Microneedle/nanoencapsulation-mediated transdermal delivery: mechanistic insights.

A systematic study was undertaken to gain more insight into the mechanism of transdermal delivery of nanoencapsulated model dyes across microneedle (MN)-treated skin, a complex process not yet explored. Rhodamine B (Rh B) and fluorescein isothiocyanate (FITC) as model hydrophilic and hydrophobic small/medium-size molecules, respectively, were encapsulated in poly lactic-co-glycolic acid (PLGA) nanoparticles (NPs) and delivered through full thickness porcine skin pretreated with MN array. Permeation through MN-treated skin was affected by physicochemical characteristics of NPs and the encapsulated dyes. Dye flux was enhanced by smaller particle size, hydrophilicity, and negative zeta potential of NPs. Regarding encapsulated dyes, solubility at physiological pH and potential interaction with skin proteins proved to outweigh molecular weight as determinants of skin permeation. Data were verified using confocal laser scanning microscopy imaging. Findings coupled with the literature data are supportive of a mechanism involving influx of NPs, particularly of smaller size, deep into MN-created channels, generating depot dye-rich reservoirs. Molecular diffusion of the released dye across viable skin layers proceeds at a rate determined by its molecular characteristics. Data obtained provide mechanistic information of importance to the development of formulation strategies for more effective intradermal and transdermal MN-mediated delivery of nanoencapsulated therapeutic agents.

Effect of microneedle treatment on the skin permeation of a nanoencapsulated dye.

OBJECTIVES: The aim of the study was to investigate the effect of microneedle (MN) pretreatment on the transdermal delivery of a model drug (Rhodamine B, Rh B) encapsulated in polylactic-co-glycolic acid (PLGA) nanoparticles (NPs) focusing on the MN characteristics and application variables. METHODS: Gantrez MNs were fabricated using laser-engineered silicone micro-mould templates. PLGA NPs were prepared using a modified emulsion-diffusion-evaporation method and characterised in vitro. Permeation of encapsulated Rh B through MN-treated full thickness porcine skin was performed using Franz diffusion cells with appropriate controls. KEY FINDINGS: In-vitro skin permeation of the nanoencapsulated Rh B (6.19 ± 0.77 µg/cm²/h) was significantly higher (P < 0.05) compared with the free solution (1.66 ± 0.53 µg/cm²/h). Mechanistic insights were supportive of preferential and rapid deposition of NPs in the MN-created microconduits, resulting in accelerated dye permeation. Variables such as MN array configuration and application mode were shown to affect transdermal delivery of the nanoencapsulated dye. CONCLUSIONS: This dual MN/NP-mediated approach offers potential for both the dermal and transdermal delivery of therapeutic agents with poor passive diffusion characteristics.

Flux of ionic dyes across microneedle-treated skin: effect of molecular characteristics.

Drug flux across microneedle (MN)-treated skin is influenced by the characteristics of the MN array, formed microconduits and physicochemical properties of the drug molecules in addition to the overall diffusional resistance of microconduits and viable tissue. Relative implication of these factors has not been fully explored. In the present study, the in vitro permeation of a series of six structurally related ionic xanthene dyes with different molecular weights (MW) and chemical substituents, across polymer MN-pretreated porcine skin was investigated in relation of their molecular characteristics. Dyes equilibrium solubility, partition coefficient in both n-octanol or porcine skin/aqueous system, and dissociation constants were determined. Results indicated that for rhodamine dyes, skin permeation of the zwitterionic form which predominates at physiological pH, was significantly reduced by an increase in MW, the skin thickness and by the presence of the chemically reactive isothiocyanate substituent. These factors were generally shown to override the aqueous solubility, an important determinant of drug diffusion in an aqueous milieu. The data obtained provided more insight into the mechanism of drug permeation across MN-treated skin, which is of importance to both the design of MN-based transdermal drug delivery systems and of relevance to skin permeation research.

Laser-engineered dissolving microneedles for active transdermal delivery of nadroparin calcium.

There is an urgent need to replace the injection currently used for low molecular weight heparin (LMWH) multidose therapy with a non- or minimally invasive delivery approach. In this study, laser-engineered dissolving microneedle (DMN) arrays fabricated from aqueous blends of 15% w/w poly(methylvinylether-co-maleic anhydride) were used for the first time in active transdermal delivery of the LMWH nadroparin calcium (NC). Importantly, an array loading of 630IU of NC was achieved without compromising the array mechanical strength or drug bioactivity. Application of NC-DMNs to dermatomed human skin (DHS) using the single-step 'poke and release' approach allowed permeation of approximately 10.6% of the total NC load over a 48-h study period. The cumulative amount of NC that permeated DHS at 24h and 48h attained 12.28±4.23IU/cm(2) and 164.84±8.47IU/cm(2), respectively. Skin permeation of NC could be modulated by controlling the DMN array variables, such as MN length and array density as well as application force to meet various clinical requirements including adjustment for body mass and renal function. NC-loaded DMN offers great potential as a relatively low-cost functional delivery system for enhanced transdermal delivery of LMWH and other macromolecules.

Lyophilized inserts for nasal administration harboring bacteriophage selective for Staphylococcus aureus: in vitro evaluation.

Nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) poses an infection risk and eradication during hospitalization is recommended. Bacteriophage therapy may be effective in this scenario but suitable nasal formulations have yet to be developed. Here we show that lyophilization of bacteriophages in 1ml of a viscous solution of 1-2% (w/v) hydroxypropyl methylcellulose (HPMC) with/without the addition of 1% (w/v) mannitol, contained in Eppendorf tubes, yields nasal inserts composed of a highly porous leaflet-like matrix. Fluorescently labeled bacteriophage were observed to be homogenously distributed throughout the wafers of the dried matrix. The bacteriophage titer fell 10-fold following lyophilization to 10(8)pfu per insert, then falling a further 100- to 1000-fold over 6 to 12months storage at 4°C. This compares well with a total dose of 6×10(5)pfu in 0.2ml liquid applied into the ear during a recent clinical trial in humans. The residual water content of the lyophilized inserts was reduced upon the addition of mannitol to HPMC, but this did not have any correlation to the lytic activity. Mannitol underwent a transition from its amorphous to crystalline state during exposure of the inserts to increasing relative humidities (as would be experienced in the nose), although this transition was suppressed by higher HPMC concentrations and the presence of buffer containing gelatin and bacteriophages. Our results therefore suggest that lyophilized inserts harboring bacteriophage selective for S. aureus may be a novel means for the eradication of MRSA resident in the nose.

Correlation between in vitro and in vivo erosion behaviour of erodible tablets using gamma scintigraphy.

In vitro and in vivo erosion behaviour of erodible tablets consisting of glyceryl behenate and low-substituted hydroxypropylcellulose manufactured using three different methods: direct compression (DC), melt granulation (MG) and direct solidification (DS) was investigated. In vitro erosion behaviour was studied using gravimetric and scintigraphic methods. For scintigraphic investigations, the radiolabel was adsorbed onto activated charcoal and incorporated into tablets at a concentration that did not affect the erosion profile. A clinical study was carried out in six healthy volunteers using gamma scintigraphy. Tablet erosion was affected by the preparation method and was found to decrease in the order of preparation method, DC>MG>DS tablets. The mean in vivo onset time for all tablets (DC: 6.7±3.8 min, MG: 18.3±8.1 min, DS: 67±18.9 min) did not differ significantly from in vitro onset time (DC: 5.3±1 min, MG: 16.8±3.9 min, DS: 61.8±4.7 min). The mean in vivo completion times were found to be 36.6±9.7 (DC tablets), 70±18.3 min (MG tablets) and 192.5±39.9 min (DS tablets). Among the three different erodible tablets, MG tablets showed the highest correlation between in vitro and in vivo mean erosion profile and suggested a potential platform to deliver controlled release of water-insoluble compounds.

Synthesis, processing and solid state excipient interactions of cucurbit[6]uril and its formulation into tablets for oral drug delivery.

The synthesis, processing, and solid state excipient interactions of cucurbit[6]uril (CB[6]) and its formulation into oral tablets has been examined using a range of physical chemistry techniques. Rapid precipitation from HCl by the addition of water yields microcrystalline CB[6] with smaller and more consistent particle size (30-165 µm) compared with the sieved CB[6] (50-540 µm) produced from large crystals grown by slow evaporation from HCl. The microcrystalline particles also contain fewer water molecules in the crystal compared with the sieved particles: 10 and 16% respectively. Microcrystalline CB[6] can be formulated into tablets suitable for oral delivery with a CB[6] content of 1-50% w/w, with the other excipients including lactose, talc, Avicel, magnesium stearate and Ac-Di-Sol. In the solid state microcrystalline CB[6] does not interact significantly with the talc, Ac-Di-Sol or Avicel, but significant interactions are observed when mixed or ground with either magnesium stearate or lactose, resulting in the lowering of the melting points of both excipients. This work represents the first study of the physical processing and solid state chemistry of CB[n]s for pharmaceutical formulation and represents an important development step in the use of CB[n]s as drug delivery vehicles.

In-vitro and in-vivo erosion profiles of hydroxypropylmethylcellulose (HPMC) matrix tablets.

The purpose of this study was to evaluate and compare the in-vitro and in-vivo erosion profiles of two tablet formulations primarily consisting of hydroxypropylmethylcellulose (HPMC) and lactose. HPMC was used at concentrations below and above the reported values for polymer percolation threshold in controlled release matrix formulations: 20 and 40% (w/w) HPMC. In-vitro erosion behaviour was studied using traditional gravimetric and scintigraphic methods, with radiolabelled charcoal used as a marker to quantify erosion profiles in scintigraphic studies. Six healthy male subjects participated in a randomised crossover scintigraphic erosion study. Both in-vitro and in-vivo erosion profiles determined using the gravimetric and/or scintigraphic method for matrix tablets were dependent upon the concentration of HPMC, and erosion was faster for tablets containing 20% (w/w) HPMC than those containing 40% (w/w) HPMC. Good correlation was found between in-vitro gravimetric and scintigraphic erosion profiles for both tablets. Tablets containing 40% (w/w) HPMC (polymer level above percolation threshold) demonstrated robust in-vivo performance and showed stronger correlation with in-vitro erosion profiles. The study demonstrated that a matrix formulation with a lower concentration of HPMC and higher lactose concentration is more likely to perform poorly in the in-vivo environment.

Solid state stabilisation of the orally delivered drugs atenolol, glibenclamide, memantine and paracetamol through their complexation with cucurbit[7]uril.

The inclusion of the cardiovascular beta-blocker drug atenolol, the antidiabetic drug glibenclamide, the Alzheimer's NMDA glutamate receptor drug memantine and the analgesic/antipyretic drug paracetamol by cucurbit[7]uril (CB[7]) has been studied by (1)H nuclear magnetic resonance spectroscopy, electrospray ionisation mass spectrometry, molecular modelling, fluorescence displacement assays and differential scanning calorimetry. All four drugs form 1 : 1 host-guest complexes with CB[7], but the exchange kinetics and location of the binding is different for each drug. Atenolol is bound over the central phenyl ring with a binding constant of 4.2 x 10(4) M(-1), whereas glibenclamide is bound over the terminal cyclohexyl group with a binding constant of 1.7 x 10(5) M(-1), and memantine is totally bound within the CB[7] cavity. Paracetamol is bound in two locations, over the central phenyl ring and over the methyl group, with the CB[7] molecule shuttling quickly between the two sites. Inclusion by CB[7] was shown by differential scanning calorimetry to physically stabilise all four drugs, which has applications preventing drug degradation and improving drug processing and formulation.

A chemical preformulation study of a host-guest complex of cucurbit[7]uril and a multinuclear platinum agent for enhanced anticancer drug delivery.

Single crystal and powder X-ray diffraction have been used to examine the host-guest complex of cucurbit[7]uril (CB[7]) and the model dinuclear platinum anticancer complex trans-[{PtCl(NH(3))(2)}(2)mu-dpzm](2+) (di-Pt, dpzm= 4,4'-dipyrazolylmethane). The single crystal structure shows that the host-guest complex forms with the di-Pt dpzm ligand within the CB[7] cavity and with the platinum groups just beyond the macrocycle portals. Binding is stabilised through hydrophobic interactions and six hydrogen bonds between the platinum ammine ligands and the dpzm pyrazole amine to the CB[7] carbonyls. Each host-guest complex crystallises with two chloride counterions and 5.5 water molecules. The unit cell comprises four asymmetric units, each of which contains three crystallographically independent CB[7]-di-Pt moieties. X-Ray powder diffraction demonstrated structural consistency of the bulk crystals with a single polycrystalline phase that is identical with the single crystal structure. Finally, the effect of CB[7] encapsulation of the thermal stability of di-Pt was examined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). From the TGA experiments it was found that free CB[7] and the CB[7]-di-Pt complex lose 11 and 3.5% of their mass respectively, through the loss of water molecules, upon heating to 160 degrees C. The DSC results showed that the free dpzm ligand melts between 186 and 199 degrees C, with a standard enthalpy of fusion of 27.92 kJ mol(-1). As a 2+ inorganic salt the metal complex does not melt but undergoes several decomposition events between 140 and 290 degrees C. Encapsulation by CB[7] completely stabilises di-Pt with no decomposition of either the macrocycle or metal complex at temperatures up to 290 degrees C.

In vivo performance of an oral MR matrix tablet formulation in the beagle dog in the fed and fasted state: assessment of mechanical weakness.

PURPOSE: To evaluate the behaviour of an oral matrix modified release formulation in the canine gastrointestinal tract, and establish if a mechanical weakness previously observed in clinical studies would have been identified in the dog model. MATERIALS AND METHODS: In vitro release profiles were obtained for two modified release matrix tablets containing UK-294,315, designed to release over either 6 (formulation A) or 18 (formulation B) hours. Tablets were labelled with (153)samarium and in vivo pharmacoscintigraphy studies were performed in four beagle dogs in the fasted state for both formulations, and following ingestion of an FDA high fat meal for formulation B. RESULTS: The matrix tablet formulations displayed significantly different in vitro release profiles (F (2) < 50), with time to 80% release for formulation A and B of 406 and 987 min respectively. Complete in vivo disintegration occurred at 339 +/- 181 and 229 +/- 171 for formulation A and B respectively in the fasted state, and at 207 +/- 154 min for formulation B in the fed state, in disagreement with in vitro release. CONCLUSION: The fed/fasted dog model would have predicted a lack of physical robustness in the matrix tablet formulation B, however it would not have predicted the clear fed/fasted effects on performance observed previously in man.

Evaluation of the clearance of a sublingual buprenorphine spray in the beagle dog using gamma scintigraphy.

PURPOSE: The aim of this study was to evaluate clearance from the buccal cavity and pharmacokinetic profiles of a sublingual spray formulation in the dog, to assist in interpretation of future pharmacokinetic studies. METHODS: Radiolabelled buprenorphine in a spray formulation (400 microg/100 microl in 30% ethanol) was administered sublingually to four beagle dogs, and the residence in the oral cavity was determined using gamma scintigraphy. Pharmacokinetic sampling was performed to facilitate correlation of location of dose with significant pharmacokinetic events. RESULTS: Scintigraphic imaging revealed that clearance of the formulation from the oral cavity was rapid, with a mean T 50% clearance of 0.86 +/- 0.46 min, and T 80% clearance of 2.75 +/- 1.52 min. In comparison, absorption of buprenorphine was relatively slow, with a T max of 0.56 +/- 0.13 h. Good buccal absorption despite short residence time can be explained by lipophilicity of buprenorphine enabling rapid sequestration into the oral mucosa, prior to diffusion and absorption directly into systemic circulation. CONCLUSION: This study demonstrated rapid clearance of a sublingual solution from the canine oral cavity, with T 50% similar to results previously reported in man, providing initial confidence in using a conscious dog model to achieve representative residence times for a sublingual solution.

The use of simple dynamic mucosal models and confocal microscopy for the evaluation of lyophilised nasal formulations.

A range of methods is reported in the literature for assessing hydration and adhesion parameters in the performance of nasal bioadhesive formulations; however, these tests do not always represent the dynamic conditions in the nasal cavity. Lyophilised formulations intended for nasal administration were evaluated using in-vitro tests designed in an attempt to mimic relevant processes in the nasal cavity, and intended to discriminate between different formulations. Initial investigative studies using scanning electron microscopy revealed that the lyophilisate had a highly porous internal structure, expected to provide an ideal porous pathway for re-hydration. Vapour sorption analysis demonstrated substantial weight gain of the lyophilisates on exposure to 95% relative humidity, ranging from 38% to 66%. Agar was used as a synthetic mucosal model designed to provide a standardised quantity of water available for rehydration of the formulations in in-vitro tests. A dynamic adhesion test and a texture analyser sliding test were designed to quantify different aspects of the spreading and adhesion of the hydrating formulations on the synthetic mucosal surface. Examination of the lyophilised formulations using confocal microscopy allowed visualisation and quantification of the initial rate of water ingress into the lyophilisates, which was found to consist of an initial rapid phase, followed by a slower steady-state phase. The results demonstrated that the use of a combination of methods representing the dynamic conditions of the nasal cavity is advisable in order to evaluate a formulation fully and to avoid misleading conclusions.

In-vitro/in-vivo correlation of pulsatile drug release from press-coated tablet formulations: a pharmacoscintigraphic study in the beagle dog.

The aim of the current study was to investigate the in-vitro and in-vivo performance of a press-coated tablet (PCT) intended for time delayed drug release, consisting of a rapidly disintegrating theophylline core tablet, press-coated with barrier granules containing glyceryl behenate (GB) and low-substituted hydroxypropylcellulose (L-HPC). The PCTs showed pulsatile release with a lag time dependent upon the GB and L-HPC composition of the barrier layer. In-vivo gamma-scintigraphic studies were carried out for PCTs containing GB:L-HPC at 65:35 w/w and 75:25 w/w in the barrier layer in four beagle dogs, in either the fed or fasted state. The in-vivo lag time in both the fed and fasted states did not differ significantly (p>0.05) from the in-vitro lag time. Additionally, no significant difference (p<0.05) between in-vivo fed and fasted disintegration times was observed, demonstrating that in-vivo performance of the PCT was not influenced by the presence or absence of food in the gastrointestinal tract. A distinct lag time was obtained prior to the appearance of drug in plasma and correlated (R2=0.98) with disintegration time observed from scintigraphic images. However, following disintegration, no difference in pharmacokinetic parameters (AUC(0-6 dis), K(el), Cmax) was observed. The current study highlighted the potential use of these formulations for chronopharmaceutical drug delivery.

Nasal residence of insulin containing lyophilised nasal insert formulations, using gamma scintigraphy.

Bioadhesive dosage forms are a potential method for overcoming rapid mucociliary transport in the nose. A lyophilised nasal insert formulation previously investigated in sheep demonstrated prolonged absorption of nicotine hydrogen tartrate suggestive of extended nasal residence, and increased bioavailability. The current study was performed to quantify nasal residence of the formulations using gamma scintigraphy, and to investigate the absorption of a larger molecule, namely insulin. A four-way crossover study was conducted in six healthy male volunteers, comparing a conventional nasal spray solution with three lyophilised nasal insert formulations (1-3% hydroxypropylmethylcellulose (HPMC)). The conventional nasal spray deposited in the posterior nasal cavity in only one instance, with a rapid clearance half-life of 9.2 min. The nasal insert formulations did not enhance nasal absorption of insulin, however an extended nasal residence time of 4-5 h was observed for the 2% HPMC formulation. The 1% HPMC insert initially showed good spreading behaviour; however, clearance was faster than for the 2% formulation. The 3% HPMC nasal insert showed no spreading, and was usually cleared intact from the nasal cavity within 90 min. In conclusion, the 2% HPMC lyophilised insert formulation achieved extended nasal residence, demonstrating an optimum combination of rapid adhesion without over hydration.

In vivo evaluation of nicotine lyophilised nasal insert in sheep.

The nasal route offers an attractive means of delivering a drug directly to the systemic circulation and avoiding hepatic first-pass metabolism, although rapid mucociliary clearance can be detrimental to nasal absorption. The in vitro and in vivo characteristics of a nasal insert formulation prepared by lyophilisation of a viscous HPMC gel solution designed to overcome this problem were studied. In vitro release of nicotine from the lyophilised insert was compared with powder and spray formulations. Stability and characterisation studies were carried out using dynamic vapour sorption, scanning electron microscopy and HPLC analysis. Nicotine formulations were administered to eight wether sheep in a randomised four-way cross-over study, and plasma nicotine assessed comparing the nasal insert formulation with conventional nasal powder, nasal spray and IV doses. In vitro release studies demonstrated prolonged nicotine release from the nasal insert formulation compared to a powder and liquid. In vivo plasma profiles appeared to show prolonged plasma nicotine levels compared to the conventional formulations, although T(max), C(max) and AUC parameters for the insert were not significantly different due to high variability in the pharmacokinetic data. In conclusion, the nasal insert displayed a promising prolonged plasma profile, which must be investigated further to provide statistical significance to prove the effect.