A Non-Destructive Method of Predicting the Particle Size of the Bulk Drug Powder in an Acetaminophen Suppository by Near-Infrared Spectroscopy

Abstract

This paper describes a non-destructive method for determining the particle size of the bulk drug powder in an acetaminophen suppository using near infrared (NIR) spectrometry combined with chemometrics. Acetaminophen bulk powder samples were obtained by sieving through 75–1400 μm screens. Suppository samples containing the bulk powder with various particle sizes were obtained at 50°C. They consisted of the bulk powder (4.5 w/w%), hard fat and plastic suppository container. Spectra of 36 standard suppository samples were recorded using a NIR spectrometer, fitted with a fibre-optic probe, in the range of 4000–12,500 cm−1. The spectra were divided to a calibration set and a validation data set. Various pre-treatments were tested and partial least squares regression used to develop the calibration models which were tested against the samples in the validation set. Chemometric calculations were also performed on long range (4000–12,500 cm−1) and short range (5000–10,000 cm−1) data sets, respectively. The best model was obtained when using the short range, the pre-treatment of smoothing, standard normal variate plus area normalisation and eight principal components, to achieve a standard error of cross validation of 100 μm. The plot of the predicted values versus the actual values for a validation set of suppositories gave a straight line with a regression coefficient of determination of 0.957 and standard error of prediction of 98 μm. The correlation spectrum of the best model suggested that the specific positive and negative peaks were due to hard fat and drug particle size, respectively. These results demonstrate that it was possible to predict the particle size of acetaminophen bulk powder in a suppository without destroying the sample.