Minocycline: Effects, Uses & Risks

Minocycline is a drug from the class of tetracyclines. The antibiotic is used to treat respiratory tract infections, urinary tract infections, or to treat Lyme disease.

What is minocycline?

Because of its broad spectrum of activity, minocycline is used to treat many diseases. Minocycline is a tetracycline. Tetracyclines are drugs that have antibiotic activity and are produced by bacteria of the species Streptomyces. Unlike chlortetracycline, minocycline is not a natural substance but a semisynthetic derivative. It is synthesized from oxytetracycline in a multi-step process. Bacteria of the species Streptomyces rimosus are suitable for obtaining oxytetracycline. Due to its broad spectrum of activity, minocycline is used for the treatment of many diseases. Indications for the antibiotic are skin infections, eye infections, pneumonia, otitis media, syphilis, Lyme disease or chronic bronchitis.

Pharmacological action

Minocycline is an antibiotic. Antibiotics are drugs that kill bacteria or stop the growth of bacteria. Tetracyclines, such as minocycline, fight both Gram-positive bacteria and Gram-negative bacteria. Gram-positive bacteria, such as streptococci or staphylococci, do not have an additional cell outer wall, unlike Gram-negative bacteria, such as Neisseria, Campylobacter or Brucella. Minocycline plays a special role in the treatment of infections caused by cell wall-less bacteria such as rickettsiae, chlamydiae or mycoplasmas. Due to the lack of a cell wall, standard antibiotics such as cephalosporins or penicillins are unable to do anything against these bacteria. However, more and more germs that are resistant to the antibiotic are appearing, especially in hospitals. In particular, some Proteus bacteria or bacteria of the Enterobacter species no longer respond to minocycline. Most pathogens from the Pseudomonas aeruginosa group are also considered resistant. Minocycline inhibits protein biosynthesis at the ribosomes of bacteria. The accumulation of aminoacyl-tRNA is prevented, so that the bacteria cannot multiply. Current research shows that minocycline also does not have an exclusively antibiotic effect. For example, trials showed neuroprotective and anti-inflammatory effects in the nervous system.

Medical application and use

Despite the increase in resistance to minocycline, the antibiotic is still the agent of choice for the treatment of Lyme disease and urethritis. Lyme disease is a disease transmitted by a tick bite. The pathogens are borrelia (spirochetes). After multiplication at the site of entry, there is spread by the bloodstream. Various organ systems are affected. After some time, the clinical picture of the so-called Lyme borreliosis results. Lyme disease is characterized by muscle and joint pain, swelling of the lymph nodes, paralysis, nerve pain and chronic fatigue. Urethritis is the inflammation of the urethra. The disease is accompanied by itching, pain during urination and discharge. Minocycline is only effective against bacterial urethritis not caused by Neisseria gonorrhoeae, the causative agent of gonorrhea. Furthermore, the antibiotic is used for venereal diseases such as syphilis and for kidney and urinary tract infections. Infections with chlamydia are also treated with minocycline. Minocycline is also used to treat respiratory infections. These include tonsillitis, sinusitis, and pneumonia. Minocycline is also given for middle ear infections (otitis media). Rare indications for minocycline are bacterial infectious diseases such as ornithosis, bartonellosis, plague, rickettsiosis, or brucellosis. Listeriosis, an infectious disease associated with flu-like symptoms, is also treated with minocycline. Furthermore, the drug can also be used to treat severe acne. Minocycline can also be used for preventive treatment against meningitis after contact with people infected with meningococcus.

Risks and side effects

Minocycline may cause enamel hypoplasia. This can cause irreversible yellowish to brownish discoloration of the teeth. Therefore, the antibiotic should not be used during pregnancy and before the age of eight.Other contraindications include renal dysfunction and hepatic dysfunction. Minocycline may cause photosensitization. This is an excessive photosensitivity of the skin. Edema or erythema may therefore develop on exposed areas of the body while taking minocycline. Common side effects also include heartburn, inflammation of the esophagus, flatulence, diarrhea, fatty stools, and vomiting. Occasionally, fatigue, dizziness, muscle weakness, liver disorders, or the development of black hair tongue occur. Occasionally, Stevens-Johnson syndrome develops with extensive skin rash and fever. Rarely, blood cell formation in the bone marrow is disturbed. In addition, blood pressure may drop sharply, the larynx may swell, or intracranial pressure may increase. Severe diarrhea during or after therapy may be caused by pseudomembranous colitis. In the event of such antibiotic-induced intestinal inflammation, therapy with minocycline must be stopped immediately and replaced with treatment with vancomycin. When other antibiotics are administered simultaneously, mutual attenuation of their effect is possible. Acid-binding drugs, iron preparations, calcium preparations, and activated charcoal inhibit the absorption of minocycline from the intestine. Barbiturates and antiepileptic drugs may also weaken the effect of the antibiotic. Hormonal contraceptives such as the “pill” may lose their effectiveness while taking minocycline. In addition, the effect of antidiabetics or anticoagulants may be impaired by the drug. The simultaneous administration of the acne medication isotretinoin increases the risk of an increase in intracranial pressure. In addition, it should be noted that the side effects of various anesthetics, theophylline, cyclosporine, and methotrexate may be increased by minocycline.