mrsD -

I inadvertently posted the link to only the abstract of Tramadol/paracetamol combination tablet for postoperative pain following ambulatory hand surgery: a double-blind, double-dummy, randomized, parallel-group trial, Rawal N, Macquaire V, Catalá E et al, J Pain Res. 2011 Apr 8; 4:103-10, ONLINE TEXT @ http://www.ncbi.nlm.nih.gov/pmc/arti.../jpr-4-103.pdf, however that abstract included its own link to the full text article, which does a very good job of explaining the mechanism of 325 mg. of Acetaminophen/Tylenol/Paracetamol in supplementing the analgesic effect of 37.5 mg. of Tramadol, which has significantly fewer side effects than the analgesia equivalent ("monotherapy") dose of 50 mg. of Tramadol, although both were significantly higher than what could have been acheived by using oxycodone alone:

Nausea was the most common event in both groups (25.8%
for tramadol/paracetamol vs 36.4% for tramadol) followed
by dizziness (15.9% vs 18.6%) and somnolence (9.1% vs 14%).

At 108.

But I found the comparisons between the Prescribing Information sheets for Oxycodone and Tramadol the most instructive, however you didn't comment on that information as such.

Nevertheless, I think the most important point of clarification is that we cannot lump opioids - such as Oxycodone - and true opiates together in looking at their profiles for side effects. See, e.g., Epidural oxycodone or morphine following Ggynaecological surgery, Yanagidate F, Dohi S, Br J Anaesth. 2004 Sep;93(3):362-7, 366, Epub 2004 Jun 25, ONLINE TEXT @ http://bja.oxfordjournals.org/content/93/3/362.full.pdf:

Undesirable side-effects such as pruritus and nausea are common with epidural morphine and are believed to be caused via mu-opioid receptor stimulation at the supraspinal level.23–25 It is not clear why the need for anti-emetics was significantly less in those who received epidural oxycodone 12 mg day−1 in our study. Since patient characteristics were similar between the three groups, it may be that oxycodone, when administered in the epidural space, is less emetogenic than morphine. Although oxycodone has effects at both mu- and kappa-opioid receptors, the affinity of oxycodone for the mu-opioid receptor has been reported to be one-tenth that of morphine.26 This may account for the fewer side-effects and less analgesia when compared with the same dose of epidural morphine.

Notes
23 Gustafsson LL, Schildt B, Jacobsen K. Adverse effects of extradural
and intrathecal opiates; report of a nationwide survey in Sweden.
Br J Anaesth 1982; 54: 479–86.
24 Martin WR. Clinical evidence for different narcotic receptors and
relevance for the clinician. Ann Emerg Med 1986; 15: 1026–9.
25 Yaksh TL. Opioid receptor systems and the endorphins: a review of
their spinal organization. J Neurosurg 1987; 67: 157–76.
26 Kalso E, Vainio A, Mattila MJ, Rosenberg PH, Seppala T. Morphine
and oxycodone in the management of cancer pain: plasma levels
determined by chemical and radioreceptor assays. Pharmacol
Toxicol 1990; 67: 322–8.

I spent most of last night looking for any published study showing that Tramadol had a dose equivalent level of nausea less than or equal to that of Oxycodone, when all the evidence I saw was to thew contrary. If you or anyone else knows of such studies, I would be most appreciative.

Mike