Some patients have a genetic mutation which means they are more at risk of hearing loss after taking antibiotics called aminoglycosides. Experts, writing in the British Medical Journal (BMJ) believe that screening patients for this genetic mutation may prevent this.

The writers, Maria Bitner-Glindzicz and Shamima Rahman, the Institute of Child health, London, England, explain that aminoglycosides are valuable antibiotics for such serious infections as complicated urinary tract infections, tuberculosis and septicemia. They are known to potentially cause damage to the ear (otoxicity). However, what isn't well known is that there are people who have an inherited predisposition that makes them extremely sensitive to the effects - they can end up with severe and permanent hearing loss.

Approximately 5% of deafness in children in the UK is caused by this mutation, known as m.1555A-G. About 1 in 40,000 people in the UK have this mutation. Studies in other countries have indicated much higher incidences, in New Zealand it is thought to occur in 1 in 206 cases of newborns, and 1 in 1,161 in the USA (also newborns).

Families carrying this mutation, even if they never take aminoglycosides, may develop some degree of deafness later in life.

A study carried out in Spain found that 27% of families which included two deaf people were positive for this mutation. It was also found that everybody who had this mutation in Spain and took aminoglycosides suffered from hearing loss. A person who had taken aminoglycosides had a 96.5% of becoming deaf by the age of 30 if he/she had been exposed to aminoglycosides, while 38.9% of those who had never taken it became deaf.

The authors write that aminoglycosides are a major environmental modifier of the m.1555A-G mutation.

The writers ask whether it is cost effective to screen for this mutation before deciding whether to prescribe aminoglycosides. A test in the UK costs approximated £35 ($70). This cost would probably go down considerably if they were carried out in much larger numbers. It costs the NHS £61,000 ($122,000) for every child who becomes deaf (over his/her lifetime), plus about £18,000 ($36,000) in educational costs. US estimates have placed the lifetime cost to society for a child who loses his/her hearing before acquiring language at one million dollars.

It is possible to prevent deafness brought on by aminoglycosides in individuals who have this genetic mutation, explain the authors. Doctors who have patients who are deaf are well aware of this mutation. Many doctors, however, do not know about this susceptibility, and many others do not know that mutation testing is available.

The authors propose that the true prevalence of this mutation be ascertained for the UK, so that the cost-effectiveness of screening everyone who is prescribed aminoglycosides can be determined. Until this is done, people who are likely to be receiving multiple courses of aminoglycosides should be screened, such as leukemia patients and infants admitted to special care baby units.

They conclude that test results should be produced rapidly, and until they appear the patient should be given some other type of antibiotic.

"Editorial: Ototoxicity caused by aminoglycosides"
Maria Bitner-Glindzicz, Shamima Rahman
BMJ 2007;335:784-785 (20 October), doi:10.1136/bmj.39301.680266.AE
Click here to view abstract online

Written by: Christian Nordqvist