Table 3.

Characteristics of commonly used opioids

Opioid	Receptor binding	Routes of administration	Metabolic pathway	Ceiling dose	Onset of effect	Duration of effect
Morphine	μ, κ (weak)	Oral tablet, oral liquid, intramuscular or subcutaneous, epidural or intrathecal, intravenous, rectal	Glucuronidation	None	NA	ER or IR
Hydrocodone	μ, κ	Oral	CYP2D6	Yes for combination products, no for pure hydrocodone	Rapid	ER or IR
Oxycodone	μ, κ (strong)	Oral, rectal	CYP3A4 CYP2D6	Yes for combination product, no for pure oxycodone	Rapid	ER or IR
Buprenorphine	μ (antagonist), κ (agonist, weak partial)	Transdermal, transmucosal	CYP3A4, glucuronidation	Yes	Slow	Long
Hydromorphone	μ, κ (weak), δ (weak)	Oral, intramuscular or subcutaneous, intravenous, rectal	Glucuronidation	None	N/A	ER or IR
Oxymorphone	μ	Oral, intravenous, rectal	Glucuronidation	None	N/A	ER or IR
Levorphanol	μ, κ, δ	Oral	Glucuronidation	6–12 mg/d	Rapid	Long
Tapentadol	μ, 5-HT, NE	Oral	Glucuronidation CYP2C9 (minor) CYP2C19 (minor)	500 mg/d	Slow	ER or IR
Fentanyl	μ, κ (weak)	Transdermal, transmucosal, intranasal, intravenous	CYP3A4	None	Very rapid (transmucosal, intravenous) Very slow (transdermal)	Very short Very long (transdermal)
Methadone	μ, κ (weak), δ (strong), NMDA	Oral	CYP3A4 CYP2B6 CYP2C8 CYP2C19 CYP2D6 CYP2C9	None	Slow	Long

Abbreviations: 5-HT, serotonin; CYP, cytochrome P450; d, day; ER, extended release; IR, immediate release; N/A, not applicable; NE, norepinephrine; NMDA, N-methyl-D-aspartate.