In severe poisoning the main risk is of epileptiform convulsions.
The benefit of gastric decontamination is uncertain. Consider activated charcoal if the patient presents within 1 hour of ingestion of more than 20 mg/kg.
Consider gastric aspiration/lavage in adults within 1 hour of a potentially life-threatening overdose, providing the airway can be protected.
Treatment should be directed to the control of convulsions. Control convulsions initially with intravenous diazepam or lorazepam. Phenytoin is ineffective and not advised as Isoniazid tablets inhibits the metabolism of phenytoin. Large doses of pyridoxine may limit the occurrence of other adverse effects. Metabolic acidosis may require sodium bicarbonate infusion. The drug is removed by dialysis.
None known.
Side-effects have been reported mainly in association with high doses or in slow acetylators who develop higher blood levels of the drug.
Tabulated list of adverse reactions
Undesirable effects are listed by MedDRA System Organ Classes.
Assessment of undesirable effects is based on the following frequency groupings:
Very common: >1/10
Common: >1/100 to <1/10
Uncommon: >1/1,000 to <1/100
Rare: >1/10,000 to <1/1,000
Very rare: <1/10,000
Not known: cannot be estimated from the available data
| Blood and lymphatic system disorders | Not known: Agranulocytosis Anaemia including haemolytic, sideroblastic and aplastic Eosinophilia Thrombocytopenia |
| Immune system disorders | Not known: Lupoid syndrome |
| Metabolism and nutrition disorders | Not known: Pellagra Hyperglycaemia |
| Psychiatric disorders | Not known: Psychosis |
| Nervous system disorders | Not known: Peripheral neuropathy Optic neuritis Convulsions |
| Eye disorders | Not known: Optic atrophy |
| Vascular disorders | Not known: Vasculitis |
| Gastrointestinal disorders | Not known: Pancreatitis |
| Hepatobiliary disorders | Uncommon: Hepatitis Not known: Function liver abnormal Jaundice |
| Skin and subcutaneous tissue disorders | Rare: Toxic epidermal necrolysis Eosinophilia systemic symptoms Not known: Alopecia Allergic skin reaction (including erythema multiforme) Purpura Rash Exfoliative dermatitis |
| Reproductive system and breast disorders | Not known: Gynaeco-mastia |
| General disorders and administration site conditions | Not known: Fever |
Description of selected adverse reactions
Isoniazid tablets, especially if given with rifampicin, may induce abnormalities in liver function, particularly in patients with pre-existing liver disorders, in the elderly, the very young and the malnourished.
Peripheral neuropathy may be preventable with pyridoxine.
Severe and sometimes fatal hepatitis may occur with Isoniazid tablets therapy.
Reporting of suspected adverse reactions
Reporting suspected adverse reactions after authorisation 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 via the Yellow Card Scheme, Website: www.mhra.gov.uk/yellowcard.
There are no pre-clinical data of relevance to the prescriber which are additional to that already included in other sections of the SPC.
For all forms of pulmonary and extra-pulmonary tuberculosis.
Pharmacotherapeutic group: Combinations of drugs for treatment of tuberculosis
ATC code: J04AM
Isoniazid tablets is a highly active tuberculostatic drug, and at high concentrations it is bactericidal to mycobacterium tuberculosis, possibly acting by interference with the synthesis of mycolic acid (a constituent of the bacterial cell wall).
Isoniazid tablets is not appreciably protein-bound and diffuses readily throughout the body. It affects intracellular as well as extracellular bacilli. The primary metabolic route involves acetylation the rate of which is determined genetically.
Care is required in chronic alcoholism and when prescribing Isoniazid tablets for patients with pre-existing hepatitis. Convulsions and psychotic reactions have occurred , especially in patients with a previous history of these conditions. These manifestations usually subside rapidly when the drug is withdrawn. Isoniazid tablets should therefore be given with caution to patients with convulsive disorders and should be avoided in those with manic or hypomanic psychoses.
Isoniazid tablets is metabolised by acetylation, which is subject to genetic variation. The 'slow acetylators' may be more susceptible to drug-induced peripheral neuropathy. However, dose adjustment is not normally required.
In patients with porphyria, Isoniazid tablets should only be used where no safer alternative is available. Precautions should be considered in these patients.
It is recommended if Isoniazid tablets-induced pancreatitis is proven that the drug should be permanently avoided.
Isoniazid tablets, especially if given with rifampicin, may induce abnormalities in liver function, particularly in patients with pre-existing liver disorders, in the elderly, the very young and the malnourished. Monthly review is suggested to detect and limit the severity of this side-effect by stopping treatment if plasma transaminases exceed three times the upper limit of normal.
Patients should be warned of the possibility of convulsions, psychosis and optic neuritis.
Isoniazid tablets 50 mg/2 ml Solution for Injection is for intramuscular, intravenous, intrapleural, or intrathecal injection.
Adults and children
The usual intramuscular or intravenous dose for adults is 200 to 300 mg as a single daily dose, for children 100 to 300 mg daily (10 - 20 mg/kg), but doses much larger than these are sometimes given, especially in conditions such as tuberculous meningitis. It is recommended to give an intravenous dose slowly as an undiluted bolus injection, although other methods may be employed.
Neonates
The recommended intravenous or intramuscular dose for neonates is 3-5 mg/kg with a maximum of 10 mg/kg daily. Isoniazid tablets may be present in the milk of lactating mothers.
The elderly
No dosage reduction is necessary in the elderly.
Intrapleural use
50 to 250 mg may be instilled intrapleurally after aspiration of pus, the dosage of oral Isoniazid tablets on that day being correspondingly reduced. The ampoule solution is also used for the local treatment of tuberculous ulcers, for irrigation of fistulae, etc.
Intrathecal use:
It should be noted that CSF concentrations of Isoniazid tablets are approximately 90% of plasma concentrations. Where intrathecal use is required, 25 - 50 mg daily has been given to adults and 10 - 20 mg daily for children, according to age.
It is usual to give Isoniazid tablets together with other antituberculous therapy, as determined by current practice and/or sensitivity testing.
It is recommended that pyridoxine be given during Isoniazid tablets therapy to minimise adverse reactions, especially in malnourished patients and those predisposed to neuropathy (eg. diabetics and alcoholics).
Patients with renal impairment
No dosage reduction of Isoniazid tablets is necessary when given to patients with mild renal failure. Patients with severe renal failure (glomerular filtration rate of less than 10 ml/minute) and slow acetylator status might require a dose reduction of about 100mg to maintain trough plasma levels at less than 1 mcg/ml.
Isonaizid is removed by both haemodialysis and peritoneal dialysis therefore Isoniazid tablets should be administered immediately after dialysis.
Patients with hepatic impairment
The possible risks of administration of Isoniazid tablets to patients with pre-existing non-tuberculous hepatic disease should be balanced against the benefits expected from treating tuberculosis.
None.
