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IMAGE INTERPRETATION · PET AND ONCOLOGY

Medications to Stop Before an MIBG Scan

MIBG scan — pre-scan medication preparation
MIBG scan — pre-scan medication preparation

CC BY 4.0 · Wikimedia Commons · source file

Question

Before performing an I-123 or I-131 MIBG scan, certain medications must be discontinued to prevent interference with MIBG uptake. Which of the following medications MUST be discontinued before MIBG imaging?

  1. AAspirin and NSAIDs
  2. BTricyclic antidepressants (e.g., amitriptyline), labetalol, and calcium channel blockers — these block the norepinephrine transporter (NET) that MIBG uses for uptake
  3. CBeta-1 selective blockers (metoprolol, atenolol)
  4. DACE inhibitors and ARBs
Show the answer and explanation

B. Tricyclic antidepressants (e.g., amitriptyline), labetalol, and calcium channel blockers — these block the norepinephrine transporter (NET) that MIBG uses for uptake

MIBG is taken up by chromaffin cells via the norepinephrine transporter (NET). Several medications block NET and reduce MIBG uptake, causing false-negative results: (1) TRICYCLIC ANTIDEPRESSANTS (amitriptyline, nortriptyline, imipramine) — block NET directly; (2) LABETALOL — the only antihypertensive that blocks NET (other beta-blockers do not); (3) CALCIUM CHANNEL BLOCKERS (some); (4) COCAINE and sympathomimetics; (5) Certain antipsychotics. These must be stopped before MIBG imaging (typically 2 weeks for tricyclics, 48–72 hours for labetalol). Notably, beta-1 selective blockers (metoprolol, atenolol) do NOT significantly block NET and can be continued.

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