Visual acuity ethambutol

Optic neuritis (a decrease in visual acuity and changes in color perception), which appears to be related to the dose given and die duration of treatment, has occurred in some patients receiving ethambutol. Usually, tiiis adverse reaction disappears when the drug is discontinued. Other adverse reactions are dermatitis, pruritus, anaphylactoid reactions (unusual or exaggerated allergic reactions), joint pain, anorexia, nausea, and vomiting. 

ETHAMBUTOL The nurse monitors for any changes in visual acuity and promptiy reports any visual changes to tlie primary health care provider. Vision changes are usually reversible if tlie drug is discontinued as soon as symptoms appear. The patient may need assistance with ambulation if visual disturbances occur. Psychic disturbances may occur. If die patient appears depressed, withdrawn, noncommunicative, or has otiier personality changes, the nurse must report the problem to the primary health care provider. 

The drug can likely be used safely in older children but should be used with caution in children less than 5 years of age, in whom visual acuity cannot be monitored. In younger children, ethambutol at the dose of 15 mg/kg per day can be used if there is suspected or proven resistance to isoniazid or rifampin. 

Retrobulbar neuritis is the major adverse effect noted in patients treated with ethambutol. Patients usually complain of a change in visual acuity and/or inability to see the color green. Vision testing should be performed on all patients who must receive ethambutol for more than 2 months. 

The major toxicity associated with ethambutol use is retrobulbar neuritis impairing visual acuity and red-green color discrimination this side effect is dose related and reverses slowly once the drug is discontinued. Mild GI intolerance, allergic reaction, fever, dizziness, and mental confusion are also possible. Hyperuricemia is associated with ethambutol use due to a decreased renal excretion of urates gouty arthritis may result. 

Hypersensitivity to ethambutol is rare. The most common serious adverse event is retrobulbar neuritis, resulting in loss of visual acuity and red-green color blindness. This dose-related adverse effect is more likely to occur at dosages of 25 mg/kg/d continued for several months. At 15 mg/kg/d or less, visual disturbances are very rare. Periodic visual acuity testing is desirable if the 25 mg/kg/d dosage is used. Ethambutol is relatively contraindicated in children too young to permit assessment of visual acuity and red-green color discrimination. 

Ethambutol suppresses the growth of isoniazid- and streptomycin-resistant tubercle bacilli. The most important but not common side effects are optic neuritis, decreased visual acuity, and inability to perceive the color green. 

For instance, blurring of vision and diplopia are caused by the use of imipramine, iproniazid, chlorpromazine, thioridazine, and promethazine. Impairment of visual acuity is caused by chlorpropamide, tolbutamide, alcohol, chlorpromazine, phenylbutazone, indomethacin, chloroquine, sulfonamides, ethambutol, chloramphenicol, isonex, clioquinol, quinine, streptomycin, and paraaminosalicylate. Yellow vision (xanthopsia) has been traced to the use of sulfonamides, streptomycin, methaqualone, barbiturates, chlorothiazide,... 

Retrobulbar neuritis is the major adverse effect noted in patients treated with ethambutol, Patients usually complain of a change in visual acuity and/or inability to see the color green. Vision testing should be performed on all patients who must receive ethambutol for more than 2 months. Impairment of eighth cranial nerve function is the most important adverse effect of streptomycin, Vestibular function is most frequently affected, but hearing may also be impaired. Audiometric testing should be performed in patients who must receive streptomycin for more than 2 months. Streptomycin occasionally causes nephrotoxicity. 

Color vision deficiencies are probably the most sensitive indicator of early ethambutol optic neuropathy and can occur even before visual acuity and visual fields are affected. Sometimes, contrast sensitivity can be affected before either visual acuity or color vision becomes impaired. 

Once changes have occurred in visual acuity, visual field, or color vision, these functional changes may continue to deteriorate even after ethambutol has been discontinued. More often, however, there is recovery of pretreatment visual acuity and visual field several months or years after discontinuation of the drug. The degree of recovery depends largely on the extent to which ethambutol has compromised optic nerve function. If the ocular toxicity is not recognized early, the drug can cause permanent loss of vision, especially in older patients. 

The onset of visual loss can be sudden and dramatic, with color vision defects in the red-green or blue-yellow spectra, as well as variable field defects. In acute cases, disc edema is accompanied by sphnter hemorrhages. Retrobulbar neuritis with ethambutol can be predominantly axial, presenting with reduced visual acuity and central scotoma, or periaxial, with peripheral field defects. In non-acute tjrpes the fundi and discs appear normal (13). Visual defects can be unilateral or bilateral. 

A 40-year-old patient underwent unsuccessful cadaver kidney transplantation and was treated with ethambutol and isoniazid (27). Bilateral retrobulbar neuropathy with an unusual central bitemporal hemianopic scotoma developed and ethambutol was withdrawn, but there was only a small improvement. When isoniazid was also withdrawn, there was dramatic improvement in visual acuity. 

Ethambutol i Inhibits synthesis of arabinogalactan (cell-wall component) Dose-dependent retrobulbar neuritis visual acuity and red-green discrimination... 

Ethambutol is not recommended for children under 5 years of age, in part because of concern about the ability to test their visual acuity. Children from ages 6 to 12 years should receive 10 to 15 mg/kg per day. 

The use of ethambutol in the chemotherapy of tuberculosis is described in the following text. The most important side effect is optic neuritis, resulting in decreased visual acuity and loss of ability to differentiate red from green. The incidence of this reaction is proportional to the dose of ethambutol and is observed in 15% of patients receiving 50 mg/kg day, in 5% of patients receiving 25 mg/kg per day, and fewer than 1% of patients receiving daily doses of 15 mg/kg (the recommended dose for treatment of tuberculosis). The intensity of the visual difficulty is related to the duration of therapy after the decreased visual acuity first becomes apparent, and may be unilateral or bilateral. Tests of visual acuity and red-green discrimination prior to the start of therapy and periodically thereafter are thus... 

Ethambutol produces very few untoward reactions. Fewer than 2% of nearly 2000 patients who received daily doses of 15 mg/kg of ethambutol had adverse reactions 0.8% experienced diminished visual acuity, 0.5% had a rash, and 0.3% developed drug fever. Other side effects that have been observed are pruritus, joint pain, gastrointestinal upset, abdominal pain, malaise, headache, dizziness, mental confusion, disorientation, and possible hallucinations. Numbness and tingling of the fingers owing to peripheral neuritis are infrequent. Anaphylaxis and leukopeifia are rare. 

THERAPEUTIC USES Ethambutol (myambutol) has been used with notable success in the therapy of tuberculosis when given concurrently with isoniazid and largely has replaced aminosalicylic acid. Ethambutol is available for oral administration in tablets. The usual adult dose is 15 mg/kg given once a day. Some clinicians use 25 mg/kg/day for the first 60 days, followed by 15 mg/kg/day, particularly for those treated previously. Dose adjustment is necessary in patients with impaired renal function. Ethambutol is not recommended for children under 5 years of age because of concern about the ability to test their visual acuity. Children from ages 6-12 years should receive 10-15 mg/kg/day. 

Ocular toxicity due to ethambutol is dose-dependent and is usually reversible when the drug is discontinued. Thiamine is not protective. Periodic testing of visual acuity is advisable during treatment. Ethambutol is relatively contraindicated in children too young for assessment of their visual acuity and red-green color discrimination. The answer is (C). 

A 32-year-old Pakistani man developed bilateral, painless visual loss after taking ethambutol for 3 months. His visual acuities were 20/40... 

Reduced visual acuity and central or centro-cecal scotomas on visual field testing have been reported as the usual presentation of eth-ambutol-induced optic neuropathy. Bilateral temporal hemianopia has been reported in a case of ethambutol toxicity [64 ]. 

A 75-year-old woman developed progressively worse peripheral vision in both eyes after taking ethambutol 1200 mg/day for almost 1 year, plus clarithromycin and rifampicin for infection with Mycobacterium avium complex and Mycobacterium kansasii. Best corrected visual acuity was 20/80— in the right eye and 20/60-1-in the left eye. Eye movements were full. Slit lamp exam showed -1-1 nuclear sclerosis in both eyes. On fundoscopy the optic discs were not swollen or pale. A 30-2 Humphrey visual field showed bitemporal hemianopia. An MRI scan of the brain was normal, as was optical coherence tomography. 

In a retrospective study of 857 Korean patients who took ethambutol, 89 had impaired vision [65 ]. Ethambutol-induced optic neuropathy was diagnosed in during a mean follow-up period of 13 months. The average dose of ethambutol was 18 mg/kg/ day and the duration of therapy was 9.4 months. Ophthalmic findings included reduced visual acuity (n = 58), abnormal visual fields (n = 58), abnormal color vision (55), optic disc pallor (34), and increased latency on VEP tests (58). Slightly less than one-third of the patients had improved visual function after discontinuing ethambutol. The mean time to recovery was 5.4 months. However, no patient with optic disc pallor at the time of diagnosis had improved visual function. Renal dysfunction and the daily dose of ethambutol, but not the duration of treatment, contributed. The authors estimated the incidence of ethambutol-induced optic neuropathy in Koreans to be under 2%. Thus, visual function after withdrawal of ethambutol is reversible in only a minority of patients and does not occur if optic disc pallor is present. 

Two patients who developed reduced visual acuity after taking ethambutol for several months for Mycobacterium avium-intracellulare infection had bitemporal visual field defects that suggested damage to the optic chiasm [66 ]. 

In a prospective evaluation of various visual parameters for early detection of ethambutol toxicity in 52 patients with tuberculosis attending a Directly Observed Treatment Strategy Centre [67 visual acuity, visual fields, visual-evoked responses, stereoacuity, and retinal nerve fiber layer thickness on optical coherence tomography were assessed after 1 and 2 months of treatment, and 1 month after withdrawal. There was no visual functional defect at baseline. On follow-up, visual acuity, color vision. 

In a series of cases reported from Japan (40<=) 3 eyes out of a total of 58 with serious diminution of visual acuity showed no improvement 3 years after withdrawal of ethambutol. In the remainder those who received subconjunctival injection of corticosteroids recovered more rapidly than those who did not. 

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