title: Elucidation of the variability in consistency of pharmacopoeia quality petrolatum.
abstract: The Pharmacopeia monograph for petrolatum poorly defines the material's physical properties. Indeed, differences between petrolatum grades can be substantial; yield stress varies between 65 and 280 Pa which can be compared with the consistency of respectively thin cream or thick ointment. This variation is not only due to differences in composition or refining process but also as a result of different processing; for example, thermal history influences petrolatum structure considerably. Slow cooling of petrolatum resulted in a yield stress of 26 Pa and fast cooling in 79 Pa. X-ray showed that crystallinity was 0.7% for the first cooling case and 1.5% for the second one. Crystallite size was estimated to be 20-50 nm. To investigate if this relatively small difference in crystallinity may induce the difference in consistency, 15 nm SiO2particles were added to petrolatum. Indeed, a small increase in SiO2concentration led to a major increase in yield stress. This was argued to be due to the small size of the particles, resulting in a large increase in absolute number of particles. The Pharmacopeia does not unambiguously define the pharmaceutical excipient petrolatum. As a consequence, the formulator has to take care of selecting the appropriate grade as well as to carefully control the processing of the material in order to achieve a consistent pharmaceutical product.
authors.affiliation: a Department of Pharmaceutics , Utrecht Institute for Pharmaceutical Sciences, Utrecht University , Utrecht , The Netherlands.|b Department of Research & Development , Tiofarma B.V , Oud-Beijerland , The Netherlands.
authors.forename: Anton Joris Pancras
authors.initials: AJ
authors.lastname: van Heugten
authors.affiliation: c Department of Inorganic Chemistry and Catalysis , Debye Institute for Nanomaterials Science, Utrecht University , Utrecht , The Netherlands.
authors.forename: Marjan
authors.initials: M
authors.lastname: Versluijs-Helder
authors.affiliation: a Department of Pharmaceutics , Utrecht Institute for Pharmaceutical Sciences, Utrecht University , Utrecht , The Netherlands.|b Department of Research & Development , Tiofarma B.V , Oud-Beijerland , The Netherlands.|d Department of Clinical Pharmacy, Division of Laboratory Medicine & Pharmacy , University Medical Centre Utrecht , Utrecht , The Netherlands.
authors.forename: Herman
authors.initials: H
authors.lastname: Vromans
mesh_terms: D002626:Chemistry, Pharmaceutical / Q000379:methods; D005079:Excipients / Q000737:chemistry; D009824:Ointments / Q000737:chemistry*; D010316:Particle Size; D010577:Petrolatum / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry
chemical_list: D005079:Excipients; D009824:Ointments; D012822:Silicon Dioxide; D010577:Petrolatum
keywords: Petrolatum; X-ray; crystallinity; thermal history; yield stress