Page 287 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

Pharmacology ` PHARMACOLOGY—AUTONOMIC dRUGS Pharmacology ` PHARMACOLOGY—AUTONOMIC dRUGS SEcTIoN II 243

Norepinephrine vs NE  systolic and diastolic pressures as a result of α 1 -mediated vasoconstriction Ž  mean arterial
isoproterenol pressure Ž reflex bradycardia. However, isoproterenol (rarely used) has little α effect but causes
β 2 -mediated vasodilation, resulting in  mean arterial pressure and  heart rate through β 1 and
reflex activity.

Norepinephrine (α > β) Epinephrine (α ≈ β) Isoproterenol (β > α)

Widened β 1
pulse
Blood pressure Systolic α 1
pressure
MAP
2
Diastolic β > α 1 β
2
β , reflex tachycardia
1
β
Heart rate 1

Reflex bradycardia

Peripheral resistance Unopposed α 1 β > α 1 Unopposed β 2

2
CO ↑ ↑ CO ↑ CO ↑↑
HR ↑ HR ↑
MAP ↑↑ MAP ↑ MAP
HR ↑↑ ↑
PP ↑ PP ↑ PP ↑↑

Sympatholytics (α 2 -agonists)
dRUG APPLICATIONS AdVERSE EFFECTS
Clonidine, guanfacine Hypertensive urgency (limited situations), CNS depression, bradycardia, hypotension,
ADHD, Tourette syndrome, symptom control respiratory depression, miosis, rebound
in opioid withdrawal hypertension with abrupt cessation
α-methyldopa Hypertension in pregnancy Direct Coombs ⊕ hemolysis, drug-induced
lupus, hyperprolactinemia
Tizanidine Relief of spasticity Hypotension, weakness, xerostomia

FAS1_2019_05-Pharmacology.indd 243 11/7/19 4:08 PM