Development and validation of a sensitive LC-MS/MS assay of GT-14, a novel Gαi2 inhibitor, in rat plasma, and its application in pharmacokinetic study

A sensitive and selective LC-MS/MS method was developed and validated for the quantitation of a novel Gαi2 inhibitor, GT-14, in rat plasma using a SCIEX 6500+ triple QUAD LC-MS system equipped with an ExionLC UHPLC unit. GT-14 (m/z 265.2 → 134.1) and griseofulvin (Internal Standard, IS) (m/z 353.1 → 285.1) were detected in a positive mode by electrospray ionization (ESI) using multiple reaction monitoring (MRM). The assay was linear in the concentration range of 0.78-1000 ng/mL in rat plasma. Both accuracy and precision values were within the acceptance criteria of ±15 %, as established by FDA guidance. The matrix effect was negligible from plasma, with signal percentages of 98.5-106.9 %. The mean recovery was 104.5 %, indicating complete extraction of GT-14 from plasma. GT-14 was found to be stable under different experimental conditions. The validated method was successfully applied to evaluate plasma protein binding and in vivo pharmacokinetics of GT-14 in rats.

Fast-dissolving microparticles fail to show improved oral bioavailability

Oral dosage forms are the preferred means of delivering drugs for systemic absorption. However, development problems occur for drugs with poor water solubility and/or gastrointestinal permeability. It is generally believed that the in-vivo bioavailability of poorly water-soluble drugs from Class II of the Biopharmaceutics Classification System can be improved by increasing the dissolution rate. We have attempted to increase the in-vivo oral bioavailability of a model Class II drug (griseofulvin) by preparing rapidly-dissolving particles. The solvent-diffusion method was used to prepare particles with hydrophilic surfactants (Brij 76/Tween 80 surfactant blend) and in-vivo studies were conducted in rats. The griseofulvin particles produced were bipyramidal in habit with a particle size of 2.18 ± 0.12 mm; they contained crystalline drug and a relatively large proportion (12% w/w) of hydrophilic surfactant. The latter and the small particle size ensured rapid particle dispersion and dissolution in-vitro. Thus, within 30 min of the in-vitro dissolution test, the bipyramidal particles had released ∼70% of drug compared with ∼10% from the starting material (particle size 12.61 ± 1.11 μm). However, the rapid and increased drug dissolution in-vitro was not translated to rapid and enhanced absorption in-vivo, and the oral bioavailability of the model drug was found to be the same from the control and from the bipyramidal particles. The poor in-vivo performance of the bipyramidal particles showed that although the dissolution rate of a Class II drug is thought to be a good indicator of its in-vivo bioavailability, this is not always the case.

Evaluation of in vivo dissolution behavior and GI transit of griseofulvin, a BCS class II drug

Mean plasma concentration-time profile of griseofulvin, a BCS class II drug, orally administered as powders into rats, was predicted based on GITA model. However, it was very difficult to predict the individual plasma profile because of large inter-individual difference. As the absorption of griseofulvin would be rate-limited by the dissolution process, we tried to analyze the in vivo dissolution kinetics of griseofulvin by focusing on gastric emptying and intestinal transit as physiological factors influencing the in vivo dissolution kinetics. After oral administration of griseofulvin, theophylline and sulfasalazine into rats, gastric emptying and intestinal transit were simultaneously estimated by analyzing the absorption kinetics of theophylline and observing the appearance of sulfapyridine in plasma, respectively. Gastric emptying kinetics was not significantly correlated with absorption or dissolution behavior of griseofulvin. On the other hand, the cecum-arriving time reflecting the intestinal transit was significantly correlated with both AUC and total dissolved amount of griseofulvin. T(max) of griseofulvin also increased with the increase of cecum-arriving time. These results clearly indicate that the longer residence time could lead to the higher dissolution and absorption of griseofulvin and that the variance of intestinal transit could be responsible for the inter-individual difference of the in vivo absorption behavior.

In vitro and in vivo evaluation of a fast-disintegrating lyophilized dry emulsion tablet containing griseofulvin

Development of a fast-disintegrating lyophilized dry emulsion (LDE) tablet that enhanced the in vitro dissolution and in vivo absorption of griseofulvin (GF) is presented. The LDE tablets were prepared by freeze-drying o/w emulsions of GF, a drug for which bioavailability is known to be enhanced by fat co-administration. Oil-in-water emulsions were prepared using a gelatin solution (2%, w/v) as the water phase and medium chain triglycerides (Miglyol) or sesame oil as the oil phase. In addition, different emulsifiers were evaluated. The influence of formulation parameters on the disintegration and in vitro dissolution of GF from LDE tablets along with other tablet characteristics were investigated. A significant influence of the emulsifier type on the tablet disintegration time was seen (p<0.01). Results obtained from dissolution studies showed that LDE tablets of GF improved the dissolution rate of the drug compared to the plain drug. The extent of absorption of GF from a selected LDE tablet formulation as compared to an immediate release conventional tablet as reference after single oral dose (125mg) administration was determined in four healthy subjects using a randomized crossover design. In this study, the rate of absorption of GF from LDE tablet was faster than that from the reference tablet and had significantly higher (p=0.02) peak plasma concentration (more than three times higher) and shortened time to C(max) by 4h (p=0.014). The extent of absorption expressed by AUC was 85% larger as compared to the commercial tablet. Stability results, after 6 months storage of LDE tablets at 25 degrees C and 60% relative humidity, showed a slight increase in disintegration time and residual moisture content, while results from dissolution studies showed slightly slower initial drug release.

Metabolization of Porphyrinogenic Agents in Brain: Involvement of the Phase I Drug Metabolizing System. A Comparative Study in Liver and Kidney

(1) We evaluated the involvement of brain mitochondrial and microsomal cytochrome P-450 in the metabolization of known porphyrinogenic agents, with the aim of improving the knowledge on the mechanism leading to porphyric neuropathy. We also compared the response in brain, liver and kidney. To this end, we determined mitochondrial and microsomal cytochrome P-450 levels and the activity of NADPH cytochrome P-450 reductase. (2) Animals were treated with known porphyrinogenic drugs such as volatile anaesthetics, allylisopropylacetamide, veronal, griseofulvin and ethanol or were starved during 24 h. Cytochrome P-450 levels and NADPH cytochrome P-450 reductase activity were measured in mitochondrial and microsomal fractions from the different tissues. (3) Some of the porphyrinogenic agents studied altered mitochondrial cytochrome P-450 brain but not microsomal cytochrome P-450. Oral griseofulvin induced an increase in mitochondrial cytochrome P-450 levels, while chronic Isoflurane produced a reduction on its levels, without alterations on microsomal cytochrome P-450. Allylisopropylacetamide diminished both mitochondrial and microsomal cytochrome P-450 brain levels; a similar pattern was detected in liver. Mitochondria cytochrome P-450 liver levels were only diminished after chronic Isoflurane administration. In kidney only mitochondrial cytochrome P-450 levels were modified by veronal; while in microsomes, only acute anaesthesia with Enflurane diminished cytochrome P-450 content. (4) Taking into account that delta-aminolevulinic acid would be responsible for porphyric neuropathy, we investigated the effect of acute and chronic delta-aminolevulinic acid administration. Acute delta-aminolevulinic acid administration reduced brain and liver cytochrome P-450 levels in both fractions; chronic delta-aminolevulinic acid administration diminished only liver mitochondrial cytochrome P-450. (5) Brain NADPH cytochrome P-450 reductase activity in animals receiving allylisopropylacetamide, dietary griseofulvin and delta-aminolevulinic acid showed a similar profile as that for total cytochrome P-450 levels. The same response was observed for the hepatic enzyme. (6) Results here reported revealed differential tissue responses against the xenobiotics assayed and give evidence on the participation of extrahepatic tissues in porphyrinogenic drug metabolization. These studies have demonstrated the presence of the integral Phase I drug metabolizing system in the brain, thus, total cytochrome P-450 and associated monooxygenases in brain microsomes and mitochondria would be taken into account when considering the xenobiotic metabolizing capability of this organ.

The effect of different lipid based formulations on the oral absorption of lipophilic drugs: The ability of in vitro lipolysis and consecutive ex vivo intestinal permeability data to predict in vivo bioavailability in rats

The purpose of this study was to investigate the impact of different lipid based formulations of lipophilic drugs on in vitro solubilization and intestinal ex vivo permeability processes. Thereafter, to evaluate the ability of these in vitro and ex vivo results to predict the corresponding in vivo oral bioavailability data. The dissolution of dexamethasone and griseofulvin in long (LCT), medium (MCT) and short (SCT) chain triglyceride formulations was tested in a dynamic in vitro lipolysis model. Following the completion of the lipolysis, the permeability through the gut wall was tested in an ex vivo side-by-side diffusion chamber model. The absolute oral bioavailability of the drugs from the tested formulations was investigated in rats. The dynamic in vitro lipolysis experiments indicated an equivalent performance of the different formulations for dexamethasone, and a performance rank order of MCT>LCT>SCT>H(2)O for griseofulvin. In the subsequent ex vivo permeability studies, the SCT formulation caused enhanced permeation with doubled permeability coefficient for both drugs. The in vivo bioavailability of both drugs correlated well with the in vitro data, i.e., LCT=MCT=SCT for dexamethasone and MCT>LCT>SCT>H(2)O for griseofulvin, despite the significant augmented intestinal permeability produced by the SCT formulation. In conclusion, the in vitro lipolysis model was found to be useful in the intelligent optimization of oral lipid formulations for lipophilic drugs, even in the case where the intestinal permeability is enhanced by the formulation. The SCT vehicle showed to be a potential permeability enhancer; however, for class 2 compounds, the permeability does not correlate with in vivo bioavailability.

Novel generic UPLC/MS/MS method for high throughput analysis applied to permeability assessment in early Drug Discovery

A novel generic ultra performance liquid chromatography-tandem mass spectrometric (UPLC/MS/MS) method for the high throughput quantification of samples generated during permeability assessment (PAMPA) has been developed and validated. The novel UPLC/MS/MS methodology consists of two stages. Firstly, running a 1.5min isocratic method, compound-specific multiple reaction monitoring (MRM) methods were automatically prepared. In a second stage, samples were analyzed by a 1.5min generic gradient UPLC method on a BEH C18 column (50mmx2.1mm). Compounds were detected with a Waters Micromass Quattro Premier mass spectrometer operating in positive electrospray ionization using the compound-specific MRM methods. The linearity for the validation compounds (caffeine, propranolol, ampicillin, atenolol, griseofulvin and carbamazepine) typically ranges from 3.05nM to 12,500nM and the limits of detection for all generically developed methods are in the range between 0.61nM and 12nM in an aqueous buffer. The novel generic methodology was successfully introduced within early Drug Discovery and resulted in a four-fold increase of throughput as well as a significant increase in sensitivity compared to other in-house generic LC/MS methods.

Electrospray ionization LC-MS/MS validated method to quantify griseofulvin in human plasma and its application to bioequivalence study

A simple, sensitive and rapid liquid chromatography/tandem mass spectrometry (LC-MS/MS) method has been developed and validated to quantify griseofulvin in human plasma using propranolol hydrochloride as internal standard (IS). Samples were prepared using solid phase extraction and analysed without drying and reconstitution. The analytes were chromatographed on Hypersil, hypurity C18 reverse phase column under isocratic conditions using 0.05% formic acid in water:acetonitrile (30:70, v/v) as the mobile phase. Total chromatographic run time was 3.0 min. Quantitation was done on a triple quadrupole mass analyzer API-3000, equipped with turbo ion spray interface and operating in multiple reaction monitoring (MRM) mode to detect parent-->product ion transition for analyte and IS. The method was validated for sensitivity, matrix effect, accuracy and precision, linearity, recovery and stability studies. Linearity in plasma was observed over the concentration range 20-3000 ng/mL for griseofulvin. Lower limit of quantification (LLOQ) achieved was 20 ng/mL with precision (CV) less than 10% using 5 microL injection volume. The absolute recovery of analyte (87.36%) and IS (98.91%) from spiked plasma samples was consistent and reproducible. Inter-batch and intra-batch coefficients of variation across four validation runs (LLOQ, LQC, MQC and HQC) was less than 7.5%. The accuracy determined at these levels was within +/-4.2% in terms of relative error. The method was applied to a pilot bioequivalence study of 500 mg griseofulvin tablet in six healthy human subjects under fed condition.

Enhancement of the dissolution rate and oral absorption of a poorly water soluble drug by formation of surfactant-containing microparticles

The slow dissolution rate exhibited by poorly water-soluble drugs is a major challenge in the drug development process. Following oral administration, drugs with slow dissolution rates generally show erratic and incomplete absorption which may lead to therapeutic failure. The aim of this study was to improve the dissolution rate and subsequently the oral absorption and bioavailability of a model poorly water-soluble drug. Microparticles containing the model drug (griseofulvin) were produced by spray drying the drug in the absence/presence of a hydrophilic surfactant. Poloxamer 407 was chosen as the hydrophilic surfactant to improve the particle wetting and hence the dissolution rate. The spray dried particles were characterized and in vitro dissolution studies and in vivo absorption studies were carried out. The results obtained showed that the dissolution rate and absolute oral bioavailability of the spray dried griseofulvin/Poloxamer 407 particles were significantly increased compared to the control. Although spray drying griseofulvin alone increased the drug's in vitro dissolution rate, no significant improvement was seen in the absolute oral bioavailability when compared to the control. Therefore, it is believed that the better wetting characteristics conferred by the hydrophilic surfactant was responsible for the enhanced dissolution rate and absolute oral bioavailability of the model drug.

Effect of Chitosan on Gastrointestinal Absorption of Water-Insoluble Drugs Following Oral Administration in Rats

Chitosan is widely used as a dietary weight-loss supplement in Japan. In the present study, we examined the effect of chitosan on the gastrointestinal absorption profiles of the water-insoluble drugs, indomethacin and griseofulvin, and the water-soluble drugs, acetaminophen and cephalexin, after oral administration in rats. Rats received oral administration of chitosan (5 mg/kg or 25 mg/kg) dissolved in 5% acetic acid or vehicle 15 min before oral administration of each drug. Chitosan at a dose of 25 mg/kg, but not 5 mg/kg, significantly decreased the plasma concentrations of indomethacin and griseofulvin after administration as a suspension with a significant delay of the time to reach maximum concentration compared to the corresponding control values (vehicle-pretreated rats). However, pretreatment of chitosan (25 mg/kg) did not change the pharmacokinetics of indomethacin administered as a solution. Further, the same dose of chitosan had no effect on the pharmacokinetics of acetaminophen. The gastrointestinal absorption profile of an amino-beta-lactam antibiotic, cephalexin, which is actively absorbed via carrier-mediated transport system, was also unchanged. The present findings at least suggest the possibility that chitosan at high dose reduces the gastrointestinal absorption of water-insoluble drugs such as indomethacin and griseofulvin, but not water-soluble drugs, by diminishing the surfactant-like effect of bile acids.

Dissolution rate enhancement by adsorption of poorly soluble drugs on hydrophilic silica aerogels

The aim of this work is to evaluate the feasibility of hydrophilic silica aerogels as drug carriers and to investigate the influence of the aerogels properties on the release rate of poorly water-soluble drugs. Hydrophilic silica aerogels of different densities were loaded with two model drugs, ketoprofen and griseofulvin, by adsorption from their solution in supercritical CO2. It is demonstrated that up to 30 wt% of ketoprofen and 5.4 wt% of griseofulvin can be deposited on hydrophilic aerogels through physical adsorption. The obtained drug-aerogel formulations were characterized by IR- and UV-spectroscopy, X-ray diffraction and scanning electron microscopy. Release kinetics of both drugs were studied in vitro. The release rate of ketoprofen from the drug-aerogel formulation is much faster than that of the corresponding crystalline drugs. The release rate of ketoprofen increases in 500% and that of griseofulvin in 450%, respectively. The reasons for the release enhancement are the enlarged specific surface area of drugs by adsorption on aerogels compared to their crystalline form and the immediate collapse of aerogel network in aqueous media. The dissolution rate of poorly water soluble drugs can be significantly enhanced by adsorption on highly porous hydrophilic silica aerogels.

Intracutaneous distributions of fluconazole, itraconazole, and griseofulvin in Guinea pigs and binding to human stratum corneum

We have compared the distribution of fluconazole (FLC) with that of itraconazole (ITC) and griseofulvin (GRF) in the abdominal skin tissues after a single oral dose was administered to guinea pigs. The FLC concentrations in the stratum corneum reached a peak at 2 h after administration and were similar to those of ITC and higher than those of GRF in spite of the administration of a lower dose. GRF was eliminated from the stratum corneum faster than FLC and ITC. The FLC concentrations were also remarkably higher than those of ITC and GRF in the epidermis-cutis but lower in the subcutaneous fatty tissue. The distribution characteristics of each drug result from differences in their physicochemical properties. Following the administration of multiple doses, the FLC concentrations in the stratum corneum were highest in the abdominal skin tissues; those at 24 h after each administration increased gradually and were maintained at a level more than 10 times higher than that of the plasma concentrations. The FLC concentrations in the planta pedis stratum corneum and in the nail showed good dose proportionality and obvious accumulation and were 60 and 40 times as high as that in plasma on day 14. The extent of binding of FLC to human corneous keratin in vitro was about 10%, which is lower than those of ITC (94 to 97%) and GRF (36 to 38%). FLC, unlike ITC, therefore, is presumed to exist in the stratum corneum at high concentrations in an active nonbinding form. These excellent intracutaneous pharmacokinetic properties of FLC probably account in large part for the in vivo efficacy of FLC.

[Griseofulvin]

Griseofulvin is a metabolic product of Penicillium spp. It was the first available oral agent for the treatment of dermatophytoses and has now been used for more than forty years. Griseofulvin is fongistatic, the exact mechanism in witch it inhibits the growth of dermatophytes is doubtful. Several ways are invoked: inhibition of fungal cell mitosis and nuclear acid synthesis, probable interference with the function of microtubules. Griseofulvin is poorly absorbed from the gastrointestinal tract. Absorption is enhanced by administration with fatty meal. Peak plasma occurs four hours after oral administration. Griseofulvin is detected in the outer layer of the stratum corneum soon after it is ingested, it is diffused from the extracellular fluid and sweat. There is no information regarding the mechanism by witch the drug is delivered to nails and hair. Deposition in the newly formed cells could be the major factor. Griseofulvin has also anti-inflammatory properties and some direct vasodilatory effects when it is used in high doses. It is metabolised by the liver microsomial enzyme system and excreted in the urine. The half-life is 9 to 21 hours. Griseofulvine has been used in the therapy of dermatophyte onychomycosis, treatment periods from 6 to 18 months were necessary with disappointing results and numerous relapses. Newer oral antifungal agents are now preferred especially in toenail infections. For many authors griseofulvin is still the treatment of choice of tinea capitis. Doses are 15-20 mg/kg/d for 6 to 8 weeks in children with the microsized form. Clinical response rates have been reported between 80 and 90 p. 100 in controlled studies. Griseofulvin is well-tolerated particulary in children. More frequent side effects are minor: headaches, gastrointestinal reactions and cutaneous eruptions. The major drug interactions has been noted with phenobarbital, anticoagulants and oral contraceptives.

Preparation of griseofulvin for topical application using N-methyl-2-pyrrolidone

We attempted to prepare a new griseofulvin formulation for topical application using N-methyl-2-pyrrolidone (NMP). Griseofulvin dissolves poorly in both water and oil, but dissolves in NMP to a concentration of about 100 mg/ml. A soybean oil-water emulsion with soybean lecithin and NMP as emulsifier and co-solvent, respectively, was prepared using a Microfluidizer, a high-pressure homogenizer. The size of the droplets in emulsion was about 200 nm, and the emulsion was stable for over 3 months. The skin permeation of griseofulvin through Yucatan micropig skin was studied in vitro using vertical type cells under donor phase open conditions. The permeation of griseofulvin from the NMP-water mixture (0-40%) into the skin tended to increase with increasing NMP concentration, although this finding was not statistically significant. Permeation from emulsion (oil phase, 20%; NMP 10-40%) was significantly higher than that from the water-NMP mixture. Permeation from the oil-NMP mixture was highest among the formulations investigated, and permeation from emulsion under donor phase closed conditions was significantly lower than that under open conditions. We believe that the evaporation of water from the emulsion after application to the skin was an important factor in skin permeation enhancement. When the emulsion containing 3% l-menthol was applied, a sufficient skin concentration (47 microg/cm3 in dermis) was obtained.

An integrated model for determining causes of poor oral drug absorption

PURPOSE

To develop an integrated absorption model for estimating the fraction of dose absorbed and determining the causes of poor oral drug absorption.

METHODS

Both analytical and numerical methods were used to estimate the fraction of dose absorbed.

RESULTS

An integrated absorption model was developed by considering transit flow, dissolution, and permeation processes, simultaneously. A framework was proposed to determine permeability-, dissolution-, and solubility-limited absorption. Digoxin, griseofulvin, and panadiplon were employed to illustrate the applications of the integrated model in identifying the causes of poor absorption and guiding formulation development.

CONCLUSIONS

The integrated absorption model was successfully applied to digoxin, griseofulvin, and panadiplon to estimate the fraction dose absorbed and to roughly determine the causes of poor oral drug absorption.

Mechanism of drug release from poly(L-lactic acid) matrix containing acidic or neutral drugs

The release profiles of acidic and neutral drugs from poly(L-lactic acid) [P(L)LA] matrices were investigated to reveal their release mechanism. Cylindrical matrices (rods; 10 mmx1 mm diameter) were prepared by the heat compression method. The acidic and neutral drugs investigated were dissolved in the P(L)LA rods. It was found that the release profiles consisted of two sequential stages. At the first release stage, P(L)LA remained in an amorphous state and the drugs diffused through the hydrated matrices. At the second release stage, P(L)LA transformed to a semicrystalline state and the drugs diffused through water-filled micropores developed by polymer crystallization. In addition, the drugs were also found to precipitate out as crystals in the rods, resulting in a transformation of the rods into drug-dispersed matrices. On the basis of these findings, we derived a modified diffusion equation for the drug release at the second stage. This equation showed good fits to the release profiles of these drugs. Furthermore, the availability of the derived equation was supported by the acceleration in the fractional drug release rate noted both with decreases in the drug content in the rod and increases in the pH of the medium.

Pharmacokinetics of fluconazole in skin and nails

Two studies on the pharmacokinetics of fluconazole in skin and nails are reported here. In 1 study, 12 healthy volunteers received fluconazole 50 mg once daily for 12 days and 11 healthy volunteers received fluconazole 150 mg once weekly for 2 weeks. Fluconazole assays were performed on samples of serum, stratum corneum, dermis-epidermis, and eccrine sweat. In a second study, 36 patients with toenail onychomycosis received either fluconazole 150 mg once weekly or griseofulvin 1000 mg once daily for 12 months. Fluconazole assays were performed on nail clippings and serum samples from the patients receiving fluconazole. Tissue concentrations of fluconazole regularly exceeded plasma concentrations in these studies. In the skin study, the highest concentrations were achieved in stratum corneum, with accumulation occurring up to the end of dosing. Subjects who received 50 mg once daily had higher levels of fluconazole in stratum corneum, sweat, and epidermis-dermis than those subjects who received 150 mg once weekly. In the toenail study, fluconazole concentrations increased for the first 6 months, reaching levels much higher than serum concentrations (P < .001), with no significant difference between healthy and diseased nails.

Enhancement of bioavailability of griseofulvin by its complexation with beta-cyclodextrin

Griseofulvin is a poorly soluble antifungal antibiotic drug, the solubility of which can be enhanced by complexation with beta-cyclodextrin. The inclusion complex was prepared by coprecipitation method in various molar ratios of 1:1, 2:1, 3:1, and 1:2 of the drug and beta-cyclodextrin, respectively. The inclusion complex was characterized and evaluated by UV-VIS spectral studies and FTIR. The in vitro drug release studies indicated that the 1:2 molar ratio complex form of the drug significantly increased the dissolution rate when compared to the free form. The acute toxicity studies clearly indicated that the beta-cyclodextrin complex was nontoxic and the safety range was close to other Griseofulvin formulations. The in vivo study of the beta-cyclodextrin was carried out in both animals and human beings by administering in four different rabbits and volunteers, respectively. Pellets made with Griseofulvin-beta-cyclodextrin complex also showed a significant increase in the dissolution of the drug, revealing that beta-cyclodextrin plays an important role in the solubilization of Griseofulvin.

Micronization: a method of improving the bioavailability of poorly soluble drugs

For poorly soluble drugs, the digestive absorption depends on their rate of dissolution. Decreasing the particle size of these drugs improves their rate of dissolution. Fine grinding mills are use to micronize powders: either jar mills or fluid energy mills. Theses processes were applied to griseofulvin, progesterone, spironolactone and diosmin. For each drug, micronization improved their digestive absorption, and consequently their bioavailability and clinical efficacy.

Toxic effects of griseofulvin: disease models, mechanisms, and risk assessment

Griseofulvin (GF) has been in use for more than 30 years as a pharmaceutical drug in humans for the treatment of dermatomycoses. Animal studies give clear evidence that it causes a variety of acute and chronic toxic effects, including liver and thyroid cancer in rodents, abnormal germ cell maturation, teratogenicity, and embroyotoxicity in various species. No sufficient data from human studies are available at present to exclude a risk in humans: therefore, attempts were made to elucidate the mechanisms responsible for the toxic effects of GF and to address the question whether such effects might occur in humans undergoing GF therapy. It is well documented that GF acts as a spindle poison and its reproductive toxicity as well as the induction of numerical chromosome aberrations and of micronuclei in somatic cells possibly may result from disturbance of microtubuli formation. Likewise, a causal relationship between aneuploidy and cancer has been repeatedly postulated. However, a critical survey of the data available on aneuploidogenic chemicals revealed insufficient evidence for such an association. Conceivably, other mechanisms may be responsible for the carcinogenic effects of the drug. The induction of thyroid tumors in rats by GF is apparently a consequence of the decrease of thyroxin levels and it is unlikely that such effects occur in GF-exposed humans. The appearance of hepatocellular carcinomas (HCC) in mice on GF-supplemented diet is preceded by various biochemical and morphological changes in the liver. Among these, hepatic porphyria is prominent, it may result from inhibition of ferrochelatase and (compensatory) induction of ALA synthetase. GF-induced accumulation of porphyrins in mouse liver is followed by cell damage and necrotic and inflammatory processes. Similar changes are known from certain human porphyrias which are also associated with an increased risk for HCC. However, the porphyrogenic effect of GF therapy in humans is moderate compared with that in the mouse model, although more detailed studies should be performed in order to clarify this relationship on a quantitative basis. A further important effect of GF-feeding in mice is the formation of Mallory bodies (MBs) in hepatocytes. These cytoskeletal abnormalities occur also in humans, although under different conditions; their appearance is associated with the induction of liver disease and HCC. Chronic liver damage associated with porphyria and MB formation, enhanced cell proliferation, liver enlargement, and enzyme induction all may contribute to the hepatocarcinogenic effect of GF in mice. In conclusion, further investigation is required for adequate assessment of health risks to humans under GF therapy.

DeMonS--a new deconvolution method for estimating drug absorbed at different time intervals and/or drug disposition model parameters using a monotonic cubic spline

DeMonS-a new numerical deconvolution method for estimating the amount of drug absorbed at different time intervals and/or drug disposition model parameters-is presented here. In DeMonS, the amount of drug absorbed at different time intervals and/or drug disposition model parameters are the unknown parameters to be calculated. The Fritsch-Butland non-decreasing cubic spline was constructed from the cumulative amount of drug absorbed-time data directly derived from the calculated amount of drug absorbed at different time intervals. The drug absorption rate, which is the derivative of this non-decreasing cubic spline, is therefore represented by a piecewise non-negative quadratic function. The drug concentrations were obtained by convoluting the drug absorption rate quadratic function with the drug disposition model function. The nonlinear optimization method with simple parameter bounds was used to estimate the optimal set of unknown parameters by minimizing the sum of squares of residuals between the observed and predicted drug concentrations. DeMonS has been applied to (i) the griseofulvin data for estimating drug absorbed at different time intervals when the drug disposition model parameters were determined separately from intravenous data, (ii) veralipride double-peak phenomenon data to estimate simultaneously the percentage of cumulative veralipride absorbed and the veralipride disposition model parameters without reference intravenous data, (iii) a comparative bioequivalence study of gastrointestinal therapeutic system (GITS) pseudoephedrine HCI (PeHCI) controlled-release oral dosage forms when the drug disposition model parameters were not available, and (iv) estimation of both drug disposition model parameters and the absorption rate of drug from Testoderm (testosterone transdermal system) in the presence of endogenous testosterone production. DeMonS was implemented using MATLAB and NAG MATLAB Toolbox, and is available for Windows 3.1.

Estimation of the increase in solubility of drugs as a function of bile salt concentration

PURPOSE

The objective of this study was to develop a model to predict the extent to which bile salts can enhance the solubility of a drug, based on the physicochemical properties of the compound. The ability to predict bile salt solubilization of poorly soluble drugs would be a key component in determining which drugs will exhibit fed vs. fasted differences in drug absorption.

METHODS

A correlation between the logarithm of the octanol/water partition coefficient [log P] of six steroidal compounds and their solubilities in the presence of various concentrations of sodium taurocholate at 37 degrees C, log [SR] = 2.234 + 0.606 log [P] (r2 = 0.987) where SR is the ratio of the stabilization capacity of the bile salt to the solubilization capacity of water for the drug, was used to predict the solubility of the compounds in presence of sodium taurocholate were then measured.

RESULTS

The predicted solubilities were within 10% of the experimentally observed solubilities for griseofulvin, cyclosporin A and pentazocine. The model overpredicted the solubility of phenytoin and diazepam in 15 mM sodium taurocholate solution by a factor of 1.33 and 1.62 respectively.

CONCLUSIONS

The expected increase in solubility as a function of bile salt concentration can be estimated on the basis of the partition coefficient and aqueous solubility of the compound.

Griseofulvin absorption from different sites in the human small intestine

The site-dependent small-intestinal absorption pattern of griseofulvin was investigated in man. Griseofulvin was chosen as a model substance having extremely low water solubility and moderate lipid solubility. A conventional steady-state perfusion technique (triple-lumen tubing system with a 20 cm test segment) was applied. Dissolved griseofulvin (10.0 mg L-1) was perfused (10 mL min-1) during 160 min into different parts of the small intestine with the middle of the test segment between 85 cm and 270 cm beyond the teeth. Each of the ten healthy volunteers was examined twice with the test segment localized in different regions to allow for intraindividual comparisons. Mean drug absorption rates calculated from intestinal aspirate concentrations were similar in the two intestinal parts (proximal, 15.0 +/- 5.9 micrograms (20 cm min)-1; distal, 16.2 +/- 4.3 micrograms (20 cm min)-1; mean +/- SD). Absorption rate was strongly correlated to the amount of griseofulvin offered to the test segment per unit time. Extrapolating these findings it follows that an amount of griseofulvin, once dissolved, would be absorbed completely (> 99%) along 100 cm of the small intestine. A significant, positive correlation between the rate of transmucosal fluid transport and the absorption rate of griseofulvin was observed in the distal parts investigated.

The gastro-intestinal absorption of griseofulvin can be enhanced by encapsulation into liposomes

Liposomes are microscopic structures consisting of one or more lipid bilayers enclosing a definite aqueous space. They are widely used as a drug carrier and for the delivery of drugs through membranes. Drugs can be encapsulated into the inner water phase or lipidic wall, depending on their own hydro- or lipophilicity. The characteristics of the vesicles is fusion with cells and natural endocytosis uptake. We applied the properties of liposomes to overcome the poor gastro-intestinal (GI) absorption of griseofulvin and compared results with the traditional dosage form. In this experiment, the maximum plasma concentration obtained from griseofulvin liposomes was about 2.6 times than that from griseofulvin suspension. We used the lipids to prepare liposomes that consisted of phosphatidycholine, cholesterol, and dicetylphosphate in the molar ratio, 1:1.6:0.2, which is similar to the membrane composition of red blood cells. We examined some factors affecting the encapsulation ratin (E.R.%) and physicochemical properties of liposomes. When the lipid-to-griseofulvin weight ratio approached 38:1, the encapsulation ratio reached 94%. The different lipid/aqueous ratio (19/1 48/1 96/1) appeared to have little effect on E.R. value. The stability of griseofulvin liposomes in terms of leakage of griseofulvin was negligible over a period of 18 days at 4 degrees C. The sedimentation of vesicles bearing negative charges exhibited the best flocculation state. The plasma level-time profile of griseofulvin obtained from ingestion of liposomal dosage form showed itself to be significantly higher (P<0.01) Cmax, AUC, Ka, and t1/2 than that from suspension.

Oral bioavailability of griseofulvin from aged griseofulvin:lipid coprecipitates: in vivo studies in rats

The bioavailabilities of aged coprecipitates of griseofulvin (Gris), dimyristoylphosphatidylcholine (DMPC), or egg phosphatidylcholine (EPC) and cholesterol (CHOL) in rats and correlations with their in vitro dissolution behaviors were determined. In vivo absorption studies of Gris:DMPC (4:1, w/w) or Gris:DMPC:CHOL [4:1(1:0.33 mole ratio)] coprecipitates yielded evidence of a 40% increase in the peak concentration in plasma (Cmax) and a 2.5- to 3-fold decrease in the time to reach Cmax (tmax), compared with those obtained with micronized Gris but a statistically unchanged area under the concentration in plasma--time curve (AUC) when 1-day-aged samples at equivalent doses were used. On the other hand, a 10% decrease in the AUC, a 20% increase in the Cmax, and a three- to fourfold decrease in the tmax were observed for the same formulations aged for 90 days. In comparison, the Cmax produced by the 1-day-aged Gris:EPC:CHOL [4:1(1:0.33 mole ratio)] coprecipitate was the same as that produced by micronized Gris, but the tmax and the AUC were significantly lower; the Cmax produced by the 90-day-aged coprecipitate was 30% higher than that produced by micronized Gris, but the tmax and the AUC remained unchanged. The Gris concentrations after 5 and 30 min (dissolution parameters) and the percent dissolution efficiency also showed excellent correlations with the concentration in plasma after 1 h, the Cmax, and the AUC (in vivo parameters) for all formulations, but the individual in vitro parameters showed poor correlations with the AUC results.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of terbinafine in the nail

Oral terbinafine is an effective therapy for dermatophyte onychomycosis, presumably because it reaches the infected areas of the nail rapidly and in fungicidal concentrations. For planning optimal clinical dosage regimes, it is necessary to know the rate of terbinafine movement through the nail plate, the concentrations achieved, and the persistence in the nail plate after stopping treatment. In a study of 12 patients receiving terbinafine at 250 mg/day for up to 48 weeks, measurement of terbinafine in distal nail clippings demonstrated that the drug was first detectable 3-18 weeks after starting therapy. A level of 0.25-0.55 ng/mg was quickly achieved and remained stable. Concentrations of terbinafine in distal clippings of unaffected nails were similar to those in affected nails. Although the average nail concentrations are within the fungicidal range for dermatophytes, the anatomy of an infected nail may result in relatively protected areas of infection. This results in the occasional persistence or recurrence of dermatophytic infection observed in some cases. However, the results of this study justify further trials of 'short-term' oral terbinafine therapy for onychomycosis. A current study is addressing the relationship of oral dosage to nail drug concentration and its later persistence in the nail plate.

Itraconazole compared with griseofulvin in the treatment of tinea corporis/cruris and tinea pedis/manus: an interpretation of the clinical results of all completed double-blind studies with respect to the pharmacokinetic profile

Itraconazole is an orally active triazole antifungal which has been compared to griseofulvin in a number of double-blind trials. In dermatophytosis with a non-fixed treatment regimen for a maximum of 3 months, itraconazole 100 mg o.d. has produced a 100% mycological cure rate as compared with a 67% rate with griseofulvin 500 mg o.d. (p less than 0.01). Based on the pharmacokinetic profile, 100 mg itraconazole daily was then compared with 500 mg ultramicronized griseofulvin daily using a fixed treatment schedule of 15 days in tinea corporis and/or cruris and 30 days in tinea pedis and/or manus. In all studies in tinea corporis/cruris (n = 277), the superiority of itraconazole was shown for the clinical outcome at the last follow-up visit 2 weeks post-therapy (88 vs. 69%, p less than 0.01) and in the mycological outcome at the last follow-up visit (81 vs. 65%, p less than 0.05). In tinea pedis/manus (n = 210), the clinical response was virtually the same for the two treatment groups, but the most important finding was the mycological outcome with a significantly better result in favor of itraconazole at the end of treatment (77 vs. 61%, p less than 0.05) even more pronounced at the follow-up visit (85 vs. 48%, p less than 0.01). We conclude that itraconazole 100 mg daily in the treatment of tinea corporis/cruris and in tinea pedis/manus is significantly more effective than 500 mg griseofulvin daily when fixed treatment regimens are used. Furthermore, the best results are obtained with itraconazole 2-3 weeks after the end of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Intestinal absorption of drugs. The influence of mixed micelles on on the disappearance kinetics of drugs from the small intestine of the rat

The solubilization of the hydrophilic drugs paracetamol and theophylline, and the lipophilic drugs dantrolene, griseofulvin and ketoconazole has been determined in mixed micellar aqueous dispersions composed of 10 mM taurocholate + 5 mM oleic acid. The solubilization of dantrolene and paracetamol has also been determined in aqueous (mixed) micellar dispersions of 1 g L-1 lysophosphatidyl-choline (LPC), or taurocholate/LPC. The influence of these (mixed) micelles on the absorption of the model drugs from solution was studied in the rat chronically isolated internal loop. Absorption kinetics of the drugs were evaluated on the basis of the disappearance rate of the drug dissolved in the perfusion medium in this loop. Absorption experiments with taurocholate/oleic acid in the perfusate resulted in a reduction of the disappearance rate for the lipophilic drugs and the hydrophilic drug theophylline. This could partly be ascribed to the decreased fraction of drug free in solution as a result of its micellar solubilization for dantrolene, griseofulvin and ketoconazole, but the decrease in the disappearance rate of theophylline was unexpected. Taurocholate/oleic acid, LPC and taurocholate/LPC micelles had no effect on the disappearance of paracetamol. The disappearance rate of dantrolene in the presence of LPC alone was not altered, in spite of the decreased fraction of the drug free in solution owing to its micellar solubilization. In contrast, taurocholate/LPC micelles caused a reduction in the rate of disappearance of dantrolene, as expected according to the phase-separation model. In-vitro, taurocholate and taurocholate/LPC reduced the molecular cohesion of porcine intestinal mucus, whereas LPC alone did not exhibit an effect on the gel structure of mucus.(ABSTRACT TRUNCATED AT 250 WORDS)

Dissolution rate of griseofulvin in bile salt solutions

Bile salts increase the apparent solubility of lipophilic poorly water-soluble drugs like griseofulvin. In this study, the dissolution kinetics of griseofulvin in solutions of bile salts (sodium taurocholate and sodium cholate) were investigated. A rotating disk apparatus was chosen to monitor dissolution kinetics; it well-defined hydrodynamic conditions allowed for analysis of the behavior of bile salt micelles under different conditions. Griseofulvin solubility and dissolution rate increased with increasing bile salt concentration in the dissolution medium. The enhancement of the dissolution rate was not linearly related to the solubility increase, as diffusional transport of the solubilized drug proved to be less efficient than transport of the unsolubilized ("free") drug. The dissolution process proved to be controlled by convective diffusion. An analysis of the data with the phase separation model provided results for the micellar diffusion coefficient comparable with literature data obtained with different techniques.

[Bioavailability of griseofulvin in the form of liposomes]

Liposomes containing griseofulvin have been prepared by shaking method. Lecithin and cholesterol were used to compose phospholipid bilayer of liposomes. The suspension of liposomes in 0.9% sodium chloride and the suspension of griseofulvin in 0.25% iostonic methylcellulose solution were used in the comparative study in vivo. Both suspensions were administered intragastricly to rats. Parameters of bioavailability have been found on the basis of the changes in griseofulvin plasma concentrations versus time. Intragastric administration of griseofulvin in liposomes suspension demonstrates ca. 40% higher Cmax and AUC when compared to these of griseofulvin suspension which indicates a better bioavailability.

Griseofulvin: a new look at an old drug

Griseofulvin is the oral antifungal agent of choice for the treatment of dermatophytoses. This article reviews the history, pharmacokinetics, adverse reactions, and traditional therapeutic applications of griseofulvin. In addition, reports since 1960 of the use of the drug in the treatment of Raynaud's phenomenon, progressive systemic sclerosis, lichen planus, mycosis fungoides, herpes zoster, eosinophilic fasciitis, and molluscum contagiosum are discussed, noting the varying degree of therapeutic success.

The bioavailability of griseofulvin from microsized and ultramicrosized tablets in nonfasting volunteers

Tablets of either microsized or ultramicrosized griseofulvin (2 x 125 mg), were administered to 6 healthy volunteers of either sex just before a breakfast containing 4o g. of butter. The plasma concentration of griseofulvin were determined 1, 3, 5, 7, 9, 24, and 32 h. after dosing using a spectrofluorometric method, and pharmacokinetic parameters (Cp max, t max, AUC 0 - greater than 32) were calculated. These parameters were found to be; Cp max = 0.0.681 +/- 0.1 mu/ml, t max. = 2.51 +/- 0.33 h. and AUC = 14.14 +/- 2.33 micrograms h/ml for microsized tablets and Cp max = 0.80 +/- 0.08 +/- g/ml, t max = 2.44 +/- 0.54 and AUC = 16.25 +/- 1.16 microgram h/ml for ultramicrosized tablets. Our results show that mean peak plasma level and AUC (0 - greater than 32) are only slightly higher for the ultramicrosized preparation and the time to peak plasma level is similar in two preparations. Therefore, it is concluded that coadministration of griseofulvin with food will tend to reduce the difference between the bioavailability of the two type of preparations.

Intestinal absorption of drugs. III. The influence of taurocholate on the disappearance kinetics of hydrophilic and lipophilic drugs from the small intestine of the rat

The influence of sodium taurocholate (TC) on the intestinal absorption of drugs was studied in vivo in a chronically isolated internal loop in the rat. The hydrophilic drugs paracetamol (PA) and theophylline (TP) and the lipophilic drugs griseofulvin (GF) and ketoconazole (KE) were used as model drugs. The drug concentrations were kept below the saturation concentration. Absorption kinetics of the drugs were evaluated on the basis of disappearance rates of the drug from luminal solutions in the intestinal loop. Concentrations of TC above the critical micelle concentration (CMC) did not affect the absorption rate of the hydrophilic drugs PA and TP; the barrier function of the intestinal wall for PA and TP was not altered in the presence of taurocholate. The addition of concentrations of TC above the CMC in the perfusion solution resulted in a reduction of the absorption rate of GF and KE. The reduction in the absorption kinetics of GF in the presence of TC correlated well with the reduction of the drug-free fraction in solution due to micellar solubilization. For KE this relation was less clear. It was not possible to determine, on the basis of the phase-separation model, to what extent the fraction of the drug incorporated in TC micelles contributes to the overall diffusion of GF and KE across the preepithelial diffusion barrier. It was concluded that TC exhibits only a minor, if not negligible, effect on the barrier function of the aqueous diffusion barrier adjacent to the intestinal wall.

Percutaneous absorption of coumarin, griseofulvin and propranolol across human scalp and abdominal skin

The objective of this study was to investigate the role of the transfollicular pathway in the diffusion process of chemicals through excised human skin in vitro. Skin was obtained from 5 cadavers (3 males, 3 females) within 24 h of death. The age of the subjects varied between 18-77 years. Three radiolabelled drugs, namely 14C-coumarin, 3H-propranolol and 3H-griseofulvin, were studied. The permeation parameters such as flux, lag time, diffusion coefficient and permeability constant were determined across scalp and abdominal skin using the Thomas Diffusion Cell. For all tested substances the flux through scalp skin was higher than across abdominal skin and the lag time was decreased. The differences were statistically significant at p less than 0.05 for coumarin and propranolol. These data suggest that the transfollicular pathway in permeation might have a significant impact on the diffusion parameters for some drugs. Also, in the case of coumarin, permeability seems to be epidermis/dermis-controlled, whereas for griseofulvin and propranolol the Stratum corneum apparently is the permeability limiting barrier.

In vitro skin penetration of griseofulvin in rat and human skin from an ointment dosage form

Penetration and permeation of griseofulvin into and across the rat skin after application of three ointment formulations containing either dimethylacetamide (DMAC) or diethylene glycol monoethylether (DGME) or the ointment base alone (control--without DMAC or DGME) were studied, in vitro. Penetration and permeation of griseofulvin into and across the human skin after application of DGME ointment was also studied. Permeation of griseofulvin across the rat skin was highest for the DMAC ointment, followed by the DGME ointment and lowest for the control. Concentration of griseofulvin in the upper layers of the skin (i.e., surface to 100 micron depth) was also highest for DMAC and lowest for the control. However, the skin levels from the DGME ointment could not be distinguished (statistically) from the other two formulations. In comparison to rat skin, human skin is much less permeable. Amount of griseofulvin (from DGME ointment) that permeated through the rat skin was 14 times the amount that permeated through the human skin. Concentration of griseofulvin in the upper layers of the rat skin were 4 times the concentration of the drug in the upper layers of the human skin. The concentration of griseofulvin in the various layers of the human skin after one topical application were far greater than those reported after prolonged peroral administration.

Characteristics of drug-phospholipid coprecipitates. II: Bioavailability studies of griseofulvin in rats

The bioavailabilities of griseofulvin and dimyristoylphosphatidylcholine (DMPC) coprecipitates prepared from chloroform have been determined in rats. The dissolution rate of griseofulvin in pH 2.0 HCl:KCl buffer under sink conditions increased nonlinearly with an increase in DMPC in the coprecipitates. The initial dissolution rate, the amount dissolved after 60 min, Cmax, and AUC were all approximately twofold greater for coprecipitates than for griseofulvin over the range of 19:1 to 1.5:1 griseofulvin:DMPC weight ratio. In contrast, physical mixtures of griseofulvin:DMPC yielded results which were not significantly different from those of griseofulvin alone. The correlation between in vitro and in vivo parameters was at least 0.95. Thus, the reduction in particle size and solubilization of griseofulvin which is observed in vitro are believed to also occur in vivo and provide improved bioavailabilities.

Pharmacokinetic profile of orally administered itraconazole in human skin

Itraconazole is an orally effective antifungal agent with a high affinity for tissues. The skin kinetics in human volunteers have been studied after administration of 100 and 200 mg of itraconazole daily. From day 7 onward, tissue levels in the beard region and on the back were consistently higher than the corresponding plasma levels. The levels in the palmar stratum corneum were lower than the corresponding plasma levels but persisted for 3 weeks after discontinuation of therapy. Stratum corneum levels in the beard area were still measurable 4 weeks after the end of therapy. With the 200-mg dose, sweat levels became detectable 24 hours after the first drug intake. The sweat levels were usually lower than the corresponding plasma levels and followed the same curve as the plasma levels. Sebum levels of itraconazole were 10 times as high as the corresponding peak plasma levels. Sebum levels were undetectable 14 days after discontinuation of therapy. The results indicate that oral intake of itraconazole will result in therapeutic levels in the skin and these levels vary, depending on the region of skin tested. There are at least three routes of delivery of itraconazole to the skin: (1) passive uptake by keratinocytes in the basal layer (as shown by the continued presence of the drug in the palmar stratum corneum at a moment when plasma, sebum, and sweat levels are again undetectable); (2) a less significant excretion through the sweat glands (as shown by the lower drug levels compared with the plasma levels); and (3) a massive excretion through the sebaceous glands (as shown by the sebum levels compared with the plasma levels).

Instantaneous input hypothesis in pharmacokinetic studies

Observed venous plasma concentrations of furosemide, propranolol, griseofulvin, and theophylline at 0.33 and 0.66 min after intravenous bolus injections to unanesthetized dogs were compared with those extrapolated using the instantaneous input hypothesis. At 0.33 min, extrapolated/observed plasma level ratios as high as 20.5, 65.5, 226, and 1.17 were found for these four drugs, respectively. Venous plasma levels peaked at 1 min postinjection in all studies. Total plasma areas (AUC0-->infinity) estimated using the instantaneous input principle were higher by as much as 6.0, 6.8, and 19.6% for propranolol, griseofulvin, and furosemide, respectively, when compared with experimental data. The effect on theophylline was negligible. These results suggest the need for cautious interpretation of some venous pharmacokinetic data. More studies in animals and humans are required to assess the magnitude of deviation from the instantaneous input hypothesis for drugs in general.