I think intraperitoneal administration is easier to achieve from the perspective of compound solubility and injection volume. IV administration requires that the compound be dissolved, and limits the injection volume. For a compound with poor solubility, IV may be not allow a sufficient quantity of the compound to be administered in a single dose. Another option, is IV infusion, in which the dose is delivered by an infusion pump over several hours, allowing a larger volume/more dilute solution, and therefore greater exposure to the compound.