Isoniazid (H)

Therapeutic action

– Antibacterial with bactericidal activity

Presentation

– 100 mg and 300 mg tablets
– 50 mg/5 ml oral solution

Dosage

– Child under 30 kg: 10 mg/kg (7 to 15 mg/kg) once daily
– Child over 30 kg 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

50 mg per 5 ml
oral solution

5

35-75

5 ml

6

42-90

6 ml

7

49-105

7 ml

8

56-120

8 ml

9

63-135

9 ml

10

70-150

10 ml

11

77-165

11 ml

12

84-180

12 ml

13

91-195

13 ml

14

98-210

14 ml

15

105-225

15 ml

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

200

2 tab

46-55

300

1 tab

56-70

300

1 tab

> 70

300

1 tab

Contra-indications, adverse effects, precautions

– Do not administer to patients with severe hepatic impairment.
– May cause:
• peripheral neuropathy, especially in malnourished, alcoholic, diabetic, HIV-infected patients, pregnant and breast-feeding women, patients with renal impairment or chronic hepatic disease and patients receiving high doses of isoniazid;
• hepatic disorders, especially in alcoholic patients, patients taking rifampicin, patients > 35 years;
• hypersensitivity reactions; psychotic reactions.
– For the management of adverse effects, see Chapter 9 and Appendix 10.
– Administer with caution and monitor patients taking phenytoin, carbamazepine, benzodiazepines (risk of toxicity), warfarin (risk of bleeding), cycloserine (increased risk of peripheral neuropathy, drowsiness, dizziness).
– Administer concomitantly pyridoxine (vitamin B6) to patients at risk of peripheral neuropathy (child: 5 to 10 mg/day; adult: 10 mg/day).
Pregnancy and breast-feeding: no contra-indication. To prevent peripheral neuropathy, administer pyridoxine (10 mg/day). In addition, supplement the breast-fed infant with pyridoxine (5 mg/day).

Monitoring

– Symptomatic monitoring

Patient instructions

– Take without food.
– Avoid alcohol during treatment.

Remarks

– For patients on first-line treatment, isoniazid is given as part of a fixed dose combination.
– Isoniazid is included in Group 1 however, when used in high doses (16 to 20 mg/kg/day), it is included in Group 5.
 Storage: below 25°C -  -