Ethambutol hydrochloride is a primary antitubercular agent, which inhibits the synthesis of metabolites resulting in impairment of cell metabolism, arrest of multiplication, and ultimately cell death. It is active against Mycobacterium tuberculosis but not against fungi, other bacteria, or viruses. It is used in Pulmonary tuberculosis in combination with other tuberculostatic drugs (ritampicin and/or isoniazid) .
It is contraindicated in patients with hypersensitivity to ethambutol, pre-existing optic neuritis, and in children under 13 years of age.
It should be used with caution and in reduced dosage in clients with gout and impaired renal function and in pregnant women.
Its' side effects may include:
Ophthalmologic: Optic neuritis (possible oedematous and hyperaemic disc with splinter haemorrhages), decreased visual acuity (reduced contrast sensitivity, VEP), loss of colour (green or blue yellow) discrimination, visual field changes (annular, central, centrocaecal or hemianopias), photophobia, temporary loss of vision or blurred vision.
Gastro Intestinal: Nausea and vomitting, anorexia, abdominal pain.
CNS: Fever, headache, dizziness, confusion, disorientation, malaise, hallucinations. Allergic: Pruritus, dermatitis, anaphylaxis.
Miscellaneous: Peripheral neuropathy (numbness, tingling), precipitation of gout, thrombocytopenia, joint pain, toxic epidermal necrolysis. Renal damage. Also anaphylactic shock, peripheral neuritis (rare), hyperuricemia, and decreased liver function.
Adverse symptoms usually appear during the early months of therapy and disappear thereafter. Periodic renal and hepatic function tests as well as uric acid determinations are recommended.
Drug Interactions: Aluminum may delay and decrease the absorption of ethambutol.
Adults, initial treatment: 15 mg/kg/day until maximal improvement noted; for retreatment: 25 mg/kg/day as a single dose with at least one other tuberculostatic drug; after 60 days: 15 mg/kg/day.
The protocol for screening patients on Ethambutol
1. Referrals received from the prescribing Department
2. Appointment with an optometrist arranged within two weeks of receiving the referral
3. The following procedures to be carried out by the optometrist:-
- Distance and near visual acuity recorded for each eye
- Refraction details recorded
- Details of medication recorded including dosage and duration of use
- Symptoms of any impaired vision recorded, including distortion, reduced VA, field defect and glare.
- Central visual field Amsler chart assessment using a red grid on a black background
- Monocular assessment of colour vision using the Ishihara test
- Slit lamp examination
- Assessment of macular changes using direct ophthalmoscopy/Volk lens assessment
- OCT imaging if required
4. Patients showing any abnormality to be seen in Consultant Ophthalmologist's clinic within one month, otherwise no further appointment to be given.