A new propylene glycol-free and reduced-volume formulation of diclofenac sodium 75 mg/mL designed for intradeltoid administration has been found to be bioequivalent to a reference formulation of diclofenac sodium 75 mg/3 mL given via the intragluteal route in normal healthy volunteers. Standard needles may not reach the gluteus maximus muscle in many cases, especially in the obese. The objective of this study was to determine the pharmacokinetic parameters of the new formulation and compare the bioavailability of intradeltoid diclofenac sodium 75 mg/mL with that of the intragluteal 75 mg/3 mL reference formulation in obese volunteers.
A comparative, two-way, single-dose, bioavailability study was carried out in 10 obese (body mass index > 25) male Indian volunteers after a washout period of seven days. Blood samples were collected until six hours following drug administration and analyzed using a prevalidated high-pressure liquid chromatography method.
The mean maximum plasma concentration and time to reach maximum plasma concentration for the test formulation were 1.30 μg/mL and 0.50 hours, respectively, versus 0.93 μg/ mL and 1.08 hours for the reference formulation. The mean areas under the curve from 0 to last measurable time point (AUC 0–t) for the test and reference formulations were 2.71 μg·h/mL and 2.73 μg·h/mL, respectively. The mean AUCs from 0 to infinity (AUC 0–∞) for the test and reference formulations were 3.71 μg·h/mL and 3.75 μg·h/mL, respectively.
The results suggest that the test formulation of diclofenac sodium 75 mg/mL has an AUC 0–t and AUC 0–∞ comparable with the reference intragluteal formulation of diclofenac sodium 75 mg/3 mL, but with an earlier time to reach maximum plasma concentration and a trend towards a higher maximum plasma concentration. This could be attributed to faster absorption from the deltoid region than from the gluteal region. The test formulation could be helpful in the management of pain in obese or overweight patients and those with dense subcutaneous fat in the gluteal area.