The different aminoglycosides

There are differences between the available formulations and the use of antibiotics belonging to the aminoglycosides group.

In this step, you will learn more about the different aminoglycosides that are available and their place in therapy. Please be aware that because our educators are based in the United Kingdom, the aminoglycosides provided as examples are the ones used in clinical practice here. Towards the end of this step, you will see brief examples of other aminoglycosides used in special cases and clinical practice elsewhere.

Gentamicin

Gentamicin is the aminoglycoside of choice in the UK and is widely used for the treatment of serious infections. It has a broad spectrum of activity but has poor activity against haemolytic streptococci and pneumococci. When used as empirical therapy for undiagnosed serious infections, it is usually given in conjunction with a penicillin or metronidazole (or both).

Gentamicin can be used together with other antibiotics to treat infective endocarditis.

Available medicinal preparations in the UK include topical (eye and ear drops) and parenteral formulations (solution for injection, infusion). Unless prescribed by an Ear, Nose and Throat specialist, it is contraindicated to be used in the ear in the following patient groups:

• patent grommet
• perforated tympanic membrane

Nebulised gentamicin may be used off-license in the UK as a suppression therapy for non-cystic fibrosis bronchiectasis.

Amikacin

Amikacin is used in the treatment of serious infections caused by gentamicin-resistant Gram-negative bacilli and is one of the aminoglycosides of choice for treating Mycobacterial infections.

It is more stable against many aminoglycoside-modifying enzymes, which is a key mechanism of resistance to these antibiotics. A number of clinical areas are now increasingly using amikacin due to high local gentamicin resistance rates, and it is also being favoured for empirical aminoglycoside therapy in patients who are immunosuppressed because the European Committee on Antimicrobial Susceptibility Testing (EUCAST) no longer recommends the use of gentamicin to treat Pseudomonas aeruginosa infection. Amikacin can also be used intravenously for the treatment of severe exacerbations of cystic fibrosis.

Amikacin is available as a solution for injection or as a liposomal inhaled form.

Tobramycin

Tobramycin is available as a solution for injection, dry powder inhalation or nebuliser liquid. It demonstrates similar activity to gentamicin, although it is slightly more active against P. aeruginosa, but shows less activity against certain other Gram-negative bacteria. It can be used intravenously for the treatment of severe exacerbations of cystic fibrosis as well as other indications including septicaemia and meningitis.

For the treatment of chronic pulmonary P. aeruginosa, tobramycin can be administered by nebuliser or by inhalation of powder on a cyclical basis (28 days of tobramycin followed by a 28-day tobramycin-free interval). However, resistance may develop and some patients do not respond to treatment.

It is recommended that lung functioning monitoring is performed on patients receiving inhalation forms of tobramycin to monitor for bronchospasm.

Neomycin sulfate

Neomycin sulfate is generally considered too toxic for systemic use and is mostly used for infections of the skin or mucous membranes, to reduce the bacterial colonisation of the colon prior to bowel surgery or in hepatic failure. Oral administration may lead to malabsorption. In patients with hepatic failure or inflammatory/ulcerative gastrointestinal disease, small amounts of neomycin sulfate may be absorbed from the gut. These patients may also have concomitant poor renal function, causing cumulation, resulting in ototoxicity.

Available medicinal forms of neomycin include oral (oral solution and tablets (tablets are, however, unlicensed in the UK) and topical formulations (cream, ear, eye, and nose drops).

The British National Formulary (BNF) consider neomycin sulfate cream ‘less suitable for prescribing’ and as such, this medication is not usually considered a drug of first choice due to the risk of toxicity with dermal absorption. However, its use may be necessary in some circumstances.

Netilmicin

Netilmicin is only available as eye drops in the UK, although it is available as a solution for injection in other countries to treat infections systemically. Netilmicin eye drops may also be combined with dexamethasone to treat eye infections. Netilmicin is used to treat gentamicin-resistant Gram-negative infections.

Summary

The table below summarises available preparations and indications of these agents in the UK. Please note that this may vary depending on your location, so you should always consult your national and local formularies to understand what is used where you are based.

If you require a text version of the above image, this is available as a PDF.

Specialist use

Below is a selection of other aminoglycosides not licensed for use in the UK. These agents may be used in locations globally and may be used off-license for specialist cases.

• Streptomycin may be used off-license in the UK to treat special cases of Mycobacterium tuberculosis infection.
• Plazomicin is more stable against common aminoglycoside-modifying enzymes. In certain cases, it may be used for treating multi-drug resistant Gram-negative infections.
• Spectinomycin is used to treat non-pharyngeal gonococcal infections in patients with penicillin allergies.
• Paromomycin is used to treat intra-intestinal amoebic infection

In the next step, connect with other learners in the comments section by sharing your experiences of aminoglycosides in your own practice.