Iraqi Journal of Veterinary Sciences, Vol. 35, No. 3, 2021 (535-539) 535 Iraqi Journal of Veterinary Sciences www.vetmedmosul.com Comparative antinociceptive effect of aspirin and aspirin nanoparticles in semisolid formulae in mice L.H. Al- Alsadoon 1 , M.T.AL-Saffar 2 and G.A. Taqa 2 1 Mosul Technical Institute, Northern Technical University, 2 Department of Dental Basic Sciences, College of Dentistry, University of Mosul, Mosul, Iraq Article information Abstract Article history: Received May 17, 2020 Accepted June 26, 2020 Available online June 24, 2021 Aspirin are commonly used analgesic, anti-inflammatory, and anti-pyretic drug in medicine, oral route is the most common one for drug administration as a result it will produce different adverse effects like peptic ulcer, nephropathy, and thrombocytopenia even with low and continuous therapeutic dose, so the alternative topical route is preferable with minimal adverse effects and effective concentration. Therefore, in the present study was to investigate whether the antinociceptive property of aspirin would enhance if used aspirin as nanoparticles after preparing it in several forms (gel, cream and ointment). Thirty-two healthy male mice weighing 30-35 gm. were used in the present study. The animals were divided as a randomized design. Each mouse was treated topically. All drug concentration of aspirin was prepared using gel, cream and ointment as vehicle and topically application on fore and hind paw of experimental animals. Pain was induced by application of hot plate for assessment of latency of pain stimulus. Time from placement to jumping or hind paw licking was recorded as latency of response. The result showed that the median effective concentration (EC50) for analgesic effect of aspirin (gel, cream, and ointment) were 0.848, 0.958 and 1.00% respectively while these EC50s were decrease when used nanoparticles aspirin (gel, cream and ointment) to 0.72, 0.657, and 0.701% respectively. In conclusion, topical applied of aspirin will produce effective therapeutic antinociceptive effects in mice although gel preparation produce a better response followed by cream, then ointment due to pharmacokinetic properties. Also nanoparticle preparation will produce superior response in all forms, whether Nano aspirin is prepared in gel form, cream or ointment. Keywords: Aspirin gel Aspirin cream Aspirin ointment Nanoparticles Hot plate technique Correspondence: G.A. Taqa ghadataqa@uomosul.edu.iq DOI: 10.33899/ijvs.2020.127138.1467, ©2021, College of Veterinary Medicine, University of Mosul. This is an open access article under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/). Introduction Acetylsalicylic acid (aspirin) is one of the most common drug used in medicine and it have been used since Hippocrates time for their analgesic, antipyretic, and anti- inflammatory effects (1). The analgesic property was produced by mechanism similar to other non-steroidal anti- inflammatory drugs by inhibition of prostaglandin synthesis through different steps which results finally to the inhibition of cyclooxygenase enzymes (COX) (2,3). These enzymes enhance the production of prostaglandin E2 from arachidonic acid usually COX present in two form, COX-1 which is the constitutive form and COX-2 which is the inducible form, aspirin inhibit both enzymes irreversibly, the COX-2 produce therapeutic effects while COX-1 inhibition leading to irritation of gastric mucosa and affect kidney functions (4). When aspirin administrated orally they are rapidly and completely absorbing in a large degree in small intestine and to lesser degree in stomach, and are accompanied by different side effects like gastric upset, blood loss, and to lesser extent Reys syndrome which is rare but fetal adverse effect (5) As a consequence of various