in order to manage ovarian dysfunction inpostpartumdairy cows (Kim et al. 2004 ).
The PRID 1 device has evolved for successful intravaginal progesterone delivery
in several species. Controlled internal drug release (CIDR 1 , InterAg) dispenser
implants were originally developed as an alternative to sponges in sheep with the
advantages of higher retention rates and a reduced mucus discharge. Full details of
the manufacturing process are given in Rathbone et al. ( 1997 ); a high-temperature
injection mould process is used to cure a drug-impregnated silicone matrix over a
nylon spine (Fig.3b). CIDR 1 designs have been marketed for sheep, goats and
cattle, but different vaginal physiology makes them less suited for horses and pigs.
Biodegradable CIDR 1 prototypes for cattle using poly caprolactone (PCL) have
also been described (Rathbone et al. 2002 ). These have the advantage of using a
cooler temperature manufacturing step, which could allow more heat labile drugs
to be incorporated, as well as dealing with the environmental issue of device
disposal. The PCL device is registered by Pfizer Animal Health in Australia and
New Zealand. Cross et al. ( 2004 ) have also described an “intelligent breeding”
intravaginal device, in which release of the drug can be controlled electronically to
permit pulsed or continuous release using a gas-piston mechanism, which is
triggered in response to monitored local drug concentrations. Finally, intravaginal
delivery is also being investigated in companion animals for CR of anti-microbial
agents from mucoadhesive tablets containing microparticles. Chitosan micro-
spheres containing acriflavine and methacrylates were sufficiently “sticky”, and
released active drug for up to 8 h in vitro (Gavini et al. 2002 ).
3.5 Intramammary Formulations for Ruminants
CR formulations of antibiotics have the potential for intramammary administration
for prevention and treatment of mastitis in cattle. The optimum period for
aDimensions: 3.5 x 28.5 x 0.1 cmbDimensions: 15.0 x13.5 x 1.6 cmFig. 3Diagram of typical
cattle intravaginal devices.
(a) PRID 1 (progesterone-
releasing intra-vaginal
device); (b) CIDR-B 1
(controlled internal drug
release-bovine)
92 D.J. Brayden et al.