The structure of zanamivir contains multiple hydrophilic functional groups that willallow it to easily dissolve within the aqueous contents of the GI tract. The carboxylic acid andthe guanidine functional groups will be extensively ionized at an intestinal pH=5 which furtherincreases the overall water solubility of the molecule. Although the structure of zanamivircontains a hydrocarbon chain and ring, the overall balance between water and lipid solubilityhinders its ability to effectively cross the GI membrane. The oral absorption of zanamivir hasbeen reported to be between 1% and 5%. Due to this, zanamivir must be administered viaoral inhalation.