SULFADIAZINE Tablets Ref.[7862] Active ingredients: Sulfadiazine

Caution in elderly, renal or hepatic impairment and jaundice. Use with caution in patients with predisposition to folate deficiency. Sulfonamides inhibit the absorption and metabolism of folic acid and may cause folic acid deficiency potentially resulting in serious blood disorders (e.g., macrocytosis and pancytopenia), this can be normalised by administration of folic acid or folinic acid (leucovorin). Reactions are more likely in acquired immune deficiency syndrome, lupus erythematosus, glucose-6-phosphate dehydrogenase deficiency or history of allergy or asthma.

Life-threatening cutaneous reactions Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) have been reported with the use of Sulfadiazine. Patients should be advised of the signs and symptoms and monitored closely for skin reactions. The highest risk for occurrence of SJS or TEN is within the first weeks of treatment. If symptoms or signs of SJS or TEN (e.g. progressive skin rash often with blisters or mucosal lesions) are present, sulfadiazine treatment should be discontinued. The best results in managing SJS and TEN come from early diagnosis and immediate discontinuation of any suspect drug. Early withdrawal is associated with a better prognosis. If the patient has developed SJS or TEN with the use of Sulfadiazine, Sulfadiazine must not be re-started in this patient at any time.

Full blood counts should be carried out during prolonged therapy with sulfadiazine in order to detect blood dyscrasias (see Section 4.8). Discontinue sulfadiazine treatment immediately if blood disorders develop. Urinalyses with microscopic examination may be required prior to and periodically during treatment to detect crystalluria and/or urinary calculi formation in patients on long-term or high dose therapy and in patients with impaired renal function. To reduce the risk of crystalluria, fluid intake should be high (5-6 pints in 24 hours), to maintain a high urine output (minimum of 1200mL daily). If necessary, the urine may be rendered alkaline to prevent crystallisation of acetyl Sulfadiazine.

Anaesthetics, general: sulphonamides may potentiate the effect of thiopentone anaesthetics.

Anti-infectives: Like other sulphonamides, Sulfadiazine demonstrated synergy with the difolate reductase release inhibitors, pyrimethamine and trimethoprim. Risk of pancytopenia and megloblastic anaemia with concurrent pyrimethamine. Increased risk of crystalluria with methenamine.

Anticoagulants: sulphonamides may potentiate the effects of coumarins, such as warfarin.

Antidiabetics: antidiabetic effect of sulphonylureas, e.g. chlorpropramide and tolbutamide, may be enhanced.

Antiepileptics: sulphonamides may potentiate the effect of phenytoin.

Antipsychotics: avoid concurrent clozapine (increased risk of agranulocytosis); see Section 4.3.

Aspirin: the toxcicty of sulphonamides may be increased by aspirin.

Ciclosporin: plasma ciclosprin concentrations may be reduced; increased risk of nephrotoxicity).

Diuretics: caution should be exercised with diuretics such as thiazide due to the importance of maintaining urinary output; increased risk of crystalluria (see Section 4.4).

Local anaesthetics: antibacterial activity of sulphonamides may be antagonised by benzocaine or tetracaine. The action of sulphonamides may be antagonised by p-aminobenzoic acid (PABA) and compounds derived from it, particularly potassium aminobenzoate and the procaine group of local anaesthetics. There is an increased risk of methaemoglobinaemia when sulphonamides administered with prilocaine

Methotrexate: sulphonamides may potentiate the effect of methotrexate

Oestrogen-containing oral contraceptives: sulphonamides may reduce the contraceptive effect of oestrogen-containing oral contraceptives-additional contraceptive precautions should be taken during treatment and for seven days after stopping.

Potassium aminobenzoate: may antagonise action of sulfadiazine.

Probenecid: sulphonamides are displaced by probenecid. This interaction is theoretical and unlikely to be clinically significant.

Vaccines: antibacterials should be avoided for 3 days before and after oral typhoid vaccination

Interference with diagnostic tests: sulphonamides may produce false-positive Benedict’s test for urinary glucose; may interfere with test for urinary urobilinogen.

Pregnancy

There is epidemiological evidence of the safety of Sulfadiazine in human pregnancy, but the clinician should assess the risk benefit factors before recommending Sulfadiazine to pregnant women. There is evidence of embryotoxicity and teratogenicity in animals at high dosage, especially during the first trimester. It is generally considered that sulphonamides are not given late in pregnancy because of the risk of haemolytic anaemia in the newborn. Fear of increased risk of kernicterus in neonates appears to be unfounded. Although kernicterus has been reported in neonates following direct administration of sulphonamides, kernicterus in the neonate following in utero exposure has not been reported.

Lactation

Sulphonamides are excreted in the breast milk in small amounts and should be used with caution in nursing mothers of healthy newborn, ill, stressed or premature infants, or infants with jaundice or hyperbilirubinaemia (risk of kernicterus) and mothers of infants with glucose-6-phosphate dehydrogenase (G6PD) deficiency (risk of haemolytic anaemia). A decision to continue/discontinue breast-feeding or to continue/discontinue therapy with sulfadiazine should be made following careful risk benefit evaluation.

Not known.

These are common to all sulphonamides and more likely in slow acetylators.

Blood and lymphatic system disorders: Occasional blood disorders include, agranulocytosis, aplastic anaemia, thrombocytopenia, leucopenia, neutropenia, hypoprothrombinaemia, eosinophilia; methaemoglobinaemia with cyanosis; rarely, acute haemolytic anaemia (with glucose-6-phosphate dehydrogenase deficiency).

Immune system disorders: hypersensitivity. Hypersensitivity reactions may take the form of fever, rashes, photosensitivity, exfoliative dermatitis, toxic epidermal, necrolysis, urticaria, pruritus, erythema nodosum, erythema multiforme, erythroderma, fixed drug eruption, Stevens-Johnson syndrome, contact dermatitis, systemic lupus erythematosus, serum sickness like syndrome, liver necrosis, hepatitis, hepatomegaly, jaundice, myocarditis, pancreatitis, pulmonary eosinophilia, fibrosing alveolitis, vasculitis, including polyarteritis nodosa, nephrotoxic reactions (interstitial nephritis, tubular necrosis) may result in renal failure. Anaphylaxis is very rare.

Metabolism and nutrition disorders: hypoglycaemia, hypothyroidism.

Psychiatric disorders: depression, psychosis, hallucinations

Nervous system disorders: neurological reactions (including aseptic meningitis, ataxia, benign intracranial hypertension, convulsions, dizziness, vertigo, drowsiness, fatigue, headache, insomnia, peripheral or optic neuropathies).

Ear and labyrinth disorders: tinnitus

Respiratory, thoracic and mediastinal disorders: cough, dyspnoea

Gastrointestinal disorders: Most commonly, nausea, anorexia, vomiting, diarrhoea, stomatitis. Pseudomembranous colitis may occur with alterations in bacterial flora of the gastrointestinal tract. Salivary gland enlargement.

Hepatobiliary disorders: hepatitis, jaundice and kernicterus in premature neonates.

Skin and subcutaneous tissue disorders: purpura, severe cutaneous adverse reactions (SCARS): Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) have been reported (see section 4.4)

Renal and urinary disorders: Crystalluria may occur, with lumbar pain, haematuria, oliguria and anuria. Reduce risk by high fluid intake. Treat by alkalinisation of urine. Increased blood urea and serum creatinine concentrations.

Reporting of suspected adverse reactions

Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme at www.mhra.gov.uk/yellowcard.

Not applicable.