Pentanedioic acid, compd. with (1S,4R)-4-[2-amino-6-(cyclopropylamino)-9H-purin-9-yl]-2-cyclopentene-1-methanol (1:1)

Biodegradation in water: screening tests

Description of key information

Two studies have been carried out to assess the analogue materials Abacavir Succinate and Abacavir Hemisulphate for biodegradation.

Abacavir Succinate

Jenkins (1996): Substances are considered to be ultimately degradable in this test if the level of degradation achieves 60% after 28 days. The test material cannot therefore be considered to be ultimately degradable. The results of HPLC analysis at the end of the test suggests that the parent molecule may have been subject to primary degradation the extent of which ranged from 41% to 94%.

Abacavir Hemisulphate

Swarbrick & Smyth (2004): Analysis of the biotic exposure at the end of the 14 day test period showed mean degradation of equal to or >99%.

Additional information

Two studies have been carried out to assess the analogue materials Abacavir Succinate and Abacavir Hemisulphate for biodegradation.

Both studies have been carried out to OECD and GLP requirements and can therefore be considered to be reliable.

The most recent study showed the analogue material Abacavir Hemisulphate to have a mean degradation of equal to or > 99% at the end of the 14 day study period.

The earlier study indicated the analogue material Abacavir Succinate achieved 27% degradation in 28 days. As this study was carried out over a longer period of time and gave a result of not readily biodegradable, this study was considered to be the study of interest and allocated as the key study.

Jenkins (1996)

Introduction

The objective of this study was to assess the ultimate degradation of the test material Abacavir Succinate under conditions based on the Modified Sturm Test (OECD Procedure 301B). The study was designed to meet the requirements of the U.S. Food and Drug Administration's Environmental Assessment Technical Handbook, Method 3.11, Aerobic degradation in water (March 1987). The study was preceded by a five-day bacterial inhibition assay conducted under the conditions of the Closed Bottle Test (OECD Procedure 30lD).

Material and Methods

1592U89, was received on 12 April 1996 and was stored at ambient temperature, protected from light. Throughout this report, test concentrations are expressed in terms of the material as received (1592U89 succinate salt). The results of the five-day bacterial inhibition test showed that the test material at 10 mg/L did not inhibit degradation of the reference material sodium benzoate. In this preliminary test, the test material was degraded to 10% of its Theoretical Oxygen Demand (ThOD_ammonia= 1.35 mgO₂/mg).

In the main degradability test, the test material was added to three vessels containing mineral salts medium and a composite inoculum prepared from a soil suspension and sewage effluent, to give a nominal test concentration of 10 mgC/L (18.7 mg 1592U89 succinate/L). Control and reference vessels were established in triplicate and respectively contained inoculated mineral salts medium alone or inoculated mineral salts medium plus sodium benzoate (10 mgC/L). All vessels were aerated for 28 days and the CO₂produced by each culture was trapped in a series of Drechsel bottles containing barium hydroxide. The residual barium hydroxide was determined at intervals by titration.

The concentrations of 1592U89 in test and control vessels were determined by an HPLC method of analysis at the start of the test and after 27 days.

Results

Sodium benzoate was degraded to a mean of 70% after seven days and 91% after 28 days, which fulfils the validity criterion for this test (60% degradation in 28 days). The mean cumulative CO₂production in the controls after 28 days (44.5 mgCO₂) was acceptable for this type of assay system (OECD Procedure 301B recommends a maximum of 120 mgCO₂for a three-litre culture after 29 days). Degradation of 1592U89 was slow but progressive throughout the test; the mean cumulative CO₂production was equivalent to 27% of the TCO₂(range 25 to 29%) after 28 days.

HPLC analysis confirmed that at the start of the test, 1592U89 levels ranged from 93% to 97% of the intended value (18.7 mg/L). On Day 27, mean measured levels in replicates were variable and ranged from 1.11 mg/L to 10.3 mgIL (6% to 59% of the respective initial level). Final levels of 1592U89 were lower than those expected after allowance was made for the observed level of ultimate degradation in each vessel (12.5 to 13.4 mg/L), which suggests that the parent molecule may have been subject to primary degradation the extent of which ranged from 41% to 94%.

Conclusion

Substances are considered to be ultimately degradable in this test if the level of degradation achieves 60% after 28 days. The test material cannot therefore be considered to be ultimately degradable. The results of HPLC analysis at the end of the test suggest that the parent molecule may have been subject to primary degradation.

Swarbrick & Smyth (2004)

A study was conducted on the test material Abacavir Hemisulphate according to OECD Guidelines for the Testing of Chemicals (1993). Test Guideline 302B, Zahn-Wellens/EMPA Test. Adopted 17 July 1992.

Test substance concentration: 10mg/L

Duration of test: 14 days

Reference substance: Aniline (300 mg C L)

Results:

Time	Abacavir sulphate	Chemical control	Reference substance
	% degradation	% degradation	% biodegradation
0h	-	-	-
1 h	-	-	-
4 h	-	-	-
8 h	29	-	<5
2 d	96	<5	12
5 d	>99	-	86
8 d	>99	-	96
12 d	>99	-	96
14 d	>99	42	96

Comments:

Analysis of the biotic exposure at the end of the 14 day test period showed mean degradation of>99%. Analysis of the chemical control at the end of the 14 day test period showed mean degradation of 42%. It is, therefore, considered that the degradation of abacavir sulphate in this study was, predominantly, a biotic process