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Imidazoline Decongestants |  |
| The imidazoline derivatives,
oxymetazoline,
xylometazoline,
tetrahydrozoline, and
naphazoline are found in topical ophthalmic and nasal decongestants available OTC. They are generally used as topical vasoconstrictors in the nose and eyes for temporary relief of nasal congestion due to colds, hay fever or other upper respiratory allergies, or sinusitis. |
| Imidazolines are sympathomimetic agents, with primary effects on α-adrenergic receptors and little if any effect on β-adrenergic receptors. Oxymetazoline is readily absorbed orally. Effects on α-receptors from systemically absorbed oxymetazoline hydrochloride may persist for up to 7 hr after a single dose. The elimination half-life in humans is 5-8 hr. It is excreted unchanged both by the kidneys (30%) and in feces (10%). |
| Clinical Findings: |
| In dogs, signs of intoxication may include vomiting, bradycardia, cardiac arrhythmias, poor capillary refill time, hypotension or hypertension, panting, increased upper respiratory sounds, depression, weakness, nervousness, hyperactivity, or shaking. These signs appear within 30 min to 4 hr postexposure. In general, imidazoline decongestant exposure may affect the GI, cardiopulmonary, and nervous systems. |
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| Treatment: |
| Decontamination may not be practical due to the rapid absorption and onset of clinical signs. Heart rate and rhythm and blood pressure should be assessed, and an ECG obtained if needed. IV fluids should be given, along with atropine at 0.02 mg/kg, IV, if bradycardia is present. Diazepam (0.25-0.5 mg/kg, IV) can be given if CNS signs (eg, apprehension, shaking) are present. Serum electrolytes (ie, potassium, sodium, chloride) should be assessed and corrected as needed.
Yohimbine, which is a specific a2-adrenergic antagonist, can also be used at 0.1 mg/kg, IV, and repeated in 2-3 hr if needed. |
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