Citing package inserts in NLM format is left up to the imagination to varying degress. Variations appear in "quick reference" sheets across the Internet, but NIH actually provides relevant examples buried deep in Citing Medicine, 2nd edition.
Official NLM Examples
Printed Package Insert
Example located at http://www.ncbi.nlm.nih.gov/books/NBK7271/#A34483
Nasarel (flunisolide) nasal spray, 29 mcg. Mississauga (ON): Pantheon, Inc.; 2006 Sep. Package insert. Distributed by TEVA Specialty Pharmaceuticals.
Package Insert via DailyMed
Example located at http://www.ncbi.nlm.nih.gov/books/NBK7273/#A57898
Sanofi-Aventis U.S. LLC. Ambien cr (zolpidem tartrate) tablet, coated. 2007 [rev. 2007 Sep; cited 2009 Apr]. In: DailyMed [Internet].  - . [about 20 p.]. Bethesda (MD): National Library of Medicine (US). Available from: http://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=5420
Unofficial NLM/Vancouver Examples (Inaccurate?)
ACPHS (Vancouver style) uses an alternate syntax for the package insert:
Cialis [package insert]. Indianapolis, IN: Eli Lilly & C0; 2003.
Butler (AMA style) uses that same syntax:
Xarelto [package insert]. Titusville, NJ: Jansen Pharmaceuticals; 2011.
Same with Queensland (Vancouver style):
Lamasil [package insert]. East Hanover, NJ: Sandoz Pharmaceuticals Corp; 1993.
Although the NLM is theoretically the authoritative style guide for the Vancouver style, the treatment of package inserts as books and the treatment of online package inserts (i.e., DailyMed) as database entries rather than online books has likely contributed to the continued variation in recommended citation formats through various online resources. Due the variation, any author should begin by consulting official contributor guidlelines to determine whether a specific journal has a "house style" that they should follow.