in just now checking the OCD entry on Antonius, I find the following:

...in 51 he was quaestor. As tribune in 49 he defended Caesar's interests in the senate, fled to his camp when the 'last decree' was passed, took part in the fighting in Italy, and was left incharge of Italy during Caesar's Spanish campaign. In 48 he served in Greece and commanded Caesar's left wing at Pharsalus. Caesar then sent himto impose order on Italy as his magister equitum (til late 47), but he was only partially successful, and held no further post till 44 when he was Caesar's consular colleague.

I would gather from all that, that he never did hold the praetorship.