What Theodotus accomplished at this time we know not, but the next year (219 BC) we find him serving under the immediate command of Antiochus himself, and bearing an important share in the action against Nicolaus the general of Ptolemy IV Philopator (221–204 BC), near Porphyreon, as well as shortly after at the siege of Rabbatamana.
The formidable revolt of Molon and Alexander in the eastern provinces of the kingdom seemed to demand all the attention of Antiochus, but Hermeias persuaded him to entrust the conduct of the army sent against the insurgents to his generals, Xenon and Theodotus, while he advanced in person to attack Coele-Syria.