  We study THz-driven condensate dynamics in epitaxial thin films of MgB$_{2}$,
a prototype two-band superconductor (SC) with weak interband coupling. The
temperature and excitation density dependent dynamics follow the behavior
predicted by the phenomenological bottleneck model for the single-gap SC,
implying adiabatic coupling between the two condensates on the ps timescale.
The amplitude of the THz-driven suppression of condensate density reveals an
unexpected decrease in pair-breaking efficiency with increasing temperature -
unlike in the case of optical excitation. The reduced pair-breaking efficiency
of narrow-band THz pulses, displaying minimum near $\approx0.7$ T$_{c}$, is
attributed to THz-driven, long-lived, non-thermal quasiparticle distribution,
resulting in Eliashberg-type enhancement of superconductivity, competing with
pair-breaking.
