[3] After completing his Medical Toxicology fellowship, Seifert served on the staff of the Arizona Poison and Drug Information Center in Tucson, after which he served as the Medical Director of the Nebraska Poison Center in Omaha.

[4] In 2005, he developed and chaired “Snakebites in the New Millennium,” a progenitor meeting of the Venom Week Symposiums.

He was an investigator in a number of clinical trials of antivenoms that resulted in FDA-licensed pharmaceuticals.

[6][7] He has over 200 peer-reviewed, scientific publications including a review of snake envenomations in the New England Journal of Medicine,[8] and medical textbook chapters, including in Goldman-Cecil Medicine,[9] Critical Care Toxicology,[10] Conn's Current Therapy,[11] UpToDate,[12] and Medical Toxicology, 3e (Lippincott Williams & Wilkins)[13] He co-edited Clinical Toxinology in Australia, Europe and Americas (Springer).

[28] Seifert has published non-medical works of scientific research, as well as humor and fiction, including: "On Batting Order" in the Baseball Research Journal (1994; 23: 101-105), the official journal of the Society for American Baseball Research, "Sherlock Holmes: Academic Toxicologist" in the Baker Street Journal (2001; 51, no.

[29][30][31][32] Seifert was also a jazz, tenor saxophonist who, since 2012, had performed regularly in the "Arts-in-Medicine" concert series at the University of New Mexico Hospital and other venues with his combo, "Once Again.