Flucloxacillin Vs Amoxicillin: 2 Most Popular Antibiotics

Flucloxacillin Vs Amoxicillin: 2 Most Popular Antibiotics

Detailed information about the 2 Antibiotics is a boon. When Flucloxacillin and Amoxicillin that works almost similar, you need to know more. Find it below.

January 05, 2021
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Post Highlights

Amoxicillin is the most commonly prescribed antibiotic in the UK, with over 6 mln prescriptions issued in the last 12 months. Flucloxacillin is less prevalent, with around 3.6 mln prescriptions published simultaneously (OpenPrescribing.net, 2021).

Both antibiotics' distinct popularity comes mainly from 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: 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 prescriptions. Flucloxacillin is not listed as medicines allowed on the FP10D type of NHS prescription.

Children can use flucloxacillin to treat chest and ear infections.
Flucloxacillin stays in your system for about 8 hours, while Amoxicillin stays 6-8 hours. Both are removed from the body through urine.
Amoxicillin can be used for STDs after taking the medication for 7 days.

Licensed Use of Flucloxacillin And Amoxicillin

In the UK, flucloxacillin is a preferable antibiotic in treating 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 both drugs.

Amoxicillin Flucloxacillin
Otitis media Skin and soft tissue infections include: boils, cellulitis, infected burns abscesses.
Bacterial sinusitis Impetigo
Streptococcal tonsillitis and pharyngitis Skin infections in acne, ulcers, eczema
Chronic bronchitis: Acute exacerbations Protection for skin grafts
Community-acquired pneumonia Carbuncles
Cystitis Furunculosis
Asymptomatic bacteriuria in pregnancy Infected wounds
Acute pyelonephritis Otitis media and externa
Typhoid and paratyphoid fever Pneumonia
Dental infections Lung abscess
Prosthetic joint infections Empyema
Helicobacter pylori eradication Sinusitis
Lyme disease Pharyngitis, tonsillitis and quinsy
Prophylaxis of endocarditis Osteomyelitis, urinary tract infection, enteritis, meningitis, endocarditis and septicaemia

Why Is Flucloxacillin Recommended Antibiotic For Skin Infections?

Flucloxacillin is classified as a narrow-spectrum antibiotic. 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 as 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
Capsules Capsules
Powder for oral suspensions Powder for oral suspensions
Powder for injections Powder for injections

Sachets and dispersible tablets

Child Formulations For Flucloxacillin And Amoxicillin

Both flucloxacillin and Amoxicillin are available as powders for oral suspensions, 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 cost for children's storage and expiry dates of liquid antibiotics.

Differences In Administration

I will not go into the details of recommended administration methods for each antibiotic. Amoxicillin is generally taken three times a day, whereas flucloxacillin is 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. The absorption of Amoxicillin is not affected by food (eMC, 2020).

Flucloxacillin Vs Amoxicillin: Common Side Effects

Flucloxacillin Amoxicillin
Diarrhoea & stomach upset Diarrhoea
Nausea (feeling sick) Nausea (feeling sick)
Heartburn and indigestion

Skin rash

Source: Product information leaflets for flucloxacillin and Amoxicillin.

Gastrointestinal side effects such as upset stomach, diarrhoea, and feeling sick are usually mild and may disappear 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

Patients should not take flucloxacillin and Amoxicillin with suspected or known sensitivity to penicillins. Patients should not take flucloxacillin 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 (December-January), whereas flucloxacillin during summer (June to August).

The reason behind seasonality is preferred use in different infection types. Buying Amoxicillin in UK 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

Plenty of antibiotics is 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. 

  • 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