Topical Semisolid Drug Product Critical Quality Attributes with Relevance to Cutaneous Bioavailability and Pharmacokinetics: Part I-Bioequivalence of Acyclovir Topical Creams.

PURPOSE: To develop a toolkit of test methods for characterizing potentially critical quality attributes (CQAs) of topical semisolid products and to evaluate how CQAs influence the rate and extent of active ingredient bioavailability (BA) by monitoring cutaneous pharmacokinetics (PK) using an In Vitro Permeation Test (IVPT). METHODS: Product attributes representing the physicochemical and structural (Q3) arrangement of matter, such as attributes of particles and globules, were assessed for a set of test acyclovir creams (Aciclostad® and Acyclovir 1A Pharma) and compared to a set of reference acyclovir creams (Zovirax® US, Zovirax® UK and Zovirax® Australia). IVPT studies were performed with all these creams using heat-separated human epidermis, evaluated with both, static Franz-type diffusion cells and a flow through diffusion cell system. RESULTS: A toolkit developed to characterize quality and performance attributes of these acyclovir topical cream products identified certain differences in the Q3 attributes and the cutaneous PK of acyclovir between the test and reference sets of products. The cutaneous BA of acyclovir from the set of reference creams was substantially higher than from the set of test creams. CONCLUSIONS: This research elucidates how differences in the composition or manufacturing of product formulations can alter Q3 attributes that modulate myriad aspects of topical product performance. The results demonstrate the importance of understanding the Q3 attributes of topical semisolid drug products, and of developing appropriate product characterization tests. The toolkit developed here can be utilized to guide topical product development, and to mitigate the risk of differences in product performance, thereby supporting a demonstration of bioequivalence (BE) for prospective topical generic products and reducing the reliance on comparative clinical endpoint BE studies.

Fourteen days of etoricoxib 60 mg improves pain, hyperalgesia and physical function in individuals with knee osteoarthritis: a randomized controlled trial.

OBJECTIVE: Mounting evidence points to the heterogeneity of osteoarthritis (OA) pain, increasing the need for more comprehensive assessment of the efficacy of standard interventions. This study investigated whether 14 days of the selective Cox-2 inhibitor etoricoxib (60 mg/day) would modify self-report of pain intensity and quality, and physical measures of hyperalgesia and function in individuals with knee OA. DESIGN: This double-blind placebo-controlled trial included 80 community-recruited volunteers with painful knee OA (≥3/10 VAS), randomly allocated to Active or Placebo groups. Self-report measures of pain, stiffness, function Western Ontario and McMaster University Osteoarthritis Index (WOMAC) and pain quality (PainDETECT, Pain Quality Assessment Scale [PQAS]) and physical measures of locomotion and local (knee) and widespread (elbow) hyperalgesia were assessed at Days 0, 4 and 14. Repeated Measures ANOVA analysed group differences. RESULTS: Significant group × time interaction effects were found for all measures of pain (all p < 0.001), with WOMAC pain sub-score improving by 30.7% by Day 14 and index knee mechanical hyperalgesia improving by 32.6%, whilst Placebo group values worsened. Both self-report and physical tests of function improved (p < 0.001-p = 0.006): WOMAC-function by 28.4%, sit-to-stand and walk time by 13%, pain during locomotion tasks by 12.4-32.6%. Pain quality also significantly improved for the Active and declined for the Placebo group (p < 0.001): PainDETECT score reduced by 23.6% and PQAS paroxsysmal and surface sub-scores by 36.9% and 29.4%. There were also significant improvements in local cold hyperalgesia and widespread mechanical hyperalgesia (10-13.8%). CONCLUSION: Just 14 days of etoricoxib significantly improves pain intensity and quality, function and local and widespread hyperalgesia, measured by both self-report and physical tests.

Human skin penetration and local effects of topical nano zinc oxide after occlusion and barrier impairment.

Public health concerns continue to exist over the safety of zinc oxide nanoparticles that are commonly used in sunscreen formulations. In this work, we assessed the effects of two conditions which may be encountered in everyday sunscreen use, occlusion and a compromised skin barrier, on the penetration and local toxicity of two topically applied zinc oxide nanoparticle products. Caprylic/capric triglyceride (CCT) suspensions of commercially used zinc oxide nanoparticles, either uncoated or with a silane coating, were applied to intact and barrier impaired skin of volunteers, without and with occlusion for a period of six hours. The exposure time was chosen to simulate normal in-use conditions. Multiphoton tomography with fluorescence lifetime imaging was used to noninvasively assess zinc oxide penetration and cellular metabolic changes that could be indicative of toxicity. We found that zinc oxide nanoparticles did not penetrate into the viable epidermis of intact or barrier impaired skin of volunteers, without or with occlusion. We also observed no apparent toxicity in the viable epidermis below the application sites. These findings were validated by ex vivo human skin studies in which zinc penetration was assessed by multiphoton tomography with fluorescence lifetime imaging as well as Zinpyr-1 staining and toxicity was assessed by MTS assays in zinc oxide treated skin cryosections. In conclusion, applications of zinc oxide nanoparticles under occlusive in-use conditions to volunteers are not associated with any measurable zinc oxide penetration into, or local toxicity in the viable epidermis below the application site.

Analysing the skin barrier from down under.

Over the past 40 years the Australian contribution to the field of skin science has been led by Michael Roberts. One of his earliest papers on membrane permeation was published in Nature, setting the scene for his huge contribution to both the fundamental understanding of skin permeability and the application of that knowledge to improved clinical outcomes, new delivery technologies and minimizing toxicological risk. His work has been characterized by a mechanistic, mathematical approach to defining skin permeation. He defined the parameters important to skin permeation, established structure-penetration relationships and demonstrated the importance of maximum flux from a clinical and toxicological viewpoint. Through his systematic approach, Mike showed a parabolic relationship between maximum flux and lipophilicity, and established that this is driven mainly by variations in solubility of the solute in the stratum corneum. One of the significant strengths of Mike's work is the ability to express biological concepts in mathematical terms. He has developed mathematical models that enhance our understanding of epidermal, dermal, deep tissue permeation and follicular transport. Throughout his career Mike has been involved in pioneering new technologies both for analysing the skin barrier and influencing permeation across it. His fundamental work in the area of iontophoresis provided models that defined the parameters influencing its permeation enhancement. Mike's research has been translated into improved clinical outcomes, reduced toxicological risk and changes to the regulation of skin products. This article provides an insight into Mike Roberts and the Australian contribution to skin science.

Effect of formulation factors on incorporation of the hydrophilic peptide dalargin into PLGA and mPEG-PLGA nanoparticles.

The objective of this study was to examine formulation factors that influence the incorporation of the hydrophilic peptide dalargin into poly(D, L-lactic-co-glycolic acid) (PLGA) and methoxy-polyethylene glycol (mPEG)-PLGA nanoparticles. In particular, the effect of ionic additives and nanoparticle method of preparation on the incorporation of dalargin and resultant nanoparticle properties was investigated. Biodegradable nanoparticles were prepared from mPEG-PLGA and PLGA by both solvent evaporation and solvent diffusion methods with inclusion of ionic additives of dextran sulphate (DS), sulfobutyl ether-beta-cyclodextrin (SB-CD), or sodium dodecyl sulfate (SDS). The resultant nanoparticles were analyzed for their mean particle size and size distribution, zeta-potential, peptide loading, yield, and morphology. The inclusion of ionic additives in the nanoparticle formulation significantly influenced dalargin entrapment efficiency (EE). For example, with the PLGA/SDS formulation EE increased from 13.3% to 91.2% and from 4.1% to 68.6% with the solvent diffusion and evaporation methods, respectively. The inclusion of ionic surfactant SDS has also lead to the formation of smaller size of nanoparticles. Isothermal titration microcalorimetry revealed a strong interaction between dalargin and DS, medium level interaction with SDS, and weak interaction with SB-CD. The results of this study suggest that a strong ionic interaction between peptides and additives may lead to enhanced peptide incorporation but also increased particle size. Intermediate ionic interaction, especially when it is associated with the formation of reversed micelles in a hydrophobic polymer solution, could be used to enhance the incorporation of hydrophilic peptides in PLGA and mPEG-PLGA nanoparticles.

Influence of cyclodextrins on in vitro human skin absorption of the sunscreen, butyl-methoxydibenzoylmethane.

The effects of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and sulfobutylether-beta-CD (SBE7-beta-CD) on in vitro human skin penetration and retention of the sunscreen agent butyl-methoxydibenzoylmethane (BM-DBM) were investigated. The interaction between the UV filter and the cyclodextrins was studied in water by phase-solubility analysis. Solid complexes were prepared by the co-evaporation method and characterized by (1)H NMR spectroscopy, thermal analysis and powder X-ray diffraction. Solutions containing BM-DBM free or complexed with cyclodextrins were applied to excised human skin in Franz diffusion cells and the amount of sunscreen permeated after 6 h into the stratum corneum, viable epidermis, dermis and receptor fluid was assessed by HPLC. As much as 14.10-16.78% of the applied dose of BM-DBM penetrated within the skin tissue. No sunscreen was detected in the dermis and in the receiver phase. The greater proportion (84.6-95.5%) of the absorbed UV filter was localized in the stratum corneum with no significant differences between uncomplexed or complexed BM-DBM. Notable levels (2.29% of the applied dose) of the sunscreen agent accumulated in the epidermis from the preparation containing free BM-DBM. The epidermal concentration of the UV filter was markedly reduced (0.66% of the applied dose) by complexation with SBE7-beta-CD, whereas HP-beta-CD had no effect. The decreased BM-DBM retention in the epidermal region achieved by SBE7-beta-CD limits direct contact of the sunscreen and of its reactive photolytic products with the skin viable tissues.

Drug delivery across the blood-brain barrier.

The brain is protected and isolated from the general circulation by a highly efficient blood-brain barrier. This is characterised by relatively impermeable endothelial cells with tight junctions, enzymatic activity and active efflux transport systems. Consequently the blood-brain barrier is designed to permit selective transport of molecules that are essential for brain function. This creates a considerable challenge for the treatment of central nervous system diseases requiring therapeutic levels of drug to enter the brain. Some small lipophilic drugs diffuse across the blood-brain barrier- sufficiently well to be efficacious. However, many potentially useful drugs are excluded. This review provides an insight into the current research into technologies to target small molecules, peptides and proteins to the brain. A brief review of the nature of the blood-brain barrier and its transport mechanisms is provided. Strategies to target and improve transport across the blood-brain barrier include the prodrug-lipidisation approach, sequential metabolism chemical delivery systems, drug-vectors, liposomes and nanoparticles. Included is the discussion of techniques to minimise clearance from the circulation by the reticuloendothelial system in order to extend circulation residence time and optimise the opportunity for interaction between the drug delivery system and the blood-brain barrier.

Can increasing the viscosity of formulations be used to reduce the human skin penetration of the sunscreen oxybenzone?

The effect of adding thickening agents on the penetration of a sunscreen benzophenone-3 through epidermal and a high-density polyethylene membrane was studied using both very thick (infinite dose) and thin (in use) applications. Contradictory results were obtained. Thickening agents retard skin penetration, in a manner consistent with a diffusional resistance in the formulation, when applied as an infinite dose. In contrast, when applied as in thin (in use) doses, thickening agents promote penetration, most likely through greater stratum corneum diffusivity arising from an enhanced hydration by the thicker formulations. The two key implications from this work are (i) a recognition of the danger in the potential extrapolation of infinite dosing to in use situations, and (ii) to recognize that thicker formulations may sometimes enhance the penetration of other topical agents when applied "in use".

Ion-pair formation as a strategy to enhance topical delivery of salicylic acid.

An in-vitro study was carried out to determine the possibility of improving the efficiency of transdermal delivery of salicylate through human epidermis by ion-pair formers (alkylamines and quaternary ammonium ions). Further, the relationship between the physicochemical properties of the counter-ions and salicylate flux was examined. It was found that flux can be related to the conductivity associated with the penetrant solution, molecular size of the counter-ion and lipophilicity expressed as either octanol/water partition coefficient of the ion pairs or the carbon chain-length of the counter-ions. Equations have been developed to predict salicylate flux from these physicochemical parameters.

Effect of ion pairing with alkylamines on the in-vitro dermal penetration and local tissue disposition of salicylates.

Hydrophilic ionic drugs can be rendered lipophilic by ion-pair formation with hydrophobic counter-ions. This study examines the value of forming ion pairs between anionic salicylate and a series of amines as model cationic counter-ions to facilitate topical delivery and skin penetration. The in-vitro translocation of salicylate ions from a nonaqueous vehicle through human epidermis was estimated in the presence or absence of amines. The distribution into, and accumulation of the salicylate ion in various tissues following topical application to anaesthetised rats were also investigated. Although the epidermal permeation constants of the salicylate-amine ion pairs were lower than that of salicylate itself (enhancement ratios: 0.74-0.87), salicylate retention and localisation in the underlying rat tissues increased in the presence of some of the counter-ions studied. Salicylate concentrations (microg (g tissue)(-1)) in the dermis were 877.2+/-78.6 for salicylate alone and 1098+/-121.9-2586+/-332.5 for salicylate-amine ion pairs. The levels of salicylate in tissues up to the top muscle layer were 1.2-3.7-fold higher in the presence of the counter-ions. It is concluded that, although amine counter-ions have the ability to influence the penetration of salicylate, in-vitro permeability studies do not reflect the in-vivo increases in tissue concentrations resulting from probable changes in systemic clearance.

Assessment and clinical implications of absorption of sunscreens across skin.

Topical sunscreen products are widely used for protection of the skin against the harmful effects of exposure to ultraviolet radiation. Sunscreen agents are incorporated into many everyday-use cosmetics as well as so called 'beach' products. An ideal sunscreen product will provide effective protection against UV radiation with minimal skin absorption of the active ingredients. There is now clear evidence that a common sunscreen chemical, benzophenone-3, is absorbed systemically following topical application to the skin. Other more lipophilic sunscreens are absorbed into the skin, but penetration to deeper tissues and the cutaneous circulation appears to be limited. However, the extent to which sunscreens that are absorbed into the stratum corneum are absorbed to deeper tissues and the systemic circulation over time is currently unknown. The formulation vehicle in which the sunscreen is presented to the skin has a significant effect on absorption into and through the skin. Alcohol-based formulations appear to increase sunscreen absorption. In addition, some sunscreen chemicals may enhance the skin absorption of other sunscreens when applied in combination. Clearly, further research into the influence of sunscreen and formulation properties on skin absorption could lead to optimal design of sunscreen products with respect to efficacy and minimizing absorption. Despite the extensive use of sunscreen products, there have been few reports of adverse effects, and these tend to be limited to acute dermatitis and allergies. Some recent reports have raised concerns that sunscreen chemicals may damage tissues, particularly in the presence of UV radiation. Further research into the toxicity of sunscreens is urgently required. Given the information currently available and the importance of protecting the skin against sun damage, there is no clear justification for restricting the use of sunscreen products at this time.

Absorption of sunscreens across human skin: an evaluation of commercial products for children and adults.

AIMS: Topical sunscreens are routinely applied to the skin by a large percentage of the population. This study assessed the extent of absorption of a number of common chemical sunscreen agents into and through human skin following application of commercially available products. METHODS: Sunscreen products were applied to excised human epidermis in Franz diffusion cells with the amount penetrating into and across the epidermis assessed by h.p.l.c. for 8 h following application. RESULTS: All sunscreen agents investigated penetrated into the skin (0.25 g m-2 or 14% of applied dose), but only benzophenone-3 passed through the skin in significant amounts (0.08 g m-2 or 10% of the applied dose). With one exception, suncreen agents in corresponding products marketed for adults and children had similar skin penetration profiles. CONCLUSIONS: Whilst limited absorption across the skin was observed for the majority of the sunscreens tested, benzophenone-3 demonstrated sufficiently high penetration to warrant further investigation of its continued application.

Self promotion of deep tissue penetration and distribution of methylsalicylate after topical application.

PURPOSE: To determine how changes in cutaneous blood flow induced in-vivo by methylsalicylate (MeSA), compared to non-rubefacient triethanolamine salicylate (TSA), affected topical salicylate absorption and distribution, and to assess formulation therapeutic potential by comparing tissue concentrations to published antiinflammatory concentrations. METHODS: Flux of salicylate from MeSA and TSA formulations applied to full-thickness rat skin was determined using in vitro diffusion cells. Anaesthetised rats were then used to quantify salicylate concentrations in plasma and tissues underlying the application site for the two formulations over a 6h period. In vitro and in vivo absorption profiles were then compared and the effect of MeSA on cutaneous blood flow assessed. RESULTS: In vitro flux of salicylate from the MeSA formulation was 40% higher, though after correcting for differences in formulation concentrations the ratio of permeability coefficients was reversed. Contrary to the in vitro predictions, in vivo tissue and plasma concentrations of salicylate in rats rose rapidly in the first 1 hr and were more than the predicted 1.4-fold higher for MeSA. This effect was mirrored by the increase in blood flow induced by MeSA in human cutaneous vessels and that reported in the literature. Potential therapeutic levels were not seen below superficial muscle layers. CONCLUSIONS: Direct tissue penetration of salicylate occurs below application sites from both MeSA and TSA formulations. Tissue concentrations of MeSA were higher than predicted due to its rapid distribution in the blood.

In vitro human epidermal and polyethylene membrane penetration and retention of the sunscreen benzophenone-3 from a range of solvents.

PURPOSE: To study epidermal and polyethylene membrane penetration and retention of the sunscreen benzophenone-3 (BP) from a range of single solvent vehicles and evaluate solvent effects on permeability parameters. METHODS: The solubility of BP was measured in a number of solvents. Penetration of BP across human epidermis and high density polyethylene (HDPE) membranes was studied from 50% saturated solutions in each solvent. RESULTS: Maximal BP fluxes from the solvents across the two membranes varied widely. Highest fluxes were observed from 90% ethanol (EtOH) for epidermis and from isopropyl myristate (IPM) and C12-15 benzoate alcohols (C12-15 BA) for HDPE membrane. Both the flux and estimated permeability coefficient and skin-vehicle partitioning of BP appeared to be related to the vehicle solubility parameter (delta(v)). The major effects of solvents on BP flux appear to be via changes in BP diffusivity through the membranes. CONCLUSIONS: Minimal penetration of sunscreens such as BP is best achieved by choosing vehicles with a delta(v) substantially different to the solubility parameter of the membrane.

Percutaneous absorption of sunscreen agents from liquid paraffin: self-association of octyl salicylate and effects on skin flux.

This study provides an investigation of the availability of octyl salicylate (OS), a common sunscreen agent, from liquid paraffin and the effect of OS on skin permeability. A model membrane system to isolate the vehicle effect from membrane permeability has been developed. Partitioning of OS between liquid paraffin and aqueous receptor phases was conducted. Partition coefficients increased with increase in OS concentration. A range of OS concentrations in liquid paraffin was diffused across human epidermis and synthetic membranes into 4% bovine serum albumin in phosphate-buffered saline and 50% ethanol. Absorption profiles of OS obtained from silicone and low-density polyethylene (LDPE) membranes were similar to each other but higher than for the high-density polyethylene [HDPE (3 times)] membrane and human epidermis (15 times). The steady state fluxes and apparent permeability coefficients (Kp') obtained from the diffusion studies showed the same trends with all membranes, except for the HDPE membrane which showed greater increase in flux and Kp' at concentrations above 30%. IR spectra showed that several bands of OS were shifted with concentrations, and the molecular models further suggested that the main contribution to the self-association is from non-1,4 van der Waals interactions.

Chronic neuropathic pain and its control by drugs.

The medical treatment and some currently known aspects of the aetiology of five neurogenic pain states are discussed. Neurogenic pain can be described as pain resulting from noninflammatory dysfunction of the peripheral or central nervous system without nociceptor stimulation or trauma. The enormity of the field has limited this review to post-herpetic neuralgia, complex regional pain syndromes, phantom pain, trigeminal neuralgia and diabetic neuralgia. Evidence suggests that many neurogenic pain states are not effectively controlled. This may be due in part to a lack of understanding of the aetiology of these conditions and to the lack of high quality studies evaluating existing treatments. A compact review of the literature is presented with some treatment options and possible future directions. Where appropriate surgical management and physical therapy have been discussed; however, a thorough appraisal of nondrug treatments was not the main priority of this review.

Reversible blockade of retrograde axonal transport in the rat sciatic nerve by vincristine.

Altered axoplasmic transport has been implicated as a contributing factor in neuropathic pain states. Treatments which produce transient axoplasmic transport blockade have shown initial promise as therapeutic procedures in the management of chronic neuropathic pain. The present study evaluated the capacity of the vinca alkaloid, vincristine to produce reversible blockade of retrograde axoplasmic transport. Results indicated that intraneural administration of 10(-5)M vincristine resulted in blockade of retrograde axoplasmic transport of [3H]leucine 24 h following administration. Importantly, the effect reversed over the next four days and axoplasmic transport was re-instated fully at day five. The implications of these results are discussed in relation to the potential use of axoplasmic transport blocking agents in the management of chronic neuropathic pain.

High-performance liquid chromatographic assay for common sunscreening agents in cosmetic products, bovine serum albumin solution and human plasma.

This paper reports the development of a reversed-phase high-performance liquid chromatographic assay for quantifying five of the most common sunscreen agents, namely 2-ethylhexyl-p-dimethyl aminobenzoate (Escalol 507), 2-ethylhexyl-p-methoxycinnamate (Parsol MCX); 4-tert.-butyl-4'-methoxydibenzoylmethane (Parsol 1789), 2-hydroxy-4-methoxybenzophenone-3 (oxybenzone) and 2-ethylhexyl-salicylate (octylsalicylate). The assay permits analysis of the sunscreen agents in formulations and in biological fluids, including bovine serum albumin (BSA) solution, a common additive to in vitro skin diffusion cell receptor fluids, as well as human plasma. Separation was achieved using an ODS C154 column with a methanol-water (88:12) mobile phase. The analytes were detected by ultraviolet light absorption at a wavelength of 315 nm. The assay was linear with minimum detectable limits, calculated as greater than 3-times the baseline noise level: for oxybenzone and Escalol 507, 0.05 microgram/ml; for Parsol 1789 and Parsol MCX, 0.1 microgram/ml; for octylsalicylate, 1 microgram/ml. Recoveries from both plasma and 2% BSA were within the range 89-107%. The inter- and intra-day coefficients of variation for the five agents were not more than 4% at the upper end of the linear range and not more than 10% at the lower end. Preliminary stability studies of the sunscreen agents in a commercial product and in two diffusion cell receptor fluids were also conducted.