What Does Fluxacin 500 Do? Understanding the Antibiotic Flucloxacillin

October 7, 2025 •

4 min read

Flucloxacillin, a penicillin-class antibiotic, is often sold under brand names like Fluxacin 500 and is effective against a range of Gram-positive bacteria. It works by actively killing the bacteria responsible for infections, rather than just slowing their growth.

Quick Summary

Fluxacin 500 (Flucloxacillin) is a penicillin antibiotic used to treat various bacterial infections, including those of the skin, bone, and soft tissue. It functions by inhibiting bacterial cell wall synthesis, leading to the death of susceptible bacteria. Dosing and precautions, particularly regarding liver and kidney function, are critical.

Key Points

Antibiotic Action: Fluxacin 500 (Flucloxacillin) is a penicillin-class antibiotic that kills susceptible bacteria by disrupting their cell wall synthesis.
Primary Uses: It is used to treat bacterial infections, particularly of the skin (cellulitis), bone (osteomyelitis), and soft tissues, caused by Staphylococcus aureus and other Gram-positive cocci.
Administration: For optimal absorption, Fluxacin 500 capsules should be taken as directed by a healthcare professional.
Key Warning: A rare but serious risk of liver damage (cholestatic jaundice) is associated with flucloxacillin, especially in older patients or those on treatment longer than two weeks.
Ineffective Against Viruses and MRSA: Fluxacin 500 will not work against viral infections, like colds or flu, and is not effective against methicillin-resistant Staphylococcus aureus (MRSA).
Drug Interactions: It can interact with other medications, including methotrexate, warfarin, probenecid, and some oral contraceptives.
Importance of Completing Course: Patients should finish the entire course of medication as prescribed by their doctor to prevent the infection from returning and to avoid contributing to antibiotic resistance.

What is Fluxacin 500?

Fluxacin 500 is a brand name for the antibiotic medication flucloxacillin. Flucloxacillin belongs to a group of medicines known as penicillins, specifically a narrow-spectrum, semi-synthetic penicillin. It is primarily prescribed to combat infections caused by susceptible, usually Gram-positive, bacteria. The '500' in Fluxacin 500 typically indicates the dosage strength of each capsule. It is important to note that flucloxacillin, including Fluxacin 500, is ineffective against infections caused by viruses, such as the common cold or flu, and is also not effective against methicillin-resistant Staphylococcus aureus (MRSA).

How does Fluxacin 500 work?

Flucloxacillin's mechanism of action involves disrupting the bacterial cell wall, which is essential for the bacteria's survival and replication. The process involves several steps:

Binding to Penicillin-Binding Proteins (PBPs): Flucloxacillin works by binding to specific proteins known as penicillin-binding proteins inside the bacterial cell wall.
Inhibiting Cell Wall Synthesis: By binding to PBPs, the antibiotic prevents the final stage of bacterial cell wall synthesis, specifically the cross-linking of peptidoglycan polymer chains.
Causing Cell Lysis: The weakened cell wall is no longer able to withstand internal pressure, leading to cell lysis (breaking open) and the eventual death of the bacteria.
Overcoming Resistance: As a penicillinase-resistant penicillin, flucloxacillin is more stable against breakdown by certain enzymes produced by bacteria, making it effective against penicillinase-producing Staphylococcus aureus.

Medical uses of Fluxacin 500

Doctors prescribe Fluxacin 500 to treat a wide array of bacterial infections, including:

Skin and Soft Tissue Infections: These are some of the most common uses for flucloxacillin. Conditions include cellulitis, impetigo, infected wounds, boils, and carbuncles.
Bone and Joint Infections: It is used effectively in treating osteomyelitis (infection of the bone) and infections of the joints.
Ear, Nose, and Throat Infections: For certain bacterial infections in these areas, flucloxacillin is a suitable treatment option.
Respiratory Infections: Some chest infections, including certain types of pneumonia, may be treated with flucloxacillin, sometimes in combination with other antibiotics.
Endocarditis: In some cases, it can be used to treat infections of the heart.
Surgical Prophylaxis: It may also be administered before major surgery, particularly heart or orthopedic surgery, to prevent infections.

Potential side effects and warnings

While effective, Fluxacin 500 can cause side effects. Common ones are generally mild, but more serious reactions are possible and require immediate medical attention.

Common side effects

Nausea and vomiting
Diarrhea or loose bowel motions
Stomach upset
Mild skin rash
Oral or vaginal thrush (fungal infection) due to disruption of normal bacterial flora

Serious side effects and warnings

Severe allergic reaction: Signs include swelling of the face, lips, throat or tongue, severe itchy rash, or difficulty breathing.
Liver damage (Cholestatic Jaundice): This is a rare but serious side effect, particularly in older patients or those on long-term treatment. Symptoms include yellowing of the skin and eyes, dark urine, and pale stools. This can occur weeks after stopping treatment.
Severe diarrhea: Watery or bloody diarrhea, possibly with stomach cramps, can be a sign of a serious bowel condition called Clostridium difficile-associated diarrhea.
Drug-induced eosinophilia and systemic symptoms (DRESS): A severe skin reaction with fever and systemic involvement.

It is contraindicated for individuals with a known allergy to penicillin or a history of flucloxacillin-associated liver problems.

Comparison of Flucloxacillin vs. Cloxacillin

Flucloxacillin and Cloxacillin are both semi-synthetic, penicillinase-resistant penicillins, often used interchangeably, but there are some distinctions in their use and side-effect profiles.


Feature	Flucloxacillin	Cloxacillin
Classification	Narrow-spectrum penicillinase-resistant penicillin	Narrow-spectrum penicillinase-resistant penicillin
Primary Uses	Skin infections (cellulitis, impetigo), bone infections, ear infections, surgical prophylaxis	Very similar indications, including skin, soft tissue, and bone infections
Effectiveness	Effective against penicillinase-producing Staphylococcus aureus	Effective against penicillinase-producing Staphylococcus aureus
MRSA Coverage	Not effective against MRSA	Not effective against MRSA
Severe Hepatic Side Effects	Higher, though rare, incidence of severe hepatic adverse effects reported	Lower incidence of severe hepatic adverse effects reported
Renal Side Effects	Lower incidence of renal adverse effects reported	Higher incidence of renal adverse effects reported
Global Usage	More commonly used in the UK and Europe	More commonly used in the United States and Canada

Conclusion

Fluxacin 500, or flucloxacillin, is a targeted antibiotic used to treat a range of serious bacterial infections, particularly those caused by Staphylococcus aureus. Its ability to resist penicillinase allows it to be effective where other penicillins might fail. However, it is not a cure-all and is specific to certain bacterial types. Crucially, it must be taken as prescribed and patients should be aware of potential side effects, including the rare but severe risk of liver damage. As with any medication, it is essential to follow a doctor's instructions and complete the full course of treatment to ensure effectiveness and minimize the risk of antibiotic resistance.

For more detailed information, consult the National Health Service (NHS) guide on flucloxacillin.

Frequently Asked Questions

Fluxacin 500 is a brand name for the generic drug Flucloxacillin 500mg. The active ingredient and dosage strength are the same; the difference is in the manufacturer's name for the product.

While most infections show improvement within a few days of starting treatment, the exact onset and duration of effect can vary based on the specific infection and individual patient factors.

There is no known direct interaction between alcohol and flucloxacillin, but it is generally recommended to avoid alcohol while taking antibiotics, as it can worsen side effects like nausea and diarrhea and may stress the liver.

If you miss a dose, take it as soon as you remember, unless it's almost time for your next dose. In that case, skip the missed dose and continue with your regular schedule. Do not take a double dose to make up for a missed one.

Flucloxacillin appears to be safe for use during pregnancy and breastfeeding, but you should always consult your doctor to discuss the risks and benefits before taking any medication while pregnant or breastfeeding.

Signs of an allergic reaction can include a skin rash, itching or hives, and swelling of the face, lips, tongue, or throat. If you experience any of these, stop taking the medication and seek immediate medical attention.

Taking Fluxacin 500 as recommended, such as before a meal, may help ensure that the drug is absorbed efficiently into your bloodstream. Food can sometimes interfere with this process, potentially reducing the medication's effectiveness.

Flucloxacillin capsules should be stored in a cool, dry place below 25°C, away from direct sunlight, heat, and moisture. Keep them in their original packaging and out of the reach of children.