Verapamil

Class & subclass

• Non-dihydropyridine (non-DHP) phenyl-alkyl-amine CCB
• Potent AV-nodal suppressant → negative chronotrope, inotrope, dromotrope.

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TGA-Approved & PBS-listed uses

Indication	Practical Australian notes
Chronic stable vasospastic or unstable angina	PBS General Schedule modified-release 180 mg & 240 mg tablets (e.g. Isoptin SR, Cordilox SR)
Hypertension (add-on or monotherapy when ACEi/ARB/intolerance)	Heart Foundation regards CCBs as a first-line option, usually added to ACEi/ARB or thiazide if BP > 140/90 mm Hg despite lifestyle change heartfoundation.org.au
SVT (acute IV termination & oral maintenance) PSVT prophylaxis	Standard of care in ED/ICU protocols (KEMH guideline) kemh.health.wa.gov.au

2. Important off-label Australian uses

• AF / AFl rate control when β-blockers unsuitable.
• Cluster-headache prophylaxis – start 80 mg TDS, uptitrate every 1-2 weeks; typical maintenance 240-480 mg/day; doses ≤ 960 mg with specialist/ECG monitoring australianprescriber.tg.org.au.
• Hypertrophic cardiomyopathy symptoms (if β-blocker not tolerated).
• Idiopathic verapamil-sensitive VT (diagnosed by EP study).

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3. Mechanism of action

• Blocks L-type Ca²⁺ channels in cardiac myocytes, nodal tissue, and vascular smooth muscle.
  • ↓ SA & AV nodal conduction
  • ↓ Myocardial contractility
  • Coronary & peripheral arteriolar dilation → ↓ afterload, ↑ O₂ supply.

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4. dosing guide

Setting	Initial	Target / Max	Formulation tips
Hypertension	IR 40–80 mg TDS OR SR 120 mg mane	160 mg TDS or SR 240 mg mane (max 480 mg/day)	Take SR with food do not crush/chew.
Angina	IR 80 mg TDS	120–160 mg TDS	PBS-listed SR products ≈ equal efficacy.
AF / AFl (rate)	IV 0.075–0.15 mg/kg over ≥2 min → may repeat 10 mg after 15–30 min.
Oral SR 180 mg mane	240–480 mg/day	Avoid IV if wide-complex rhythm.
SVT (acute)	2.5 – 5 mg IV over ≥2 min (3 min if ≥65 y)	Additional 5–10 mg after 15–30 min; total max 20–30 mg
Cluster HA prophylaxis	80 mg TDS	240–480 mg/day (ECG at each 80 mg step)	Off-label; cardiology input if >480 mg.

Dose reductions: Child-Pugh ≥B – ↓ oral dose ~20 %, IV dose ~50 % 
Monitor PR interval and BP closely.

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5. Adverse effects & monitoring

• Very common:
  • constipation (advise fibre ± laxative)
  • ankle oedema
  • fatigue.
• Important:
  • gingival hyperplasia
  • brady- or high-grade AV block
  • worsening HFrEF.
• Lab / ECG: BP, HR, PR interval; LFTs if >6 months therapy.
• Pregnancy:
  • Category C – avoid in 1st trimester; IV acceptable for SVT when adenosine fails (obstetric consult).
• Breast-feeding: RID ≈ 1 %; generally safe, observe infant HR/BP.

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6. Contraindications

• SBP < 90 mm Hg
  • Verapamil is a negative inotrope (↓ contractility) and vasodilator (↓ SVR).
  • In an already hypotensive patient, additional depression of contractility and after-load can precipitate circulatory collapse.
• severe LV dysfunction
• sick-sinus or ≥2° AV block unless paced
  • Verapamil slows SA automaticity and prolongs AV-node refractoriness via Ca²⁺ channel blockade.
  • Intrinsic nodal disease leaves no “reserve” conduction.
• WPW/LGL with AF/AFl (risk of VF).
  • In WPW, accessory fibres conduct impulses rapidly to ventricles.
  • Verapamil slows the AV node but does not block the accessory tract;
  • atrial impulses preferentially travel down the pathway → very fast ventricular rates.
• Concomitant IV β-blocker.
  • Both drug classes depress AV conduction and contractility
  • IV–IV co-administration produces a sudden synergistic effect.
• Decompensated HFrEF (NYHA III-IV) – use amlodipine instead.
  • In systolic HF, cardiac output is preload- and sympathetic-dependent.
  • Verapamil blunts sympathetic drive and contractility, and raises LV end-diastolic pressure.

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7. Toxicity pearls (CCB overdose)

Brady-cardia + hypotension ± hyperglycaemia → treat with:

1. IV calcium gluconate/chloride bolus ± infusion
2. High-dose insulin euglycaemic therapy (HIET)
3. Vasopressors (nor-adrenaline preferred)
4. Lipid emulsion → VA-ECMO if refractory.

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Where does Verapamil fit among Calcium-Channel Blockers?

Class	Main AU examples	Predominant site	Typical uses	Cautions
Non-DHP – Phenylalkylamine	Verapamil	Cardiac > vascular	SVT rate-control AF angina cluster HA	Avoid in HFrEF, combine cautiously with β-blockers
Non-DHP – Benzothiazepine	Diltiazem	Cardiac ≈ vascular	Angina rate-control AF hypertension	Similar but milder cardiac depression vs verapamil
Dihydropyridines	Amlodipine Felodipine Lercanidipine Nifedipine SR Nimodipine (SAH) Clevidipine IV (ICU)	Vascular >> cardiac	Hypertension chronic stable angina Raynaud’s cerebral vasospasm	Reflex tachycardia (short-acting) ankle oedema gingival hyperplasia (rare)

→ Quick rule-of-thumb: “DHP = Dilate arterioles, Non-DHP = Node depression.” australianprescriber.tg.org.au

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Practical tips

• Route matters:
  • do not convert mg-for-mg between IR ↔ SR ↔ IV without checking product information.
• Drug interactions:
  • CYP3A4 inhibitors (e.g. erythromycin, grapefruit) ↑ verapamil levels; verapamil ↑ digoxin & DOAC exposure.
• ECG gate-keeping:
  • baseline + after each 80 mg titration if total daily dose > 240 mg.
• Patient counselling:
  • take SR with food
  • don’t crush
  • report dizziness, syncope, swollen ankles, gingival bleeding.