Microbiology
Infections
Question 52 of 180
A 45 year old known intravenous drug user presents to ED with a fever complaining of pain over his big toe which has been getting worse over the past month. The big toe is red, swollen, hot and tender. Imaging shows changes suspicious of osteomyelitis. A recent screening swab on the computer system shows that the patient is positive for MRSA. Which of the following antibiotics is the most appropriate first-line treatment for this patient:
Answer:
The most common cause of osteomyelitis is Staphylococcus aureus, especially given the history of intravenous drug use. The first-line treatment of osteomyelitis is with intravenous flucloxacillin unless MRSA is suspected and then vancomycin (or teicoplanin) would be indicated first line.Osteomyelitis
Microbiology / Infections
Last Updated: 20th April 2022
Infective Agents
- Staphylococcus aureus (most common)
- Streptococcus pyogenes
- Haemophilus influenzae
- Escherichia coli
- Salmonella spp. (in sickle cell disease)
- Mycobacterium tuberculosis
Pathogenesis
- Haematogenous spread - distant infection causes bacteraemia and subsequent osteomyelitis
- Adjacent joint infection - septic arthritis can spread from the joint to the bone
- Direct infection - trauma, surgery or a deep ulcer can infect adjacent bone
Clinical Disease
- Systemic features: fever, malaise
- Localised pain over bone
- Erythema, swelling and pus drainage through sinuses
- Pathological fractures
Diagnosis
- Clinical diagnosis
- X-ray - changes only visible after 7 - 10 days, bone destruction and joint effusions
- MRI - bone destruction, effusions and joint damage
- Swab pus for M, C & S
- Blood cultures
Treatment
- Immobilise bone
- Antibiotic therapy
- Flucloxacillin first line (clindamycin if penicillin allergic)
- Vancomycin (or teicoplanin) if MRSA suspected
- Consider adding fusidic acid or rifampicin for initial 2 weeks
- Suggested duration of treatment 6 weeks for acute infection
- Surgical therapy
- Drainage and excision of the sequestrum
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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 |
