title: Fentanyl remaining in a transdermal system following three days of continuous use.
abstract: OBJECTIVE
  To determine whether there was a sufficient amount of fentanyl remaining in a patch that had been used continuously for 3 days to warrant establishment of disposal policies to prevent diversion of fentanyl.
  
  
  METHODS
  Nine patches were applied and removed by hospice nurses after 3 days of continuous use on hospice patients with cancer. Patches were analyzed for the remaining fentanyl contents using the Coat-A-Count Fentanyl radioimmunoassay. Five 2.5-mg patches and four 10.0-mg patches were opened, solubilized with methanol, diluted with water, and analyzed in duplicate. An unused 2.5-mg patch also was analyzed as a control and showed a 94% recovery of fentanyl. A methanol blank was negative for fentanyl.
  
  
  METHODS
  The study determined the amount of fentanyl in milligrams remaining in a used patch. Using pharmacokinetics principles, this quantity was compared with a potential lethal dose of fentanyl.
  
  
  RESULTS
  Analysis showed 0.7-1.22 mg remaining in the 2.5-mg patches and 4.46-8.44 mg remaining in the 10.0-mg patches. These numbers represent 28-84.4% of the original contents. Using the pharmacokinetic values of the volume of distribution of 4L/kg and a potential lethal blood concentration of 3.7 micrograms/L, one can calculate the potential lethal dose for a 70-kg person to be 1036 micrograms. This is well within the amount remaining in the patch. This study also demonstrated that a wide patient variability exists in the absorption of fentanyl from the patch.
  
  
  CONCLUSIONS
  There is a sufficient amount of fentanyl available for abuse and misuse after 3 days of therapeutic use. Adequate disposal policies currently are not established and need to be implemented.
authors.affiliation: University of California, Davis, USA.
authors.forename: K A
authors.initials: KA
authors.lastname: Marquardt
authors.forename: R S
authors.initials: RS
authors.lastname: Tharratt
authors.forename: N A
authors.initials: NA
authors.lastname: Musallam
mesh_terms: D000279:Administration, Cutaneous; D000701:Analgesics, Opioid / Q000008:administration & dosage* / Q000032:analysis; D002908:Chronic Disease; D005283:Fentanyl / Q000008:administration & dosage* / Q000032:analysis; D006801:Humans; D017744:Medical Waste Disposal; D009369:Neoplasms / Q000503:physiopathology; D010146:Pain / Q000188:drug therapy; D011863:Radioimmunoassay; D012869:Skin Absorption; D019966:Substance-Related Disorders / Q000517:prevention & control; D013997:Time Factors
chemical_list: D000701:Analgesics, Opioid; D017744:Medical Waste Disposal; D005283:Fentanyl