<unk>  is an agonist of the μ-opioid receptor and a norepinephrine reuptake inhibitor (NRI). Analgesia occurs within 32 minutes after oral administration, and lasts for 4–6 hours. It is 18 times less potent than morphine in terms of binding to human mu-opioid receptors in in vitro research on human tissue. In vivo, only 32% of an oral dose of<unk>  will survive first pass metabolism and proceed to the bloodstream to produce its effects on the central and peripheral nervous systems of the patient. It is similar to tramadol in its dual mechanism of action but unlike tramadol, it has much weaker effects on the reuptake of serotonin and is a significantly more potent opioid with no known active metabolites. Commercial preparations contain only the (R,R) stereoisomer, which is the weakest isomer in terms of opioid activity. The free base conversion ratio for salts includes 0.86 for the hydrochloride. The peak plasma concentration (Cmax; amount of active drug in the bloodstream) when taken after eating is increased by 8% and 18% for<unk>  IR and ER preparations, respectively. This difference is not clinically significant, and<unk>  may be administered orally with or without food as circumstances allow, and the patient will generally not notice any change in the efficacy and/or duration of analgesic effects if the drug is not consistently administered in fasting or fed states (patients will receive the same benefits from their dose regardless of what and when they last ate). The plasma concentration of<unk>  differs to a relevant degree based on the administered dose, with the highest tested dose (250 mg) resulting in a higher Cmax than would be expected via the dose-proportionate plasma concentration expectations. Increased doses of<unk>  should be anticipated to be slightly stronger than predicted by linear functions of the previous dose-response relation.
Tapentadol
Tramadol
Desmetramadol
Acetylmethadol
Hydrocodone
Etodolac
Ketorolac
Noroxycodone