Tab diltiazem for SVT
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diltiazem oral "supraventricular tachycardia"
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I now have comprehensive information. Here is a full summary of oral (tablet) diltiazem for SVT:
Diltiazem Tablets for SVT
Mechanism of Action
Diltiazem is a non-dihydropyridine calcium channel blocker that:
- Inhibits L-type calcium channels
- Slows AV nodal conduction
- Increases the AV node's refractory period
- Decreases automaticity
- Prolongs the PR interval
These effects make it effective for arrhythmias dependent on AV nodal conduction (e.g., AVNRT, AVRT) and for ventricular rate control in AF/flutter.
Indications for Oral Diltiazem in SVT
- Paroxysmal SVT (PSVT) - termination and prevention
- Rate control in AF/atrial flutter (most common use in practice)
- Transition from IV infusion once rate control is achieved in AF
Note: Verapamil is used more often than diltiazem for acute SVT termination (conversion rate ~90%, similar to adenosine), while diltiazem is more commonly used for rate control in AF.
Oral Dosing
Immediate-release (IR) tablets:
- Starting dose: 30-60 mg PO TID or QID (three to four times daily)
- Usual range: 120-360 mg/day in divided doses
- IR onset: 30-60 minutes, peak at 2-4 hours
Extended-release (ER) tablets:
- Once stable on IR, can transition to equivalent total daily dose given once or twice daily
- ER tablet onset: peak at 11-18 hours
Transitioning from IV to oral:
When transitioning from an IV infusion to oral:
- Use the IR formulation first
- Approximate conversion (Tintinalli's formula):
- IV infusion rate 10 mg/h → oral ~240 mg/day
- IV infusion rate 15 mg/h → oral ~360 mg/day
- Once stable on IR, switch to an equivalent ER formulation
Pharmacokinetics
| Parameter | IR Tablet | ER Tablet |
|---|---|---|
| Absorption | ~98% | ~93-95% |
| Oral bioavailability | ~40% (extensive first-pass) | ~40% |
| Protein binding | 70-80% | 70-80% |
| Metabolism | Hepatic (CYP450) | Hepatic (CYP450) |
| Half-life | 3-4.5 h | 6-9 h |
| Onset | 30-60 min | Longer |
| Peak | 2-4 h | 11-18 h |
Contraindications
- WPW syndrome / pre-excitation with SVT - HIGH RISK of life-threatening ventricular arrhythmia (blocks AV node, forcing conduction down accessory pathway)
- Wide-complex tachyarrhythmias (unless known SVT with aberrancy)
- Sick sinus syndrome (without pacemaker)
- 2nd or 3rd degree AV block (without pacemaker)
- Severe hypotension / cardiogenic shock
- Concurrent IV beta-blockers (risk of severe bradycardia/heart block)
- Ventricular tachycardia
Adverse Effects
- Bradycardia / bradyarrhythmia
- AV block
- Hypotension
- Peripheral edema
- Headache, dizziness, fatigue
- Syncope
- Asystole (rare)
Key Clinical Points
- Oral diltiazem is a secondary option for acute SVT - adenosine IV is first-line for acute termination; oral diltiazem is used for prevention of recurrence or rate control.
- Always rule out WPW before giving - a delta wave on baseline ECG or irregular, wide-complex AF should raise suspicion.
- Avoid combining with IV beta-blockers - serious bradycardia/heart block risk.
- Use IR first when starting orally; switch to ER once dose is established.
Sources: Tintinalli's Emergency Medicine, pp. 170-171; Katzung's Basic and Clinical Pharmacology 16e; Braunwald's Heart Disease
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