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Indications and Dosage
Oral
Tuberculosis Adult: 150 mg/kg/day in 3-4 equally divided doses Take with acidic food (e.g. apple sauce, yoghurt, orange juice). Child: 200-300 mg/kg/day in 3-4 equally divided doses. Oral Crohn's disease Adult: 1.5 g/day (unlabelled use). Rectal Ulcerative colitis Adult: 2 g once a day as an enema in patients who are intolerant to sulphasalazine.
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Renal Impairment
Haemodialysis: Administer dose afterwards and give 50% dose. Continuous arteriovenous haemofiltration: give 50% dose.
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Contraindications
G6PD deficiency; severe renal disease.
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Special Precautions
Pregnancy, lactation; renal and hepatic impairment, sodium salt in heart failure; gastric ulcer. Monitor patient closely for 1st 3 mth of treatment and counsel to report: sore throat, fever, unusual bleeding or bruising, persistent nausea or vomiting, or abdominal pain.
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Adverse Reactions
Nausea, vomiting, diarrhoea, abdominal pain; thyroid goitre, hypoglycaemia; pericarditis, vasculitis; encephalopathy, fever, skin eruptions, agranulocytosis, haemolytic anaemia, leucopenia, thrombocytopenia, hepatitis, jaundice, optic neuritis, eosinophilic pneumonia.
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Overdosage
Acute symptoms: Crystalluria, renal failure, nausea and vomiting. Treatment: Sodium bicarbonate (alkalinise urine) and forced diuresis to prevent crystalluria and nephrotoxicity.
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Drug Interactions
May decrease absorption of digoxin and vitamin B12; additive adverse effects of aminosalicylates and salicylates; probenecid may increase toxicity by delaying renal excretion and enhancing plasma concentrations of aminosalicylate; activity of aminosalicylic acid may be antagonised by ester-type local anaesthetics such as procaine; may enhance effect of oral anticoagulants (may need to adjust dose); ammonium chloride may increase risk of crystalluria (do not use concurrently).
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Food Interaction
May be taken with food; sprinkle on apple sauce or yoghurt or suspend in tomato or orange juice; granules have an acid resistant coating that dissolves within a minute at neutral pH.
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Lab Interference
Interferes with tests for glucosuria using copper reagents and for urobilinogen using Ehrlich's reagent.
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Action
Description: Para-aminosalicylic acid (also known as aminosalicyclic acid) is bacteriostatic and active against M. tuberculosis. Other mycobacteria are usually resistant. It prevents plate biosynthesis in sensitive organisms. It has a relatively weak action compared with other anti-TB drugs and resistance may develop quickly if it is used alone, however it is still sometimes used in multi-drug resistant tuberculosis in combination with other anti-TB drugs.
Pharmacokinetics: Absorption: Readily absorbed (>90%); peak plasma concentration after oral dosing: 1-4 hr. Time to peak, serum: 6 hr. Distribution: Diffuses into most body tissues and fluids (including breast milk) except CSF (unless meninges inflamed). Plasma protein binding: sodium salt: 15%; acid: 50-70%. Metabolism: Intestinally and hepatically (>50%) mainly by acetylation. Excretion: Via urine: ≥80% dose within 24 hr (50% as acetylated metabolite). Half-life: approx 1 hr (reduced in renal impairment). |
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Storage
Granules: Before dispensing: <15°C. Once dispensed: <25°C for short periods of time. Not to be used if packet is swollen or granules are dark brown or purple.
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