Opioid Conversion meds specific details

Question 1

Fentanyl patches

1. how do they work?
2. avoid in…
3. especially remember:

Answer 1

1. they are very lipophilic, and skin is hydrophilic, so it takes a long time for the medication to cross
2. malnourished or frail pts
3. DO NOT apply heat

Question 2

What do we need to remember when converting to/administering fentanyl?

Answer 2

• ONLY convert FROM and TO MORPHINE
• apply patch @ next scheduled dose & use breakthru meds to cover 12 hr window until fentanyl takes effect
• takes 3-6 days to reach steady state

(we do not need to compensate for incomplete cross tolerance here)

• ONLY for opioid TOLERANT pts

Question 3

Methadone

Answer 3

QTc prolonging
- monitor regularly

• less euphoria
• NMDA antag activity
• works for nerve-based pn

*no linear change from other opioids

Question 4

Methadone conversion tips

Answer 4

1. 10:1 ratio
2. ONLY from MORPHINE

(do not have to worry abt incomplete cross tolerance)

• again, go with lower if between 2
• if lower than available forms: 2.5 mg q12h initially

Question 5

Methadone metabolism

Answer 5

CYP3A4

inhibitors (decr. dose 25%)

• amiodarone
• azole antifungals

inducers (incr dose after 1 week)

• phenytoin
• rifampin

Question 6

Methadone follow-up/ general tips

Answer 6

follow-up in a week after changing dose
- pt MUST take UD

can be used as breakthru, but not generally bc affects basal dose (use SA prior opioid for breakthru)