The netilmycin/dexamethasone combination is an important resource in the treatment of conjunctivitis, a very common condition, both in adults and children, and can have a wide variety of aetiologies, infectious and non-infectious.
Pathology
Conjunctivitis is one of the most common diseases of the anterior segment of the eye. It is an inflammation of the conjunctiva, the transparent mucous membrane that covers the anterior portion of the eyeball, with the exception of the cornea, and the inner wall of the lower and upper eyelids, up to the lid margin.
The causes
Conjunctivitis can be caused by:
1) Biological agents (bacteria, viruses; mycetes; parasites);
2) from physical agents (e.g. ultraviolet radiation or thermal radiation);
3) from chemical agents (e.g. cosmetics or drugs);
4) from environmental factors (e.g. smoke or dust).
There are also allergic and/or immune-mediated conjunctivitis and conjunctivitis due to an alteration of the tear film.
Symptoms
The most common forms of conjunctivitis are of bacterial origin and are characterised by:
- redness;
- burning;
- itching or feeling of a foreign body;
- more or less abundant lacrimation;
- photophobia (sense of discomfort towards light);
- yellow/white purulent discharge.
Treatment
The treatment of conjunctivitis involves the instillation of antibiotic eye drops, the indication and dosage of which must be strictly prescribed by the ophthalmologist. Self-medication in these cases can prolong and/or make a condition that can be treated difficult to resolve.
Precautions
It must be kept in mind that conjunctivitis is contagious and, therefore, the patient suffering from it must adhere to certain important hygienic measures:
a) Avoid rubbing your eyes;
b) Wash your hands often and thoroughly;
c) Remove purulent secretions with sterile wipes;
d) Use a personal towel;
Antibiotic therapy
In most cases of infectious conjunctivitis, the origin is viral, but a bacterial aetiology is also possible, usually recognisable by the presence of purulent discharge.
In these cases, effective treatment requires both the elimination of the inflammation of the ocular surface and the eradication of the responsible bacterial strain. For this reason, although conjunctivitis is often self-limiting in nature, patients are usually prescribed a broad-spectrum topical antibiotic.
Antibiotic-anti-inflammatory combinations
Since conjunctivitis in the active phase is best controlled with preparations containing steroids, combinations of steroids and topical antibiotics are often used.
The combination of steroid and antibiotic treatment is also necessary because microbiological evaluation is not routinely performed in the case of conjunctivitis.
Advantages
The administration of these combinations also has numerous advantages, which include:
- better compliance;
- lower costs;
- the reduction of the potential wash-out effect.
How to choose a steroid/antibiotic combination
The choice between the different available fixed steroid/antibiotic combinations depends on the pattern of bacterial resistance to the antibiotic included in the formulation. One of the available fixed steroid/antibiotic combinations contains dexamethasone and netilmicin (specifically, 0.1% dexamethasone and 0.3% netilmicin), and is appropriate for all ocular inflammatory conditions for which a corticosteroid is indicated and where a superficial bacterial ocular infection or risk of bacterial ocular infection is present.
Dexamethasone
Dexamethasone is one of the most widely used corticosteroids in ophthalmology and has proven highly effective in the treatment of ocular inflammation.
Netilmicin
The antibiotic component of this combination, netilmicin, is a third-generation aminoglycoside, formerly used by injection for the treatment of urinary and pulmonary infections. Compared to previous-generation aminoglycosides, Netilmicin is able to resist the action of aminoglycoside-inactivating enzymes, justifying its efficacy even in cases of resistance to gentamicin and tobramycin.
Since the late 1990s, netilmicin has only been used topically ophthalmically and this has allowed, unlike for example fluoroquinolones, its susceptibility profile to be maintained over time.
This microbiological profile is particularly evident not only with regard to Gram-negative bacteria (which has been known since its systemic use) but also with regard to the Gram-positive bacteria most frequently involved in ocular infections, such as S.Aureus and Coagulase-negative Staphylococci.
Also noteworthy is the antibiotic's strong activity against the 'difficult' bacteria increasingly involved in ocular infections, namely methicillin-resistant staphylococci, known as MRSA (in the case of S.Aureus) and MRCoNS (in the case of Coagulase-negative Staphylococci).
Netilmicin's activity against them is equal to that of antibiotics not used topically but known to be the 'gold standard' in methicillin-resistant infections (such as vancomycin). These are all concepts to bear in mind when prescribing an antibiotic in the absence of culture data, as is the case in the vast majority of ocular infections.
Finally, a further aspect to emphasise is the absence of netilmycin toxicity to the conjunctival and corneal epithelium, an aspect not to be overlooked in the choice of treatment, especially when compared with the obvious toxicity of all fluoquinolones and antiseptics. P
Summary of the Characteristics of Netilmicin
- a broad spectrum of activity, including methicillin-resistant strains;
- a low level of conjunctival and corneal toxicity;
- a high rate of efficacy in the treatment of bacterial conjunctivitis.
Efficacy of the combination netilmycin/dexamethasone in the treatment of bacterial conjunctivitis
The combination netilmycin/dexamethasone in the treatment of external ocular inflammation requiring antibiotic treatment has proven effective in reducing the signs and symptoms of conjunctival inflammation and conjunctival discharge.
Moreover, this combination has also been shown to be safe and effective in controlling ocular inflammation after cataract surgery.
The extent of the reduction in conjunctival hyperemia obtained after treatment is in fact 70%, with no rebound effect at the end of therapy. Furthermore, the response rate (i.e. the percentage of patients showing a clinically significant improvement) is approximately 90%.
These results also proved to be equivalent to those of the dexamethasone/tobramycin combination. In fact, one studio A multicentre double-blind equivalence study, conducted on approximately 140 patients, compared the efficacy of the dexamethasone/netilmycin combination with that of the dexamethasone/tobramycin combination in the treatment of external ocular inflammation requiring antibiotic treatment.
The results of the study showed that the two fixed steroid/antibiotic combinations were equivalent in reducing signs and symptoms.
The data also confirm that bacterial pathogens are isolated from a low percentage of patients with clinical signs of conjunctivitis (one third in the study), but that this result does not affect the clinical efficacy of a steroid/antibiotic combination. However, a high eradication rate was observed in the case of infection in all patients, confirming the efficacy of aminoglycosides in the treatment of infections of the anterior segment of the eye.
Antibiotic resistance
Definitely the antibiotic phenomenon-resistance constitutes one of the most serious threats to the pharmacological weapons that enable us to fight infections. Inappropriate use of antibiotics in humans, together with their massive use in animal husbandry, has contributed to selecting microbial strains that have acquired multiple resistances, i.e. directed towards many (if not all) antibiotic families at the same time: the dreaded 'multi-drug-resistant' (MDR) microorganisms. The advice, therefore, from all international health protection bodies is to avoid abuse and to use antibiotics consciously.
Topical ophthalmic antibiotic therapy, specifically, is certainly less affected by the phenomenon of antibiotic resistance than systemic antibiotic therapy.
This is because of the high concentrations of antibiotic reached at the level of the eye, which are often able to exceed the levels required to exert their antibacterial action even against theoretically resistant microorganisms. However, the topical use of antibiotics not used for systemic use is certainly preferable to reduce the risk of encountering antibiotic resistance.
The main rules to follow are still to use an antibiotic according to local susceptibility/resistance data (where available), to administer it at a full dose and for a reasonable time (usually not less than 4-5 days).
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