Studies on antigenic variation of cyclically transmitted Trypanosoma congolense.

Antigenic variants of T. congolense transmitted by G. m. morsitans through normal and X-irradiated mice were investigated by means of the neutralization test and IFAT. Clones of a cyclically passaged derivative strain were isolated from irradiated and normal mice. The IFAT revealed cross immunofluorescent reactions between most of the stabilates, whereas only the two clones obtained from irradiated mice were totally neutralized by their homologous antisera. These two antisera showed no cross neutralizing activity. The results indicate a possible antigenic heterogeneity of the extruded metacyclic forms.

Safety aspects of midazolam.

The LD50 in the rat and the mouse is about 1600 mg/kg (oral administration) and 75 mg/kg (rat) and 50 mg/kg (mouse) on intravenous administration. Subchronic oral studies over 13 weeks in doses of 5, 15 and 45 mg/kg/day in the dog and 50, 100 and 200 mg/kg/day in the rat have demonstrated minimal toxicity for midazolam, as for other benzodiazepines. High doses produced increased liver weight in the rat and the expected increases in alkaline phosphatase in the dog (species-specific reaction). Detailed blood and urine analyses as well as histological examination of organs produced no indication of changes relevant for man. Subchronic parenteral studies (i.v. and i.m. for five weeks) using up to 6 mg/kg/day in dogs and rats showed the compound to be not only systemically, but also locally, extremely well tolerated. Reproduction toxicology studies have shown that midazolam is neither embryotoxic nor teratogenic and that it has no effect on the fertility and post-natal development of animals. In the AMES test and the fluctuation test, midazolam had no mutagenic effect.

The lack of hepatotoxicity in the rat with the new and reversible MAO-A inhibitor moclobemide in contrast to iproniazid.

In phenobarbital-pretreated rats iproniazid produces distinct hepatotoxic symptoms, whereas moclobemide (Ro 11-1163) does not. Iproniazid's hepatotoxic effect is most impressive in histopathology where marked liver necrosis can be seen. Differences between the two compounds are also noted in the body weight development, mortalities and some haematological and blood chemistry parameters. The reversible and specific monoamine oxidase (MAO)-A inhibitor moclobemide, a benzamide, is therefore completely different from the classical irreversible MAO inhibitors of the hydrazine type and, as also confirmed in the clinical studies, does not have any hepatotoxic effect.

Toxicological investigations with the benzodiazepine antagonist flumazenil.

The benzodiazepine antagonist ethyl 8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4] benzodiazepine-3-carboxylate (flumazenil, Ro 15-1788, Anexate) was investigated in a series of toxicological studies. In a single intravenous injection study in male and female mice and rats, the highest non-lethal (maximum tolerated) doses were found to be between 62.5 and 125 mg/kg (the amounts of flumazenil present in the aqueous ampoules available for intravenous injection in man are 0.5 and 1.0 mg). In intravenous studies of 4 weeks duration, 10 mg/kg/d were systemically well tolerated in dogs and rats. In 13-week oral studies, 80 mg/kg/d were very well tolerated in dogs (capsule administration) and, after 125 mg/kg/d (by feed-admix) in rats, no untoward compound-related findings apart from a 10-15% increase of the liver weights in females were made. In reproductive toxicity studies, flumazenil revealed no drug-related embryotoxic or teratogenic effect and no adverse effects upon fertility of dosed animals themselves or on the peri- and postnatal development of their offspring. There was no indication for mutagenic potential of flumazenil in vitro concerning induction of gene mutations or clastogenic effects. An in vivo DNA repair test using germ cells of male mice did not yield DNA-damaging activities. From all these toxicological investigations it can be concluded that the risk in man given therapeutic doses or even intentional or accidental overdoses of flumazenil is extremely small.

Preclinical safety evaluation of intravenously administered mixed micelles.

Mixed micelles, with their main constituents lecithin and glycocholic acid, form a new principle for the parenteral administration of compounds which are poorly water-soluble. Their composition of mainly physiological substances as well as their comparatively good stability substantiate their attractivity in comparison to existing solvents. A decomposition due to physical influences such as heat or storage for several years will almost exclusively affect the lecithin component in the form of hydrolysis into free fatty acids and lysolecithin. Their toxicity was examined experimentally in various studies using both undecomposed and artificially decomposed mixed micelles. In these studies the mixed micelles were locally and systemically well tolerated and proved to be neither embryotoxic, teratogenic nor mutagenic. Only when comparatively high doses of the undecomposed mixed micelles were administered, corresponding to approximately 30 to 50 times the anticipated clinical injection volume (of e.g. diazepam mixed micelles), did some vomitus (dogs), slight liver enzyme elevation (rats and dogs), and slightly increased liver weights (dogs) occur. After repeated injections of the artificially decomposed formulation (approximately 25% of lecithin hydrolyzed to free fatty acids and lysolecithin) effects such as intravascular haemolysis, liver enzyme elevations and intrahepatic cholestasis (dogs only) were observed but only when doses exceeding a threshold of approximately 40 to 60 mg lysolecithin/kg body weight were administered. All alterations were reversible after cessation of treatment.