ro studies. antituberculous drugs used with ethambutol have included cycloserine, ethionamide, pyrazinamide, viomycin and other drugs. isoniazid, aminosalicylic acid, and streptomycin have also been used in multiple drug regimens. alternating drug regimens have also been utilized.

mg/lb) of body weight, as a single oral dose once every 24 hours. concurrently administer at least one other antituberculous drug to which the organisms have been demonstrated to be susceptible by appropriate in-vitro tests. suitable drugs usually consist of those not previously used in the treatment of the patient. after 60 days of ethambutol hydrochloride administration, decrease the dose to 15 mg/kg (7 mg/lb) of body weight, and administer as a single oral dose once every 24 hours. during the period when a patient is on a daily dose of 25 mg/kg, monthly eye examinations are advised. see table for easy selection of proper weight-dose tablet(s). weight-dose table 15 mg/kg (7 mg/lb) schedule weight range daily dose pounds kilograms --------------------------------- in mg under 85 lbs. under 37 kg --------------------------------- 500 85 – 94.5 37 – 43 --------------------------------- 600 95 – 109.5 43 – 50 --------------------------------- 700 110 – 124.5 50 – 57 --------------------------------- 800 125 – 139.5 57 – 64 --------------------------------- 900 140 – 154.5 64 – 71 --------------------------------- 1000 155 – 169.5 71 – 79 --------------------------------- 1100 170 – 184.5 79 – 84 --------------------------------- 1200 185 – 199.5 84 – 90 --------------------------------- 1300 200 – 214.5 90 – 97 --------------------------------- 1400 215 and over over 97 --------------------------------- 1500 25 mg/kg (11 mg/lb) schedule under 85 lbs. under 38 kg --------------------------------- 900 85 – 92.5 38 – 42 --------------------------------- 1000 93 – 101.5 42 – 45.5 --------------------------------- 1100 102 – 109.5 45.5 – 50 --------------------------------- 1200 110 – 118.5 50 – 54 --------------------------------- 1300 119 – 128.5 54 – 58 --------------------------------- 1400 129 – 136.5 58 – 62 --------------------------------- 1500 137 – 146.5 62 – 67 --------------------------------- 1600 147 – 155.5 67 – 71 --------------------------------- 1700 156 – 164.5 71 – 75 --------------------------------- 1800 165 – 173.5 75 – 79 --------------------------------- 1900 174 – 182.5 79 – 83 --------------------------------- 2000 183 – 191.5 83 – 87 --------------------------------- 2100 192 – 199.5 87 – 91 --------------------------------- 2200 200 – 209.5 91 – 95 --------------------------------- 2300 210 – 218.5 95 – 99 --------------------------------- 2400 219 and over over 99 --------------------------------- 2500

harts are recommended for testing of visual acuity. studies have shown that there are definite fluctuations of one or two lines of the snellen chart in the visual acuity of many tuberculous patients not receiving ethambutol. the following table may be useful in interpreting possible changes in visual acuity attributable to ethambutol. initial snellen reading reading indicating significant decrease significant number of lines decrease number of points 20/13 20/25 3 12 20/15 20/25 2 10 20/20 20/30 2 10 20/25 20/40 2 15 20/30 20/50 2 20 20/40 20/70 2 30 20/50 20/70 1 20 in general, changes in visual acuity less than those indicated under "significant number of lines" and "decrease number of points", may be due to chance variation, limitations of the testing method or physiologic variability. conversely, changes in visual acuity equaling or exceeding those under "significant number of lines" and "decrease number of points" indicate the need for retesting and careful evaluation of the patient's visual status. if careful evaluation confirms the magnitude of visual change and fails to reveal another cause, ethambutol should be discontinued and the patient reevaluated at frequent intervals. progressive decreases in visual acuity during therapy must be considered to be due to ethambutol. if corrective glasses are used prior to treatment, these must be worn during visual acuity testing. during 1 to 2 years of therapy, a refractive error may develop which must be corrected in order to obtain accurate test results. testing the visual acuity through a pinhole eliminates refractive error. patients developing visual abnormality during ethambutol treatment may show subjective visual symptoms before, or simultaneously with, the demonstration of decreases in visual acuity, and all patients receiving ethambutol should be questioned periodically about blurred vision and other subjective eye symptoms. recovery of visual acuity generally occurs over a period of weeks to months after the drug has been discontinued. some patients have received ethambutol hydrochloride again after such recovery without recurrence of loss of visual acuity. other adverse reactions reported include: hypersensitivity, anaphylactic/anaphylactoid reaction, dermatitis, erythema multiforme, pruritus, and joint pain; anorexia, nausea, vomiting, gastrointestinal upset, and abdominal pain; fever, malaise, headache, and dizziness; mental confusion, disorientation, and possible hallucinations; thrombocytopenia, leucopenia, and neutropenia. numbness and tingling of the extremities due to peripheral neuritis have been reported. elevated serum uric acid levels occur and precipitation of acute gout has been reported. pulmonary infiltrates, with or without eosinophilia, also have been reported during ethambutol hydrochloride therapy. liver toxicities, including fatalities, have been reported. (see warnings ). since ethambutol hydrochloride is recommended for therapy in conjunction with one or more other antituberculous drugs, these changes may be related to the concurrent therapy. hypersensitivity syndrome consisting of cutaneous reaction (such as rash or exfoliative dermatitis), eosinophilia, and one or more of the following: hepatitis, pneumonitis, nephritis, myocarditis, pericarditis. fever and lymphadenopathy may be present.

rmalities of the cervical vertebra were seen in the newborn of rats treated with high doses of ethambutol hydrochloride during pregnancy. rabbits receiving high doses of ethambutol hydrochloride during pregnancy gave birth to two fetuses with monophthalmia, one with a shortened right forearm accompanied by bilateral wrist-joint contracture and one with hare lip and cleft palate.

is excreted in the feces as unchanged drug. no drug accumulation has been observed with consecutive single daily doses of 25 mg/kg in patients with normal kidney function, although marked accumulation has been demonstrated in patients with renal insufficiency. ethambutol diffuses into actively growing mycobacterium cells such as tubercle bacilli. ethambutol appears to inhibit the synthesis of one or more metabolites, thus causing impairment of cell metabolism, arrest of multiplication, and cell death. no cross resistance with other available antimycobacterial agents has been demonstrated. ethambutol has been shown to be effective against strains of mycobacterium tuberculosis but does not seem to be active against fungi, viruses, or other bacteria. mycobacterium tuberculosis strains previously unexposed to ethambutol have been uniformly sensitive to concentrations of 8 or less mcg/ml, depending on the nature of the culture media. when ethambutol has been used alone for treatment of tuberculosis, tubercle bacilli from these patients have developed resistance to ethambutol hydrochloride by in-vitro susceptibility tests; the development of resistance has been unpredictable and appears to occur in a step-like manner. no cross resistance between ethambutol and other antituberculous drugs has been reported. ethambutol has reduced the incidence of the emergence of mycobacterial resistance to isoniazid when both drugs have been used concurrently. an agar diffusion microbiologic assay, based upon inhibition of mycobacterium smegmatis (atcc 607) may be used to determine concentrations of ethambutol in serum and urines.