Colfen

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Colfen

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Medically reviewed

Laura Arias

Last updated on 22/12/2025

This page provides general, reference-level information compiled from official medical sources. It is not a substitute for professional medical advice, diagnosis, or treatment. For decisions about your health, please consult a qualified healthcare professional.

Overview of Colfen

Quick Facts

Property Description
Active ingredient Florfenicol
Form Injectable Solution, Oral Solution, Premix
Pharmacological class Broad-spectrum Antibiotic (Amphenicol Group)
Common use Control of bacterial infections in animals
Origin Synthetic, Fluorinated analog

Colfen: Definition, Composition, and Pharmacological Class

Colfen is a brand name for a synthetic antibacterial agent used exclusively in veterinary medicine, classified as a broad-spectrum antibiotic designed to control susceptible infections in various animal populations. The active component is Florfenicol, which is categorized as an amphenicol antibacterial compound. The substance is a fluorinated synthetic analog of Thiamphenicol, a derivative structurally related to Chloramphenicol. This specific modification helps enhance the stability and efficacy of the compound against a wide array of pathogens.

Available Forms and General Therapeutic Purpose

Florfenicol is formulated in multiple dosage forms tailored for efficient veterinary delivery, primarily including injectable solutions for parenteral use, oral solutions intended for drinking water, and a solid premix for medicated feed additives. The drug’s overarching therapeutic purpose is to interrupt the progression of bacterial infections to contain outbreaks in groups of animals. Florfenicol achieves this by acting as a protein synthesis inhibitor, which effectively halts the bacteria’s ability to multiply. This foundational bacteriostatic action supports the host’s natural immune response in clearing the pathogens and ultimately aids in the resolution of disease symptoms caused by susceptible microorganisms.

What side effects are possible with Colfen?

The safety profile of Colfen (Florfenicol) is characterized by specific adverse reactions that are classified based on frequency and documented by regulatory agencies, such as the EMA and FDA.

Adverse Reactions and Frequency

Side effects related to the gastrointestinal system and administration site are classified as Very Common (affecting more than 1 in 10 treated animals) in regulatory summaries. These typically include diarrhoea, transient reduction in food and water consumption, and peri-anal and rectal erythema (redness and swelling). In the case of injectable forms, swelling, induration (hardening), and pain at the injection site are also very commonly documented local reactions. Systemic effects, such as pyrexia (fever) or moderate depression, have been reported, but their frequency is often considered undetermined as it cannot be precisely estimated from available data.

Special Safety Considerations

The label includes specific safety constraints for certain populations. The use of Colfen is contraindicated in boars intended for breeding purposes due to evidence of potential adverse effects on the male reproductive system, including testicular degeneration and atrophy, found in animal toxicity studies. The product is also not recommended during pregnancy and lactation as safety has not been established in these populations. Serious reactions, such as anaphylaxis and collapse, have been reported on rare occasions. Furthermore, the label stipulates that the product must not be mixed with other medicinal products in the absence of documented compatibility studies.

Overdose and Emergency Response

Overdose and When to Seek Help

Mandatory Emergency Actions

Official regulatory documents state that immediate medical attention is required in cases of accidental human exposure, specifically following an accidental self-injection. It is mandated to consult a physician immediately and to show them the product's packaging or information leaflet. For any instance of accidental contact with the eyes or skin, medical advice must be sought if irritation persists after initial flushing.

Documented Manifestations and Risks

The official overdose profile is based on signs observed in animal tolerance studies following exposure to high doses. These manifestations include reduced food and water consumption, softening of faeces, and perianal oedema.

Severe and prolonged exposure carries regulatory warnings about the potential for systemic toxicity, specifically involving changes in hematopoietic parameters and documented damage to organ systems. Toxicity studies have linked high-dose administration with testicular degeneration and potential reproductive and developmental toxicities. Due to these documented risks, regulatory guidance advises that pregnant women should exercise caution or avoid handling this product.

Supportive Measures

In an overdose scenario, the mandated procedure is to provide symptomatic and supportive treatment. For accidental ingestion, specific instruction is often given to NOT induce vomiting.

Therapeutic Uses of Colfen

What Colfen Treats: Main Uses and Benefits

Colfen (Florfenicol) is commonly used in addressing the bacterial causes of conditions that produce acute and disruptive symptom patterns in livestock and aquatic species. It is applied across domains where additional symptomatic support is needed, primarily for acute respiratory conditions like Bovine Respiratory Disease (BRD) and Swine Respiratory Disease (SRD), painful interdigital phlegmon (foot rot) in cattle, and systemic septicemic diseases such as Enteric Septicemia of Catfish (ESC). The compound is utilized for the therapeutic management of respiratory tract infections in cattle and acute outbreaks of respiratory disease in pigs.

“The primary therapeutic role is to provide supportive relief during difficult episodes by managing the underlying bacterial load.”

This medication is relevant when symptoms create noticeable physiological strain, assisting with containing severe disease outbreaks and contributing to improved comfort during symptomatic periods.


Quick Fact: Relief for Acute Symptomatic Episodes Colfen is commonly used when groups of symptoms, such as respiratory distress or painful inflammation, appear suddenly and create temporary functional strain. It supports the management of these acute bacterial manifestations.

Regulatory References

  1. Union Register of medicinal products - European Commission

Eligibility and Restrictions for Use

Colfen (Florfenicol) use is strictly regulated based on the animal's species and production status, with certain populations explicitly prohibited from receiving the medicine by regulatory authorities.

Populations Not Eligible (Contraindicated)

Classification Restricted Groups
Absolute Prohibition Female dairy cattle 20 months of age or older (due to potential for drug residues in milk or calves).
Veal Production Calves intended to be processed for veal.
Hypersensitivity Animals that have shown hypersensitivity to the florfenicol substance.
Breeding Stock Adult bulls and animals intended for breeding purposes.

Restricted and Conditional Use

Certain groups have use restrictions or require specific veterinary re-evaluation:

  • Reproductive Status: Safety of use in pregnant or lactating swine has not been determined, leading to their regulatory exclusion from use.
  • Age and Development: A withdrawal period for pre-ruminating calves has not been established in regulatory labeling.
  • Organ Function: European labels define contraindications for animals suffering from impaired hepatic, cardiac, or renal function.
  • Finfish: Following a course of therapy, fish should be reevaluated by a veterinarian before beginning any further treatment.

What should I know about interactions with other medicines?

Interactions with other medicines and products

This section summarizes the official interaction information for Colfen (florfenicol), based strictly on government regulatory documents, focusing on documented compatibility restrictions and the absence of specific drug-drug interaction warnings.

Documented Drug-Drug Interactions

Official regulatory prescribing information does not explicitly document interactions with other medicinal products in the categories of metabolic, transporter-based, or pharmacodynamic effects. Therefore, there are no specific warnings regarding the co-administration of other medications altering florfenicol exposure or vice versa. No specific medicinal products or therapeutic classes are listed as being contraindicated due to a direct drug-drug interaction risk.

Administration Environment Constraints

Regulatory agencies impose specific restrictions related to the chemical and physical environment during the administration of the florfenicol oral solution:

Interaction Type Specific Restriction
Equipment Incompatibility Do not use or store in galvanized metal watering systems or containers
Water Treatment Incompatibility Chlorinators must not be operated while the oral solution is being administered

These constraints focus on maintaining product stability and preventing chemical reactions with the delivery system. No timing-based rules or population-specific interaction considerations for drug-drug combinations are defined in the regulatory label.

Mechanism of Action

Targeted Inhibition of Bacterial Protein Synthesis

Florfenicol exerts its core action by specifically binding to the 50S ribosomal subunit within susceptible bacteria, acting as an inhibitor of the Peptidyl Transferase Center. This direct molecular blockade prevents the essential formation of peptide bonds, thereby arresting the elongation of all bacterial proteins.

Disruption of the Pathogen Replication Cycle

The consequence of this molecular interference is the primary bacteriostatic effect, which halts the bacteria's ability to proliferate and multiply. The resultant stagnation of the pathogen population permits the host's natural immune system to engage in clearance. This sequence of events constitutes the full mechanistic cascade.

Constraints on Mechanistic Efficacy

The mechanism is subject to specific constraints, notably the potential for acquired resistance mediated by bacterial resistance genes. Mechanisms such as the activation of the FloR efflux pump actively reduce the effective drug concentration at the ribosomal target, functionally overriding the inhibition mechanism.

Dosage and Administration Information

How to Use Colfen: Administration Guidelines

The administration of Florfenicol (Colfen) follows established protocols which standardize the delivery process. The medicine is restricted to use by or on the order of a licensed veterinarian, requiring professional oversight for preparation and delivery.


Administration Scope

Entity Instruction
Routes Intramuscular (IM), Subcutaneous (SC), and Oral via medicated water or feed.
Dosing Regimen The dose is calculated based on the route and species. Examples include a single subcutaneous injection of 40 mg/kg body weight for cattle, or two intramuscular doses of 15 mg/kg for swine. Oral doses, such as those for fish, are administered at 10 to 15 mg per kg of fish body weight per day.
Frequency Injectable use follows a strict pattern of either a single dose or two doses administered 48 hours apart. Oral administration is given continuously for a 5 to 10-day course, depending on the species and formulation.
Special Conditions Parenteral administration must occur only in the neck, with a limit of 10 mL per injection site. Oral solutions are mixed into the drinking water for ad libitum consumption or into feed as the sole ration.

Population Restrictions

There are clear limits on use for specific animal classes. The medicine is restricted to beef and non-lactating dairy cattle, and it is not approved for female dairy cattle 20 months of age. Furthermore, it is not authorized for use in nursing piglets or animals intended for breeding purposes. If a satisfactory response is not observed within 72 hours of initiating treatment, a re-evaluation of the administration protocol is required.

Recent Clinical Evidence

Research Evidence / Overview of Studies for Colfen (Florfenicol)

The available research for Colfen (Florfenicol) includes clinical evaluations in specific acute conditions in animal populations. This evidence primarily consists of Randomized Controlled Trials (RCTs), large-scale field trials, and subsequent analyses published in peer-reviewed scientific literature and summarized by regulatory agencies like the European Medicines Agency (EMA) and the U.S. Food and Drug Administration (FDA).


Evidence for Use in Bovine and Swine Respiratory Conditions

Research has examined Colfen's role in conditions characterized by outcomes monitoring physiological strain or stress related to the respiratory tract, specifically Bovine Respiratory Disease (BRD) and Swine Respiratory Disease (SRD). These studies were conducted during periods of increased symptom activity where outcomes linked to inflammatory or irritative states were monitored.

Studies on Clinical Response and Mortality in BRD

Short-term RCTs and intermediate-term field trials were used in research exploring how symptoms change over time in cattle. These studies monitored outcomes such as fever, signs of respiratory distress, and the frequency of needing retreatment. Studies also monitored mortality rates as a recorded outcome. The findings describe patterns observed in the studies regarding changes in clinical signs and measurements of retreatment rates.

Studies on Herd Health Outcomes in SRD

Research for swine, involving field trials and meta-analyses, was studied for its application in herd health in conditions like SRD. Outcomes examined included changes in clinical signs like coughing, metrics related to population well-being, and post-mortem observations of lung health. Studies report how symptoms evolved in the observed populations and findings describe patterns observed in the studies related to metrics of population well-being.


Duration of Evidence and Follow-Up Periods

The body of research in regulatory filings primarily uses short-term or intermediate-term follow-up durations. This means that studies generally focused on episodes where symptoms become more noticeable and tracked outcomes for a defined period (e.g., days or a few weeks) immediately after treatment. The evidence landscape currently provides limited information for long-term outcomes or data that extensively characterize the durability of the observed response over an animal's full lifetime.

What is Still Uncertain About Colfen's Research Record

The body of research relied upon by regulatory bodies still includes areas where certainty remains low. Evidence quality varies across studies, leading to some mixed findings regarding specific retreatment rates or outcomes in different geographical regions. Ongoing research, in the form of continuous surveillance, may track the susceptibility of target bacteria. Shifts in bacterial response can occur over time, making this research relevant.

Key Studies & References

  1. Union Register of medicinal products - Nuflor 300 mg/ml solution for injection for cattle and sheep (Florfenicol)
  2. FOI Summary for the Original Approval of ANADA 200-760 Florfeniject™ (florfenicol) Injectable Solution (References NADA 141-063 for BRD and Foot Rot)
  3. NADA 141-206 - FREEDOM OF INFORMATION SUMMARY (NUFLOR 2.3% Concentrate Solution for Swine Respiratory Disease)
  4. NADA 141-246 AQUAFLOR Type A Medicated Article (florfenicol) (For control of mortality in catfish due to ESC)
  5. florfenicol | Ligand page - IUPHAR/BPS Guide to PHARMACOLOGY

Frequently Asked Questions (FAQ)

Common questions about Colfen (FAQ)


Q: Is Colfen used for long-term conditions or just short-term use?

Regulatory guidelines define Colfen's use over short, finite periods, such as a 5- to 10-day course for oral forms or a single injection. Official documentation indicates that the protocols studied and described do not include chronic or long-term administration.


Q: Does Colfen need to be taken with food, or can I take it on an empty stomach?

The way Colfen is administered depends on its form. Oral forms are typically mixed into the drinking water or medicated feed, which is required to be the sole source during the treatment period. For injectable forms, official documents do not contain specific instructions regarding the consumption of food beforehand.


Q: What is the longest period of time people usually take Colfen for?

Official dosing protocols indicate that the longest approved duration of therapy is 10 consecutive days, which applies to specific oral uses (e.g., finfish). Treatment for other species and routes is often shorter, sometimes consisting of only one or two doses.


Q: How does Colfen interact with common blood pressure medications?

Colfen is a drug approved for veterinary use in animals. Because of this focus, regulatory documents do not specify interactions with human therapeutic classes, such as blood pressure medications. Official product information only focuses on constraints relevant to the species it is approved to treat.


Q: Is Colfen safe to take if I have pre-existing kidney problems?

Official product information states that Colfen is contraindicated (not to be used) in animals suffering from impaired renal function. The term renal function refers to the normal working of the kidneys.


Q: Does alcohol change the way Colfen works in the body?

As Colfen is a veterinary-approved drug, regulatory documents do not contain information regarding interactions with human alcohol consumption. The constraints listed on the official label relate primarily to incompatibilities with certain metallic equipment or water treatments.


Q: If I have a history of allergies, is Colfen safe for me?

According to official label instructions, Colfen is contraindicated for use in any animal that has shown hypersensitivity to the active substance, florfenicol. Hypersensitivity means a severe or abnormal reaction, often referred to as an allergy.


Q: Does Colfen interact with herbal supplements like St. John's Wort?

Regulatory documents do not contain specific information regarding interactions between Colfen and herbal supplements, such as St. John's Wort. Official interaction summaries primarily address constraints related to administration and known incompatibilities.


Q: How does Colfen affect the liver?

Official regulatory documents note that use is contraindicated in animals with impaired hepatic function. The term hepatic refers to the liver. Furthermore, toxicity studies have noted changes in liver weight in test subjects.


Q: How quickly can I expect Colfen to start working?

Clinical improvement has been observed in most treated subjects within 24 hours of initiating the therapy, according to clinical data. This finding is cited in official regulatory documents regarding the drug’s effectiveness.


Q: Does Colfen have a generic or is it only available as a brand name?

The active ingredient in Colfen is florfenicol. This substance is marketed under the brand name Colfen, but it is also available under various other brand names and as a generic formulation.


Q: What happens if I miss taking a scheduled dose of Colfen?

Official guidance emphasizes the need to consult the licensed veterinarian immediately, as skipping a dose may reduce the drug's effectiveness or contribute to the development of bacterial resistance. The official label does not provide specific instructions for a missed dose.


Q: Does Colfen affect sleep patterns or cause insomnia?

Regulatory safety data sheets have noted potential effects on the central nervous system (CNS). This system is responsible for neurological functions, including the regulation of sleep.


Q: If Colfen stops working after a while, what does that usually mean?

Official documents indicate that if a positive response is not noted within 72 hours of starting treatment, the administration protocol requires re-evaluation. This process addresses concerns over lack of efficacy, which can be related to factors like bacterial resistance or an incorrect diagnosis.


Q: Are there different versions or strengths of Colfen?

Colfen is manufactured in different formulations and concentrations, as listed in regulatory specifications, to suit various routes of administration. These versions include injectable solutions, oral concentrates, and medicated feed premixes.


Q: Are there any specific laboratory tests required before starting Colfen?

The label does not explicitly mandate specific pre-treatment laboratory tests. However, official information notes that a dose-related decrease in hematopoietic tissue, which affects blood-forming cells, may occur, suggesting that blood parameters may be a consideration.


Q: Is Colfen ever used in children?

Colfen is a veterinary drug, so its use is defined in terms of animal age and development. Use is permitted in certain juvenile animals, such as young swine and finfish, but it is specifically contraindicated for others, including nursing piglets and calves intended for veal.


Q: Is Colfen considered a controlled substance?

Colfen is classified as a restricted drug under federal law, often requiring a specific Veterinary Feed Directive (VFD) for its use. This means its use must be by or on the order of a licensed veterinarian, but it is not classified as a DEA-scheduled controlled substance associated with abuse potential.


Q: Can Colfen cause weight gain or loss?

Studies and adverse reaction data indicate that treated animals may experience a transient reduction in food and water consumption. This reduction has been associated with bodyweight loss in toxicity studies.


Q: Is Colfen suitable for use by older adults?

Colfen is a veterinary drug. Regulatory labels do not define specific age-related restrictions for geriatric animals. However, the label does restrict use in animals intended for breeding purposes.


Q: Can Colfen affect the results of common blood tests?

Official adverse reaction data indicates that Colfen can affect blood counts. Specifically, it notes that a dose-related decrease in hematopoietic (blood-forming) tissue may occur.


Q: Do I need a special prescription or form to get Colfen?

Federal law strictly restricts this drug to being used by or on the order of a licensed veterinarian. This requires a special authorization, such as a Veterinary Feed Directive (VFD) document for medicated feed forms.


Q: What is the risk of dependence or addiction with Colfen?

Colfen is an antibiotic, and official regulatory labeling does not include warnings for dependence or addiction risk. The product's mechanism of action is focused on bacterial inhibition, not neurological effects related to addictive potential.


Q: Does Colfen come with a 'Black Box Warning' in official materials?

While the specific term 'Black Box Warning' is not typically used for this veterinary product, the label contains specific 'WARNINGS' and severe contraindications. These include prominent safety alerts, such as prohibiting its use in animals intended for breeding and for female dairy cattle over 20 months of age.

How should Colfen be stored and disposed of?

The official storage and disposal instructions for Colfen (Florfenicol) are strictly defined by regulatory documents to maintain product quality.

Storage Requirements

Storage Factor Official Requirement
Temperature Store Injectable Solution between 2, C and 30, C (refrigeration is not required). Oral solution must not be stored above 25, C.
Protection Protect the product from light. Keep the container tightly closed and away from heat or ignition sources.
Stability The Injectable Solution must be used within 28 to 30 days after the first vial puncture.
Safety Keep the veterinary medicinal product out of the sight and reach of children.

Disposal Instructions

Disposal of unused or expired Colfen must be done according to local and national regulatory requirements. The product should not be released into the environment, especially waterways, and containers must be disposed of at an approved waste disposal plant.

Attention! Always consult to a doctor or pharmacist before using pills or medicines.

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