Ethambutol dosing

Orally administered ethambutol is well absorbed (70-80%) from the gut, and peak serum concentrations are obtained within 2 to 4 hours of drug administration it has a half-life of 3 to 4 hours. Ethambutol is widely distributed in all body fluids, including the cerebrospinal fluid, even in the absence of inflammation. A majority of the unchanged drug is excreted in the urine within 24 hours of ingestion. Up to 15% is excreted in the urine as an aldehyde and a dicarboxylic acid metabolite. Ethambutol doses may have to be modified in patients with renal failure. 

Ethambutol should not be given with antacids. The ethambutol dose should be reduced to three times per week in patients with renal failure. Retrobulbar neuritis is the major adverse effect. Patients may complain of a change in visual acuity, the inability to see the color green, or both. They should be monitored monthly while on the drug using Snellen wall charts for visual acuity and Ishihara red-green color discrimination cards. ... 

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 Take this drug once a day at the same time each day. If a dose is missed, do not double the dose the next day. Notify the primary health care provider of any changes in vision or the occurrence of a skin rash. 

Which of the following is a dose-related adverse reaction to ethambutol ... 

Because they are hepatically cleared, isoniazid and rifampin do not require dose modification in renal failure.31,36,39 Pyrazinamide and ethambutol typically are reduced to three times weekly to avoid accumulation of the parent drug (ethambutol) or metabolites (pyrazinamide).28,31 Renally cleared TB drugs include the aminoglycosides (e.g., amikacin, kanamycin, and streptomycin), capreomycin, ethambutol, cycloserine, and lev-ofloxacin.28,31,33,39 Dosing intervals need to be extended for... 

The answer is e. (Katzung, p 807.) Retrobulbar neuritis can occur with the use of ethambutol. It is dose related and typically occurs with prolonged therapy. The drug is not recommended for young children whose symptoms may not be easily assessed. 

Clarilhromycin 500 mg orally twice daily, plus ethambutol 15 mg/kg/day orally (Al), and For advanced disease, rifabutin 300 rng/day (dose may need adjustment with ART) (Al) ... 

Table 49-4 lists options for treatment of culture-positive pulmonary TB caused by drug-susceptible organisms. Doses of antituberculosis drugs are given in Table 49-5. The standard TB treatment regimen INH, RIF, pyrazinamide, and ethambutol for 2 months followed by INH and RIF for 4 months. 

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. 

In nearly all patients, INH and RIF do not require dose modifications in renal failure. Pyrazinamide and ethambutol typically require a reduction in dosing frequency from daily to three times weekly (Table 49-6). 

Ethambutol Yes 15-25 mj kg per dose three times per week (not daily)... 

EthambutoL The cause of its specific antitubercular action is unknown. Ethambutol is given orally. It is generally well tolerated, but may cause dose-dependent damage to the optic nerve with disturbances of vision (red/green blindness, visual field defects). 

Treatment of disseminated MAC infections 600 mg/day in combination with ethambutol at the recommended daily dose of 15 mg/kg. 

HIV - The initial phase of a 6-month tuberculosis regimen consists of isoniazid, rifabutin, pyrazinamide, and ethambutol for patients receiving therapy with protease inhibitors or nonnucleoside reverse transcriptase inhibitors. These drugs are administered a) daily for at least the first 2 weeks, followed by twice weekly dosing for 6 weeks or b) daily for 8 weeks to complete the 2-month induction phase. The second phase of treatment consists of rifabutin and isoniazid administered twice weekly or daily for 4 months. 

Following a single oral dose of 15 to 25 mg/kg, ethambutol attains a peak of 2 to 5 mcg/mL in serum 2 to 4 hours after administration. Serum levels are similar after prolonged dosing. The serum level is undetectable 24 hours after the last dose except in some patients with abnormal renal function. 

Ethambutol (Myambutel) [Antitubercular Agent] Uses Pulm TB other mycobacterial Infxns, MAC Action i RNA synth Dose Adults Feds >12 y. 15-25 mg/kg/d PO single dose X in renal impair, take w/ food, avoid antacids Caution [B, +] Contra Unconscious pts, optic neuritis Disp Tabs SE HA, hyperuricemia, acute gout, abd pain, T LFTs, optic neuritis, GI upset Interactions T Neurotox W/ neurotoxic drugs X effects W/ A1 salts EMS May affect glucose (hypoglycemia) may cause vision problems OD Sxs unknown activated charcoal may be effective symptomatic and supportive... 

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. 

Do not skip drug doses and take ethambutol for the full course of therapy, which may be months or years... 

Fixed dose combination of ethambutol with INH other than the following ... 

Ethambutol hydrochloride, 15-25 mg/kg, is usually given as a single daily dose in combination with isoniazid or rifampin. The higher dose is recommended for treatment of tuberculous meningitis. The dose of ethambutol is 50 mg/kg when a twice-weekly dosing schedule is used. 

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 Inhibits mycobacterial arabinosyl transferases, which are involved in the polymerization reaction of arabinoglycan an essential component of the mycobacterial cell wall Bacteriostatic activity against susceptible mycobacteria Given as four-drug initial combination therapy for tuberculosis until drug sensitivities are known also used for atypical mycobacterial infections Oral t mixed clearance (half-life 4 h) dose must be reduced in renal failure Toxicity Retrobulbar neuritis... 

ETHAMBUTOL ANTIVIRALS-DIDANOSINE Possibly t adverse effects (e.g. peripheral neuropathy) with didanosine Additive side-effects Monitor closely for development of peripheral neuropathy but no dose adjustment is required... 

Dose. 15 to 25 mg/kg of ethambutol hydrochloride daily 50 mg/ kg has been given twice weekly. 

The optic nerve is of interest here because some drugs are toxic to this tissue.The antibiotics chloramphenicol, ethambutol, streptomycin, and sulfonamides can cause optic neuritis. Vitamin A, especially in large doses, can result in papilledema. Digitalis can cause retrobulbar neuritis (see Chapter 35). 

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