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Toxicological information

Direct observations: clinical cases, poisoning incidents and other

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Administrative data

Endpoint:
direct observations: clinical cases, poisoning incidents and other
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Unclear if a double-blind clinical trial. No record of performance to GCP. No control group. Dose mixing for each subject. Very limited number of subjects in trial. Results should be treated as preliminary at best.

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
1990
Report Date:
1990

Materials and methods

Study type:
study with volunteers
Endpoint addressed:
basic toxicokinetics
Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
Pharmacokinetic clinical trial using randomized oral dosing of a weekly dose of the test substance for three weeks to six volunteers with measurement of plasma concentrations of benzoic acid and hippuric acid and urinary concentrations of hippuric acid.
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Details on test material:
No data given

Method

Type of population:
general
Subjects:
- Number of subjects exposed: six
- Sex: male
- Age: 22 to 34 y (mean 28.8 y)
- Race:
- Demographic information:
- Known diseases: No
- Other:
Ethical approval:
confirmed and informed consent free of coercion received
Route of exposure:
oral
Reason of exposure:
intentional
Exposure assessment:
measured
Details on exposure:
Three different doses (40, 80 and 160 mg/kg) of the substance dissolved in 300 mL water were orally administered to each volunteer in randomized sequence, at least one week apart. The volunteers ate a constant diet containing 1.5 g/kg/day protein for 3 days before each of the trial days. Subjects fasted for 6 h after dosing but with free access to tap water.
Examinations:
Benzoic acid and hippuric acid in plasma and urine were determined: Blood samples were collected at 0 (predose), 0.5, 1, 1.5, 2, 3, 4.5, 6, 9 and 12 h postdose. Urinary samples were collected at the following intervals: - 1.5 to 0 (baseline), 0 to 1.5, 1.5 to 3, 3 to 4.5, 4.5 to 6, 6 to 9, 9 to 12 and 12 to 24 h postdose.
Medical treatment:
None stated

Results and discussion

Clinical signs:
No information provided
Results of examinations:
Individual data on plasma benzoic acid and hippuric acid concentrations and % dose of hippuric acid excreted in urine with time in the six volunteers are shown in Fig. 1 (see attached document).
The post-absorption phase benzoic acid concentration-time curves revealed a so-called "hockey stick" appearance, and the slopes of the "shafts" increased with increasing doses of the test substance, as seen in Fig. 1 (left panel). The mean values for the declining slopes of the plasma benzoic acid concentration-time data were 35.3, 75.6 and 84.7 μg.mL/h after the test substance 40, 80 and 160 mg/kg. Plasma hippuric acid concentrations rose rapidly and the observed Cmax values were comparable after the three doses (Fig. 1, middle panel). The urinary excretion rates of hippuric acid ranged from 0.087 to 0.377 mg/kg/h when no test substance was administered. The cumulative urinary excretion of hippuric acid reached a plateau by 6 h after the 40 and 80 mg/kg doses in all individuals (right panel) and by 12 h after the 160 mg/kg dose in 4 of 6 individuals.
The relationships between the dose of the test substance and the AUC of benzoic acid and between the dose of test substance and the AUC of hippuric acid are illustrated in Fig. 2 (attached document). There was a disproportionate increase in the AUC of benzoic acid (left panel), but not of hippuric acid (right panel), with increasing doses of test substance. The corresponding mean AUC values of plasma benzoic acid after test substance 80 and 160 mg/kg were 3.7 and 12.0 times greater than after the 40 mg/kg dose. The mean AUCs of hippuric acid, however, were roughly proportional to the dose of test substance, the mean AUCs after the doses of 80 and 160 mg/kg test substance being 2.0 and 4.2 times greater than after 40 mg/kg.
The mean cumulative amounts of hippuric acid excreted in urine were 82.9 (4.7), 90.3 (5.4) and 73.1 (2.1) % of the administered doses of 40, 80 and 160 mg/kg test substance, respectively. 
Effectivity of medical treatment:
No information provided
Outcome of incidence:
No information provided

Any other information on results incl. tables

Model-independent pharmacokinetic parameters of benzoic acid and hippuric acid

Dose of the test substance (mg/kg)

Benzoic acid

Hippuric acid

Cmax(μg/mL)

tmax(h)

AUC (μg·h/mL)

Cmax(μg/mL)

tmax(h)

AUC (μg·h/mL)

Ae (% of dose)

CLR(L/h/kg)

40

99.7

0.5

104.4

30.9

1.3

53.7

82.9

0.53

80

202.8

0.8

385.4

35.0

2.1

109.3

90.3

0.57

160

336.5

1.8

1257.0

36.9

4.1

223.5

73.1

0.45

Cmax=maximum plasma concentration;

tmax=time to reach maximum concentration;

AUC=the area under the plasma concentration-time curve;

Ae=amount of hippuric acid excreted in urine extrapolated to infinity.

Applicant's summary and conclusion

Conclusions:
The results showed that the AUC of benzoic acid, but not of hippuric acid, increases disproportionately with increasing oral doses of the test substance from 40 to 160 mg/kg: the respective AUCs of benzoic acid after the 80 and 160 mg/kg doses were 3.7 and 12.0 times greater than after the 40 mg/kg dose. This finding indicates that the biotransformation of benzoic acid to hippuric acid follows saturable or Michaelis-Menten kinetics in humans following oral the test substance. Indeed, the graph of the test substance dose versus the AUC of benzoic acid showed a curvilinear relationship, like that derived from Michaelis-Menten kinetic behaviour.
Executive summary:

Plasma concentration-time data for benzoic and hippuric acids and urinary excretion-time data for hippuric acid were analyzed simultaneously after oral doses of 40, 80 or 160 mg/kg the substance administered at least one week apart to 6 healthy subjects. The mean AUCs of benzoic acid after the doses of 80 and 160 mg/kg of the substance were 3.7 and 12.0 times greater, respectively, than after 40 mg/kg. However, the mean AUC of hippuric acid was roughly proportional to the test substance doses. The observed data were explained by a onecompartment model with first-order rate absorption and Michaelis-Menten elimination of benzoic acid, together with a one-compartment model with first-order elimination for hippuric acid.