ISONIAZID
DOSAGE
Adults: 300mg once a day (oral or intravenous). Consider 5mg/kg once a day if low body weight (oral or intravenous); or for DOT supervised regimen: 15mg/kg three times a week (oral).
Children: 10mg/kg (max. 300mg) once a day (oral or intravenous); or for DOT supervised regimen: 15mg/kg (max. 900mg) three times a week (oral).
Doses should be rounded up to facilitate administration of suitable volumes of liquid or an appropriate strength of tablet.
Isoniazid should be taken 30-60 minutes before food, or 2 hours after food.
Low level isoniazid resistance:
Children: 15-20mg/kg once a day
Adults: Doses of 16-18mg/kg once a day have been used.
Pyridoxine can be used to reduce the risk of peripheral neuropathy in all patients taking isoniazid. In particular it should be prescribed for those most at-risk, such as patients with diabetes, alcohol abuse or malnutrition.
All patients prescribed high-dose isoniazid must also be prescribed pyridoxine as there is an increased risk of peripheral neuropathy.
PREPARATIONS
Oral: 100mg capsules.
Liquid (as a manufactured ‘special’ - unlicensed medicine).
Rifinah® 300/150 tablets (rifampicin 300mg, isoniazid 150mg).
Rifinah® 150/100 tablets (rifampicin 150mg, isoniazid 100mg).
Rifater tablets (rifampicin 120mg, isoniazid 50mg, pyrazinamide 300mg).
Voractiv® tablets (rifampicin 150mg, isoniazid 75mg, pyrazinamide 400mg, ethambutol 275mg).
Paediatric oral fixed dose combinations (dissolvable in water):
*Ethambutol should be added in the intensive phase for children with extensive disease or living in settings where the prevalence of HIV or of isoniazid resistance is high.
Parenteral: 50mg/2mL ampoules.
DRUG LEVEL MONITORING
Indications for monitoring:
Timing of sample:
Adherence Monitoring
INH strips can be used to measure adherence to isoniazid treatment.
ADVERSE EFFECTS
COMMON:
Neurological: Peripheral Neuropathy.
Hepatic: Transient increases in LFTs.
SERIOUS:
Dermatological: Skin reactions e.g. urticaria (uncommon).
Haematologic: Agranulocytosis, megaloblastic anaemia, thrombocytopaenia.
Hepatic: Hepatotoxity (rare).
Immunological: Drug-induced lupus (rare).
Musculoskeletal: Arthralgia, rhabdomyolysis.
Neurological: Seizure, psychosis (rare).
ADVERSE EFFECTS: MONITORING
Routine tests as per generic MDR-TB treatment monitoring guidelines.
INTERACTONS
Carbamazepine: increased plasma concentration of carbamazepine. Increased risk of hepatoxicity.
Food: Reduced absorption. Take isoniazid 30-60 minutes before food, or 2 hours after food.
Food: Possible increased risk of headache, sweating, palpitations, flushing, hypotension when eating certain foods such as cheese, skipjack tuna or other tropical fish, or red wine. Usually, no dietary restrictions are required unless symptoms are experienced. This reaction is thought to be due to the high histamine or tyramine content of these foods and drink, resulting in an exaggerated histamine poisoning reaction due to inhibition of histamine metabolism by isoniazid, or the sympathomimetic action of tyramine due to inhibition of mono-amine oxidase by isoniazid.
This information is not inclusive of all drug interactions. Please discuss with a pharmacist.
CONTRA-INDICATIONS & CAUTIONS
Contraindications:
Hypersensitivity: To isoniazid.
Cautions:
Liver disease, alcohol abuse, hepatitis B co-infection: monitor LFTs closely.
Malnutrition, HIV co-infection, diabetes mellitus, and alcohol dependence: Increased risk of peripheral neuropathy; prescribe prophylactic pyridoxine.
LABORATORY INFORMATION
Please find up to date information at www.assayfinder.com regarding individual providers of drug level monitoring tests. Click on the provider to discover contact details. Turnaround time varies depending on the test and whether it is run locally or sent to an external lab. By contacting laboratories in advance, turnaround time can significantly be reduced.
Sample Type: Plasma.
Volume Required: 2 ml.
Sample Container: Fluoride Oxalate.
Container Type: Any.
Availability: Office Hours.
Turnaround Time: 7 Days.
Adults: 300mg once a day (oral or intravenous). Consider 5mg/kg once a day if low body weight (oral or intravenous); or for DOT supervised regimen: 15mg/kg three times a week (oral).
Children: 10mg/kg (max. 300mg) once a day (oral or intravenous); or for DOT supervised regimen: 15mg/kg (max. 900mg) three times a week (oral).
Doses should be rounded up to facilitate administration of suitable volumes of liquid or an appropriate strength of tablet.
Isoniazid should be taken 30-60 minutes before food, or 2 hours after food.
Low level isoniazid resistance:
Children: 15-20mg/kg once a day
Adults: Doses of 16-18mg/kg once a day have been used.
Pyridoxine can be used to reduce the risk of peripheral neuropathy in all patients taking isoniazid. In particular it should be prescribed for those most at-risk, such as patients with diabetes, alcohol abuse or malnutrition.
All patients prescribed high-dose isoniazid must also be prescribed pyridoxine as there is an increased risk of peripheral neuropathy.
PREPARATIONS
Oral: 100mg capsules.
Liquid (as a manufactured ‘special’ - unlicensed medicine).
Rifinah® 300/150 tablets (rifampicin 300mg, isoniazid 150mg).
Rifinah® 150/100 tablets (rifampicin 150mg, isoniazid 100mg).
Rifater tablets (rifampicin 120mg, isoniazid 50mg, pyrazinamide 300mg).
Voractiv® tablets (rifampicin 150mg, isoniazid 75mg, pyrazinamide 400mg, ethambutol 275mg).
Paediatric oral fixed dose combinations (dissolvable in water):
*Ethambutol should be added in the intensive phase for children with extensive disease or living in settings where the prevalence of HIV or of isoniazid resistance is high.
Parenteral: 50mg/2mL ampoules.
DRUG LEVEL MONITORING
Indications for monitoring:
- Known or suspected malabsorption.
- Poor treatment response.
Timing of sample:
- 2 hours post dose.
- Repeat at 6 hours if suspect delayed absorption.
- Drug levels need not be routinely measured.
Adherence Monitoring
INH strips can be used to measure adherence to isoniazid treatment.
- BBL Taxo INH Test Strips are absorbent paper strips that colour green, blue or purple in the presence of isonicotinic acid (a metabolite of isoniazid)
- BBL Taxo INH Test Control is an isoniazid-impregnated disc that will yield a positive result in the test procedure.
ADVERSE EFFECTS
COMMON:
Neurological: Peripheral Neuropathy.
Hepatic: Transient increases in LFTs.
SERIOUS:
Dermatological: Skin reactions e.g. urticaria (uncommon).
Haematologic: Agranulocytosis, megaloblastic anaemia, thrombocytopaenia.
Hepatic: Hepatotoxity (rare).
Immunological: Drug-induced lupus (rare).
Musculoskeletal: Arthralgia, rhabdomyolysis.
Neurological: Seizure, psychosis (rare).
ADVERSE EFFECTS: MONITORING
Routine tests as per generic MDR-TB treatment monitoring guidelines.
INTERACTONS
Carbamazepine: increased plasma concentration of carbamazepine. Increased risk of hepatoxicity.
Food: Reduced absorption. Take isoniazid 30-60 minutes before food, or 2 hours after food.
Food: Possible increased risk of headache, sweating, palpitations, flushing, hypotension when eating certain foods such as cheese, skipjack tuna or other tropical fish, or red wine. Usually, no dietary restrictions are required unless symptoms are experienced. This reaction is thought to be due to the high histamine or tyramine content of these foods and drink, resulting in an exaggerated histamine poisoning reaction due to inhibition of histamine metabolism by isoniazid, or the sympathomimetic action of tyramine due to inhibition of mono-amine oxidase by isoniazid.
This information is not inclusive of all drug interactions. Please discuss with a pharmacist.
CONTRA-INDICATIONS & CAUTIONS
Contraindications:
Hypersensitivity: To isoniazid.
Cautions:
Liver disease, alcohol abuse, hepatitis B co-infection: monitor LFTs closely.
Malnutrition, HIV co-infection, diabetes mellitus, and alcohol dependence: Increased risk of peripheral neuropathy; prescribe prophylactic pyridoxine.
LABORATORY INFORMATION
Please find up to date information at www.assayfinder.com regarding individual providers of drug level monitoring tests. Click on the provider to discover contact details. Turnaround time varies depending on the test and whether it is run locally or sent to an external lab. By contacting laboratories in advance, turnaround time can significantly be reduced.
Sample Type: Plasma.
Volume Required: 2 ml.
Sample Container: Fluoride Oxalate.
Container Type: Any.
Availability: Office Hours.
Turnaround Time: 7 Days.