A comparison of the anti-inflammatory and anti-nociceptive activity of nitroaspirin and aspirin

1 Nitroaspirin (2.5-50 mg kg(-1), i.p. or 2.5-100 mg kg(-1), p.o.) and aspi rin (2.5-100 mg kg(-1) i.p. or p.o.) exhibit anti-inflammatory activity in the carrageenan-induced hindpaw oedema model in the rat. When administered i.p., nitroaspirin was a more effective anti-oedema agent than aspirin part icularly in the 'early' phase (i.e. up to 60 min) of the response. The ED50 values for nitroaspirin and aspirin as inhibitors of the 'late' phase resp onse (measured at 180 min) were 64.3 mu mol kg(-1) and >555 mu mol kg(-1), respectively. When administered p.o., neither nitroaspirin nor aspirin exhi bited significant anti-inflammatory activity in the 'early' phase and were of similar potency in the 'late' phase. Thus, at the highest dose used (100 mg kg(-1), 360 min) orally administered nitroaspirin (aspirin in parenthes is) inhibited oedema formation by 46.9 +/- 1.6% (47.2 +/- 3.8%, both n = 6, P < 0.05). 2 Nitroaspirin and aspirin (25-200 mg kg(-1), p.o.) caused dose-related inh ibition of the hyperalgesia to mechanical stimulation following intraplanta r injection of carrageenan in the rat. ED50 values were 365 mu mol kg(-1) a nd 784 mu mol kg(-1), respectively. Neither drug influenced the threshold f or mechanical stimulation in the contralateral (i.e. untreated) hindpaw. 3 Nitroaspirin and aspirin (2.5-100 mg kg(-1), p.o.) caused dose-related in hibition of acetic acid induced abdominal constrictions in the mouse (ED50 values of 154.7 mu mol kg(-1) and 242.8 mu mol kg(-1), respectively). 4 Nitroaspirin and aspirin (> 200 mg kg(-1), p.o.) reduced the 'late' phase (but not the 'early' phase) of the formalin-induced hindpaw licking assay in the mouse. Similarly, nitroaspirin and aspirin (> 50 mg kg(-1), p.o.) pr olonged tail withdrawal latency following application of a noxious heat sti mulus in the mouse.