Final answer:
Tetracycline needs to be used carefully in growing dogs due to its effects on bones and teeth, and the risk of developing antibiotic resistance.
Step-by-step explanation:
The drug that must be used cautiously in young growing dogs is tetracycline. This antibiotic, along with other related compounds such as doxycycline, can affect bone growth and tooth enamel development in puppies because of their role in calcium binding and protein synthesis inhibition within the body. The use of antimicrobial drugs in animals can also lead to the development of resistance, which may be cross-resistant to drugs used for humans, further emphasizing the need for cautious use.