Drugs Affecting the PNS (Part 4) Flashcards
What do indirect/mixed acting sympathomimetics do?
1: Generally used for CNS effects
2: Behavior modification
What are the indirect/mixed acting sympathomimetics?
1: Tricyclic antidepressants
2: Monamine oxidase inhibitors
What is the tricyclic antidepressants we discussed?
Clomipramine
What is the monamine oxidase inhibitors we discussed?
Selegiline
What are the indications of clomipramine?
1: Canine and feline compulsive disorders
2: Used in birds to treat feather picking
What are the indications of selegiline?
1: Canine cognitive dysfunction
2: Canine hyperadrenocorticism
What is the mechanism of action for phenylproanolamine?
1: Mixed sympathomimetic
Direct - alpha-1 receptor agonist
Indirect - increase in NE in bladder neck/urethra
What form is phenylproanolamine available in?
1: Tablet
2: ER
3: Oral solution
What are the indications for phenylproanolamine?
1: Used in small animals primarily to treat urinary incontinence due to urethral sphincter hypotonus/incompetence
What are the drug-drug interactions for phenylproanolamine?
Estrogens —> up-regulate alpha-1 receptors in internal urethral sphincter, so when used with estrogen containing hormonal therapy may see synergism
What are the precautions for phenylproanolamine?
1: Urine retention
2: Tachycardia
3: Hypertension
4: Restlessness
5: Occasionally anorexia
6: Few side effects at therapeutic doses
What is the mechanism of action for ephedrine?
1: Mixed sympathomimetic
Direct - alpha-1 ad beta-receptor agonism
Indirect - increase in NE release
What are the indications and main effects for ephedrine?
1: Used as a CRI to maintain blood pressure under anesthesia
2: Increases blood pressure —> vasoconstriction and direct cardiac stimulation
3: Bronchodilation —> some beta-2 effects
4: Urinary sphincter contraction —> urinary retention
5: Mydriasis
What are the precautions for ephedrine?
1: Hypertension
2: Arrhythmias
What is the mechanism of action for phenoxybenzamine?
1: Non-specific alpha antagonist, binds irreversibly
What are the indications of phenoxybenzamine?
1: Urinary retention due to urethral hypertonicity
2: Pheochromocytoma
What are the fast facts of pheochromocytoma?
1: Tumor of the adrenal medulla
2: Active tumor —> catecholamine secretion
3: Typically malignant —> metastasis to other organs
4: Vessel invasion common
What are the precautions for phenoxybenzamine?
1: Hypotension
2: Reflex tachycardia
3: Miosis and changes in IOP
4: GI signs
5: Recently has been expensive
What is the mechanism of action for prazosin?
1: Sympatholytic alpha-1 receptor antagonist
2: More specific for alpha-1 receptor than phenoxybenzamine
What are the indications for prazosin?
1: Urinary retention due to urethral hypertonicity
2: Adjunctive treatment of congestive heart failure, systemic or pulmonary hypertension
What are the precautions and contraindications for prazosin?
1: Caution in patients with chronic renal failure
2: Relativity contraindicated with pre-existing hypotension conditions
3: Bradycardia possible
4: Nausea, vomiting, diarrhea, constipation
5: Lethargy, dizziness
6: 3rd eyelid protrusion
What is the mechanism of action for propranolol?
1: Non-selective/nonspecific beta-antagonist
2: Decreases SA node firing —> bradycardia
3: Decreases AV conduction —> decreases cardiac output and myocardial oxygen demand (MvO2)
4: Increases airway resistance
5: Readily crosses the BBB
6: Significant first-pass effect
7: Relatively short duration of action
8: Excretion is mostly through he urine as metabolites
What form is propranolol available in?
1: Oral
2: Injectable
What are the indication of propranolol?
1: Generally used to treat tacharrhyhmias
2: Feline hyperthyroidism
What are the precautions and contraindications for propranolol?
1: Bradycardia, hypotension, bronchospasm
2: Receptor desensitization and up regulation
3: Contraindicated with overt heart failure, sinus bradycardia, heart block
What is the mechanism of action for beta-1 selective antagonists?
Sympatholytic beta-1 receptor selective antagonism
What are the indications of beta-1 selective antagonists?
1: No significant beta-2 effects at usual doses
What are the beta-1 selective antagonists?
1: Arenolol
2: Esmolol
Describe atenolol
1: Longer half-life than propanolol
2: Lack of beta-2 effects
Describe esmolol
Ultra short acting B1-antagonist
What is the indirect acting sympatholytic drug we discussed?
Reserpine
What is the mode of action for reserpine?
Blocks NE uptake
What is reserpine used for?
Calming equines
