It's more likely that the patient would be allergic to antibiotics.

"L'utilizzo eccessivo di antibiotici (AB) può mettere il paziente in pericolo, da una parte per lo sviluppo di batteri multiresistenti e dall'altra ... "

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Note added at 3 hrs (2018-09-04 07:15:43 GMT)
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Another example of AB = antibiotici here. You can find lots of examples if you just do a search for "antibiotici AB" in Google.

You'll also find this expansion in Acromed ... it's the most comprehensive online resource for Italian medical acronyms. Free to download.

http://acromed.blogspot.com/

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Note added at 3 hrs (2018-09-04 07:20:20 GMT)
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Le classi di antibiotici (AB) più utilizzati negli ospedali (dati IMS 2014 su AB iniettabili) sono i beta lattamici delle penicilline (30%), delle ...

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Note added at 12 hrs (2018-09-04 15:39:48 GMT)
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Another source for Italian acronyms, just for people's interest, although Acromed by far contains the most entries:

http://www.ufrgs.br/imunovet/molecular_immunology/abbreviati...

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Note added at 2 days 1 hr (2018-09-06 05:37:02 GMT) Post-grading
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Glad to help. And it looks like AB is also used to abbreviate 'antibiotic' in English.

One of many examples: Abbreviations: AB, antibiotic; ABS, antibiotic stewardship; AMR, antimicrobial resistance; LMIC, low- and middle-income countries; R&D, research and development; ... etc. This one is found below, but you can find lots of "antibiotic AB" pairings in English files on the internet.

https://academic.oup.com/cid/article/60/12/1837/2462778