Meds and you

27 September 2013

Isoniazid

Isoniazid is an antibiotic used as first-line treatment of tuberculosis.

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(Also known as INH)

Isoniazid is the active ingredient of Be-Tabs Isoniazid (Nappi Code: 823589-005). Isoniazid is also one of multiple active ingredients found in Rifafour (Nappi Code: 701608001/2/3/4/5), Rifinah (Nappi Code: 760641-015, 702502-001), Rimactazid (Nappi Code: 702376-001, 702373-002), Rimactazid Paed (Nappi Code: 863971-008/16, 704472-001 ), Rimcure Paed (Nappi Code: 863998-003/011/038) and Rimstar 4-FDC (Nappi Code: 702384-004/5/6).

General information
Isoniazid is an antibiotic used as first-line treatment of tuberculosis.

It is often used in combination with other antibiotics to provide a broader spectrum of action, and to reduce the risk of certain bacteria developing a resistance against this drug.

In South Africa isoniazid is registered for the treatment of tuberculosis and mycobacterium infections other than tuberculosis.

Isoniazid is also used as preventative treatment against tuberculosis in those exposed to high-risk environments.

For isoniazid to be effective it has to be taken regularly, even if you do not notice an immediate effect.

It should best be taken 1 hour before, or 2 hours after a meal. If taken with a meal gastro-intestinal irritation will be less, but absorption of the drug may then be impaired.

Isoniazid may deplete levels of pyridoxine (vitamin B6) in the body. Because low levels of this vitamin may lead to permanent nerve damage, pyridoxine supplements are advised in those taking high doses of isoniazid.

Treatment with isoniazid should not be stopped abruptly, even if you feel better. To prevent the infection from returning as a result of premature stoppage, you should decrease your dose only as directed by your doctor, only when instructed to do so.

How does isoniazid work?
Isoniazid prevents bacteria from manufacturing certain components needed for the formation of bacterial cell walls. Without a cell wall the bacteria will die.

Fast facts

Drug schedule: schedule 3
Available as: isoniazid is available as tablets.
What does it do? Isoniazid has an anti-biotic action.
Overdose risk: high
Dependence risk: low
Is Isoniazid available as a generic? yes
Is Isoniazid available on prescription only? yes

User information

Onset of effect: the full effect of this drug may only be seen after a few days of treatment.
Duration of action: 12-24 hours
Dietary advice: isoniazid should best be taken 1 hour before, or 2 hours after a meal. If taken with a meal gastro-intestinal irritation will be less, but absorption of the drug may then be impaired.
Stopping this medicine: treatment with isoniazid should not be stopped abruptly, even if you feel better. To prevent the infection from returning as a result of premature stoppage, you should decrease your dose only as directed by your doctor, only when instructed to do so.
Prolonged use: prolonged use may lead to pyridoxine deficiency and associated nerve damage, as well as liver damage. Periodic blood and liver function tests are advised.

Special precautions
Consult your doctor before using this drug if:

  • you have epilepsy

  • you have liver or kidney disease

  • you are an alcoholic

  • you have been diagnosed with porphyria

  • you have diabetes

  • you are taking other medication

Pregnancy: avoid. It is unknown how this medication may affect your baby. Consult your doctor before using this drug, or if you are planning to fall pregnant.
Breastfeeding: avoid. It is unknown how this medication may affect your baby. Consult your doctor before use.
Porphyria: avoid. This medication may cause serious adverse effects. Consult your doctor before use.
Infants and children: this medication is safe for use in children at the recommended dose.
The elderly: caution is advised in the elderly as the risk of adverse effects is increased.
Driving and hazardous work: no special precautions need to be taken.
Alcohol: avoid concomitant use of alcohol with this medication.

>Possible side effects

Side Effect
Frequency
Consult your doctor

Common
Rare
Only if severe
In all cases
diarrhoea

X
X

nausea and vomiting

X
X

abdominal pain

X
X

fatigue

X

X
psychosis

X

X
mood changes

X

X
seizures

X

X
loss of coordination

X

X
yellow tinge to skin/eyes

X

X
rash

X

X
double vision/change in eyesight

X

X

Interactions

alcohol increased risk of liver damage and sedation
antacids may reduce absorption of isoniazid – take at least 2 hours apart
diazepam risk of diazepam toxicity
isoflurane increased risk of liver damage
oral contraceptive risk of contraceptive failure
phenytoin risk of phenytoin toxicity
carbamazepine risk of carbamazepine toxicity
paracetamol risk of paracetamol toxicity
theophylline risk of theophylline toxicity

Some other drugs may also interact with rifampicin. It is important to consult your doctor or pharmacist before combining any drug with rifampicin.

Disease interactions
Consult your doctor before using this drug if you have epilepsy, liver or kidney disease, porphyria or if you have diabetes.

Overdose action
A large overdose of this medication can be fatal. Seek immediate emergency medical attention.

Recommended dosage
Adults: oral, 5 mg/kg/day up to a maximum of 300 mg/day

This material is not intended to substitute medical advice, but is for informational purposes only. Please consult a physician for specific treatment and recommendations.
 
 

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