Lecture 33: Antihypertensive and Vasodilator Drugs Flashcards
What is BP?
CO x SVR
Pressure = Flow * Resistance
V = IR
R = V/I
What is SVR?
peripheral vascular resistance * renal vascular resistance
What is CO?
SV * HR
What are the 5 types of HTN drugs?
- Diuretics
- Calcium Channel Antagonists (Calcium channel blockers)
i. non-Dihydropyridines
ii. Dihydropyridines - RAAS inhibitors
- Vasodilators
- Sympatholytics
What is the pathophysiology of hypertension?
- increased CO
- increased PVR (peripheral vascular resistance)
- increased fluid volume
What is the rate limiting step in the RAAS pathway?
Renin
What happens when you have reduction in blood pressure?
- SNS activity = increase in HR and contractility = increased CO
- SNS activity = increase in peripheral vascular resistance (through adrenergic receptor) = increased PVR
- Increased renin activity = increased angiotensin II = increased PVR
- Increased renin = increased aldosterone/Na retention = increased fluid volume retention
Where does thiazide act?
At the DISTAL tubule of the nephron
Distal convoluted Na-Cl symporter
Example: Hydrochorthiazide (HCTZ)
What are loop diuretics?
Acts on the loop of henle
MoA: Inhibits the Na-K-2Cl Symporter on the Loop of Henle
-therefore, inhibits reabsorption of Na, K and Cl and promotes natriuresis and kaliuresis
Example: Furosemide
What is furosemide?
A loop diuretic
What is Hydrochorthiazide (HCTZ)?
A thiazide diuretic
What is the mechanism of diuretics?
Acute effect = sodium loss that leads to decreased in volume and BP
Chronic effect = decrease in vascular resistance that then decreases BP
What are the compensatory mechanisms counteract the acute effects long term?
Decreased plasma volume, increased renin + aldosterone
Plasma volume is restored but somehow the BP is still depressed (that’s the mystery)
What is the difference between a responder and nonresponder?
Responder is someone who responded well to the therapy (blood pressure dropped)
What is the MoA of Thiazide diuretics?
NaCl cotransporter in apical cell membrane of the Distal Convoluted Tubule (DCT)
Blocks Na-Cl symporter
Therefore blocks reabsorption of Na and Cl in DCT
(also thought to increase calcium reabsorption)
What are the key characteristics of thiazide diuretics?
- diuretic, natriuretic and kaliuretic
- Long duration of action
- African-Americans are generally more responsive
What is CRI?
Cardiac Risk Index
What is kaliuresis?
Process of excreting potassium in the urine
What are the toxicities of thiazide diuretics?
- Sulfa Allergy
- hypokalemia
- promote insulin resistance (increase plasma glucose)
- increase TG and LDL cholesterol
What is a diuretic that promotes insulin resistance, increases TG and increases LDL?
Thiazide diuretics
What diuretic should someone with sulfa allergy NEVER be put on?
Thiazide
What is the clinical use of thiazide diuretics?
First line treatment for uncomplicated hypertension, elderly patients with ISH and African-American patients
What is ISH?
Isolated systolic HTN
When systolic pressure is the only one that is high
How do thiazides reduce BP?
- reduces SV
2. reduces Peripheral Vascular Resistance
How do CCAs reduce BP?
- Reduce heart rate
- Reduce PVR
Specifically blocks “L”-type calcium channels
What is the role of calcium in vascular smooth muscle cells?
- Ca influx via voltage channels and binds to calmodulin
- Calmodulin-Ca complex activates MLC kinase
- myosin is phosphorylated and activated
- Activated myosin combines with actin resulting in a contraction
Maintains smooth muscular tone that allows you to stand, etc
What is the role of Ca in cardiac MYOCYTES?
- Ca influx via voltage sensitive channels after initial depolarization
- Ca influx causes release of Ca stores from SR
- Ca binds troponin and allows contraction to occur
- In SA and AV nodes, Ca influx is also important in spontaneous depolarization
- necessary for pacemaking because Ca is important in slow myocyte tissue
What is the role of Ca in muscle function?
A. Voltage-sensitive channels are an important pathway for Ca entry
B. Vascular SMCs depend mostly on Ca influx
C. Cardiac myocytes depend upon both Ca influx and intracellular stores
D. Skeletal muscle depends almost exclusively on intracellular Ca STORES
What are the specific calcium specific channels?
L, T, N, R and Q types
L is found on membrane of ALL muscle cells
Majority of CCAs affect only L type channels
Why are cardiac and smooth cells most affected by extracellular Ca?
Because they are the tissues most affected by agents
Skeletal muscles are not in tetany because they get their calcium from intracellular stores
What are the Calcium channel antagonists?
- Non Dihydropyridine
2. Dihydropyridine
What are the types of NON-dihydropyridine calcium channel antagonists?
- verapamil (Isoptin)
2. Diltiazem (Cardizem
What is verapamil?
A calcium channel antagonist
A non-dihydropyridine
Aka Isoptin
Binds to L-type calcium channels in the OPEN state
What is Diltiazem?
A calcium channel antagonist
A non dihydropyridine
Aka isoptin
Binds to L-type calcium channels in the OPEN state
What are the types of dihydropyridines?
- Nifedipine (Procardia)
2. Amlodipine (Norvasc)
What is Nifedipine?
A calcium channel antagonist
A dihydropyridine
Aka Procardia
Binds to L-type calcium channels during the RESTING state
What is the MoA of CCAs?
All CCAs interfere with Ca entry into cells via voltage sensitive “L” channels” Each class preferentially binds during a specific functional state of the channel
What is the difference between non-dihydropyridines and dihydropyridines?
Non diyhydropyridines bind while the L channel is OPEN
Dihydropyridines bind during the RESTING STATE of the L channel
When do you want to administer non-dihydropyridines?
When your target cell (with the L-type channel) has rapid frequency of stimulation
Eg. Tachycardic tissue
This is because faster conduction tissue leads to more of the L-type Ca being in the open state
So faster conducting tissue = more effective blockade by non-dihydropyridines (verapamil and diltiazem)
When do you administer dihydropyridines?
When you have cells that are slow-normal conducting so that it can bind to L-type during resting state
Example: Nifedipine, amlodipine
How can you tell if something is a dihydropyridine?
If it ends with “-ipine” it is a DHP
What is significant of MoA of CAAs in cardiac myocytes?
When targeting myocardium to reduce HR use Verapamil first
Verapamil > diltiazem > nifedipine
If you want to decrease cardiac contractility and reduce O2 demand
Use Verapamil as well
What is the MoA of CCAs in SMCs?
Channels are infrequently activated in SMCs
Use nifedipine for first line (by a long shot)
Nifedipine (amlodipine)»_space; verapamil»_space; diltiazem
Leads to vasodilation in all arteries including coronary arteries
What are the key characteristics of verapamil?
MoA: binds to L-type Ca channels during the OPEN state
Treats:
i. paroxysmal SVT
ii. Angina (to decrease myocardial O2 demand and increase coronary blood flow by slowing down heart rate and increasing diastolic filling)
What is the most notable side effect of verapamil?
Constipation
Can also be contraindicated in CHF and post-MI
What are the key characteristics of Diltiazem?
MoA: binds to L-type calcium channels during the OPEN state
Treats: SVT
Not a great antihypertensive drug
But has the lowest incidence of side effects
What are the key characteristics of Nifedipine?
MoA: binds to L-type calcium channels in the RESTING state (acts predominately on SMC)
Treats:
i. HTN by reducing PVR (through vasodilation)
ii. May be used in conjunction with Bblocker to prevent reflex tachycardia
What is Nifedipine contraindicated for?
Post MI (because it causes further hypovolemia) Congestive heart failure (because it causes further hypovolemia)
What are the side effects of Nifedipine?
Post MI (because it causes further hypovolemia) Congestive heart failure (because it causes further hypovolemia)
What are the side effects of Nifedipine?
Most side effects out of the CCA’s
- Facial flushing
- Headaches
- dizziness
- ankle swelling
What are important considerations when prescribing dihydropyridines like nifedipine?
Dihydropyridines cause profound peripheral vasodilation and limited DIRECT myocardial effects
May produce reflex tachycardia and increase contractility
This increases myocardial work load and can increase the risk of having a MI in patients who are susceptible
What drug produces reflex tachycardia and increased contractility?
Dihydropyridines
Nifedipine…contraindicated in patients with angina that can’t get enough supply to coronaries
What are the key characteristics of peripheral vasodilators?
Drugs that produce a direct relaxation of vascular smooth muscle cells
Direct = not dependent upon innervation and their effect is not mediated by known receptors
What are the types of peripheral vasodilators
- venous = nitrates
- arterial = hydralazine, minoxidil
- both venous and arterial
i. nitroprusside
What are the venodilators?
Organic nitrates
AKA Nitrates
What are the key characteristics of hydralazine?
MoA = unknown
Direct arteriolar dilation with no effect on veins
Preferentially affects the renal, peripheral, splanchnic and coronary arteries
Decrease in PVR leads to lower blood pressure
What is the toxicity of hydralazine?
Excessive vasodilation (flushing, sweating, palpitations, hypotension and angina)
SLE like syndrome (for boards)
-arthralgia, myalgia, fever and rash
-seen in females who are slow acetylators within 6 months
What vasodilator leads to SLE symptoms?
Hydralazine if given for over 6 months
What are the limitations of the hydralazine?
Limited utility…only used for HTN during pregnancy or preeclampsia
Frequently used for HTN during pregnancy including preeclampsia
Used in combination with beta adrenergic antagonist to blunt SNS reflex
What are the key characteristics of minoxidil?
MoA = activates ATP modulated K channel in arteries to allow K+ to leave cell, causing hyperpolarization and relaxation
Increase K channel permeability = decreased excitability = decreased SMC contractility
Direct arteriolar vasodilation with no effect on veins
Decrease in PVR and thus lowers BP
Compensatory mechanism:
Reflex SNS activation, Na retention and increased renin production to return BP to baseline
What are important side effects/consequences of minoxidil use?
Can increase hair growth: HYPERTRICHOSIS
Can be blunted with concomitant use of beta blockers and diuretics
Minoxidil = rogaine because it increases hair growth lol
What are the characteristics of sodium nitroprusside?
MoA = metabolized by SMCs into NO which activates guanylate cyclase
Vasodilates both arterioles and veins; decreases PVR and venous return (afterload and preload respectively)
What are the consequences associated with taking nitroprusside?
Formed by a complex of Fe, cyanide and nitrosamine
Can be metabolized to cyanide so you need to add SODIUM THIOSULFATE to prevent cyanide toxicity
Unstable in direct sunlight
What are the therapeutic applications of sodium nitroprusside?
- Drug of choice for HTN emergencies
- Rapid onset (2 mins) and consistent (because everyone responds)
- Easily titrated
- Initiated therapy with beta blocker prior to discontinuing infusion
What should we remember about diuretics, CCAs, and vasodilators?
- Potent vasodilators of vasculature (direct vasodilator)
- All of them induce reflex tachycardia/compensatory mechanisms
- Use beta blocker and ACE inhibitors to account for the compensatory mechanisms
- Hydralazine can lead to SLE
Where are the adrenergic receptors located?
Alpha1 = vascular smooth muscle (vasoconstriction) and genitourinary smooth muscle (constriction)
Alpha 2 = vascular smooth muscle (vasoconstriction
Beta 1 = heart and kidney
Beta 2 = vasodilation and bronchodilation
What are the type of sympatholytic antihypertensive drugs?
- beta-blocker (beta adrenergic antagonists)
- peripheral alpha 1, alpha 2 adrenergic antagonists
- centrally acting alpha2 adrenergic agonists
- adrenergic neurotransmitter release blockers
What are the beta-blockers used for HTN?
- propranolol (B1 and B2 blockers)
- metoprolol (B1 blocker)
- atenolol (B1 blocker)
What are the MoA of beta-blockers as only antihypertensives?
- reduction in HR
2. reduction in renin release
Which of the beta-blockers are selective to beta 1 receptor?
Metoprolol
Atenolol
Which of the beta-blockers are non-selective?
Propanolol
What are the key characteristics of peripheral alpha adrenergic antagonists?
Prototypical:
i. Prazosin (Alpha 1 and 2 antagonist)
ii. Doxazosin (alpha 1)
iii. Terazosin (alpha 1)
MoA = vasodilates and reduces in PVR by antagonizing alpha adrenergic receptors
Used to treat benign prostate hypertrophy
3rd line HTN
What are the key characteristics of alpha and beta receptor antagonist combination drugs?
Alpha 1 receptor antagonist effect Non selective beta receptor antagonist effect Include: i. Labetolol ii. Carvedilol
What are the effects of carvedilol and labetolol?
Combined alpha/beta receptor antagonist
- antagonize peripheral vasoconstriction actions of NE
- Reduces heart rate
- reduces renin release
What are the key characteristics of centrally-acting alpha 2 adrenergic AGONISTS?
MoA = stimulate preganglionic A2 receptors on adrenergic neurons in medulla
Reduces sympathetic outflow creating unopposed vagal tone because A2 receptor agonist is done on the PREganglionic receptor
What is significance of methyldopa?
Not used because of CNS depressant effect
Can cause suicide
What is the significance of clonidine?
MoA: binds the Presynaptic ganglionic Alpha2 receptors in the vasomotor system of medlla
-this decreases presynaptic calcium levels, thereby DECREASING NE release
-decreasing NE release leads to lower PVR and CO
Prevents autonomic variability that we see in blood pressure
Ideal patient = autonomic neuropathy because clonidine will act as a compensatory system in place of the autonomic neuropathy that occurred
Which beta-blocker has a sympathomimetic effect?
Oxprenolol, pindolol, penbutolol, acebutolol
These guys can exert a low level of agonist activity at B-receptor site despite being antagonists as well
Useful for patients with bradycardia but don’t give post-MI
What is TLC?
Therapeutic Lifestyle Change
What are the complications of hypertension?
- hemorrhage/stroke
- retinopathy
- peripheral vascular disease
- LVH, CHD and CHF
- nephropathy
What is uncomplicated HTN?
HTN without compelling causation
Diastolic BP <11 mmHg without symptoms of end HTN and does not require acute treatment
What is the best antihypertensive drug combination?
Beta blockers + CCAs Diuretics + Beta blockers ACEIs, ARBs + CCAs ACEIs, ARBs + Diuretics Nothing horrible
What antihypertensives do you want to avoid?
Alpha1 receptor blockers like Prazosin
