Hospital people correct me if I'm wrong, but I don't think people routinely
take levels of these meds.  Tricyclics like nortriptyline might be screened
for in emergent situations (e.g., overdose).  I think the question is,
whether it's necessary in cases like yours to measure the levels, since
one's usually really interested (with these drugs) in the clinical response
(reduction of severity of pain, frequency, side effects, etc.) and not the
levels per se.  As for washout periods, it depends on what drug he's being
switched to, but neither of the drugs mention sound like major concerns to
me.