GENERAL RECOMMENDATIONS FOR THERAPEUTIC DRUG USE IN AUSTRALIAN MAMMALS
Based on studies and observations of drug efficacy and side effects in Australian marsupials, the following general recommendations can be made.
• For those species of Australian mammals that have a primarily herbivorous or folivorous diet, drugs required to have a systemic effect generally have improved absorption if not administered PO, although the eastern ringed-tail possum may be the exception (Scheelings et al.
2015) (see section 2.1.1). Some drugs administered PO may bind to fibrous ingesta rather than crossing the small intestinal wall into the circulation.• Therapeutic drugs can generally be divided into those that are ‘lipophilic’ (fat-soluble and thus can cross cell membranes) or ‘lipophobic’ (or water-soluble, hydrophilic or polar). Lipophilic drugs once ‘absorbed’ have a greater chance of reaching extravascular and intracellular targets. Lipophilic drugs will cross the placenta, enter the mammary gland and cross the blood-brain barrier. These include sedatives, general anaesthetics, doxycycline, macrolides, fluoroquinolones and many parasiticides. Lipophobic drugs are largely confined to the intravascular compartments (blood). Most therapeutic drugs are more lipophilic than lipophobic. Therefore, animals with a lower percentage of body fat may require a lower dose for fatsoluble drugs than that recommended for domestic
animal species of similar size and diet. The major water-soluble drugs are penicillin, some cephalosporins, aminoglycosides, furosemide and digoxin.
• Drug binding to plasma proteins can vary between species. The antibacterial cefovecin has low protein binding in those Australian marsupials tested to date (see section 2.2.1) compared with dogs and cats; consequently, cefovecin is likely to have a short duration of action in some Australian marsupials.
• Differences in metabolism pathways may affect the PK profiles of species. For example, it has been shown that koalas, common brush-tailed possums and eastern ring-tailed possums metabolise the NSAID meloxicam and possibly carprofen (see 2.3.2) more rapidly than rats, cats and dogs.
• Drug PK profiles may not always represent the complex relationship between drug disposition and effect on pathogens. Clinical observations may not always support the PK profile for some drugs. Clinicians should use clinical evidence of drug efficacy in combination with drug PK studies (if available) in therapeutic decision making.
• Antibiotic-induced dysbiosis is a risk when administering some antibacterial drugs to some species (see section 3). Both oral and/or systemic administration of some antibiotics can lead to dysbiosis. This may be of particular significance in obligate folivorous species and herbivores.