Trometamol

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Effect on fertility: via oral route

Dose descriptor:

NOAEL

1 000 mg/kg bw/day

Additional information

A reproduction/developmental toxicity screening test was performed with 2-amino-2-(hydroxyl methyl)-1,3-propanediol (trometamol) according to OECD 421, to assess the potential reproductive and fertility effects of trometamol (Ellis-Hutchings, 2012). Doses of 100, 300 and 1000 mg/kg bw/day of the test substance were administered by gavage to rats during pre-mating, mating, gestation and until lactation day 4. The males were exposed for 29 days and the females for up to 54 days. The test substance was adjusted to pH 9 due to animal welfare considerations. As no systemic effects were observed up to and including the highest dose level, the NOAEL for systemic toxicity is considered to be ≥ 1000 mg/kg bw/day. Irritation effects on the limiting ridge of the forestomach were attributed to the local irritating effect of trometamol. This effect is not relevant to humans, as they do not have a forestomach. However, the observation leads to a NOAEL for local toxicity of 100 mg/kg bw/day. In the parental generation, the reproduction parameters (including mating index, fertility index, gestation period, delivery index, and number of live pups) were not affected by treatment with the test substance up to and including the highest dose level of 1000 mg/kg bw/day. The NOAEL for reproduction is therefore considered to be ≥ 1000 mg/kg bw/day.

 

In the pups (F1-generation), no effects on viability were observed. The body weight of male pups in the 250 mg/kg bw/day group was significantly increased, compared to that of the control group, at the time of birth. As it was not dose-related, only observed in one sex and at one time point, it is considered to have no biological significance. No treatment-related histopathological findings were noted at study termination. A statistically significant difference in the sex ratio (No. males/No. live born pups = 0.64) was observed in the control group only and is considered to be incidental. Therefore, the NOAEL for teratogenicity was considered to be ≥ 1000 mg/kg bw/day.

 

Potential analogues for the target substance trometamol are other 2-amino-1,3-propanediols. Therefore, source substances are members of the aminopropanediol category: 2-amino-2-ethyl-1,3-propanediol (AEPD), 2-amino-2-methyl-1,3-propanediol (AMPD) and 2-amino-1,3-propanediol (APD). Trometamol and the 2-amino-1,3-propanediols are expected to show comparable toxicokinetic characteristics, and it is anticipated that the absorbed amounts of all the aminopropanediols have limited systemic bioavailability and are rapidly eliminated by the kidneys. No relevant metabolism is expected, based on experimental data and on QSAR predictions. The modelling of potential metabolites using the OECD QSAR toolbox v.2.0 (2010) did not predict relevant metabolites of TROMETAMOL or of any of the 2-amino-1,3-propanediols. Therefore, no metabolism by cytochrome P450 enzymes in-vivo is expected.

 

Available studies via the oral, dermal or intraperitoneal route on these substances caused no systemic toxicity. The results of the acute studies, as well as the repeated dose studies, demonstrate that the main cause of toxicity was the intrinsic alkalinity of the respective test substances at the site of contact. Inhalation is of no concern, because the low vapour pressure of the pure substances means that exposure is unlikely to occur. In case of spray applications of technical products containing the neat substance, the concentration is very low (< 1%). The Cramer classification (related mainly to the oral route) also indicates a low toxicological concern for TROMETAMOL and the 2-amino-1,3-propanediols. Thus, both trometamol and 2-amino-1,3-propanediols are of low concern with regard to systemic toxicity. Due to the structural similarity and the similar toxicological properties between TROMETAMOL and the 2-amino-1,3-propanediols, read-across using an analogue approach is justified.

 

A combined oral repeated dose toxicity study and reproduction/developmental toxicity screening test was also performed with AEPD, according to OECD 422 (Ishida, 2004). No effects on reproduction or fertility and no systemic toxicity were observed up to and including the highest dose level of 1000 mg/kg bw/day. This result supports the hypothesis that aminopropanediols show no toxicity to reproduction, and is in line with Regulation (EC) 1907/2006, Annex XI regarding the use of data on similar or surrogate substances as part of a weight of evidence approach to cover an endpoint.   

 

According to Regulation (EC) 1907/2006, Annex IX, a tiered approach should be applied to determine if further testing is required for the endpoint toxicity to reproduction. If effects on reproduction parameters are noted in a subacute or sub-chronic repeated dose toxicity study, a 2-generation reproduction toxicity study should be performed.  

 

In a GLP-compliant sub-chronic toxicity study according to OECD 408, rats were administered 0, 62.5, 250 or 1000 mg/kg bw/day of the analogue substance APD via gavage for 90 consecutive days. There were no deaths and no treatment- related clinical signs, changes in body weights, body weight gains or food consumption during the study. Animals receiving 1000 mg/kg bw/day APD had altered haematology parameters indicative of a compensatory anaemia due to stomach ulcers in the glandular mucosa. Serum calcium was also elevated in high-dose animals. No effects were observed on female and male reproductive organs, and on sperm parameters. Liver, kidney and epididymis organ weights were increased at the high-dose which were associated with minimal histopathological alterations. No treatment-related effects were observed at lower dose levels. Based on these results the NOAEL in the 90-day study was determined to be 250 mg/kg bw/day.

 

In summary, trometamol shown to have low bioavailability via the oral route of exposure in humans. Low oral bioavailability of trometamol is supported by the minimal systemic toxicity observed in repeated-dose studies by the oral route across multiple species. Because trometamol is a proton acceptor with a pK of 7.8, it is an effective buffer that can be used to maintain the pH of body fluids. Thus, much of the available toxicity data is via the intravenous route of exposure. Intravenous toxicity of trometamol was minimal at neutral pH. In an alkaline pH range trometamol caused irritation and secondary effects associated with the intrinsic alkalinity of trometamol at the site of contact. There is no historical evidence that trometamol causes adverse effects on reproduction from the available human and animal studies. Additionally, there were no adverse effects on reproduction in a screening reproductive and developmental toxicity study in rats at doses up to 1000 mg/kg/day for the target substance trometamol and the source substance AEPD. These data together with trometamol’s historical safe use in medical and leave-on cosmetic formulations provide strong support that trometamol does not pose a risk to reproduction. 

 

Literature not cited in IUCLID

·        Ishida, 2004, 2-Amino-2-ethyl-1,3-propanediol toxicity tests for Acute oral, Repeated dose and Reproductive/Developmental Toxicity and Genetic Toxicity. Report no. R-870

 

Short description of key information: 

Reproduction/developmental toxicity screening study (OECD 421), rat, oral:  

NOAEL systemic (P, F1) ≥ 1000 mg/kg bw/day  

NOAEL fertility (P) ≥ 1000 mg/kg bw/day  

NOAEL reproduction (P) ≥ 1000 mg/kg bw/day  

NOAEL local (P) ≥ 100 mg/kg bw/day

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Effects on developmental toxicity

Description of key information

NOAEL teratogenicity (F1) ≥ 1000 mg/kg bw/day

Effect on developmental toxicity: via oral route

Dose descriptor:

NOAEL

1 000 mg/kg bw/day

Additional information

There are no animal data available that assesses the potential developmental toxicity of 2-amino-2-(hydroxymethyl)-1,3-propanediol (trometamol) alone. However, a reproduction/developmental toxicity screening test was performed with trometamol according to OECD 421, to assess the potential reproductive and fertility effects of trometamol (Ellis-Hutchings, 2012). No adverse effects on developmental parameters (including number of live pups, viability, body weight, sex ratio) in the F1-generation were observed following treatment with doses of TROMETAMOL up to and including 1000 mg/kg bw/day.

 

In addition, there are reliable data for other substances considered suitable for read-across using the analogue approach. Potential analogues for the target substance trometamol are other 2-amino-1,3-propanediols. Therefore, source substances are members of the aminopropanediol category: 2-amino-2-ethyl-1,3-propanediol (AEPD), 2-amino-2-methyl-1,3-propanediol (AMPD) and 2-amino-1,3-propanediol (APD). Trometamol and the 2-amino-1,3-propanediols are expected to show comparable toxicokinetic characteristics, and it is anticipated that the absorbed amounts of all the aminopropanediols have limited systemic bioavailability and are rapidly eliminated by the kidneys. No relevant metabolism is expected, based on experimental data and on QSAR predictions. The modelling of potential metabolites using the OECD QSAR toolbox v.2.0 (2010) did not predict relevant metabolites of trometamol or of any of the 2-amino-1,3-propanediols. Therefore, no metabolism by cytochrome P450 enzymesin vivois expected.

 

Available studies via the oral, dermal or intraperitoneal route on these substances also caused no systemic toxicity. The results of the acute studies, as well as the repeated dose studies, demonstrate that the main cause of toxicity was the intrinsic alkalinity of the respective test substances at the site of contact. Inhalation is of no concern, because the low vapour pressure of the pure substances means that exposure is unlikely to occur. In case of spray applications of technical products containing the neat substance, the concentration is very low (< 1%). The Cramer classification (related mainly to the oral route) also indicates a low toxicological concern for trometamol and the 2-amino-1,3-propanediols. Thus, both trometamol and 2-amino-1,3-propanediols are of low concern with regard to systemic toxicity Due to the structural similarity and the similar toxicological properties between trometamol and the 2-amino-1,3-propanediols, read-across using an analogue approach is justified.

 

In a combined oral repeated dose toxicity and reproduction/developmental toxicity screening study according to OECD 422, no adverse effects on developmental parameters (including number of live pups, viability, body weight, sex ratio) in the F1-generation were observed following treatment with doses of AEPD up to and including 1000 mg/kg bw/day (Ishida, 2004).

 

In addition, in a non-guideline reproduction/developmental toxicity screening study, the potential of AMPD to cause reproductive and developmental toxicity in rats was investigated (Rasoulpour and Andrus, 2011). Female rats were administered AMPD from before mating until gestation day 14. During the pre-mating period the groups were administered either increasing doses from 100 up to 1000 mg/kg bw/day (34 days) or 1000 mg/kg bw/day, the limit dose (6 days). The rats were sacrificed on gestation day 14 and examined. No differences were observed between the control group and the treatment groups regarding numbers of corpora lutea, implantation rates and implantation position, resorption rates, pre-implantation loss, post-implantation loss, pup viability and number of normal embryos per litter. The examination of the reproductive tract did not reveal treatment-related effects.

 

The potential of AMPD to cause embryotoxicity was assessed in an in-vitro limb bud micromass assay by exposing undifferentiated rat embryo limb bud mesenchymal cells to AMPD concentrations of 0.01 to 1000 µM in the cell culture medium (Ellis-Hutchings and Marshall, 2011). Following cell differentiation into chondrocytes, specific parameters (cell differentiation, cell viability, cell number, neutral red uptake, cell growth) were determined. Under the scope of the assay, the results predict a lack of developmental toxicity for AMPD.

 

The studies performed with trometamol, AMPD and AEPD support the hypothesis that aminopropanediols have the same toxicity profile with respect to systemic toxicity and, specifically, developmental toxicity. In line with Regulation (EC) 1907/2006, Annex XI, the available data on these substances are used as part of a weight of evidence approach to show that no toxicity to reproduction is likely to occur.

 

An OECD 414 guideline developmental toxicity study in rats is available for the source substance ADP. Female rats were treated daily by oral gavage to 0, 100, 300 or 1000 mg/kg bw/day from gestation day 6 (GD 6) through gestation 19 (GD 19). No clinical signs of maternal toxicity were observed up to the highest dose level of 1000 mg/kg bw/day. There were no toxicologically relevant adverse effects on foetal parameters or external, visceral or skeletal malformations in any treated group. Skeletal variations ascribed to slightly delayed ossification occurred in a small number of fetuses at 1000 and 300 mg/kg bw/day. No signs of maternal toxicity were detected during the study based on clinical signs and bodyweight; however, in the 90-day rat repeated dose toxicity study with this test item, systemic toxicity was observed, in the absence of body weight or clinical signs. The foetal skeletal findings were considered to reflect a non-adverse, slight retardation of ossification. The NOAEL maternal toxicity, fetal toxicity and foetal malformations/skeletal development was determined to be 1000 mg/kg bw/day. The NOEL for skeletal development was 100 mg/kg bw/day.

In the available standard guideline teratogenicity study for the source substance APD, there is no evidence of developmental toxicity, only slight developmental delay which was attributed to maternal toxicity. Reproductive screening studies for the target substance trometamol and source substance AMPD did not induce developmental effects at the highest dose tested of 1000 mg/kg bw/day. AMDP was not embryo toxic inlimb bud micro-mass. In accordance with Regulation (EC) 1907/2006, Annex XI, which specifies that read-across of data from a suitable substance may be used to avoid unnecessary animal testing, no further testing in rabbits is necessary to assess the developmental toxicity of the target substance, trometamol.

Literature not cited in IUCLID

·        Ellis-Hutchins and Marshall, 2011, ANGUS MOLECULES (DMAMP, AMPD AND 3-AB): IN VITRO EMBRYOTOXICITY SCREENING STUDY IN THE RAT EMBRYO LIMB BUD MICROMASS ASSAY, Report no. 100118, Company study no. DR-0050-0118-010

 

·        Rasoulpour and Andrus, 2011, ANGUS MOLECULES (DMAMP, AMPD AND 3-AB): IN VIVO DEVELOPMENTAL TOXICITY SCREENING STUDY IN Crl:CD(SD) RATS, Report no. 100176, Company study no. DR-0050-0118-011

 

·        Ishida, 2004, 2-Amino-2-ethyl-1,3-propanediol toxicity tests for Acute oral, Repeated dose and Reproductive/Developmental Toxicity and Genetic Toxicity. Report no. R-870

 

Justification for classification or non-classification

The available data on the reproduction, fertility and teratogenic toxicity, and on effects on or via lactation of the test substance do not meet the criteria for classification according to Regulation (EC) 1272/2008 or Directive 67/548/EEC, and are therefore conclusive but not sufficient for classification.