Will entropy be lost by using a DRBG?
A Deterministic Random Bit Generator (DRBG) would typically be used, when you have entropy input that is either 


biased,
inefficiently generated, or
both of the above.


If you have a True Random Bit Generator that outputs unbiased bits efficiently, there is no apparent reason to use a DRBG in the first place. This is particularly true in case you require information theoretic security. Using a DRBG means you get pseudo random bits with computational security, typically expressed in the conventional way as 128-bits of security, 256-bits of security, etc. 

This means that reseeding of DRBG, such as NIST SP 800-90A, should not be expected to be designed to address loss of entropy in the information theoretic sense, but only in a practical sense. It is done to reduce the risks (not eliminate the risks) associated with internal states being compromised through side channel attacks, etc.