Flucloxacillin vs Amoxicillin: 2 most POPULAR antibiotics

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Amoxicillin is the most commonly prescribed antibiotic in the UK, with over 6 mln prescriptions issued in the last 12 months. Flucloxacillin is less popular with around 3.6 mln prescriptions issued during the same time (OpenPrescribing.net, 2021). Both antibiotics’ distinct popularity comes mainly from different recommended use in the treatment of bacterial infections, even though both drugs belong to the same class of antibiotics: penicillins. This post focuses on highlighting the main differences between drugs. Flucloxacillin vs amoxicillin, a summary of the post:

  • The legal classification of flucloxacillin and amoxicillin
  • Licensed use of flucloxacillin and amoxicillin
  • Forms available
  • Child formulations for flucloxacillin and amoxicillin
  • Differences in administration 
  • Common side effects
  • Seasonality in prescribing

Flucloxacillin vs amoxicillin: legal classification

Both drugs are classified as prescription-only medicines (POM) and with this amoxicillin and flucloxacillin need to be prescribed by a qualified doctor, dentist or another qualified prescriber. Dentists, however, cannot prescribe flucloxacillin on NHS prescription. Flucloxacillin is not listed as medicines allowed on FP10D type of NHS prescription.

Licensed use of flucloxacillin and amoxicillin

In the UK, flucloxacillin is a preferable antibiotic in the treatment of skin infections and is usually reserved for this use. Flucloxacillin is almost ‘exclusively’ used to treat skin and soft tissue infections (Francis et al., 2016).  

The difference in the licensed use between flucloxacillin and amoxicillin is the main driving factor for significant variation in prescribing of both drugs.

Amoxicillin Flucloxacillin
Otitis mediaSkin and soft tissue infections including: boils, cellulitis, infected burns abscesses.
Bacterial sinusitisImpetigo
Streptococcal tonsillitis and pharyngitisSkin infections in acne, ulcers, eczema
Chronic bronchitis: Acute exacerbationsProtection for skin grafts
Community acquired pneumoniaCarbuncles
CystitisFurunculosis
Asymptomatic bacteriuria in pregnancyInfected wounds
Acute pyelonephritisOtitis media and externa
Typhoid and paratyphoid feverPneumonia
Dental infectionsLung abscess
Prosthetic joint infectionsEmpyema
Helicobacter pylori eradication Sinusitis
Lyme diseasePharyngitis, tonsillitis and quinsy
Prophylaxis of endocarditisOsteomyelitis, urinary tract infection, enteritis, meningitis, endocarditis and septicaemia

Why is flucloxacillin recommended antibiotic for skin infections?

Flucloxacillin is classified as narrow-spectrum antibiotics, which means it is effective against infections caused by a limited number of bacteria, particularly Staphylococcus aureus, which commonly cause bacterial skin infections.

Broad-spectrum antibiotics, such as amoxicillin may offer treatment against a wider group of bacteria. The main disadvantage of broad-spectrum antibiotics is the potential to contribute to bacterial resistance across different bacteria types (Melander et al., 2017).

Flucloxacillin vs amoxicillin: different formulations 

In the community, flucloxacillin and amoxicillin are usually prescribed in the form of capsules (adults) or as a powder for oral suspensions, when used to treat infections in children. The table below list all formulations available for both drugs:

Flucloxacillin Amoxicillin
CapsulesCapsules
Powder for oral suspensionsPowder for oral suspensions
Powder for injectionsPowder for injections
Sachets and dispersible tablets

Child formulations for flucloxacillin and amoxicillin

Both flucloxacillin and amoxicillin are available as powders for oral suspensions, which are usually prescribed to treat infections in children. When a prescription is brought into the pharmacy for one of the antibiotics, a certain amount of water is added during the dispensing process. Mixing of antibiotics powder is done by a pharmacy team unless instructed otherwise. 

Storage instruction for both antibiotics may be different. Generally, many made-up oral antibiotics need to be kept in the fridge. Read about the storage requirements on the box. I also dedicated a separate ost on storage and expiry dates of liquid antibiotics for children.

Diffrencces in administration

I will not go into the details for recommended methods of administration for each antibiotic. Amoxicillin is generally taken three times a day, whereas flucloxacillin four times a day. This dosing is not a general rule. Follow the directions of your prescriber.

Perhaps one of the most important differences between both drugs is the administration in relation to food stomach content.  

  • Flucloxacillin should be taken on an empty stomach. This means one hour before food or two hours after food.
  • Amoxicillin can be taken on an empty stomach or with food. Absorption of amoxicillin is not affected by food (eMC, 2020).

Flucloxacillin vs amoxicillin: common side effects

Flucloxacillin Amoxicillin
Diarrhoea & stomach upsetDiarrhoea
Nausea (feeling sick) Nausea (feeling sick)
Heartburn and indigestionSkin rash

Source: Product information leaflets for flucloxacillin and amoxicillin.

Gastrointestinal side effects such as the upset stomach, diarrhoea and feeling sick are usually mild and may go away after a few days.

Use of flucloxacillin and amoxicillin in the pregnancy

Penicillins can be used in pregnancy. They are not known to be harmful (Joint Formulary Committee, 2019).

Who should not take flucloxacillin or amoxicillin

Both flucloxacillin and amoxicillin should not be taken by patients with suspected or known sensitivity to penicillins.

Flucloxacillin should not be taken by patients with a history of liver problems (liver dysfunction or jaundice).

Prescribing statistics and seasonality

When looking at prescribing trends for both antibiotics, it can be easily seen that there is seasonality to prescribing for both drugs. Amoxicillin prescribing peaks during the winter times (December-January), whereas flucloxacillin during summer (June to August).

The reason behind seasonality is prefered use in different infection types. Amoxicillin would be the first choice in respiratory infections (infections peak in the winter), one the other hand, as already discussed, flucloxacillin would be the first choice in the skin and soft tissue infections, for example, caused by infected insect bites (peak in the summer months).

Alternative treatment options

There are plenty of antibiotics available on the market, including different oral antibiotics and antibiotic creams. However, each antibiotic has its licensed use and is prescribed according to national and local guidelines. Antibiotic resistance is one of the critical public health concerns. The resistance of bacteria to the treatment means that antibiotics stop being effective.

Looking for more answers? Leave the comment below and I will try to answer your question.

References

eMC (2020). SmPC: Amoxicillin 500 mg Capsules. Available at: https://www.medicines.org.uk/emc/product/10638/smpc Accessed on 02/01/2021

Joint Formulary Committee (2019) British National Formulary (online). BMJ Group and Pharmaceutical Press. Available at: https://bnf.nice.org.uk Accessed on 02/01/2021

Francis NA, Hood K, Lyons R, Butler CC. Understanding flucloxacillin prescribing trends and treatment non-response in UK primary care: a Clinical Practice Research Datalink (CPRD) study. J Antimicrob Chemother. 2016;71(7):2037-2046. doi:10.1093/jac/dkw084 Available at: https://dx.doi.org/10.1093%2Fjac%2Fdkw084 Accessed on 02/01/2021

Melander Roberta J., Daniel V. Zurawski, and Christian Melander (2017). Narrow-spectrum antibacterial agents. Available at: https://dx.doi.org/10.1039%2Fc7md00528h Accessed on 02.01/2021

OpenPrescribing.net, EBM DataLab, University of Oxford (2021). GP prescribing data for flucloxacillin and amoxicillin. Available at: https://openprescribing.net/ Accessed on 02/01/2021

Author: Michal

I am a community pharmacist working in UK. I blog about drugs, health and pharmacy. View all posts by Michal

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