A double-blinded randomized clinical trial: Topical Sahasthara extract versus diclofenac for treating primary knee osteoarthritis using microemulsions as a topical delivery system

Sahasthara (SHT), a traditional Thai herbal remedy used for anti-inflammatory and musculoskeletal disorders, lacks clinical evaluation as a topical formulation employing microemulsion (ME) technology. This study aimed to assess the efficacy and safety of a Sahasthara microemulsion (SHT-ME) compared with a diclofenac microemulsion (DF-ME) in patients with primary knee osteoarthritis (OA). Eighty-four patients aged 40–70 years were randomized to receive either 1% SHT-ME or 2% DF-ME, applied three times daily for 28 days. Efficacy was evaluated using pain visual analogue scale (VAS), 100-meter walking time, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores, and global assessments. Safety assessments included physical examinations, laboratory tests, and adverse-event monitoring. Both formulations significantly reduced VAS pain scores, improved walking time, and decreased WOMAC scores at days 14 and 28 compared with baseline (P < 0.05). No significant efficacy differences were observed between groups (P > 0.05). Liver and renal function, blood pressure, and biochemical parameters remained within normal ranges, and no severe or skin-related adverse events occurred in either group. SHT-ME provided efficacy comparable to DF-ME in relieving pain and improving mobility in knee OA. Both treatments were well tolerated and safe. These findings suggest that SHT-ME, a natural herbal alternative, and DF-ME, a synthetic drug formulation, are equally effective topical microemulsions for knee osteoarthritis management. NCT06184685 ( ClinicalTrials.gov ) • This is the first clinical study comparing topical SHT-ME, an essential Thai herbal anti-inflammatory drug, and DF-ME in OA knee patients. • SHT-ME was developed from an oral medication due to its side effects that can cause stomach discomfort or dry mouth. • 1%SHT-ME provides localized drug delivery with the same efficacy as 2%DF-ME in the treatment of OA knee. • Both treatments showed no serious adverse effects both symptomatically and in laboratory studies. • SHT-ME was more effective compared with the oral dose, which used only 60 mg/day or 5 times less than the oral administration.