Registration Dossier

Administrative data

screening for reproductive / developmental toxicity
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
Justification for type of information:
In accordance with Annex XI, section 1 of Regulation No. 1907/2006, in vivo testing on 4-aminobenzoyl-b-alanine does not appear scientifically necessary for the following reasons:

In the event that any 4-Aminobenzoyl-b-alanine (here-on in referred to as ABA) comes into contact with skin and manages to penetrate the outer layer, or in the event that any respirable particles are inhaled, ABA will be rapidly converted to its N-acetylated metabolite (NABA) via N-acetylation in the skin or lungs. Based on the oral bioavailability of ABA (approx. 14%, see separate IUCLID summary on oral TK), it is predicted that any dermal absorption would be relatively low, so loading of the N-acetylation pathway would not be high and therefore extensive (and possibly complete) metabolism to the NABA is likely to occur which would then be rapidly excreted from the body via urine (see IUCLID TK endpoint oral rat). Similarly, for the inhalation route, N-acetylation is expected to occur, followed by rapid excretion of NABA.

The following key points have been taken from publically available documents:

“Sufficient information has been provided - by the sponsor supporting balsalazide disodium approval - to the FDA to support their claim that the acetylation of ABA is not genetically controlled” (Clinical Pharmacology and BioPharmaceutical Reviews)

This means that variation between genotypes for acetylation in human individuals (i.e. fast/slow acetylators) will not affect the rate of conversion of ABA to its N-acetylated metabolite (NABA).

Center for Drug Evaluation and Research (application number 20-610); pharmacology review states:

Absorption of ABA in rat: following a single oral dose of 14C-ABA in rat, maximum plasma levels of ABA and NABA were reached after 15 minutes.
Metabolism of ABA in rat: Within 15 minutes of oral dosing, the ratio of NABA to ABA was 3.4:1 (approx. 80% conversion of ABA to NABA). Clearly in a very short time after exposure, metabolism of ABA to the N-acetylated metabolite occurs very quickly in rat.
Excretion of ABA in rat: most of the radioactivity in the urine was associated with NABA following oral dose, whereas the majority of radioactivity in urine after i.v. dose was associated with ABA (approx. 80% of dose). Plasma radioactivity declined quickly and was below the limit of detection within 24 hr of oral dosing.

This is clearly indicative that ABA undergoes rapid metabolism to its N-acetylated metabolite when it passes through the GI tract and liver but not when it bypasses this route by entering directly into the bloodstream (i.e. intravenous).

This is an important point, as it suggests the potential for similarly rapid N-acetylation of ABA if it enters the skin after any dermal exposure or lung membranes after any inhalation exposure, since the N-acetyl transferase (NATs) enzymes that convert ABA to NABA in the liver and GI tract also exist in significant amounts in human skin and lungs (references for NATs in human skin:; and Reference for NATs in human lung:

From the review of study number 20060: A comparative tolerability and pharmacokinetic study of balsalazide sodium (Colazide®), Sulfasalazine (Salazopyrin®) and Mesalazine (Asacol®) following a single oral dose.

The conclusion of the review of this study in relation to ABA was that, although it was detected in plasma, it appeared to be excreted only as its N-acetylated metabolite in urine in normal, healthy male human volunteers. The ratio of the relative maximum plasma concentrations of NABA to ABA was 4.3:1, which interestingly is similar to the ratio found in the rat TK data. The plasma AUClast of ABA was 81 ng*hr/ml compared to 1422 ng*hr/ml for NABA again providing an idea of the high conversion of ABA to the metabolite which is easily excreted via urine, thus limiting the potential for accumulation to toxic levels in the body.

From the review of study number 20061: The tolerability and pharmacokinetics of single and repeated oral doses of balsalazide disodium (Colazide®)

The review of this study stated that all human volunteers had readily quantifiable concentrations of NABA in the urine and renal clearance values exceeded normal creatinine clearance values which may indicate active secretion of this metabolite.
The review also stated that the sponsor to the study admitted that the total amount in urine and clearance values should be considered as supporting data since there was no guarantee that urine collections were complete and accurately timed.
However, the rapid metabolism of orally dosed ABA to NABA and its rapid excretion via urine is consistent with Study 20060, Study GLY01/93 and with the rat TK data.

From review of study number GLY01/93 title: Pharmacokinetic study of balsalazide disodium in Patients with Ulcerative Colitis receiving long-term maintenance treatment.

Review of this study states that the mean clearance value for NABA exceeded normal creatinine clearance values which as for Study 20061, is suggestive of active secretion of this metabolite via kidneys. The data showed that the patients in this study retained a high capacity to clear the acetylated metabolite of ABA in the kidneys, thus minimising the systemic exposure to the carrier portion (i.e. ABA) of balsalazide, via its metabolite NABA.

Overall, from rat and more importantly human data, it is clear that when the body is exposed to ABA where it is not directly injected into the blood, e.g. oral, dermal and inhalation exposure, that significant metabolism of any ABA which passes into the membrane (skin/GI tract/lungs) will occur via N-acetyl transferases (NATs) converting ABA to NABA which is then rapidly excreted from the body via the urine (potentially via active secretion in kidneys). It can also reasonably be expected that absorption via skin would be much slower and to a lesser degree than via oral, allowing more time for conversion of relatively less absorbed ABA to NABA which would then be rapidly removed from the body as soon as reaching the systemic circulation.

An additional argument relates to the relative thickness of the rat skin and human skin. Human skin is thicker than rat skin, and most likely will have an N-acetylation capacity exceeding that of rats, due to higher NAT levels (and more types of NAT in humans) and longer transit time. Therefore, it is considered that non-human models for dermal exposure may not actually be suitable for producing reliable data for repeated dose toxicity of ABA. Hence, any vertebrate testing would be considered scientifically unnecessary and not in the interests of animal welfare.

In the case of the Annex VIII studies for which this waiver applies, relevant exposure would only be for dermal and inhalation routes, as only professionals are handling the substance. Furthermore, it should be noted that professionals would be working under strict GMP conditions, as they are using the ABA as a chemical reagent to manufacture balsalazide acid (which is subsequently used to make an API) and in this case there is a strict requirement to protect the pre-API from human contamination, meaning that appropriate PPE would be worn. It can therefore be concluded that the potential for exposure of ABA to the skin or lungs of professional workers would in reality be negligible.

Given the argumentations detailed above and in the interest of animal welfare, it is therefore considered scientifically unnecessary to perform a reproductive screening test on ABA.

Data source

Materials and methods

Results and discussion

Applicant's summary and conclusion