title: [Pharmacokinetics of levonorgestrel after a single dose of biodegradable microspheres containing levonorgestrel in rats].
abstract: Pharmacokinetics of levonorgestrel (LNG) in the form of injectable microspheres made of biodegradable co-polymer of polylactic acid and polyglycolic acid(9: 1 PLGA) that contained 17.76% LNG, were tested in rats. Rats were given a single intramuscular injection (im) of LNG microspheres at doses of 20.4, 41.1 and 83.3 mg.kg-1. Six rats were treated with a single im of LNG microcrystals at dose of 35.0 mg.kg-1. Plasma samples obtained before injection and at various time after injection were analyzed for LNG by RIA method. Peak plasma LNG level of 67.66 nmol.L-1 was obtained 4.88 h after im of LNG microcrystals, T1/2 = 5.78 d, MRT = 10.16 d and T < 0.32 nmol.L-1 = 41.50 d. Plasma LNG levels among rats after im of three different doses of LNG microspheres showed similar biphasic changes. Cmax1 (the first phase) were 15.19, 33.61 and 38.55 nmol.L-1; Tp1 were 6, 4.67 and 4.33h; Ctrough were 1.21, 4.36 and 9.06 nmol.L-1; Ttrough were 55, 53.67 and 54.83 d; Cmax2 (the second phase) were 3.80, 9.48 and 19.68 nmol.L-1; Tp2 were 100.49, 102.21 and 89.27 d; AUC were 440.27, 1082.82 and 1931.47 nmol.d.L-1; MRT were 69.23, 65.12 and 63.25 d; T < 0.32 nmol.L-1 were 167.81, 169.73 and 167.23 d after im of LNG microspheres in doses of 20.4, 41.1 and 83.3 mg (LNG).kg-1, respectively. Cmax1, Ctrough, Cmax2 and AUC showed significantly positive correlation with LNG dose, while Tp1, Tp2, Ttrough, MRT and T < 0.32 nmol.L-1 did not.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Zhejiang Academy of Medical Sciences, Hangzhou.
authors.forename: L C
authors.initials: LC
authors.lastname: Zhang
authors.forename: G W
authors.initials: GW
authors.lastname: Sang
authors.forename: Q X
authors.initials: QX
authors.lastname: Shao
mesh_terms: D000818:Animals; D003692:Delayed-Action Preparations; D016503:Drug Delivery Systems; D005260:Female; D007773:Lactates; D019344:Lactic Acid; D016912:Levonorgestrel / Q000008:administration & dosage / Q000493:pharmacokinetics*; D008863:Microspheres; D011091:Polyesters; D011100:Polyglycolic Acid; D011108:Polymers; D051381:Rats
chemical_list: D003692:Delayed-Action Preparations; D007773:Lactates; D011091:Polyesters; D011108:Polymers; D011100:Polyglycolic Acid; D019344:Lactic Acid; C033616:poly(lactide); D016912:Levonorgestrel