a) CNS infection

H.T. is a 55-year-old man in the status of post neurosurgery secondary to head trauma sustained from a motor vehicle crash. H.T. is intubated and sedated but has spiked multiple fevers (maximum temperature, 39°C) over the past 24 hours. There is no change in oxygen requirements and laboratory test values are stable with normal renal function. Blood and urine culture and sensitivity results are pending. 

 a) Dr. Fernando, a medical officer of the night shift, made an enquiry on the concern of possible central nervous system ("CNS") bacterial source for empirical antibiotic coverage. (4 marks) 

(i) Suggest TWO common pathogens the empirical treatment should cover. 

(ii) List TWO antibiotics in combination as empirical treatment for H.T. (Note: antibiotic dosages are not required) 

I will stick to using IMPACT, you can also cross reference with the antibiotics chart Antibiotics spectrum of activity

(i) Suggest TWO common pathogens the empirical treatment should cover. 

As it is trauma from a motor vehicle crash, plus surgery, it is reasonable to suggest there will be risk from skin flora entering the brain, that is S. aureus (SA) and Streptococci.

In IMPACT under CNS infections there are two scenarios - brain abscess and meningitis, but you should also take into account that in this case external brain trauma plus surgery has occurred. Also under the heading for brain abscess the organisms listed is generalised to 'polymicrobial', so does not help for this particular question.

(ii) List TWO antibiotics in combination as empirical treatment for H.T. (Note: antibiotic dosages are not required)

Note the examiner has stated two drugs to be used in combination.

Referring to IMPACT, for brain abscess it is ceftriaxone or cefotaxime plus metronidazole, for meningitis it is ceftriaxone or cefotaxime plus vancomycin.

Ceftriaxone and cefotaxime have identical spectrums, ceftriaxone is more convenient to use as it is once a day and achieves higher CNS levels vs cefotaxime which is q6-8 hrly (but cheaper). They are third generation cephalosporins which mostly target gram negatives, but are also able to target Streptococci. They have some activity against Staphylococci, although not as good as the typical anti-staphylococcal penicillins eg amox-clav and the first generation cephalosporins eg cefalexin. They do however achieve better CNS levels plus target Streptococci which is an important cause of meningitis, so they are often used in CNS infections.

As I have suggested in part i) that SA is a concern then cef plus vancomycin may be a better answer as vancomycin can give additional SA coverage, plus it can also cover MRSA. (Note outside of CNS infection Vancomycin is not normally used for methicillin sensitive S. aureus (MSSA)). Vancomycin will also cover for resistant strains of Streptococci.

Under alternative treatment there is meropenem which is very broad spectrum antibiotic which can cover Streptococci and SA, but not MRSA. If MRSA is a concern then Vancomycin can be co-administered.

Also in part b) it says it is suspected bacterial meningitis.

Antibiotics spectrum of activity


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