Isobutyl isobutyrate

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

9/14/2001 - 5/11/2003

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

Study was conducted at GLP facility to OECD guidelines

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2005

Materials and methods

Objective of study:

toxicokinetics

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Isobutyl isobutyrate

EC Number:

202-612-5

EC Name:

Isobutyl isobutyrate

Cas Number:

97-85-8

Molecular formula:

C8H16O2

IUPAC Name:

2-methylpropyl 2-methylpropanoate

Radiolabelling:

no

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

Male Sprague Dawley rats [CRL:CD(SD)IGS BR] were purchased from Charles-River Laboratories. This species and strain has been used extensively for toxicity testing. The test animals were young adults at the start of the study, weighing between 250 and 400 g (approximately 8- 11 weeks of age). For the dose selection studies, animals previously implanted with only a femoral vein cannula were purchased. For the in vitro analytical stability studies, uncannulated animals were used. For the probe and definitive iv dose pharmacokinetic studies, animals were purchased with both femoral and jugular vein Teflon® cannula implanted. The cannulated animals were not held in isolation upon receipt, and the cannula were flushed and refilled as prescribed by Charles River Laboratories until the in-life portion of the study was completed. Animals were selected from the study animal pool using a random number generator (Hewlett-Packard 32S IT scientific calculator). The calculator requires a seed number to generate the first random number. That random number then becomes the seed for the next random number. A seed number consisting of 6 digits representing the month, day, and year of the study was used.

The non-cannulated animals were housed in wire-mesh, stainless-steel cages. Cages and racks were washed once per week. Absorbent paper, used to collect excreta, was changed daily. Cannulated animals were housed in polycarbonate "shoe-box" rodent cages with wood chip bedding; the bedding was changed 3 times per week. Room lighting followed a 12-hour light/dark cycle. Room temperatures and relative humidities were maintained at target levels of 22 ± 4 °C and 30 to 70%, respectively. Ventilation was provided at a rate of at least 10 to 15 room changes per hour. Animals were fed certified rodent diet (PMI, Inc., 5002) ad libitum. Domestic tap water (Monroe County Water Authority, NY) was available ad libitum

Administration / exposure

Route of administration:

intravenous

Vehicle:

other: Saline with 1% Tween 20

Details on exposure:

Prior to dose administration (time zero), an approximately 150 uL blood sample was aspirated from the jugular cannula into a heparinized (1IU) length of 0.85 mm ID Teflon tubing. A small portion of this sample was used for hematocrit determination, and the balance was transferred into a tared 1.5 mL polypropylene tube containing a weighed amount (nominally 100 mg) of an internal standard solution. The internal standard solution consisted of 0.4 M aqueous sulfuric acid containing 203.8 uM 2-pentanol, 203.8 uM 2-heptanone, and 206.2 uM n-butyric acid. IBIB was prepared as an emulsion at 125 mM in 0.9% saline containing 1%Tween 20 as an emulsifying agent. The mixture was prepared gravimetrically and then homogenized for 60s (Polytron with PT42-2K generator, Brinkman Instruments, Westbury NY) to form a foamy emulsion. Over several hours, the air whipped into the emulsion would rise to the top and escape, leaving a creamy top layer and a milky base. These two layers could be easily mixed to form a uniform suspension by manually swirling the container. For dose administration, the suspension was aspirated into a 1 mL glass/Teflon gas-tight syringe and administered over 2 to 3 s as a single, bolus injection at 5 ml/kg via the femoral vein cannula.

Duration and frequency of treatment / exposure:

Serial blood samples were collected every 10 seconds over 20 sample times.

Doses / concentrations

Dose / conc.:

125 other: uM/kg

No. of animals per sex per dose / concentration:

6 male rats at one dose level. The concentration was the highest non-sedating concentration.

Control animals:

no

Positive control reference chemical:

no

Details on study design:

Rats were administered a bolus dose of IBIB via a jugular catheter, and blood samples were collected every 10 seconds and analyzed for concentrations of IBIB and putative metabolites.

Details on dosing and sampling:

Rats were administered a bolus dose of IBIB via a jugular catheter, and blood samples were collected every 10 seconds and analyzed for concentrations of IBIB and putative metabolites.

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on excretion:

IBIB was administered as a bolus dose at 125 ,umol/kg (1 ml/kg) via a femoral vein Teflon cannula, and samples were rapidly collected from the jugular vein Teflon cannula using a chemically inert, micro-volume sampling tee on a total of seven male Sprague-Dawely rats. These animals typically displayed a mild reaction to the dose consisting of brief (5 s) agitation followed by brief disorientation or partial anesthesia of variable intensity lasting 15 to 20 s. No depression of respiratory rate was observed. Accurate clinical observations were complicated by the level of animal restraint required for dose administration and immediate sample collection. Nineteen or twenty blood samples (plus a blank predose sample) of approximately 80 to 100 uL each were collected from each rat over an approximately 220 s period postdosing. Of the seven animals administered the 125 umol/kg IBIB iv bolus dose, one animal (rat# N6926, 5/8/03) appears to have received a partial dose, judging from his reaction to the administration (no anesthetic effect noted) and the low levels of IBIB and metabolites measured in the blood. The data for this animal are not included in PK data reported here. The IBIB parent compound concentrations were found to be high, and quite variable in the initial blood samples collected following the dose administration. IBIB concentrations fell rapidly in subsequent samples, and were below the limit of quantitation of the method in all animals by approximately 90s following the dose. The estimated blood elimination half-life for IBIB from the pooled data from the 6 animals is 11.1 seconds. This estimate excludes samples with IBIB concentrations above (2042 uM, 1 sample) or below (10.4 uM, 26 samples), which are beyond the limits of quantitation of the analytical method. Many blood samples collected beyond 60 to 90 sec post dosing contained low, slowly declining levels of IBIB, probably resulting from carryover of IBIB in the sampling tee from the very high concentration early samples. IBOH levels were substantial in the earliest blood samples collected following the IBIB bolus dose, and increased during the first half minute of sample collection before declining slowly in subsequent samples. Pharmacokinetic analysis of the IBOH concentrations estimated a maximum IBOH concentration of 194 uM at 37 s, with a blood elimination half -life of 115 s. IBA concentrations measured in rat blood following the IBIB dose administrations were somewhat higher, but similar in kinetics to those for IBOH. The estimated maximum blood concentration for IBA was 279 uM at 41.5 s, with an estimated blood elimination half-life of 87 s.

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

Hydrolysis meatbolites isobutanol and isobutyric acid were identified.

Any other information on results incl. tables

PK Parameter	IBIB	IBOH	IBA
PK Model Type	One compartment, Bolus input, First-order output	One compartment, Bolus input, First-order output,	One compartment, Bolus input, First-order output
Kelim	0.06238	0.00604	0.00801
Kelim Half	11.1 s	114.8 s	86.5 s
Tmax	N A (bolus dose)	36.7	41.5
Cmax	N A (bolus dose)	194.4	279.2
Pharmacokinetic values estimated from the pooled blood data of six male SD rats administered a 125 umol/kg IBIB iv bolus dose. The IBIB estimates exclude samples with IBIB concentrations above (2042 uM 1 sample) or below (10.4 uM.26 samples), which arc beyond the limits of quantitation of the analytical method.

Applicant's summary and conclusion

Conclusions:

These data indicate that IBIB, even at high blood concentrations, is very rapidly hydrolyzed to its component alcohol and acid in vivo, which in turn are quickly eliminated from the bloodstream of male rats.

Executive summary:

The objective of these studies was to determine the blood elimination rate of intravenously administered isobutyl isobutyrate (IBIB) in male ratsin vivo.IBIB was administered to male Sprague-Dawely rats as a bolus dose at 125 umol/kg (1 ml/kg) via a femoral vein Teflon® cannula. This dose level was found to be the maximum tolerated iv dose of IBIB thatdidnot produce severe anesthetic effects in the rats. Serial blood samples were collected rapidly (approximately every 10 sec) from the jugular vein Teflon® cannula, and the elimination of IBIB and the formation of the postulated metabolites isobutyl alcohol (IBOH) and isobutyric acid (IBA) were monitored by chromatographic analysis of the serial blood samples. IBIB concentrations were found to be high and variable in the initial blood samples collected following the dose administration, fell rapidly in subsequent samples, and were below the limit of quantitation in all animals by approximately 90s following the dose. The estimated blood elimination half-life for IBIB from the pooled data from 6 animals is 11.1 seconds. IBOH levels were substantial in the earliest blood samples collected following the IBIB bolus dose, and reached an estimated maximum concentration of 194,uMat 37s, with an estimated blood elimination half-life of 115 s. IBA concentrations measured in rat blood following the IBIB dose administrations were somewhat higher, but similar in kinetics, to those for IBOH. The estimated maximum concentration for IBA was 279uMat 41.5 s, with an estimated elimination half-life of 87 s. These data indicate that IBIB, even at high blood concentrations, is very rapidly hydrolyzed to its component alcohol and acidin vivo,which in turn are quickly eliminated from the bloodstream of male rats.