MOAs Flashcards
Mechanism for enhancing/decreasing potassium reabsorption
cannot be influenced by drugs
How do acidic drugs cause gout?
They compete with uric acid for excretion by OAT carrier, causing increased serum uric acid levels and gouty attacks
Diffusion rate depends on
lipid solubility, pKa, pH
→ weak acids at low pH remain mostly unionized/lipid soluble→ easily diffuse
Carbonic anhydrase inhibitors (Acetazolamide)
Proximal tubule and loop of henle
Inhibit carbonic anhydrase:
→ no H+ + HCO3 production inside of cells→ decreased H+ in cell for exchange with Na+ in lumen (by Na+/H+ antiporter) → increase Na+ and H2O loss
→ In lumen: H2CO3 can’t convert to H2O + CO2 by CA → bicarb trapped
Loop diuretics (furosemide) block
Thick ascending limb of loop of henle
Block the Na+/K+/2 Cl- cotransporter (reabsorption)
→reduced renal medulla concentration gradient→impaired concentration and dilution
Loop diuretics (furosemide) induce
Induce kidney prostaglandins
→ decreased salt transport
→ renal and systemic vasodilation
Loop diuretics mechanism for improving pulmonary edema
reduce congestion by venodilation→ increased systemic venous capacitance→ decreased cardiac return→ decreased RV volume→ decreased pulmonary BP
Thiazide diuretics Effects on Sodium
Inhibition of Na+ reabsorption by Na+ Cl+ co-transporter at early distal tubule (not a major site of Na+ reabsorption→ less potent)
Increased luminal Na+ → increased cell membrane potential→ increased Ca++ reabsorption by PTH dependent Ca++ channels (good for nephrolithiasis)
Loop diuretics for hypercalcemia
reduce K+ gradient→ decreased Mg++ and Ca++ reabsorption
Thiazide diuretics effects are dependent on
Effects are dependent on prostaglandin synthesis and GFR
Thiazide diuretics systemic effects
Increased systemic ATP-dependent K+ channel opening→ hyperpolarization of cell membranes→ relaxation of smooth muscle cells→ vasodilation
→ also causes reduced insulin secretion
Potassium-sparing diuretics effects
Interfere with Na+ reabsorption at distal exchange site→ loss of Na+ and H2O → conservation of K+. Weak. Used in combination with other K+ losing drugs.
Spironolactone MOA
Competitive inhibitor of aldosterone:
Promotes excretion of Na+ and retention of K+ at late distal tubule and collecting duct:
- less Na+ channels
- blocked Na+ conductance→ hyperpolarized cell→ decreased K+ excretion
- decreased Na+/K+ ATPase activity→ decreased K+ excretion
Eplerenone MOA
Selective aldosterone receptor antagonist (SARA)
Spironolactone effects at aldosterone receptor with decreased affinity for other steroid receptors
Spironolactone at high doses
inhibits glucocorticoid and sex hormone receptors
Amiloride/Triamterene MOA
Inhibit Na+/K+ ion exchange in an aldosterone independent manner:
- Directly inhibit aldosterone sensitive Na+ channel (ENaC)–> increased sodium loss
- Leads to decreased K+ excretion (sparing)
Desmopressin MOA
Synthetic ADH agonist→ activation of V2 (some V1) receptors→ decreased H2O excretion
Conivaptan/tolvaptan MOA
ADH antagonist:
Non-peptide V1a and V2 receptor antagonist→ increased Na+ concentration and increased free H2O clearance
Digitalis/Digoxin MOA for contractility
Cardiac glycoside→ inhibition of membrane Na+/K+ ATPase (digitalis receptor)
→ increased intracellular Na+
→ decreased expulsion of intracellular Ca++ → increased SR storage→ increased actin-myosin interaction by Ca++ → increased contractility
Digitalis/Digoxin MOA for heart rate in the normal heart
antiarrhythmic:
sensitization of baroreceptors→ stimulate central vagal nuclei→ vagal stimulation→ increased SA node sensitivity to ACh (PNS: slows HR)
CO doesn’t increase due to increased PVR
Digitalis/Digoxin MOA for heart rate in the failing heart
Sensitization baroreceptors→ stimulate central vagal nuclei→ vagal stimulation→ increased SA node sensitivity to ACh (PNS: slows HR)
Sympathetic tone is already high, will be reduced by increased contractility→ reduced heart rate. CO increases because peripheral vasoconstriction response does not occur
Milrinone MOA
Inhibits cAMP phosphodiesterase→ increased cAMP→ increased Ca++ (similar to dobutamine)→ vasodilation
Positive inotropic drug+vasodilation= inodilator
Dobutamine MOA
Selective B1 agonist→ Inotropic
Diuretics for Heart failure
Decrease Na+ + H2O retention
Decrease venous pressure→ less edema, decreased cardiac size
Spironolactone/epleronone for heart failure
reduce mortality
blocking aldosterone receptors is beneficial compared to other diuretics
Dopamine in low doses
D1 receptors in kidney→ renal vasodilation
Dopamine in moderate doses
B1 receptors in heart → inotropic effect
Dopamine in high doses
Alpha receptors in vessels→ vasoconstriction
Angiotensin II in heart failure causes
increased afterload, increased preload, increased remodeling
Use ACE-I/ARBs to counteract
ACE inhibitors (captopril) MOA
inhibit angiotensin converting enzyme
Angiotensin II antagonists (ARBs) (losartan) MOA
block angiotensin II from binding to AT1 receptor
Decreasing aldosterone in HF causes
decreased preload (Na+ isn’t retained)
Dry cough side effect of ACE-I or Sacubitril comes from
Reduction in bradykinin metabolism (increased levels of bradykinin)→ dry cough
Sacubitril/Valsartan MOA
2 drugs (ARNI)
Sacubitril: neprilysin inhibitor
Neprilysin degrades natruretic peptides, bradykinin
Inhibtion: decreased vasoconstriction, soidum retention, cardiac remodeling
Valsaratan: ARB
Beta blockers and early heart failure
Decrease mortality:
Decrease renin secretion, HR, remodeling
Up-regulate B receptors
Attenuate effect of high concentrations of catecholamines
Beta blockers and end stage heart failure
Dangerous due to negative inotropic effect
Vasodilators (Sodium nitroprusside, Isosorbide dinitrate, hydralazine) for heart failure
Reduce preload (venodilation) Reduce afterload (arteriolar dilation) Decrease damaging remodeling
Ivabradine MOA
Blocks If current in heart→ reduced HR (when B blockers can’t)
Improvement in mortality rates, hospitalizations
No benefit in cardiovascular endpoints
Thiazide monotherapy for htn
decreases BP
Thiazide combination therapy for htn
enhances efficacy of other antihypertensive drugs, counteracts sodium and fluid retention
Thiazide which is a direct vasodilator and beneficial in hypertension
Indampamide
Thiazide for diuresis vs for hypertension
diuresis requires a much higher dose
Thiazide short term effects on BP
reduce Na+ stores which decreases blood volume and CO
Thiazide long term effects on BP
decrease Na+ in muscle cells, activate K+ channels which decreases sensitivity to vasopressors
→ decreased peripheral resistance→ BP lowered 10-15 mmHg
Central alpha agonists (clonidine, methyldopa) MOA
Stimulate medullary a2→ decreased peripheral sympathetic nerve activity
Stimulate presynaptic a2 receptors→ decreased transmitter release
→ decreased sympathetic outflow and renin secretion→ decreased BP
Prazosin, terazosin, doxasozin MOA
Block alpha-1 adrenergic receptors→ reduce NE vasoconstriction→ artery/vein dilation→ decreased peripheral resistance→ decreased BP