Sympatholytics, Calcium Channel Blockers, Ivabradine and Ranolazine
Apply the seven-step pathway to explain each class, compare drugs and predict what changes in the patient.
Nicholas B. Norgard, PharmD · Companion to the cardiovascular pharmacology lecture
The same seven questions
Before the drug: explain the normal physiology and identify the problem. Then use the seven questions to connect the drug’s action to the patient’s response.
TargetWhere does it act?
ActionWhat does it do there?
Tissue effectWhat changes directly?
Body responseHow does the body respond?
Uses and outcomesWho benefits, and how?
SafetyWhat could go wrong?
PharmacokineticsDoes exposure change the answer?
Give the recommended integration points extra attention; keep all seven steps connected. The emphasized rows match the class priorities in the course framework and linked labs. They identify useful connections to practice, not official USMLE content weights or permission to skip the other steps.
Tissue effect is the direct change caused by the drug. Body response adds reflexes, hormonal responses and adaptation over time. A DHP relaxes arterioles directly; the subsequent tachycardia can be a baroreflex response.
The displayed order is a study sequence. Pharmacokinetics (PK) changes exposure upstream; safety effects can branch directly from the mechanism; compensation feeds back. A favorable physiological effect alone does not establish improved survival.
How to study a class
Start with one prototype. Read its seven-step explanation and trace the important causal connections.
Compare one nearby alternative. Change receptor selectivity, target tissue, onset, rhythm or ventricular function. State which prediction changes and why.
Explain it without looking. Attempt the class practice task and choose a self-check answer before opening the explanation. Use the lecture and lab links to revisit a missed connection.
Terms used throughout: SVR = systemic vascular resistance; CO = cardiac output; NE = norepinephrine; HFrEF = heart failure with reduced ejection fraction; LVEF = left ventricular ejection fraction; AF = atrial fibrillation. Afterload is the load opposing ventricular ejection. Inotropy is contractile strength. Chronotropy is heart rate; dromotropy is conduction; lusitropy is relaxation.
Independent study question bank
Build the reasoning with 24 framework questions, then apply it to 16 Step 1–style clinical vignettes. Choose an answer before reading feedback; every choice has an explanation and a link back to the relevant lecture topic.
The question bank includes topic filters, retry controls, saved progress and a printable answer key. It is separate from the live lecture.
Central α₂ agonists
Clonidine · guanfacine · methyldopa
Recommended integration points · Action + Body response Trace central receptor signaling to reduced sympathetic outflow; compare the response during treatment with abrupt clonidine withdrawal.
Starting point: Sympathetic output from the brainstem supports cardiac stimulation, vascular tone and renin release. Activating an inhibitory receptor in this circuit can reduce those peripheral effects.
1 · Target
Central inhibitory α₂ receptors in sympathetic-control networks, including the rostral ventrolateral medulla (RVLM). Presynaptic α₂ autoreceptors also restrain norepinephrine (NE) release. Receptor location helps explain the response.
2 · ActionRecommended integration point
α₂ activation engages Gi/o: adenylyl cyclase activity and cAMP fall. Parallel increases in K⁺ conductance and inhibition of Ca²⁺ entry reduce neuronal firing and transmitter release. The channel effects should not all be drawn as consequences of reduced cAMP. Clonidine also acts at central imidazoline I₁ receptors.
3 · Tissue effect
Less sympathetic drive means less cardiac β₁ stimulation, vascular α₁ tone and renal sympathetic stimulation. Heart rate and contractile drive can fall, vessels relax, and renin release decreases. These are downstream consequences of central action—not direct blockade of each peripheral receptor.
4 · Body responseRecommended integration point
Central sympatholysis lowers BP and blunts reflex tachycardia. Cardiac output need not remain reduced; the net effect depends on the drug and time course. Abrupt clonidine cessation removes inhibition and can produce a sympathetic surge with hypertension and tachycardia. Peripheral α₂ activation at high exposure can contribute to a pressor response, so an agonist’s effect depends on location as well as receptor name.
5 · Uses and outcomes
Clonidine and immediate-release guanfacine treat hypertension; extended-release guanfacine has an ADHD indication. Clonidine can reduce autonomic symptoms of opioid withdrawal (off-label). Methyldopa is an established pregnancy option. These roles are distinct; BP lowering alone does not explain every clinical use.
6 · Safety
Sedation, dry mouth, bradycardia and hypotension can accompany central suppression. Taper clonidine rather than stopping abruptly. Methyldopa can cause hepatic injury and, rarely, immune hemolytic anemia; a positive direct Coombs test alone does not prove hemolysis.
7 · Pharmacokinetics
Methyldopa requires conversion to α-methylnorepinephrine, which can replace NE in vesicles and preferentially activate α₂ receptors after release. This is not exclusive binding to presynaptic receptors. Clonidine acts directly; its patch delivers drug over a week but takes roughly 2–3 days to establish an effect after initial application. Renal impairment can prolong exposure to some agents.
Apply the pathway
Practice task: Compare a patient with sedation and bradycardia while taking clonidine with a patient who develops hypertension and tachycardia after missing doses.
Learning goal: Explain excessive drug effect versus loss of central inhibition using the same pathway.
Self-check
After several missed clonidine doses, a patient develops headache, sweating, hypertension and tachycardia. Which explanation best fits?
Increased central inhibitory α₂ signaling
Loss of central inhibition with sympathetic activation
Direct blockade of vascular α₁ receptors
Show explanation
B. Loss of central inhibition with sympathetic activation
Loss of central inhibition allows sympathetic activity to rise. Increased inhibition would favor bradycardia and lower pressure; vascular α₁ blockade would favor vasodilation. Timing distinguishes withdrawal from excessive drug effect.
Recommended integration points · Action + Body response Compare reversible with irreversible blockade, then combine vasodilation, baroreflex activation and loss of presynaptic α₂ feedback.
Starting point: Vascular α₁ receptors support constriction. Presynaptic α₂ receptors provide negative feedback that limits further NE release. Blocking both removes two different controls.
1 · Target
Both α₁ and α₂ adrenergic receptors. The vascular α₁ effect explains much of the fall in pressure; loss of presynaptic α₂ feedback helps explain greater cardiac stimulation.
2 · ActionRecommended integration point
Phentolamine is a reversible competitive antagonist. Phenoxybenzamine produces irreversible blockade, so increasing agonist concentration cannot readily overcome the occupied receptors. Reversibility and receptor selectivity are separate properties.
3 · Tissue effect
Arterioles and veins relax. Systemic vascular resistance (SVR) and venous return fall, reducing arterial pressure. At sympathetic nerve terminals, removal of α₂ feedback permits more NE release.
4 · Body responseRecommended integration point
Falling pressure activates the baroreflex, increasing sympathetic drive to the heart. More NE release after α₂ blockade can amplify β₁ stimulation, producing marked tachycardia. On standing, impaired vascular constriction worsens pooling and may reduce cerebral perfusion.
5 · Uses and outcomes
Used for selected catecholamine-excess settings, especially pheochromocytoma. Phenoxybenzamine provides sustained preoperative α blockade; phentolamine has acute uses, including NE extravasation. In pheochromocytoma, establish adequate α blockade before adding a β blocker for persistent tachycardia.
6 · Safety
Orthostatic hypotension, tachycardia and arrhythmias follow the mechanism. Increased cardiac work can aggravate ischemia; phentolamine is contraindicated in coronary insufficiency or prior MI. Phenoxybenzamine can produce prolonged hypotension.
7 · Pharmacokinetics
Phentolamine has relatively brief action. Phenoxybenzamine’s prolonged effect reflects persistent receptor binding (pharmacodynamics), not simply drug remaining in plasma; recovery requires replacement of functional receptors.
Apply the pathway
Practice task: Predict the pulse response to a similar BP fall with nonselective α blockade versus selective α₁ blockade.
Learning goal: Explain why both can activate the baroreflex but loss of α₂ feedback adds another source of tachycardia.
Self-check
Two drugs cause comparable vasodilation. Drug A blocks α₁ only; drug B blocks α₁ and α₂. What additional change with drug B promotes tachycardia?
Direct inhibition of SA-node funny current
Increased inhibitory autoreceptor feedback
Less presynaptic restraint on NE release
Show explanation
C. Less presynaptic restraint on NE release
α₂ blockade removes inhibitory feedback on NE release, adding cardiac β₁ stimulation to the baroreflex response. The drugs do not directly inhibit the funny current.
Recommended integration points · Action + Body response Preserve the α₂ feedback distinction and predict the response to standing; then compare vascular and urinary effects.
Starting point: Standing shifts blood toward dependent veins, reducing venous return. The normal baroreflex increases vascular constriction to defend arterial pressure and cerebral perfusion.
1 · Target
α₁ receptors on vascular and lower urinary-tract smooth muscle. Tamsulosin and silodosin favor α₁A receptors; alfuzosin has functional urinary selectivity without marked α₁A-subtype selectivity.
2 · ActionRecommended integration point
Reversible competitive α₁ antagonism reduces NE-mediated contraction while preserving presynaptic α₂ negative feedback. Compared with nonselective blockade, less additional NE is released because of lost autoreceptor restraint.
3 · Tissue effect
Vascular relaxation lowers resistance and venous tone. Relaxation of prostate and bladder-neck smooth muscle reduces urinary-outlet resistance, improving flow in benign prostatic hyperplasia (BPH). The prostate does not shrink.
4 · Body responseRecommended integration point
The baroreflex may increase cardiac sympathetic activity, but the blocked vessels cannot constrict normally. Standing can therefore cause a larger BP fall and cerebral hypoperfusion, especially after an initial dose or dose increase. Syncope is loss of consciousness from inadequate perfusion; lying flat helps restore venous return—it is not a deliberate command by the brain to fall.
5 · Uses and outcomes
Terazosin and doxazosin can treat BPH and hypertension; α₁ blockers are not routine first-line hypertension therapy. Tamsulosin, silodosin and alfuzosin mainly treat urinary symptoms. In ALLHAT, doxazosin had more combined cardiovascular events, approximately twice the heart-failure risk and higher stroke risk (RR 1.19) than chlorthalidone; BP lowering alone did not establish equivalent protection.
6 · Safety
First-dose orthostasis or syncope, additive hypotension with PDE5 inhibitors, ejaculatory dysfunction and intraoperative floppy iris syndrome. Patients should rise carefully and tell their cataract surgeon about current or prior use. Urinary selectivity reduces vascular effects but does not eliminate orthostasis.
7 · Pharmacokinetics
Exposure and formulation help distinguish agents. Alfuzosin’s prostatic distribution and gradual extended-release absorption likely contribute to urinary selectivity. Silodosin exposure rises with renal impairment; CYP-mediated interactions matter for several urinary agents.
Apply the pathway
Practice task: Explain both improved urine flow and dizziness on standing after an α₁ blocker, using the tissue involved in each finding.
Learning goal: Connect a shared smooth-muscle action to two different clinical consequences without assuming prostate shrinkage.
Self-check
A patient becomes dizzy on standing after the first prazosin dose. Which impaired response most directly explains the event?
Reflex constriction of vascular smooth muscle
Direct activation of ventricular contraction
Renal excretion of excess sodium
Show explanation
A. Reflex constriction of vascular smooth muscle
α₁ blockade limits the vascular constriction needed to compensate for postural pooling. Venous return and pressure can fall enough to reduce brain perfusion. A reflex rise in pulse does not guarantee adequate compensation.
Compare metoprolol, propranolol, carvedilol, labetalol, nebivolol and esmolol
Recommended integration points · Target + Body response Identify the receptor profile before predicting tissue effects. Distinguish immediate cardiac suppression, compensation and sustained benefit in stable HFrEF.
Starting point: β₁ stimulation increases cardiac rate, conduction, contraction and renin release. That response supports circulation acutely, but persistent adrenergic stimulation can worsen myocardial stress and remodeling in heart failure.
1 · TargetRecommended integration point
Metoprolol, bisoprolol, atenolol and esmolol favor β₁; propranolol, nadolol and timolol block β₁ + β₂. Carvedilol and labetalol add α₁ blockade. Nebivolol combines β₁ preference with NO-mediated vasodilation. β₁ selectivity is relative and becomes less pronounced at higher exposure.
2 · Action
Block catecholamine signaling through β receptors, reducing Gs–adenylyl cyclase–cAMP signaling. This does not directly activate Gi or directly block the L-type Ca²⁺ channel. Agents with intrinsic sympathomimetic activity are partial agonists: they provide some stimulation while limiting stronger catecholamine effects.
3 · Tissue effect
Reduced cAMP slows sinus-node pacing; reduced nodal Ca²⁺ signaling slows AV conduction. Less PKA-dependent Ca²⁺ cycling reduces myocardial contractility. Renal β₁ blockade reduces renin release. β₂ blockade can impair bronchodilation and glucose mobilization; added vasodilator actions change vascular resistance.
4 · Body responseRecommended integration point
A β₁ blocker blunts the reflex or exercise-related rise in heart rate; it does not eliminate every baroreflex component. A nonvasodilating β blocker may initially reduce cardiac output while reflex SVR rises. With sustained therapy, BP can fall as vascular and renin-related responses evolve. In stable HFrEF, early negative inotropy can coexist with later protection from persistent sympathetic injury and adverse remodeling.
5 · Uses and outcomes
Useful for selected rate-control problems, angina through reduced O₂ demand, and appropriate cardiac indications in hypertension. Carvedilol, metoprolol succinate ER and bisoprolol improve outcomes in stable HFrEF. Do not extend that evidence to every β blocker or formulation. Symptom relief in angina is a different claim from improved survival.
6 · Safety
Bradycardia, AV block and excessive negative inotropy; β₂-related bronchospasm and impaired recovery from hypoglycemia. Adrenergic warning symptoms can be masked. Verapamil or diltiazem adds cardiac suppression. Begin HFrEF therapy when clinically stable and titrate carefully; abrupt withdrawal can provoke tachycardia and ischemia. Severe poisoning: glucagon can bypass β receptors through cAMP signaling to support HR and contractility. It is an adjunct to emergency treatment, not complete reversal.
7 · Pharmacokinetics
Esmolol: rapid esterase clearance permits brief IV effects. Metoprolol: hepatic CYP2D6 metabolism can vary. Atenolol/nadolol: renal clearance matters. Ophthalmic timolol: systemic absorption can still cause cardiac or pulmonary effects. Receptor selectivity does not determine clearance or CNS penetration.
Apply the pathway
Practice task: Compare metoprolol during exercise, after standing, and during the first doses versus months of stable HFrEF treatment.
Learning goal: Explain which cardiac response is directly blocked and how time and the patient’s condition change its clinical meaning.
Self-check
A patient with stable HFrEF begins low-dose evidence-based β blockade. Which statement best reconciles its early and later effects?
Early β₁ stimulation raises output; later β₁ blockade lowers it
Early vasoconstriction guarantees later survival benefit
Early contractility can fall; sustained therapy limits harmful sympathetic effects
Show explanation
C. Early contractility can fall; sustained therapy limits harmful sympathetic effects
The immediate effect is reduced adrenergic support, not stimulation of the weak heart. Over time, reduced adrenergic injury, arrhythmia risk and maladaptive remodeling can improve outcomes. Clinical stability and gradual titration help patients tolerate the early effect.
Recommended integration points · Target + Uses and outcomes Connect direct sinus-node If inhibition to additional heart-rate reduction with β blockade, then identify the HFrEF population and outcome supported by evidence.
Starting point: Sinus-node pacemaker cells gradually depolarize during phase 4. The funny current contributes to this process and helps set the sinus rate.
1 · TargetRecommended integration point
HCN channels carrying If (the funny current) in the SA node. If is a mixed Na⁺/K⁺ current. This is distinct from β₁ receptors, L-type calcium channels and ventricular late Na⁺ current.
2 · Action
Inhibits If and reduces the slope of spontaneous phase-4 depolarization, so the sinus node reaches threshold less frequently.
3 · Tissue effect
Sinus heart rate falls without the same direct negative inotropic effect as β blockade or verapamil. Slower rate lengthens diastole. Sinus-node slowing is not an AV-nodal rate-control strategy for AF.
4 · Body response
Lower sinus rate reduces the number of beats per minute and changes filling time. Net cardiac output depends on both rate and stroke volume; an increase in output is not guaranteed. No distinctive vasodilator baroreflex is needed to explain its principal action.
5 · Uses and outcomesRecommended integration point
For the adult US HFrEF indication: stable symptomatic HF, LVEF ≤35%, sinus rhythm and resting HR ≥70/min, with maximally tolerated β blockade or a contraindication to it. The established labeled benefit is reduced hospitalization for worsening HF. Sinus rhythm follows from the target; the EF/HR thresholds identify the studied and labeled population. Ivabradine has no U.S. angina indication.
6 · Safety
Bradycardia, atrial fibrillation and luminous visual phenomena (phosphenes). Review rhythm and pulse; slowing the sinus node will not control an AF-driven ventricular response. Fetal toxicity is an important counseling issue.
7 · Pharmacokinetics
CYP3A4 metabolism creates interaction risk. Strong inhibitors are contraindicated; verapamil and diltiazem should be avoided because they increase exposure and add rate slowing.
Apply the pathway
Practice task: Compare an otherwise eligible HFrEF patient in sinus rhythm with a patient whose rapid pulse is due to AF.
Learning goal: Use the target to explain the rhythm requirement, and separate the proven hospitalization outcome from a general claim of improved survival.
Self-check
Why does ivabradine’s sinus-node mechanism fail to make it an appropriate ventricular rate-control drug for AF?
It increases α₁-mediated vasoconstriction
Its principal action requires ventricular Na⁺ channels
AF does not depend on SA-node pacing to drive the ventricles
Show explanation
C. AF does not depend on SA-node pacing to drive the ventricles
During AF, atrial impulses reach the ventricles through the AV conduction system; slowing the SA node does not control that input. The target explains the sinus-rhythm requirement, while clinical trials and labeling establish which HF patients benefit.
Recommended integration points · Tissue effect + Body response Explain the arterial effect first, then add the baroreflex. Use onset to explain why similar vascular effects can produce different early pulse responses.
Starting point: Ca²⁺ entering vascular smooth muscle binds calmodulin and activates myosin light-chain kinase (MLCK), promoting myosin phosphorylation and contraction.
1 · Target
L-type Ca²⁺ channels, with greater functional effects in arterial smooth muscle than in cardiac tissue at usual therapeutic exposure. This is a tissue preference, not a different vascular-only channel family.
2 · Action
Reversible inhibition of inward Ca²⁺ current reduces calcium entry during depolarization, weakening Ca²⁺–calmodulin activation of MLCK.
3 · Tissue effectRecommended integration point
Less myosin phosphorylation means arteriolar relaxation → lower SVR and afterload, the load against which the ventricle ejects. Coronary relaxation can relieve spasm. DHPs provide little direct AV-nodal slowing at usual doses; they are not substitutes for verapamil or diltiazem in rate control.
4 · Body responseRecommended integration point
A rapid fall in arterial pressure reduces baroreceptor firing and raises sympathetic output, causing reflex tachycardia. Immediate-release nifedipine illustrates this more clearly than gradual-onset amlodipine. A faster pulse is compensation for vasodilation, not direct cardiac β stimulation by the drug.
5 · Uses and outcomes
Hypertension and angina, including vasospastic angina. Angina relief and cardiovascular-risk reduction through BP treatment are distinct goals. Enteral nimodipine improves neurologic outcomes after aneurysmal subarachnoid hemorrhage; IV nicardipine and clevidipine allow titratable BP control. These roles do not imply improved HFrEF survival.
6 · Safety
Headache, flushing, hypotension, gingival enlargement and ankle edema. Precapillary arteriolar dilation raises capillary hydrostatic pressure, favoring fluid movement into tissue; edema need not represent total-body volume overload. Rapid hypotension and reflex tachycardia can worsen ischemia.
7 · Pharmacokinetics
Onset and formulation change the reflex response: compare immediate-release nifedipine with long-acting formulations and amlodipine. Most agents have hepatic CYP3A interactions. Clevidipine is a rapidly esterase-cleared IV exception. Nimodipine is given enterally, never intravenously.
Apply the pathway
Practice task: Predict BP, SVR and pulse after rapid versus gradual arterial dilation. Then explain ankle swelling despite a normal lung examination.
Learning goal: Separate direct vasodilation, reflex cardiac stimulation and local capillary fluid movement.
Self-check
Two vascular CCBs eventually lower BP similarly. One acts abruptly and the other gradually. With intact reflexes, which early effect is more likely after the abrupt-onset drug?
A larger reflex increase in heart rate
Greater direct slowing of AV conduction
A larger fall in heart rate from SA-node blockade
Show explanation
A. A larger reflex increase in heart rate
The rapid pressure fall more strongly recruits the baroreflex. Tissue preference explains the primary vascular action; time course explains the different compensatory pulse response.
Recommended integration points · Tissue effect + Safety Use nodal and myocardial effects to explain both benefit and harm. Add ventricular function, conduction disease or another nodal drug to change the prediction.
Starting point: Ca²⁺ current supports nodal depolarization and triggers Ca²⁺ release for myocardial contraction. These functions differ from fast Na⁺-dependent conduction in working ventricular tissue.
1 · Target
L-type Ca²⁺ channels in the SA and AV nodes, myocardium and arterial smooth muscle. Their prominent cardiac effects distinguish them from DHPs.
2 · Action
Reduce calcium entry. In nodal cells, this slows calcium-dependent conduction; in myocytes, less trigger calcium reduces Ca²⁺-induced Ca²⁺ release from the sarcoplasmic reticulum.
3 · Tissue effectRecommended integration point
Sinus rate, AV conduction and contractility decrease. Slower AV conduction can lengthen PR; this is not the same as QRS widening from ventricular Na⁺-channel blockade. Both drugs also dilate arteries. Verapamil generally has stronger negative inotropic effects than diltiazem.
4 · Body response
Vasodilation can activate sympathetic feedback, but direct nodal and myocardial depression generally limits or outweighs the cardiac reflex response. The net pulse effect therefore differs from a predominantly vascular DHP.
5 · Uses and outcomes
Selected supraventricular tachycardias and ventricular rate control in AF, with appropriate ventricular function; angina through lower cardiac work and coronary dilation. Rate control does not prevent AF-related thromboembolism. These agents do not improve HFrEF survival.
6 · SafetyRecommended integration point
Bradycardia and AV block reflect nodal suppression; worsening systolic failure reflects negative inotropy. A β blocker adds to these effects. Avoid in HFrEF and in pre-excited AF, where blocking the AV node can favor dangerous conduction through an accessory pathway. Verapamil commonly causes constipation.
7 · Pharmacokinetics
CYP3A interactions can alter exposure to the CCB or another drug. Verapamil inhibits P-glycoprotein and can increase digoxin exposure. That PK interaction is separate from the additive AV-nodal suppression both drugs produce.
Apply the pathway
Practice task: Add verapamil to a patient already taking metoprolol, then compare the predicted change with adding amlodipine instead.
Learning goal: Explain why drugs acting at different targets can still produce additive nodal and myocardial depression.
Self-check
After verapamil is added to metoprolol, a patient develops marked bradycardia and second-degree AV block. Which mechanism best explains this?
Loss of presynaptic α₂ feedback
Additive suppression of AV-nodal conduction
Selective reduction of ventricular late Na⁺ current
Show explanation
B. Additive suppression of AV-nodal conduction
β₁ blockade reduces adrenergic support of nodal signaling; verapamil directly reduces L-type Ca²⁺ current. The targets differ, but their effects converge on slower nodal conduction. Amlodipine usually adds vascular dilation without comparable direct nodal suppression.
Recommended integration points · Tissue effect + Safety Connect reduced late Na⁺ entry with Ca²⁺ loading and diastolic tension, then distinguish that proposed benefit from IKr-related QT prolongation.
Starting point: During ischemia, persistent inward Na⁺ current can contribute to intracellular Na⁺ and Ca²⁺ accumulation, increasing diastolic tension and impairing relaxation.
1 · Target
The late inward Na⁺ current in cardiac myocytes. Distinguish it from the large, brief peak Na⁺ current responsible for the rapid ventricular upstroke. Ranolazine also inhibits the repolarizing K⁺ current IKr.
2 · Action
Inhibits late Na⁺ entry at therapeutic concentrations. This is an established electrophysiologic action; the complete mechanism of its antianginal benefit remains incompletely defined.
3 · Tissue effectRecommended integration point
Less Na⁺ accumulation can reduce secondary Ca²⁺ loading and improve diastolic relaxation. Angina can improve with little average change in heart rate or BP. This helps explain its role when further rate or pressure reduction would be undesirable.
4 · Body response
Marked reflex tachycardia is not a defining response because there is little primary change in rate or BP. Do not add a large baroreflex effect simply to fill this step.
5 · Uses and outcomes
Treatment of chronic angina. The intended benefit is symptom relief and improved exercise tolerance; do not infer a survival benefit from those effects.
6 · SafetyRecommended integration point
IKr inhibition can prolong QT—a separate current from the proposed late-Na⁺ benefit. Consider other QT-prolonging drugs and increased exposure. Dizziness, nausea and constipation occur. Liver cirrhosis is a contraindication; impaired renal function warrants attention.
7 · Pharmacokinetics
CYP3A is central to exposure. Strong CYP3A inhibitors and CYP3A inducers are contraindicated; moderate inhibitors such as verapamil or diltiazem require limiting ranolazine dosing. Check interactions rather than assuming its small BP effect makes combinations harmless.
Apply the pathway
Practice task: Consider persistent angina in a patient whose low BP and slow pulse limit additional hemodynamic therapy; then add a CYP3A inhibitor.
Learning goal: Explain why ranolazine may fit the physiology while an exposure-related QT risk still changes the decision.
Self-check
Ranolazine relieves angina with little change in pulse or BP. Which separate action explains its potential to prolong QT?
Inhibition of the IKr potassium current
Activation of central α₂ receptors
Blockade of vascular α₁ receptors
Show explanation
A. Inhibition of the IKr potassium current
IKr inhibition delays repolarization. The safety concern should not be attributed to the same late-Na⁺ current used to explain reduced calcium loading. A drug can have clinically important effects at more than one target.
Identify each drug from its mechanism and clinical clues. Explain your reasoning before revealing the answer.
Who am I? — Sympatholytics
Clue 1
I reduce central sympathetic outflow through α₂ and imidazoline signaling. I come as an oral drug or weekly patch. Abrupt cessation can cause rebound hypertension.
Reveal answer and explanation
Clonidine
Clonidine fits the first description. Activating central inhibitory receptors reduces sympathetic outflow and lowers blood pressure. Abrupt withdrawal removes that inhibition and can produce a sympathetic surge. The weekly patch is an exposure clue; a newly applied patch has a delayed onset of effect.
Clue 2
I reversibly block α₁ and α₂ receptors. My rapid, short parenteral action is useful for acute catecholamine-mediated hypertension. Marked reflex tachycardia can occur.
Reveal answer and explanation
Phentolamine
Phentolamine fits the second description. α₁ blockade relaxes vessels and lowers pressure, recruiting the baroreflex. Simultaneous presynaptic α₂ blockade removes feedback inhibition of norepinephrine (NE) release, adding to cardiac adrenergic stimulation and tachycardia. Selective α₁ blockers preserve that feedback. Phentolamine’s reversible, short parenteral action distinguishes it from phenoxybenzamine, whose irreversible blockade persists while functional receptors are replaced.
Clue 3
I selectively block α₁ receptors, treat both HTN and BPH, and have a ~22-hour half-life. My ALLHAT arm had more heart failure than the chlorthalidone arm.
Reveal answer and explanation
Doxazosin
Doxazosin fits the third description. α₁ blockade relaxes vascular and prostate/bladder-neck smooth muscle, linking its mechanism to both hypertension treatment and relief of benign prostatic hyperplasia (BPH) symptoms. Impaired reflex vasoconstriction also explains orthostatic hypotension. Its prolonged exposure supports once-daily use. ALLHAT supplies a separate clinical-outcome finding: lowering BP with doxazosin did not provide the same cardiovascular protection as chlorthalidone.
I block β₁ and β₂, enter the CNS readily, and can be used for essential tremor and hyperthyroid symptoms.
Reveal answer and explanation
Propranolol
Propranolol fits the first description: it blocks β₁ and β₂ receptors, enters the brain readily, and can reduce essential tremor and hyperthyroid symptoms. Nonselectivity also explains its bronchospasm concern.
Clue 2
I prefer β₁, am relatively hydrophilic, and require attention to renal function.
Reveal answer and explanation
Atenolol
Atenolol fits the second description. Its β₁ preference limits β₂ blockade at appropriate exposure, while renal elimination makes kidney function important for dosing and accumulation.
Clue 3
I block β₁, β₂ and α₁, and have HFrEF outcome evidence.
Reveal answer and explanation
Carvedilol
Carvedilol fits the third description. β blockade reduces cardiac stimulation, α₁ blockade adds vasodilation, and clinical trials establish its role in HFrEF.
Clue 4
I am given IV, prefer β₁, and have an elimination half-life of approximately 9 minutes.
Reveal answer and explanation
Esmolol
Esmolol fits the fourth description. Rapid esterase metabolism gives this intravenous β₁-preferring drug a half-life of about nine minutes. Its short action is useful when the response must be adjusted promptly. Identify each drug from the combination of receptor profile, exposure, and clinical role rather than from one isolated clue.
I produce gradual arteriolar dilation, have a 30–50-hour half-life, and commonly cause dose-related ankle edema.
Reveal answer and explanation
Amlodipine
Amlodipine fits the long-half-life, predominantly vascular description. Its gradual action supports sustained blood-pressure control, while preferential arteriolar dilation explains dependent ankle edema.
Clue 2
I slow AV conduction and can cause prominent constipation; avoid me in HFrEF.
Reveal answer and explanation
Verapamil
Verapamil fits the strong AV-nodal effect with constipation. The same calcium-channel blockade that slows conduction can reduce myocardial contractility, explaining its concern in HFrEF.
Clue 3
My immediate-release formulation can produce abrupt hypotension and reflex tachycardia.
Reveal answer and explanation
Nifedipine
Immediate-release nifedipine fits the abrupt vasodilation and reflex-tachycardia description. The faster heart rate is a baroreflex response to falling pressure, not the direct vascular drug effect.
Clue 4
I am a non-DHP used for AV-nodal rate control and angina, usually with less negative inotropy than verapamil.
Reveal answer and explanation
Diltiazem
Diltiazem fits the non-DHP with both cardiac and vascular actions and generally less negative inotropy than verapamil. That relative difference does not make it an appropriate substitute in HFrEF. For each answer, connect the identifying feature to the target tissue and then to the clinical consequence.
Return to the same physiological variables—rate, AV conduction, contractility, vascular resistance and renin—while keeping the immediate drug targets distinct.
Explain the location of action: central α₂ agonists reduce sympathetic output; peripheral α/β blockers change receptor responses; CCBs act on calcium entry in effector tissues. Ivabradine and ranolazine have their own ion-current targets.
Compare these predictions
Pressure falls and pulse rises: begin with vascular relaxation, then add the baroreflex. Ask whether presynaptic α₂ feedback remains intact.
Pulse and AV conduction slow: compare β₁ blockade with non-DHP calcium-channel blockade. Different targets can converge on the same tissue effect and combine to cause harm.
Rate slows with little direct change in contraction: locate the sinus-node funny current and verify sinus rhythm before invoking ivabradine.
Angina improves despite little change in pulse or BP: consider ranolazine, then check its separate QT and exposure concerns.
A weak heart improves with chronic β blockade: distinguish early loss of inotropic support from protection against sustained sympathetic injury. Name the agent, formulation and outcome evidence.
CardioRx: mechanisms, drug comparisons, and clinical cases. Explore coronary flow reserve and oxygen supply–demand balance, review nitrate pharmacology, then apply the drug comparisons to patient cases.
Check your explanation
Can you identify the target, explain the direct effect, add relevant compensation, name a supported benefit, predict a major harm and identify an exposure change that matters? You do not need seven equally long answers. You do need the links that make your conclusion defensible.