A study of water vapor transmission rate of blister packs by USP standard and continuous gravimetric protocol

The water vapor transmission rate (WVTR) is essential in determining the shelf life of pharmaceutical products in the package. The WVTR of blister pack was determined by using USP 671 and the continuous gravimetric protocols. The WVTR values from the two protocols were compared and the accuracy was validated.The WVTR of the blister pack determined using the USP 671 protocol was 0.0452 mg/day/blister with a standard error of 0.0010 while the WVTR using the continuous gravimetric protocol was 0.0652 mg/day/blister with a standard error of 0.0067. The WVTR were compared using t-statistic for unequal sample size with unequal variance and no significant difference was detected. The accuracy of the two protocols was compared through the pooled variance of the data points. USP 671 standard protocol had a pooled variance of 4.99 x 10-4 while for the continuous gravimetric protocol it was 2.13 x 10-5. Therefore the continuous gravimetric protocol showed higher accuracy than the USP standard protocol.Several recommendations have been suggested for the USP standard protocol in order to make the protocol more accurate: for the WVTR of the blister pack, the unsteady state should be considered and excluded from the calculation, Monitoring of the humidity and temperature is critical, Chamber size and the time of equilibrium for the specific relative humidity needs to be outlined.