# Possible Drug–Radiopharmaceutical Interaction in 99mTc-Sestamibi Parathyroid Imaging

## TL;DR

A patient's medications affected a radiotracer scan, leading to a false-negative result until the drugs were stopped and a repeat scan confirmed a parathyroid adenoma.

## Contribution

First report in Jamaica showing how P-gp substrate medications can interfere with 99mTc-MIBI parathyroid imaging.

## Key findings

- Initial scan showed reduced tracer uptake due to ongoing P-gp substrate medications.
- Repeat scan after 72 h medication discontinuation detected a parathyroid adenoma.
- Histology confirmed the scan findings, emphasizing the need to review medications before imaging.

## Abstract

Drug–radiopharmaceutical interactions can significantly alter radiotracer biodistribution, complicating diagnostic accuracy. This case report describes a 64-year-old male who underwent a Technetium-99m-methoxyisobutyl isonitrile (99mTc-MIBI) parathyroid scan for suspected primary hyperparathyroidism. Initially, the patient was asked to discontinue his medications for his chronic illnesses for 24 h prior to the scan. However, the images revealed significantly reduced counts/tracer uptake in the thyroid, parathyroid and cardiac tissues in both the early and delayed phases. After a detailed review of his medication profile, it was postulated that there were potential interactions involving multiple P-glycoprotein (P-gp) substrates with specific emphasis on amlodipine, atorvastatin and telmisartan. The patient was advised to discontinue all medications for 72 h prior to the date of a repeat scan which was scheduled for two weeks after his initial scan. The repeat scan successfully detected a small focus of marked tracer retention in the left inferior parathyroid bed, suggestive of a small parathyroid adenoma. Post-surgery, the focus identified on the scan was removed and histologically confirmed to be a parathyroid adenoma. This is the first report of its kind among nuclear medicine patients in Jamaica. It highlights the importance of reviewing medication history prior to nuclear imaging, particularly when using radiotracers affected by P-gp mechanisms. This is crucial for mitigating against false-negative results, thus ensuring accurate diagnosis and appropriate clinical management.