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| Pharmacovigilance of Anti Tuberculosis Drugs. |
Number of the medicines are used today to treat Tuberculosis (TB) and one should be well aware of their related adverse drug reactions (ADRs). Patients take more than one anti TB medicines simultaneously and treatment lasts from six months to two years or more. This increases the risk of drug reactions and most of these are severe. Drug regimen for drug resistance TB is more complex and hence pose more drug reactions. One of the consequences is the drug resistance TB.
Pharmacovigilance of Anti TB Drugs-Ethambutol
Number of the medicines are used today to treat Tuberculosis (TB) and one should be well aware of their related adverse drug reactions (ADRs). Patients take more than one anti TB medicines simultaneously and treatment lasts from six months to two years or more. This increases the risk of drug reactions and most of these are severe. Drug regimen for drug resistance TB is more complex and hence pose more drug reactions. Adverse drug reactions of Ethambutol and its management is as under.
Adverse Drug Effects (ADEs)
1-Ocular toxicity (eyes): Optic Neuritis
Clinical Presentation
- Blurred vision.
- Spot in the field of vision of patient.
- Red/green colour blindness.
Frequency/Characteristics
Rare and minor with a dose of 25mg/kg/day for 60 days, then reduced to 15mg/kg/day for the rest of therapy
- Optic neuritis has not been documented in children
- Dose related (↑ dose = ↑ ocular toxicity)
- Uncommon with intermittent therapy
- Generally reversible if ethambutol is discontinued with the start of initial symptoms
- There may be Permanent vision damage if ethambutol is continued after symptoms occur
Management
- Children with complaints of vision changes should be referred to the Tuberculosis Clinic for evaluation
- Discontinue ethambutol therapy.
2-Neurotoxicity (nervous system)
Clinical Presentation:
Peripheral neuropathy: prickling, tingling or burning sensation of the fingers and/or toes
Frequency/Characteristics
- Rare
- If a patient continues to experience peripheral neuropathy even after stop taking the isoniazid then consider the ethambutol as the causative agent.
Management
Refer to Peripheral Neuropathy Management.
3-Arthalgias (joint pain)
Clinical Presentation
- Symptoms: tenderness, pain and/or swelling of joints (usually mild).
- Signs: high serum uric acid concentrations secondary to inhibition of urate secretion
Frequency/Characteristics:
- Most of patients develop mild hyperuricemia while taking ethambutol.
- Acute gouty arthritis is rare.
Management: Refer to Arthralgia Management Unit
4-Hypersensitivity (immune mediated reaction).
Clinical Presentation
- hives (raised, itchy rash)
- fever may occur Frequency/Characteristics2 very rare
Management: Refer to the Hypersensitivity Management Unit
Drug Interactions
Antacids (Aluminium and magaldrate containing)
- Results in decreased ethambutol absorption
- Separate administration times by > 2 hours
Monitoring of ADEs
- Symptom assessment
- Measurement of baseline visual acuity and red-green colour perception in adults
- On the basis on results of symptom assessment, repeat testing should be done
Recommendations: Baseline and monthly monitoring of visual acuity and colour vision.