Comparative and Veterinary Pharmacology

and growth promoters. The majority of long- acting parenteral products have
been developed for production animal medicine and these tend to be very profi-
table (Medlicott et al. 2004 ). Table 6 presents some authorised and research
examples using various types of delivery system technology for use in production
animals.
Long-acting (depot) injectable formulations have made less of an impact in
companion animal medicine than in livestock, as a consequence of a combination
of commercial and practical issues. For example, spot-on and oral deliveries are
simpler and administration by a veterinarian is not essential. Long-acting antipar-
asitic products for dogs include s.c. injections of moxidectin microspheres
(ProHeart 1 6, Fort Dodge), providing a 6 month period of CR to prevent canine
heartworm (Lok et al. 2005 ), re-introduced in 2008 following initial safety con-
cerns. A second example of extended duration formulations is lufenuron (Pro-
gram 1 , Novartis Animal Health), a benzoyl urea derivative and chitin inhibitor.
It was formulated as an aqueous suspension for s.c. injection to cats to give 6-month
protection against fleas (Blagburn et al. 1999 ) and has become a viable alternative
that owners might prefer to monthly oral dosing with this species. Long-acting

Table 6Long-acting injectable formulations, for cattle (unless otherwise stated)
Formulation/Product Comment Reference
Recombinant bovine somatotropin
(Posilac 1 , Elanco) for increased
feed conversion efficiency and
milk yield

Slow release from an oil-based

sterile suspension, dosed at 14

day intervals (non-EU)

Gulay et al. ( 2004 )

Florfenicol antibiotic (Nuflor 1 ,
Schering-Plough) for respiratory
disease and foot-rot

Solution in non-aqueous vehicle;

solubility controlled; 1–2 doses

in 48 h

Aslan et al. ( 2002 )

Vitamin B12 entrapped in
microspheres for lambs on
cobalt-deficient pasture
(SMARTShot-TMB12,
AgResearch)

First veterinary product using PLG

microspheres; single s.c. or i.m.

injection releasing B12 over

many weeks

Grace et al. ( 2003 )

Injectable steroid implants for
growth promotion

Pellets containing range of growth

stimulants (oestrogenic or

androgenic) implanted into back

of ear (s.c.) (Non EU)

Rossi ( 2006 )

Long-acting ivermectin
(IVOMEC^1 , Merial) s.c.
injection as a prophylactic
endectocide for sheep

Solid-dispersion of ivermectin and

castor oil crushed to make

aqueous suspension; 60 day

persistence

Xu et al. ( 2007 )

Long-acting oxytetracycline-poly
(ethylene) glycol, PEG (Bio-
Mycin 1 200, Boehringer-
Ingelheim) for treatment of
infectious respiratory diseases

Injected (i.m., s.c) to provide

therapeutic concentrations for up

to 4 days. Reduced absorption

rate due to properties of PEG

Dowling and Russell

( 2000 )

Hydrogenated castor oil
nanoparticle carriers for the
macrolide, tilmicosin

Improved PK, maintains serum

concentrations for 8 days versus

5 h normally

Han et al. ( 2009 )

96 D.J. Brayden et al.