In vitro human skin permeation and distribution of the fragrance material linalool (3,7-dimethyl-1,6-octadien-3ol, CAS No. 78-70-6) following application in a range of single and mixed vehicles was determined, under unoccluded and occluded conditions, using human epidermal membranes. Vehicles were (70/30 v/v) ethanol [EtOH]/water, dipropyleneglycol [DPG], diethyl phthalate [DEP], (25/75 v/v) EtOH/DEP, (25/75 v/v) EtOH/ DPG and petrolatum.Worst case absorbed dose values (% applied dose) for linalool under unoccluded conditions varied from 1.84% (DPG) to 4.08% (EtOH/water) and under occluded conditions from 5.9% (DEP) to 14.7% (EtOH/water). Occlusion always increased absorption but the magnitude of the effect varied with the vehicle from 2 to 6-fold.This study demonstrated that in vitro human skin permeation of linalool varied quite widely between test vehicles and that the magnitude of the effect of occlusion was also vehicle dependent. This was particularly significant in view of the reported variations in biological responses using different vehicles (Lalko et al., 2004; Politano et al., 2006).

Transdermal drug delivery is limited by the barrier properties of the outer skin layer. Microneedles (MNs) effectively circumvent the skin barrier to offer this route as a potential alternative to oral and parenteral delivery of therapeutics. Biodegradable microneedles offer particular advantages however processing commonly requires elevated temperatures that may adversely affect heat-labile molecules and macromolecules. In this study, solid amorphous sugar glasses containing low residual quantities of water were created by dehydration of trehalose and sucrose sugar combination solutions. Biodegradable sugar glass MNs were fabricated following optimisation of a simple and novel low temperature vacuum deposition micromoulding methodology. These had absolute morphological fidelity to silicon master structures and demonstrated sufficient structural rigidity to efficiently penetrate excised human breast skin. Sugar glass MNs incorporating a marker compound dissolved rapidly and completely in situ releasing dye into deeper skin layers. The biological activity of a model macromolecule was partially retained over extended storage following incorporation into sugar glass. This is the first demonstration that MNs created from amorphous sugar glasses can be used for incorporating and delivering molecules, and potentially biologically active macromolecules, via the transdermal route.

What is known and Objective: 3,4-diaminopyridine (3,4-DAP; amifampridine) is used for symptomatic treatment of LambertEaton myasthenic syndrome. Until recently, it was only available as a compounded product, which raises safety concerns because of possible high variability in active drug substance content. The objective of this study was to evaluate the variability in dosage form weight, active content variability and impurity of compounded oral 3,4-DAP drug products.Methods: Ten samples each of 9 oral 3,4-DAP compounded products were weighed, extracted with water and the 3,4-DAP content determined by ultra high-performance liquid chromatography.Results and Discussion: Variability in dosage form weight ranged from 0.81% relative standard deviation (RSD) to 4.82% RSD. In the 90 samples tested, 3,4-DAP content ranged from 22.2% to 125.2% of declared label content. All 10 samples of one compounded product had active drug substance content well below the declared label content (35.0%, 51.7% RSD). No compounded product achieved the Good Manufacturing Practice (GMP) standard of 95-105% range limit of declared label content; one achieved 90-110%, and four others achieved 80-120% of declared content for all 10 samples. There was no evidence of a significant presence of degradation products or related substances in any compounded product.What is new and Conclusion: Compounded 3,4-DAP products are subject to considerable variability in active drug substance content. This variability seems to be principally because of heterogeneous formulated material rather than variation in dosage form weight.

Ethyl (HE), propyl (HP), butyl (HB), octyl (HO) and decyl (HD) O-acyl esters of haloperidol (HA) were evaluated for permeation across full-thickness human and guinea pig skin. The inclusion of 0.5 mg mL−1 cetrimide as a receptor phase solubilising agent did not significantly alter the barrier properties of the membranes. The permeation of the parent drug, HA, across guinea pig skin was found to be greater than that of its derivatives. Prodrug hydrolysis by cutaneous esterases was minimal. The permeation of HE, HP and HB across freshly excised guinea pig skin was subsequently investigated, however, prodrug hydrolysis remained low. Hydrolysis studies using a skin extract revealed only limited prodrug metabolism. However, in the presence of a liver extract, hydrolysis of all prodrugs was rapid. It was proposed that GGGX esterases, required for the hydrolysis of tertiary esters, were not present at a sufficiently high concentration within the skin for substantial prodrug hydrolysis to occur. This does not necessarily detract from the system as post-transdermal delivery liberation of HA in vivo is an equally useful mode for delivering this drug to the systemic circulation.

In-vitro human skin permeation and distribution of geranyl nitrile (GN) was determined using epidermal membranes following application (5μl/cm2) in 70% ethanol, under non-occlusive conditions, at maximum in-use concentration (1%). Permeation was measured (12 time-points over 24h) using 6% (w/v) Oleth-20 in pH 7.4 phosphate buffered saline as receptor. Permeation of reference benzoic acid was assessed using the same skin donors. Overall recovery of GN at 24h was low (14.1±0.4%) due to evaporation. Evaporative loss of GN from polytetrafluoroethylene (PTFE) sheet, under the same conditions was rapid (93% over 24h) although this overestimated loss during permeation where evaporation competed with uptake. At 24h, 1.89±0.15μg/cm2 GN, (3.74±0.30% of applied dose) (mean±standard error, SE, n=12), had permeated. Following rapid initial permeation, the absorption plateaued due to depletion. Levels of GN in the epidermis (plus any remaining stratum corneum after tape stripping), filter paper membrane support and receptor fluid were combined (as per SCCNFP guidelines) to produce a total absorbed dose value of 4.72±0.32%. Systemic exposure resulting from the use of GN as a fragrance ingredient, under unoccluded conditions, would be low based on the currently reported use levels.

In vivo plasma profiles from formulations containing 5% ibuprofen were compared after a single topical application in a randomised, double-blind, cross-over trial. Ibuleve gel (Dermal Laboratories, UK) contained only ibuprofen whilst Deep Relief gel (Mentholatum, UK) also contained 3% menthol. In contrast to results obtained when these products were compared under in vitro conditions, there was no statistically significant difference in vivo between delivery of ibuprofen. Estimated relative bioavailability fraction (Deep Relief gel/Ibuleve gel) from log-transformed AUC((0-24h)) was 0.99 (95% CI: 0.94-1.04), estimated C(max )ratio was 0.96 (95% CI: 0.91-1.00) and estimated t(max) ratio was 1.01 (95% CI: 0.81-1.20). Menthol produces local vasodilation, which reduces skin barrier function, and these data demonstrate that it is inappropriate to extrapolate from in vitro data where formulation components produce biologically-mediated enhancement of permeation which cannot be modelled ex vivo. In clinical use, these products deliver comparable amounts of ibuprofen, but only Deep Reliefgel provides the secondary immediate benefit of the direct analgesic action of menthol.

Concern has been raised over the safety of diethanolamine (DEA) which may be present as a minor component of alkanolamide ingredients of cosmetic formulations. Skin penetration data were therefore generated for a range of typical formulations under in-use conditions. Seven rinse-off formulations (A-E, G and H), a leave-on emulsion (F), representing prototype cosmetic formulations and containing representative levels of DEA were prepared. Target levels of DEA were attained by inclusion of DEA as either (14)C-DEA or a combination of (14)C-DEA and unlabeled DEA. Skin permeation and distribution were evaluated using human skin in vitro, static diffusion cells and phosphate buffered saline (pH 7.4) as the receptor phase. At least 12 replicate epidermal membranes were prepared from a minimum of four donors for each test group. Receptor phase samples were taken at appropriate time intervals. At the end of the test period, radioactivity remaining on the skin surface and on the diffusion cell donor cap was determined before the skin samples were tape-stripped. The remaining tissue was solubilized and radioactivity determined. Permeation was very low from all vehicles applied under in-use conditions (range 1-48 ng/cm(2) over 24 h). Comparison was also made between permeation and distribution of DEA from an infinite dose of a simple aqueous solution and the leave-on formulation (F) through paired samples of fresh and frozen full thickness skin from the same donors. When applied as an infinite dose in aqueous solution DEA permeation at 24 h was greater through frozen than through fresh skin. From the leave-on formulation, permeation was similar and very low for both fresh and frozen skin. Recovery of DEA after application of the aqueous solution to fresh human skin and subsequent aqueous and organic extraction of the epidermal and dermal tissue indicated that the majority (>98%) of DEA was in the aqueous extract, suggesting that DEA was in the free state and not associated with the lipid fraction. These data provide a basis for the estimation of the potential systemic exposure and safety margins for DEA in representative cosmetic formulations.

A biosensor is a sensor that uses biological selectivity to limit its perception to particular key molecules and can be defined as an analytical device possessing a biological or biologically derived sensing element integrated with or associated closely with a physicochemical transducer. In the future it is likely that a number of key developments in therapeutic monitoring and intelligent drug delivery will rely on real-time feedback information in order to deliver an appropriate response. However due to issues of integration and the fragility and unreliability of the bio-molecule, biosensors are currently unable to fulfil this role. Molecular imprinted polymers are viable alternatives to both antibodies and enzymes and this review considers the current position of molecular imprinted polymer sensing.

The synthesis of a new polymerisable fluorescent monomer, 4-(3-aminopropylene)-7-nitrobenzofurazan, is described. This compound was further used to prepare a fluorescent atrazine imprinted polymer as a component of a homogeneous pseudofluoroassay. (C) 2004 Published by Elsevier Ltd.

The literature on the use of molecularly imprinted polymers (MIPs) in antibody-like sorbent assay using radio, fluoro and enzyme-linked approaches is comprehensively reviewed, and their current status discussed. Although immunoassays are still commonly carried out using antibodies, recent developments have demonstrated that molecularly imprinted polymers can be viable alternatives. It is predicted that both traditional antibody-based and MIP sorbent assays will continue to develop in parallel, with each having superiority in certain areas.

2′,3′-Dideoxynucleosides (ddNs) are among the most potent of nucleoside analogues active against human immunodeficiency virus (HIV) in cell culture. d4T (2′,3′-dideoxy-2′,3′-didehydrothymidine) is clinically effective acting through competitive inhibition of viral reverse transcriptase and/or incorporation and subsequent chain termination of the growing viral chain. Activation occurs via intracellular conversion to the 5′-triphosphate, the kinase-mediated formation of the monophosphate being the rate-limiting step and, therefore, strategies to deliver the monophosphate have been sought. This study uses a molecularly imprinted HPLC stationary phase to separate single diastereomers for a number of nucleoside monophosphates prodrugs from synthetic mixtures. The biological activity of some individual diastereomers are unknown and a need to efficiently separate them from synthetic mixtures, has been identified. Due to cross-reactive affinity for the imprinted polymer one imprinted stationary phase was used to isolate a single diastereomer from a range of prodrug synthetic mixtures.

Molecular imprinting is a means of introducing sites of specific molecular arrangement into an otherwise uniform polymeric matrix. This is achieved by formation of a pre-polymerisation complex between complementary monomers and the template molecule. Subsequent polymerisation in the presence of a crosslinker, in a porogenic environment, results in the production of a macroporous polymer capable of specific molecular recognition. This paper considers potential roles for molecularly imprinted polymers within a pharmaceutical remit. Applications including controlled release, drug monitoring devices and biological receptor mimetics are discussed. Histamine and ephedrine molecularly imprinted polymers (MIPs) were studied as potential biological receptor mimics whilst a propranolol MIP was investigated for its use as a rate attenuating selective excipient in a transdermal controlled release device. Preliminary studies concerning the preparation of a theophylline selective transcutaneous monitoring device, using a theophylline MIP, are also described.

This work tested the hypothesis that a stereospecific topical formulation could be used to engineer differential permeation rates for each enantiomer of an applied racemate across human skin in vitro. Racemic and enantiomerically pure R or S propranolol HCI were formulated with cellulose tris(3,5-dimethyl phenyl carbamate) (CDMPC) and applied to excised human skin using side-by-side Franz-type diffusion cells. When the pure enantiomers were used, there was a marked difference between the penetration rates of R and S propranolol (flux ratio: 2.06; P = 0.04). When racemic propranolol was used, the difference was reduced, although still statistically significant (flux ratio: 1.2; P = 0.08), particularly in view of the differential activities of the two enantiomers. Control experiments, in which no CDMPC was present, produced equal permeation rates. The results can be rationalised in terms of differential adsorption onto CDMPC within the vehicle, whereby S-propranolol is preferentially bound relative to R-propranolol. This causes an imbalance in the apparent donor phase concentrations that (in accordance with Fickian diffusion laws and thermodynamic activity) gives rise to differences in permeation rates. The diminished differential observed when the racemate was used, rather than individual enantiomers, is less easily rationalised. In this work, it was the permeation of the eutomer (S-propranolol) that was retarded, although the general principle of stereoselectively retarded skin permeation has been established.

This chapter focuses on preparation, biomedical applications and technical challenges of molecularly imprinted polymers (MIPs). Molecular recognition is fundamental to the function of biological systems. Enzyme activity, receptor binding systems and the immune response require that the presence of one molecular species be perceived by another. Although biological systems are often very highly specific, the capacity for adaptation and apparent nonspecificity is inherent. The polymeric system that provides the basis for these recognition events is the protein and nature's creation has been put to good use within the laboratory. The fundamental process in the formation of all imprinted polymers is the formation of a stable noncovalent pre-polymerization complex between the template molecule and functional polymerizable units. In this approach, the template is noncovalently bound to the polymerizable moiety. The complex is copolymerized in the presence of a cross-linking reagent to yield a rigid, macroporous product. The integrity of the prepolymerization complex is maintained entirely by noncovalent interactions. Typically, proton transfer events, giving rise to ionic species, and hydrogen bonds are central to the formation of the complex and its persistence. The basic methodology involved in MIP preparation and application is highly attractive in its simplicity and the range of potential uses is very large and diverse.