A 45-year-old man has had low-dose aspirin secondary prophylaxis for more than a year following a s

Fråga: A 45-year-old man has had low-dose aspirin secondary prophylaxis for more than a year following a small cerebellar infarction. The aspirin dose was initially 125 mg daily but was later lowered to 75 mg. The patient has recovered satisfactorily but is now complaining of tinnitus, especially in the evenings. He has no complaints of hearing loss. Can low-dose aspirin treatment cause tinnitus?

Sammanfattning: Aspirin-induced tinnitus is a rather well-defined side-effect that seems to be reversible and dose dependent when using anti-inflammatory, and higher, doses. We have, however, found no studies evaluating the possible ototoxic effects of low-dose aspirin treatment, but such effects, if existent, are thought to be nonsignificant. In the present case, therefore, a causative relation seems less probable.

Svar: A recent and extensive review article (1) summarises the present knowledge concerning aspirin-induced ototoxicity, ie hearing loss and tinnitus. Both of these ototoxic effects are considered dose dependent and, in almost all cases, reversible after cessation of salicylate administration (1).

Hearing loss caused by salicylates is typically mild to moderate and bilaterally symmetric. The loss may be flat or more pronounced in the high frequencies (1). There is little evidence of permanent salicylate-induced hearing loss. Studies also differ significantly regarding the amount of hearing loss caused by aspirin and there seem to exist differences in sensitivity both between individuals and between species (1).

Although there is a low correlation between the effects of oral doses of aspirin and serum concentrations on hearing loss, some studies have found a high correlation between serum salicylate level and hearing loss (1). The findings in a recent study by Day et al (2), an investigation of the effects of 1.95 to 5.85 gram/day of aspirin on 8 normal subjects, also suggest that there is no minimum threshold concentration for ototoxicity, as was previously thought. In this study hearing loss was found to be linear between serum levels ranging from 50 to 400 mg/l (2).

Only a few investigators seem to have examined the relationship between tinnitus and serum salicylate concentrations (1). Previous studies have indicated that a threshold concentration of about 200 mg/l was required for tinnitus to develop (1). However, more recent studies conclude that tinnitus is not specific for such high salicylate concentrations (1,2). Day et al (2) also reported a continuous increase in the intensity of tinnitus over the range of concentrations studied (approximately 40-320 mg/l) although the data were said to be less consistent than those concerning hearing loss (2).

The concentrations achieved by anti-platelet doses of aspirin (below 500 mg/day) are frequently found to be below 10 mg/l (2). We have found no studies investigating the ototoxic effects of such low doses, but, according to (2), they would appear to be very low.

The mechanisms of salicylate ototoxicity are not fully understood but different effects on the outer or inner hair cells or on the cochlear blood supply have been discussed (1).