Florfenicol for Pigs: Uses, Dosing & Side Effects

This information is for educational purposes only. Never give your pet any medication without your veterinarian's guidance. Dosing, frequency, and safety depend on your pet's specific health profile.

Florfenicol is a prescription antibiotic in the phenicol class. In pigs, it is used under your vet's direction to treat certain bacterial infections, especially swine respiratory disease. It works by blocking bacterial protein synthesis at the 50S ribosomal subunit, which slows or stops bacterial growth.

In U.S. swine practice, the best-known injectable product is Nuflor-S. The labeled swine indication is for respiratory disease associated with Actinobacillus pleuropneumoniae, Pasteurella multocida, Salmonella Choleraesuis, Streptococcus suis, Bordetella bronchiseptica, and Glaesserella (Haemophilus) parasuis. Your vet may choose this medication when the herd history, exam findings, and response pattern suggest these bacteria are likely involved.

Because pigs are food animals, florfenicol use also has food-safety rules. It is prescription-only, must be used exactly as labeled unless your vet gives a lawful alternative plan, and treated pigs must observe the labeled withdrawal period before slaughter. That is one reason it is important not to dose based on guesswork or leftover medication.

Florfenicol is used most often for bacterial respiratory infections in growing pigs. Your vet may consider it when pigs have fever, depression, increased breathing effort, coughing, poor appetite, or other signs consistent with swine respiratory disease. It is not a treatment for viral disease itself, but it may be used when bacterial pneumonia is suspected along with viral problems such as PRRS or influenza.

The labeled swine use is focused on respiratory pathogens, not every infection a pig can develop. That matters because antibiotics work best when they match the likely bacteria and the stage of disease. In some cases, your vet may recommend diagnostics such as necropsy, culture, PCR panels, or herd-level review before choosing treatment.

Florfenicol is not labeled for nursing piglets and not for swine of reproductive age intended for breeding. If a pig falls into one of those groups, your vet may discuss other treatment options that better fit the animal's age, production role, and residue requirements.

For the labeled U.S. injectable swine product Nuflor-S, the dose is 15 mg/kg intramuscularly in the neck, followed by a second dose 48 hours later. On the label, that equals 1 mL per 45 lb body weight. The dose volume should not exceed 10 mL per injection site.

This medication should be given only under your vet's guidance because accurate body weight, injection technique, and case selection all matter. Underdosing can reduce effectiveness and may contribute to antimicrobial resistance. Overdosing increases the risk of side effects, including reduced feed and water intake.

Your vet may also talk with you about timing. The label advises re-evaluating the diagnosis if there is no positive response within 24 hours after the second injection. In practical terms, that means florfenicol is often part of a bigger plan that may include temperature checks, hydration support, ventilation review, and herd-level disease control.

For food safety, pigs treated with labeled injectable florfenicol must not be slaughtered within 11 days of the last intramuscular treatment. Keep clear treatment records and confirm the withdrawal timeline with your vet before any marketing decision.

The most recognized side effects in pigs are usually temporary gastrointestinal and rectal-area changes. The product labeling reports perianal inflammation, rectal eversion, rectal prolapse, and diarrhea as possible transient reactions after treatment. These effects can look alarming, so it is wise to contact your vet promptly if you notice swelling, straining, tissue protrusion, or loose stool after dosing.

If the labeled dosage regimen is exceeded, pigs may have decreased feed and water consumption. That can be especially important in already sick pigs, because reduced intake can worsen dehydration and slow recovery. Injection-site tissue reactions can also occur after intramuscular dosing and may persist for days to weeks.

Call your vet sooner rather than later if a treated pig seems more depressed, stops eating, has worsening breathing effort, or develops severe diarrhea or rectal prolapse. Those signs may reflect a medication reaction, progression of the original disease, or a different diagnosis that needs a new plan.

Published swine-specific interaction data for florfenicol are limited, so your vet will usually review the full treatment plan rather than looking for one single major interaction. In general, it is important to tell your vet about any other antibiotics, anti-inflammatories, water medications, feed medications, supplements, or recent injections the pig has received.

Because florfenicol is an antimicrobial, your vet may avoid combining it with other drugs that are unnecessary, duplicative, or likely to complicate residue tracking. In food animals, interaction planning is not only about safety. It is also about judicious antimicrobial use, treatment records, and making sure withdrawal instructions remain clear.

Do not mix medications in the same syringe unless your vet specifically instructs you to do so. If a pig is on multiple treatments, ask your vet which products can be used together, whether they should be spaced apart, and which withdrawal period controls if more than one medication has been given.