Isoniazid - High dose (Hh)

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    Update: November 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: 15 to 20 mg/kg once daily
    • Child 30 kg and over and adult: 10 to 15 mg/kg once daily
    • Maximum dose: 600 mg daily

     

    Weight
    (kg)

    Daily dose
    (mg)

    300 mg

    tablet

    100 mg

    tablet

    5

    75-100

    tab

    6

    90-120

    tab

    7

    105-140

    1½ tab

    8

    120-160

    1½ tab

    9

    135-180

    1½ tab

    10

    150-200

    2 tab

    11

    165-220

    2 tab

    12

    180-240

    2 tab

    13

    195-260

    2 tab

    14

    210-280

    2 tab

    15

    225-300

    3 tab

    16

    240-320

    3 tab

    17

    255-340

    tab

    18

    270-360

    tab

    19

    285-380

    tab

    20

    300-400

    3 tab

    21

    315-420 4 tab

    22

    330-440 4 tab

    23

    345-460 4 tab

    24

    360-480 4 tab

    25

    375-500 4 tab

    26

    390-520 4 tab

    27

    405-540 4 tab

    28

    420-560 4½ tab

    29

    435-580 4½ tab

     

    30-35

    450

    1½ tab

    36-45

    450 1½ tab

    46-55

    600

    2 tab

    56-70

    600

    2 tab

    > 70 600 2 tab

     

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

    Contra-indications, adverse effects, precautions

    • 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.
    • Avoid or monitor combination with cycloserine or terizidone and thionamides (increased risk of neurotoxicity).
    • For the management of adverse effects, see Appendix 17.
    • Administer concomitantly pyridoxine (vitamin B6): child: 1 to 2 mg/kg (usual range: 10 to 50 mg) once daily; adult: 100 mg once daily.
    • Pregnancy and breastfeeding: no contra-indication. Administer pyridoxine to the mother (as above). Observe the breast-fed neonate or infant for adverse effects and supplement it with pyridoxine (1 to 2 mg/kg once daily).

    Monitoring

    • Symptomatic monitoring.
    • Liver function.

    Patient instructions

    • Take without food.
    • Dispersible tablets should be dispersed in 10 ml water.
    • Avoid alcohol during treatment.

    Storage

     
    –  
     
    –  Below 25 °C