Adleman, FOCS'78 showed that any randomized circuit for inputs of length $n$ can be non-uniformly derandomized. However, the construction effectively duplicates the original circuit  $O(n)$ times, so the derandomized circuit is larger than the original one by a factor of $O(n)$. Is there any more efficient construction out there that multiplies the circuit size by a smaller factor  ?
More efficient non-uniform derandomization ?
derandomization