Final answer:
Tetracycline should not be used by pregnant women or children under 8 years old due to the risk of discoloring developing teeth, while erythromycin is considered safe for use during pregnancy.
Step-by-step explanation:
The antibiotic that should not be taken by a pregnant woman or children under the age of 8 years due to the risk of permanent discoloration of developing teeth is Tetracycline. This antibiotic, along with others such as doxycycline and minocycline, are known to bind to calcium ions in developing teeth, leading to a yellow-brown discoloration that can be permanent. It is important to avoid these medications during pregnancy and early childhood to prevent these potential side effects. On the other hand, erythromycin is generally considered safe during pregnancy and is used to treat a variety of bacterial infections, including those that may be present during childbirth.