There are various defenses that can be used in a DUI case in Pennsylvania. The specific defenses that would apply would depend on the specific facts and circumstances of the case. For example, it may be able to be challenged that the stop of the driver, the stop of the vehicle was unlawful and anything obtained in doing so, be it the breathalyzer or blood test of the driver, could be suppressed as evidence as fruit of the poisonous tree. There's a two-hour requirement, that the breathalyzer has to be done within two hours of the stop. If that does not take place, the breathalyzer results can be challenged. The calibration of the breathalyzer can be challenged.
Additionally, if a driver gave a statement and the driver was in subject to custodial interrogation, would be subject to or had the right to their Miranda rights. If they gave the statement, "You got me, officer. I've been drinking," it may be possible to suppress that statement. There's various DUI specific defenses and there's also defenses that are more general in nature. An experienced Pennsylvania DUI attorney will know what defense would be best for your case and they should be involved from as early as possible in the case.