OTHER ALPHA/BETA AGONISTS

Question 1

Phenylephrine

Answer 1

• Selective alpha-1 agonist
• Available in oral or injectable formulations, intranasal and ophthalmic. Some human formulations
  may contain other drugs (eg. cough and cold mixtures).

Question 2

Is Phenylephrine a true catecholamine?

Answer 2

Phenylephrine is not technically a catecholamine but as a direct-acting sympathomimetic it shares some clinical similarities with the group when used systemically.

Question 3

What does Phenylephrine do/treat?

Answer 3

Can be used systemically to treat hypotension/shock by increasing peripheral vascular resistance
(vasopressor) with less direct cardiac stimulation.
o Immediate onset with IV use and short duration of vasopressor action (

Question 4

Cautions with Phenylephrine?

Answer 4

Cautions: Use with caution systemically. Systemic effects can occur when used topically in small
patients (eg.

Question 5

Brimonidine

Answer 5

Brimonidine (Ophthalmic): Will be covered with ophthalmic medications.

Question 6

Ractopamine and Zilpatero

Answer 6

• Agonist at beta-1, beta-2 and particularly beta-3 receptors
• Referred to as ‘partitioning agents’ to reduce fat deposition and increase muscle deposition in late
  finishing meat-producing animals.

Question 7

Alpha-2 agonists:

Answer 7

Xylazine, dexmedetomidine, romifidine, detomidine – sedatives (will be covered with CNS drugs).
- Brimonidine – will be covered with ophthalmic medications.

Question 8

Selective beta-2 agonists:

Answer 8

Will act primarily at beta-2 receptors with generally minimal beta-1 activity, however at high
doses beta-1 activity should always be considered possible. May also improve ciliary function
(‘cilia augmenters’).
- Used to treat bronchoconstriction (acute or chronic) in patients with reactive airway diseases such
as asthma (felines) or COPD (equines).

Question 9

Cautions with beta-2 agonists?

Answer 9

Caution:
o Related mostly to the potential beta-1 effects (cardiac stimulation) or unintended beta-2 effects (vasodilation, uterine relaxation) so caution should be used in cardiac patients, pregnant patients, or any other situations where those effects are detrimental.
o May see nervousness, sweating, muscle tremors, weakness, vomiting (not common). o Receptor downregulation may occur over time leading to tolerance.

Question 10

examples of beta-2 agonists?

Answer 10

Albuterol/Salbutamol, Clenbuterol ,

Terbutaline

Question 11

Albuterol/Salbutamol

Answer 11

o Available as an oral, aerosol or solution for nebulization (human)
o Poor oral absorption (very high pKa) but very good mucosal absorption via inhalation so
more often used in the aerosol form.
 Rapid onset (response within 5 mins) and duration up to ~7hrs

Question 12

What is the most common administered form for Albuterol?

Answer 12

Inhalational administration is used in horses and cats (and less commonly dogs, asthma is less frequent in that species).
 AeroKatTM, AeroHippusTM and AeroDawgTM are specially designed metered-dose inhaler delivery systems for veterinary use. They consist of an aerosol chamber and mask that is size-appropriate for each species and facilitate the use of inhalers for veterinary patients.

Question 13

Salmeterol

Answer 13

Salmeterol (Serevent®) is a very similar drug is sometimes used in metered-dose inhalers alone or in combination with the steroid Fluticasone (Advair®).

Question 14

Clenbuterol

Answer 14

o Available as a veterinary approved oral syrup for use in equines primarily for the
management of COPD. In addition to bronchodilation it also appears to be an effective
mucokinetic agent in horses.
o Not permitted in food animals
o Outside the US available as injectable formulation sometimes used in equine dystocia.

Question 15

Terbutaline

Answer 15

o Available as a human approved oral (tablet) or injectable.
o Minimal beta-1 effects and virtually no alpha effects at typical doses.
o Oral bioavailability in equines is terrible (

Question 16

Isoxsuprine

Answer 16

o A Beta-2 agonist that acts as a peripheral vasodilator (skeletal muscle, distal limb) and causes uterine relaxation.
o Sometimes used as a tocolytic in cattle (c-section, fetal manipulation, embryo transplant)  (Previously used in horses for navicular disease in the 90’s but not effective and
not used much now)