THERAPEUTICS
2.1 Pharmacology
Very little pharmacological research has been done on macropods. Pharmacokinetic publications to date are limited to injectable antibiotics (see Chapter 11). Oral administration of drugs has not been studied.
Published dosages are largely extrapolated from other species, and supported by anecdotal evidence of safety and apparent efficacy (see Appendix 4).Kirkwood et al. (1988) reported a long elimination half-life of oxytetracycline in three red-necked wallabies with lumpy jaw. This appeared to support proposed metabolic scaling methods to extrapolate drug dosages to marsupials (Sedgwick 1993). However, in subsequent studies in healthy tammar wallabies (N. eugenii), pharmacokinetic parameters were similar to eutherians, with no apparent influence of metabolic rate (McLelland et al. 2009; McLelland et al. 2011).
Renal blood flow (RBF) and glomerular filtration rate (GFR) in tammar wallabies appear to be comparable to eutherians (McLelland et al. 2011). However, macropods are capable of significantly greater reductions in RBF and GFR in response to dehydration (Denny and Dawson 1977; Bradshaw et al. 2001), suggesting that pharmacokinetics of renally excreted drugs could vary substantially with hydration status. Further, water conservation physiology varies between macropod species, including between species adapted to arid conditions (Bradshaw et al. 2001), suggesting species variation in pharmacokinetic profiles across the Macropodidae is likely.
2.2 Antimicrobials
Long-acting preparations are of great interest in macropods to avoid potential risks associated with frequent restraint and hospitalisation for drug administration.
Following IM amoxicillin trihydrate (10 mg/kg) to tammar wallabies, plasma concentrations remained above reported minimum inhibitory concentration (MIC) breakpoints of common bacteria for up to 8 hr (McLelland et al.
2009). Long-acting oxytetracycline and procaine-benzathine penicillin G administered q 2-3 d appear unlikely to sustain clinically effective plasma concentrations, except for the most sensitive of bacteria (McLelland et al. 2011) (see Chapter 32).Ceftiofur crystalline free acid (Excede®, Zoetis Australia Pty Ltd, Rhodes, NSW) has been used in macropods (see Appendix 4) with apparent clinical efficacy and without adverse effect. It may prove to be a clinically useful broad-spectrum long-acting preparation in macropods. Pharmacokinetic studies are required.
Cefovecin (Convenia®, Zoetis Australia Pty Ltd, Rhodes, NSW) provides sustained antibiosis from a single injection in a limited range of taxa (Gull et al. 2012). Protein-binding of cefovecin in several marsupials has been investigated (see Chapter 11). The pharmacokinetic profile of cefovecin in macropods is unknown; however, based on protein binding, duration of effect is likely to be brief.
Thermoreversible poloxamer (pluronic) gels with suspended antibiotic or antifungal medications have been successfully used in a range of conditions in macropods, including macropod progressive periodontal disease (see Chapter 32) and fungal rhinosinusitis (see section 4.1.3c; Rose et al. 2018).
2.3 Antiparasitic drugs (see section 4.1.4.a)
Albendazole (3.8 mg/kg PO) was more effective than ivermectin (0.2 mg/kg) and moxidectin (1 mg/kg and 2 mg/kg) in reducing strongyle faecal egg counts (FEC) in free-ranging eastern grey kangaroos; the same trend was found with the inhibition of larval development in vitro (Cripps et al. 2013).
Ivermectin (0.2 mg/kg SC) temporarily reduced Stron- gyloides-like egg counts but had no impact on strongyle egg counts or body condition, relative to untreated controls, in translocated brush-tailed bettongs (Bettongia penicillata) (Northover et al. 2015).
2.4 Psychotropic drugs
Fluoxetine has been used to treat inappropriate aggression in two castrated male red-necked wallabies (Olds 2017).
Treatment was initiated at 0.5 mg/kg bid for 2 mo then tapered and stopped. Aggressive behaviours ceased after 2 wk of treatment. One wallaby relapsed following premature dose reduction. Mild sedation was noted in one wallaby but resolved without a change in dosing.Trazodone at 7-10 mg/kg PO bid as an individual or group treatment has been reported anecdotally to positively affect behaviour in the face of short term stressful situations. Dosages for neuroleptic drugs have been reported (Vogelnest and Portas 2008; see Chapter 9 and Appendix 3).
2.5 Spinal anaesthesia
Lumbosacral spinal anaesthesia was described in a 10-mo-old male red kangaroo with urolithiasis to aid placement of a urinary catheter (McCready et al. 2023). Lidocaine (2 mg/kg) was slowly injected in the subarachnoid space between L6 and S1. Epidural anaesthesia was intended by the authors; however, CSF was obtained when placing the spinal needle, indicating that the thecal sac extends to the lumbosacral level. Anatomical studies are required to determine if this is consistent across the Macropodidae.
3.