In "double tetracycline labeling", a second dose is given 11–14 days after the first dose, and the amount of bone formed during that interval can be calculated by measuring the distance between the two fluorescent labels.Tetracycline is also used as a biomarker in wildlife to detect consumption of medicine- or vaccine-containing baits. Side effects
Use of tetracycline antibiotics can:
Discolor permanent teeth (yellow-gray-brown), from prenatal period through childhood and adulthood. Children receiving long- or short-term therapy with a tetracycline or glycylcycline may develop permanent brown discoloration of the teeth. Be inactivated by calcium ions, so are not to be taken with milk, yogurt, and other dairy products
Be inactivated by aluminium, iron, and zinc ions, not to be taken at the same time as indigestion remedies (some common antacids and over-the-counter heartburn medicines)
Cause skin photosensitivity, so exposure to the sun or intense light is not recommended
Cause drug-induced lupus, and hepatitis
Cause microvesicular fatty liver
Cause tinnitus
Interfere with methotrexate by displacing it from the various protein-binding sites
Cause breathing complications, as well as anaphylactic shock, in some individuals
Affect bone growth of the fetus, so should be avoided during pregnancy
Fanconi syndrome may result from ingesting expired tetracyclines.Caution should be exercised in long-term use when breastfeeding. Short-term use is safe; bioavailability in milk is low to nil. According to the U.S. Food and Drug Administration (FDA),  cases of Stevens–Johnson syndrome, toxic epidermal necrolysis, and erythema multiforme associated with doxycycline use have been reported, but a causative role has not been established.
Tetracycline, sold under various brand names, is an oral antibiotic in the tetracyclines family of medications, used to treat a number of infections, including acne, cholera, brucellosis, plague, malaria, and syphilis.Common side effects include vomiting, diarrhea, rash, and loss of appetite. Other side effects include poor tooth development if used by children less than eight years of age, kidney problems, and sunburning easily. Use during pregnancy may harm the baby. It works by inhibiting protein synthesis in bacteria.Tetracycline was patented in 1953 and came into commercial use in 1978. It is on the World Health Organizations List of Essential Medicines. Tetracycline is available as a generic medication. Tetracycline was originally made from bacteria of the Streptomyces type. Medical uses
Spectrum of activity
Tetracyclines have a broad spectrum of antibiotic action. Originally, they possessed some level of bacteriostatic activity against almost all medically relevant aerobic and anaerobic bacterial genera, both Gram-positive and Gram-negative, with a few exceptions, such as Pseudomonas aeruginosa and Proteus spp., which display intrinsic resistance. However, acquired (as opposed to inherent) resistance has proliferated in many pathogenic organisms and greatly eroded the formerly vast versatility of this group of antibiotics. Resistance amongst Staphylococcus spp., Streptococcus spp., Neisseria gonorrhoeae, anaerobes, members of the Enterobacteriaceae, and several other previously sensitive organisms is now quite common. Tetracyclines remain especially useful in the management of infections by certain obligately intracellular bacterial pathogens such as Chlamydia, Mycoplasma, and Rickettsia. They are also of value in spirochaetal infections, such as syphilis, and Lyme disease.