Our health system is looking at a reformulated premixed vancomycin injection product which contains the additive NADA. What is the safety data regarding NADA in pregnancy?

Comment by InpharmD Researcher

Available data on N-acetyl-D-alanine (NADA) in pregnancy are extremely limited and do not allow for a reliable safety assessment. No clinical studies, case reports, or human data evaluating maternal or fetal outcomes with NADA exposure have been identified, and it is not included in established excipient safety databases or references. Nonclinical data from FDA review documents indicate that NADA is a novel excipient evaluated primarily in animal studies, where intravenous exposure in rabbits during organogenesis was associated with fetal cardiovascular and skeletal abnormalities at high doses, with a no-observed-adverse-effect level identified but no established safe exposure threshold in humans. Earlier vancomycin formulations containing NADA (and polyethylene glycol 400) carried warnings against use in early pregnancy based on these findings; however, in a reformulated product with PEG 400 removed, the FDA eliminated pregnancy-related boxed warnings, though this change reflects removal of a known risk contributor rather than new evidence supporting NADA safety. Therefore, in the absence of human data and with only limited animal toxicity findings, the safety of NADA in pregnancy remains uncertain and cannot be established.

A targeted search was conducted in PubMed and Google Scholar using combinations of keywords and MeSH terms including “N-acetyl-D-alanine” OR “NADA” AND “pregnancy” OR “embryo-fetal development” OR “reproductive toxicity,” as well as “vancomycin excipients pregnancy,” with no filters initially applied and then limited to human and animal studies. Additional gray literature and regulatory sources (e.g., FDA reviews, prescribing information, and excipient safety databases such as STEP and KIDS lists) were reviewed to identify unpublished or nonclinical safety data, given the absence of clinical studies.

Background

According to the U.S.  Food & Drug Administration (FDA) review of the supplemental new drug application (sNDA) for Tyzavan (vancomycin injection), received September 26, 2023, the manufacturer submitted a reformulation of the drug product to remove the excipient polyethylene glycol 400 (PEG 400). As a result of this formulation change, the FDA approved the removal of the Boxed Warning related to potential risks of excipient exposure during early pregnancy. Corresponding pregnancy-related warnings and recommendations for pregnancy testing were also removed from the prescribing information, and pediatric dosing sections were updated to clarify limitations of the available strengths. [1]

A comprehensive search of the published literature and excipient safety databases did not identify any data on the use or safety of N-acetyl-D-alanine (NADA) in pregnancy. No clinical studies, case reports, or regulatory assessments specifically addressing maternal or fetal outcomes with NADA exposure were found. Therefore, its safety in pregnancy cannot be assessed or recommended based on current evidence. The search was extended to broader reviews of excipient safety in neonates and pediatric populations, which highlight that many inactive ingredients used in adult formulations are also present in medicines administered to newborns, often without clear toxicity signals, but sometimes requiring careful dose-based risk assessment. These reviews underscore that while most adverse effects stem from active ingredients, excipients can contribute to the overall safety profile of a formulation, particularly in vulnerable populations. However, NADA is not listed among excipients with known or characterized safety data in these reviews or in established reference databases (e.g., KIDS list, STEP database), indicating a lack of available reproductive or developmental toxicity information. In the absence of such data, the use of formulations containing NADA during pregnancy cannot be recommended or reliably evaluated for safety. [2], [3], [4]

According to a 2019 FDA multi-disciplinary review for NDA 211962, PEG 400 and NADA were introduced as excipients in a ready-to-use vancomycin formulation and were evaluated primarily through nonclinical reproductive and toxicology studies rather than clinical pregnancy or pediatric safety trials. Animal embryo-fetal development studies demonstrated that intravenous PEG 400 exposure in rabbits during organogenesis was associated with fetal spinal abnormalities, with a no-observed-adverse-effect level (NOAEL) for fetal toxicity of 500 mg/kg (approximately 162 mg/kg human-equivalent dose), while higher exposures produced skeletal findings; similarly, NADA studies identified fetal cardiovascular and skeletal abnormalities in rabbits at ≥1680 mg/kg/day, with a fetal NOAEL of 560 mg/kg (approximately 181 mg/kg human-equivalent dose). These data supported labeling that the formulation is not recommended for use during pregnancy due to potential embryo-fetal toxicity from PEG 400 and NADA. Pediatric use guidance reflects dosing limitations related to fixed single-dose bag strengths rather than established excipient safety thresholds, and the product is not appropriate for neonates; no specific safe exposure limits for PEG 400 or NADA in pregnant or pediatric patients were established in humans within the review. Additionally, NADA is described as a novel excipient not previously qualified in approved FDA products, and the document does not identify other marketed products containing comparable quantities of NADA. [5]

Relevant Prescribing Information

Vancomycin injection [1]

Dosage Form [1]
Vancomycin Injection, USP is a ready to use clear, colorless to light brown solution in single-dose flexible bags containing 500 mg vancomycin in 100 mL, 750 mg vancomycin in 150 mL, 1 g vancomycin in 200 mL, 1.25 g vancomycin in 250 mL, 1.5 g vancomycin in 300 mL, 1.75 g vancomycin in 350 mL and 2 g vancomycin in 400 mL of liquid

Boxed Warning [1]
Potential Risk of Exposure to Excipients During the First or Second Trimester of Pregnancy
If use of vancomycin is needed during the first or second trimester of pregnancy, use other available formulations of vancomycin. This formulation of vancomycin injection contains the excipients polyethylene glycol (PEG 400) and N-acetyl D-alanine (NADA), which resulted in fetal malformations in animal reproduction studies at dose exposures approximately 8 and 32 times, respectively, higher than the exposures at the human equivalent dose

Pregnancy Risk Summary
This formulation of Vancomycin Injection is not recommended for use during the first or second trimester of pregnancy because it contains the excipients, PEG 400 and NADA, which caused fetal malformations in animal reproduction studies. Advise pregnant women of the potential risk to the fetus. If therapy with Vancomycin Injection is needed during the first or second trimester of pregnancy, use other available formulations of vancomycin, free of PEG 400 and NADA.

The available data on use of this formulation of Vancomycin Injection (with the excipients PEG 400 and NADA) in pregnant women are insufficient to evaluate for a drug-associated risk of major birth defects, miscarriage, or other adverse maternal or fetal outcomes. Available published data on vancomycin (without the excipients PEG 400 and NADA) use in pregnancy during the second and third trimesters have not shown an association with adverse pregnancy-related outcomes. There are no available data on first-trimester use of vancomycin in pregnant women to assess the risk of major birth defects or miscarriage. Vancomycin alone did not show adverse developmental effects when administered intravenously to pregnant rats and rabbits during organogenesis at doses less than or equal to the recommended maximum human dose based on body surface area.

Reproduction studies in rabbits with intravenous doses of PEG 400 at approximately 8 times the maximum daily human dose based on systemic exposures of PEG 400 during organogenesis resulted in fetal spinal malformations. Reproduction studies in rabbits and rats using intravenous doses of NADA at approximately 32 and 20 times the maximum daily human dose, respectively, based on systemic exposures of NADA resulted in maternal toxicity and fetal spinal and cardiovascular malformations in rabbits, and maternal toxicity with no adverse embryo-fetal effects in rats. Vancomycin alone did not show adverse developmental effects when administered intravenously to pregnant rats and rabbits during organogenesis at doses less than or equal to the recommended maximum human dose based on body surface area

Tyzavan (vancomycin injection) [2]

How supplied [2]
TYZAVAN (Vancomycin Injection, USP) is supplied as a ready-to-use clear, colorless to light brown
solution in single-dose flexible bags containing 500 mg, 750 mg, 1 g, 1.25 g, 1.5 g, 1.75 g and 2 g
vancomycin in 100 mL, 150 mL, 200 mL, 250 mL, 300 mL, 350 mL and 400 mL of liquid (consists
of water for injection together with the excipients NADA and lysine)

Use in Special Populations [2]
Pregnancy
Risk Summary
The available data on the use of this formulation of TYZAVAN (which includes the excipient NADA) in pregnant women are insufficient to evaluate for a drug-associated risk of major birth defects, miscarriage, or other adverse maternal or fetal outcomes. Available published data on vancomycin (without the excipient NADA) use in pregnancy during the second and third trimesters have not shown an association with adverse pregnancy-related outcomes. There are no available data on first-trimester use of vancomycin in pregnant women to assess the risk of major birth defects or miscarriage.