The question
Work it with the BNF open before you show the answer. At exam pace this item has 1 min 12 s.
A 64-year-old man is reviewed on the acute medical unit on day 3 of an admission with fever and rigors from an infected peripheral cannula site in the left forearm; the cannula was removed on admission. Two sets of blood cultures taken before any antibacterial have grown Staphylococcus aureus, and the laboratory has reported sensitivities. He was started on empirical intravenous vancomycin on admission and has been afebrile for 24 hours, eating and drinking normally.
PMH: Type 2 diabetes mellitus; hypertension.
DH: Vancomycin 1 g IV 12-hrly; metformin hydrochloride 1 g PO twice daily (12-hrly); ramipril 5 mg PO daily. No known drug allergies — he completed a course of amoxicillin last year without reaction.
SH: Non-smoker; retired postal worker. A transthoracic echocardiogram shows no vegetation and he has no prosthetic valve, joint or indwelling line.
On examination: Temperature 36.7°C, HR 84/min and rhythm regular, BP 128/76 mmHg, RR 16/min, O₂ sat 97% breathing air. Left forearm cannula site clean and dry with no residual cellulitis; no new murmur and no peripheral stigmata of endocarditis. Weight 78 kg.
Investigations: Hb 126 g/L (130–170) WCC 11.2 ×10⁹/L (4.0–11.0) (16.8 on admission) Platelets 268 ×10⁹/L (150–400) Na⁺ 138 mmol/L (137–144) K⁺ 4.2 mmol/L (3.5–5.3) U 5.4 mmol/L (2.5–7.0) Cr 82 µmol/L (60–110) eGFR 92 mL/min/1.73 m² (>60) CRP 68 mg/L (<5) (214 on admission) Vancomycin 16.4 mg/L (15–20), pre-dose (trough) level taken immediately before the fifth dose Blood cultures 2 of 2 sets (<24) positive (aerobic and anaerobic bottles), taken on admission before treatment: Staphylococcus aureus — sensitive to flucloxacillin (meticillin), co-amoxiclav, doxycycline, gentamicin, rifampicin, vancomycin and linezolid; resistant to penicillin, amoxicillin, erythromycin and clindamycin; laboratory comment: meticillin-sensitive Staphylococcus aureus (MSSA), beta-lactamase producer, please discuss with microbiology if patient is penicillin allergic Repeat blood cultures 0 of 2 sets (<24) positive, taken at 48 hours: no growth to date
- add gentamicin 5 mg/kg IV daily to the vancomycin
- continue vancomycin 1 g IV 12-hrly
- switch to co-amoxiclav 1.2 g IV 8-hrly
- switch to doxycycline 100 mg PO 12-hrly
- switch to flucloxacillin 2 g IV 6-hrly
Answer and marking
switch to flucloxacillin 2 g IV 6-hrly
Marks2
ExplanationThe attached grid reports penicillin R but flucloxacillin (meticillin) S: this is meticillin-sensitive Staphylococcus aureus. At the 48–72 hour antimicrobial review, empirical vancomycin must therefore be de-escalated to the antistaphylococcal penicillin, which is more effective than a glycopeptide against a meticillin-sensitive isolate. With no allergy, normal renal function and an uncomplicated cannula-related bacteraemia, switch to flucloxacillin 2 g IV 6-hrly.
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How to approach a data interpretation item
The repeatable method from the Data Interpretation section guide.
- Spot the abnormalityRead every result against its range. Note direction and, where given, the trend.
- Decide whether it is significantDoes it cross a threshold that changes management, or is it noise?
- Link it to a medicineWhich drug could have caused it, and which drug's dosing depends on it?
- Find the action thresholdMonitoring requirements or renal impairment sections state when to act.
- Continue, adjust, hold or stopChoose the action, and only the action, the threshold calls for.
Before you submit
- Have I found the result tied to a medicine, not just an abnormal one?
- Is it significant, or noise?
- Which drug does this threshold apply to?
- Is my action the one the threshold calls for, no more and no less?
- Would a second result confirm a trend before acting?
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