Isoniazid - Standard dose (H)

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    Update: January 2022

     

    Forms and strengths

    • 300 mg and 100 mg tablets
    • 100 mg and 50 mg dispersible tablets, to be dispersed in 10 ml water

    Dosage

    • Child under 30 kg: 10 mg/kg (7 to 15 mg/kg) once daily
    • Child 30 kg and over and adult: 5 mg/kg (4 to 6 mg/kg) once daily
    • Maximum dose: 300 mg daily

     

    Weight
    (kg)

    Daily dose
    (mg)

    300 mg
    tablet

    100 mg
    tablet

    5

    35-75

    ½ tab

    6

    42-90

    1 tab

    7

    49-105

    1 tab

    8

    56-120

    1 tab

    9

    63-135

    1 tab

    10

    70-150

    1½ tab

    11

    77-165

    1½ tab

    12

    84-180

    1½ tab

    13

    91-195

    2 tab

    14

    98-210

    2 tab

    15

    105-225

    2 tab

    16

    112-240

    2 tab

    17

    119-255

    2 tab

    18

    126-270

    2 tab

    19

    133-285

    2 tab

    20

    140-300

    2 tab

    21

    147-300

    1 tab

    22

    154-300

    1 tab

    23

    161-300

    1 tab

    24

    168-300

    1 tab

    25

    175-300

    1 tab

    26

    182-300

    1 tab

    27

    189-300

    1 tab

    28

    196-300

    1 tab

    29

    203-300

    1 tab

     

    30-35

    150

    ½ tab

    36-45

    300

    1 tab

    46-55

    300

    1 tab

    56-70

    300

    1 tab

    > 70

    300

    1 tab

     

    Alternatively, 50 mg dispersible tablets may be used instead of ½ tablets of 100 mg.

    Contra-indications, adverse effects, precaution

    • Do not administer to patients with severe hepatic impairment. 
    • May cause:
      • peripheral neuropathy;
      • hepatotoxicity;
      • hypersensitivity reactions, arthragias, optic neuritis, psychotic reactions, seizures and depression.
    • Monitor closely:
      • pregnant and breastfeeding women; patients with renal impairment, diabetes, malnutrition or HIV infection (increased risk of neuropathy);
      • patients with alcohol dependence (increased risk of neuropathy and hepatotoxicity);
      • patients with chronic hepatic disease or taking rifampicin or ≥ 35 years (increased risk of hepatotoxicity);
      • patients taking antiseizure medications, benzodiazepines (risk of toxicity), warfarin (risk of bleeding). Dose adjustment may be required.
    • For the management of adverse effects, see Appendix 17.
    • Administer concomitantly pyridoxine (vitamin B6) to patients at risk of peripheral neuropathy (child: 5 to 10 mg once daily; adult: 10 mg once daily).
    • Pregnancy and breastfeeding: no contra-indication. Administer pyridoxine to the mother (as above) and the breast-fed neonate or infant (5 mg once daily).

    Monitoring

    • Symptomatic monitoring.

    • Liver function in patients with hepatic disease.

    Patient instructions

    • Take without food.
    • 100 mg dispersible tablet should be dispersed in 10 ml water.
    • Avoid alcohol during treatment.

    Remarks

    • For patients on drug-susceptible TB treatment, isoniazid is given as part of a fixed-dose combination.
    • For the 6HRZEto regimen for drug-susceptible TB meningitis, the dose of isoniazid is 20 mg/kg once daily (max. 400 mg daily).
    • Isoniazid is also used in the treatment of latent TB infection and multidrug-resistant TB treatment (at high dose - Hh).

    Storage

     
    –  
     
    –  Below 25 °C