How the dose is calculated
Cloxacillin is dosed in mg/kg/day divided every 6 hours. Standard oral dosing covers most mild-moderate staphylococcal skin/soft-tissue infections; the higher-dose IV regimen is used for more severe infections such as bone/joint infection or bacteraemia.
Typical dosing by indication
| Indication | Dose | Frequency | Max |
|---|---|---|---|
| Standard oral | 50 mg/kg/day | every 6h (4×/day) | 2000 mg/day |
| Severe (IV) | 100 mg/kg/day | every 6h (4×/day) | 8000 mg/day |
Clinical use
- Cloxacillin is a penicillinase-resistant (anti-staphylococcal) penicillin, making it first-line for confirmed methicillin-susceptible Staphylococcus aureus (MSSA) skin, soft-tissue, and bone/joint infections.
- Not active against methicillin-resistant Staphylococcus aureus (MRSA) — a different agent is needed if MRSA is suspected or confirmed.
- Oral bioavailability is reduced by food — best given on an empty stomach where practical.
- IV dosing is used for more severe infections such as osteomyelitis, septic arthritis, or bacteraemia, typically for a longer course than oral therapy.
Frequently asked questions
What is cloxacillin used for?
Cloxacillin is a penicillinase-resistant penicillin used specifically for infections caused by Staphylococcus aureus that has not developed methicillin resistance (MSSA) — skin, soft-tissue, and bone/joint infections in particular.
Does cloxacillin treat MRSA?
No — cloxacillin is not active against methicillin-resistant Staphylococcus aureus (MRSA). A different agent (such as clindamycin, vancomycin, or linezolid depending on severity) is needed if MRSA is suspected or confirmed.
Should cloxacillin be taken with food?
It's best given on an empty stomach where practical, since food can reduce its oral absorption.
Why would cloxacillin be given by IV instead of orally?
More severe staphylococcal infections — such as bone/joint infections, bacteraemia, or endocarditis — need the higher, more reliable blood levels that IV dosing provides, compared to oral therapy for milder skin infections.
References
- Stevens DL, et al. Practice Guidelines for Skin and Soft Tissue Infections (IDSA). Clin Infect Dis. 2014.
- British National Formulary for Children (BNFc) — Flucloxacillin/Cloxacillin.
- American Academy of Pediatrics Red Book — Staphylococcus aureus Infections.