herefore, ophthalmological and audiological tests should be carried out both prior to the institution of therapy with Desferal and at 3-monthly intervals during treatment particularly if ferritin levels are low. By keeping the ratio of the mean daily dose (mg/kg of Desferal) divided by the serum ferritin (micro g/L) below 0.025 the risk of audiometric abnormalities may be reduced in thalassaemia patients. A detailed ophthalmological assessment is recommended (visual field measurements, fundoscopy, and colour vision testing using pseudoisochromatic plates and the Farnsworth D-15 colour test, slit lamp investigation, visual evoked potential studies).
If disturbances of vision or hearing do occur, treatment with Desferal should be stopped. Such disturbances are usually reversible. If Desferal therapy is re-instituted later at a lower dosage, close monitoring of ophthalmological/auditory function should be carried out with due regard to the risk-benefit ratio.
Paediatrics: growth retardation
The use of inappropriately high doses of Desferal in patients with low ferritin levels or young children (<3 years at commencement of treatment) has also been associated with growth retardation; dose reduction has been found to restore the growth rate to pretreatment levels in some cases. Three monthly checks on body weight and height are recommended in children.
Growth retardation if associated with excessive doses of Desferal must be distinguished from growth retardation from iron overload. Growth retardation from Desferal use is rare if the dose is kept below 40 mg/kg; if growth retardation has been associated with doses above this value, then reduction of the dose may result in return in growth velocity, however, predicted adult height is not attained.
Acute respiratory distress syndrome
Acute respiratory distress syndrome has been described following treatment with excessively high i.v. doses of Desferal in patients with acute iron intoxication, and also in thalassaemic patients (see section 4.8 Undesirable effects). The recommended daily doses should therefore not be exceeded.
It should be noted that desferrioxamine will affect aluminium levels and may necessitate some dosage adjustment of erythropoietin if co-prescribed.
4.5 Interaction with other medicinal products and other forms of interaction
Oral administration of vitamin C (up to a maximum of 200 mg daily, given in divided doses) may serve to enhance excretion of the iron complex in response to Desferal; larger doses of vitamin C fail to produce an additional effect. Monitoring of cardiac function is indicated during such combined therapy. Vitamin C should be given only if the patient is receiving Desferal regularly and should not be administered within the first month of Desferal therapy. In patients with severe chronic iron-storage disease undergoing combined treatment with Desferal and high doses of vitamin C (more than 500 mg daily) impairment of cardiac function has been encountered; this proved reversible when the vitamin C was withdrawn. Vitamin C supplements should not, therefore, be given to patients with cardiac failure.
Desferal should not be used in combination with prochlorperazine (a phenothiazine derivative) since prolonged unconsciousness may result.
Gallium67 imaging results may be distorted because of the rapid urinary excretion of Desferal-bound radiolabel. Discontinuation of Desferal 48 hours prior to scintigraphy is advised.
4.6 Pregnancy a |
