4-methylpentan-2-one

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2004

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP Guideline study

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

2004

Report date:

2004

Reference 2

Reference Type:

publication

Title:

Comparative metabolism of methyl isobutyl carbinol and methyl isobutyl ketone in male rats

Author:

Gingell R, Régnier JF, Wilson DM, Guillaumat PO & Appelqvist T

Year:

2003

Bibliographic source:

Toxicology Letters 136 (2003) 199-204

Materials and methods

Objective of study:

absorption

metabolism

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Deviations:

yes

Remarks:

only 1 dose level tested

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

4-methylpentan-2-one

EC Number:

203-550-1

EC Name:

4-methylpentan-2-one

Cas Number:

108-10-1

Molecular formula:

C6H12O

IUPAC Name:

4-methylpentan-2-one

Details on test material:

- Name of test material (as cited in study report): Methyl isobutyl ketone (MIBK)
- Physical state: colorless liquid
- Analytical purity: 99.874/99.903
- Lot/batch No.: 99010101 and 40010101
- Expiration date of the lot/batch: December 2001 (batch no. 990101010)
- Stability under test conditions: Not reported
- Storage condition of test material: at room temperature and protected from light

Radiolabelling:

no

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS:
- Source: Charles River Laboratories, L'Arbresle, France
- Age at study initiation: 7 to 8 weeks old
- Weight at study initiation: mean body weight of 237 g (range: 226 to 250 g; first arrival) and mean body weight of 205 g (range: 199 to 214 g; second arrival).
- Fasting period before study: fasted for an overnight period of at least 14 hours
- Housing: 3 rats of the same group were housed in a suspended wire-mesh cage
- Individual metabolism cages: no
- Diet (e.g. ad libitum): A04 C pelleted maintenance diet, batch no. 00622 (UAR, Villemoisson, Epinay-sur-Orge, France), ad libitum
- Water (e.g. ad libitum): tap water (filtered with a 0.22 µm filter), ad libitum
- Acclimation period: 7 to 12 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21 ± 2
- Humidity (%): 50 ± 20%
- Air changes (per hr): approximately 12 cycles/hr of filtered, non-recycled air
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: Each test item was administered as a solution in the vehicle. Each test item was mixed with the required quantity of vehicle in order to achieve a concentration of 2.5 mmol/mL and then homogenized using a magnetic stirrer. The quantities of test items used for the dosage forms were calculated taking into consideration their respective molecular weight.

VEHICLE
- Justification for use and choice of vehicle (if other than water): Not provided
- Concentration in vehicle: 2.5 mmol/mL
- Amount of vehicle (if gavage): Not reported
- Lot/batch no. (if required): batch no. 89H0149 and 70K0127
- Purity: Not reported

HOMOGENEITY AND STABILITY OF TEST MATERIAL: Not reported

Duration and frequency of treatment / exposure:

Single dose exposure

Doses / concentrations

Remarks:

Doses / Concentrations:
501 mg/kg body weight (5 mmol/kg body weight; 2.5 mmol/mL)

No. of animals per sex per dose / concentration:

Test 1: 9 males
Test 2: 3 males

Control animals:

no

Positive control reference chemical:

None used.

Details on study design:

- Dose selection rationale: The 5 mmol/kg (500 mg/kg) dose was selected for this study because it is in the range of doses (1.5/6 mmol/kg) used in
previous rat oral MIBK metabolism studies (Duguay and Plaa, 1995), and approaches the limit dose (1000 mg/kg) that would be used in any OECD guideline toxicity studies for MIBC.

- Rationale for animal assignment (if not random): The required number of animals was selected according to body weight and clinical condition and allocated to the groups, according to a computerized stratification procedure, so that the average body weight of each group was similar.

Details on dosing and sampling:

Test 1 (Study No. 20991 PAR):
PHARMACOKINETIC STUDY (Absorption and metabolism)
- Tissues and body fluids sampled: blood, plasma
- Time and frequency of sampling:
Blood samples from the first 3 animals/group were sampled at 0.125, 0.75, and 3 hours post-dosing
Blood samples from the second 3 animals/group were sampled at 0.25, 1, and 4.5 hours post-dosing.
Blood samples from the third 3 animals/group were sampled at 0.5, 1.5, and 6 hours post-dosing.

Test 2 (Study No. 22776 PAR):
METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: blood, plasma
- Time and frequency of sampling: Sampled at 9 and 12 hours post-dosing
- From how many animals: 3 animals
- Method type(s) for identification: GC-MS
- Limits of detection and quantification: >0.005 mmol/L
- Other: Blood samples (1 mL per sampling) were taken into tubes containing lithium heparinate, from the orbital sinus of the animals. For the blood sampling, the animals were lightly anesthetized by isoflurane. The blood samples were kept on ice (+4 °C) until centrifugation to obtain plasma (4000 rpm for 10 min at +4°C). The plasma was stored frozen in individual tubes at -20 °C until analyzed for MIBK, methyl isobutyl carbinol (MIBC), and the common metabolite, 4-hydroxy-4-methyl-2-pentanone (HMP, which is also known as DAA).

Statistics:

Statistical analysis was not performed (not required).

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:

Following oral administration of MIBK at a nominal dose-level of 5 mmol/kg to male rats, the mean (±SD) plasma parent material levels increased quickly from the first quantifiable time-point at 0.125 hours post-gavage to reach a Cmax (0.644 ± 0.221 mmol/L) at 0.25 hours, post-gavage. Thereafter, the plasma levels fell slowly to time-point 9 hours (0.0584 ± 0.0396 mmol/L) post-gavage, after passing through a second peak at time-point 3.0 hours post-gavage (0.550 ± 0.167 mmol/L).

Toxicokinetic parameters

Toxicokinetic parameters 1

Toxicokinetic parameters:

AUC: 3.558 mmol*h/L (MIBK)

Toxicokinetic parameters 2

Toxicokinetic parameters:

AUC: 13.756 mmol*h/L (HMP)

Toxicokinetic parameters 3

Toxicokinetic parameters:

AUC: 0.089 mmol*h/L (MIBC)

Toxicokinetic parameters 4

Toxicokinetic parameters:

Cmax: 0.644 mmol/L at 0.25 h (MIBK)

Toxicokinetic parameters 5

Toxicokinetic parameters:

Cmax: 2.030 mmol/L at 9.0 h (HPM)

Toxicokinetic parameters 6

Toxicokinetic parameters:

Cmax: 0.014 mmol/L (MIBC)

Toxicokinetic parameters 7

Toxicokinetic parameters:

half-life 1st: 2.529 h (MIBK)

Toxicokinetic parameters 8

Toxicokinetic parameters:

half-life 1st: 4.831 h (HMP)

Toxicokinetic parameters 9

Toxicokinetic parameters:

half-life 1st: 4.657 h (MIBC)

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

methyl isobutyl carbinol (MIBC)
4-hydroxy-4-methyl-2-pentanone (HMP)

Any other information on results incl. tables

No mortality or morbidity was noted. No clinical signs were observed.

After administration of MIBK, the plasma primary metabolite (MIBC) levels rose slowly after gavage to a Cmax at time-point 1.0 hours (0.0118 ± 0.0046 mmol/L) and then declined slowly to time-point 9 hours (0.00610 ± 0.00043 mmol/L) post-dosing; again a secondary peak was noted at time-point 3.0 hours post-gavage (0.0143 ± 0.0001 mmol/L). The Cmax of parent MIBK (0.64 mmol/L) was reached at 0.25 hours, and levels were maintained until 3 hours then decreased with a half life of 2.5 hour. MIBK and its metabolite were no longer detected at the time-point 12 hours after dosing. The plasma secondary metabolite (HMP) levels, increased slowly after gavage to reach a Cmax at 9 hours (2.03 ± 0.07 mmol/L) post-dosing and then decline at the last time-point 12 hours after dosing (1.32 ± 0.45 mmol/L) with a half life of 3.8 hours. MIBK, as well as MIBC and HMP plasma levels showed a slight to considerable inter-animal variability. The area under the curve (AUC)(0 to12 h) for MIBK was 3.56, for MIBC was 0.09 and for HMP was 13.76 mmol*h/L. No other metabolites were present in the blood. 

Table 1: Selected Pharmacokinetic Parameters after Oral Administration of MIBK

Test Substance	Analyte	Cmax [mmole/L]	Time of Cmax[hr]	Half Life [hr]	AUC0-12hr  [mmole*hr/L]	% Total AUC
MIBK    Total AUC	MIBC	0.014	NA	4.657	0.089	0.05
	MIBK	0.644	0.25	2.529	3.558	20
	HMP	2.030	9	4.831	13.756	79
					17.436

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): no bioaccumulation potential based on study results
MIBK is rapidly absorbed into the blood, and is metabolized to HMP, which is the major material in blood after 3 hours; metabolism of MIBK to MIBC is negligible.

Executive summary:

The absorption and metabolism of MIBK was studied in male Sprague-Dawley rats orally administered a single dose of 5 mmol/kg body weight of MIBK in corn oil, equivalent to 501 mg/kg body weight, by gavage. MIBK was rapidly absorbed into the systemic circulation following oral exposure, with a mean maximum plasma concentration (C_max) of 0.644 mmol/L occurring at 0.25 hours [(time to maximum plasma concentration (t_max)] post-administration. MIBK was detected at very low levels (0.006 mmol/L) at 9 hours post-administration. The plasma levels of methyl isobutyl carbinol (MIBC) were very low (<0.012 mmol/L) all over the study. The major material in the blood was 4-hydroxymethyl-4-methyl-2-pentanone (referred to as HMP based on the chemical name) [i.e., diacetone alcohol (DAA], with a Cmax of 2.03 mmol/L at 9 hours and remained detectable at 12 hours post-dosing. Neither MIBK nor MIBC were detectable in 12-hour samples. No compounds other than HMP and MIBK were detected in the blood. The 12-hour area under the plasma concentration time curve (AUC_{0-12 h}) for MIBK, MIBC and HMP were 0.089, 3.558 and 17, 436mmol·hour/L, respectively. HMP and MIBK represented 79% and 20% of the total AUC, respectively. The plasma elimination half-life (t_1/2) of MIBK and HMP were 2.529 and4.831hours, respectively. Based on the results of this study, MIBK is rapidly absorbed into the blood in rats following oral exposure and is rapidly and extensively metabolized to HMP (the major metabolite in blood after 3 hours).