Cost effectiveness of vaccination strategies in adults without a history of chickenpox

PURPOSE

Some authorities recommend varicella antibody testing or vaccination for adults without a history of chickenpox, but the cost effectiveness of these interventions is uncertain.

SUBJECTS AND METHODS

Using a Markov decision model, we estimated the cost effectiveness of three strategies for adults with no history of chickenpox: no vaccination, varicella antibody testing followed by vaccination for those without antibody, and vaccinating all. Societal and third-party payer perspectives were taken, with costs and benefits discounted at 3% per year. Assumptions for the baseline analysis were chosen to bias against no vaccination.

RESULTS

In the baseline analysis for 20- to 29-year-old patients, testing followed by vaccination compared with no vaccination is cost saving from a societal perspective and costs $6,670 per quality-adjusted life-year (QALY) gained from a third-party payer perspective. When less favorable assumptions are used, results are sensitive to the rates of compliance with vaccination follow-up; testing followed by vaccination costs more than $50,000 per QALY if <75% comply. For patients 30 years of age and older, the incremental cost of testing followed by vaccination is at least $97,100 per QALY compared with no vaccination, with costs greater than $50,000 per QALY unless testing costs less than $7.73, the chickenpox case-fatality rate is >0.067% (baseline 0.025%), or immunity with no chickenpox history is <25% (baseline 71%). In either age group, vaccinating all has an incremental cost of $2 to $16 million per QALY gained compared with testing followed by vaccination.

CONCLUSION

Testing followed by vaccination for varicella in US adults aged 20 to 29 years may be cost effective by conventional criteria but is sensitive to rates of compliance with vaccination protocols. Testing or vaccination of older adults is expensive but may be cost effective in patients with lower probabilities of immunity or in those who have a greater risk of complications from chickenpox.

An isolated in-situ rat head perfusion model for pharmacokinetic studies

PURPOSE

To develop a viable, single pass rat head perfusion model useful for pharmacokinetic studies.

METHODS

A viable rat head preparation, perfused with MOPS-buffered Ringer's solution, was developed. Radiolabelled markers (red blood cells, water and sucrose) were injected in a bolus into the internal carotid artery and collected from the posterior facial vein over 28 minutes. The double inverse Gaussian function was used to estimate the statistical moments of the markers.

RESULTS

The viability of the perfusion was up to one hour, with optimal perfusate being 2% bovine serum albumin at 37 degrees C, pH 7.4. The distribution volumes for red blood cells, sucrose and water (from all studies, n = 18) were 1.0 +/- 0.3 ml, 6.4 +/- 4.2 ml and 18.3 +/- 11.9 ml, respectively. A high normalised variance for red blood cells (3.1 +/- 2.0) suggests a marked vascular heterogeneity. A higher normalised variance for water (6.4 +/- 3.3) is consistent with additional diffusive/permeability limitations.

CONCLUSIONS

Analysis of the physiological parameters derived from the moments suggested that the kinetics of the markers were consistent with distribution throughout the head (weight 25 g) rather than just the brain (weight 2 g). This model should assist in studying solute pharmacokinetics in the head.

Can tissue drug concentrations be monitored by microdialysis during or after isolated limb perfusion for melanoma treatment?

Isolated limb perfusion (ILP) with melphalan is used to treat recurrent melanoma. This study aimed to develop a microdialysis technique for melphalan tissue concentration measurement during ILP. The effects of melphalan concentration (50-600 microg/ml), microdIalysis flow rate (0.55-17.5 microl/min), probe length (5-50 mm) and temperature (25-41.5 degrees C) on in vitro recovery were studied. In addition, in vivo recovery was measured in rat hindlimbs perfused with melphalan using 50 mm microdialysis probes implanted subcutaneously and into muscle. Both dialysate and tissue sample melphalan concentrations were determined by high performance liquid chromatography. The in vitro recovery of melphalan was not affected by melphalan concentration or temperature, but increased with probe length and decreased with flow rate. The melphalan concentrations in subcutaneous and muscle dialysates were not significantly different. A linear relationship was found between tissue dialysate concentrations and actual tissue concentrations of melphalan (r2 = 0.97). Microdialysis is a potential method for tissue drug monitoring which may assist in the efficacious use of cytotoxics in human ILP.

The back diffusion of glucose across human skin in vitro

For diabetic patients, blood glucose monitoring is an important part in the management of their disease, however the acquisition of blood requires the use of invasive and often painful methods, and the development of a technique that removes these problems would represent a major advance. The uppermost membrane of the skin, the stratum corneum, has been shown to be the main barrier to percutaneous absorption, but there have been claims that polar water-soluble compounds diffuse across it via aqueous pathways. In this study, skin diffusion cells were used to investigate the back diffusion of tritiated water and the convective transport of 3H-glucose across full thickness human skin after the application of a number of different materials to the stratum corneum. Significant amounts of 3H-glucose back diffused only after complete removal of the stratum corneum by tape stripping, and it is likely that any future attempts to monitor blood glucose levels using non-physical techniques will require a certain degree of damage to the stratum corneum. The extraction through the skin of tritiated water and 3H-glucose after the application of solutions with different osmotic pressures were consistent with the theory that solutions with high osmotic pressures dehydrate the stratum corneum which suggests that passive transport of these radiolabelled molecules through porous pathways was insignificant.

Statistical moments for placental transfer of solutes in man

The placental transfer of red blood cells and solutes in man has been investigated by statistical moment analysis, using the impulse-response technique. Model compounds of different lipophilicity (sucrose, water, antipyrine, propranolol and labetalol) were injected with a vascular reference (labelled red blood cells) as boluses into either the foetal or maternal circulation of a single-pass perfused placental lobule. Maternal and foetal venous outflow fractions were collected at intervals ranging from 1 to 600 s. Perfusion was conducted at maternal flow rates of 4 and 6 mL min(-1) and foetal flow rates of 2 and 3 mL min(-1), respectively, to yield a constant materno-foetal flow ratio of 2. The outflow concentration-time profile curves were analysed by statistical moment analysis. The sum of foetal and maternal recovery was close to 100% for red blood cells, sucrose, water and antipyrine, but lower for propranolol and labetalol. The mean transit time (MTT) values ranged from 20 to 500 s. The normalized variance (CV2) for red blood cells in the foetal and maternal circulation of the placenta were in the ranges 2.31 to 3.86 and 2.00 to 2.03, respectively. The shape of the outflow concentration-time profiles after bolus input is consistent with that of vascular residence time models such as the dispersion model. The heterogeneity in red blood cell transit times, as defined by CV2, is greater than in either the perfused leg or perfused liver.

Diffusion modeling of percutaneous absorption kinetics. 1. Effects of flow rate, receptor sampling rate, and viable epidermal resistance for a constant donor concentration

A diffusion model for the percutaneous absorption of a solute through the skin is developed for the specific case of a constant donor concentration with a finite removal rate from the receptor due to either perfusion rate or sampling. The model has been developed to include a viable epidermal resistance and a donor-stratum corneum interfacial resistance. Numerical inversion of the Laplace domain solutions were used for simulations of solute flux and cumulative amount absorbed and to model specific examples of percutaneous absorption. Limits of the Laplace domain solutions were used to define the steady-state flux, lag time, and receptor concentration. Steady-state approximations obtained from the solutions were used to relate the steady-state flux and the effective permeability coefficient to the viable epidermis resistance, a donor-stratum corneum interfacial resistance, receptor removal rate, and partitioning between the receptor and donor phases. The lag time was shown to be dependent on these parameters and on the volume of the receptor phase. It is concluded that curvilinear cumulative amount and flux-time profiles are dependent on the processes affecting percutaneous absorption, the shapes of the profiles reflecting the processes most determining transport.

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.

Can a controlled-release oral dose form of oxycodone be used as readily as an immediate-release form for the purpose of titrating to stable pain control?

Two separate trials compared controlled-release (CR) oral oxycodone (administered every 12 hours) with immediate-release (IR) oxycodone (4 times a day) to determine whether patients with chronic pain could be titrated to stable pain control as readily with the CR as with the IR formulation. In one study, 48 patients with cancer pain were randomized to open-label titration with either CR or IR oxycodone (maximum dose, 400 mg/day) for a period of up to 21 days. In a study of similar design, 57 patients with low back pain were titrated with either CR or IR oxycodone (maximum dose, 80 mg/day) for a period of up to 10 days. The majority of patients in both studies were converted to oxycodone from other opioid analgesics. Results of both studies showed no difference between CR and IR oxycodone with respect to both the percentage of patients achieving stable pain control, the time to achieve stable pain control, and the degree of pain control achieved. Among cancer patients, 85% achieved stable analgesia, 92% with the CR formulation and 79% with the IR formulation. Among noncancer patients, 91% achieved stable pain control, 87% with the CR formulation and 96% with the IR formulation. The most commonly reported adverse effects in both studies were similar for the two formulations and were those anticipated with opioids: nausea, vomiting, constipation, somnolence, dizziness, and pruritus. Nausea and vomiting were the most frequently cited reasons for treatment discontinuations. These studies suggest that dose titration can be accomplished as readily with oral CR oxycodone as with IR oxycodone in patients with chronic, moderate to severe pain.

Behavior and therapeutic efficacy of beta-glucuronidase-positive mononuclear phagocytes in a murine model of mucopolysaccharidosis type VII

Bone marrow transplantation (BMT) is relatively effective for the treatment of lysosomal storage diseases. To better understand the contribution of specific hematopoietic lineages to the efficacy of BMT, we transplanted beta-glucuronidase-positive mononuclear phagocytes derived from either the peritoneum or from bone marrow in vitro into syngeneic recipients with mucopolysaccharidosis type VII (MPS VII). Cell surface marking studies indicate that the bone marrow-derived cells are less mature than the peritoneal macrophages. However, both cell types retain the ability to home to tissues rich in cells of the reticuloendothelial system after intravenous injection into MPS VII mice. The half-life of both types of donor macrophages is approximately 7 days, and some cells persist for at least 30 days. In several tissues, therapeutic levels of beta-glucuronidase are present, and histopathologic analysis demonstrates that lysosomal storage is dramatically reduced in the liver and spleen. Macrophages intravenously injected into newborn MPS VII mice localize to the same tissues as adult mice but are also observed in the meninges and parenchyma of the brain. These data suggest that macrophages play a significant role in the therapeutic efficacy of BMT for lysosomal storage diseases and may have implications for treatments such as gene therapy.

A physiological pharmacokinetic model for solute disposition in tissues below a topical below a topical application site

PURPOSE

Many compounds are applied to the skin with the aim of targeting deeper underlying tissues. This work sought to define the pharmacokinetics of solutes in tissues below a topical application site in terms of perfusate binding, tissue binding and perfusate flow rate.

METHODS

The disposition kinetics of diclofenac in a single pass perfused limb preparation after dermal application disposition was studied using dextran and bovine serum albumin (BSA) containing perfusates. A pharmacokinetic model was then developed to relate the tissue retention half lives for diclofenac, diazepam, water, lignocaine and salicylate to their fraction unbound in the tissues, their fraction unbound in the perfusate and the perfusate flow rate.

RESULTS

Diclofenac had estimated tissue retention half lives of 18.1 hr and 3.5 hr for the dextran and BSA containing perfusates, respectively. The fraction of diclofenac and other solutes unbound in the tissues correlated with their corresponding fraction unbound in the perfusate. The tissue retention half lives for diclofenac and other solutes could be described in terms of the fraction of solute unbound in the tissues and perfusate, together with the flow rate.

CONCLUSION

The tissue pharmacokinetics of solutes below a topical application are a function of their binding in the tissues, binding in perfusate and local blood flow.

Interconnected-tubes model of hepatic elimination: steady-state considerations

In the interconnected-tubes model of hepatic transport and elimination, intermixing between sinusoids was modelled by the continuous interchange of solutes between a set of parallel tubes. In the case of strongly interconnected tubes and for bolus input of solute, a zeroth-order approximation led to the governing equation of the dispersion model. The dispersion number was expressed for the first time in terms of its main physiological determinants: heterogeneity of flow and density of interconnections. The interconnected-tubes model is now applied to steady-state hepatic extraction. In the limit of strong interconnections, the expression for output concentrations is predicted to be similar in form to those predicted by the distributed model for a narrow distribution of elimination rates over sinusoids, and by the dispersion model in the limit of a small dispersion number D(N). More generally, the equations for the predicted output concentrations can be expressed in terms of a dimensionless 'heterogeneity number'H(N), which characterizes the combined effects of variations in enzyme distribution and flow rates between different sinusoids, together with the effects of interconnections between sinusoids. A comparative analysis of the equations for the dispersion and heterogeneity numbers shows that the value of H(N)can be less than, greater than or equal to the value of D(N)for a correlation between distributions of velocities and elimination rates over sinusoids, anticorrelation between them, and when all sinusoids have the same elimination rate, respectively. Simple model systems are used to illustrate the determinants of H(N)and D(N).

Modeling of hepatic elimination and organ distribution kinetics with the extended convection-dispersion model

The conventional convection-dispersion (also called axial dispersion) model is widely used to interrelate hepatic availability (F) and clearance (Cl) with the morphology and physiology of the liver and to predict effects such as changes in liver blood flow on F and Cl. An extended form of the convection-dispersion model has been developed to adequately describe the outflow concentration-time profiles for vascular markers at both short and long times after bolus injections into perfused livers. The model, based on flux concentration and a convolution of catheters and large vessels, assumes that solute elimination in hepatocytes follows either fast distribution into or radial diffusion in hepatocytes. The model includes a secondary vascular compartment, postulated to be interconnecting sinusoids. Analysis of the mean hepatic transit time (MTT) and normalized variance (CV2) of solutes with extraction showed that the discrepancy between the predictions of MTT and CV2 for the extended and unweighted conventional convection-dispersion models decreases as hepatic extraction increases. A correspondence of more than 95% in F and Cl exists for all solute extractions. In addition, the analysis showed that the outflow concentration-time profiles for both the extended and conventional models are essentially identical irrespective of the magnitude of rate constants representing permeability, volume, and clearance parameters, providing that there is significant hepatic extraction. In conclusion, the application of a newly developed extended convection-dispersion model has shown that the unweighted conventional convection-dispersion model can be used to describe the disposition of extracted solutes and, in particular, to estimate hepatic availability and clearance in both experimental and clinical situations.

Relationship of Bacillus subtilis clades associated with strains 168 and W23: a proposal for Bacillus subtilis subsp. subtilis subsp. nov. and Bacillus subtilis subsp. spizizenii subsp. nov

Earlier phylogenetic studies based on the inferred DNA sequences of the polC, rpoB and gyrA genes suggested that strains of the species Bacillus subtilis formed two clusters, indicating the presence two closely related taxa; one contained the laboratory strain 168 and the other the laboratory strain W23. Significant sexual isolation was found between strain 168 and members of the group containing W23, but no sexual isolation was observed between strain 168 and other members of the 168 group. DNA reassociation between the two groups ranged from 58 to 69% and intragroup DNA relatedness ranged from 82 to 100%. Because group 168 strains were highly related to the B. subtilis type strain, they were considered to be bona fide members of the species. About 99.5% sequence identity was observed between the 16S rRNA genes of the 168 and W23 groups. Ribitol and anhydroribitol were principal cell wall constituents of the W23 but not of the 168 group. These observations revealed two closely related but genetically and phenotypically distinct groups within B. subtilis that correspond to two historically important strains. Subspecies distinction is proposed for the 168 and W23 groups, with the names Bacillus subtilis subsp. subtilis subsp. nov. and Bacillus subtilis subsp. spizizenii subsp. nov., respectively. The type strain of the former is NRRL NRS-744T and the latter NRRL B-23049T.

Structure-hepatic disposition relationships for phenolic compounds

Phenolic compounds are widely used in therapeutic, environmental, and industrial applications. The present work seeks to define the hepatic disposition of 11 phenolic compounds with varying lipophilicities and molecular weights. The hepatic disposition kinetics were studied in a once-through in situ rat liver perfusion preparation in order to avoid extra-hepatic metabolism and recirculation effects. The phenols were administered using the impulse-response technique and the time course of hepatic venous effluent concentration was examined by moments and a two-compartment dispersion model. While the extraction of the phenolic compounds was relatively independent of lipophilicity, the estimated permeability-surface area (PS) product for influx of solutes into the hepatocytes could be related to the compounds' octanol-buffer partition coefficients (log Papp). This log PS-logPapp relationship was consistent with that reported earlier for another series of solutes with a wide range of lipophilicity. The metabolites produced from each of the phenolic compounds used in this study had mean transit times similar to those of their corresponding parent phenols, suggesting that the metabolites were not trapped in the liver as a consequence of their higher polarity. It is concluded that the strong solute lipophilicity-toxicity and lipophilicity-skin penetration relationships often seen for aqueous solutions of phenols are not evident for the hepatic extraction of these compounds. Such a conclusion is consistent with the hepatic extraction of phenolic compounds being mainly determined by a blood flow limitation in delivery of the phenol to the liver, rather than the intrinsic liver metabolic enzyme activities at the doses injected.

Informatics and process improvement. The clinical design unit

Seeking to integrate departments and services, reduce costs, and enhance quality, administrators at a university medical center implemented a clinical design unit. The authors describe the operations of the unit in testing new processes before rollout to the entire center.

An analysis of solute structure-human epidermal transport relationships in epidermal iontophoresis using the ionic mobility: pore model

This study sought to examine the extent the ionic mobility-pore model, used to describe epidermal iontophoretic structure-permeability relationships, could describe a range of published iontophoretic data. The model incorporates, as determinants of iontophoretic transport, solute size, solute mobility, total current applied, presence of extraneous ions, determined by conductivities of both donor and receptor solutions, permselectivity of the epidermis, as well as a solute pore interaction term which together provided an excellent regression for iontophoretic permeability. The 'pore' radii for solute transport estimated from literature iontophoretic permeabilities using the model ranged from 6.8 to 17 A depending on the degree of hydration and conformation of solute assumed. The pore size range is consistent with transport through the polar intercellular and transappendageal pathway for transport. The pore restriction form of the model better describes the data obtained to date than other models described previously (Yoshida, N.H., Roberts, M.S., Solute molecular size and transdermal iontophoresis across excised human skin. J. Control. Release 25 (1993) 177-195).

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.

Defining a model to predict the distribution of topically applied growth factors and other solutes in excisional full-thickness wounds

Controversy over the efficacy of many topical wound treatments, particularly growth factors, is common, with many clinical practitioners still confused as to the real value of these agents. A serious lack of knowledge appears to exist concerning the diffusion and distribution of topically applied solutes in wounds. Without this basic understanding there seems little chance of accurately predicting the therapeutic window of drugs targeted at cellular activities, such as division and chemotaxis, and processes, such as collagen lattice deposition and contraction, occurring below the surface of the granulating layer. This study was designed to determine the absorption and distribution of a number of radiolabeled solutes (water, sodium chloride, lidocaine) and growth factors (basic fibroblast growth factor, epidermal growth factor) applied topically to full-thickness excisional wounds in rats during the early (2 d), mid (7 d), and late (12 d) stages of repair. Results showed that water and sodium penetrated deepest into wound sites and that changes in water distribution and retention in the wound paralleled the healing process. Multiple stepwise regression showed that molecular weight and tissue depth, but not day of healing, were significant factors in predicting the concentration of each solute in wound and underlying tissue sites. This finding was consistent with a tissue diffusion model developed in this study. Basic fibroblast growth factor and epidermal growth factor only penetrated slightly into the upper granulating layers of the wound site, and calculation of therapeutic doses, based on the percentage of applied solute reaching the deeper granulating layers, is presented.

Lateral iontophoretic solute transport in skin

PURPOSE

The lateral iontophoretic transport of three solutes (sodium, ethanolamine, lidocaine) from an active electrode through skin and other tissues to an indifferent electrodes was investigated.

METHODS

Anodal epidermal iontophoresis was carried out on an in vivo rat model using constant direct current of 0.38 mA/cm2. Cells were fixed on the epidermis of anesthetized rats at distances of adjacent, 3 cm and 7 cm apart. After iontophoresis, tissues were dissected at I cm intervals between the electrodes. Concentrations of the radiolabelled solutes in tissues were determined by liquid scintillation counting or gamma counting.

RESULTS

The concentration of each solutes in the epidermis, dermis and other tissues was found to decrease in an exponential manner with lateral distance from the active electrode to the indifferent electrode. The detectable lateral distance for ethanolamine and lidocaine was less than 2 cm from the donor sites, at which distance the concentrations were not significantly different to those found in the corresponding contralateral site. The lateral drift velocities for all solutes in the epidermis and dermis were consistent with diffusivities of the order of 10(-6) cm2/s. The drift velocity of sodium was greater than either lidocaine or ethanolamine.

CONCLUSIONS

The decline in solute concentration with lateral distance is mainly due to clearance from the site of application by the skin's microcirculation and decreases with distance from the active electrode until a baseline concentration, similar to the contralateral tissue concentration is reached.

Focused antithrombotic therapy: novel anti-platelet salicylates with reduced ulcerogenic potential and higher first-pass detoxification than aspirin in rats

The use of aspirin as an anti-platelet drug is limited by its propensity to induce gastric injury and by its adverse effect on vascular prostacyclin formation. Two phenolic non-steroidal anti-inflammatory drugs (salicylic acid and diflunisal) were modified by esterification with a series of O-acyl moieties. The short-term ulcerogenic in vitro and in vivo anti-platelet properties, pharmacodynamic profiles, and extent of hepatic extraction of these phenolic esters were compared with aspirin (acetylsalicylic acid). The more lipophilic esters (longer carbon chain length in O-acyl group) show significantly less gastrotoxicity in stressed rats than does aspirin after a single oral dose. The in vitro and in vivo anti-platelet studies show that these phenolic esters inhibited (1) arachidonate-triggered human platelet aggregation and (2) thrombin-stimulated rat serum thromboxane A2 production by platelets in the clotting process almost as effectively as aspirin. The hepatic extractions of these O-acyl derivatives are significantly higher than those of aspirin. The pharmacodynamic studies show that these O-acyl derivatives of salicylic acid and diflunisal probably bind to, or combine with, the same site on the platelet cyclooxygenase as aspirin. Replacing the O-acetyl group with longer chain O-acyl moiety in this series of phenolic esters markedly reduced the potential of these agents to induce short-term gastric injury but did not lessen their activity as inhibitors of platelet aggregation. These non-acetyl salicylates may therefore represent a novel class of anti-platelet drugs with less ulcerogenic potential.

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.

Cost effectiveness of newer antiviral agents for herpes zoster: is the evidence spotty?

Famciclovir and valaciclovir were approved for use in the treatment of herpes zoster despite controversy over antiviral therapy in zoster due to high costs and uncertain benefits. To explore these issues, a Markov decision model was developed, and the incremental cost effectiveness of antiviral treatment for herpes zoster was estimated using these agents compared with no antiviral therapy. A third-party payer perspective was taken. Sensitivity analyses were performed, modeling differences in antiviral efficacy, postherpetic neuralgia (PHN) risk, and other illness parameters. Treatment of severely symptomatic acute zoster was found reasonable from a cost-effectiveness standpoint in base-case and worst-case scenarios. Treatment of mildly symptomatic acute zoster was more expensive but would likely be considered cost effective in scenarios where PHN risk was higher, PHN duration longer, or antiviral shortening of PHN greater. Further research comparing antiviral efficacy in herpes zoster is needed.