Why is flucloxacillin not used in the USA

Flucloxacillin is a narrow spectrum penicillinase resistant antibiotic commonly used in the United Kingdom and parts of Europe to treat skin and soft tissue infections caused by staphylococci. Despite its widespread use overseas, flucloxacillin is not available in the United States. This article explains what flucloxacillin is, why it lacks FDA approval, how its American equivalents differ, and when patients and clinicians should consider alternative treatments.

What flucloxacillin is
Flucloxacillin belongs to a class of penicillins that resist breakdown by the bacterial enzyme penicillinase. It is active against Penicillinase producing Staphylococcus aureus and other Gram positive cocci. Orally administered flucloxacillin is well absorbed with food and eliminated mainly via the liver. In clinical practice it is prescribed for cellulitis, infected eczema, boils and surgical site infections where staphylococcal species are suspected or confirmed.

FDA approval and regulatory history
The United States Food and Drug Administration requires manufacturers to submit comprehensive safety and efficacy data before a drug can be marketed. No pharmaceutical company applied for flucloxacillin’s approval in the US. Instead, American clinicians rely on dicloxacillin and oxacillin—very similar penicillinase resistant agents that underwent FDA review decades ago. As a result, flucloxacillin never gained US regulatory status and cannot legally be prescribed or dispensed.

Dicloxacillin versus flucloxacillin
Dicloxacillin and flucloxacillin share the same mechanism of action and spectrum. Both agents resist staphylococcal beta lactamase and treat similar infections. They differ subtly in pharmacokinetics and chemical structure. Dicloxacillin exhibits slightly higher acid stability and more consistent oral absorption in American formulations. Flucloxacillin relies more heavily on hepatic metabolism, whereas dicloxacillin is eliminated primarily by the kidneys. These small differences influenced the choice of dicloxacillin for FDA approval.

Clinical implications for US prescribers
When treating penicillinase producing staphylococcal infections, US clinicians typically prescribe dicloxacillin for oral therapy or nafcillin or oxacillin for intravenous use. These alternatives have proven safety profiles in American populations and align with Infectious Diseases Society of America guidelines. Although flucloxacillin may be familiar to clinicians trained in Europe or the UK, they should use the FDA approved agents in the US to ensure regulatory compliance and insurance coverage.

Safety considerations and side effects
Dicloxacillin shares flucloxacillin’s side effect profile including gastrointestinal upset, rash and rare liver enzyme elevations. Both drugs carry a small risk of cholestatic hepatitis, particularly in older patients. Toxicity monitoring and patient education on recognising jaundice or severe diarrhoea are identical regardless of which penicillinase resistant penicillin is used. The absence of flucloxacillin in the US does not compromise care because equivalent agents are available.

Global variations in antibiotic naming and availability
Drug nomenclature and availability vary by country. What the UK calls flucloxacillin is not registered in the US market, where dicloxacillin fills the same niche. Other regions use cloxacillin or oxacillin depending on local regulatory approvals and clinical preferences. This variation highlights the importance of understanding generic names and equivalence when reviewing international medical literature or collaborating on global health projects.

When to seek specialist advice
In cases of complex staphylococcal infections, suspected resistant strains or patient intolerance to penicillinase resistant penicillins, infectious disease consultation can guide selection of glycopeptides, lipopeptides or newer agents. If a patient treated abroad on flucloxacillin relocates to the US, clinicians can safely transition them to dicloxacillin using equivalent dosing regimens while monitoring for response and side effects.

Summary
Flucloxacillin is not used in the United States because it never obtained FDA approval. American clinicians treat penicillinase producing staphylococcal infections with dicloxacillin, nafcillin or oxacillin—all FDA approved and clinically equivalent options. Understanding this regulatory distinction ensures appropriate prescribing and seamless care for patients moving between healthcare systems.