Inhibition of salivary glands to reduce uptake of radioactive Iodine

After multiple Iodine-131 treatments, patients can be confronted with
persistent xerostomia and reduced quality of life. Salivation can be inhibited
with anticholinergic / antimuscarinergic pharmaceuticals. Glycopyrronium
bromide (GPB) inhibits salivary glands and prevents vasodilatation of afferent
vasculature. We therefore assume that inhibition with GPB will lead to reduced
accumulation of Iodine in salivary glands, and thus may be able to prevent
xerostomia in patients treated with Iodine-131.

Primary: to determine if inhibition with GPB can provide a significant (>30%)
reduction in the accumulation of orally administered Iodine-123 in salivary
glands, measured at 4h after administraion. Secondary: to determine if a
reduction at 4h persists at 24h, if accumulation in the stomach can also be
reduced, if the uptake in other normal organs is influenced, and
(conditionally) if a half dose GPB can also provide the desired effect.

Single center prospective interventional phase II study.

Pharmaceutical intervention is one intramuscular administration of 0.4 mg GPB
(conditionally 0.2 mg after the first 5 patients). Diagnostic interventions are
two Iodine-123 imaging procedures (one without GPB and one with GPB), at least
one week apart.

Participation in this study has no significant risks. Participation does not
induce a delay in diagnosis or treatment. A single intramuscular administration
of 0.4 mg GPB may induce temporary side effects related to the desired effect
(dry mouth, dry skin) and a low risk of general side effects like feeling
drowsy or tachycardia. Patients will receive two Iodine-123 imaging procedures
(with at least 1 week interval), which both involve intravenous administration
of 18,5 MBq Iodine-123 followed planar scintigraphic imaging of the head-neck
area from anterior and posterior at 4h and 24 after administration. This
provides a very limited radiation dose in the absence of functional thyoid
tissue. The estimated radiation dose of participation is 2 administrations x
18,5 MBq x 0,011 mSv/MBq = 0,4 mSv in total. This dose is well below the range
of normal diagnostic procedures and does not induce a significant risk,
especially not in this population in follow-up after high-dose Iodine-131
treatment for thyroid carcinoma.