Ethambutol is the name given to a special antibiotic. It is used to treat tuberculosis.
What is ethambutol?
Ethambutol is a specialized antibiotic that belongs to the tuberculostatics. It is considered a classic drug for the treatment of tuberculosis. It is also suitable for the treatment of other infections caused by mycobacteria. It is used only in combination with other preparations against mycobacteria. Ethambutol has been used in Europe since the 1960s. In Germany, the active ingredient is sold as a monopreparation under the names Myambutol and EMB-Fatol.
Pharmacological action
Ethambutol belongs to the group of tuberculostatics. The drug can exert both growth-inhibiting and bactericidal activity, which depends on its concentration. Ethambutol acts against mycobacteria that are outside the body’s cells, but also against specimens that hide in the phagocytes. However, for this purpose, a concentration of ethambutol must be administered that is seven times higher than normal. Among the advantages of ethambutol is the low resistance of mycobacteria to the antibiotic. For example, only about two percent of the bacterial genus Mycobacterium tuberculosis is insensitive to the tuberculostatic drug. For this reason, the drug is usually classified as a first-line agent. In addition, ethambutol can exert its effect if there are incompatibilities with other tuberculosis drugs. Ethambutol has the property that it is rapidly absorbed by mycobacteria. In doing so, it causes an obstruction of the normal structure of the cell walls. Thus, the antibiotic disrupts the production of mycolic acid, an important cellular building block of lipids. This in turn has a negative effect on the cell wall structure of the pathogens in rapid growth phases. The same applies to mycobacteria in a dormant state, so that the drug’s mechanism of action is independent of the particular phase of bacterial growth. However, it takes about 24 hours for significant inhibition of growth to set in. Ethambutol also supports the action of other tuberculostatics such as rifampicin or isoniazid. After ingestion, the antibiotic enters the gastrointestinal tract quickly and almost completely. Around two to four hours after ingestion, the active substance reaches its maximum concentration in the blood. Ethambutol is excreted from the body almost unchanged by the kidneys. A small amount leaves the organism via the bile. Because ethambutol is accumulated by erythrocytes (red blood cells) as well as by macrophages and alveolar cells in the lungs, its concentration within these cells turns out to be higher than in blood serum.
Medical application and use
The main use of ethambutol is in the treatment of tuberculosis caused by the mycobacterium family. Among the most common species is Mycobacterium tuberculosis. Mycobacterium africani, Mycobacterium microti and Mycobacterium bovis are less common. The antibiotic is effective against the pathogens in all stages of the disease, even if other tissues outside the lungs are affected. However, it is important to combine it with other drugs that are effective against tuberculosis. Often, the drug is also administered if tuberculosis breaks out again. In case of proven resistance of the bacteria, ethambutol serves as a reserve drug. The antibiotic is administered in the form of film-coated tablets. The patient takes the drug once a day, which is done regardless of meals. It is recommended to take the tablets on an empty stomach.
Risks and side effects
The use of ethambutol may cause unwanted side effects in some people. These primarily include inflammation of the optic nerve, which depends on the dose level and duration of therapy. Initially, the patient’s color vision is disturbed. In the further course, there is a risk of visual field defects and, in the worst case, visual disturbances or even blindness. For this reason, the administration of ethambutol must be closely monitored by an ophthalmologist. Other common side effects include increased uric acid levels, dizziness, headache, numbness in the limbs, finger tremors, orientation problems, confusion and hallucinations.Furthermore, allergic reactions such as fever, skin rash or itching, damage to the kidneys, blood count changes or liver dysfunction may occur. More rarely, bloating, abdominal pain, nausea, and allergic shock may occur. In the event of shock, ethambutol therapy should be discontinued immediately. It is also important to alert an emergency physician. In case of color vision disorders, the patient must consult an ophthalmologist. Hypersensitivity to ethambutol is a contraindication to its use. The same applies in the presence of ocular impairments that make it impossible to accurately control vision. In the presence of inflammation of the optic nerve, gout, or renal dysfunction, the physician must carefully weigh the risks and benefits of ethambutol therapy. Harmful effects of ethambutol in pregnancy are not known, although the antibiotic may penetrate the placenta. In addition, transfer of the drug into breast milk occurs, and its concentration is similar to that in the mother’s blood. In principle, ethambutol may be administered during pregnancy and lactation only after detailed review by the physician. Treatment with ethambutol in children can only be given from the age of 6. Thus, vision tests are possible from this age onwards, which can be used to monitor any deterioration in vision. When ethambutol and other medications are taken at the same time, interactions are possible. For example, aluminum hydroxide and similar acid inhibitors can reduce the effect of the antibiotic. Moreover, this risk exists with the administration of magnesium and the excipient [[spermine]].
