Consumer medicine information

Myambutol

Ethambutol hydrochloride

BRAND INFORMATION

Brand name

Myambutol

Active ingredient

Ethambutol hydrochloride

Schedule

S4

 

Consumer medicine information (CMI) leaflet

Please read this leaflet carefully before you start using Myambutol.

What is in this leaflet

This leaflet answers some common questions about MYAMBUTOL. It does not contain all the available information. It does not take the place of talking to your doctor or pharmacist.

All medicines have risks and benefits. Your doctor has weighed the risks of you taking MYAMBUTOL against the benefits this medicine is expected to have for you.

If you have any questions about taking this medicine, ask your doctor or pharmacist.

Keep this leaflet. You may need to read it again.

What MYAMBUTOL is used for

The name of your medicine is MYAMBUTOL. It contains the active ingredient ethambutol.

MYAMBUTOL is an antibiotic which is used to treat all forms of tuberculosis (including tuberculosis of the lung, skin, genital tract, urinary tract, bone and joint, eye and the brain). Importantly, MYAMBUTOL will not cure any other bacterial, viral or fungal diseases.

Your doctor may have prescribed MYAMBUTOL for another purpose.

Ask your doctor if you have any questions about why it has been prescribed for you.

This medicine is available only with a doctor's prescription.

MYAMBUTOL is not addictive.

Before you take it

When you must not take it:

Do not take MYAMBUTOL if:

  • you have ever had an allergic reaction to ethambutol, or any of the ingredients listed at the end of this leaflet
    Some of the symptoms of an allergic reaction to a ethambutol may include rash, itching or hives on the skin, swelling of the face, lips, tongue or other parts of the body, shortness of breath, wheezing or troubled breathing.
  • the expiry date (EXP) printed on the pack has passed.
    It may have no effect at all, or worse, an entirely unexpected effect, if you take it after the expiry date.
  • the packaging is torn or shows signs of tampering. If this is the case, take the tablets back to your pharmacist.

Before you start to take it

You should notify your doctor if you have or have had any eye problems as MYAMBUTOL may affect your eyesight. If you feel your eyesight is being affected (for example your vision becomes blurred) please consult your doctor immediately.

If your daily dose is 15 mg/kg of bodyweight or more, you should arrange with your doctor to have monthly eye examinations.

You must tell your doctor if you have any other medical problems, especially kidney disease or gout. The dose of MYAMBUTOL may need to be changed for you.

There is no evidence of any harmful effects to unborn babies when MYAMBUTOL is taken by pregnant women, however if you are pregnant you must inform your doctor.

Taking other medicines

Tell your doctor if you are taking any other medicines, including medicines you buy without a prescription from a pharmacy, supermarket or health food shop.

There may be interference between MYAMBUTOL and some other medicines. These medicines may be affected by MYAMBUTOL or may affect how well it works. You may need to take different amounts of your medicine or you may need to take different medicines.

If you have not told your doctor or pharmacist about any of the above, tell them before you start taking MYAMBUTOL.

How to take it

MYAMBUTOL will be prescribed with other anti-tuberculosis drugs. Your doctor will decide on the best combination of drugs for you to take.

MYAMBUTOL tablets should be taken once every 24 hours with or without food.

The size of the dose to be taken will depend on whether you have previously received treatment for tuberculosis. It also depends on your bodyweight.

It can take up to 2 years of treatment with MYAMBUTOL to cure you of tuberculosis. It is important that you keep taking the medicine for the full time of treatment. Do not stop taking it if you start feeling better. You must have regular checkups.

Follow all directions given to you by your doctor or pharmacist carefully. They may differ from the information contained in this leaflet.

If you do not understand the instructions on the bottle, ask your doctor or pharmacist for help.

Initial Treatment
If you have not been treated for tuberculosis before, the usual dose is 15 mg/kg of bodyweight of MYAMBUTOL to be taken as a single dose once every 24 hours.

Re-Treatment
If you have been treated for tuberculosis before, the usual dose is 25 mg/kg of bodyweight of MYAMBUTOL to be taken as a single dose, once every 24 hours. After 60 days the dose will be lowered to 15 mg/kg of bodyweight.

These dosages may be changed by your doctor.

Take MYAMBUTOL tablets with a glass of water.

How long to take it

Continue taking it until your doctor tells you to stop.

If you forget to take it

If it is almost time for your next dose, skip the dose you missed and take your next dose when you are meant to. Otherwise, take it as soon as you remember, then go back to taking it as you would normally.

Do not try to make up for missed doses by taking more than one dose at a time.

If you are not sure what to do, ask your doctor or pharmacist.

If you have trouble remembering to take your medicine, ask your pharmacist for some hints.

If you take too much (overdose)

Immediately telephone your doctor or Poisons Information Centre (telephone 13 11 26) for advice, or go to Accident and Emergency at your nearest hospital if you think you or anyone else may have taken too much MYAMBUTOL. Do this even if there are no signs of discomfort or poisoning. You may need urgent medical attention.

While you are taking it

Things you must do:

If you are about to start taking any new medicines, tell your doctor or pharmacist that you are taking MYAMBUTOL.

If you become pregnant while taking MYAMBUTOL, tell your doctor immediately.

Things you must not do:

Do not give this medicine to anyone else, even if their symptoms seem similar to yours.

Do not use MYAMBUTOL to treat any other medical complaints unless told to by your doctor.

Things to be careful of:

Only use MYAMBUTOL at the times and doses recommended by your doctor.

Side Effects

Tell your doctor or pharmacist as soon as possible if you do not feel well while you are taking MYAMBUTOL.

MYAMBUTOL is effective in most people, but may have unwanted side effects in some. All medicines can have side effects. Sometimes they are serious, most of the time they are not. You may need medical treatment if you get some of the side effects.

About 3% of patients treated with MYAMBUTOL find that their vision becomes blurred. This effect however is generally reversible if the treatment is stopped promptly. If you feel you have had any deterioration in your eyesight since starting MYAMBUTOL please contact your doctor immediately.

MYAMBUTOL may cause allergic reactions, dermatitis, pain in the joints, loss of appetite, nausea, vomiting, upset stomach, fever, headache, dizziness, mental confusion, disorientation, possible hallucinations and numbness and tingling in the feet and hands. MYAMBUTOL may aggravate gout.

Medicines can have different effects on different people. The above list of side effects may be incomplete.

This is not a complete list of all possible side effects. Others may occur in some people and there may be some side effects not yet known.

Tell your doctor if you notice anything else that is making you feel unwell, even if it is not on this list.

Ask your doctor or pharmacist if you do not understand anything in this list.

Do not be alarmed by this list of possible side effects. You may not experience any of them.

After using it

Storage

Keep this medicine where young children cannot reach it. A locked cupboard at least one-and-a-half metres above the ground is a good place to store medicines.

Keep MYAMBUTOL in a cool, dry place where it stays below 25ºC. Do not store it, or any other medicine, in a bathroom or near a sink.

Do not leave it in the car or on window sills. Heat and dampness can destroy some medicines.

Disposal

If your doctor tells you to stop taking MYAMBUTOL, or the tablets have passed their expiry date, ask your pharmacist what to do with any left over.

Product description

MYAMBUTOL is supplied as either a 100 mg or 400 mg tablet in a white plastic bottle in two pack sizes; 56’s and 100’s.

What it looks like

MYAMBUTOL 100 mg tablets are round, glossy and yellow with no markings.

MYAMBUTOL 400 mg tablets are round and non-glossy white to off white with no markings.

Ingredients

MYAMBUTOL 100 mg tablets contain 100 mg of ethambutol hydrochloride as the active ingredient. It also contains:

  • Sucrose
  • Gelatin
  • Sorbitol solution
  • Magnesium stearate
  • Stearic acid
  • Shellac
  • Purified talc
  • Quinoline yellow CI47005
  • Povidone
  • Acetylated monoglyceride

MYAMBUTOL 400 mg tablets contain 400 mg of ethambutol hydrochloride as the active ingredient. It also contains:

  • Calcium hydrogen phosphate
  • Gelatin
  • Sorbitol
  • Magnesium Stearate
  • Maize starch
  • Ethyl cellulose
  • Hypromellose
  • Polyethylene glycol
  • Titanium dioxide

Manufacturer

MYAMBUTOL is supplied in Australia by:

Aspen Pharma Pty Ltd
34-36 Chandos Street
St Leonards NSW 2065
Australia

This leaflet was last revised in December 2008.

® Registered Trademark

Australian Registration Numbers:

MYAMBUTOL 100 mg tablets - AUST R 47887

MYAMBUTOL 400 mg tablets - AUST R 147246

Published by MIMS February 2021

BRAND INFORMATION

Brand name

Myambutol

Active ingredient

Ethambutol hydrochloride

Schedule

S4

 

1 Name of Medicine

Ethambutol hydrochloride.

2 Qualitative and Quantitative Composition

Myambutol 100 mg tablets.

Each tablet contains ethambutol hydrochloride equivalent to 100 mg ethambutol.

Myambutol 400 mg tablets.

Each tablet contains ethambutol hydrochloride equivalent to 400 mg ethambutol.
For the full list of excipients, see Section 6.1 List of Excipients.

3 Pharmaceutical Form

Myambutol ethambutol hydrochloride tablets 100 mg 56's, are yellow tablets, glossy, round, standard biconvex, 5/16" diameter.
Myambutol ethambutol hydrochloride tablets 400 mg 56's, are white to off-white smooth round, biconvex, film coated tablets plain on both the sides.

4 Clinical Particulars

4.1 Therapeutic Indications

Oral administration.

Myambutol is indicated for the treatment of pulmonary tuberculosis, as shown by a large number of studies by investigators throughout the world. It has also been used successfully in cases of primary tuberculosis and extrapulmonary forms of tuberculosis including miliary tuberculosis, tuberculous meningitis, tuberculosis of bones and joints, genitourinary tuberculosis, tuberculosis of the skin and tuberculous eye diseases. It should not be used as the sole antituberculosis drug, but should be used in conjunction with at least one other antituberculosis drug. Selection of the companion drug should be based on clinical experience, considerations of comparative safety and appropriate in vitro susceptibility studies.
In patients who have not received previous antituberculosis therapy, i.e. initial treatment, the most frequently used regimens have included three of the following drugs: Myambutol, isoniazid, rifampicin and streptomycin for the first 2-4 months; for example, Myambutol plus isoniazid plus rifampicin, or Myambutol plus isoniazid plus streptomycin, then continuing with a two drug regimen such as Myambutol plus isoniazid, or Myambutol plus rifampicin.
In patients who have received previous antituberculosis therapy, mycobacterial resistance to other drugs used in initial therapy is frequent. Consequently, in such retreatment cases, Myambutol should be combined with at least one of the second line drugs not previously administered to the patient and to which bacterial susceptibility has been indicated by appropriate in vitro studies. Antituberculosis drugs used with Myambutol 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 utilised.

4.2 Dose and Method of Administration

Oral.

Myambutol should not be used alone, in initial treatment or in retreatment. Myambutol should be administered on a once every 24 hour basis only. Absorption is not significantly altered by administration with food. In general, therapy should be continued until bacteriological conversion has become permanent and maximal clinical improvement has occurred.

Initial treatment.

In patients who have not received previous antituberculosis therapy, administer Myambutol 15 mg/kg (7 mg/lb) body weight, as a single oral dose once every 24 hours. In the more recent studies, isoniazid has been administered concurrently in a single, daily, oral dose.

Retreatment.

In patients who have received previous antituberculosis therapy, administer Myambutol 25 mg/kg (11 mg/lb) body weight, as a single oral dose once every 24 hours. Concurrently administer at least one other antituberculosis drug to which the organisms have been demonstrated to be susceptible by an appropriate in vitro test. Suitable drugs usually consist of those not previously used in the treatment of the patient. After 60 days of Myambutol administration, decrease the dose to 15 mg/kg (7 mg/lb) 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.

Intermittent therapy.

An alternative method of administration, in both initial treatment and retreatment cases, is to give the abovementioned daily dosage of 15 or 25 mg/kg/day for two months or longer, depending on the type and extent of disease and the bacteriological and roentgenographic response (or until at least one negative sputum is obtained). Thereafter, Myambutol may be given in a dosage of 50 mg/kg twice weekly. When isoniazid is administered concomitantly, the usual dosage is 14 mg/kg twice weekly with 10 mg of pyridoxine for each 100 mg of isoniazid.
The usual daily dosage of isoniazid in adults is 300 mg, or 5 mg/kg on the basis of body weight. In children the usual daily dosage is 5 to 20 mg/kg. See Table 1.

4.3 Contraindications

Myambutol is contraindicated in patients who are known to be hypersensitive to this drug. It is also contraindicated in patients with known optic neuritis unless clinical judgement determines that it may be used.
No absolute contraindications to the administration of ethambutol have been reported.

4.4 Special Warnings and Precautions for Use

Changes in visual acuity.

Because this drug may have adverse effects on vision, physical examination should include ophthalmoscopy, finger perimetry and testing of colour discrimination. In patients with visual defects such as cataract, recurrent inflammatory conditions of the eye, optic neuritis and diabetic retinopathy, the evaluation of changes in visual acuity is more difficult, and care should be taken to be sure the variations in vision are not due to the underlying disease conditions. In such patients, consideration should be given to the relationship between benefits expected and possible visual deterioration, since evaluation of visual changes is difficult. (For recommended procedures, see Section 4.8 Adverse Effects (Undesirable Effects)).

Assessment of organ function.

As with any potent drug, periodical assessment of organ functions, including the renal, hepatic and haematopoietic systems, should be made during long-term therapy.

Use in renal impairment.

Reduction of dosage, as determined by serum level of Myambutol, should be made in patients with decreased renal function since the main path of excretion is by the kidneys.

Use in the elderly.

No data available.

Paediatric use.

No data available.

Effects on laboratory tests.

No data available.

4.5 Interactions with Other Medicines and Other Forms of Interactions

No data available.

4.6 Fertility, Pregnancy and Lactation

Effects on fertility.

No data available.
(Category A)
When pregnant mice or rabbits were treated with high doses of ethambutol hydrochloride, foetal mortality was slightly but not significantly (P < 0.05) increased. Female rats treated with ethambutol hydrochloride displayed slight but insignificant (P < 0.05) decreases in fertility and litter size.
In foetuses born of mice treated with high doses of ethambutol hydrochloride during pregnancy, low incidences of cleft palate, exencephaly and abnormality of the vertebral column were observed. Minor abnormalities of the cervical vertebrae 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 foetuses with monophthalmia, one with a shortened right forearm accompanied by bilateral wrist joint contracture and one with harelip and cleft palate.
 No data available.

4.7 Effects on Ability to Drive and Use Machines

The effects of this medicine on a person's ability to drive and use machines were not assessed as part of its registration.

4.8 Adverse Effects (Undesirable Effects)

Myambutol may produce decreases in visual acuity which appear to be due to optic neuritis. This effect may be related to dose and duration of treatment. Incidence with the recommended dosage has averaged about 2 to 3% of patients. This effect is generally reversible when administration of the drug is discontinued promptly. In rare cases recovery may be delayed for up to one year or more. Irreversible blindness has been reported.
Optic neuropathy including optic neuritis or retrobulbar neuritis occurring in association with Myambutol therapy may be characterised by one or more of the following events: decreased visual acuity, scotoma, colour blindness, and/or visual defect. These events have also been reported in the absence of a diagnosis of optic or retrobulbar neuritis.
Patients should be advised to report promptly to their physician any change in visual acuity.
The change in visual acuity may be unilateral or bilateral and hence each eye must be tested separately and both eyes tested together. Testing of visual acuity should be performed before beginning Myambutol therapy and periodically during drug administration, except that it should be done monthly when a patient is on a dosage of more than 15 mg/kg/day. Snellen eye charts 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 Myambutol.
The following table (Table 2) may be useful in interpreting possible changes in visual acuity attributable to Myambutol.
In general, changes in visual acuity less than those shown in Table 2 may be due to chance variation, limitations of the testing method or physiological variability. Conversely, changes in visual acuity equalling or exceeding those shown in the table 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, Myambutol should be discontinued and the patient re-evaluated at frequent intervals. Progressive decreases in visual acuity during therapy must be considered to be due to Myambutol. If corrective glasses are used prior to treatment, these must be worn during visual acuity testing. During one to two 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. When visual abnormality develops during treatment, patients may have subjective visual symptoms before, or simultaneously with, the demonstration of decreases in visual acuity, and all patients receiving Myambutol 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 Myambutol again after such recovery without recurrence of loss of visual acuity.
Other adverse reactions reported include anaphylactoid reaction, dermatitis, pruritus, joint pain, anorexia, nausea, vomiting, gastrointestinal upset, abdominal pain, fever, malaise, headache, dizziness, mental confusion, disorientation and possible hallucinations. Numbness and tingling of the extremities due to peripheral neuritis have been reported infrequently.
Rarely, Stevens-Johnson syndrome, toxic epidermal necrolysis. One case of reversible thrombocytopenia has been reported.
Elevated serum uric acid levels and precipitation of acute gout have been reported. Pulmonary infiltrates and eosinophilia also have been reported during Myambutol therapy. Transient impairment of liver function, as indicated by abnormalities in liver function tests, is not an unusual finding. Since Myambutol is used in conjunction with one or more other antituberculosis drugs, these changes may be related to the concurrent therapy. Moreover, extensive tests of liver function led to the conclusion that Myambutol, when given in recommended doses even for prolonged periods, does not cause hepatic damage.

Reporting suspected adverse effects.

Reporting suspected adverse reactions after registration of the medicinal product is important. It allows continued monitoring of the benefit-risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions at www.tga.gov.au/reporting-problems.

4.9 Overdose

For information on the management of overdose, contact the Poisons Information Centre on 13 11 26 (Australia).

5 Pharmacological Properties

5.1 Pharmacodynamic Properties

Mechanism of action.

Myambutol is an oral chemotherapeutic agent that is specifically effective against actively growing microorganisms of the genus Mycobacterium, including Mycobacterium tuberculosis.
Myambutol diffuses into actively growing Mycobacterium cells such as tubercle bacilli. Myambutol 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.
Myambutol 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 Myambutol have been uniformly sensitive to concentrations of 8 microgram/mL or less, depending on the nature of the culture media. When Myambutol has been used alone for treatment of tuberculosis, tubercle bacilli from these patients have developed resistance to Myambutol as shown 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 Myambutol and other antituberculosis drugs has been reported. Myambutol has reduced the incidence of the emergence of mycobacterial resistance to isoniazid when both drugs have been used concurrently.
An agar diffusion microbiological assay, based upon inhibition of Mycobacterium smegmatis (ATCC 607) may be used to determine concentrations of Myambutol in serum and urine. This technique has not been published, but further information can be obtained upon inquiry to Lederle Laboratories.

Animal pharmacology.

Toxicological studies in dogs given high doses for long periods revealed evidence of myocardial damage and failure, as well as depigmentation of the tapetum lucidum of the eye, the significance of which is not known. Degenerative changes in the central nervous system, apparently not dose related, have also been noted in dogs receiving ethambutol hydrochloride over a prolonged period.
In the rhesus monkey, neurological signs appeared after treatment with high doses given daily over a period of several months. These were correlated with specific serum levels of ethambutol hydrochloride and with definite neuroanatomical changes in the central nervous system. Focal interstitial carditis was also noted in monkeys which received ethambutol hydrochloride in high doses for a prolonged period.

Clinical trials.

No data available.

5.2 Pharmacokinetic Properties

Absorption and distribution.

Myambutol, following a single oral dose of 25 mg/kg of body weight, attains a peak of 2 to 5 microgram/mL in serum 2 to 4 hours after administration. When the drug is administered daily for longer periods of time at this dose, serum levels are similar. The serum level of Myambutol falls to undetectable levels by 24 hours after the last dose, except in some patients with abnormal renal function. The intracellular concentrations of erythrocytes reach peak values approximately twice those of plasma and maintain this ratio throughout the 24 hours.

Metabolism and excretion.

During the 24 hour period following oral administration of Myambutol, approximately 50% of the initial dose is excreted unchanged in the urine, while an additional 8 to 15% appears in the form of metabolites. The main path of metabolism appears to be an initial oxidation of the alcohol to an aldehydic intermediate, followed by conversion to a dicarboxylic acid. From 20 to 22% of the initial dose is excreted in the faeces 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.

5.3 Preclinical Safety Data

Genotoxicity and carcinogenicity.

No data available.

6 Pharmaceutical Particulars

6.1 List of Excipients

The inactive ingredients in Myambutol 100 mg tablets contain: sucrose, gelatin, sorbitol solution (70 per cent) (non-crystallising), magnesium stearate and stearic acid, shellac, purified talc, purified water, quinoline yellow and Opaglos.
The inactive ingredients in Myambutol 400 mg tablets are: gelatin, magnesium stearate, sorbitol, calcium hydrogen phosphate dihydrate, maize starch, ethylcellulose, hypromellose, macrogol 6000 and titanium dioxide.

6.2 Incompatibilities

Incompatibilities were either not assessed or not identified as part of the registration of this medicine.

6.3 Shelf Life

In Australia, information on the shelf life can be found on the public summary of the Australian Register of Therapeutic Goods (ARTG). The expiry date can be found on the packaging.

6.4 Special Precautions for Storage

Myambutol 100 mg tablets.

Store below 25 degrees Celsius. Protect from moisture.

Myambutol 400 mg tablets.

Store below 30 degrees Celsius. Protect from moisture.

6.5 Nature and Contents of Container

Myambutol 100 mg tablets are stored in a LDPE bottle with a polypropylene child resistant cap.
Myambutol 400 mg tablets are stored in a HDPE bottle with a yellow wadless polypropylene cap.

6.6 Special Precautions for Disposal

In Australia, any unused medicine or waste material should be disposed of by taking to your local pharmacy.

6.7 Physicochemical Properties

Ethambutol hydrochloride is a white crystalline powder that is freely soluble in water, soluble in alcohol and methanol, and very slightly soluble in ether and in chloroform. A 2% solution in water has a pH of 3.7 to 4.0.
The chemical formula of ethambutol hydrochloride is (+)-2,2'(Ethylenediimino)-di-1-butanol dihydrochloride.
Molecular formula: C10H24N2O2,2HCl and molecular weight = 277.2.

Chemical structure.

The structural formula of ethambutol hydrochloride is:

CAS number.

1070-11-7.

7 Medicine Schedule (Poisons Standard)

S4 (Prescription Only Medicine).

Summary Table of Changes