Table 4. Novel medications for the treatment of opioid-induced constipation.

Name	Class	Efficacy	Clinical effects
Naloxone	Non-selective opioid antagonist	Reverses opiate-induced delay in orocecal and colonic transit.	Naloxone PR formulation prevents OIC in patients who received PR oxycodone.
Methylnaltrexone	Opioid antagonist	Reverses effects of opiates in health and of chronic methadone treatment on orocecal transit; no effect on small intestinal or colonic transit delayed by codeine (30 mg q.i.d.) in opiate-naive healthy subjects.	S.c. methylnaltrexone (0.15 mg/kg) on alternate days was effective in inducing laxation in patients with advanced illness.
Alvimopan	PAMORA	8 mg oral dose accelerated colonic transit and Reversed the effects of codeine in opiate-naive healthy volunteers who received codeine, 30 mg q.i.d.	0.5 mg Alvimopan dose efficacious in treating OIC; rare instances of ischemic heart disease
Tapentadol	Narcotic analgesic plus norepinephrine reuptake inhibitor	ND	Tapentadol ER 100-250 mg b.i.d. equally effective for moderate to severe chronic steoarthritis-related knee pain compared to oxycodone HCl (CR) 20 – 50 mg b.i.d., given daily with less bowel dysfunction symptoms
NKTR-118	PAMORA; PEGylated naloxol conjugate	Normalized morphine-induced delay in orocecal transit.	25 and 50 mg NKTR-118 had increased numbers of SBM during the first week and during 4 weeks of treatment of OIC patients
TD-1211	PAMORA	ND	5 and 10 mg/day TD-1211 increased average SBM/week over 2 weeks in OIC patients

CR, Controlled release; ER, Extended release; ND, Not done; OIC, Opiate-induced constipation; PAMORA, Peripherally-restricted –opioid receptor antagonist; PEG, Polyethylene glycol; PR, Prolonged release; SBM, Spontaneous bowel movement; s.c., Subcutaneous administration