La reducción del número de animales de experimentación y el cálculo del tamaño muestral: una mesa con cinco patas / Reduction of the number of animals in experiments and sample size calculation: a five-legged table

El cálculo del tamaño muestral necesario para la consecución de los objetivos de un experimento está basado en cuatro factores interdependientes: tamaño de efecto, nivel de significación, potencia estadística, y variabilidad de la muestra. El trabajo de planificación previo a la ejecución del estudio es fundamental para obtener el máximo de información con el número mínimo de animales (AU)

Sample size calculation to accomplish with the objectives of an experiment is based in four interdependent factors: effect size, significance level, statistical power and sample variability. The planning of the study, prior to execution, is fundamental to obtain the maximum of information from the minimum number of animals (AU)

Twenty-four-month oral carcinogenicity study of ebrotidine in rats.

Three groups of Sprague-Dawley CD rats (males and females) were initially administered p.o. with ebrotidine, a novel H2-receptor antagonist, mixed with the diet, at 50, 200, and 500 mg/kg/d, respectively. Two concurrent control groups of animals were used. After 13 months, initial 200 mg/kg was lowered to 150 mg/kg, and a new group was administered with 300 mg/kg, due to the body weight reduction observed in the top dose group. After 24 months, survivors were killed and necropsied, and a histopathological study was performed. The frequencies of the different tumour types that were found were not raised due to the treatment. Lower frequencies of some types of pituitary and mammary gland tumours, in the groups treated with the higher doses, were the only statistically significant changes. Among the non-neoplastic effects, a lower body weight increment and food consumption (500 and 300 mg/kg, both sexes), lower survival (500 mg/kg, males), presence of lipoid pneumonia (500 mg/kg, only in males, and 300 mg/kg, both sexes), and lithiasis in urinary system (500 mg/kg) were observed. No changes in gastric mucosa (the main target organ) were attributable to ebrotidine. Regarding the non-neoplastic effects, 150 mg/kg was the no observed adverse effect level. According to the previous results of the carcinogenicity study in mice, conjointly with those of the study in rats reported here, there is no evidence of carcinogenic risk either in males or in females in these species.

Effect of ebrotidine on ethanol-induced gastric mucosal damage in the rat. Comparative study with other H2-receptor antagonists.

Ebrotidine (N-[(E)-[[2-[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio]ethyl ] amino]methylene]-4-bromo-benzenesulfonamide, CAS 100981-43-9, FI-3542) is a novel H2-receptor antagonist with additional gastroprotective effect. The gastroprotective effect of oral doses of ebrotidine against ethanol-induced mucosal damage in female rats was compared with the effect of cimetidine, ranitidine and famotidine. Macroscopically, ebrotidine showed dose-dependent inhibition of the lesion, with significant differences from that of controls at doses of > or = 12.50 mg/kg (ED50 was 26.54 mg/kg). None of the other drugs tested showed gastroprotective effect under the same conditions. The histopathological study revealed significant reduction in the number of deep and superficial ulcers in ebrotidine-treated animals. The gastroprotective effect of ebrotidine is patent even in the presence of indometacin suggesting that prostaglandins play a rather negligible role in gastroprotective action. These results suggest that ebrotidine may be more useful than the classically known H2-antagonists in the treatment of peptic ulcers.

Study on the increment of the amount of gastric mucus in rats after repeated-dose administration of ebrotidine.

Ebrotidine (N-[(E)-[[2-[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio]ethyl ] amino]methylene]-4-bromo-benzenesulfonamide, CAS 100981-43-9, FI-3542) is a novel H2-receptor antagonist that also exhibits a potent gastroprotective action against ethanol damage. This study was designed to ascertain under physiological conditions the effect of ebrotidine on the secretion of gastric mucus, probably the main component of the mucosal barrier. Two groups of 20 rats each were given a daily oral dose of 10 or 35 mg/kg ebrotidine, respectively, for 17 days. A third group of 20 rats was used as a control. Once the administration period had concluded, the animals were killed and their stomachs were removed and processed by the periodic acid-Schiff (PAS) histochemical method, selective for mucopolysaccharides. PAS-positive areas exhibited a characteristic carmine colour, allowing morphometric study by computerized image analysis. All the histological sections studied were from the same region of the stomach. A significant increase in the PAS-positive area corresponding to glandular mucus was found in all treated groups. This action is consistent with an increased secretion of mucopolysaccharides and represents one of the main mechanisms of the cytoprotective action of ebrotidine.

Acute toxicity studies of ebrotidine.

The acute toxicity of two formulations of ebrotidine (N-[N-[(E)-[[2-[[[2-[(diaminomethylene)amino]-4-thiazolyl] methyl]thio]ethyl]amino]methylene]-4-bromo-benzenesulfonamide, CAS 100981-43-9, FI-3542) was studied in rats and mice by different routes of dosing: oral and intraperitoneal routes in rats and mice (suspension), intravenous and oral routes in mice and intravenous route in rats (injectable solution). LD50 values for the oral route were indeterminable in all cases. For the intraperitoneal route. LD50 values were 316 mg/kg (rat) and 366 mg/kg (mouse), and for the intravenous route LD50 values were 100 mg/kg (rat) and 107 mg/kg (mouse).

Subacute toxicity of ebrotidine in rats and dogs.

Subacute toxicity studies of ebrotidine (N-[(E)-[[2-[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl] thio]ethyl]amino]methylene]-4-bromo-benzenesulfonamide, CAS 100981-43-9, FI-3542) were performed in Spragu-Dawley rats and Beagle dogs. Both animal species were administered with the same dose levels (50, 200 and 500 mg/kg) for 4 and 7 weeks, respectively. In a previous 4-week subacute toxicity study in the rat, ranitidine and cimetidine at 500 mg/kg were used as reference drugs. The results indicated that ebrotidine was well tolerated at 50 mg/kg, while there were dose-related effects at 200 and 500 mg/kg. Probably due to its pharmacokinetics, ebrotidine was more toxic in dogs than in rats, since the most severe effects were the death or sacrifice in extremis of two dogs from the high dose group which had undergone rectal prolapse, while no deaths occurred in the rats. The changes that were very likely related to treatment (500 mg/kg) were a lower weight in both species, a slight decrease of hematocrit and red blood cells in rats, single increments of transaminases, alkaline phosphatase and lactate dehydrogenase in dogs (some animals of the 200 mg/kg dose group were also affected) and a higher liver weight. These effects with a few exceptions were found to be common to cimetidine and ranitidine.

Chronic toxicity of ebrotidine in rats and dogs.

The results obtained in the chronic toxicity studies of ebrotidine (N-[(E)-[[2-[[[2-[(diaminomethylene)amino]-4-thiazolyl] methyl]thio]ethyl]amino]methylene]-4-bromo-benzenesulfonamide, CAS 100981-43-9, FI-3542) by oral route in rats and in Beagle dogs are reported. Rats were administered for 6 months and dogs for 12 months. The doses were 50, 200 and 500 mg/kg in rats and 50, 200 and 400 mg/kg in dogs. The dose of 400 mg/kg was reduced to 350 mg/kg after 3 months of treatment, due to its toxicity. The effects probably related to the administration of ebrotidine were as follows: three dogs from the high dose group died after 3, 4.5 and 8 months of treatment (in rat there was no mortality); occult blood in faeces; lower weight gain in the high dose group (in rats only females were affected); lower food consumption in rats from the high dose group (and also females from the middle dose group); reduction of erythrocyte count and packed cell volume, only in rats and at the end of the study; alkaline phosphatases increment in rats and dogs; proteinemia decrease in rats; and a tendency to decrease in the testicular weight, which was not statistically significant (p > 0.05). The only histopathological changes observed were moderate erosions or ulcerations in the intestinal mucosa of some dogs from the high dose group. These effects coincide with those published for other competitive H2-receptor inhibitors. The maximum toxic effect-free level was 50 mg/kg for both rats and dogs, which provides a wide safety margin with respect to the therapeutic dose.

Toxicity of ebrotidine on reproduction. Toxicity on fertility and general reproductive performance, embryo-fetal toxicity and peri- and postnatal toxicity.

Reproduction toxicity studies of ebrotidine (N-[(E)-[[2-[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl] thio]ethyl]amino]methylene]-4-bromo-benzenesulfonamide, CAS 100981-43-9, FI-3542) are presented in this paper. Rats dosed with 50, 200 and 500 mg/kg p.o. of ebrotidine were used for the fertility and peri- and postnatal toxicity studies, and rabbits dosed with 25, 100 and 250 mg/kg and rats dosed with 50, 200 and 500 mg/kg of ebrotidine were used for the embryotoxicity study. The fertility study was designed in accordance with a 2-generation study protocol. The results showed that ebrotidine did not interfere with male and female gametogenesis, fertility, organogenesis, postnatal development and lactation in F0 or F1 animals. Only general or non-specific effects were attributed to treatment, such as a lower weight gain in parents or fetuses in rats, or a somewhat slower bone calcification in rats, which was shown to be recoverable and had no peri- or postnatal repercussions. Neither did the fertility study reveal a possible longer duration of gestation nor did the peri- and postnatal study show a lower weight of the F1 offspring. There was only an increase in rabbit embryonic mortality, probably related to some cases of abortion at the high dose. No potential antiandrogenic effect on the reproductive function has been found. Among the different doses used in both animal species, the maximum toxic effect-free dose was that of 25 mg/kg.

Genotoxicity studies on ebrotidine.

Five genotoxicity studies on ebrotidine (N-[(E)-[[2-[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio] ethyl]amino]methylene]-4-bromo-benzenesulfonamide, CAS 100981-43-9, FI-3542), including at least four of the battery of tests recommended by toxicological regulatory guidelines for new drugs, were conducted. These tests were the Ames test for determination of bacterial gene mutations, sex-linked recessive lethal mutation test in Drosophila for gene mutations in eukaryotic systems, in vitro chromosome aberration test and micronucleus test for evaluation of structural and numerical aberrations, and sister chromatid exchange frequency test for assessment of non-specific damage to chromatin. Negative and positive controls were used in all the experiments. The effects were investigated in the absence or presence of metabolic activation by S-9 microsomal fraction from rat liver homogenate. A dose range toxicity study was also performed to determine the dosage levels or concentrations to be tested for the assessment of genotoxic effects. None of the tests showed a significant increase in the genotoxic parameters, both in vitro and in vivo in somatic or germ cells. It is, therefore, concluded that ebrotidine has not caused mutagenic or clastogenic effects in any of the experimental systems tested.

Carcinogenicity studies on ebrotidine.

The results from two carcinogenicity studies on ebrotidine (N-[2-(E)-[[2-[[[2-[(diaminomethylene)amino]-4-thiazolyl] methyl]thio]ethyl]amino]methylene]-4-bromo-benzenesulfonamide, CAS 100981-43-9, FI-3542) conducted in mice and rats are reported. Oral doses of 50, 200 and 500 mg/kg were administered to mice for 18 months and 50, 200 (150), 300 and 500 mg/kg were administered to rats for 24 months. The study design was prepared according to EEC guidelines, and the recommendations by the International Agency for Research on Cancer were used for the statistical analysis of data. Weekly palpations were made along the course of studies and general parameters were monitored. The only effects attributed to ebrotidine administration were a slight decrease in the survival rate of female mice given the 500 mg/kg dose and a lower weight gain in rats of both sexes. The histopathological data revealed that lipoid pneumonia and kidney calculi are more frequent in rats treated with doses of 500 and 300 mg/kg. No increment in the spontaneous occurrence of tumours or significant presence of tumours in treated animals differing from that in control animals was observed, and a decrease in the time required for their onset that could be related to ebrotidine was not observed either. There were no differences in hyperplastic and/or dysplastic changes between treated and control animals. Therefore, it is deduced that ebrotidine does not induce neoplastic or preneoplastic effects in rats or mice even at doses of 500 mg/kg, at which some general toxicity effects are seen.

Study of the population of antral G-cells and enterochromaffin-like cells in the rat and mouse gastric mucosa after long-term treatment with ebrotidine.

The potential effect of ebrotidine (N-[(E)-[[2-[[[2-[(diaminomethylene]amino]-4-thiazolyl]methyl]thio]ethyl ] amino)methylene]-4-bromo-benzenesulfonamide, CAS 100981-43-9, FI-3542) on two types of enteroendocrine cell populations in the gastric mucosa, antral G-cells and enterochromaffin-like cells, was investigated. The study of the population of antral G-cells was performed in a group of male rats treated with ebrotidine 500 mg/kg p.o. for 60 days; a control group receiving 10 ml/kg of an aqueous agar solution was used. A PAP (peroxidase-antiperoxidase) system-associated antigastrin immunohistochemical method was used for cell identification. The population of enterochromaffin-like cells was assessed by quantifying the density of argyrophilic cells in mouse gastric mucosa after an 18-month treatment with ebrotidine 500 mg/kg. Grimelius silver staining method was used for cell identification. In both studies, cell count was performed using a light microscope at 400 x magnification and cell density was calculated by computer-assisted image analysis. Compared to control, ebrotidine did not cause any significant differences in the cell density of the populations studied.

Comparative study of plasma gastrin levels in rats after two months of ebrotidine administration.

Four groups of male rats were orally administered for 60 days with daily doses of ebrotidine (N-[(E)-[[2-[[[2-[(diaminoethylene) amino]-4-thiazolyl]methyl]thio]ethyl]amino]methylene]-4-bromo- benzenesulfonamide, CAS 100981-43-9, FI-3542) (500 mg/kg), ranitidine (500 mg/kg), cimetidine (500 mg/kg) and omeprazole (43.5 mg/kg). A fifth group received no treatment and was used as control. The curve of gastrinemia was obtained on days 1, 15 and 60 of administration. On each of these days gastrinemia was assessed at 0, 1, 5, 8, and 24 h on day 1, and 1, 5, 8, 10 and 24 h on days 15 and 60. The purpose of this study was to compare the plasma gastrin level profile in association with the administration of test drugs on days 1, 15 and 60 of treatment. The results showed a significant difference in the duration of hypergastrinemia of H2-receptor antagonists as compared to proton pump blockers. Although peak plasma gastrin levels were attained for all products between 5 and 8 h after day 1 of administration, H2-receptor antagonists, unlike omeprazole, achieved recovery of gastrin baseline levels within 24 h. On days 15 and 60 of ebrotidine, treatment, plasma gastrin levels returned to normal range at 5 and 8 h after administration, respectively. After ranitidine and cimetidine, hypergastrinemia was still present at this time, but normal levels were attained before 24 h. With omeprazole plasma gastrin levels did not return to normal range within 24 h after each administration, and a cumulative effect occurred during treatment. The omeprazole treated group showed the highest and more sustained plasma gastrin levels. It was concluded that ebrotidine was the antisecretory agent with the lowest hypergastrinemic effect during long-term treatment. With ebrotidine daily baseline gastrin levels were more rapidly recovered after each administration.

Continuous intragastric pH monitoring in the evaluation of ebrotidine, cimetidine and placebo on gastric acidity in healthy volunteers.

This study was conducted to determine the efficacy and tolerance of ebrotidine (N-[(E)-[[2-[[[2-[(diaminomethylene)amino]-4-thiazolyl) methyl]thio]ethyl]amino]methylene]-4-bromo-benzenesulfonamide, CAS 100981-43.9, FI-3542), a new H2-receptor antagonist, on reducing gastric acidity after a single 800 mg dose, compared with cimetidine 800 mg once daily and placebo by means of a continuous intragastric pH monitoring. A total of 30 healthy volunteers were allocated to receive in a double blind, parallel design the study medication. Clinical observations, physical examinations and visual analogue scales (VAS) were performed during the study to assess the tolerability of the three treatments. Ebrotidine and cimetidine caused a greater and longer-lasting gastric acid inhibition than placebo. With ebrotidine, significantly (p < 0.05) higher median pH values (and interquartile range, IQR) were reached in the post-administration (2.61, IQR 2.02-3.93), postprandial (3.38, IQR 2.82-3.91) and nocturnal (2.83, IQR 1.69-3.77) periods than with placebo: 1.82 (IQR, 1.66-2.09), 2.81 (IQR, 2.02-3.28), and 1.89 (IQR, 1.44-2.13), respectively. Cimetidine showed significant differences compared to placebo in the post-administration (2.36, IQR 1.89-3.46) and nocturnal (2.46, IQR 1.88-4.33) periods. No statistical differences were observed between the active treatments. Ebrotidine caused a significantly higher percentage of time above pH 2.0 in the post-administration and nocturnal periods compared to placebo (p < 0.05), and above pH 3.0 in the post-administration, postprandial and nocturnal periods. No serious adverse effects, or disturbances in the VAS or in the vital signs were reported, and all medications were well tolerated. It is concluded that a single dose of ebrotidine 800 mg is as effective as cimetidine 800 mg in reducing total and nocturnal intragastric acidity. The study also confirms the excellent safety profile of the new drug.

Study of the population of enterochromaffin-like cells in mouse gastric mucosa after long-term treatment with ebrotidine.

The possible hyperplastic effect on the mouse gastric mucosa following administration of 500 mg/kg of ebrotidine for 18 mo was investigated. The animals were taken from the study of carcinogenesis in mouse carried out with this product. Two different aspects were considered to assess such a possible hyperplastic effect. The height of the fundic and antral mucosa was microscopically measured in several points. Histologic sections obtained from standardized levels of the stomach were used. The density of argyrophil cells in the gastric mucosa has been also quantified, in order to identify enterochromaffin-like (ECL) cells, the most abundant among the cells that have this property. Grimelius' silver staining method was used to identify ECL cells. The cell count was performed under x400 magnification, and the length of mucosa examined was determined by computer-assisted image analysis. This study complements the mouse carcinogenesis study, in which no differences in tumor incidence were found between treated and control animals. The results show that administration of 500 mg/kg/day of ebrotidine for 18 mo to mice did not induce any hyperplastic effect on the gastric mucosa comprising its various cell types or any specific, diffuse, or focal hyperplasia of ECL cells.

Ocular tolerance of sertaconazole gel.

The in vitro and in vivo tolerance of sertaconazole gel, a new topical azole antifungal, was studied. Ketoconazole gel (Panfungol) was used as a reference substance. The methods applied for tolerance assessment were the bovine corneal opacity and permeability test for the in vitro assay and a modified Draize test for the in vivo assay. The results obtained show that both substances can be classified as slightly irritant and with acceptable tolerance. However, unlike ketoconazole gel, sertaconazole gel did not cause a positive lesion index in vivo. Ketoconazole was 5.25 times more irritant in vitro than sertaconazole gel, whose effect was similar to that of saline solution. Consequently, the negligible irritant effect of sertaconazole gel on a type of epithelium that is extremely sensitive, i.e. the cornea, confirms the good tolerance of this new antifungal gel on other structures such as the skin and mucous membranes.

Effect of ebrotidine on the density of antral G-cells in the gastric mucosa in the rat.

Two groups of male rats were treated orally for 60 days with ebrotidine and cimetidine, used as reference standard, respectively. The dose used of both drugs was 500 mg/kg. A third group, used as control, received 10 ml/kg of an aqueous agar suspension. After receiving the last dose, the animals were killed by inhalation of CO2 in a sealed chamber and the stomachs were removed for histological preparation. The purpose of this study was to count antral G-cells throughout the gastric mucosa by light microscope. A PAP system-associated antigastrin immunohistochemical method was used for cell identification. Cell density, with respect to their location in the gastric mucosa and the treatments given, was calculated using image analysis techniques. The results showed that ebrotidine did not cause any significant differences in the density of the population of these cells compared with the control group, while cimetidine induced a significant proliferation of antral G-cells.

Subacute toxicity and maximum tolerable dose of sertaconazole in repeated administration studies.

28-Day oral and dermal subacute toxicity studies of 7-chloro-3-[1-(2,4-dichlorophenyl)-2-(1H-imidazol-1-yl) ethoxy-methyl] benzo [b] thiophene (sertaconazole, FI-7045, CAS 99592-32-2), were carried out. The oral studies included the evaluation of subacute toxicity in rat (dose levels of 50, 150 and 300 mg/kg) and maximum tolerable dose in repeated administration in ferrets (consecutive dose levels in accordance with a geometric progression of 50, 75, 112.5, 168 and 250 mg/kg), which were the animal species intended for chronic toxicity studies. The dermal studies included the evaluation of subacute toxicity in rats and rabbits (1 ml/kg of a 2% cream). The results, in general, have shown low toxic effects, which can be summarized as a slight non-significant hepatomegalia in the rat with increased gamma-GTP and alkaline phosphatase values and a high urinary pH value; no histopathological changes were observed. These effects are characteristic of azole derivatives and are therefore common to other antifungals with this chemical group.

Chronic toxicity studies of sertaconazole after oral administration to rats and ferrets.

Six-month chronic oral toxicity studies of 7-chloro-3-[1-(2, 4-dichlorophenyl)-2-(1H-imidazol-1-yl)ethoxy-methyl] benzo[b]thiophene (sertaconazole, FI-7045, CAS 99592-32-2) were carried out in rats and ferrets. The dose levels used were 50, 150 and 300 mg/kg in rats and 50, 150 and 250 mg/kg in ferrets. There was no mortality associated with the drug in either of the two species. The results obtained show that the toxic effects may be summarized as a smaller body weight increase in rats at 150 and 300 mg/kg and in male ferrets at 250 mg/kg. Food consumption decreased significantly in rats at 300 mg/kg, and was not proportional to the doses of 150 and 50 mg/kg. In serum biochemistry, increases in alkaline phosphatase in rats, ALT in male ferrets at 150 and 250 mg/kg and AST only at 250 mg/kg were observed. BUN increased at 150 and 250 mg/kg in ferrets.

Reproduction toxicity of sertaconazole. Segment II (teratology) and Segment III (peri-postnatal toxicity).

The reproduction toxicity of 7-chloro-3-[1-(2,4-dichlorophenyl)-2- (1H-imidazol-1-yl)ethoxy-methyl]benzo[b]thiophene (sertaconazole, FI-7045, CAS 99592-32-2) (50, 100 and 150 mg/kg by oral route) has been investigated by performing two studies: the embryotoxicity or teratology study in rats and rabbits, and the peri-postnatal toxicity study in rats. According to the results obtained from the embryotoxicity studies, there was no maternal toxicity in either of the two species studied. The only embryofoetal abnormalities with statistical and toxicological significance were observed at the dose of 150 mg/kg in the teratology study on rabbits: hepatomegalia, pericardial oedema and peritoneal and hepatic haemorrhages. The results of the peri-postnatal study showed that the only maternal effect relating to the drug was an increase, proportional to the dose, in the weight of the ovaries, which was significant at the dose of 150 mg/kg. With reference to the offspring, only a reduction in the viability index at 150 mg/kg was observed. The non observed effects level (NOEL) for all three studies can be estimated at 100 mg/kg.

Genotoxicity studies on sertaconazole.

A series of 6 studies has been performed to evaluate the potential genotoxic effect of 7-chloro-3-[1-(2,4-dichlorophenyl)-2-(1H- imidazol-1-yl)ethoxy-methyl]benzo[b]thiophene (sertaconazole, FI 7045, CAS 99592-32-2). From these studies, the reverse mutation assay on Salmonella typhimurium, sex-linked recessive lethal mutations on Drosophila and genetic mutations in cultured mammal cells allowed to study the genetic mutations in prokaryotes and eukaryotes. In vitro and in vivo chromosomal aberrations were studied using human lymphocytes cytogenetic test, micronucleus test and sister chromatid exchange test. The results obtained in these studies, which are complemented one another, demonstrated that sertaconazole did not induce any signs of promutagenic, mutagenic or clastogenic activity or interference with the chromosomal segregation process.