  We prove that the known formulae for computing the optimal number of
maximally entangled pairs required for entanglement-assisted quantum
error-correcting codes (EAQECCs) over the binary field hold for codes over
arbitrary finite fields as well. We also give a Gilbert-Varshamov bound for
EAQECCs and constructions of EAQECCs coming from punctured self-orthogonal
linear codes which are valid for any finite field.
