I.V. propacetamol, administered as a 15-min infusion, is a fast-acting analgesic agent. It is more effective in terms of onset of analgesia than a similar dose of oral acetaminophen.

We compared an acetaminophen (paracetamol) 1 g (n = 51) formulation for infusion with propacetamol 2 g (n = 51) and placebo (n = 50) in a randomized, controlled, double-blind, parallel group trial in patients with moderate-to-severe pain after third molar surgery. Treatment efficacy was assessed in house for 6 h after starting the 15-min infusion. Significant effects versus placebo (P < 0.01) were obtained with both active treatments on pain relief, pain intensity difference on a 100-mm visual analog scale, and on a categorical scale (except for propacetamol at 6 h). No significant differences were noted between active groups except at 1 h. Six-hour weighted sums of primary assessments showed significantly better efficacy than placebo (P < 0.0001) and no difference between active treatments. Median stopwatch time to onset of pain relief for active treatment was 6-8 min after infusion start. Active treatments showed comparable efficacy with a significantly longer duration of analgesia and better patients' global evaluation compared with placebo. The incidence of patients reporting local pain at the infusion site was significantly less frequent after IV acetaminophen or placebo (0%) in comparison with propacetamol (49%). In conclusion, acetaminophen 1 g and propacetamol 2 g were superior to placebo regarding analgesic efficacy, with a more frequent incidence of local pain at the infusion site for propacetamol.

This randomized, double-blind, placebo-controlled study compared the time to onset of analgesia and the analgesic efficacy of two formulations of acetaminophen 1000 mg--an effervescent solution and tablet--in 242 patients with moderate or severe pain following dental surgery. Onset of analgesia was determined using a two-stopwatch procedure. Analgesia was assessed over a 4-hour period. Treatments were compared using standard indexes of pain intensity and pain relief and summary measures. Both acetaminophen formulations were significantly more effective than their corresponding placebo for all efficacy assessments. The median time to onset of analgesia was significantly shorter with effervescent acetaminophen (20 minutes) compared to tablet acetaminophen (45 minutes). During the first 45 minutes after administration, effervescent acetaminophen was significantly more effective at each scheduled assessment time than tablet acetaminophen. The median time to meaningful pain relief was significantly shorter with effervescent acetaminophen (45 minutes) compared to tablet acetaminophen (60 minutes). At 4 hours after administration, the pain relief was significantly better with tablet acetaminophen than with effervescent acetaminophen. No other significant differences were observed between the active treatments. In conclusion, effervescent acetaminophen produces a significantly faster onset of analgesia than tablet acetaminophen.