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Endpoint:
basic toxicokinetics, other
Type of information:
other: Expert statement
Adequacy of study:
weight of evidence
Study period:
29 April 2019
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: Expert statement
Objective of study:
other: Toxicokinetics expert statement
Qualifier:
no guideline required
GLP compliance:
no
Specific details on test material used for the study:
Substance name: Balsalazide acid
CAS No.: 80573-04-2
EC No.: 617-116-8

Relevant physico-chemical properties:
Molecular weight: 357.32
Water solubility: 1.62 g/L at 20 °C (Fragomeni V., 2018))
Octanol-water 1.00 (Fragomeni V., 2018)
partition coefficient
(log Pow):
Vapour pressure: 3.80E-05 Pa (Urbani M., 2018)
Details on absorption:
ORAL ROUTE
Balsalazide acid absorption is predicted to be very limited via the oral route (based on human clinical evidence on the sodium salt of balsalazide acid – refer to IUCLID endpoint summaries; human clinical evidence 1 and 2). It should be noted that the absorption referred to in pharmacological terminology is actually the oral bioavailability, which was < 1% of applied dose. Actual absorption from the GI tract may have been higher than this, with subsequent reduction of the compound in the liver via the first pass effect prior to systemic availability. It should also be noted that Balsalazide (sodium salt) is designed to remain intact and have minimal absorption/first-pass effect, in order to be able to deliver a therapeutic effect in the colon in ulcerative colitis sufferers, by virtue of azo-reduction of the molecule by bacteria in the colon. In order to do this, without over-dosing to achieve the therapeutic effect, its absorption in the small intestine must be low.

INHALATION ROUTE
Balsalazide acid is predicted to have low (but not necessarily negligible) absorption via the inhalation route, based on low oral absorption.

DERMAL ROUTE
Balsalazide acid is predicted to have very low absorption via the dermal route, based on low oral absorption and the fact that dermal absorption is usually lower than oral absorption.
Details on distribution in tissues:
There is minimal available information relating to distribution. Distribution of Balsalazide acid (sodium salt) to organs was not assessed in human clinical trials and the data is missing from the available information on the animal TK study.
Details on excretion:
The majority (approx. 65%) of the Balsalazide (sodium salt) dosed (in clinical trials) was detected in the faeces as both ABA and ASA and their N-acetylated metabolites (NABA and NASA). Balsalazide (sodium salt) was recovered in the urine of all the subjects although the quantities were very limited.
In a rat oral TK test, following a single oral dose, 4-ABA (one of the metabolites) was found in large quantities in faeces and in small amounts in the plasma. The majority (approx. 92%) of the applied radioactivity was found in the faeces and a small (approx. 5-8%) amount in the urine for both dose levels. In the urine, low amounts of Basalazide (sodium salt) were recovered, with the major metabolite being NABA.
Metabolites identified:
yes
Details on metabolites:
Four main metabolites have been identified in human clinical trials and in rat ADME:

1). 5-aminosalicylic acid (ASA, derived from Azo-reductase of the Balsalazide acid (sodium salt)
2). N- acetyl-5-amino-salicylic acid (NASA, derived by N-acetylation of ASA)
3). 4-aminobenzoyl-5-alanine (ABA, derived from Azo-reductase of the Balsalazide acid (sodium salt)
4). N-acetyl-4-aminobenzoyl-5-alanine (NABA, derived by N-acetylation of ABA)
Conclusions:
ABSORPTION
Balsalazide acid absorption is predicted to occur to a small extent via the oral route.
Balsalazide acid is predicted to have low (but not necessarily negligible) absorption via the inhalation route.
Balsalazide acid is predicted to have very low absorption via the dermal route.

DISTRIBUTION
There is minimal available information relating to distribution.

METABOLISM
Four main metabolites have been identified in human clinical trials and in the rat TK study and these are expected to be the same for Balsalazide acid:

1) 5-aminosalicylic acid (ASA, derived from Azo-reductase of the Balsalazide acid (sodium salt)
2) N- acetyl-5-amino-salicylic acid (NASA, derived by N-acetylation of ASA)
3) 4-aminobenzoyl-5-alanine (ABA, derived from Azo-reductase of the Balsalazide acid (sodium salt)
4) N-acetyl-4-aminobenzoyl-5-alanine (NABA, derived by N-acetylation of ABA)

EXCRETION
Balsalazide acid is predicted to be predominantly excreted via faeces in the form of its metabolites ABA and ASA and their N-acetylated metabolites (NABA and NASA). Very limited amounts of Balsalazide acid is predicted to be excreted via urine.
Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
Not specified
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Objective of study:
toxicokinetics
Qualifier:
no guideline followed
Principles of method if other than guideline:
- Principle of test:
- Short description of test conditions: radiolabelled Basalazide sodium (BSZ) was administered to rats as a single i.v. dose at 120 mg/kg
- Parameters analysed / observed: Blood, urine and Faeces was sampled and levels of BSZ and its metabolites were determined. Tissue samples from a variety of organs were collected for distribution study. Radioactivity was determined via LSC.
GLP compliance:
not specified
Specific details on test material used for the study:
The study was performed on balsalazide disodium, but it will reach a common moiety in the blood after oral dosing , whether BSZ or BSA.
Radiolabelling:
yes
Species:
rat
Strain:
not specified
Sex:
not specified
Route of administration:
oral: gavage
Vehicle:
not specified
Duration and frequency of treatment / exposure:
Single dose
Dose / conc.:
120 mg/kg bw/day (actual dose received)
Dose / conc.:
2 000 mg/kg bw/day (actual dose received)
No. of animals per sex per dose:
Not stated
Control animals:
no
Positive control:
Not stated
Details on dosing and sampling:
TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood
- Time and frequency of sampling: 1,3,6,9,12,18 and 24 hours after dosing

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: urine, faeces, tissues,
- Time and frequency of sampling: 1,3,6,9,12,18 and 24 hours after dosing
- Method type(s) for identification HPLC-UV, Liquid scintillation counting
Statistics:
None specified
Type:
absorption
Results:
Oral bioavailability was very low (0.52-0.62%)
Type:
distribution
Results:
Missing page in review document. No distribution information available
Type:
metabolism
Results:
Four metabolites were formed. 5-amino salicylic acid (ASA) which is N-acetylated to N-acetyl-5-amino-salicylic acid (NASA). 4 aminobenzoyl-5-alanine (ABA) which is N-acetylated to N-acetyl-4-aminobenzoyl-5-alanine (NABA).
Type:
excretion
Results:
Following a single oral dose, 4-ABA (one of the metabolites) was found in large quantities in Faeces and in small amounts in plasma. The majority of the applied radioactivity (approx 92%) was found in the faeces and a small (approx 5-8%) in the urine.
Details on distribution in tissues:
No information available.
Details on excretion:
Following a single oral dose, 4-ABA (one of the metabolites) was found in large quantities in Faeces and in small amounts in plasma. The majority of the applied radioactivity (approx 92%) was found in the faeces and a small (approx 5-8%) in the urine for both dose levels. In the urine, low amounts of basalazide acid (sodium salt) was recovered with the major metabolite being NABA.
Metabolites identified:
yes
Details on metabolites:
Four metabolites were reported. These were assigned as:
1) 5-aminosalicylic acid (ASA)
2) N- acetyl-5-amino-salicylic acid (NASA, derived by N-acetylation of ASA)
3) 4-aminobenzoyl-5-alanine (ABA)
4) N-acetyl-4-aminobenzoyl-5-alanine (NABA, derived by N-acetylation of ABA)

Single dose of Balsalazide to rat

Compound

Dose of Balsalazide (mmol/kg)

Route/group

Cmax

(nmol/ml)

Tmax (h)

AUC

(nmol.h/ml)

Urine

(nmole/24h)

Clr

(ml/min)

Radioactivity

0.274

Oral (A)

3.574

9.00

40.72

NA

NA

Radioactivity

4.573

Oral(B)

26.78

12.00

373.8

NA

NA

Radioactivity

0.274

IV

NA

NA

269.0

NA

NA

Balsalazide

0.274

Oral (A)

1.091

1.00

3.072

273.5

1.484

Balsalazide

4.573

Oral(B)

8.505

1.00

42.56

3470

1.359

Balsalazide

0.274

IV

NA

NA

491.9

18452

0.625

NABA

0.274

Oral (A)

1.838

9.00

15.73

1897

2.009

NABA

4.573

Oral(B)

10.71

12.00

137.0

10382

1.263

NABA

0.274

IV

NA

NA

ID

1303

ID

NASA

0.274

Oral (A)

7.585

9.00

50.75

6867

2.255

NASA

4.573

Oral(B)

51.28

9.00

622.0

75690

2.028

NASA

0.274

IV

NA

NA

29.16

5580

3.189

ABA

0.274

Oral (A)

0.310

9.00

ID

ID

ID

ABA

4.573

Oral(B)

3.974

12.00

34.20

6238

3.040

ABA

0.274

IV

ID

ID

ID

ID

ID

ASA

0.274

Oral (A)

1.946

9.00

ID

ID

ID

ASA

4.573

Oral(B)

73.05

12.00

522.2

17700

0.565

ASA

0.274

IV

NA

NA

ID

ID

ID

ID = Insufficient data to derive parameter

NA = not applicable

Conclusions:
The results of the i.v. dosing are quite different to the oral dosing. After dosing, radioactivity in the plasma declines much faster than the same dose via the oral route. Excretion of a high (38% dose) percentage as intact balsalazide via urine is quite interesting as the in vitro plasma protein binding was determined to be 96-99% and protein bound molecules cannot be filtered through the kidney into urine. Clearly, in vivo the parent molecule can be excreted despite high plasma protein binding suggesting that either the plasma protein binding in vivo is much lower than in vitro indicates, or there is reversal of the binding within the kidneys.
Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
Not specified
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Objective of study:
toxicokinetics
Qualifier:
no guideline followed
Principles of method if other than guideline:
- Principle of test:
- Short description of test conditions: radiolabelled Basalazide sodium (BSZ) was administered to rats as a single i.v. dose at two dose levels of 120 mg/kg
- Parameters analysed / observed: Blood, urine and Faeces was sampled and levels of BSZ and its metabolites were determined. Tissue samples from a variety of organs were collected for distribution study. Radioactivity was determined via LSC.
GLP compliance:
not specified
Specific details on test material used for the study:
The study was performed on balsalazide disodium, but it will reach a common moiety in the blood after i.v. dosing , whether BSZ or BSA.
Radiolabelling:
yes
Species:
rat
Strain:
not specified
Sex:
not specified
Route of administration:
intravenous
Vehicle:
not specified
Duration and frequency of treatment / exposure:
Single dose
Dose / conc.:
120 mg/kg bw/day (actual dose received)
No. of animals per sex per dose:
Not stated
Control animals:
no
Positive control:
Not stated
Details on dosing and sampling:
TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, blood
- Time and frequency of sampling: 1,3,6,9,12,18 and 24 hours after dosing

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: urine, faeces, tissues,
- Time and frequency of sampling: 1,3,6,9,12,18 and 24 hours after dosing
- Method type(s) for identification HPLC-UV, Liquid scintillation counting
Statistics:
None specified
Type:
absorption
Results:
Not applicable for i.v.
Type:
distribution
Results:
Missing page in review document. No distribution information available
Type:
metabolism
Results:
Azo of parent to two smaller molecules, 5-amino salicylic acid (ASA) which is N-acetylated to N-acetyl-5-amino-salicylic acid (NASA) and 4 aminobenzoyl-5-alanine (ABA) which is N-acetylated to N-acetyl-4-aminobenzoyl-5-alanine (NABA).
Type:
excretion
Results:
Radioactivity was recovered in both faeces (approx 58%) and urine (approx 39%). The majority of this was ABA and intact BSZ in the faeces and urine respectively
Details on absorption:
Not applicable for i.v.
Details on distribution in tissues:
No information available.
Details on excretion:
Radioactivity was recovered in both faeces (approx 58%) and urine (approx 39%). The majority of this was ABA and intact BSZ in the faeces and urine respectively.
Metabolites identified:
yes
Details on metabolites:
Four metabolites were reported. These were assigned as:
1) 5-aminosalicylic acid (ASA)
2) N- acetyl-5-amino-salicylic acid (NASA, derived by N-acetylation of ASA)
3) 4-aminobenzoyl-5-alanine (ABA)
4) N-acetyl-4-aminobenzoyl-5-alanine (NABA, derived by N-acetylation of ABA)

Single dose of Balsalazide to rat (the oral equivalent is also shown for additional information and comparison)

Compound

Dose of Balsalazide (mmol/kg)

Route/group

Cmax

(nmol/ml)

Tmax (h)

AUC

(nmol.h/ml)

Urine

(nmole/24h)

Clr

(ml/min)

Radioactivity

0.274

Oral (A)

3.574

9.00

40.72

NA

NA

Radioactivity

4.573

Oral(B)

26.78

12.00

373.8

NA

NA

Radioactivity

0.274

IV

NA

NA

269.0

NA

NA

Balsalazide

0.274

Oral (A)

1.091

1.00

3.072

273.5

1.484

Balsalazide

4.573

Oral(B)

8.505

1.00

42.56

3470

1.359

Balsalazide

0.274

IV

NA

NA

491.9

18452

0.625

NABA

0.274

Oral (A)

1.838

9.00

15.73

1897

2.009

NABA

4.573

Oral(B)

10.71

12.00

137.0

10382

1.263

NABA

0.274

IV

NA

NA

ID

1303

ID

NASA

0.274

Oral (A)

7.585

9.00

50.75

6867

2.255

NASA

4.573

Oral(B)

51.28

9.00

622.0

75690

2.028

NASA

0.274

IV

NA

NA

29.16

5580

3.189

ABA

0.274

Oral (A)

0.310

9.00

ID

ID

ID

ABA

4.573

Oral(B)

3.974

12.00

34.20

6238

3.040

ABA

0.274

IV

ID

ID

ID

ID

ID

ASA

0.274

Oral (A)

1.946

9.00

ID

ID

ID

ASA

4.573

Oral(B)

73.05

12.00

522.2

17700

0.565

ASA

0.274

IV

NA

NA

ID

ID

ID

ID = Insufficient data to derive parameter

NA = not applicable

Conclusions:
Intact balsalazide (approx 39% of dose) is excreted into urine, after i.v. dosing. The remaining balsalazide is metabolised to ABA and ultimately excreted in the faeces. Metabolites formed are the similar to those after oral dose.
Endpoint:
basic toxicokinetics, other
Remarks:
Human volunteers
Type of information:
other: Human data
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
The assays used for determination of balsalazide and its metabolites in plasma, urine and faeces had some deficiencies. Assay validation at the lower limits of the calibration curves were inadequate or inaccurate. This should be taken into account when considering results.
Objective of study:
absorption
distribution
excretion
Principles of method if other than guideline:
24 adult, male, human volunteers were split into two groups, A and B.
Group A: six of the subjects received a single dose of Balsalazide followed by a single dose of another pharmaceutical compound sulfasalazine. The two doses were seperated by a 13-day washout period. The other six subjects underwent the same treatment except that they received the single dose of Sulfasalazine prior to the single dose of Balsalazide.
Group B: As Group A, but the other pharmaceutical was Mesalazine.
For the purpose of this summary, only the effects after dosage of the Balsalazide are summarised.
GLP compliance:
no
Remarks:
not applicable as human volunteers
Radiolabelling:
no
Route of administration:
oral: capsule
Duration and frequency of treatment / exposure:
Single dose
Dose / conc.:
2.25 other: g
Details on dosing and sampling:
Administration of a single dose (2.25 g) of the study drug took place at 8.00 am on day 1. Blood urine and faecal samples were collected over the next four days for PK analyses. Standard meals and drinks were provided from the eve of day 1 until the end of day 4 at predesignated times. Subjects were not permitted to consume any alcohol or caffeine-containing beverages for 24 hrs prior to nor throughout the study duration.
Biological sampling:
Blood- samples were colleced immediately before and at 1,2,4,6,8,10,12,14,24,30,36,48,72 and 86 hrs after drug administration.
Urine - samples were collecged over the following intervals: 0-4 hr, 4-8 hr, 8-12 hr, 12-16 hr, 16-24 hr, 24-36 hr, 36-48 hr and 72-96 hr.
Faeces - collections were made of all faeces voided between the eve of study drug administration and 96 hrs post-dose.
Statistics:
Summary statistics were presented for demographic data and adverse events. The incidence of adverse events was compared using Fisher's exact test.
Plasma, urine and faecal concentrations and computed parameters were listed and summarised by dose (mean, SD, minimum and maximum). Mean and individual plasma concentrations versus time curves were plotted for each dose.
Statistical analyses were performed using the SAS procedure, PROC GLM. Analysis of the computed kinetic parameters for ASA and NASA was carried out with an ANOVA model appropriate for crossover design. The model included terms for treatment, sequence, period and subject within sequence. The analyses were performed for Groups A and B independently of eachother. A p value of ≤ 0.05 was considered to be statistically significant.
Details on absorption:
Balsalazide appeared in the plasma of almost all subjects by 1 hr after dosing. The majority of the plasma concentrations were near the assay LOQ. Cmax = 18.9 ± 8.9 (ng/ml), AUClast = 37.7±43.2 ng*hr/ml based on 2.25 g dose.
Details on distribution in tissues:
No information
Details on excretion:
See table.
According to the review, the Clr was calculated using Au96hr/AUC96hr where Au96hr is the mean value for the amount of compound collected in the urine over 96 hrs and AUC 96hr is the mean area under the plasma concentration vs time curve as determined over 97 hr. The values were calculated using mean data only, i.e. Clr parameters were not determined for each individual and then averaged.
Metabolites identified:
yes
Details on metabolites:
Four metabolites were reported. These were assigned as:
1) 5-aminosalicylic acid (ASA)
2) N- acetyl-5-amino-salicylic acid (NASA, derived by N-acetylation of ASA)
3) 4-aminobenzoyl-5-alanine (ABA)
4) N-acetyl-4-aminobenzoyl-5-alanine (NABA, derived by N-acetylation of ABA)

Excretion data for Balsalazide and its metabolites

 

% recovered in urine

P value

%recovered in faeces

Clr (L/hr)

Balsalazide

0.13±0.08

-

0.04±0.14

63.7

ABA

0

 

36.55±26.63

0

NABA

2.97±1.74

 

2.62±1.6

26.9

Group A

 

 

 

 

ASA

0

-

7.05±4.11

0

NASA

20.5±8.19

 

17.24±11.13

11.2

Group B

 

 

 

 

ASA

0

-

 

-

NASA

29.2±7.32

-

 

-

 

Conclusions:
Balsalazide absorption was very limited, with less than 1% of the 2.25 g dose being recovered in the urine of faeces as intact drug. The review of this study is from the perspective of absorption in terms of bioavailability. With respect to TK for REACH purposes, it is possible that absorption from the GI tract was initially much higher than 1%, but metabolism in the liver (first pass effect) and enterohepatic circulation as well as the intended azo reduction by colonic bacterial azoreductases may have converted so much of the parent to its metabolites that very little actually entered the systemic circulation.
The majority of the balasazide dosed was detected in the faeces as both ABA and ASA and their N-acetylated metabolites (approx 65%).
Endpoint:
basic toxicokinetics, other
Remarks:
Human volunteers
Type of information:
other: Human data
Adequacy of study:
weight of evidence
Study period:
1992
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
The assays used for determination of balsalazide and its metabolites in plasma, urine and faeces had some major deficiencies. Assay validation at the lower limits of the calibration curves were inadequate or inaccurate. This should be taken into account when considering results.
Objective of study:
absorption
distribution
excretion
Principles of method if other than guideline:
The study was an open-label, noncomparative, single and multiple dose study. The subjects were twelve healthy, adult, male volunteers.
It should be noted that this study is not the same as a normal repeat dose test where the same dose is given every day. The dose varies over a 19 day period. Therefore, this will introduce some complexity. However, it should still allow an assessment of specific toxicokinetic parameters.
GLP compliance:
no
Remarks:
not applicable, as human volunteers
Specific details on test material used for the study:
Expiry date August 1995
Radiolabelling:
no
Route of administration:
oral: capsule
Duration and frequency of treatment / exposure:
Drug administration was comprised of three phases: a single dose of 1.5 g Balsalazide disodium on day 1, two daily doses on Days 4-13 and three daily doses on days 18-19.
Dose / conc.:
1.5 other: g
Remarks:
Day 1
Dose / conc.:
3 other: g
Remarks:
Comprised of 2 x 1.5 g over days 4-12
Dose / conc.:
1.5 other: g
Remarks:
Day 13
Dose / conc.:
6.75 other: g
Remarks:
Day 18
Dose / conc.:
2.25 other: g
Remarks:
Day 19
Details on dosing and sampling:
Each dose of study drug was taken with 250 ml of water. Blood, urine and faecal samples were collected at predetermined times over the study period for PK analyses.
Blood- samples were colleced immediately before and at 1,2,4,6,8,10,12,14,24,30,36,48,72 after first drug administration (days 1-3). This served as a single-dose profile.
Samples taken after this point served as repeated-dose profile.
Urine - samples were collected over the following intervals during days 1-3: 0-4 hr, 4-8 hr, 8-12 hr, 12-16 hr, 16-24 hr, 24-36 hr, 36-48 hr and 48-72 hr.
Faeces - collections were made of all faeces voided between the eve of study drug administration and 96 hrs post-dose.
Statistics:
Summary statistics were presented for demographic data. Plasma, urine and faecal concentration and computed parameters were listed and summarized by treatment (mean, SD, range). Mean and individual plasma concentrations versus time curves were plotted for each dose.
Details on absorption:
Balsalazide was absorbed very quickly with Tmax values of approximately 1 hr. See table for plasma parameters after administrations.
Mean Tmax values indicate some absorption of balasalazide in the upper GI tract, as the drug would not be expected to reach the colon and be absorbed within 1 hr. Although the mean Tmax for day 19 was arounf 4 hrs, 8/9 subjects with measureable balsalazide concentrations had Tmax values of 1 or 2 hrs.
Details on distribution in tissues:
No information was presented in review document
Details on excretion:
See table for excretion of balsalazide.
BSZ was recovered in the urine of all the subjects although the quantities were very limited. The very large values obtained for the renal clearance of BSZ is most likely a function of the incomplete characterisation of the BSZ plasma concentrations vs time curves used in the Clr calculations
Metabolites identified:
yes
Details on metabolites:
Four metabolites were reported. These were assigned as:
1) 5-aminosalicylic acid (ASA)
2) N- acetyl-5-amino-salicylic acid (NASA, derived by N-acetylation of ASA)
3) 4-aminobenzoyl-5-alanine (ABA)
4) N-acetyl-4-aminobenzoyl-5-alanine (NABA, derived by N-acetylation of ABA)

Balsalazide (BSZ) plasma PK parameters after administration of drug

 

Cmin (ng/ml)

Cmax(ng/ml)

Tmax(hr)

AUClast (ng*hr/ml)

Day 1

(1.5 g BSZ)

-

7.9±4.9

(0-12.9)

1.1±0.8

(0-2)

 5.7±5.7

(0 -17.4)

Day 13**

(1.5 g BSZ bid)

0

7.2±5.5

(0-13.5)

1.0±0.9

(0-2)

 7.5±9.6

(0 -32.4)

Day 19***

(2.25 g BSZ tid )

0

11.9±7.6

(0-19.6)

3.9±10.1

(0-36)

 13.9±10.4

(0 -28.3)

** Day 13 – only one dose was administered early in the morning. The bid refers to the double dose received from days 4-12

*** Day 10- only one dose was administered early in the morning. The tid refers to the triple dose received on day 18.

Balsalazide(BSZ) excretion in urine and faeces

 

%BSZ recovered in faeces

%BSZ recovered in urine

Renal clearance (L/hr)*

Day 1 (1.5 g BSZ)

0

[N=1]

0.1±0.1

(0-0.02)

[N=12]

150±85

(47-302)

[N=9]

Day 13 (1.5 g BSZ bid)

9.2±11.5

(0-29.6)

[N=8]

0.1±0.1

(0-0.3)

[N=12]

143±73

(42-254)

[N=8]

Day 19 (2.25 g BSZ tid)

7.9±7.5

(0.2-26.2)

[N=9]

0.2±0.1

(0.1-0.3)

[N=11]

182±212

(0-604)

[N=9]

*Renal clearance was determined over the 0 -4 hr collection interval

BSZ and metabolite recovery in urine and faeces*

 

Faeces

Urine

Total

Day 1

13.4% (N=1)

19.7% (N=12)

33.1%

Day 13

239.5% (N=8)

15.7% (N=12)

255.2%

Day 19

87.5% (N=9)

6.2% (N=11)

93.7%

Conclusions:
According to the review article, Balsalazide disodium salt was quickly absorbed into the systemic circulation, but only in very limited quanties. The substance which is being registered under REACH is balsalazide acid. However, in the GI tract, the disodium salt and acid would both be expected to reach the same ratio of acid and salt at the various pHs present in the GI tract, based on the pKa. It is reasonable to conclude therefore that balsalazide acid would also be quickly absorbed, but only to a very limited extent.
Only small amounts of balsalazide were found in the urine or faeces, clearly indicating significant metabolism.
The bulk of the 2.25 g dose of BSZ (this is the triple dose of 2.25 g on Day 18 and then one dose on day 19) was recovered in the faeces as the parent compound and its four metabolites. ASA and ABA were detected in the largest quantities. Since balsalazide is intended to largely reach the colon intact before cleavage by azo-reductase bacteria, this is not surprising.
Accumulation of balsalazide or ABA was not considered likely during the multiple dosing.
With regards to the metabolites, ABA appeared almost exclusively in plasma as the N-acetylated metabolite with virtually none detected in the urine. ASA, NASA and NABA were readily detected in the plasma of all subjects, although limited quantities of these compounds were recovered in the urine. Accumulation of ASA, NASA and NABA was observed during the administration of 2.25 gm tid for 4 doses.
The presence of the metabolites in the plasma may come from colonic absorption of the metabolites (ASA and ABA) produced by cleavage of BSZ, and the NASA and NABA could be produced by N-acetylation in the colon and/or N-acetylation in other parts of the body (e.g. liver). The appearance in some subjects of NASA and NABA before ASA and ABA is suggestive of conversion of ASA/ABA to these metabolites and then faster absorption of the NASA/NABA and/or much lower absorption of the ASA/NASA.

In conclusion, it can be seen that Balsalazide has rapid but very limited oral absorption, extensive metabolism to 4 metabolites (which may occur in the colon before absorption) and excretion of unchanged parent and metabolites predominantly via faeces and to a much lesser extent via urine. It is considered that accumulation in tissues is not likely.

Description of key information

ABSORPTION

Balsalazide acid absorption is predicted to occur to a small extent via the oral route.

Balsalazide acid is predicted to have low (but not necessarily negligible) absorption via the inhalation route.

Balsalazide acid is predicted to have very low absorption via the dermal route.

DISTRIBUTION

There is minimal available information relating to distribution.

METABOLISM

Four main metabolites have been identified in human clinical trials and in the rat TK study and these are expected to be the same for Balsalazide acid:

1) 5-aminosalicylic acid (ASA, derived from Azo-reductase of the Balsalazide acid (sodium salt)  

2) N- acetyl-5-amino-salicylic acid (NASA, derived by N-acetylation of ASA)

3) 4-aminobenzoyl-5-alanine (ABA, derived from Azo-reductase of the Balsalazide acid (sodium salt)  

4) N-acetyl-4-aminobenzoyl-5-alanine (NABA, derived by N-acetylation of ABA)

EXCRETION

Balsalazide acid is predicted to be predominantly excreted via faeces in the form of its metabolites ABA and ASA and their N-acetylated metabolites (NABA and NASA). Very limited amounts of Balsalazide acid is predicted to be excreted via urine.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential

Additional information