Influence of Transcutol CG on the skin accumulation and transdermal permeation of ultraviolet absorbers

The objective of this study was to determine the influence of Transcutol CG concentration on the transdermal permeation and skin accumulation of two ultraviolet (UV) absorbers, 2-hydroxy-4-methoxybenzophenone (oxybenzone) and 2-octyl-4-methoxycinnamate (cinnamate). The concentration of the UV absorber was held constant at 6% (w/w) for all vehicle systems while the concentration of Transcutol CG was varied from 0 to 50% (w/w). Data showed that both UV absorbers exhibited increases in skin accumulation with increasing concentrations of Transcutol CG. Skin accumulation of oxybenzone was significantly (P<0.05) greater than that of cinnamate for all formulations investigated. Oxybenzone skin accumulation ranged from 22.9+/-2.8 microg/mg (0% Transcutol CG) to 80.8+/-27.2 microg/mg (50% Transcutol CG). Cinnamate skin accumulation ranged from 9.0+/-0.9 microg/mg to 39.8+/-12.2 microg/mg at 0 and 50% Transcutol CG, respectively. No significant differences were found in the transdermal permeation of oxybenzone or cinnamate for any of the formulations tested. The results of this study demonstrate that the inclusion of Transcutol CG in sunscreen formulations increases the skin accumulation of the UV absorbers oxybenzone and cinnamate without a concomitant increase in transdermal permeation.

Pharmacokinetic-pharmacodynamic relationship of levodopa with and without tolcapone in patients with Parkinson's disease

OBJECTIVE

To investigate the effect of administration of the catechol-Omethyltransferase (COMT) inhibitor tolcapone on the concentration-effect relationship of levodopa in patients with advanced Parkinson's disease and on-off fluctuations.

DESIGN

Nonblind single-group 2-period pharmacokinetic-pharmacodynamic study.

PATIENTS AND PARTICIPANTS

12 patients, mean age 59 years, with idiopathic Parkinson's disease and response fluctuations.

METHODS

The pharmacokinetics [plasma concentrations of levodopa and 3-O-methyldopa (3-OMD)] and motor effects [global score of the Columbia University Rating Scale (CURSsigma)] of levodopa (plus the peripheral decarboxylase inhibitor benserazide 1:4) were determined for 4 consecutive dosage intervals (4 hours each, starting at 8.00am) in 12 patients before (day 1) and during (day 8) coadministration of tolcapone 100 mg 3 times daily for 7 days.

RESULTS

Under tolcapone, exposure to levodopa [area under the plasma concentration-time for the dosage interval (AUCt)] observed for the separate doses increased by 1.6- to 2.2-fold, and peak plasma drug concentrations (Cmax) increased by 1.1 - to 2.1 -fold. 3-OMD concentrations at day 8 were reduced to about 20% of the values at day 1. At baseline (day 1, before the first levodopa dose), CURSsigma averaged 40 +/- 10 points. After the first levodopa dose. CURSsigma declined to 20 +/- 9 points. At day 8. the predose CURSsigma decreased to a final score of 31 +/-13 points, and the maximal decline after the first levodopa dose was to a final score of 16 +/- 8 points. Population analysis (NONMEM) of the concentration-effect relationship of levodopa according to a sigmoidal Emax model and over all dosage intervals did not show differences in levodopa responsiveness with or without tolcapone. The population mean of the 50% effective concentration (EC50) of levodopa was 1350 microg/L with an standard error of the population parameter estimate of 18%: adding tolcapone treatment as a covariate did not significantly change the population fit. Circadian influences on levodopa respon- siveness were not evaluable by the NONMEM model due to overparametrisation, but visual inspection of plotted data did not suggest differences in the concentration-effect relationship between the 4 consecutive dosage intervals on days 1 and 8.

CONCLUSIONS

The gain in clinical improvement with levodopa under tolcapone can be fully explained by tolcapone-induced changes of peripheral levodopa pharmacokinetics. We suggest that this interaction study, performed in patients and using clinical data, excludes any central effects of tolcapone or any inhibiting effect of 3-OMD on levodopa permeation through the blood-brain barrier, which otherwise would have led to a decrease in the EC50 of levodopa.

Azomethine prodrugs of (R)-alpha-methylhistamine, a highly potent and selective histamine H3-receptor agonist

The histamine H3 receptor is considered a potential target for novel drugs as it regulates the activity of various neurotransmitters in the peripheral and the central nervous system. Particularly H3-receptor agonists have been suggested to become valuable drugs for the treatment of several CNS disorders, inflammatory and acid related diseases. Due to its strong basicity and polarity the highly potent and selective histamine H3-receptor agonist (R)-alpha-methylhistamine hardly penetrates biological membranes and is furthermore rapidly inactivated in vivo. Thus, lipophilic, non-basic azomethine prodrugs of (R)-alpha--methylhistamine have been developed to overcome its pharmacokinetic disadvantages. This bioreversible derivatization decreased its basicity, increased its lipophilicity and reduced its metabolization. As a result the biological half-life was prolonged and oral absorption as well as penetration into the brain were significantly increased. By systematic variation of the pro-moiety we were able to optimize the pharmacokinetic properties which allow for both peripheral and central delivery of the parent amine. The azomethine prodrugs described herein display satisfactory stability to be orally administered while being adequately labile to deliver (R)-alpha-methylhistamine at sufficient concentrations in vivo. At present, these azomethines not only serve as valuable tools for pharmacological studies related to the histamine H3 receptor, but also represent a promising approach to achieve therapeutic application of the histamine H3-receptor agonist (R)-alpha-methylhistamine. Currently the parent compound of the prodrugs is under clinical development phase II.

Stripping method to quantify absorption of two sunscreens in human

With the aim to know the remanence of two sunscreens, PEG-25 PABA and benzophenone, two cases have been considered: the application of aqueous solution of two filters studied for the application of oil-in-water (O/W) emulsions containing the same two filters on the skin of 21 voluntary women. In order to determine the quantity of filter remaining in the stratum corneum after times of application, which vary from 1 to 7 h, a series of six strippings have been carried out. The sunscreen agents were assessed by HPLC. With this study, it has been possible to emphasize the best remanence of benzophenone 4. Moreover, the incorporation of photo-protective agents in a O/W emulsion promotes their penetration, and this is particularly due to benzophenone 4.

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".

Comparative toxicological study on the hepatic safety of entacapone and tolcapone in the rat

Entacapone and tolcapone are novel COMT (catechol-O-methyltransferase) inhibitors indicated for the adjunctive treatment of Parkinson's disease (PD) in combination with levodopa. The marketing authorisation of tolcapone was suspended in the European Union (EU) in 1998 mainly due to severe abnormal hepatic reactions. This fact raised concern about the safety of COMT inhibitors in the treatment of parkinsonian patients. In order to investigate whether these COMT inhibitors exhibit different effects on the liver comparative toxicological studies were performed in the rat. Short term toxicological studies in rats at high oral doses of entacapone and tolcapone (200, 400 or 600mg/kg daily) were carried out. Tolcapone (400 mg/kg/day or 600 mg/kg/day) increased mortality after only one week treatment and induced signs of toxicity such as a rise in body temperature, stimulation of respiration and rapid onset of rigor mortis after death. Entacapone did not show any adverse effects at the tested dose levels. In the histopathological examination liver cell necrosis was observed in the tolcapone (400 and 600mg/kg/day) treated rats, but it revealed no treatment related signs of toxicity in entacapone-treated rats. We conclude that the toxicological profile of the two COMT inhibitors, entacapone and tolcapone, differ from each other, tolcapone--unlike entacapone--showed hepatotoxicity.

LC analysis of benzophenone-3: II application to determination of 'in vitro' and 'in vivo' skin penetration from solvents, coarse and submicron emulsions

The aim of this study was to determine the skin penetration of benzophenone-3 in vitro and in vivo in order to investigate a possible influence of formulation. Six different vehicles, three solvents and three different emulsion types were evaluated in vitro and in vivo. Each vehicle was applied to the skin model at 2 mg cm(-2). First, histological studies on ear pigskin and human skin were evaluated. In vitro measurements were performed with static diffusion cells using pigskin at 1, 2, 4, and 8-h. In vivo, benzophenone-3 concentration in stratum corneum was evaluated by the stripping method after 30-min application on forearm of volunteers. It was shown that ear pigskin and human skin appear similar and in both experiments significant differences between vehicles were noticed. The six vehicles could be ranked in the same order of benzophenone-3 skin concentration. At 8-h, the highest concentration of benzophenone-3 in skin was obtained with propylene glycol, and O/W submicron emulsion. On the contrary. the two oily solvents. W/O emulsion and O/W coarse emulsion restrain the concentration of this UV-filter in the skin. At each time, permeability in vitro and in vivo were well correlated. Low concentrations were measured in the receptor fluid suggesting that percutaneous absorption of this UV-filter across the skin would be minimal. The in vitro and in vivo skin penetration capacity of benzophenone-3 from six vehicles was confirmed and quantified. A satisfactory relationship between binary in vitro and in vivo was established.

The specificity of glucuronidation of entacapone and tolcapone by recombinant human UDP-glucuronosyltransferases

The COMT inhibitors entacapone and tolcapone are rapidly metabolized in vivo, mainly by glucuronidation. In this work, the main UGT isoforms responsible for their glucuronidation in vitro were characterized by using a subset of representative cloned and expressed human UGT isoforms. Entacapone in particular was seen to be an exceptionally good substrate for UGT1A9 with an even higher reaction velocity value at 500 microM substrate concentration compared with that of the commonly used substrate, propofol (1.3 and 0.78 nmol min(-1) mg(-1), respectively). Neither entacapone nor tolcapone was glucuronidated by UGT1A6. Tolcapone was not detectably glucuronidated by UGT1A1, and the rate of glucuronidation of entacapone was also low by this isoform. However, UGT1A1 was the only UGT capable of catalyzing the formation of two glucuronides of the catecholic entacapone. Both COMT inhibitors were glucuronidated at low rates by the representative members of the UGT2B family, UGT2B7 and UGT2B15. Michaelis-Menten parameters were determined for entacapone and tolcapone using recombinant human UGT isoforms and human liver microsomes to compare the kinetic properties of the two COMT inhibitors. The kinetic data illustrates that UGT1A9 exhibited a much greater rate of glucuronidation and a far lower K(m) value for both entacapone and tolcapone than UGT2B15 and UGT2B7 whose contribution is minor by comparison. Entacapone showed a 3 to 4 times higher V(max) value and a 4 to 6 times lower K(m) value compared with those of tolcapone both in UGT1A9 cell lysates and in human liver microsomes.

Percutaneous absorption of sunscreens in vitro: interspecies comparison, skin models and reproducibility aspects

Appropriate evaluation of sunscreens is required to provide better knowledge of their safety and efficacy. One of the most important elements of this evaluation is the assessment of percutaneous absorption. In vitro methods are largely used for such assessments, and the accuracy of the measurements generated with these methods depends on the use of a proper methodology. This study was designed to evaluate an in vitro protocol for investigating the percutaneous absorption of two sunscreens under standardized experimental conditions. Octyl methoxycinnamate and benzophenone 4 were each incorporated in a typical oil-in-water emulsion and tested separately. Salicylic acid was tested as a reference compound. In vitro percutaneous absorption was evaluated using two species, the pig and human, and two models, full-thickness and split-thickness skin. The reproducibility of study results was evaluated by comparing the data generated by two industrial laboratories, L'Oréal and Hoffmann-La Roche. The correlation of quantitative data between pig skin and human skin was very good, and the split-thickness skin model seemed to be more appropriate for measuring the absorption of sunscreens. Results obtained for salicylic acid demonstrated the relevance of the protocol in terms of prediction of in vivo percutaneous absorption. Finally, the comparison of pig skin data between the two laboratories demonstrated a good correlation and underlined the need for a standardized in vitro procedure.

Synthesis and preliminary analysis of a P-glycoprotein-specific [3H]-benzophenone photoaffinity label based on (-)-stipiamide

A benzophenone photoaffinity label 9 based on the polyene natural product (-)-stipiamide has been constructed using a diaminoethane spacer and the radioactive agent [3H]-BZDC (N-succinimidyl p-benzoyl-(2,3-3H)-dehydrocinnamate). Photoaffinity experiments show specific binding to human P-glycoprotein (Pgp) in the presence of cis-flupentixol but not with cyclosporin A.

Tolcapone increases maximum concentration of levodopa

No significant increase of the maximum concentration (Cmax) of levodopa after addition of catechol-O-methyltransferase inhibitor tolcapone occurred in previous pharmacokinetic studies predominantly on healthy volunteers. We compared pharmacokinetics of levodopa in plasma before and after addition of tolcapone in 13 treated parkinsonian subjects under standardized conditions. We found a significant increase of Cmax of levodopa after the addition of tolcapone. This may represent one cause for the occurrence of dyskinesia previously early in the course of treatment with tolcapone.

Population pharmacokinetics of levodopa in patients with Parkinson's disease treated with tolcapone

OBJECTIVE

To use pharmacostatistical models to evaluate the overall exposure of patients with Parkinson's disease to levodopa in the presence and absence of tolcapone.

METHODS

Four hundred twelve patients with Parkinson's disease with fluctuating and nonfluctuating responses to levodopa participated in three multicentered, parallel, double-blind, placebo-controlled dose-finding studies and received either placebo or tolcapone in addition to levodopa-decarboxylase inhibitor therapy. Sparse blood samples were obtained from 393 patients for levodopa and 3-O-methyldopa assay, and the data were analyzed with use of the NONMEM program.

RESULTS

The fraction of levodopa metabolized to 3-O-methyldopa was substantially reduced by the co-administration of tolcapone (by 65%, 74%, and 84% with tolcapone doses of 50, 200, and 400 mg, respectively, in fluctuators, and by 50% and 90% with doses of 200 and 400 mg, respectively, in nonfluctuators). This led to an overall reduction in levodopa clearance (CL) of approximately 15% to 25% in fluctuators and 20% to 30% in nonfluctuators. Because this was partly compensated for by a reduction in levodopa dose in these studies, the total daily exposure of patients to levodopa was only slightly increased (11% to 16%). The peak-trough fluctuations of plasma levodopa (Cmax-Cmin) were reduced in both populations in a dose-dependent fashion.

CONCLUSIONS

Tolcapone effectively inhibited the formation of 3-O-methyldopa and resulted in a decrease in levodopa CL. The consequent increase in levodopa bioavailability was mostly offset by reductions in levodopa dose. It is possible that decreased fluctuations in plasma levodopa concentrations rather than increased levodopa exposure may explain the clinical benefits obtained with tolcapone.

NTP technical report on the toxicity studies of benzophenone (CAS No. 119-61-9). Administered in feed to F344/N rats and B6C3F mice

Benzophenone is used as a photoinitiator, a fragrance enhancer, an ultraviolet curing agent, and, occasionally, as a flavor ingredient; it is also used in the manufacture of insecticides, agricultural chemicals, and pharmaceuticals and is an additive for plastics, coatings, and adhesives. In 14-week studies conducted to determine the toxicity of benzophenone, groups of 10 male and 10 female F344/N rats and B6C3F1 mice were given 0, 1,250, 2,500, 5,000, 10,000, or 20,000 ppm benzophenone in feed. These exposure concentrations resulted in the following average daily doses: 75, 150, 300, 700, or 850 mg benzophenone per kilogram body weight for male rats; 80, 160, 300, 700, or 1,000 mg/kg for female rats; 200, 400, 800, 1,600, or 3,300 mg/kg for male mice; and 270, 540, 1,000, 1,900, or 4,200 mg/kg for female mice. Animals were evaluated for clinical pathology, reproductive system effects, liver cytochrome P450 effects, and histopathology. Genetic toxicity studies were conducted in Salmonella typhimurium and mouse bone marrow polychromatic erythrocytes. Benzophenone was unpalatable at 20,000 ppm. All 20,000 ppm rats had significant body weight loss and were terminated for humane reasons before the end of studies. All male mice and four female mice in the 20,000 ppm group died. There was no exposure-related mortality in the remaining groups. Significantly decreased body weights relative to the controls were observed in all exposed groups of female rats and all exposed groups of male rats except the 1,250 ppm group. Lower body weights were apparent in 10,000 ppm male mice and in 5,000 ppm or greater female mice. In rats, the liver and kidney were identified as target organs of benzophenone toxicity. Treatment-related increases in liver weights were attributed to hypertrophy and/or cytoplasmic vacuolization of hepatocytes. Increased kidney weights were associated with a spectrum of renal changes in exposed males and females. Unique lesions observed in animals that died early as well as in survivors were well demarcated, wedge-shaped areas of prominent tubule dilatation. The lesion occurred in 2,500 ppm or greater males and in 10,000 and 20,000 ppm females. Foci of tubule regeneration were increased relative to the controls in exposed males and females. In exposed mice, significant microscopic findings were limited to centrilobular hypertrophy in the liver that corresponded to increased liver weights. The severity of hepatocyte hypertrophy was exposure-concentration dependent, with marked severity in all 20,000 ppm animals. Clinical chemistry analyses confirmed liver toxicity. In rats, increases in serum bile salt concentrations indicated cholestatic liver disease. On day 22, a 15-fold increase was evident in the 20,000 ppm groups, and at week 14, a twofold increase was seen in the 10,000 ppm groups. Increases in alanine aminotransferase and sorbitol dehydrogenase activities were mild in mice; however, more convincing of liver damage were increased alkaline phosphatase activities and serum bile salt concentrations, especially in 20,000 ppm females. Biochemical data indicated that benzophenone was a relatively potent inducer of the phenobarbital-type (2B) cytochrome P450 enzymes. Overall, induction was greater in rats than in mice. The gross (increased organ weights) and microscopic (hepatocellular hypertrophy) liver changes associated with benzophenone administration in rats and mice accompanied benzophenone-induced increases in pentoxyresorufin dealkylase activity. Benzophenone was not mutagenic in S. typhimurium strain TA98, TA100, TA1535, or TA1537, with or without S9 activation, and it did not induce micronuclei in bone marrow erythrocytes of male mice administered benzophenone by intraperitoneal injection. In conclusion, the liver is the primary target organ of benzophenone toxicity in rats and mice based on increases in liver weights, hepatocellular hypertrophy, clinical chemistry changes, and induction of liver microsomal cytochrome P450 2B isomer. The kidney was also identified as a target organ of benzophenone toxicity in rats only, based on exposure concentration-related increases in kidney weights and microscopic changes. The no-observed-adverse-effect level for benzophenone was not achieved in these studies.

Clinical, pharmacokinetic, and pharmacodynamic effects of tolcapone withdrawal in levodopa-treated patients with parkinsonism

The effect and clinical significance of tolcapone withdrawal on erythrocyte catechol-O-methyltransferase (COMT) activity, levodopa pharmacokinetics, and levodopa requirements were investigated in 59 patients with fluctuating parkinsonism who were randomized to receive placebo or tolcapone 100 or 200 mg three times daily for 6 weeks. Tolcapone withdrawal caused a transient elevation in COMT activity by 64% in patients receiving 100 mg three times daily and by 128% in those receiving 200 mg three times daily at approximately 1-2 weeks after discontinuation of drug. Thereafter, COMT activity was declining but did not reach baseline values by the 12-week study endpoint. However, this had no effect on plasma levodopa and 3-O-methyldopa (3-OMD) concentrations or on levodopa requirements. During treatment, tolcapone increased "on" time and decreased "off" time; after discontinuation of study medication and levodopa dose adjustment, on and off times were similar to baseline. Withdrawal was generally well tolerated; no patients withdrew from the trial during the posttreatment period, and no serious adverse events were observed. In conclusion, the transient increase in erythrocyte COMT activity observed after discontinuation oftolcapone is not associated with changes in peripheral levodopa metabolism and therefore has no significant clinical consequences in terms of levodopa requirements, clinical symptoms, or adverse events.

Population pharmacokinetics of tolcapone in parkinsonian patients in dose finding studies

AIMS

To use pharmacostatistical models to characterize tolcapone's pharmacokinetics in parkinsonian patients, and to identify any demographic subpopulations which may be at risk of either under- or over-exposure to this catechol-O-methyltransferase (COMT) inhibitor.

METHODS

Four hundred and twelve patients participated in three multicentre, parallel, double-blind, placebo-controlled, dose-finding studies and received either placebo or tolcapone (50, 200 or 400 mg three times daily) in addition to levodopa/decarboxylase inhibitor therapy. Sparse blood samples were obtained from 275 patients for tolcapone assay and the concentrations (1414 in total) were analysed using the NONMEM program.

RESULTS

The pharmacokinetic model which best described the data was a two-compartment open model with first-order absorption and possibly a lag-time. Tolcapone pharmacokinetics were shown to be stable, with no systematic trend between 2 and 6 weeks of treatment. The absorption of the drug was shown to be rapid and concomitant food intake had only a minor effect on the relative bioavailability (10-20% reduction compared with fasting). The overall clearance of tolcapone could be estimated with good precision (approximately 4. 5-5 l h-1 ), and none of the investigated covariates (e.g. sex, age, body weight) had any clinically significant influence on this parameter. The volume of distribution showed relatively high variability and was calculated to be approximately 30 l, leading to an estimated half-life in patients of approximately 5-8 h.

CONCLUSIONS

Using sparse concentrations and mixed effect-effects modelling analysis it is possible to describe the pharmacokinetics of tolcapone in parkinsonian populations. The parameter estimates obtained agreed with those obtained from conventional pharmacokinetic studies and no subpopulation was shown to be at risk of either under- or over-exposure to tolcapone.

Tolcapone: a novel approach to Parkinson's disease

The pharmacology, pharmacokinetics, clinical efficacy, adverse effects, and dosage and administration of tolcapone are reviewed. Tolcapone is the first drug brought to market from the new class of selective and reversible inhibitors of catechol-O-methyltransferase. Tolcapone is indicated for use in the treatment of Parkinson's disease as an adjunct to levodopa-carbidopa therapy in patients who are experiencing fluctuations in symptoms and who are not responding to or are not appropriate candidates for other adjunctive therapies. The absolute bioavailability of tolcapone after an oral dose is about 65%. Clinical trials have demonstrated that tolcapone 50-200 mg three times daily reduces "off" time in patients refractory to levodopa-carbidopa, Unified Parkinson's Disease Rating Scale scores, and the dosage of levodopa-carbidopa required for symptom suppression. The most frequent adverse effects of tolcapone are dyskinesia, nausea, sleep disorders, dystonia, orthostatic hypotension, diarrhea, dizziness, and hallucinations; also, there is a potential for elevation of liver transaminase concentrations in the blood. To date, three deaths from fulminant hepatic failure in association with tolcapone have been reported. Extensive liver function testing is required of all patients before and during therapy. The recommended starting dosage is 100 mg orally three times daily as an adjunct to levodopacarbidopa therapy; a concurrent reduction in the levodopa dosage of about 30% is suggested. Patient response should be monitored carefully during the first three weeks of therapy; treatment should be discontinued in patients failing to respond during this initial use. Tolcapone is of benefit in fluctuating Parkinson's disease, but benefits must be carefully weighed against risks in individual patients.

Percutaneous absorption of sunscreens through micro-yucatan pig skin in vitro

PURPOSE

The objectives of this study were to develop an in vitro model for studying sunscreen permeation in skin, and evaluate the influence of formulation differences.

METHODS

The sunscreens studied were two of the most widely used agents, octyl methoxycinnamate (OMC) and benzophenone-3. Preparations containing radiolabeled actives were applied to micro-Yucatan pig skin dermatomed to a thickness of 250-300 microm as a finite dose in a flow-through diffusion system. At the end of each experiment the amounts removed by washing, retained inside stratum corneum (SC) and penetrated into receptor and viable skin were determined.

RESULTS

The two sunscreens reached a peak level in SC within an hour. Benzophenone-3 penetrated skin to a greater extent than OMC. The opposite was true when comparisons of SC retention were made. The ratio of retained to penetrated amount of sunscreens from a hydroalcoholic formulation at the end of 10 hours was higher when the sunscreens were present together than alone.

CONCLUSIONS

Despite the highly lipophilic nature of sunscreens, particularly OMC, SC is the rate limiting skin layer for penetration. Penetration and SC retention were formulation dependent. The ratio of SC content to the amount penetrated is a useful tool for evaluating sunscreen permeation.

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.

Metabolism and excretion of tolcapone, a novel inhibitor of catechol-O-methyltransferase

AIMS

To investigate the rate of excretion and routes of metabolism of tolcapone, a novel inhibitor of catechol-O-methyltransferase (COMT).

METHODS

Six healthy male volunteers were given 200 mg [14C]-tolcapone (approximately 50 muCi) orally. To assess excretion balance and to identify metabolites, urine and faeces were collected before administration and until radioactivity fell below 75 d min-1 ml-1 (urine) and 100 d min-1 mg-1 (faeces). Blood samples were collected frequently before and after administration to determine plasma radioactivity, to identify tolcapone metabolites and to measure plasma tolcapone and its methylated derivative 3-O-methyltolcapone (3-OMT).

RESULTS

The mean proportion of the dose excreted in urine was 57.3% and in faeces 40.5%. Excretion was almost complete (more than 95%) in all participants after 9 days. The major early metabolite present in plasma was the 3-O-beta, d-glucuronide conjugate, which was detectable within 2 h after dosing. The major late metabolite in plasma was 3-OMT. The 3-O-beta, d-glucuronide was also the most abundant metabolite in urine and faeces, accounting for 27% and 33%, respectively, of the total radioactivity excreted by these routes and for 26% of the original dose. Reduction of the nitro moiety yields an amine derivative, detected in both urine and faeces, with subsequent modifications, such as acetylation of the amine group and conjugation with glucuronic acid or sulphate, or both. Oxidative reactions due to cytochrome P450 enzymes are of small significance, as is 3-O-methylation by COMT.

CONCLUSIONS

Tolcapone is almost completely metabolized and excreted in urine and faeces (only 0.5% of tolcapone was excreted unchanged); glucuronidation is the most important route of metabolism. The relatively long duration of excretion is caused by the long half-life of 3-OMT.

Comparison of tilidine/naloxone, tramadol and bromfenac in experimental pain: a double-blind randomized crossover study in healthy human volunteers

AIM

The analgesic efficacy and safety of single oral doses of two centrally acting compounds, the combination of 50 mg tilidine and 4 mg naloxone (Valoron N) and 50 mg tramadol (Tramal), were compared to 25, 50 and 75 mg of the non-steroidal antiinflammatory bromfenac in experimental pain.

SUBJECTS AND METHODS

It was a placebo-controlled double-blind 6-way crossover study design with 12 human volunteers. Acute pain was generated by electrical tooth pulp stimulation. Treatment effects were determined by recording somatosensory-evoked potentials and by subjective pain rating.

RESULTS

The tilidine/naloxone combination clearly was the most potent medication in this study, followed by bromfenac 75 mg, which produced an early pain relief. Tramadol produced poor analgesia, as did bromfenac 25 and 50 mg. There was no dose-response relationship for bromfenac. Control of plasma levels revealed pronounced interindividual differences in peak plasma concentrations for bromfenac, but not for tramadol. Tilidine/naloxone exerted adverse effects in 9, tramadol in 3 volunteers. Under medication with 25 and 50 mg bromfenac, respectively, only one subject reported adverse effects. No adverse effects were experienced with 75 mg bromfenac or placebo.

CONCLUSION

The results support previous conclusions about the analgesic efficacy of tilidine/naloxone and tramadol in experimental pain. Moreover, the findings suggest that 75 mg bromfenac might be suitable for fast but short relief of pain of non-inflammatory genesis.

Determination of the catechol-O-methyltransferase inhibitor tolcapone and three of its metabolites in animal and human plasma and urine by reversed-phase high-performance liquid chromatography with ultraviolet detection

Reversed-phase HPLC procedures were developed for the determination of tolcapone (Ro 40-7592) and its metabolites Ro 40-7591, Ro 61-1448, and Ro 47-1669 in plasma and in urine samples. One of the procedures for plasma involved the determination of tolcapone and its metabolite Ro 40-7591 and the other, the determination of the two other metabolites. The urine assay enabled the simultaneous determination of tolcapone and all metabolites in one run. Sample preparation in plasma involved protein precipitation with acetonitrile. Urine was simply diluted. The compounds of interest were monitored in the UV at 270 nm. The limits of quantification were 0.05 microg/ml for each compound (plasma assay) and 0.2 microg/ml for the urine assay. The mean inter-assay precisions (C.V.) were < or = 6% (plasma assay) and < or = 8% (urine assay). The procedures were successfully applied to the sample analysis of animal pharmacokinetic (rat, dog, mouse, rabbit and cynomolgus monkey) and clinical pharmacology studies.

Biokinetics of gidazepam, derivatives of peptideaminobenzophenones and their metabolites

Results of a comparative study of biokinetics of two prodrugs gidazepam (I) and the derivative of peptideaminobenzophenone, 2-N-carbobenzylglycyl-glycylamido-5-bromobenzophenone (II) and their main physiologically active metabolite-7-brom-5-phenyl-dihydro-3H-1,4-benzodiazepine (III) were investigated in mice. It was shown earlier that I undergoes intensive N1-desalkylation with the formation of a metabolite: (III) and products of its further oxidation. Metabolism of II is characterized by hydrolysis of the peptide fragment and subsequent intramolecular condensation resulting in the formation of III, its oxi- and metoxylated derivatives and other minor metabolites. The difference between kinetics of 14C-contents in organs and tissues of mice following administration of prodrugs I, II and their metabolite III are demonstrated: In the first two cases no rapid distribution phase of I and II was detected; maximal levels of III were achieved faster (0.25-0.35 min) and its elimination proceeded with higher rates. For all substances the organs and tissues studied are not "stores" of slow exchange of 14C-material between serum and brain and are essentially different. After administration of I and II, the relationship between 14C-contents in brain and serum change demonstrating a loop over the whole period of the experiment which allows to suggest that serum acts as the central compartment, whereas brain is a peripheral compartment of a kinetic scheme of distribution of prodrugs in mice. Following administration of III, we observed a linear relationship between serum and brain 14C-contents which did not depend on the experimental time. This finding suggests that the studied biosubstrates act as one (central) compartment of a kinetic scheme of distribution of III. It is demonstrated that the peculiarities of their pharmacologic action of prodrugs are explained by the nonlinearity of the processes of their biotransformation and specific of biokinetics.

Clinical pharmacokinetics and pharmacodynamics of bromfenac

Bromfenac is a nonsteroidal anti-inflammatory drug whose peak plasma concentration is reached 0.5 hours after oral administration. Bromfenac binds extensively to plasma albumin. The area under the plasma concentration-time curve is linearly proportional to the dose for oral doses up to 150 mg. The relationship between the total plasma and analgesic effect has been established. Only small amounts of bromfenac are eliminated unchanged, with the remaining drug being biotransformed into glucuronide metabolites which are excreted in urine and bile. Rapid elimination occurs in healthy individuals (half-life 0.5 to 4.0 h). Renal disease, hepatic disease and aging alter the disposition kinetics of bromfenac, and dosage adjustment may be advisable. Bromfenac modestly decreases free phenytoin concentrations. Bromfenac can cause idiosyncratic hepatic toxicity and has been withdrawn by its manufacturer pending further investigation of these case reports.

Prevention of DNA photodamage by vitamin E compounds and sunscreens: roles of ultraviolet absorbance and cellular uptake

Topical application of alpha-tocopherol (alphaTH), the most prominent naturally occurring form of vitamin E, inhibits ultraviolet (UV) B-induced photocarcinogenesis and DNA photodamage in C3H mice in vivo. In this study, we compared alphaTH with other vitamin E compounds and with three commercial sunscreen compounds for their ability to inhibit DNA photodamage in C3H mouse skin in vivo. When applied in a 5% dispersion in a neutral cream vehicle, alpha-tocopherol (alphaTH), gamma-tocopherol (gammaTH), and delta-tocopherol (deltaTH) each produced a statistically significant inhibition of thymine dimer formation, whereas alpha-tocopherol acetate (alphaTAc) and alpha-tocopherol methyl ether (alphaTOMe) did not. Application of 5% dispersions of the commercial sunscreen agent octylmethoxycinnamate also inhibited dimer formation, whereas ethylhexyl salicylate and oxybenzone did not, despite their considerably greater UVB absorbances than alphaTH. To test the hypothesis that cellular uptake and distribution are necessary for optimal photoprotection by tocopherols, photoprotection was studied in mouse 308 keratinocyte cells in vitro. Preincubation of 308 cells with 1 microM alphaTH for at least 2 h before exposure to 2.5 J/m2/s UVB for 10 min significantly (P < 0.05) attenuated thymine dimer formation. Pre-incubation with 1 microM gammaTH, deltaTH, alphaTAc, or alphaTOMe for 2 h did not inhibit thymine dimer formation significantly. Uptake of alphaTH was measured after incubation with 1 microM [2H3]alphaTH (d3-alphaTH) and resulted in a time-dependent increase in alphaTH levels. Use of d3-alphaTH allowed separate, simultaneous measurement of added d3-alphaTH and unlabeled endogenous alphaTH by gas chromatography-mass spectrometry. Accumulation of 167 +/- 62 pmol d3-alphaTH/mg protein was measured within 1 h in whole-cell fractions. d3-AlphaTH in the nuclear fraction reached levels of 15 +/- 4 pmol d3-alphaTH/mg protein at 2 h. Accumulation of alphaTH in the whole cell and nuclei corresponded temporally with significant protection against DNA photodamage. The kinetics of accumulation of the three tocopherols in whole cells and in nuclei were similar. Although only alphaTH conferred significant protection compared with irradiated controls at 2 h, the differences between individual tocopherols were not statistically significant. This work suggests that incorporation of tocopherol compounds into sunscreen products confers protection against procarcinogenic DNA photodamage and that cellular uptake and distribution of tocopherol compounds is necessary for their optimal photoprotection.