welcome to HealthcareMagic
is not supposed to be used in children less than 8 yrs and in older children reduced dose is required.It is contraindicated in pregnancy because it can pass through breast milk and causes discolouration of teeth in child.As for Pectus excavatum
it is considered as genetic birth defect
and is seen in 1 in 1000 birth with a male preference of 3:1(that is it is seen in 3 males against 1 female).Also the occurrence in family is seen in 35-45% of people so see if there is any family history.It is also a result of intrauterine rickets
and in children with spinal muscular atrophy and is due to diaphragmatic breathing
.It should not necessarily have any relation to tetracycline.
I hope this answer is helpful to you.