ensure maintained drug absorption from the upper small intestine (Streubel et al.
2006 ). Oral i.r. devices have been successfully developed for production animals,
especially cattle and sheep. Different devices are based on concepts of particulates
entrapped in polymeric reservoirs, expandable devices or osmotic delivery systems
(Cardinal 1997 ; Rothen-Weinhold et al. 2000 ; Rathbone and Martinez 2002 ; Lavy
et al. 2006 ). Extensive details describing oral formulations that are either marketed
or are in research phases for production and companion animals are available (Lavy
et al. 2006 ). Drug classes and other compounds incorporated into oral i.r. formula-
tions for production animals include anthelmintics, antibacterial drugs, vitamins,
minerals and trace elements. In contrast, drugs formulated for oral CR for dogs or
humans includeb-adrenoceptor-blockers, theophylline, morphine, and a range of
non-steroidal anti-inflammatory agents (NSAIDs). Device research for ruminants
has followed a largely independent course from that for human use due to anato-
mical and physiological differences between monogastric animals and ruminants,
but recent developments of gastroretentive devices for monogastric species have
been described and are based on similar principles of flotation, density, osmotic
gradients, expansion, and bioadhesion (Streubel et al. 2006 ).
Oral i.r. examples relating to ivermectin include Merck’s Ivomec 1 SR bolus
formulation for cattle (Miller et al. 2001 ) and Ivomec Maximizer 1 for sheep
(Rehbein et al. 1998 ), releasing the drug for 135 and 100 days, respectively.
Ivermectin is a hydrophobic macrocyclic lactone derivative with potent anthel-
minthic properties. Following administration to cattle using a balling-gun, ivermec-
tin is released from high-density bolus devices on the basis of the principle of
osmotic pressure (Fig.1a). In the example of Ivomec 1 SR bolus, water enters the
device via a semi-permeable membrane and the osmotic pressure establishes the
rate of release of ivermectin. The onset of release is immediate and 12 mg per day is
Table 2Routes of drug delivery in veterinary species with examples
Route of administration Examples
Gastrointestinal Liquids (solutions, suspensions, emulsions)
Semi-solids (pastes)
Solids (tablets, powders, granules, premixes, medicated blocks)
Devices (balling guns, gastroretention)
Formulation (taste masking, modified release)
Topical Dips, spot-ons, sprays, patches, insecticidal collars, ointments,
creams, ear drops
Tracheobronchial surfaces
and alveoli
Inhalational anaesthetics, aerosols (including vaccines)Parenteral I.V, I.M, S.C, intra-articular implants, depot preparations
(excipients, stabilising agents, buffers, chelating agents, surfactants,
pyrogen-free)
Ocular and periodontal
adhesives
Eye-drops, inserts, hydrogels, (localized delivery of non-antibiotic
and antibiotic anti-microbial drugs)
Reproductive tract Intravaginal delivery systems, applicators, sponges, controlled
internal drug release (CIDR) devices, progesterone-releasing
pessaries, progesterone-loaded implantable devices
Other Intramammary infusions, ear implants (hormones)
84 D.J. Brayden et al.