Alpha-2 Adrenergics, Phenothiazines, Opioids, & Opiates

What is the preferred sedative in ruminants?

xylazine

What is the preferred xylazine reversal agent?

yohimbine

What is the drug of choice for sedating a dog for allergy skin testing and what is unusual about its dosing and what is the preferred antagonist?

• dexmedetomidine since it will not interfere with vasoactive responses elicited by the allergens

• antagonist is atipamezole

• dosing is based on body surface area

What is an equine-specific alpha2 agonist used for colic-associated pain?

romifidine

What is an alpha2 agonist/antagonist combination in which the vatinoxan minimizes side effects.

metomedine + vatinoxan

What is the common MOA for phenothiazines?

antagonists of the postsynaptic DA2 receptor (confers sedation) and can be anti-histamine → anti-emesis and/or anti-cholinergic → anti-emesis and/or anti-adrenergic → CV effects and/or anti-serotonergic → anti-serotonin syndrome effects

Know the five potential uses for acepromazine.

1. anti-emesis

2. exam room sedation/cooperation

3. travel sedation

4. equine laminitis

5. foal rejection

Know the genital side effect of acepromazine and other phenothiazines and how can this information be helpful when purchasing a horse.

equine persistent penile prolapse

Know the unique use for cyproheptadine in regards to serotonin.

anti-serotonergic activity, specifically is a 5HT receptor antagonist → useful for treating the serotonin syndrome, if severe

What is the common MOA for opioids?

• activate opioid receptors (GPCRs) → dampen action potentials in pain-transducing neurons

• activate pre-synaptic heteroreceptors → prevent the release of GABA from pain-blocking pre-synaptic neurons

What are the three most important side effects of opioids?

1. respiratory depression

2. constipation

3. vomiting

What is the difference between an opioid and an opiate?

opiates are the naturally occurring compounds (ex. morphine) and opioids are synthetic or semi-synthetic derivatives of opiates

What is the most useful opioid receptor antagonist?

naloxone

How does catnip work?

• causes euphoria and hallucinations in some cats, based on autosomal dominant trait

• active ingredient is nepetalactone → opioid receptor agonist

What is tramadol?

an effective opioid analgesic in birds, it has questionable efficacy in the dog (although many vets prescribe it for chronic use), and it is the opioid most likely to cause a seizure because of its effects on catecholamine reuptake channels.

Know the activity and uses of butorphanol.

• mixed agonist-antagonist

• well-tolerated in horses, very good for visceral pain and does not highly inhibit gut motility

• used as analgesic for mild-moderate pain for soft tissue injuries

• can be used to prevent the wind-up phenomenon

Know the activity and uses of buprenorphine.

opioid receptor agonist used for bird analgesia

Know about the use of hydrocodone as an anti-tussive, and how its abuse potential is minimized in a specific formulation.

• mu receptor activity supresses the central cough center

• homatropine is included in the syrup → anticholinergic that reduces respiratory secretions and reduces chance for abuse and illicit use

Know how to prevent the wind-up phenomenon.

wind-up phenomenon = chronic pain after an acute pain episode → prevented by preemptive analgesia whereby an opioid is administered priot to surgery and after surgery

What are the contraindications of opioids?

• epilepsy since opioids lower seizure threshold

• uremia since opioids cause urine, and thus uric acid retention

• toxemia

• hepatopathy