title: [Serum levels of levonorgestrel during long-term use of Norplant].
abstract: OBJECTIVE
  (1) Assessment of longest effective contraceptive duration of Norplant (containing levonorgestrel, LNG) by serum levonorgestrel levels. (2) To observe the possible relationships between the serum LNG levels of long-term use (5 years) and body weight.
  
  
  METHODS
  To determine serum LNG levels in 230 women among 1,356 cases at various intervals between 1 and 11 years after implantation using RIA kits provided by WHO.
  
  
  RESULTS
  The average serum levels of LNG in users of Norplant at the 1st, 3rd, 5th years were 1,273.5, 924.0 and 739.6 pmol/L respectively. From the 5th to 7th years average serum LNG levels showed almost a linear decline, and from the 7th through 10th year it did not show much changes. The average serum LNG level was (511.1 +/- 209) pmol/L. A significant negative correlation was found between serum LNG levels and body weight at the 5th years.
  
  
  CONCLUSIONS
  One set of Norplant implants may provide effective contraception for 8-10 years in women with body weights less than 60 kg.
authors.affiliation: Gynecology and Obstetrics Hospital, Shanghai Medical University, Shanghai 200011.
authors.forename: M
authors.initials: M
authors.lastname: Du
authors.forename: Q
authors.initials: Q
authors.lastname: Shao
authors.forename: X
authors.initials: X
authors.lastname: Zhou
mesh_terms: D000328:Adult; D003271:Contraceptive Agents, Female / Q000008:administration & dosage* / Q000097:blood*; D004343:Drug Implants; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D016912:Levonorgestrel / Q000008:administration & dosage* / Q000097:blood*
chemical_list: D003271:Contraceptive Agents, Female; D004343:Drug Implants; D016912:Levonorgestrel