How far in advance of a nuclear medicine thyroid update and scan should thionamides be discontinued and does this duration vary based on radio-isotope used (i.e. technetium versus RAI 123)?  

The length of time I hold the thionamide depends on the nature of the underlying thyroid disease rather than the isotope used. If the patient is mildly hyperthyroid or well-controlled on low-dose thionamide (such as in a toxic nodule or toxic MNG), then I will hold the medication longer (1-2 weeks)...