To evaluate the effects of Phyllanthus extracts on mechanical hyperalgesia induced by repeated intramuscular injections of acidic saline.

The standardized aqueous extract of Phyllanthus amarus whole plant (PAAE), Standardized methanolic extract of P. amarus leaf (PAEE), the standardized hydro-methanolic extract of P. amarus leaf (PAHEE) and standardized hydroethanolic extract of P. fraternus whole plant (PFHEE) were tested in the fibromyalgic model of acid-induced chronic pain in the rats. Mechanical hyperalgesia was assessed by measuring the withdrawal thresholds to mechanical stimuli both to the ipsilateral as well as to the contralateral paws. On 22nd day, the animals were sacrificed and the gastrocnemius muscle at the site of injection was dissected for histopathological studies.

PAAE, PAEE, PAHEE and PFHEE increased the mechanical withdrawal threshold (mechanical hyperalgesia) back towards the baseline responses. The percentage of maximum possible effectiveness and percentage inhibition of hyperalgesia also revealed the efficacy of Phyllanthus extracts. The multidose strategy did not cause tolerance.

The results of the present study suggest that in the present model, muscle-mediated pain can be alleviated by standardized extracts of Phyllanthus species and suggest that these can be useful in treatment of chronic musculoskeletal pain syndromes such as fibromyalgia.