Penicillin by DermNet New Zealand Trust.
Links for What is Penicillin?:
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https://www.dermnetnz.org/topics/penicillin/
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Penicillin by The University of California - Davis, ChemWiki, Davis, California, U.S.A..
http://chemwiki.ucdavis.edu/Biological_Chemistry/Drug_Activity/Penicillin -
Penicillin by Wikipedia, the free encyclopedia.
https://en.wikipedia.org/wiki/Penicillin