The International Association for Study of Pain defines pain as ''an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.'' Despite numerous advances in management of pain, effective treatment and pain relief remains a major challenge.1 Pain can be of multiple types and is classified as neuropathic pain, nociceptive pain, musculoskeletal pain, inflammatory and psychogenic pain.2 It has been observed that more than 100 million individuals in the United States have reported chronic pain.3 It is associated with a range of effects such as metabolic disturbances and cognitive disorders, thereby also having a huge impact on quality of life.2 Current therapeutic approaches primarily aim at symptomatic relief through the use analgesics mainly Nonsteroidal Anti-Inflammatory Drugs (NSAIDs). While NSAIDs effectively reduce inflammation and pain, their long-term use is limited by adverse effects such as gastrointestinal ulceration, renal impairment, and cardiovascular risks. Moreover, NSAIDs do not modify the underlying disease process or prevent progression of cartilage degradation. This has prompted increased interest in agents that possess disease-modifying properties as well as analgesic efficacy.4,5 Therefore, a lot of rat models for pain are being developed to aid in development of new analgesics. The reasons associated with use of rat models for development of pain include reasons such as they are physiologically and genetically similar to humans. Another reason is that rat pain models enable detailed investigations into pain mechanism. They also mimic complex pain conditions such as neuropathic, inflammatory, acute and chronic pain which help in development of analgesics.6 There are various models of pain available such as inflammatory pain models, neuropathic pain models, cancer pain models, arthritic pain models, muscle pain models, post-operative pain and visceral pain.7 Acetic acid writhing test is one of the most sensitive tests used to evaluate pain model in rats. The Writhing test is a chemical technique that involves injecting mice with irritants such as acetic acid to induce pain of peripheral origin. A reduction in the frequency of writhing indicates that the test substance has analgesic properties.8 The Acetic acid–induced writhing test in rats is a simple, rapid, and cost-effective model for evaluating peripheral analgesic activity. It reliably mimics inflammatory pain through mediator release and is highly sensitive to NSAIDs, making it ideal for early-stage drug screening.9 Diacerein, an anthraquinone derivative metabolized primarily to rhein, offers a promising alternative due to its dual action as a slow-acting symptom and disease-modifying agent in osteoarthritis(OA). It exerts its pharmacological effect mainly through the inhibition of interleukin-1β (IL-1β) and associated pro-inflammatory cytokines, which play pivotal roles in cartilage degradation and inflammation in OA. Unlike NSAIDs, diacerein has demonstrated chondroprotective effects by suppressing inflammatory mediator-induced cartilage matrix breakdown and promoting extracellular matrix preservation.10 Diacerein has a well-established anti-inflammatory and joint-protective impact, but its direct analgesic potential—especially in models of acute peripheral pain—is not as extensively studied. This study uses a methodology adopted from verified animal studies to assess the analgesic impact of diacerein utilising the well-established acetic acid writhing model in rats.

Study Design: This was an experimental, randomised, controlled study conducted in the Department of Pharmacology SCBMC, Cuttack over two months. Selection of animals: Albino rats of Wistar strain have been used earlier in many studies to observe the analgesic, anti-inflammatory and anti-arthritic properties of diacerein. Hence, 30 albino rats of Wistar strain of either sex weighing between 100 to 200 grams were procured and acclimatised under standard laboratory conditions in departmental animal house as approved by the committee (Registration Number is 431/01/c/CPCSEA for the purpose of Research and Experimentation on animals, for one week prior to experiment). The animals were maintained on 22±3°C, under 12:12 hour dark and light cycles. Animals had free access to food and water. Experiments were carried out between 10:00 to 17:00 hours. After the experiments, the used animals were kept separately from others in animal house to enable observations for development of any complication. The animals were numbered, divided into 5 groups with 6 animals in each group and kept in separate cages and the cages were numbered. Drugs and Chemicals: - Diacerein (Orcerin®) – 50, 100, 200 mg/kg p.o. (per oral) - Diclofenac sodium – 5 mg/kg p.o. (standard) - Normal saline – 1 mL/kg p.o. (control) - Acetic acid – 1% v/v (Inject 1ml/100g of body weight of the animal) prepared in distilled water Grouping of Animals: - Group I: Control – Normal saline 1 mL/kg p.o. - Group II: Diclofenac sodium 5 mg/kg p.o. - Group III: Diacerein 50 mg/kg p.o. - Group IV: Diacerein 100 mg/kg p.o. - Group V: Diacerein 200 mg/kg p.o. Procedure: 1. The animals were weighed and numbered. 2. The animals were then divided into 5 groups with 6 animals in each group. 3. Pain was induced by intraperitoneal injection of 1% acetic acid at a dose of 1 ml/100 g to the first group that acts as a control. The animals were placed individually under a glass jar for observation. 4. To the second group diclofenac sodium was given orally using an intragastric feeding cannula at a dose of 5 mg/kg. 15 minutes later acetic acid solution was administered to these animals. The animals were also placed individually under glass jars for observation. 5. To the 3rd, 4th and 5th group diacerein in doses of 50mg/kg, 100mg/kg and 200mg/kg were administered orally using the intragastric feeding cannula. 15 minutes later acetic acid solution was administered to these animals. These animals were also placed individually under glass jars for observation. 5. The time taken for onset of writhes, the number of abdominal contractions, twisting or turning of trunk and extension of hind limb were noted during a period of 10 minutes for all the animals and the values noted. Statistical Analysis: Data were expressed as mean ± SEM. Statistical analysis was performed using paired and unpaired t-test (SPSS v23.0). p<0.05 was considered statistically significant.

1. Effect in Control Group: Pain-related behaviours such as abdominal contraction, hind limb extension and twisting of trunk appeared early (onset ~6–13 min) and occurred frequently (4–12 episodes), indicating an unmitigated nociceptive response. 2. Diclofenac (5 mg/kg, standard drug): Significantly delayed onset of all three pain behaviours (e.g., abdominal contraction onset increased from 6.66 min to 13.88 min; p < 0.001). Reduced the number of episodes by ~40–50% compared with control. 3. Diacerein (50, 100, 200 mg/kg): Produced a dose-dependent prolongation of onset times and suppression of pain behaviours. At 50 mg/kg: Onset times increased by ~50–60% vs control, episode counts reduced by ~40%. At 100 mg/kg: Onset times increased by ~90–100%, episode counts reduced by ~75%. At 200 mg/kg: Maximal effect observed — onset times increased by ~120–350% depending on the parameter, with near-complete suppression of abdominal contractions and hind limb extensions (≥90% reduction in episodes). 4. Comparative Efficacy: Diacerein at higher doses (100 and 200 mg/kg) achieved effects comparable to or exceeding Diclofenac in both delaying onset and reducing episode numbers. At 200 mg/kg, Diacerein almost abolished certain pain responses (e.g., abdominal contractions reduced from 4.1 to 0.5 episodes). Observation: The observation as seen after the injecting of different solutions is shown in Table 1. Table 1- Effect of Drugs on Acetic Acid Induced Writing in Rats Sl. No. Groups Drugs Dose (mg/kg) Abdominal Contraction Extension of hind limb Twisting of trunk Onset (in mins) Number Onset (in mins) Number Onset (in mins) Number 1 1 (Control) Normal Saline (1mg/kg) 6.66 ± 0.21 4.1±0.4 13.5 ± 0.6 11.83±0.6 12.16 ± 0.16 6.66 ± 0.21 2 2 (Standard) Diclofenac 5 13.88*** ± 0.4 3.33±0.21 15.55* ± 0.56 6.66***±0.21 17.33*** ± 0.21 4.33*** ± 0.21 3 3 Diacerein 50 20*** ± 0.1 2.5±0.2 20*** ± 0.01 6.33***±0.21 20*** ± 0.1 2.83*** ± 0.16 4 4 Diacerein 100 25*** ± 0.01 2.5±0.2 25*** ± 0.01 6.5***±0.22 25*** ± 0.01 2.91*** ± 0.11 5 5 Diacerein 200 29.66*** ± 0.33 0.5±0.2 26.66*** ± 1.05 0.5***±0.22 25*** ± 0.5 0.83*** ± 0.16 Acetic acid injection produced abdominal contraction, extension of hind limb and twisting of trunk in the normal saline treated group. Diclofenac 5 mg/kg delayed onset and significantly decreased the number of writhing responses. Diacerein in all three doses also delayed the onset and decreased the number of acetic acid induced writhing. * = p<0.05; ** = p<0.01; ***=p<0.001(n=6)

The present study investigated the analgesic potential of diacerein using the acetic acid-induced writhing test in rats, a widely employed preclinical model for evaluating peripheral pain and inflammatory responses. Notably, diacerein—administered at increasing doses (50mg/kg, 100mg/kg, and 200mg/kg)—demonstrated a significant delay in onset and a marked reduction in the number of abdominal contractions, hind limb extensions, and trunk twisting compared to the control group, mirroring the effects observed with the standard drug diclofenac. The current study shows the marked reduction of pain behaviours by both diclofenac and diacerein corroborates the utility of this model in screening agents with anti-inflammatory and analgesic activities, particularly those targeting peripheral mechanisms. In a study done in 2024 which investigated the analgesic and anti-inflammatory effects, demonstrated significant analgesic effects in the acetic acid-induced writhing test, thereby confirming its sensitivity to peripheral analgesics such as NSAIDs, which act by inhibition of prostaglandin. A similar reduction in abdominal writhing was observed, consistent with the findings of the current study.12 In this study, diacerein exhibited distinct dose-dependent analgesic effects in the acetic acid–induced writhing model in rats, characterized by delayed onset of pain responses and a marked reduction in writhing frequency. At the highest dose of 200 mg/kg, diacerein almost completely abolished abdominal contractions and hind-limb extensions, marking an efficacy surpassing that of the standard NSAID, diclofenac, at 5 mg/kg. These results contribute significantly to our existing knowledge of the pharmacological characteristics of diacerein. Although diacerein is mainly recognised as a disease-modifying osteoarthritis medication because of its chondroprotective and interleukin-1β inhibitory properties, new research now suggests that it has direct analgesic effects.13 For example, diacerein's strong analgesic effects in a rat model of acute inflammatory pain were verified by Petrosino et al. (2015), in part because it inhibited the breakdown of palmitoylethanolamide.14 Moreover, additional research has demonstrated that diacerein reduces visceral pain via modulation of cytokine and glutamatergic pathways in mice.13 Although Diclofenac remains the gold standard for rapid relief in acute inflammatory pain. However, long-term use of NSAIDs—including diclofenac—carries well-documented risks such as gastrointestinal ulceration and bleeding, renal impairment, and cardiovascular adverse drug reactions such as increased risk of major vascular events like heart attack and stroke.15 Diacerein, on the other hand, has strong anti-nociceptive properties without the need for COX inhibition. In comparison to NSAIDs, it has a more favourable benefit–risk balance overall and an acceptable safety profile that is predominantly defined by minor gastrointestinal disturbances such as soft stools and diarrhoea with infrequent liver events.16 The reported analgesic effects may be related to diacerein's ability to reduce oxidative stress and prostaglandin E₂ (PGE₂) synthesis in inflammatory tissues, in addition to its suppression of IL-1β and downstream cytokines. According to mechanistic findings, diacerein suppresses inflammatory signalling in joint situations by lowering PGE₂ synthesis. Additionally, diacerein has been demonstrated to reduce oxidative stress in osteoarthritic mice by reversing the epigenetic repression of the transcription factor PPAR-γ, restoring the production of antioxidant enzymes, and minimising cartilage degradation.17 Therefore, these results show that diacerein can reduce pain by blocking prostaglandin production, lowering oxidative stress, and calming down inflammation in the nervous system. Because it works in several ways, it looks promising for treating painful conditions caused by inflammation—such as osteoarthritis and rheumatoid arthritis. This means it should be studied further to see how well it can help people with these diseases. Limitations Notwithstanding the encouraging results, this work is constrained by its concentration on acute peripheral pain in animal models; more investigation is required to ascertain the efficacy and safety of diacerein in neuropathic and chronic pain conditions, as well as in human clinical trials with bigger and more varied populations. Furthermore, long-term research is required to evaluate the analgesic duration, onset, and side effect profile of diacerein in comparison to a wider range of analgesics.

This study demonstrates that diacerein produces significant, dose-dependent analgesic effects in the acetic acid–induced writhing model in rats, with higher doses showing efficacy comparable to or greater than diclofenac. Unlike NSAIDs, diacerein also offers disease-modifying and chondroprotective benefits, with a more favourable safety profile. These findings highlight diacerein’s potential as a promising alternative for managing inflammatory pain conditions such as osteoarthritis and rheumatoid arthritis, warranting further clinical evaluation.

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