How Neomycin works
Aminoglycosides such as neomycin are particularly effective against the group of Gram-negative bacteria. The cell membrane (envelope) of these bacteria has special channels called porins. Through these, aminoglycosides such as neomycin enter the interior of a bacterium. This is where their point of attack is located: the ribosomes.
These are complexes consisting of two subunits that function as “protein factories”: Ribosomes assemble amino acids into proteins (protein biosynthesis) in precisely defined sequences. In this way, for example, structural proteins are formed for the bacterial cell membrane.
Aminoglycosides such as neomycin bind to the small subunit of the ribosomes. As a result, the building instructions for proteins cannot be read correctly – the ribosomes assemble the wrong amino acids. This results in broken structural proteins, so-called nonsense proteins. When these proteins are incorporated into the cell membrane of the bacteria, the membrane becomes excessively permeable. As a result, the bacterium dies. Neomycin and other aminoglycosides thus have a bactericidal effect.
A special feature of aminoglycosides such as neomycin is that they inhibit bacterial growth, even if the concentration in the blood has fallen below the necessary level. Physicians speak of a post-antibiotic effect.
This is how neomycin is used
The antibiotic is used exclusively locally, for example in the form of eye or ear drops or a skin ointment. It exerts its effect directly at the site of administration.
In addition to neomycin, many drugs contain a glucocorticoid (“cortisone”). It additionally provides an anti-inflammatory effect.
The following instructions for use and dosages apply unless otherwise prescribed by the attending physician.
Neomycin ear drops
For ear infections, place two to three drops in the ear three to five times daily. If symptoms are severe, use every two to three hours.
Ideally, lie down with the affected ear facing up for a few minutes after putting the drops in.
Neomycin eye drops and eye ointment
Put one drop of neomycin eye drops into the conjunctival sac of the affected eye three to six times a day. If the symptoms are severe, you can apply the drops every two hours.
After application, ideally close the tear duct of the affected eye for a short time by pressing lightly on the nasal bone at the level of the inner corner of the eye. This prevents the active ingredient from being removed too quickly. This allows it to act longer on the eye.
Do not wear contact lenses during the treatment of eye infections. If it cannot be avoided, you should take them out before applying the eye medication and put them back in at the earliest 15 minutes after the medication has been applied.
If you use several medications on the eye at the same time (e.g., including moisturizing eye drops), there should be at least five to ten minutes between applications. If you are also applying an eye ointment, this should ideally be done last (i.e., after the eye drops).
If an eye infection is to be treated with both neomycin-containing eye drops and a neomycin eye ointment, ideally use the eye drops during the day and the eye ointment before sleeping. This is because the ointment applied in particular can temporarily impair vision.
The treatment is usually continued for two weeks. If the symptoms improve, doctors recommend using the eye drops or ointment less frequently.
Shortly after application, vision may become blurred. Do not operate cars or machinery until you can see clearly again.
Neomycin creams, ointment and powder
As a rule, the preparations are used for four to eight days, depending on how someone responds to the treatment.
The rule of thumb here is: Neomycin drugs should be applied to no more than one percent of the body’s surface area. This is about the size of the palm of your hand.
Combined nasal drops and sprays
Nasal drops or sprays containing neomycin in combination with other active ingredients are also available in Austria and Switzerland. You can put one to two sprays or drops in each nostril two to four times a day. You may use the nasal spray for no more than two to three weeks.
Neomycin lozenges
Neomycin lozenges, which are also available in Austria, contain the antibiotic as well as active ingredients with disinfecting and local anesthetic properties. Adolescents over the age of twelve and adults can suck one to two tablets several times a day. The maximum dose is six tablets per day.
Toothpaste reduces the effectiveness of the tablets. Application should therefore not be made shortly before or after brushing the teeth.
When is neomycin used?
Neomycin medicines help treat bacterial infections when the pathogens are sensitive to the antibiotic.
The indications for Neomycin include:
- Inflammations of the eye, eyelids, or sebaceous glands of the eye (e.g., conjunctivitis = conjunctivitis, inflammation of the eyelid margins = blepharitis)
- Bacterial infections of the external auditory canal, pharynx or oral cavity
- Bacterial diseases and inflammations of the skin or infected wounds (use often in combination with glucorticoids)
- Bacterial infections of the nose in case of nasal mucosa inflammation
- Prevention of infections after surgery
- Burns and scalds to protect against bacterial infection
What are the side effects of neomycin?
When applied locally, neomycin is hardly absorbed into the bloodstream. Therefore, effects and side effects usually occur only directly at the site of administration.
When using the eye drops or ointment, patients occasionally suffer from watery, itchy, and reddened eyes. There may also be a foreign body sensation in the eye. In addition, pain or swelling of the eyes is possible.
Occasionally, patients react hypersensitively to the active ingredient. An allergic reaction is characterized by itching, burning or redness at the site of application.
Other ingredients of the preparations such as wool wax or the preservative benzalkonium chloride may irritate the eyes and skin.
In the case of major injuries or a disturbed skin barrier, neomycin may be absorbed into the blood. Then the following side effects are possible:
A serious side effect of neomycin (like other aminoglycosides) is damage to the kidneys (nephrotoxicity). Especially in high doses, the active substance accumulates in the renal tubules and damages the cells. As a result, kidney function declines. If the therapy is stopped early, the kidney damage is usually reversible.
Damage to the inner ear (ototoxicity) is also one of the serious side effects of aminoglycosides.
Even minor injuries to the tympanic membrane or tympanic membrane perforations cause neomycin to enter the inner ear and damage the sensory cells there. This results in irreversible (non-reversible) severe hearing loss up to deafness. In addition, the organ of equilibrium is usually affected as well – those affected develop severe balance disorders.
Neomycin reduces the number and motility of sperm. The antibiotic thus affects male fertility.
When should Neomycin not be used?
Neomycin should not be used:
- In newborns and infants under three years of age.
- in case of allergy to aminoglycosides
- when the pathogens of an infection do not respond to neomycin
If patients suffer from tuberculosis or a viral or fungal infection, the physician prescribes Neomycin only in combination with specific therapy.
If there are severe injuries in the area of application (e.g., tympanic membrane or oral mucosa) , Neomycin must not be used. This is because there is a risk of the active substance entering the bloodstream and causing serious side effects.
In certain cases, neomycin ophthalmic preparations must not be used. These include:
- ulcers of the cornea of the eye
- Injuries of the cornea of the eye
- glaucoma
The use of neomycin as a cream, ointment, or powder for the skin is not advisable for:
- Rosacea
- Acne @
- infections caused by viruses, fungi, tuberculosis or syphilis pathogens
- open and fresh wounds
Aminoglycosides such as neomycin can have a neuromuscular-blocking effect. This means they inhibit signal transmission from nerves to muscle. Therefore, in diseases associated with neuromuscular blockade, physicians carefully consider whether use of neomycin is appropriate. These diseases include, for example, myasthenia gravis and Parkinson’s disease.
These interactions may occur with Neomycin
Neomycin is used exclusively topically (externally). As a rule, hardly any active substance enters the bloodstream. Interactions with drugs that are ingested are therefore rare. However, if the skin is injured or not intact, the active substance may enter the bloodstream and have such interactions.
Neomycin has a damaging effect on the kidneys (nephrotoxic) and on the hearing (ototoxic). These side effects are exacerbated by the simultaneous use of drugs that can also cause kidney and hearing damage. Examples of such agents are other antibiotics from the group of aminoglycosides, ampothericin B (other antibiotic) and furosemide (drainage drug).
The concomitant use of muscle-relaxing drugs (muscle relaxants) may increase the neuromuscular-blocking effect of neomycin.
Neomycin in children: What should be considered?
Medicines containing neomycin should not be used in infants and young children under three years of age.
Children’s skin is thinner than that of an adult, and their skin barrier is not yet fully mature. In addition, children have a much larger skin surface area compared to their body weight. Active ingredients such as neomycin are therefore more easily absorbed through the skin and into the bloodstream.
Neomycin lozenges are suitable for patients aged twelve years and older.
Neomycin eye, ear and nose drops are already approved for children, depending on the preparation. The exact dosage is determined by the doctor in each individual case.
Neomycin during pregnancy and lactation
Neomycin preparations are unproblematic during pregnancy and breastfeeding because they are only applied locally and hardly enter the blood. During use, mothers can usually continue breastfeeding without a break.
Nevertheless, doctors prescribe the antibiotic for pregnant and breastfeeding women only if absolutely necessary. The treatment is also monitored by a doctor.
Neomycin lozenges are an exception. There are no studies on the use during pregnancy. Therefore, their use is not recommended.
How to obtain medicines with neomycin
Medicines containing neomycin require a prescription in Germany, Austria and Switzerland and are only available from pharmacies with a prescription.
