Metabolism of pinazepam by rat liver microsomes

The pathways by which pinazepam and diazepam are metabolized by rat microsomes in vitro were studied in detail. Using a gas chromatographic technique to measure either the two parent compounds or their metabolites, it was demonstrated that pinazepam and diazepam were metabolized through the same pathways, but at different rates. Pinazepam was mainly N-dealkylated, while the C3-hydroxylation was a minor metabolic pathway. Diazepam was mostly C3-hydroxylated, with very little being N-demethylated. The different rats for the two metabolic pathways could be of importance in differentiating the action of the two drugs in vivo.

Chemical conversion of anthramycin 11-methyl ether to didehydroanhydroanthramycin and its utilization in studies of the biosynthesis and mechanism of action of anthramycin

Reaction of anthramycin 11-methyl ether (AME) with trifluoroacetic acid results in formation of (1,11a)-didehydroanhydroanthramycin (DAA). Anthramycin biosynthetically labelled from DL-[3'RS(3'-3H)]; DL-[3'S(3'-3H)] and DL-[3'R(3'-3H)] tyrosine each lose approximately 50% of their tritium during this conversion to DAA confirming the labelling pattern of 3'-tritiated species of tyrosine in AME. As expected negligible losses of tritium occurred from AME biosynthetically labelled fron L-[2- or 6-3H] or L-[3- or 5-3H]tyrosine. DAA did not form a stable adduct with DNA in accord with the postulated mechanism of action of anthramycin.

Quantitative analysis of CM 6912 (ethyl loflazepate) and its metabolites in plasma and urine by chemical ionization gas chromatography mass spectrometry. Application to pharmacokinetic studies in man

A chemical ionization gas chromatographic mass spectrometric assay is described for ethyl loflazepate (CM 6912), a new benzodiazepine with a potent anti-anxiety activity, and two of its metabolites in plasma and urine. The parent drug was separated from the biological samples by simple extraction at pH 9. In all samples analysed, parent drug levels were below the detection limit, confirming its extensive biotransformation at the sites of absorption and during its first pass through the liver. Pharmacokinetic data were obtained by measuring the total levels of two of the major metabolites. Accurate data may not be obtained for both metabolites separately since one of them (M1) is chemically transformed to metabolite M2 during plasma sampling, storage and extraction. Their total levels were measured after complete degradation of the unstable metabolite and extraction of the sample at pH 9. The precision and accuracy of this method are better than 10% in the low ng range. The detection limit is 1 ng ml-1. Pharmacokinetic data were obtained from human volunteers given a single oral dose of 2 mg CM 6912 in tablet form. Cp max values ranged from 30 to 55 ng ml-1 and were reached within 1.5 to 3 h after administration. Following the achievement of peak levels the concentration declined with an apparent biexponential pattern showing an elimination half-life ranging from 51 to 103 hours in its terminal phase.

Characteristics of antischistosomal benzodiazepine binding sites in Schistosoma mansoni

The benzodiazepines, clonazepam and Ro 11-3128, have been identified as antischistosomal drugs (Stohler, 1978). Using [14C] Ro 11-3128 or [3H] clonazepam, we were able to demonstrate that male S. mansoni can specifically bind these labeled drugs. The binding sites on this parasite displayed characteristics of saturability and low affinity. The affinity of various benzodiazepines for the binding site on intact schistosomes correlated with their antischistosomal efficacy. Binding was markedly altered by agents known to destroy membrane integrity. Combined with previous studies (Pax et al., 1978), this work suggests that a specific, benzodiazepine binding site may be located on the epidermis of male S. mansoni.

[Catalytic properties of the monooxygenases that oxidize 14C-phenazepam]

Aromatic hydroxylation and oxidation of heterocyclic molecule of phenazepame were studied. The reaction of aromatic hydroxylation prevailed in microsomes of intact animals, whereas preinduction of rats using phenobarbital and 3-methylcholanthrene altered the phenazepame metabolism increasing the rate of oxidation in the heterocyclic ring. Kinetic parameters are described for oxidation of phenazepame molecule by both intact and induced rat microsomes.

Influence of phenytoin and phenobarbital on the disposition of a single oral dose of clonazepam

Clonazepam (CZP) was measured in the plasma of eight subjects for 48 hr after a 0.03-mg/kg oral dose. After pretreatment for 19 days with phenytoin (DPH, 4.3 mg/kg/day), plasma CZP concentrations were determined in the same subjects after another 0.03 mg/kg oral dose of CZP. The same protocol was followed in eight additional subjects using phenobarbital (PB, 1.4 mg/kg/day) instead of DPH. DPH pretreatment lowered mean plasma CZP concentration in 8 of the 12 time points. DPH pretreatment increased CZP clearance by 46% to 58% and decreased CZP half-life (t1/2) by 31%. Both changes were statistically significant. After PB pretreatment the mean plasma CZP concentration was lowered by an average of 11%, but the decrease was statistically significant for only 1 of the 12 time points. PB decreased mean CZP t1/2 by 11% and increased CZP clearance by 19% to 24%, but only the increase in clearance was statistically significant. Both DPH and PB increased CZP clearances and decreased the areas under the plasma concentration-time curves without altering the volumes of distribution. This observation is consistent with induction of CZP metabolism. The overall effect of DPH (4.3 mg/kg/day) was greater than the effect of PB (1.4 mg/kg/day). Neither the DPH or PB had a significant effect on the extent of CZP protein binding.

Clobazam: a review of its pharmacological properties and therapeutic use in anxiety

Clobazam1 is a 1,5-benzodiazepine with antianxiety and anticonvulsant properties, advocated for the treatment of primary anxiety and that associated with organic or functional disorders. Clobazam itself has a half-life of 18 hours, but that of the principal metabolite, N-desmethylclobazam, is about 50 hours. Although the metabolite is pharmacologically less active than the parent drug, steady-state plasma concentrations of the metabolite are 8 times higher than those of the unchanged drug. Therapeutic trials indicate that the antianxiety effect of clobazam 30 to 80 mg daily is comparable with that of half its dose of diazepam. Clobazam has minimal muscle relaxant and hypnotic activity. Although subjective drowsiness has occurred with similar frequency with clobazam and diazepam in some studies, clobazam causes less objectively measured sedation or psychomotor impairment in experimental studies. Results of studies of vigilance and psychomotor performance during therapeutic use in patients are less conclusive, but clobazam may be useful in anxious patients who experience such impairment with other benzodiazepines.

Heterogeneity of benzodiazepine receptors in the central nervous system demonstrated with kenazepine, an alkylating benzodiazepine

Binding studies using the alkylating benzodiazepine kenazepine strongly suggest the existence of several populations of benzodiazepine receptors in the CNS. Kenazepine reacts noncompetitively and irreversibly with some receptors and competitively (reversibly) with others. Cerebellum contains the largest proportion (approx. 80%) of the noncompetitive type, while hippocampus and cortex contain a preponderance of competitive-type receptors (approx. 80 and 50%, respectively). The Hill coefficients for kenazepine are approx. 0.7 in cortex and cerebellum, and near unity in dorsal hippocampus. Different populations of benzodiazepine receptors may mediate different physiologic and pharmacologic effects in vivo.

[Distribution of 14C-phenazepam and its metabolites in the liver, brain and blood plasma in single and prolonged administration to white rats]

The distribution pattern of 14C-phenazepam and some of its metabolites in the liver, brain and blood plasma at a prolonged (45 days) administration to rats does not differ from that after a single administration. The liver and brain demonstrated an increase in the content of 3-hydroxyderivative. Glycuronide was found only in the liver.

Species differences in clobazam metabolism and antileptazol effect

The antileptazol effect of clobazam lasts longer in the mouse than in the rat. After intraperitoneal injection of clobazam (10 mg kg-1) plasma and brain concentrations of the drug and its rate of disappearance were similar in both species, whereas the metabolite N-demethylclobazam was present at higher concentrations and for longer in the mouse than in the rat. Although the exact contribution of the N-desmethylclobazam to the anticonvulsant effect of clobazam cannot be assessed, the longer duration in mice than in rats seems to be associated with different brain accumulations of the metabolite.

Pharmacological activities of clobazam and diazepam in the rat: relation to drug brain levels

Brain distribution and various pharmacological effects of clobazam and diazepam were studied in rats. When given at 10 mg/kg i.p. the compounds reached peak brain levels 15 min after injection, and showed similar half lives. At peak time brain levels were proportional to the dose administered. Very little of the N-desmethylmetabolite of each compound was found in the brain. Clobazam was less effective than diazepam in protecting rats from pentetrazol convulsions. Disrupting rota-rod performance and increasing punished responses in a "conflict" test, the relative potencies ranging from 4 to 8 in the various tests. The results are discussed in relation to the importance of animal species selection for predicting favourable therapeutic effects in humans.

[Some specific features of enzymatic dehydration of tetrahydro-1,4-benzdiazepine-2-one]

Differences in the dehydration rates of tetrahydro-1,4-benzdiazepine-2-one in the liver, kidney and adrenals of mice, rats and guinea pigs have been revealed. It has been found that the enzyme catalyzing the substrate conversion into its dihydroderivative is localized in the microsomal and soluble fractions of the organs tested and has a pH optimum of 9,0. The enzyme activity depends on the concentation of phosphate ions in the incubation medium.

7-Bromo-5-(2'-chlorophenyl)-1,3-dihydro-2H-1,4-benzodiazepin-2-one (I), a new tranquillizing agent: metabolism in rats

1. After intraperitoneal injection of rats with the new benzodiazepine (compound I), four metabolites (compounds II, III, IV and V) were found in the urine. 2. Compound II was identified as 7-bromo-5-(2'-chlorophenyl)-1,3-dihydro-3-hydroxy-2H-1,4-benzodiazepin-2-one by comparison of g.l.c. and mass spectral properties of the metabolite and synthetic compound. 3. Mass spectra of compound III and its acid hydrolysis products indicate that compound III contains a hydroxyl group in the C(5)-phenyl ring. 4. Compounds IV and V were identified by mass spectrometry as products of simultaneous aromatic hydroxylation and methoxylation of the diazepine I. 5. The major urinary excretion products are compounds III, IV and V. Only very small amounts of compounds I and II were detected.

[Application of immobilized animal liver microsomal fraction to the reaction of 1,4-benzdiazepine-2-one conversion]

The albino rat strain Wistar and Shynashylla rabbit liver microsomal fraction was immobilized by incorporation into polyacrylamide gel. It is shown, that the microsomal fraction immobilized by such a method catalyzes the hydrolysis of 1,4-benzdiazepine-2 ones, 3-acetoxyderivatives, hydroxylation in position 3 of 1,4-benzdiazepine-2-ones and reduction of nitrazepame. The storage thermostability and stability of the immobilized preparations were studied. Immobilization of the animal liver microsomal fraction was conducted on sylochrome by cyanuric chloride and 2,4-toluylenediisocyanate.

DNA binding, induction of unscheduled DNA synthesis, and excision of anthramycin from DNA in normal and repair-deficient human fibroblasts

The reaction of the antitumor antibiotic anthramycin with cellular DNA and the ability of normal human fibroblasts cells and xeroderma pigmentosum (XP) cells to respond to this injury has been evaluated. The binding of [15-3H]anthramycin to cellular DNA in human skin fibroblasts occurred in a linear manner up to 6 h. Treatment with unlabeled antibiotic resulted in unscheduled (repair) DNA synthesis in human skin fibroblasts maintained in hydroxyurea, whereas negligible unscheduled DNA synthesis was observed in cells of an excision-defective strain of XP. Confluent nondividing normal skin fibroblast cells were able to remove 86% of the bound anthramycin within 72 h, however XP cells were only able to remove 49% during the same incubation period. These results are discussed in terms of the types of DNA damage produced by anthramycin in vitro and the likely repair pathways involved in removing lesions produced on DNA by anthramycin.

Kinetics of biotransformation of clonazepam to its 7-amino metabolite in the monkey

The pharmacokinetic behavior of the 7-amino metabolite of clonazepam administered exogenously and formed endogenously from the parent drug was studied in a group of rhesus monkeys using constant rate intravenous infusions. Plasma levels of the 7-amino metabolite and/or clonazepam were determined with a GC-CI-MS method. The biological half-life of the 7-amino metabolite (2.2 +/- 1.0 hr) was shorter than that of clonazepam (4.9 +/- 0.2 hr). Total body clearance of the metabolite (0.83 +/- 0.16 liters/hr/kg) was larger than that of the parent drug (0.55 +/- 0.09 liters/hr/kg). The kinetics of in vivo biotransformation were described by a two-compartment model in which formation and disposition of the metabolite follow first-order processes. The fraction of a dose of clonazepam appearing in the systemic circulation as 7-amino metabolite was 0.70 +/- 0.30. This value may underestimate the actual fraction formed, if the metabolite is susceptible to first-pass metabolism following in situ formation.

Studies on the absorption, distribution and elimination of 6-o-chlorophenyl-2,4-dihydro-2(N-methyl-piperazin-1-yl)-methylene-8-nitro-1H-imidazo[1,2-a] [1,4]benzodiazepin-1-one methanesulphonate in the male rat and rabbit

The fate of a novel imidazo-benzodiazepine (I) was studied in male rats and rabbits using 14C and 3H-labelled I. In both species the compound was rapidly and widely absorbed after an oral dose of 5 mg/kg to give peak tissue and plasma levels after 1 hour in the rat and 4 hours in the rabbit. The highest concentrations of radioactivity were present in the liver (rat) and liver, kidney and subcutaneous fat (rabbit). Plasma levels of radioactivity fell to 3% of the maximum value in 24 hours in the rat but 48 hours were required for a similar fall in the rabbit. The main route of elimination of radioactivity was via the bile followed by excretion in the faeces. For the rat the rate of biliary elimination was 16.6% of the administered dose/hour; for the rabbit this rate was 5.6%/hour. Recovery of administered radioactivity during 0-24 hours for urine and faeces respectively was 4.8% and 69% for the rat and 23.2% and 10.9% for the rabbit. Up to 97% of the radioactivity administered to rats could be recovered in the excreta in the 7 days following dosing. Up to 90% of the dose administered to rabbits appeared in the excreta during 10 days. No unchanged (I) could be detected in the urine or bile. The radioactive metabolites were polar products, some of which were in the form of glucuronide conjugates.

Time-course of interaction between carbamazepine and clonazepam in normal man

The applicability of a pharmacokinetic model for drug interactions by enzyme induction was tested by chronic dosing situation using carbamazepine (Tegretol) as the inducer and clonazepam (Clonopin) as the drug affected. Seven healthy subjects received one 1.0 mg clonazepam tablet once a day for 29 days and one 200 mg carbamazepine tablet once a day from days 8 to 29. Plasma levels of clonazepam were measured by electron-capture gas-liquid chromatography and those of carbamazepine and its epoxide metabolite by gas chromatographic-chemical ionization-mass spectrometry. Clonazepam plasma levels reached an initial steady-state by day 7 and declined to a lower steady-state over 5 to 15 days after additions of carbamazepine. The decrease in clonazepam levels ranged between 19% and 37%. Autoinduction of carbamazepine metabolism was also evident. Urinary excretion of D-glucaric acid increased 2- to 4-fold following carbamazepine administration (p less than 0.005). This increase provided additional evidence that the present interaction was due to enzyme induction. Experimental clonazepam levels were fitted to an induction pharmacokinetic model for multiple dosing with an exponentially increasing clearance. Induced half-lives of clonazepam (mean = 22.5 +/- 11.5 hr) were shorter (p less than 0.005) than control values (32.1 +/- 16.6 hr). Apparent enzyme(s) turnover half-lives ranged between 1 and 6 days.

The metabolism of a substituted aminoacetamido-benzophenone and cyclization to the corresponding benzodiazepine in the rat in vivo

1. 2-(5-Cyano-N-methyl-3,5-dimethyl-3-aza-pentanamido)-5-nitrobenzophenone, administered orally to the rat, is well absorbed and extensively metabolized with only minimal quantities of parent compound detected in plasma, bile or urine. 2. Urinary t.l.c. metabolite profiles after oral administration of a substituted aminoacetamidobenzophenone, [14C]C 72 0045, and [14C]nimetazepam were qualitatively similar but differed quantitatively. 3. Analysis by t.l.c. of plasma extracts obtained after oral administration of [14C]C 72 0045 demonstrated that nimetazepam and nitrazepam accounted for 20% of the plasma total radioactivity. Nimetazepam and nitrazepam had a combined concentration up to 22 times greater than the concentration of C 72 0045. 4. The presence of nimetazepam in plasma after oral administration of C 72 0045 was confirmed by mass spectrometry. 5. In the liver, [14C]C 72 0045 was rapidly metabolized to polar metabolites. In the same rats, the major brain metabolites were nimetazepam and nitrazepam. 6. It is concluded that [14C]C 72 0045 undergoes metabolic cyclization in the rat to form nimetazepam, which is further metabolized to form nitrazepam.

[Anti-ulcer agent pirenzepine (LS 519)--a tricyclic compound with particular physico-chemical properties (author's transl)]

Compound 5,11-dihydro-11-[(4-methyl-1-piperazinyl)acetyl]-6H-pyrido[2,3-b][1,4]benzodiazepin-6-one dihydrochloride (pirenzepine, L-S 519) represents a new type of drug in ulcer therapy. It has been selected for broad clinical investigations because of its outstanding pharmacological profile. Pirenzepine is devoid of any central activity despite certain structural similarities in relation to psychotropic tricyclic compounds. The extraordinary pharmacokinetic and pharmacodynamic behaviour of this compound can be easily derived from its inherent physicochemical properties: The inability to pass the blood-brain barrier as well as its inability to activate the unspecific and specific psychotropic receptors is due to thermodynamic factors.

Concentration of clonazepam in serum and cerebrospinal fluid of the sheep

Following intravenous administration of clonazepam to sheep there was rapid equilibration of cerebrospinal fluid and unbound serum concentrations of the drug. The pharmacokinetics of clonazepam in sheep describe a 2-compartment model and the large volume of distribution suggests tissue binding of clonazepam. There was wide variation in serum concentration and at least 2 mg of clonazepam was necessary to attain the recommended therapeutic concentration.

Determination of 7-iodo-1,3-dihydro-1-methyl-5(2'-fluorophenyl)-2h-1,4-benzodiazepin-2-one (Ro 7-9957) and its major biotransformation products in blood and urine by electron capture-gas-liquid chromatography

A sensitive and specific electron capture-gas chromatographic assay was developed for the determination of 7-iodo-1,3-dihydro-1-methyl-5(2'-fluorophenyl)-2H-1,4-benzodiazepin-2-one (I) and its major metabolites in blood and urine. The overall recovery of I and its N-desmethyl metabolite (II) from blood is apparently quantitative. The recovery of the major urinary metabolite, the N-desmethyl-3-hydroxy analog (IV), and the minor metabolites, the N-desmethyl analog (II) and the N-methyl-3-hydroxy analog (III) added to urine as authentic reference standards ranged from 80 to 85%. The sensitivity limits of detection are of the order of 2-3 ng of I and 4-5 ng of II per ml of blood or urine. The method was applied to the determination of blood levels and the urinary excretion pattern in a dog following oral and intravenous administration of a 1-mg/kg dose (total 13 mg), and in man following the intravenous administration of single 5- and 10-mg doses. The N-desmethyl metabolite II was more predominant in dog blood than was the orally or intravenously administered I, but II was barely measurable in human blood.

Determination of pinazepam and its metabolites in serum, urine and brain by gas-liquid chromatography and mass spectrometry

A sensitive and specific assay, involving electron capture gas-liquid chromatography, has been developed for the identification of pinazepam and its metabolites in serum, urine and brain samples from dogs and rats after single or repeated oral administration of the drug. Serum and urine samples from healthy humans after a single oral administration have also been analysed. The identity of gas-liquid chromatographic peaks has been established by mass spectrometry. In blood serum and brain, only pinazepam and its N-depropargylated product (demethyldiazepam) were found; from urine, 3-hydroxypinazepam and oxazepam were also recovered. The sensitivity of the gas-liquid chromatographic method is of the order of 5-10 ng of pinazepam and 15-20 ng of the other three benzodiazepines per ml of serum.