Table 2.

Studies of topical compounds using capsaicin models

Compound class	Drug	Route	Dose	Experimental pain effect	Neuropathic pain effect	Postoperative pain effect	Reference(s)
Opioid	Alfentanil	IV	75 ng/mL	Positive	Positive as a class	Positive as a class	[50, 51, 61–64]
	Remifentanil	IV	0.1 μg/kg/min	Positive
	Hydromorphone	PO	8 mg	Positive
	Morphine	PO	30 mg	Positive
	Morphine	IV	10 mg	Positive
	Alfentanil	IV	50 ng/mL	Negative
	Alfentanil	IV	200 ng/mL	Positive
NMDA antagonist	Ketamine	IV	150 ng/mL	Positive	Disappointing as a class	Positive only in combination with an opioid	[49, 50, 52, 61]
	Dextromethorphan	PO	30 mg	Negative
	Ketamine	IV	0.1 mg/kg then 7 μg/kg/min	Positive
	Magnesium	IV	0.2 mmol/kg then 0.2 mmol/kg/min for 90 min	Negative
Alpha 2 agonist	Clonidine	Intrathecal	150 μg	Positive	Positive	Positive only in combination with an opioid	[65]
	Clonidine	IV	150 μg	Negative
Alpha 2 delta ligand	Gabapentin	PO	1,200 mg	Positive	Positive as a class	Positive only in combination with an opioid	[49–52, 66–69]
	Gabapentin	PO	2,400 mg/day	Positive
	Gabapentin	PO	1,800 mg/day	Negative
	Pregabalin	PO	300 mg	Positive
Antihistamine	Diphenhydramine	PO	50 mg	Negative	Negative	Negative	[49]
	Diphenhydramine	IV	25 mg	Negative			[61, 65]
Tricyclic antidepressant	Desipramine	PO	225 mg/day	Negative	Positive	Negative	[65–67]
	Amitriptyline	IM	25 mg	Negative
GABA-A agonist	Midazolam	IM	4 mg	Negative	Negative as a class	Negative as a class	[65]
Na-channel block	Lidocaine	IV	3 μg/mL	Negative	Disappointing as a class	Disappointing as a class	[65]
	Lidocaine	IV	2 mg/kg then 3 μg/kg/h	Positive (but limited)			[68]
	Lidocaine	IV	5 mg/kg over 50 min	Positive			[69]
	Mexiletine	PO	859 mg/day	Positive (but limited)			[70]
	Lamotrigine	PO	300 mg	Negative			[53]
	Lamotrigine	PO	400 mg	Negative			[63]
Adenosine agonist	Adenosine	IV	65 μg/kg/min for 85 min	Negative	Negative	Positive (spinal)	[72]
Cannabinoids	Cannabis	Inhaled	3 doses (2%, 4%, 6%)	Positive 4%, negative 2 % and 6%	Positive 6%, negative 2 and 4%	Modest benefit	[55]
	Cannabis	Inhaled	4%	Positive	Positive (low dose)		[73]
	THC/Cannabidiol	Inhaled	3.56% THC	Equivocal	Negative (high dose) (sativex)
TRPV1 antagonist	REN-1654	PO	Oral 100 mg	Negative	Negative	N/aa	[74]
AMPA antagonist	NGX426	PO	10 mg/cc	Positive	N/ab	N/ab	[75]
Magnesium	Magnesium	IV	0.2 mmol/kg−1	Negative	N/ab	N/ab	[76]

AMPA α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, GABA γ-aminobutyric acid, IM intramuscularly, IV intravenously, NMDA N-methyl-d-aspartic acid, PO orally, THC tetrahydrocannabinol, TRPV1 transient receptor potential cation channel, subfamily V, member 1

^a The patients in this study had a neuropathic component to their pain, but not post-surgical

^b This study was done in healthy subjects without neuropathic or postoperative pain