Phetprasert Tour operates a bus from Phitsanulok to Vientiane 3 times a day. Tickets cost $10 - $21 and the journey takes 5 h 46 min. The Transport Company also services this route every 4 hours. Alternatively, Thai AirAsia, Thai Lion Mentari and Nok Air fly from Phitsanulok to Vientiane 3 times a day.
From Phitsanulok bus to Udon Thani then bus to Vientiane Talat Sao Station. 9 h 46 min ฿897. From Phitsanulok drive to Vientiane. 8 h 22 min ฿1574. From Phitsanulok taxi to Phitsanulok airport, fly to Vientiane airport, then taxi to Vientiane. 4 h 44 min ฿3571. From Phitsanulok taxi to Phitsanulok airport, fly to Udon Thani airport, taxi to Udon Thani, then bus to Vientiane. 7 h 47 min ฿4463.
No, there is no direct bus from Phitsanulok to Vientiane. However, there are services departing from Phitsanulok and arriving at Vientiane Talat Sao Station via Udon Thani. The journey, including transfers, takes approximately 9 h 46 min.