Sarafloxacin (DB11491): A Comprehensive Pharmacological and Regulatory Monograph

1.0 Executive Summary

Sarafloxacin is a second-generation fluoroquinolone antibiotic developed by Abbott Laboratories exclusively for veterinary applications.[1] Characterized as a synthetic organic small molecule, its primary intended use was the control of colibacillosis, a significant bacterial disease caused by

Escherichia coli, in poultry, specifically broiler chickens and turkeys.[3] Its mechanism of action is characteristic of its class, involving the potent inhibition of essential bacterial enzymes—DNA gyrase and topoisomerase IV—thereby disrupting DNA replication and leading to a rapid bactericidal effect.[5]

In vitro studies demonstrated that Sarafloxacin possessed a broad spectrum of activity and high potency against a range of Gram-negative and Gram-positive pathogens, with efficacy comparable to established fluoroquinolones like ciprofloxacin.[4]

Despite its promising antimicrobial profile, the clinical and regulatory trajectory of Sarafloxacin was complex and ultimately short-lived. Pharmacokinetic studies revealed significant variability across species, a factor that profoundly influenced its safety assessment. While demonstrating adequate absorption and distribution in target avian species, its oral bioavailability was found to be markedly low in humans.[8] This specific characteristic led international regulatory bodies, such as the Joint FAO/WHO Expert Committee on Food Additives (JECFA), to adopt a forward-thinking approach to its human safety evaluation. The Acceptable Daily Intake (ADI) was established not on traditional toxicological endpoints, but on the potential microbiological impact of unabsorbed drug residues on human gut flora, a decision that set a significant precedent in the assessment of veterinary antimicrobials.[9]

The ultimate fate of Sarafloxacin was sealed not by a lack of efficacy or direct toxicity in animals, but by a rising tide of public health concern regarding antimicrobial resistance. In the late 1990s and early 2000s, regulatory agencies, led by the U.S. Food and Drug Administration (FDA), grew increasingly alarmed that the use of fluoroquinolones in food-producing animals could select for resistant bacteria, such as Campylobacter, which could then be transferred to humans and compromise the efficacy of this critical class of antibiotics in human medicine.[12] In response to these concerns, Abbott Laboratories voluntarily requested the withdrawal of its New Animal Drug Applications (NADAs) for Sarafloxacin, and the FDA formally withdrew its approval effective April 30, 2001.[3] Consequently, Sarafloxacin serves as a pivotal case study in the application of the One Health principle to drug regulation, illustrating how the potential for broad public health impact can override a drug's specific benefits in veterinary medicine. Today, it is no longer used clinically but remains available as a valuable analytical standard and research chemical.

2.0 Chemical Profile and Physicochemical Properties

A precise understanding of a drug's chemical and physical nature is fundamental to interpreting its pharmacological, pharmacokinetic, and toxicological behavior. Sarafloxacin is a well-characterized synthetic compound with a defined structure and a distinct set of properties. It has been primarily formulated and studied as both a free base and a hydrochloride salt, with the latter being used in its commercial veterinary preparations.[3]

Sarafloxacin is systematically classified as a small molecule, synthetic organic compound belonging to the fluoroquinolone class of antibiotics.[1] Structurally, it is a member of the phenylquinolines and is more specifically defined as a quinoline-3-carboxylic acid derivative.[17] Its IUPAC name is 6-fluoro-1-(4-fluorophenyl)-4-oxo-7-piperazin-1-ylquinoline-3-carboxylic acid.[16] The molecule's identity is unambiguously defined by its chemical formula, C₂₀H₁₇F₂N₃O₃, and its structural representations, including its InChIKey (XBHBWNFJWIASRO-UHFFFAOYSA-N) and SMILES string (C1CN(CCN1)C2=C(C=C3C(=C2)N(C=C(C3=O)C(=O)O)C4=CC=C(C=C4)F)F).[19]

During its development and marketing, Sarafloxacin was known by several synonyms, including the research code A-56620 and the name Floxasol.[9] Its commercial formulations were marketed under the brand names SaraFlox® Injectable and SaraFlox® WSP.[17] The hydrochloride salt form, Sarafloxacin HCl, was the active ingredient in these products and possesses its own distinct set of identifiers and properties.[21]

Physicochemical data indicate that Sarafloxacin is an off-white to pale beige solid.[17] It is hygroscopic and should be protected from light and stored at refrigerated temperatures (2-8°C) for stability.[17] Its solubility is limited, being described as slightly soluble in DMSO, methanol, and aqueous base solutions.[17] The hydrochloride salt has a predicted water solubility of 0.105 mg/mL.[21] The molecule has two ionizable groups, with a predicted acidic pKa of approximately 5.74 to 6.17 and a basic pKa of around 8.68.[17] These properties influence its solubility and absorption at different physiological pH levels. Its experimental melting point is reported to be in the range of 282-285 °C.[17] Available analytical data includes a characteristic LC-MS/MS spectrum, which serves as a key identifier in residue analysis and research.[23]

The clear distinction between the base molecule and its hydrochloride salt is essential for accurate scientific interpretation. The base form has an average molecular weight of approximately 385.37 g/mol, while the hydrochloride salt has an average weight of about 421.83 g/mol.[19] This difference is critical for calculating molar concentrations and interpreting dosage information from pharmacological and toxicological studies.

Property	Sarafloxacin (Base)	Sarafloxacin Hydrochloride	Source(s)
Generic Name	Sarafloxacin	Sarafloxacin Hydrochloride	1
DrugBank ID	DB11491	DBSALT001657 (Salt)	1
CAS Number	98105-99-8	91296-87-6	19
PubChem CID	56208	56207	16
FDA UNII	RC3WJ907XY	I36JP4Q9DF	19
Molecular Formula			19
Average Molecular Weight	385.37 g/mol	421.83 g/mol	19
Monoisotopic Molecular Weight	385.1238 g/mol	421.1005 g/mol	1
IUPAC Name	6-fluoro-1-(4-fluorophenyl)-4-oxo-7-piperazin-1-ylquinoline-3-carboxylic acid	6-fluoro-1-(4-fluorophenyl)-4-oxo-7-(piperazin-1-yl)-1,4-dihydroquinoline-3-carboxylic acid hydrochloride	19
Physical Form	Solid, Off-White to Pale Beige	Powder	6
Melting Point	282-285 °C	275 °C	17
pKa (Acidic)	~5.74 - 6.17	5.74	17
pKa (Basic)	8.68	8.68	18

3.0 Pharmacology and Antimicrobial Profile

The therapeutic utility of Sarafloxacin is derived from its potent activity as an antimicrobial agent. Its pharmacological profile is defined by its specific molecular mechanism of action, its broad spectrum of activity, and its in vitro potency against clinically relevant bacterial pathogens. While this profile demonstrated considerable promise, it also placed Sarafloxacin within a class of antibiotics that would later come under intense regulatory scrutiny.

3.1 Mechanism of Action: The Fluoroquinolone Class

Sarafloxacin is a member of the fluoroquinolone family of antibiotics, a class distinguished by its unique ability to directly inhibit bacterial DNA synthesis.[5] Unlike many other antibiotic classes that target cell wall synthesis or protein production, fluoroquinolones interfere with the fundamental processes of DNA replication, transcription, and repair.[5] Their primary targets are two essential bacterial enzymes known as type II topoisomerases: DNA gyrase (also called topoisomerase II) and topoisomerase IV.[26] These enzymes are critical for managing the complex topology of bacterial DNA, introducing and removing supercoils to allow for the unwinding and separation of DNA strands during replication.[5] Mammalian topoisomerases differ structurally from their bacterial counterparts and are not susceptible to inhibition by clinically relevant concentrations of fluoroquinolones, which provides the basis for the selective toxicity of these drugs.[27]

3.2 Inhibition of Bacterial DNA Gyrase and Topoisomerase IV

Sarafloxacin exerts its bactericidal effect by dually targeting and inhibiting both DNA gyrase and topoisomerase IV.[25] The process begins with the drug binding to the complex formed between the topoisomerase and the bacterial DNA.[5] This binding action effectively traps the enzyme in an intermediate stage of its catalytic cycle, stabilizing a "cleaved complex" in which the enzyme has made a double-strand break in the DNA but is prevented from resealing it.[26]

This stabilized, broken DNA-enzyme complex acts as a physical roadblock, obstructing the progression of the DNA replication fork and transcription machinery.[5] The accumulation of these stalled complexes triggers cellular stress responses and ultimately leads to the fragmentation of the bacterial chromosome, resulting in rapid cell death.[6] This mechanism of action is concentration-dependent, with higher drug concentrations leading to a more rapid and complete bactericidal effect.[27]

While both enzymes are targeted, their relative sensitivity to fluoroquinolones can vary between bacterial species. In many Gram-negative bacteria, such as E. coli—the primary target for Sarafloxacin in poultry—DNA gyrase is considered the primary and more sensitive target.[2] In contrast, for many Gram-positive bacteria, topoisomerase IV is the principal target.[5] Sarafloxacin's ability to inhibit both enzymes contributes to its broad spectrum of activity.

3.3 Spectrum of Antimicrobial Activity and In Vitro Potency

Sarafloxacin is characterized as a broad-spectrum antibiotic, demonstrating potent activity against a wide range of both Gram-negative and Gram-positive bacteria.[6] Its development was driven by its efficacy against pathogens of veterinary importance, particularly those affecting poultry.

In vitro susceptibility testing revealed that Sarafloxacin's potency was comparable to that of other highly effective fluoroquinolones, including ciprofloxacin and enrofloxacin.[4] It demonstrated excellent activity against a collection of 823 bacterial strains from various species, inhibiting most at concentrations of 2 µg/mL or less.[4] Specific pathogens shown to be susceptible include clinical isolates of anaerobic bacteria such as

Bacteroides, Fusobacterium, Eubacterium, Actinomyces, and Peptococcus (with Minimum Inhibitory Concentrations, or MICs, ranging from 0.5 to 2 µg/mL).[29] Its activity against aerobic pathogens was also well-documented, with quality control ranges established for key organisms like

Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, and Staphylococcus aureus.[4]

The drug's primary clinical application was for treating colibacillosis, and its high activity against E. coli was a cornerstone of its profile. For isolates associated with this disease in poultry, proposed interpretive criteria defined susceptible strains as those with an MIC of ≤0.06 µg/mL.[4] In a study focused on

E. coli O78, a pathogenic strain affecting Muscovy ducks, the MIC was 0.125 µg/mL, and the Minimum Bactericidal Concentration (MBC) was 0.25 µg/mL, indicating a potent bactericidal effect (MBC/MIC ratio of 2).[2]

A crucial element of Sarafloxacin's profile is its activity against human commensal bacteria, as this formed the basis of its human safety assessment. The pivotal study for this evaluation determined the MIC₅₀ against three strains of Peptostreptococcus spp., isolated from human gut flora, to be 0.125 µg/g.[9] This value, representing the concentration needed to inhibit the most sensitive relevant bacteria in the human gastrointestinal tract, was a key input for the calculation of the microbiological ADI. This juxtaposition of high potency against animal pathogens and a measurable impact on human commensal flora highlights the central regulatory conflict that defined the drug's history. Despite its clear

in vitro power, this very potency against a wide range of bacteria, including those in the human microbiome, contributed to the safety concerns that led to its withdrawal.

Pathogen	Test Condition / Strain	MIC	MBC	MPC	Source(s)
Escherichia coli	O78 (Avian Pathogen)	0.125 µg/mL	0.25 µg/mL	1 µg/mL	2
Escherichia coli	ATCC 25922 (QC Strain)	0.008 - 0.03 µg/mL	-	-	4
Peptostreptococcus spp.	Human GI Isolates (MIC₅₀)	0.125 µg/g	-	-	9
Pseudomonas aeruginosa	ATCC 27853 (QC Strain)	0.12 - 1 µg/mL	-	-	4
Staphylococcus aureus	ATCC 29213 (QC Strain)	0.06 - 0.25 µg/mL	-	-	4
Enterococcus faecalis	ATCC 29212 (QC Strain)	0.5 - 2 µg/mL	-	-	4
Bacteroides, Fusobacterium, Eubacterium, Actinomyces, Peptococcus	Clinical Anaerobic Isolates	0.5 - 2 µg/mL	-	-	29

MIC: Minimum Inhibitory Concentration; MBC: Minimum Bactericidal Concentration; MPC: Mutant Prevention Concentration; QC: Quality Control

4.0 Multi-Species Pharmacokinetics and Metabolism

The absorption, distribution, metabolism, and excretion (ADME) profile of a drug determines its concentration and persistence in the body, which in turn dictates its efficacy and safety. For Sarafloxacin, pharmacokinetic studies across multiple species revealed significant variability, particularly in oral bioavailability. These differences were not merely academic; they proved to be a decisive factor in both its clinical application in animals and its ultimate regulatory assessment for human food safety.

4.1 Profile in Avian Species (Chickens, Turkeys, Ducks)

As poultry were the primary target for Sarafloxacin therapy, its pharmacokinetic profile in these species is of paramount importance. Studies in broiler chickens and Muscovy ducks show that the drug is rapidly absorbed and extensively distributed.

In broiler chickens, after a single oral dose of 10 mg/kg, Sarafloxacin reached peak plasma concentrations relatively quickly and demonstrated an oral bioavailability (F) of 59.6%.[8] Its elimination half-life (

) following oral administration was 3.89 hours, indicating relatively rapid clearance from the body. The steady-state volume of distribution () was 3.40 L/kg, a large value that signifies extensive penetration into tissues beyond the plasma compartment, which is a desirable trait for treating systemic infections like colisepticemia.[8]

In Muscovy ducks, the pharmacokinetic profile was even more favorable. Following a 10 mg/kg oral dose, absorption was extremely rapid, with a time to peak concentration () of only 0.44 hours.[2] Most notably, the oral bioavailability was exceptionally high at 97.6%, suggesting nearly complete absorption from the gastrointestinal tract.[2] This is significantly higher than what was observed in broiler chickens. The elimination half-life in ducks was also longer, at 8.21 hours, allowing for more sustained therapeutic concentrations. The volume of distribution was also very large (10.4 L/kg), and plasma protein binding was moderate at 39.3%.[2]

It is also relevant to note that Sarafloxacin is the major active metabolite of another veterinary fluoroquinolone, difloxacin. Following administration of difloxacin to chickens, Sarafloxacin is formed in the body and contributes to the overall antimicrobial effect.[30]

4.2 Profile in Mammalian Species (Pigs, Dogs, Rodents)

Pharmacokinetic data from mammalian species provide a broader context for understanding Sarafloxacin's behavior and were crucial for its preclinical safety evaluation.

In pigs, a single 5 mg/kg oral dose resulted in an oral bioavailability of 42.6%, which is lower than that observed in avian species.[8] The elimination half-life after oral dosing was 7.20 hours, longer than in broilers, suggesting slower elimination.[8]

In dogs, Sarafloxacin demonstrated efficient absorption, with bioavailability estimated to be between 58% and 70%.[10] However, absorption appeared to be dose-dependent, becoming less efficient as the dose increased. Tissue distribution studies in dogs confirmed the drug's ability to penetrate tissues widely, with particularly high concentrations of radiolabeled drug found in the liver, kidney, and, notably, the retina/uvea.[10]

In rodents (mice and rats), oral absorption was moderate, with estimates ranging from 16% in rats to 34-48% in mice.[10] In these species, the primary route of elimination following oral administration was via the feces, indicating a significant portion of the drug was either unabsorbed or underwent biliary excretion.[10] Metabolites identified in rodents included glucuronic acid conjugates and N-acetylated forms, demonstrating that the drug undergoes Phase II metabolism.[31]

4.3 Human Pharmacokinetic Considerations and Bioavailability

Although Sarafloxacin was never approved for human use, understanding its pharmacokinetics in humans was essential for assessing the safety of consuming food products from treated animals. Data submitted to JECFA for its safety review provided a critical piece of information: in humans, approximately 70% of a 100-mg oral dose is not absorbed from the gastrointestinal tract.[9] This implies a low fractional bioavailability of only about 30%.

This finding of low human oral bioavailability stands in stark contrast to the moderate-to-high bioavailability observed in the target veterinary species. This species-dependent difference became the central pillar of the human safety assessment. The rationale was that any Sarafloxacin residues consumed in food would be poorly absorbed by the human consumer. Consequently, a large fraction of the ingested residue would pass through the gastrointestinal tract and be available to interact directly with the commensal gut microflora. This realization shifted the focus of the safety evaluation from systemic toxicity (driven by absorbed drug) to microbiological risk (driven by unabsorbed drug in the colon), a decision that directly shaped the establishment of a highly conservative ADI.

Parameter	Broiler Chicken	Muscovy Duck	Pig	Dog	Human	Source(s)
Dose (Oral)	10 mg/kg	10 mg/kg	5 mg/kg	10 mg/kg	100 mg (total)	2
Oral Bioavailability (F)	59.6%	97.6%	42.6%	58-70%	~30% (estimated)	2
Elimination Half-Life ()	3.89 h	8.21 h	7.20 h	Biphasic	Not Available	2
Time to Peak ()	Not specified	0.44 h	Not specified	1.5 - 4 h	Not Available	2
Volume of Distribution ()	3.40 L/kg	10.4 L/kg ()	1.92 L/kg	Not specified	Not Available	2

5.0 Veterinary Medicine: Indications and Clinical Efficacy

Sarafloxacin was developed and approved as a therapeutic agent to address specific, economically significant bacterial diseases in commercial poultry production. Its clinical utility was defined by its approved indications and formulations, though its performance relative to other available fluoroquinolones ultimately cast a shadow on its long-term viability in the marketplace.

5.1 Primary Indication: Treatment of Colibacillosis in Poultry

The primary and officially approved indication for Sarafloxacin in the United States was for the control of mortality associated with Escherichia coli infections in broiler chickens and growing turkeys.[3] This condition, commonly known as colibacillosis, is a major cause of morbidity, mortality, and production losses in the poultry industry.

To meet the needs of large-scale poultry operations, Sarafloxacin was marketed by Abbott Laboratories under the brand name SaraFlox® in two distinct formulations [3]:

1. NADA 141-017 (SaraFlox® WSP): A water-soluble powder designed for mass administration to flocks via their drinking water. This is a common and practical method for treating large numbers of birds simultaneously.[3]
2. NADA 141-018 (SaraFlox® Injection): An injectable solution intended for the control of early mortality in young chicks and turkey poults associated with E. coli.[3]

These formulations provided veterinarians and producers with tools to manage a critical disease threat in poultry.

5.2 Proposed Applications in Aquaculture

Beyond its approved use in poultry, there was interest in expanding Sarafloxacin's application to aquaculture. It was proposed for use in fish feed to treat common bacterial diseases in Salmonidae (the family that includes salmon and trout), such as furunculosis, vibriosis, and enteric redmouth disease.[32] The proposed dosing regimen was 10 mg/kg of fish body weight for five consecutive days.[32] The European Union's Committee for Veterinary Medicinal Products (CVMP) reviewed data supporting this use and went as far as to recommend provisional Maximum Residue Limits (MRLs) for Sarafloxacin in salmon and trout tissues.[32] However, the committee also noted that the analytical method for detecting these residues was not yet fully validated, indicating that further work was needed before a full approval could be granted.[32]

5.3 Comparative Efficacy Analysis: Sarafloxacin vs. Enrofloxacin and Danofloxacin

While in vitro data suggested Sarafloxacin's potency was comparable to other leading fluoroquinolones, a pivotal in vivo study painted a different picture of its clinical efficacy. A head-to-head comparison was conducted to evaluate the effectiveness of Sarafloxacin, enrofloxacin, and danofloxacin in treating an experimental model of colisepticemia in chickens.[33] This model was designed to mimic the severe disease seen in commercial flocks.

The results of this study established a clear hierarchy of clinical performance. The authors concluded unequivocally that "Enrofloxacin was more efficacious than either danofloxacin or sarafloxacin" and that "danofloxacin appeared to be more effective than sarafloxacin".[33]

This conclusion was supported by multiple clinical endpoints:

• Mortality and Morbidity: Only birds treated with enrofloxacin and danofloxacin showed a statistically significant reduction in mortality compared to untreated controls. Sarafloxacin did not significantly reduce mortality.[34] Furthermore, only the continuously medicated enrofloxacin group had significantly lower morbidity.[34]
• Lesion Scores: Birds treated with any of the three fluoroquinolones generally had reduced air sac lesion scores compared to controls. However, the reduction was most pronounced with enrofloxacin. Birds treated with enrofloxacin had significantly lower lesion scores than those treated with danofloxacin or Sarafloxacin.[33]
• Severe Lesions: A significantly smaller proportion of birds treated with enrofloxacin developed severe lesions compared to the other medicated groups.[33]

This demonstrated inferiority in a controlled clinical setting suggests that despite its high in vitro potency, Sarafloxacin's in vivo performance was suboptimal. This disconnect can likely be attributed to its pharmacokinetic profile in broiler chickens. The efficacy of concentration-dependent antibiotics like fluoroquinolones is critically dependent on achieving a high ratio of the drug concentration to the pathogen's MIC at the site of infection (e.g., an AUC:MIC ratio > 125).[27] Sarafloxacin's moderate oral bioavailability (~60%) and relatively short elimination half-life (~3.9 hours) in broilers may have prevented it from achieving and sustaining the necessary therapeutic concentrations as effectively as its competitors, enrofloxacin and danofloxacin.[8] This finding of weaker clinical performance likely factored into the commercial and regulatory decisions surrounding the drug's future.

6.0 Human Safety, Toxicology, and Residue Analysis

The evaluation of human safety is a paramount concern for any veterinary drug used in food-producing animals. For Sarafloxacin, this assessment was particularly rigorous and multi-faceted, involving traditional preclinical toxicology, the establishment of human safety thresholds for food residues, and consideration of class-wide adverse effects. The approach taken for Sarafloxacin, prioritizing microbiological risk over systemic toxicity, marked a significant evolution in regulatory science.

6.1 Preclinical Toxicology and Target Organ Effects

A comprehensive set of toxicological studies was conducted in various animal species to identify potential hazards. A thorough review of these studies by the Food Safety Commission of Japan (FSCJ) provides a clear summary of the findings.[31]

The studies showed no evidence that Sarafloxacin was carcinogenic in long-term studies in mice and rats. Furthermore, it did not cause reproductive toxicity or teratogenicity (birth defects) in multi-generational rodent studies.[31]

The primary target organs for toxicity identified in these studies were the kidneys and the hematopoietic system. Specific findings included:

• Nephrotoxicity: At high doses, Sarafloxacin caused kidney damage, observed as interstitial nephritis in mice and tubular nephropathy in rats.[31]
• Hematological Effects: A consistent finding in both rats and dogs was a decrease in serum globulin concentrations.[31]
• Dermatological Effects: In dogs, which appeared to be the most sensitive species, high doses also caused skin erythema (redness) and swelling around the eyelids and ears.[31]

From this body of work, the most sensitive toxicological endpoint was identified in a 90-day study in dogs. The No-Observed-Adverse-Effect-Level (NOAEL) in this study was determined to be 5 mg/kg of body weight per day, with the critical effect being the decrease in serum globulin.[31] This NOAEL would typically be used as the starting point for calculating a toxicology-based ADI.

Species	Study Type / Duration	NOAEL (mg/kg bw/day)	Critical Endpoints at Higher Doses	Source(s)
Mouse	78-week carcinogenicity	150	Increased mortality, nephrotoxicity. No carcinogenicity.	31
Rat	104-week carcinogenicity	54	Tubular nephropathy, decreased blood proteins. No carcinogenicity.	31
Rat	Three-generation reproductive	75 (Parents)	Decrease in liver weight. No reproductive or developmental toxicity.	31
Dog	90-day subacute toxicity	5	Decrease in serum globulin.	31

6.2 Establishment of the Microbiological Acceptable Daily Intake (ADI)

In a landmark decision, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) concluded that the most sensitive and appropriate endpoint for establishing a human safety threshold for Sarafloxacin was not its systemic toxicity, but its potential microbiological effects on the human gastrointestinal flora.[9] This represented a paradigm shift, acknowledging that the indirect risk of promoting antimicrobial resistance could be a more significant public health concern than direct organ toxicity.

This decision was driven by the pharmacokinetic finding that Sarafloxacin is poorly absorbed in humans, with about 70% of an oral dose remaining in the gut.[9] This unabsorbed fraction would directly expose the gut microbiome to the antibiotic. The ADI was therefore calculated using a formula designed to protect the most sensitive beneficial bacteria in the human colon:

Using a MIC₅₀ of 0.125 µg/g for Peptostreptococcus spp., a safety factor of 2, and other standard assumptions, JECFA established the microbiological ADI for Sarafloxacin as 0-0.33 µg/kg of body weight.[9] This value is profoundly more conservative than an ADI that would have been derived from the toxicological NOAEL of 5 mg/kg bw/day. In fact, this ADI provides a margin of safety of 17,000 when compared to the lowest toxicological NOEL, underscoring the priority given to the microbiological risk.[9]

6.3 Maximum Residue Limits (MRLs) in Food-Producing Animals

The ADI serves as the basis for setting Maximum Residue Limits (MRLs) in edible tissues of food-producing animals. MRLs are legally enforceable limits that ensure consumer exposure to drug residues remains well below the ADI. For Sarafloxacin, the Codex Alimentarius Commission and other regulatory bodies established the following MRLs for chicken and turkey tissues [9]:

Tissue	MRL (µg/kg)	MRL (mg/kg)
Muscle	10	0.01
Fat / Skin	20	0.02
Liver	80	0.08
Kidney	80	0.08

Additionally, the European CVMP recommended a provisional MRL of 30 µg/kg for the muscle and skin of Salmonidae, in consideration of its proposed use in aquaculture.[32]

6.4 Fluoroquinolone Class-Associated Adverse Effects

Beyond the specific toxicology of Sarafloxacin, it is essential to consider the safety profile of the entire fluoroquinolone class. In recent years, regulatory agencies like the European Medicines Agency (EMA) have issued strong warnings regarding the risk of rare but disabling, long-lasting, and potentially irreversible side effects associated with systemic fluoroquinolone use.[36] These adverse reactions can affect multiple body systems, most notably:

• Musculoskeletal System: Tendinitis and tendon rupture, muscle pain, and joint pain.
• Nervous System: Peripheral neuropathy (pins and needles, burning pain), depression, memory impairment, and sleep disturbances.
• Senses: Changes in vision, hearing, taste, and smell.

While these warnings were issued long after Sarafloxacin was withdrawn, they reflect the high level of regulatory concern surrounding this class of antibiotics and provide important context for the precautionary approach taken by the FDA in the early 2000s.

7.0 Significant Drug-Drug Interactions

The potential for a drug to interact with other concurrently administered medications is a critical aspect of its safety profile. Sarafloxacin, like other fluoroquinolones, is subject to several clinically significant drug-drug interactions that can alter its own efficacy or the safety of other drugs. These interactions primarily occur through three well-established mechanisms: interference with absorption, inhibition of drug metabolism, and additive pharmacodynamic effects on cardiac electrophysiology.

Interference with Absorption: One of the most well-known interactions involving the fluoroquinolone class is the chelation of the antibiotic by polyvalent cations. When Sarafloxacin is co-administered with products containing aluminum, magnesium, or calcium, such as antacids (e.g., Almasilate) or phosphate binders (e.g., Aluminium phosphate, Aluminum hydroxide), insoluble complexes are formed in the gastrointestinal tract.[1] This process significantly reduces the absorption of Sarafloxacin, leading to lower serum concentrations and a high risk of therapeutic failure.[1]

Inhibition of Metabolism: Sarafloxacin has the potential to inhibit certain metabolic enzymes, likely within the Cytochrome P450 (CYP450) family. This inhibition can decrease the metabolism and clearance of other drugs that are substrates for these enzymes, leading to increased plasma concentrations and a heightened risk of toxicity. Examples of drugs whose metabolism may be decreased when combined with Sarafloxacin include the anthelmintic Albendazole, the antiplatelet agent Anagrelide, and the benzodiazepine Bromazepam.[1]

Pharmacodynamic Interactions (QTc Prolongation): A major safety concern for many fluoroquinolones is their potential to prolong the QT interval of the electrocardiogram, which can increase the risk of a life-threatening cardiac arrhythmia known as Torsades de Pointes. Sarafloxacin shares this risk. Its use in combination with other drugs that also prolong the QT interval can have an additive effect, significantly increasing the danger. A large number of drugs fall into this category, including antiarrhythmics (e.g., Amiodarone), antipsychotics (e.g., Amisulpride, Asenapine), certain antibiotics (e.g., Besifloxacin), and antihistamines (e.g., Astemizole).[1]

Other Notable Interactions:

• Increased Tendinopathy Risk: Co-administration with systemic corticosteroids (e.g., Betamethasone) can increase the risk of tendon-related adverse effects, such as tendinitis and tendon rupture, a known class effect of fluoroquinolones.[1]
• Altered Sarafloxacin Concentrations: Some medications can affect the concentration of Sarafloxacin itself. For instance, certain penicillin derivatives like Amdinocillin and Bacampicillin may increase its serum concentration, potentially raising the risk of dose-related side effects.[1]

The overall pattern of these interactions is highly characteristic of the fluoroquinolone class. This predictability means that Sarafloxacin carries the same safety liabilities as its more widely used counterparts, reinforcing the need for cautious prescribing and contributing to the high level of regulatory scrutiny applied to all members of this critically important antibiotic family.

Interaction Mechanism	Interacting Drug/Class	Potential Clinical Outcome	Source(s)
Increased QTc Prolongation	Amiodarone, Amisulpride, Asenapine, Astemizole, Atazanavir, Besifloxacin	Increased risk of serious cardiac arrhythmias (Torsades de Pointes).	1
Decreased Sarafloxacin Absorption	Aluminum hydroxide, Aluminium phosphate, Almasilate (Antacids with polyvalent cations)	Reduced serum concentration of Sarafloxacin, potentially leading to decreased efficacy and treatment failure.	1
Decreased Metabolism of Co-administered Drug	Albendazole, Alosetron, Anagrelide, Antipyrine, Bromazepam	Increased serum concentration and risk of toxicity of the co-administered drug.	1
Increased Sarafloxacin Concentration	Amdinocillin, Bacampicillin	Increased serum concentration of Sarafloxacin, potentially increasing the risk of adverse effects.	1
Increased Risk of Tendinopathy	Betamethasone (Systemic Corticosteroids)	Additive risk of tendon damage, including tendinitis and tendon rupture.	1
Increased Neuroexcitation	Balsalazide	Balsalazide may increase the neuroexcitatory activities of Sarafloxacin.	1

8.0 Regulatory History: The Withdrawal of a Veterinary Antibiotic

The regulatory history of Sarafloxacin is the most defining aspect of its story. It is a compelling narrative of a drug caught at the intersection of veterinary medicine, human food safety, and the burgeoning global crisis of antimicrobial resistance. Its withdrawal from the market was not a response to a failure in animal efficacy or safety, but rather a proactive and precautionary measure to protect public health, setting a significant precedent for the regulation of veterinary antibiotics.

8.1 U.S. FDA Approval and Subsequent Withdrawal of NADAs 141-017 and 141-018

Sarafloxacin was developed by Abbott Laboratories and gained approval from the U.S. Food and Drug Administration (FDA) in 1995 for two New Animal Drug Applications (NADAs).[3] These were:

• NADA 141-017: Approved on August 18, 1995, for SaraFlox® WSP, a water-soluble powder for controlling E. coli-associated mortality in broiler chickens and growing turkeys.[12]
• NADA 141-018: Approved on October 12, 1995, for SaraFlox® Injection, for controlling early chick mortality associated with E. coli.[12]

However, its time on the market was brief. In the late 1990s, the FDA's Center for Veterinary Medicine (CVM) began to raise serious questions about the use of the entire fluoroquinolone class in poultry. After being informed by the FDA of these concerns, Abbott Laboratories requested the voluntary withdrawal of approval for both of its Sarafloxacin NADAs.[3] By doing so, the company waived its opportunity for a formal hearing on the matter.[3]

Following this request, the FDA published a notice in the Federal Register announcing the formal withdrawal of approval for NADAs 141-017 and 141-018, with an effective date of April 30, 2001.[3] Concurrently, the agency issued a final rule to amend the Code of Federal Regulations, removing the sections that reflected the approval of Sarafloxacin for oral and injectable use, as well as the associated tolerances for its residues in food.[15]

8.2 The Rationale: Human Food Safety and Fluoroquinolone Resistance

The FDA's rationale for pursuing the withdrawal was explicit and centered entirely on public health. The official notice stated that the action was based on "a question of human food safety, due to the use of fluoroquinolones such as sarafloxacin in poultry".[3]

This action was part of a broader regulatory strategy to mitigate the risk of antimicrobial resistance. The specific concern articulated by the CVM was that the use of fluoroquinolones in poultry causes the development of fluoroquinolone-resistant Campylobacter species in the treated birds.[12]

Campylobacter is a leading cause of bacterial foodborne illness in humans. The fear was that these resistant bacteria could be transferred from poultry to humans through the food chain, leading to infections that would be difficult or impossible to treat with fluoroquinolones, a critically important class of antibiotics in human medicine.[12] Epidemiological data from the period supported this concern, with one report noting that the emergence of fluoroquinolone-resistant

Campylobacter isolates in Minnesota correlated with the introduction of Sarafloxacin and enrofloxacin for use in poultry in 1995 and 1996, respectively.[13]

The withdrawal of Sarafloxacin occurred alongside the FDA's more contentious effort to withdraw approval for enrofloxacin (Baytril®) for the same indication. While Abbott chose to voluntarily withdraw Sarafloxacin, the sponsor of enrofloxacin, Bayer Corporation, contested the FDA's proposal, leading to a lengthy legal process.[12] This divergence in corporate strategy highlights the intense regulatory pressure of the time and likely reflects, in part, Sarafloxacin's comparatively weaker clinical efficacy, which may have made a costly legal defense less commercially viable.

8.3 European Regulatory Assessment and MRL Establishment

In Europe, Sarafloxacin was also evaluated by the precursor to the European Medicines Agency (EMA), the EMEA, via its Committee for Veterinary Medicinal Products (CVMP).[32] The European assessment, documented in the late 1990s, focused primarily on establishing MRLs for its use in poultry and a proposed use in farmed salmon and trout.[32] The CVMP, like JECFA, established a microbiological ADI as the basis for these MRLs, again highlighting the international consensus on the importance of this microbiological risk pathway.[32] While the drug was never fully approved for widespread use across the EU and is not currently an approved veterinary substance, this early assessment demonstrates that similar safety considerations were being applied by regulators on both sides of the Atlantic.[39] The broader context of the EMA's current highly restrictive stance on all fluoroquinolones, due to concerns over both resistance and severe, long-lasting side effects, underscores the enduring legacy of the safety questions first raised during the era of Sarafloxacin's withdrawal.[36]

9.0 Conclusion and Expert Synthesis

Sarafloxacin (DB11491) represents far more than a discontinued veterinary antibiotic; it is a significant historical case study in the evolution of modern drug regulation and the practical application of the One Health paradigm. Its story encapsulates the complex interplay between a drug's intrinsic properties, its clinical performance, and the overarching public health context in which it exists.

The drug's profile is one of contrasts. In vitro, it was a potent, broad-spectrum fluoroquinolone with activity comparable to its successful contemporaries.[4] However, this laboratory promise did not fully translate to superior clinical performance. In a direct comparative study, it was found to be less efficacious

in vivo for treating colisepticemia in chickens than both enrofloxacin and danofloxacin, a likely consequence of a suboptimal pharmacokinetic profile in that species.[33] This disparity between

in vitro potential and in vivo reality underscores the critical importance of integrated pharmacokinetic/pharmacodynamic analysis in predicting clinical outcomes.

The most scientifically and regulatorily significant aspect of Sarafloxacin was its multi-species pharmacokinetics. The discovery of its low oral bioavailability in humans compared to target animals was a pivotal moment.[9] It prompted international bodies like JECFA to pioneer a safety assessment based not on traditional organ toxicity, but on the more subtle and forward-looking concern for the drug's impact on the human gut microbiome.[9] The establishment of a microbiological Acceptable Daily Intake (ADI) was a landmark decision that prioritized the threat of antimicrobial resistance and set a new standard for the evaluation of veterinary drug residues in food.

Ultimately, Sarafloxacin's fate was sealed by its class identity. It was withdrawn from the market as part of a proactive and precautionary regulatory action by the U.S. FDA, driven by the scientifically plausible risk that its use in poultry would contribute to the pool of fluoroquinolone-resistant bacteria, thereby threatening the utility of a critically important class of antibiotics for human medicine.[3] The withdrawal was not a reaction to a documented public health crisis caused by Sarafloxacin itself, but an action to prevent a future one. It established the powerful precedent that the potential for promoting cross-resistance is a sufficient basis for removing a veterinary drug from the market, even if it is deemed safe and effective for its intended animal patients.

Today, Sarafloxacin is no longer a therapeutic agent. Its legacy, however, endures. It serves as an indispensable research chemical and analytical standard, used in studies on fluoroquinolone mechanisms and in the development of multi-residue methods for food safety monitoring.[40] More importantly, its history serves as a definitive lesson for pharmacologists, veterinarians, and regulators on the interconnectedness of animal and human health. Sarafloxacin's journey from a promising veterinary antibiotic to a regulatory case study is a clear and compelling illustration of why the stewardship of antimicrobials must be viewed through a holistic, global, and preventative lens.

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