Pharmacology - Codeine added to paracetamol did not increase analgesia.

[RoboCodeine7610]

1 In a double-blind crossover study identical oral surgical procedures were performed on two separate occasions in 24 outpatients. 2 At one operation they were given tablets containing paracetamol + codeine phosphate (400 mg + 30 mg), and at the other plain paracetamol (400 mg). The day of operation 2 tablets were taken 3, 6 and 9 h after surgery, the following two days 1 tablet four times daily. 3 Several measurements/assessments were recorded for a paired comparison of the postoperative courses. 4 No increase In the analgesic effect could be demonstrated by addition of codeine to paracetamol. 5 On the day of operation 18 patients reported adverse effects like nausea, dizziness and drowsiness with paracetamol + codeine, while only 3 patients experienced side effects with paracetamol alone (P less than 0.001). 6 Measurements revealed almost identical swelling after the two operations. 7 Compared with results obtained in previous studies, the present findings indicate that paracetamol may exert anti-inflammatory activity and reduce postoperative swelling, even when given 3 h after surgery. 8 On the day of operation and the following two days 20 patients preferred the treatment with plain paracetamol, while only 4 favoured paracetamol + codeine (P less than 0.001).

http://www.pubmedcentral.nih.gov/art...?artid=1427610

weird, how could codeine, which has analgesic effects by itself, not increase analgesia?Could it be that the paracetamol is blocking the effects of codeine?I already posted a thread about this:

http://www.drugs-forum.com/forum/showthread.php?t=78848