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Diltiazem in PSVT

Mechanism of Action

• Slows AV nodal conduction - decreases the velocity of impulse transmission through the AV node, increasing the PR interval
• Prolongs AV nodal refractory period - blocks the slow inward calcium current during depolarization
• Decremental conduction - both effects together produce AV nodal block

• Goodman & Gilman's Pharmacological Basis of Therapeutics, p. 245-247
• Roberts and Hedges' Clinical Procedures in Emergency Medicine, p. 3737-3741

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Clinical Indications

Parenteral diltiazem is approved for temporary control of rapid ventricular rate in atrial flutter/AF and for rapid conversion of PSVT to sinus rhythm - though IV adenosine has largely supplanted it for acute termination due to its shorter onset and action.

• Goodman & Gilman, p. 247

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Position in the Treatment Algorithm

1. Vagal maneuvers (Valsalva, carotid sinus massage) - first line
2. IV Adenosine - if vagal maneuvers fail (terminates the vast majority of PSVT)
3. Non-DHP CCB (diltiazem or verapamil) and/or beta-blocker - if adenosine fails or PSVT is recurrent
4. Antiarrhythmic therapy - if above ineffective
5. Catheter ablation - for recurrent/incessant PSVT

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Dosing (IV)

• Roberts and Hedges' Clinical Procedures in Emergency Medicine, p. 3747

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Contraindications

1. Sick sinus syndrome, 2nd-degree or 3rd-degree AV block (unless internal pacer present)
2. Severe hypotension / cardiogenic shock
3. Hypersensitivity to diltiazem
4. IV beta-blocker use within a few hours (risk of compounded AV blockade and bradycardia)
5. WPW / LGL syndrome (AF or atrial flutter with accessory bypass tract) - diltiazem may paradoxically accelerate conduction down the accessory pathway, precipitating VF
6. Ventricular tachycardia - Ca²⁺ channel blockers are generally ineffective and can be dangerous; this is a key pitfall when VT is misdiagnosed as PSVT
7. Wide-complex tachycardia of uncertain origin - treat as VT until proven otherwise

• Roberts and Hedges', p. 3745

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Adverse Effects

The most dangerous scenario historically was IV diltiazem/verapamil given to a patient with VT misdiagnosed as PSVT - causing severe hemodynamic collapse.

• Goodman & Gilman, p. 252

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Diltiazem vs. Verapamil in PSVT

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Special Considerations

• WPW with PSVT: If the tachycardia is orthodromic AVRT with a concealed or known low-risk accessory pathway, diltiazem/verapamil may be used. However, if there is overt preexcitation (delta waves) with AF/flutter, avoid all AV nodal blockers - use IV procainamide or cardioversion.
• Pregnancy: PSVT treatment in pregnancy follows the same algorithm (vagal maneuvers → adenosine → CCB); diltiazem/verapamil are options when adenosine fails.
• "Pill-in-the-pocket": For patients with recurrent PSVT and known low-risk APs, a single dose of oral beta-blocker, verapamil, or diltiazem taken at episode onset can terminate the arrhythmia.
• Long-term management: Most patients with recurrent PSVT are candidates for catheter ablation, which is curative. Diltiazem oral therapy is an alternative for those who decline ablation.

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Parenteral Iron for Iron Deficiency Anemia in the 3rd Trimester

Why Parenteral Iron is Preferred in the 3rd Trimester

• There is inadequate time for GI absorption and response before delivery
• Oral iron absorption is further limited by physiologic GI changes in late pregnancy
• High iron demand in the 3rd trimester is difficult to meet with oral supplementation
• IV iron achieves target hemoglobin faster and more reliably than oral iron

• Rosen's Emergency Medicine, p. 839-840
• Creasy & Resnik's Maternal-Fetal Medicine, p. 1234-1240

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Diagnosis First

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Approved Parenteral Iron Preparations

• Creasy & Resnik's Maternal-Fetal Medicine, p. 1238
• Goodman & Gilman's Pharmacological Basis of Therapeutics

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Dosing: Iron Sucrose (Most Common in Pregnancy)

Total dose (mg) = Body weight (kg) × (Target Hb - Actual Hb) × 0.24 + 500 mg

• Target Hb: 11-12 g/dL
• Maximum per infusion: 200 mg
• Frequency: Every other day (split dosing)

60 × (12 - 8) × 0.24 + 500 = 57.6 + 500 = ~558 mg total → given as 200 mg every other day × 3 infusions

• Creasy & Resnik's, p. 1238

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Contraindications / Precautions

• Not used in the 1st trimester (organogenesis concerns; iron dextran has shown fetal harm in animals)
• Severe anaphylaxis - now rare with modern preparations; test dose only required for low-MW iron dextran
• Iron dextran (high MW) is no longer recommended due to higher anaphylaxis risk
• Sodium ferric gluconate - avoid due to benzyl alcohol

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Monitoring Adverse Effects

• Urticaria, pruritus
• Dyspnea
• Tachycardia
• Chills and arthralgias
• Hypotension (rare with modern preparations)

All IV iron infusions should be given in a facility equipped to manage hypersensitivity reactions. Monitor the patient for ≥30 minutes post-infusion.

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Role of Erythropoietin

• Subcutaneous erythropoietin + oral or IV iron has been used successfully
• In one study, erythropoietin added to oral iron normalized Hb in 2 weeks in 73% of patients
• Caution: Erythropoietin carries a thromboembolism risk (already elevated in pregnancy) - use requires careful risk-benefit assessment
• Creasy & Resnik's, p. 1242

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Summary: 3rd Trimester IDA Algorithm

IDA in 3rd trimester
        ↓
IV iron (treatment of choice)
        ↓
Iron Sucrose 200 mg every other day (most used)
OR Ferric Carboxymaltose (single/two-dose, convenient)
OR Iron Isomaltoside (single-dose option)
        ↓
Monitor Hb - expect rise of ~1 g/dL/week in severe cases
        ↓
If Hb <7 g/dL or no response → Blood transfusion
If Hb fails despite IV iron → Add Erythropoietin (with caution)

Recent evidence (Lancet Haematol, 2025 - PMID 40306833): Consensus guidelines now recommend IV iron as first-line (over oral) when Hb correction is urgently needed in late pregnancy, given its superior efficacy and safety profile.

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Injection Ferric Carboxymaltose (FCM)

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What Is It?

• Goodman & Gilman's Pharmacological Basis of Therapeutics

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Mechanism of Action

1. After IV injection, FCM is rapidly cleared from circulation
2. ~80% distributes to the bone marrow (primary site of erythropoiesis), with the remainder to liver and spleen
3. Iron is incorporated into hemoglobin synthesis, replenishing depleted stores
4. Results in: rise in serum iron → rise in serum ferritin → rise in transferrin saturation → correction of hemoglobin

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Key Pharmacological Advantage

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Indications

• Iron deficiency anemia (IDA) with intolerance to oral iron
• Unsatisfactory response to oral iron (Hb not rising after 2 weeks)
• IDA in 3rd trimester of pregnancy (treatment of choice)
• IDA with malabsorption (post-bariatric surgery, IBD, celiac disease)
• IDA in non-dialysis-dependent CKD
• IDA in heart failure (improves exercise capacity and quality of life - FAIR-HF trial)
• Patients with ongoing blood loss too great for oral supplementation

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Dosing

Standard Dosing (Adults)

Dose Calculation (Ganzoni Formula)

Total iron dose (mg) = Body weight (kg) × (Target Hb - Actual Hb g/dL) × 0.24 + 500

• Target Hb: 12 g/dL (non-pregnant); 11-12 g/dL (pregnant)

In Pregnancy (3rd Trimester)

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Administration

• Route: Intravenous only (IV infusion or slow IV push)
• Dilution: 750 mg in 100-250 mL normal saline (0.9% NaCl); do NOT dilute in dextrose
• Do NOT give IM - causes local staining and tissue necrosis
• No test dose required
• Observe patient for ≥30 minutes after infusion for hypersensitivity reactions

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Adverse Effects

Common

• Headache, dizziness
• Nausea, abdominal pain, constipation, diarrhea
• Flushing, rash
• Injection site reactions
• Transient hypertension

Important / Clinically Significant

Hypophosphatemia is FCM's distinguishing complication - monitor serum phosphate after infusion, especially with repeat dosing. This is a key exam point. [Systematic review PMID 39935027, 2025]

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Contraindications

• Known hypersensitivity to FCM or any component
• Iron overload states (hemochromatosis, hemosiderosis)
• Anemia NOT due to iron deficiency (e.g., hemolytic anemia, megaloblastic anemia)
• First trimester of pregnancy (avoid; use from 2nd trimester onward when needed)
• Non-iron deficiency anemia

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Monitoring

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Comparison: FCM vs. Iron Sucrose in Pregnancy

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Summary Points

• FCM is a high-dose, single-infusion parenteral iron ideal when rapid or convenient repletion is needed
• No test dose required, very low anaphylaxis risk
• 3rd trimester IDA - FCM is an excellent choice (1-2 infusions vs. multiple for iron sucrose)
• Unique risk: hypophosphatemia via FGF-23 elevation - monitor serum phosphate at 1 week; can cause osteomalacia/fractures if prolonged
• Does NOT interfere with erythropoiesis assessment unlike ferumoxytol's MRI effect
• In heart failure with iron deficiency, FCM improves exercise capacity and symptoms (FAIR-HF trial)

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Oral Diltiazem + Amiodarone in VT Patients

Direct Answer: Generally Contraindicated / Strongly Cautioned Against

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Why Diltiazem is Contraindicated in VT

"Both agents [verapamil and diltiazem] are contraindicated for wide-complex tachyarrhythmias." - Tintinalli's Emergency Medicine

"Ca²⁺ channel blockers usually are not effective in VT. This was a particular problem when the drugs were used mistakenly in patients with VT misdiagnosed as PSVT, causing severe hemodynamic collapse." - Goodman & Gilman's

• VT is driven by abnormal ventricular automaticity or ventricular reentry circuits - these do NOT depend on the AV node
• Diltiazem (Class IV) works by blocking the AV node - it has no direct effect on ventricular myocardium at therapeutic doses
• In VT, diltiazem causes vasodilation + negative inotropy → hemodynamic collapse without terminating the arrhythmia

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The Drug Interaction: Amiodarone + Diltiazem

"Drugs with synergistic actions, such as beta blockers or calcium channel blockers, must be given cautiously [with amiodarone]."

• Braunwald's Heart Disease, 15th Edition, p. 466

"CCB and amiodarone exacerbates sick sinus syndrome and AV block."

• Brenner and Rector's The Kidney

"β-adrenoceptor antagonists, calcium-channel blockers, digoxin, sotalol, and amiodarone are some of the agents that most commonly cause significant sinus bradycardia or AV block."

• Fuster and Hurst's The Heart, 15th Edition

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Amiodarone's Multi-Channel Profile Explains the Risk

• High-degree AV block (2nd or 3rd degree)
• Severe sinus bradycardia / sinus arrest
• Hemodynamic instability

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Pharmacokinetic Interaction (CYP3A4)

• Amiodarone increases diltiazem plasma concentrations by reducing its clearance
• The pharmacodynamic interaction (additive depression) is therefore amplified by a pharmacokinetic interaction
• Toxicity can occur at doses of diltiazem that would otherwise be safe

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What Should Be Used for VT Instead?

Mexiletine + amiodarone is a recognised and safe combination for refractory VT suppression - mexiletine (Class IB) has complementary rather than overlapping mechanisms with amiodarone.

• Lippincott Illustrated Reviews: Pharmacology

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Summary

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Indications for Amiodarone

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Vaughan Williams Classification

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FDA-Approved (Labeled) Indications

"Amiodarone is approved by the FDA for the treatment of patients with life-threatening ventricular tachyarrhythmias when other drugs are ineffective or not tolerated."

• Braunwald's Heart Disease, 15th Ed.

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Off-Label (Widely Used) Indications

Ventricular Arrhythmias

Supraventricular Arrhythmias

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Acute vs. Chronic Dosing

IV (Acute)

Oral (Chronic)

Amiodarone has an extremely long half-life (40-55 days). Steady-state without loading takes ~265 days. Loading doses are essential to achieve rapid effect.

• Braunwald's Heart Disease, 15th Ed.

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Why Amiodarone is Preferred Despite Its Toxicity

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Key Contraindications

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Important Adverse Effects (Brief Summary)

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Monitoring (Braunwald's Recommended Schedule)

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Summary in One Table

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Labetalol Dosing for Hypertensive Urgency

Urgency vs. Emergency - Key Distinction First

Rapid BP reduction in urgency is not recommended - overly aggressive lowering risks cerebral, coronary, or renal ischemia. The goal is a controlled, gradual decrease.

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Mechanism of Labetalol

• α₁-adrenergic blockade → vasodilation, reduces peripheral resistance
• Non-selective β-blockade → reduces heart rate and cardiac output

• Katzung's Basic and Clinical Pharmacology, 16th Ed.

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ORAL Labetalol - Hypertensive Urgency

"When treatment for acute-onset severe HTN is needed and IV access has not yet been initiated, a 200 mg dose of labetalol can be administered orally."

• Swanson's Family Medicine Review

• The Washington Manual of Medical Therapeutics, p. 88
• Textbook of Family Medicine, 9th Ed.

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IV Labetalol - Hypertensive Emergency

Bolus Dosing (Preferred - due to 5-8 hour half-life)

Continuous Infusion (Alternative)

"Because the half-life of labetalol is 5-8 hours, intermittent IV bolus dosing may be preferable to IV infusion."

• Washington Manual of Medical Therapeutics

Pediatric IV Dosing (for reference)

• Harriet Lane Handbook, 23rd Ed.

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Comparison with Other Agents for Hypertensive Urgency

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Special Indications Where Labetalol is Drug of Choice

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Contraindications

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Key Adverse Effects

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Summary: Dosing at a Glance

HYPERTENSIVE URGENCY (Oral):
  → Labetalol 200 mg PO
  → Repeat 200-400 mg PO after 6-12 hours if BP not controlled
  → Goal: Gradual reduction over 24-48 hours

HYPERTENSIVE EMERGENCY (IV):
  → Labetalol 20-80 mg IV bolus q5-10 min (max 300 mg total)
  → OR Infusion: 0.5-2 mg/min
  → Transition to oral 200 mg when stable

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Urticaria - Pictures and Management

Definition and Key Features

• Wheals - transient, edematous, blanching papules or plaques
• Pruritus - invariably present and often severe
• Wheal and flare - pale center with surrounding erythematous border
• Transient - individual lesions last < 24 hours, though new lesions may continuously appear
• Can be annular, serpiginous, or confluent in pattern

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Clinical Photographs

Adult Urticaria - Characteristic wheals on arm

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Urticaria - Large confluent wheals (adult)

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Pediatric Urticaria - Oval wheals covering torso and arms

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Classification

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Causes / Triggers

Aspirin and NSAIDs cause urticaria by a non-immunologic mechanism and the effect can persist for weeks after ingestion.

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Pathophysiology

• Histamine (primary mediator)
• Bradykinin, kallikrein, acetylcholine
• Slow-reacting substance of anaphylaxis (leukotrienes)

• IgE-mediated (Type I hypersensitivity) - allergen cross-links IgE on mast cells
• Non-IgE mediated - direct mast cell degranulation (drugs, foods)
• Autoimmune - anti-FcεRI or anti-IgE autoantibodies

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Management

Step 1 - Acute Urticaria (Immediate Management)

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Step-Up Treatment Algorithm for Chronic Urticaria

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Pharmacological Treatment by Step

Step 1 - Second-Generation (Non-Sedating) H1 Antihistamines - First Line

Step 2 - If Inadequate Control after 2-4 Weeks

• Increase sgAH dose up to 4× standard dose (e.g., cetirizine 40 mg/day)
• Add H2 blocker (ranitidine, famotidine) - adjunct to H1, not monotherapy
• Add leukotriene receptor antagonist (montelukast) - especially if NSAID-induced
• Add first-generation antihistamine at bedtime (hydroxyzine, diphenhydramine) for nocturnal pruritus
• Doxepin 10-25 mg at night - has both H1 and H2 blocking effects

Step 3 (Specialist Supervision) - Omalizumab

• Omalizumab 150-300 mg SC every 4 weeks
• Anti-IgE monoclonal antibody
• Highly effective in chronic spontaneous urticaria refractory to antihistamines
• Approved for chronic urticaria; significant evidence base

Step 4 - Ciclosporin (Cyclosporine)

• Ciclosporin 3-5 mg/kg/day
• For antihistamine + omalizumab-refractory cases
• Requires specialist supervision; monitor BP and renal function

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Corticosteroids

Note: A randomized ED trial of 100 adults showed no additional benefit of adding prednisone to levocetirizine for acute urticaria of <24 hours duration.

• Tintinalli's Emergency Medicine

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Refractory / Special Cases

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Summary Algorithm

Urticaria
    ↓
Anaphylaxis? → YES → IM Epinephrine immediately
    ↓ NO
Remove trigger + Start 2nd-gen H1 antihistamine
    ↓ Inadequate at 2-4 weeks
↑ Dose up to 4× + Add H2 blocker / montelukast / bedtime sedating AH
    ↓ Still inadequate
Add Omalizumab (specialist)
    ↓ Still inadequate
Add Ciclosporin (specialist)
    ↓
Short course steroids for severe flares (not chronic use)

Chronic urticaria almost always resolves with time. Reassure patients - 50% resolve within 1 year, 80-90% within 5 years. Trigger avoidance and antihistamine control are the cornerstones of treatment.