Microbiology
Infections
Question 70 of 77
A 45 year old patient presents to ED with a 24 hour history of a painful, red lower leg shown below. He suffered an insect bite the day before the rash developed. You determine he is well enough to be sent home. What is the most suitable antibiotic to discharge the patient with:
(Image by Pshawnoah [CC BY-SA 3.0 , via Wikimedia Commons)
Answer:
Flucloxacillin is the first-line antibiotic for uncomplicated cellulitis which is most commonly caused by infection with Staphylococcus aureus or Streptococcus pyogenes. Unlike other penicillins, flucloxacillin has activity against beta-lactamase-producing organisms such as Staphylococcus aureus as it is beta-lactamase stable.Cellulitis
Microbiology / Infections
Last Updated: 24th October 2023
Infective Agents
- Staphylococcus aureus (including MRSA)
- Streptococcus pyogenes
- Pseudomonas aeruginosa
- Gram-negative coliforms (immobile patients)
Risk Factors
- Pre-existing skin conditions e.g. eczema
- Skin wound e.g. burn, insect bite, cannula insertion site
- Peripheral vascular disease
- Diabetes mellitus
Clinical Disease
- Cellulitis
- Erythematous (indistinct margins), swollen, painful lesion that spreads, typically occurring on the limbs.
- Erysipelas
- Appears similar to cellulitis but the border is distinct and is typically on the face, shin or foot
Diagnosis
- Clinical diagnosis
- Swab lesions for M, C & S
- Blood cultures
Treatment
- Erysipelas
- Phenoxymethylpenicillin or benzylpenicillin
- If severe infection, replace phenoxymethylpenicillin or benzylpenicillin with high-dose flucloxacillin
- Suggested duration of treatment at least 7 days
- If penicillin-allergic, clindamycin or clarithromycin (or azithromycin or erythromycin)
- Cellulitis
- High-dose flucloxacillin
- If streptococcal infection confirmed, replace flucloxacillin with phenoxymethylpenicillin or benzylpenicillin
- If Gram-negative bacteria or anaerobes suspected, use broad-spectrum antibacterials
- If penicillin-allergic, clindamycin or clarithromycin (or azithromycin or erythromycin) or vancomycin (or teicoplanin)
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
