3.4 Intravaginal Delivery for Fertility Regulation
Non-human primates are widely used in research on reproductive management.
Recently, population control with intravaginally-administered medroxyprogesterone
acetate has been achieved in baboons (Guy et al. 2008 ) and contraceptive vaccines
have been developed for pets, farm and wild animals (Naz et al. 2005 ). In contrast,
companion animal medicine has had a greater focus on reproductive control of
hormones as a contraceptive strategy similar to humans (Winzenburg et al. 2004 ).
Intravaginal veterinary drug administration in livestock has primarily concentrated on
delivery of female steroid hormones to manage fertility and to synchronise the
oestrous cycle in cattle, sheep and pigs (reviewed in Rathbone et al. 1997 , 2001 ).
Oestrous synchrony allows all the selected females in a herd or flock to be
artificially-inseminated at the same time, leading to coordinated management of
parturition. This results in financial advantage for the farmer, which more than
offsets the cost of the steroid device. Development of progesterone-loaded implant-
able systems for livestock progressed on principles of simple low-cost manufacture,
easy insertion without inducing epithelial damage or stress, cattle vaginal retention
rates of more than 95% and simple retrieval and immediate “switch off” of drug
release (Rothen-Weinhold et al. 2000 ). Epithelium-permeating progesterone, syn-
thetic progestogens or oestrogens are leached at an appropriate rate from moulded
devices over periods of several weeks depending on the species, and their role is to
suppress oestrous and ovulation in cyclic cattle. Device composition relied origi-
nally on polyurethane or more recently on silicone over a mould, while shape
variations have progressed from sponges to coils and T-shapes.
The progesterone-releasing intravaginal device (PRID 1 , Ceva Animal Health)
for cattle consists of micronised progesterone dispersed homogenously in silicone
rubber, and cured onto a stainless steel coil to produce a cylinder (Fig.3a).
Modifications of PRID 1 include attachment of an oestradiol tablet to the device
Table 4Selected technologies for topical veterinary drug delivery: Parasiticides unless stated
Formulation Species Example Reference
Spot-on: oily base
solution
Feline/canine Fipronil (Frontline Top
Spot 1 , Merial)Hutchinson et al. ( 1998 )Spot-on: alcohol
base
Feline/canine Selemectin (Revolution 1 ,
Pfizer Animal Health)Bishop et al. ( 2000 )Spot-on: oily base
solution
Feline/canine Imidacloprid (Advantage 1 ,
Bayer)Arther et al. ( 1997 )Pour-on: dilute
isopropanol
solution
Bovine Ivermectin (Ivomec 1 Pour-
On, Merial)Whang et al. ( 1994 )Flea-collar: vinyl
matrix resina
Feline/canine Tetrachlorvinphos
(Rabon 1 , Hartz)Witchey-Lakshmanan
( 1999 )
Transdermal
reservoir patch
Canine Fentanyl opiate (human
Duragesic-50 1 patch,
J & J, off-label use)Kyles et al. ( 1996 )aSafer alternatives to pesticide collars and dips are recommended by the Environmental Protection Agency
Drug Delivery Systems in Domestic Animal Species 91