alternate method of evaluating the compressibility of pharmaceutical powders. The Gurnham equation was adapted for tablet compression and the estimated slope parameter c was proposed to represent material compressibility. Data from the compression of four commonly used excipients (microcrystalline cellulose, corn starch, lactose monohydrate, and dibasic calcium phosphate dihydrate) and one drug (acetaminophen) were evaluated using the Gurnham equation. Using compression data at different peak pressures, linear relationships between porosity and ln Pressure of the five materials were obtained. The determined parameter c expresses the compressibility of materials. The analysis of previous experimental data, including granulations, mixtures and co-processed materials also indicates that c might be a representative parameter for material compressibility.
Keywords: Compressibility; Heckel equation; Gurnham equation; Peak pressure; Porosity; Compression;

Preparation and evaluation of oral solid heparin using emulsifier and adsorbent for in vitro and in vivo studies by Yukako Ito; Tomohiro Kusawake; Y.V. Rama Prasad; Nobuyuki Sugioka; Nobuhito Shibata; Kanji Takada (114-119).
Oral anticoagulant therapy with heparin has been challenged by formulating heparin in oral solid preparation. As heparin, low molecular weight heparin (LMWH) was used. LMWH was dispersed with a surfactant used for the self-microemulsifying drug delivery system (SMEDDS), PEG-8 caprylic/capric glycerides (Labrasol), and the mixture was solidified with three kinds of adsorbents, microporous calcium silicate (Florite™ RE), magnesium alminometa silicate (Neusilin™ US2) and silicon dioxide (Sylysia™ 320). The in vitro release study showed that the T50%s were 3.2 ± 0.1 min for Sylysia 320, 4.6 ± 0.2 min for Florite RE, 13.7 ± 0.1 min for Neusilin US2. The in vivo rat absorption study showed that Florite RE system had the highest C max, 0.42 ± 0.01 IU/mL and AUC, 0.59 ± 0.06 IU h/mL, where plasma LMWH levels were measured as anti-Xa activity. Other preparations had the C max and AUC, 0.12 ± 0.01 IU/mL and 0.15 ± 0.02 IU h/mL for Neusilin US2 and 0.25 ± 0.02 IU/mL and 0.40 ± 0.03 IU h/mL for Sylysia 320, respectively. The bioavailability (BA) of LMWH from the microporous calcium silicate preparation, Florite RE, was 18.8% in rats by comparing the AUC obtained after i.v. injection of LMWH, 40 IU/kg to another group of rats. Florite RE system was evaluated in dogs after oral administration in an enteric capsule made of Eudragit S100 at the LMWH dose of 200 IU/kg. High plasma anti-Xa activity levels were obtained, i.e., the C max was 0.48 ± 0.11 IU/mL and AUC was 1.64 ± 0.32 IU h/mL. These results suggest that adsorbent system is useful as an oral solid delivery system of poorly absorbable drugs such as LMWH.
Keywords: Low molecular weight heparin; Labrasol; Adsorbent; Microporous calcium silicate; Magnesium alminometa silicate; Silicon dioxide; Absorption enhancement;

We have found that a white film forms on tablets when a coating solution consisting of hydroxypropyl methylcellulose (HPMC), polyethylene glycol (PEG 6000) and calcium lactate pentahydrate (CLP) is used. The white film has also been found in casting film consisting of HPMC and CLP, and the surface state of coated tablets has been shown to be strongly affected by addition of PEG 6000. The aim of the present study was to investigate the mechanism of formation of this white film in order to derive an appropriate film prescription. Interaction among the base ingredients of the film was investigated using differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD) and Fourier transform-infrared (FT-IR) spectroscopy. The casting film formed with HPMC and a large excess of PEG 6000 was found to be crystalline in form. In contrast, the amorphous film consisting of HPMC, PEG 6000 and excess CLP exhibited the crystallinity film by an excess addition of CLP. Although the crystalline film had many cracks, the amorphous film appeared to be excellent as a tablet coating. The most probable interaction sites between HPMC and CLP were demonstrated by FT-IR analysis of casting films consisting of HPMC, CLP and PVP.
Keywords: HPMC; Calcium lactate pentahydrate; PEG 6000; Coating; White film;

The biodegradable chitosan microspheres containing vancomycin hydrochloride (VANCO) were prepared by spray drying method with different polymer:drug ratios (1:1, 2:1, 3:1 and 4:1). Thermal behaviour, particle size and distribution, morphological characteristics, drug content, encapsulation efficiency, in vitro release assessments of formulations have been carried out to obtain suitable formulation which shows sustained-release effect when implanted. Sterilized VANCO loaded microspheres were implanted to proximal tibia of rats with methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis. Intramuscular (IM) injection of VANCO for 21 days was applied to another group for comparison. After 3 weeks of treatment, bone samples were analysed with a microbiological assay.According to the results, encapsulation efficiency and yield of microspheres in all formulations were higher than 98% and 47%, respectively. Particle sizes of microspheres were smaller than 6 μm. All microsphere formulations have shown sustained-release effect. In vitro drug release rate decreased due to the increase in polymer:drug ratio but no significant difference was seen between these results (p  > 0.05). Based on our in vivo data, rats implanted VANCO-loaded chitosan microspheres and administered IM injection showed 3354 ± 3366 and 52500 ± 25635 colony forming unit of MRSA in 1 g bone samples (CFU/g), respectively.As a result, implanted VANCO-loaded microspheres were found to be more effective than IM route for the treatment of experimental osteomyelitis.
Keywords: Vancomycin; Biodegradable microspheres; Chitosan; Spray drying method; Methicillin-resistant Staphylococcus aureus; Experimental osteomyelitis;

Controlled drug release from Gelucire-based matrix pellets: Experiment and theory by F. Siepmann; S. Muschert; M.P. Flament; P. Leterme; A. Gayot; J. Siepmann (136-143).
The aim of this work was to elucidate the underlying drug release mechanisms from lipidic matrix pellets, using theophylline and Gelucire 50/02 as model drug and carrier material, respectively. Pellets were prepared by two different techniques: melt-solidification and extrusion-spheronization. The effects of different formulations and processing parameters on the resulting drug release kinetics in 0.1N HCl and phosphate buffer pH 7.4 were studied and the obtained results analyzed using adequate mathematical models in order to get further insight into the underlying mass transport mechanisms. The type of preparation technique was found to strongly affect the underlying drug release mechanisms. Drug release from pellets prepared by the melt-solidification method was primarily controlled by pure diffusion, whereas drug release from pellets prepared by the extrusion-spheronization method was purely diffusion-controlled only at early time points. After approximately 2 h, the pellets started to disintegrate, resulting in decreased diffusion pathway lengths and, thus, increased drug release rates. Furthermore, the curing conditions significantly affected the theophylline release kinetics, whereas varying the initial drug loading from 20 to 50% (w/w) resulted only in a slight increase in the relative drug release rate. Interestingly, the effects of the size of pellets prepared by the melt-solidification method on the resulting drug release kinetics could be quantitatively predicted using an analytical solution of Fick's second law of diffusion. These predictions could be verified by independent experiments.
Keywords: Pellets; Controlled release; Extrusion-spheronization; Release mechanism; Diffusion; Gelucire;

Recombinant human parathyroid hormone 1–34: Pharmacokinetics, tissue distribution and excretion in rats by Zeping Hu; Huisheng Niu; Xiaoxia Yang; Huaifen Li; Guowei Sang; Bo Li (144-154).
The objective of this work was to characterize the preclinical pharmacokinetics, tissue distribution, and excretion profiles of recombinant human parathyroid hormone (1–34) [rhPTH (1–34)] in healthy rats. Pharmacokinetic properties of 125I-rhPTH (1–34) were examined after a single subcutaneous (s.c.) and intravenous (i.v.) bolus injection, respectively. Tissue distribution and urinary, fecal, and biliary excretion patterns of 125I-rhPTH (1–34) were also investigated following a single s.c. injection. Our results suggested that rhPTH (1–34) was rapidly distributed and cleared in a bi-exponential manner after a single i.v. bolus injection. Following a single s.c. administration, rhPTH (1–34) exhibited rapid and considerable absorption and declined in a mono-exponential manner, with the absolute bioavailability and elimination half-life of 65% and 3.4–4.1 h, respectively. The TCA-precipitated radioactivity was widely distributed and rapidly diminished in most tissues/organs. Approximately 91% and 2% of the total radioactivity was recovered in urine and feces by 72 h postdosing, respectively; whereas 6% excreted into bile up to 24 h postdosing. These findings indicated high absolute bioavailability, rapid absorption and disposition of rhPTH (1–34) following a single s.c. administration in healthy rats. The accumulation of rhPTH (1–34) in tissues/organs examined appeared to be low. The major elimination route was urinary excretion.
Keywords: Recombinant human parathyroid hormone (1–34); Pharmacokinetics; Distribution; Excretion; Bioavailability;

Investigation of factors responsible for low oral bioavailability of cefpodoxime proxetil by Vasu Kumar Kakumanu; Vinod Arora; Arvind K. Bansal (155-160).
Learning about the behavior of a drug in biological environment enables application of better formulation strategies to improve bioavailability of the same. Cefpodoxime proxetil (CP) is a prodrug, which is orally administered cephalosporin with only 50% absolute bioavailability. Despite previous studies, reasons responsible for low bioavailability of CP remain poorly understood. The present study tries to ascertain reasons for the low oral bioavailability of CP. The in vitro, in situ and ex vivo studies showed interesting results, where metabolism of CP into cefpodoxime acid (CA) inside the intestinal epithelial cell and preferential efflux of CA into lumen was identified as primary reason for low oral bioavailability of CP. Presence of specific carriers or transportation mechanism on the apical side membrane of enterocyte, than basal side of the same was observed.
Keywords: Cefpodoxime proxetil; Bioavailability; Reasons; Factors; Oral; Closed loop method; Everted sac; Tissue uptake; Permeability;

Equilibrium dialysis on povidone–iodine-solutions (Braunol®, standardized Betadine® and non-standardized iso-Betadine®) reveal that the amount of available iodine, free iodine, iodide and triiodide varies significantly both in the undiluted and diluted forms. These differences are reflected in the different bactericidal activity against Staphyloccus aureus as determined by the standard quantitative in vitro suspension test. The amount of available iodine is not an appropriate measure for an assessment of the microbicidal activity. For this, the free iodine has to be determined by means of equilibrium dialysis. The free iodine concentration in the Braunol® concentrate was found to be 22 mg/L, in the standardized Betadine® 9.7 mg/L and in the non-standardized Betadine® concentrate only 2.1 mg/L. Because of the atypical behaviour of iodophores and the increase of free iodine at dilution and because of a bactericidal level of free iodine of 5 mg/L, Braunol® and standardized Betadine® can be employed as disinfectant as such, iso-Betadine® has to be diluted before use. Summarizing all results, it can be stated that Braunol® is superior to standardized Betadine and unstandardized iso-Betadine® both as to the release of free iodine in the undiluted and in the diluted forms as in the killing rate of S. aureus.
Keywords: Povidone–iodine-commercial solutions; Determination of free iodine; Bactericidal activity;

The preparative method of a block copolymer of poly(dl-lactic acid) (PLA) and methoxypolyethylene glycol amine (MeO-PEG(N)), named PLA–(MeO-PEG), was refined. The degree of introduction of MeO-PEG(N) into PLA increased up to 55% (mol/mol) using a dichloromethane/methanol mixture (1:1, v/v) as a solvent at the reductive amination and taking all the fractions of the first peak in gel-chromatography. Plain and 1,1′-Dioctadecyl-3,3,3′,3′-tetramethylindodicarbocyanine (DiD)-loaded nanoparticles prepared using the PLA/PLA–(MeO-PEG) mixture of 45:55 (mol/mol) showed a mean size of 113 and 154 nm, respectively, and a positive zeta potential in water. DiD solution, i.v. administered, showed a lower plasma level and high distribution in liver, though DiD was distributed into the blood cells to a fair extent. Nanoparticles exhibited a higher plasma concentration of DiD than the DiD solution at 1 and 8 h, though DiD was distributed into the liver and spleen to a fair extent. Nanoparticles made of the PLA/PLA–(MeO-PEG) mixture of 44:55 (mol/mol) showed better plasma retention than those made of the PLA/PLA–(MeO-PEG) mixture of 64:36 (mol/mol). It is suggested that the PLA/PLA–(MeO-PEG) mixture nanoparticles with a higher PEG/PLA ratio should be useful as a carrier for the elevation of the plasma concentration of lipophilic drugs.
Keywords: PLA–(MeO-PEG) block copolymer; Nanoparticle; Biodistribution; DiD;

Characterising the size and shape of polyamidoamines in solution as a function of pH using neutron scattering and pulsed-gradient spin-echo NMR by Zeena Khayat; Peter C. Griffiths; Isabelle Grillo; Richard K. Heenan; Stephen M. King; Ruth Duncan (175-186).
Bioresponsive polymers are being developed as synthetic viral mimetics to enhance the intracellular delivery of macromolecular therapeutic agents such as genes, proteins and peptides. In this context we have designed pH-responsive, amphoteric polyamidoamines (PAAs) which change conformation on passing from a neutral pH (extracellular) to an acidic pH (endosomal and lysosomal) environments. PAAs have already demonstrated cytosolic delivery of genes and non-permeant toxins (e.g. gelonin and ricin A chain). The aim of this study was to use small-angle neutron scattering (SANS) to investigate the most likely shape of the hydrochloride salt form of one particular PAA (ISA23) in solution, under pH conditions that mimic those the polymer would be expected to encounter during endocytic internalisation (pH 7.4–3). It was shown that models based on a Gaussian coil representation of the polymer conformation described the SANS data better over this pH range than models based on a rod-like conformation. The conformation of ISA23 at 37 °C was expanded (radius of gyration ∼ 80 Å) at pH ∼ 3 but collapsed with an increase in pH (radius of gyration ∼ 20 Å at pH 7.4), a conclusion also reached in a model-free analysis of the neutron data. Outside this pH range – at the extremes of high and low pH – the polymer coil collapsed and interpretation of the scattering was slightly complicated by the presence of a very weak structure factor indicating that the polymer coils are highly charged. The PAA concentration did not significantly affect the polymer size over the concentration range 10–50 mg/ml. Characterisation of the dynamics of these polymer solutions – diffusion coefficients and viscosity –ostensibly suggest a very different conclusion with the polymer expanding as the pH is increased, but this arises due to weak aggregation of the amphoteric polymer coils.
Keywords: Polymer therapeutics; Endosomolytic polymers; Pulsed-gradient spin-echo NMR; Small-angle neutron scattering; Polyamidoamines;

The current anthrax vaccine in the U.S., the anthrax vaccine adsorbed, has several serious drawbacks, most notably the very lengthy and complicated dosing schedule. Thus, there is a critical need to develop an alternative anthrax vaccine with a simplified immunization schedule. To address this need, we evaluated the feasibility of topically priming or boosting onto the skin using an anthrax protective antigen (PA) protein-encoding DNA vaccine. To this end, we have shown that topical immunization of mice onto their skin with a perflubron-based microemulsion incorporated with a PA63-encoding plasmid, pGPA, led to significant PA-specific antibody responses, which have anthrax lethal toxin-neutralization activity. Moreover, topical boosting of mice primed with PA protein with the pGPA-incorporated, perflubron-based microemulsion significantly enhanced the anti-PA antibody responses induced. This topical anthrax DNA vaccine has the potential to be combined with a vaccine, such as the current AVA, to produce a simplified and more convenient dosing schedule.
Keywords: Vaccine; Transcutaneous; Ab response; Lethal toxin neutralization;

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