1 Ointment bases ●●●●● ●●●● ●●0 ●●● ●●●● Ointments bases are classified by the USP into four general groups hydrocarbon bases absorption bases water-removable bases water-soluble bases1. Ointment bases Ointments bases are classified by the USP into four general groups: - hydrocarbon bases - absorption bases - water-removable bases - water-soluble bases