Tetracyclines are generally safe and their most common adverse effects relate to gastrointestinal symptoms.
Gastrointestinal adverse effects are common, especially with high doses, and are mostly attributed
to irritation of the mucosa. They include nausea, vomiting and diarrhoea. Oesophageal ulceration has been reported, particularly
after a dose is taken with insufficient water or at bedtime.1
Photosensitivity may occur, depending on the tetracycline dose and degree of sun exposure. Symptoms
include exaggerated sunburn and itching within minutes to hours of sun exposure. In most cases, symptoms resolve within
days (provided no further sun exposure occurs). In severe cases, vesicles and bullae may develop, resulting in hyperpigmentation
of the skin, which may take weeks to months to resolve. Studies have demonstrated phototoxic reaction rates of 3%, 20%
and 42%, for doses of 100, 150 and 200 mg of doxycycline respectively.7 The use of broad-spectrum sunscreen
(UV-A + UV-B) can minimise or prevent the potential effects of a phototoxic reaction.
Autoimmune adverse effects are very rarely associated with minocycline, such as systemic lupus erythematosus,
autoimmune hepatitis, serum sickness and vasculitis, with or without the development of antinuclear antibodies or other
autoantibodies. Symptoms may be expressed as fever, malaise, loss of appetite, rash, arthralgia or myalgia. Most cases
occur in young females being treated for acne (i.e. long-term use).1 Minocycline is also very rarely associated
with blue-grey pigmentation of the skin, which may be irreversible.
Idiopathic intracranial hypertension with headache, dizziness, visual disturbances and papilloedema
has been reported in people using tetracyclines long-term. Symptoms can develop from within two weeks to one year or more
of starting a tetracycline.1
Renal and hepatic impairment
Both doxycycline and minocycline can be used with caution in people with renal impairment, however, high doses should
be avoided.2 All tetracyclines should be avoided or used with caution in patients with hepatic impairment.2
Avoid tetracyclines in children
Tetracyclines are contraindicated in children aged under 12 years, as they are associated with impaired bone growth
and permanent discoloration of teeth and enamel hypoplasia.2 This is because tetracyclines bind to calcium
molecules and are deposited in calcifying areas in bone, nails and teeth.1
Avoid tetracyclines during pregnancy and breast feeding
Tetracyclines are contraindicated in women who are pregnant or breast feeding.2
Doxycycline and minocycline are classified as pregnancy category D.* Effects on skeletal development of the embryo during
the first-trimester have been documented in animal studies. Administration during the second or third trimester may cause
discoloration of the child's teeth.2 Large parenteral doses of tetracyclines have been associated with acute
fatty necrosis of the liver in pregnant women, especially those with pyelonephritis.2,8
Chelation with calcium in breast milk is likely to reduce the adverse effects (i.e. tooth discoloration) of tetracyclines
in an infant who is breast feeding, however, they still should not be used in women who are breast feeding.2
* Category D: Drugs that have caused, are suspected to have caused or may be expected to cause, an increased incidence
of human foetal malformations or irreversible damage. These drugs may also have adverse pharmacological effects. Specialised
texts should be consulted for further details.