Mass balance study in rats

To evaluate the pattern and the rate of excretion, the residual concentration of the drug in the body one week after administration and the estimation of the absorption in case of a relevant renal excretion. The kind of study is obligatory for the registration as a drug when the rat is chosen as rodent model (in toxicology). 

The route of administration projected to be used therapeutically should be applied also in the mass balance study. If possible and solubility allows, the study should also be performed after intravenous administration and the results of both routes should be compared. Since the oral administration is the most prominent route of administration, this route is described here. The method can be adapted for other routes of administration. 

Normally, the mass balance study is performed administering a single dose per administration route. In case of extraordinary circumstances, for instance when there is a suspicion of an accumulation of any metabolite, amass balance with repeated dosing can be considered. 

The study is performed separately from the radiokinetics blood/plasma study in rats not to influence the results by collecting blood during the study course. 

Out of eight healthy male Sprague Dawley rats weighing about 200 g corresponding to an age of 6-10 weeks, 4 rats receive an oral dose of the radiolabeled drug by using a stomach tube (typically 10 mg/kg body 

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To investigate the rate and the extent of the excretion of the drug/metabolites with the bile. If required, the investigation can be supplemented to study the entero-hepatic circle. The bile fistula study becomes necessary when relevant parts of the administered radioactivity are eliminated fecally suggesting a considerable biliary excretion during the mass balance study in rats. 

Four healthy male anesthetized Sprague Dawley (or Wistar) rats weighing about 300 g (10-12 weeks old) and provided with a permanent bile fistula receive an intravenous dose (such as 5 mg/kg for instance into the tail vein, procedure see mass balance study in rats without the necessity to use the described tube for the animals). 

A mass balance study has been performed on laromus-tine (3.b), an anticancer alkylating agent that failed during clinical trials. In male rats after 7 days, the following... 

As discussed in Section 4.2.3, the elimination of 2 -MOE partially modified AS Os is attributed to slow (but continuous) nuclease-mediated metabolism in tissue, followed by ultimate excretion of these shortened metabolites in the urine. This major elimination pathway for 2 -MOE partially modified AS Os is shown graphically in Fig. 4.9, where approximately 75% of the total radiolabeled dose is excreted in the urine by 90 days after a single dose (5 mg/kg) of [3H]-ISIS 104838 to rats [26]. Another example of the ultimate elimination of this class of compound via slow metabolism in tissues, followed by the urinary excretion of metabolites, is the mass-balance study with [3H]-labeled ISIS 113715. Here, between 8% and 37 % of administered dose was excreted within the first 24 h, followed by a daily ur-... 

HMR 1556 was a drug candidate developed for treatment of hypertension. It was 14C-labeled and investigated in a rat mass balance study to determine the pattern and rate of excretion, the residual concentrations at the end of the study 168 h after administration and the mass balance following oral and intravenous route of administration. 

Both of these approaches allow for assessment of systemic absorption by not conducting complete mass balance studies (e.g., expired air to catch absorbed compound metabolized to COj or HjO expired end products). In vivo dermal absorption studies not taking into account other routes of excretion must be interpreted with caution. One extension of this mass balance excretory analysis is to assess dermal absorption by only monitoring the primary excretory route for the compound studied. Dermal bioavailability has been assessed in exhaled breath using real-time ion trap mass spectrometry to track the uptake and ehmination of compounds (e.g., trichloroethylene) from dermal exposure in humans and rats (Poet et al., 2000). A physiologically based pharmacokinetic model can be used to estimate the total bioavailability of compoimds. The same approach was extended to determine the dermal uptake of volatile chemicals imder non-steady-state conditions using real-time breath analysis in rats, monkeys, and humans (Thrall et al., 2000). 

The mass balance approach was used to develop an in vivo animal model for skin penetration of topically applied dmgs in hairless rats (Simonsen et al., 2002). Two dmgs, C-sahcylic acid and C-butyl salicylate were topically applied for the assessment of the model. Rapid and differentiated percutaneous absorption of both compounds was indicated by urinary excretion data. Total mass balance on the applied radioactivity was performed, and 90% recovery was achieved. Carver and Riviere (1989) conducted an extensive mass balance study with " C-labeled xeno-biotics after topical and intravenous administration to pigs. These authors reported that dermal absorption of C-benzoic acid, caffeine, malathion, parathion, progesterone, and testosterone was 25.7, 11.8, 5.2, 6.7, 16.2, and 8.8%, respectively, following topical administration to pigs. 

Study shows that there are no adverse effects after administration of the material at the limit (high) dose generally used in the pharmaceutical industry. An investigative mass, balance, whole-body autoradiography study provides information on absorption, distribution, metabolism, and excretion. This study also involves an investigation of suitable labeling of the material. An in vitro metabolism study (e.g., in rat vs. human hepatocytes) may also be useful for modified food additives and excipients to compare the break-down process and to show possible differences between rat and human in these processes. 

At the early stage of compound selection and optimization for deciding a clinical candidate, drug metabolism studies are often conducted in vitro with liver fractions and in vivo with rats using nonlabeled compounds to define metabolic stability, soft-spot identification, CYP inhibition/induction potential, bioactivation or toxic metabolite formation, major in vitro metabolic pathways, and the limited in vitro interspecies comparison. Mass balance (or ADME) studies with collection of plasma in animals and humans using a... 

The in vivo rat study requires 20 aniitals at each of four doses. The doses are chosen to cover the range of exposures likely to be encountered in the field. The study requires the use of radiolabeled chemical and an appropriate field solvent. A mass balance is recjuired to account for deposited pesticide vhich msy have been lost frcro the skin surface ty a route other. .than cJermal penetration. The study is expensive and should not be initiated without consultation with Dr. Robert Zendzian of TB. 

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