Minocycline

Minocycline is an antibiotic from the tetracycline group. It is a representative of the second generation of tetracyclines and is effective against gram-negative and gram-positive bacteria. It is used to treat a variety of bacterial infections.

These include:

• Pneumonia
• Skin infections with methicillin-resistant Staphylococcus aureus
• Anthrax
• Bubonic plague
• Cholera
• Amoebic dysentery
• Ehrlichiosis
• Gonorrhea
• Leprosy
• Perioral dermatitis
• Syphilis
• Borelliosis
• Urinary tract infections
• Rectal infections
• Infections of the cervix

It is also used to treat acne vulgaris and rheumatoid arthritis. It is taken by mouth or applied to the skin as a cream.

Minocycline was patented in 1961 and was approved by the U.S. Food and Drug Administration on June 30, 1971.

Pharmacodynamics

Tetracyclines, such as minocycline, enter bacterial cells through pore channels by binding with cations such as magnesium. This allows them to enter the periplasm, where they again dissociate from the cations, allowing the very lipophilic tetracycline to diffuse into the bacterial cytoplasm. Tetracyclines then prevent binding from aminoacyl-tRNA to the 30S ribosome, which is unique to bacteria, inhibiting protein synthesis. As a result, the bacteria can no longer multiply and ultimately perish.

Pharmacokinetics

Minocycline is rapidly and almost completely absorbed from the upper part of the small intestine. Taking it with food has no relevant effect on absorption. It reaches its highest blood plasma concentration after one to two hours and has a plasma protein binding of 70-75%. The substance penetrates almost all tissues, with particularly high concentrations in the gallbladder and liver. Minocycline crosses the blood-brain barrier better than other tetracyclines and also reaches therapeutically relevant concentrations in the brain. Approximately 50% of minocycline is metabolized in the liver. The remainder is excreted predominantly unchanged via the intestine. Approximately 10-15% is excreted via the kidneys. The biological half-life is approximately 14-22 hours in healthy subjects, and 30 hours or more in patients with renal impairment or hepatic insufficiency.

Interactions

The combination of minocycline with certain substances or foods containing divalent cations can result in so-called chelate complexes in which the free minocycline is bound. As a result, the drug can no longer be absorbed in the small intestine and thus loses its effectiveness.

These include, for example:

• Dairy products
• Antacids
• Calcium and magnesium preparations
• Iron preparations
• Magnesium-containing laxatives
• Bile acid sequestrants

Combination with isotretinoin, acitretin, or other retinoids may increase the risk of intracranial hypertension. Minocycline significantly decreases the concentrations of the HIV drug atazanavir in the body. Minocycline potentiates the effects of coumarin derivatives and sulfonylureas. The toxicity of methotrexate and ciclosporin is increased by minocycline. The effect of oral contraceptives is weakened by minocycline administration.

Side effects

• Stomach pain
• Diarrhea
• Dizziness
• Restlessness
• Drowsiness
• Sores in the mouth
• Headache
• Vomiting

It increases sensitivity to sunlight and may affect the quality of sleep, rarely causing sleep disturbances. Minocycline has also been associated with cases of lupus. Permanent blue discoloration of the gums or discoloration of the teeth may also occur.

Rare but serious side effects include fever, yellowing of the eyes or skin, stomach pain, sore throat, visual disturbances, and psychological changes, including changes of personality.

Contraindications

• Hypersensitivity to tetracycline antibiotics
• Severe liver dysfunction

Minocycline may cause permanent changes in teeth, especially in children. Therefore, its use after the 16th week of pregnancy and administration in children before the age of 8 years is strictly contraindicated.