In: Advances in Medicine and Biology. Vol. 107 ISBN: 978 - 1 - 53610 - 056 - 3
Editor: Leon V. Berhardt © 201 6 Nova Science Publishers, Inc.
Chapter 4
LEVONORGESTREL, PHARMACOKINETICS,
EFFICACY AND SAFETY
Usha Verma^1 , MD and Neil Verma^2
(^1) University of Miami, Miller School of Medicine, Miami, FL, US
(^2) Florida International University, Miami, FL, US
ABSTRACT
Levonorgestrel (LNG) is a dextrorotatory isomer of the synthetic
progestogen norgestrel. Norgestrel is a racemic mixture. The activity of
norgestrel resides in the dextrorotatory isomer, while the levorotatory
isomer is biologically inactive. Generally, LNG is rapidly absorbed with a
half-life of absorption of less than 1hour. The mean time taken to achieve
maximal serum concentration is less than 2 hours with a bioavailability of
over 90%. The half-life of elimination is approximately 24 hours. LNG
like other progestogens not only binds with progesterone receptors but
also binds to other steroid receptors. In conjunction with estradiol, LNG
causes anovulation dependent on the follicular stage and acts as an
effective contraceptive agent through several possible mechanisms
including endometrium lining thinning, inhibition of the corpus luteum,
thickening of the cervical mucus and retardation of sperm motility. LNG
is well tolerated and is considered to be safe. No links to pregnancy
complications or congenital disorders have been found. Lastly, the safety
of breastfeeding is well established with no deleterious effect on the
nursing infant.