J Clin Med Res

Journal of Clinical Medicine Research, ISSN 1918-3003 print, 1918-3011 online, Open Access

Article copyright, the authors; Journal compilation copyright, J Clin Med Res and Elmer Press Inc

Journal website https://www.jocmr.org

Letter to the Editor

Volume 13, Number 2, February 2021, pages 130-132

Voxelotor Modulates the Analgesic Effect of Certain Opioids

Figure

Figure 1. Effect of CYP3A4 enzyme on the metabolism of fentanyl. Equation A shows how CYP3A4 enzyme usually metabolizes fentanyl by oxidizing it to inactive metabolites and hence, decreases its concentration in blood. Equation B shows that inhibition of CYP3A4 decreases the oxidation of fentanyl to inactive metabolites and hence, maintains its concentration in blood to maintain or increase its analgesic effect.

Table

**Table 1.** Metabolism of Certain Opioids Used in Sickle Cell Disease by the Cytochrome P450 Enzymes
Opioid	CYP450 enzyme	Active metabolite
Adapted from Ballas S. K. Sickle Cell Pain, Second Edition. Washington DC: International Association for the Study of Pain; 2014. CYP450: cytochrome P450.
Codeine	CYP2D6	Morphine, hydrocodone
Hydrocodone	CYP2D6, 3A4	Hydromorphone
Oxycodone	CYP2D6, 3A4	Oxymorphone
Fentanyl	CYP3A4	None
Methadone	CYP2D6, 3A4, 2C8, 2C9, 2C19, 2B6, 1A2	None
Tramadol	CYP2D6, 3A4, 2B6	None