The most cochlear toxic drug : Neomycin>>kanyamycin>Gentamicin>amikacin< streptomycin

The severity of the cochlear damage is Neomycin>kanyamycin>Gentamicin>amikacin>streptomycin.

In Short in this article:

Kanamycin, amikacin, neomycin, and dihydrostreptomycin are preferentially cochleotoxic.

Gentamicin affects both cochlear and vestibular systems, Streptomycin affects vestibular systems.

Any drug with the potential to cause toxic reactions to structures of the inner ear, including the cochlea, vestibule, semicircular canals, and otoliths, is considered ototoxic. Drug-induced damage to these structures of the auditory and balance system can result in hearing loss, tinnitus, and dysequilibrium or dizziness.

Aminoglycosides

Multiple aminoglycoside preparations have become available, including streptomycin, dihydrostreptomycin, kanamycin, gentamicin, neomycin, tobramycin, netilmicin, and amikacin. The aminoglycosides are bactericidal antibiotics that bind to the 30S ribosome and inhibit bacterial protein synthesis. They are active only against aerobic gram-negative bacilli and cocci.

ototoxic drugs, the aminoglycosides are the most vestibulotoxic, although they vary greatly in their differential effects on the vestibular and cochlear systems. 

Kanamycin, amikacin, neomycin, and dihydrostreptomycin are preferentially cochleotoxic.

Gentamicin affects both cochlear and vestibular systems; however, most authors include gentamicin as primarily vestibulotoxic.

Streptomycin, tobramycin, and netilmicin are also primarily vestibulotoxic.

Pathophysiology

Aminoglycoside toxicity primarily targets renal and cochleovestibular systems; however, no clear correlation exists between degree of nephrotoxicity and ototoxicity. Cochlear toxicity that results in hearing loss usually begins in the high frequencies and is secondary to irreversible destruction of outer hair cells in the organ of Corti, predominantly at the basal turn of the cochlea. In the vestibular apparatus, type I hair cells are more sensitive than type II hair cells.

Signs and symptoms

Clinically, acute cochlear damage may present as tinnitus. Early hearing loss may go unrecognized by the patient and initially manifest as an increase in the threshold of highest frequencies (>4000 Hz). With progression, lower speech frequencies are affected and the patient may become profoundly deaf if the drug is continued. If the drug is stopped early in the course of damage, further loss may be prevented, and partial recovery of auditory thresholds may be possible. However, the loss is usually permanent.

Symptoms of vestibular toxicity typically include imbalance and visual symptoms. The imbalance is worse in the dark or in situations in which footing is uncertain. Spinning vertigo is unusual. The visual symptoms, called oscillopsia, occur only when the head is moving. Quick movements of the head are associated with transient visual blurring. This can cause difficulties with seeing signs while driving or recognizing people's faces while walking. Clinically, nystagmus may be present as an early sign.

Prevention

Prevention of aminoglycoside ototoxicity involves careful monitoring of serum drug levels and renal function as well as hearing evaluations before, during, and after therapy.

Specific aminoglycosides

See the list below:

• Streptomycin: Streptomycin was the first clinically applied aminoglycoside and was used successfully against gram-negative bacteria in the past. Streptomycin preferentially affects the vestibular system rather than the auditory system. Vestibular damage due to streptomycin is common with prolonged use and in patients with impaired renal function. Because of its toxicity, and because of widespread resistance, this agent is used infrequently today. However, streptomycin use has risen for treatment of tuberculosis.

• Gentamicin: As with streptomycin, gentamicin has a predilection for the vestibular system. Therapeutic peak serum levels of 10-12 mcg/mL are generally considered safe but may still be toxic in some patients. Carefully adjust dosing in patients with renal disease.

• Neomycin: This agent is one of the most cochleotoxic aminoglycosides when administered orally and in high doses; therefore, systemic use generally is not recommended. Neomycin is among the slowest aminoglycosides to clear from the perilymph; consequently, delayed toxicity (1-2 wk) may ensue after discontinuation of therapy. Neomycin is mainly used as an effective otic and ototopical agent. Although neomycin is generally considered safe when used topically in the ear canal or on small skin lesions, equally effective alternatives are available.

• Kanamycin: Although less toxic than neomycin, kanamycin is quite ototoxic. Kanamycin has a propensity to cause profound cochlear hair cell damage, marked high-frequency hearing loss, and complete deafness. The damaging effect is primarily to the cochlea, while the vestibular system is usually spared injury. Kanamycin has limited clinical use today. As with neomycin, parenteral administration is generally not recommended.

• Amikacin: Amikacin is a derivative of kanamycin and has very little vestibular toxicity. Its adverse effects primarily involve the auditory system; however, it is considered less ototoxic than gentamicin. In the treatment of severe infections, amikacin is mainly indicated on the basis of results of susceptibility tests and patient response.

ENT drugs , Medicine for Ear infections

Reference  : Pubmed Website