Antibiotics For Cellulitis

  • Yuna Chow BSc (Hons), Medicine, University of St Andrews

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Overview 

Cellulitis is a common bacterial infection of the skin, with over 14 million patients affected annually in the USA.1 Whilst normal, undamaged skin can be affected by cellulitis, it usually occurs following an injury or surgery that causes a break to the skin.2 This break allows for bacteria to enter the skin and cause infection. As cellulitis is caused by bacteria, antibiotics are the mainstay of treatment used in the condition. Required for a minimum of 5 days, these antibiotics can be administered in a number of ways, including intravenously (IV) and orally. 

Understanding cellulitis

As previously discussed, cellulitis is caused by the infiltration of bacteria into the skin. There are three main types of bacteria established to cause cellulitis, and these include:2

  1. Group A β-haemolytic streptococcus (Strep)
  2. Streptococcus pneumoniae (Strep)
  3. Staphylococcus aureus (Staph)

These bacteria are commonly found on the skin and membranes of the nose and mouth. In healthy individuals, these bacteria usually pose no issue. However, when there is damage to the skin, these bacteria are able to enter the skin and cause infection. 

Cellulitis typically presents with the following symptoms:1,2

  • Redness of the skin
  • Skin that is warm to the touch
  • Swelling of the affected area 
  • Tenderness 
  • Pain
  • Bruising 
  • Fever 
  • Blisters 
  • Chills
  • Headache 
  • Weakness/Fatigue 

It is important to note that cellulitis typically only affects one side of the body at a time. For example, if cellulitis were to develop on the lower limbs, it is most likely that only one leg would be affected, rather than both. 

Cellulitis can sometimes be considered a medical emergency, with the presence of the following symptoms warranting an immediate appointment with your healthcare provider:2 

  • A very large area of inflamed/red skin
  • Severe fever 
  • If the affected area causes changes in sensation or tingling, particularly in the regions of the feet, hands, legs or arms
  • If the skin appears black
  • If the area affected is around the region of the eyes (periorbital cellulitis) or behind the ears (mastoiditis
  • If you have diabetes or a weakened immune system and develop cellulitis. 

The role of antibiotics in cellulitis

Early antibiotic intervention is essential to prevent the spread of cellulitis. These can be administered via an oral route or intravenous route. There are numerous choices of antibiotics available for the treatment of cellulitis. In patients with mild cellulitis and with no signs of systemic infection (i.e. fever), antibiotics targeting the streptococcal species should be administered.1 Importantly, antibiotics should be administered for a minimum of 5 days. 

In patients with non-purulent forms of cellulitis (cellulitis without the presence of pus), patients should receive cephalexin every 6 hours. This is a beta-lactam antibiotic belonging to the class of antibiotics known as cephalosporins. However, if patients experience an adverse reaction when taking these medications, it is advised that they instead receive clindamycin every 6 hours.1 Importantly, clindamycin has good coverage against both streptococcal and staphylococcal agents causing cellulitis.3 

In patients with purulent cellulitis, cellulitis associated with abscesses or extensive puncture wounds, or cellulitis associated with intravenous drug use, antibiotics covering methicillin-resistant staphylococcus aureus (MRSA) should be considered.1 In these patients, dual antibiotic therapy is often considered. It is advised that treatment including trimethoprim-sulfamethoxazole (twice daily for five days) and cephalexin (every 6 hours) should be given.1 In those allergic to trimethoprim-sulfamethoxazole, clindamycin taken every 6 hours should instead be used.1 If patients do not show signs of improvement within 48 hours of antibiotic initiation, an extended duration of treatment time should be considered.1 

You may be hospitalized with cellulitis if you show evidence of systemic infection (i.e. fever, elevated heart rate). You may also be hospitalized if treatment with antibiotics has shown no improvements, if you are immunocompromised, if the area of redness is rapidly spreading, or if the area of redness is encroaching upon an implanted medical device such as a pacemaker.1 If you are hospitalized, then it is likely that your healthcare professional will initiate intravenous antibiotics (antibiotics that enter the bloodstream directly through the veins). If you have cellulitis without the risk factors for MRSA, then it is likely that you will be initiated on intravenous cefazolin (another type of cephalosporin). Upon signs of improvement, guidelines indicate the need for de-escalation to cephalexin treatment for a minimum of 5 days. If risk factors for MRSA are present, then intravenous vancomycin will first be started, before eventual de-escalation to trimethoprim-sulfamethoxazole.   

Additional measures to adopt alongside antibiotic usage 

Whilst antibiotics are the most effective treatment for cellulitis, there are other measures you should adopt to better improve the healing process:2 

  • Keeping the area dry and clean
  • Elevating the affected area to reduce the risk of recurrent infection4
  • Applying cool, wet dressings to the area of infection
  • Adequate period of rest to allow the area to heal
  • Medication for pain such as ibuprofen

Antibiotic administration and monitoring for side effects 

As previously discussed, the minimum duration required for antibiotic use in cellulitis is 5 days. These can be administered either intravenously or orally. In those that exhibit no signs of improvement, antibiotics will be given for longer than 5 days. The following doses and frequency are usually used for each antibiotic:1

  • Cephalexin: 500mg every 6 hours
  • Clindamycin: 350-450mg every 6 hours
  • Trimethoprim/sulfamethoxazole: 800mg/160mg twice daily for five days
  • Vancomycin: intravenously until able to safely de-escalate. 

Common side effects of antibiotics used in cellulitis treatment  

It is important to note that antibiotics have a number of side effects. Within this section, we will discuss the common side effects to be expected with each of the antibiotics and what to do if they occur. 

Cephalexin

Cephalexin can induce a number of common side effects, which include:5 

Whilst these side effects are not life threatening, there are some rare side effects that can occur. These should be recognised and reported immediately to your healthcare professional so that appropriate action can be taken. These include:5 

In the presence of this syndrome, your healthcare provider will likely stop your antibiotics and treat the presenting syndrome. In addition to this, there are other serious side effects of cephalexin that should prompt urgent addressing with your healthcare provider: 

  • Severe diarrhea with or without blood and mucus
  • Pale stools, dark urine or yellowing of the skin/eyes
  • Unexplained bruising on the skin. 

Clindamycin

The side effects of clindamycin are very much dependent on the way in which it is administered. When taken orally, the most common side effects encountered are nausea, vomiting, and diarrhoea.3 This often occurs as clindamycin can sometimes destroy the healthy bacteria in the gut, causing these symptoms to occur.3 In rare cases, this can lead to the development of Clostridium difficile (C.diff). To test for this, your healthcare professional will take stool samples to assess for its presence. If it is detected, you will be advised to stop clindamycin immediately, and will likely be switched to vancomycin to treat the C. diff infection. 

When administered via the intravenous (IV) route, common side effects include a metallic taste in the mouth, or, in rare cases, anaphylactic shock3. If this occurs, your healthcare professional will immediately stop the clindamycin and treat the anaphylaxis. 

Trimethoprim/Sulfamethoxazole 

This antibiotic is associated with some common side effects that do not require medical attention. These include:6 

  • Loss of appetite
  • Nausea
  • Vomiting

However, trimethoprim/sulfamethoxazole can be associated with some rarer, more severe side effects which do require urgent medical attention. These include:6 

  • Symptoms of an allergic reaction (rash, itching, hives etc)
  • Aplastic anemia: fatigue, dizziness, difficulty breathing, headaches, flu-like symptoms, sore throat, increased bleeding/bruising
  • Muscle weakness and a fast or irregular heartbeat (indicative of high potassium levels)
  • Yellowing of the skin, pale coloured stools, right upper tummy pain, darkened urine (indicative of liver damage)
  • Rash, fever, and signs of swollen lymph nodes
  • Redness, blistering, or peeling of the skin (including the skin within the mouth)
  • Vaginal discharge that is associated with an odour or itching. 

Vancomycin 

Side effects of vancomycin are dependent on its mode of administration. As it is usually given in IV form in cellulitis, the common side effects include:7 

  • Hypersensitivity reactions 
  • Hypotension
  • Nephrotoxicity 

There are also some more severe, rarer side effects associated with IV vancomycin which should prompt urgent addressing by your healthcare provider. These include:7 

  • Anaphylaxis 
  • Chills 
  • Skin rash 

Importance of completing antibiotics

Whilst the antibiotics used to treat cellulitis may appear to host a number of side effects, those that are not life-threatening should not prompt early discontinuation of the drugs. It is extremely important that you complete the intended dose of the antibiotics, as this reduces the chance of antibiotic resistance from occurring. 

Antibiotic resistance occurs when the bacteria targeted develops the ability to withstand the effects of the treatment. The risk of this increases when patients do not complete their full intended dose and time of antibiotic treatment. For example, if you use cephalexin for 4 days rather than five, you risk not having killed all of the bacteria responsible for causing the cellulitis. This may allow the bacteria to reproduce with an ability to withstand cephalexin, meaning another antibiotic would be needed to tackle the recurrent cellulitis. 

Antibiotic resistance is becoming an increasing challenge within the medical world. Causing the deaths of at least 1.27 million people a year8, there are increasingly fewer antibiotics available to treat infections. It is therefore greatly important that you complete the course of antibiotics to prevent this from developing. 

Conclusion

Cellulitis is caused by bacteria entering into the skin and causing an infection. Most crucial to treating this is the use of antibiotics. With a number available to treat cellulitis, the most commonly used are cephalexin, clindamycin, trimethoprim/sulfamethoxazole, and vancomycin. 

When considering which antibiotic to use, your healthcare provider will take into consideration risk factors such as the presence of abscesses or a history of intravenous drug use. Required for a minimum of five days, this duration may be extended in the case of no symptomatic improvement or in the presence of MRSA. Associated with a number of common side effects such as nausea, vomiting, and diarrhea, antibiotics can be associated with more severe outcomes. These can include C. diff infection, Stevens-Johnson Syndrome, and damage to the liver. 

If the side effects are not life-threatening, it is crucially important that you complete the course of antibiotics so that you can reduce the chance of resistance occurring. 

References

  1. Brown BD, Hood Watson KL. Cellulitis. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 Dec 28]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK549770/.
  2. Cellulitis [Internet]. 2019 [cited 2023 Dec 28]. Available from: https://www.hopkinsmedicine.org/health/conditions-and-diseases/cellulitis.
  3. Murphy PB, Bistas KG, Le JK. Clindamycin. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2024 Jan 4]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK519574/.
  4. Cellulitis: Information For Clinicians | CDC [Internet]. 2023 [cited 2024 Jan 7]. Available from: https://www.cdc.gov/groupastrep/diseases-hcp/cellulitis.html.
  5. Herman TF, Hashmi MF. Cephalexin. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2024 Jan 7]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK549780/.
  6. Sulfamethoxazole & Trimethoprim tablets: Uses & Side Effects. Cleveland Clinic [Internet]. [cited 2024 Jan 7]. Available from: https://my.clevelandclinic.org/health/drugs/19613-sulfamethoxazole-trimethoprim-tablets.
  7. Patel S, Preuss CV, Bernice F. Vancomycin. In: StatPearls [Internet] [Internet]. StatPearls Publishing; 2023 [cited 2024 Jan 7]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK459263/.
  8. CDC. What Exactly is Antibiotic Resistance? Centers for Disease Control and Prevention [Internet]. 2022 [cited 2024 Jan 7]. Available from: https://www.cdc.gov/drugresistance/about.html.

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Morgan Keogh

MBBS, Medicine, King's College London, UK

I am a fourth year Medical Student at Kings College London, currently intercalating in a BSc in Cardiovascular Medicine. I have a strong interest in Cardiology, Acute Internal Medicine and Critical Care. I have also undertaken a research project within the field of Cardiology whereby I explored the efficacy of a novel therapeutic test at detecting correlations between established clinical characteristics and salt-sensitive hypertension. I have broad experience with both the clinical and theoretical aspects of medicine, having engaged with a wide array of medical specialities throughout my training. I am currently acting as a radiology representative within the Breast Medicine Society and have experience with tutoring at both GCSE and A-level. I am also working closely alongside medical education platforms to ensure the delivery of content applicable to the learning of future doctors.

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