PUI stands for Pharmacie à l'Usage Intérieur. It means a pharmacy supplying medications for patients within a healthcare facility, and the normal term, I think, is "hospital pharmacy". If the facility supplied is not a hospital, "internal pharmacy" could be used, but "hospital pharmacy" is the generic term.

We had a previous question on this term:
https://www.proz.com/kudoz/french-to-english/other/2309752-p...

A few instances of "pharmacy for internal use" or "internal-use pharmacy" can be found in English documents, but I think they are translations from French, and that these are not normal terms in English-language healthcare.

See
http://www.eahp.eu/hp-practice/hospital-pharmacy
https://forum.wordreference.com/threads/pharmacie-à-usage-in...

"Analyse de l’activité question-réponse d’une pharmacie à usage intérieur. Exemple de la gestion des interactions médicamenteuses
Analysis of the question-answer activity of a hospital pharmacy. Example of the handling of drug-interactions"
https://hal-hcl.archives-ouvertes.fr/hal-01084158/document

An Australian source for the alternative:
"Public and private hospitals have internal pharmacies that provide medicines to patients of the hospital."
Lots of instances of "internal pharmacy" in this doc.
http://www.health.gov.au/internet/main/publishing.nsf/Conten...$File/review-pharmacy-remuneration-regulation-research-findings.pdf

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Note added at 2 hrs (2018-12-27 09:51:53 GMT)
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For the last reference, click on Review of Pharmacy Remuneration and Regulation – Research findings.