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within 24 h in horses with RAO (Robinson et al. 2002). Intravenous use of dexamethasone caused significant improvement in lung function of RAO affected horses within 2 h with a peak effect at 4–6 h (Cornelisse et al. 2004). In RAO challenged horses, the use of dexamethasone at 0.1 mg/kg bwt i.v. once daily, when compared to i.m. use of dexamethasone-21-isonicotinate and prednisone orally, was the only treatment that improved the lung function and decreased the percentage of neutrophils in the BALF (Robinson et al. 2002). Dexamethasone is one of the most common
glucocorticoids used for treatment of RAO (Cornelisse et al. 2004; Cou€
etil et al. 2006). As was mentioned previously, the
parenteral route is more efficacious for critical cases, but once the condition is stable, the enteral route is widely used due to the ease of administration (Robinson et al. 2002; Grady et al. 2010). The injectable formulation approved for i.v. and i.m. use, is commonly prescribed by veterinarians for extralabel use orally, as it is inexpensive and readily available when compared to the dexamethasone powder labelled for oral use (Grady et al. 2010). In a pharmacokinetic study, the injectable form of dexamethasone showed to have variable bioavailability, ranging from 28 to 88% (Grady et al. 2010), being greater in fasted animals (Cornelisse et al. 2004). It should be acknowledged that, according to the Animal Medicinal Drug Use Clarification Act (1994), due to the fact that oral formulations of dexamethasone are available in the market, the extralabel use of the drug is not allowed, unless it has been established by a veterinarian that there is no local availability of the oral form. Based on efficacy for treatment of human asthma, oral
prednisone has been used in the past to treat recurrent airway obstruction in horses; however, Peroni et al. (2002) demonstrated that prednisone is poorly absorbed, and its active metabolite prednisolone is rarely produced, with almost no plasma levels detected, therefore its therapeutic use is not recommended in horses. Since prednisone was not detected in serum after oral administration, it is thought that the lack of effectiveness is due to poor intestinal absorption; however, failure of the liver to convert prednisone to prednisolone, and the low affinity of prednisone to plasma proteins such as transcortin warrant further research (Alvinerie et al. 1988; Peroni et al. 2002). Prednisolone by contrast can be used to treat inflammatory conditions involving the lower airways, and is commonly used to manage RAO in horses. Even though prednisolone is less potent than dexamethasone, it has been shown to improve pulmonary function of affected horses at a 2 mg/kg bwt dose orally once daily after 7 days. However, dexamethasone given orally at a dose of 0.05 mg/kg bwt showed a greater improvement in the pulmonary function after 3 and 7 days of treatment, when compared to prednisolone, even under continuous antigen exposure (Leclere et al. 2010). In the authors’ clinical experience, and based on
scientific data previously described, for significant exacerbations of inflammatory lower respiratory conditions such as RAO, a positive response has been observed when using dexamethasone i.m. at an initial dose of 0.1 mg/kg bwt once daily for 3–7 days and tapering for a total of 3–4 weeks of therapy (Table 1) in conjunction with environmental management. Once the acute phase of the condition has passed (beginning at Week 2–3), treatment is continued with orally administered dexamethasone. A shorter course of
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TABLE 1: Recommended dosing schedule with parenteral use of dexamethasone for treatment of recurrent airway obstruction. Duration and dosages may vary depending on the patient’s progression
Dose (mg/kg bwt) Route 0.1*,†
0.075 0.05‡ 0.025 0.025
*Ivester and Cou€ (2010).
i.m. i.m. i.m.
Frequency Once daily
Once daily Once daily
i.m. or per os Once daily i.m. or per os
Duration 3 days
3 days 7 days 7 days
Every other day 7 days etil (2014). †Robinson et al. (2009). ‡Leclere et al.
dexamethasone (0.1 mg/kg bwt i.m. once daily for 7 days) with no taper may also be effective if comprehensive environmental changes are instituted concurrently (Ivester and Cou€
etil 2014). Similar to RAO, successful response to treatment of
horses with IAD is better when a combination of both environmental management and medical therapy is utilised. Both systemic and aerosolised glucocorticoids can be used to control the neutrophilic airway inflammation in cases of IAD (Cou€
etil et al. 2007). Positive results have been
observed with the use of oral prednisolone at a starting dose of 2.2 mg/kg bwt orally once daily for 7–10 days, then tapering to 1.0 mg/kg bwt once daily for 7–10 days, and then 1.0 mg/kg bwt every other day for 7–10 days; and in general, 2–4 weeks of glucocorticoid therapy is often prescribed for horses with IAD (Cou€
etil et al. 2007; Ainsworth
and Cheetham 2010a). In racehorses, oral dexamethasone used at a dosage of 10 mg daily every other day for a total of five doses has showed a positive effect (Berthold and Robinson 2009).
Inhalation therapy Inhalation therapy for the treatment of lower respiratory tract inflammation in horses such as RAO and IAD is becoming a more common method of treatment. Inhaled glucocorticoids result in less adverse effects for the horse because the therapeutic dose is usually lower, and the drug acts locally within the respiratory system (Lavoie 2001; Rush 2002, 2004). The response to treatment is usually positive within a short period, with significant changes observed after 72 h after initiation of therapy with fluticasone propionate; if combined with bronchodilators, the response can be even faster (Lavoie 2001; L and Cou€
eguillette 2003; Robinson et al. 2009; Ivester etil 2014). Treatment of RAO and IAD with inhaled
glucocorticoids is usually accompanied by the use of bronchodilators such as albuterol, salmeterol, fenoterol or pirbuterol. To administer an aerosolised medication, a special
delivery device should be used. The purpose of these devices is to optimise and maximise drug delivery into the lung (Rush 2002; Robinson et al. 2009). Some devices consist of a nose piece that adapts over a nostril (Fig 1a), while others are a face mask that fits the horse’s muzzle (Fig 1b). The efficacy of inhaled drugs depends on the dose and
distribution of aerosol deposited locally as well as the potency of the drug. Distribution of an aerosol is determined by particle size, and shape, as well as by patency of the airways and breathing pattern (Rush 2002). Aerosolised
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