Addisonian pernicious anaemia. Prophylaxis and treatment of other macrocytic anaemias associated with vitamin B12 deficiency. Schilling test.

Not indicated for treatment of toxic amblyopias - use Neo-Cytamen.

Route of administration: intramuscular.

Adults and Children

Addisonian pernicious anaemia and other macrocytic anaemias without neurological involvement:

Initially: 250 to 1000mcg intramuscularly on alternate days for one to two weeks, then 250mcg weekly until the blood count is normal.

Maintenance: 1000mcg monthly.

Addisonian pernicious anaemia and other macrocytic anaemias with neurological complications:

Initially: 1000mcg intramuscularly on alternate days as long as improvement is occurring.

Maintenance: 1000mcg monthly.

Prophylaxis of macrocytic anaemia associated with vitamin B12 deficiency resulting from gastrectomy, some malabsorption syndromes and strict vegetarianism:

250mcg - 1000mcg monthly.

Schilling Test:

An intramuscular injection of 1000mcg cyanocobalamin is an essential part of this test.

Hypersensitivity to cyanocobalamin or any other constituents

Cytomen should not be used for the treatment of megaloblastic anaemia of pregnancy unless vitamin B12 deficiency has been demonstrated.

Not indicated for treatment of toxic amblyopias - use Neo-Cytamen.

Precautions:

The dosage schemes given above are usually satisfactory, but regular examination of the blood is advisable. If megaloblastic anaemia fails to respond to Cytamen, folate metabolism should be investigated. Doses in excess of 10mcg daily may produce an incomplete haematological response in patients with folate deficiency. Indiscriminate administration may mask the true diagnosis. The haematological and neurological state should be monitored regularly to ensure adequacy of therapy. Cardiac arrhythmias secondary to hypokalaemia during initial therapy have been reported. Plasma potassium should therefore be monitored during this period. Platelet count should be monitored during the first weeks of use in megaloblastic anaemia due to the possible occurrence of reactive thrombocytosis.

This medicine contains less than 1mmol (23mg) sodium per dose, that is to say essentially 'sodium-free'.

Chloramphenicol-treated patients may respond poorly to Cytamen. Serum concentrations of cyanocobalamin may be lowered by oral contraceptives but this interaction is unlikely to have clinical significance.

Antimetabolites and most antibiotics invalidate vitamin B12 assays by microbiological techniques.

Cytamen should not be used for the treatment of megaloblastic anaemia of pregnancy unless vitamin B12 deficiency has been demonstrated. Cytamen is secreted into breast milk but this is unlikely to harm the infant, and may be beneficial if the mother and infant are vitamin B12 deficient.

None.

Hypersensitivity reactions have been reported including skin reactions (e.g. rash, itching) and exceptionally anaphylaxis. Other symptoms reported include fever, chills, hot flushing, dizziness, malaise, nausea, acneiform and bullous eruptions, tremor and injection site reactions including injection site pain, injection site induration and injection site necrosis. Reactive thrombocytosis can occur during the first weeks of use in megaloblastic anaemia.

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 Yellow Card Scheme Website www.mhra.gov.uk/yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store.

Treatment is unlikely to be needed in cases of overdosage.

Cyanocobalamin is a form of vitamin B12.

Cobalamins are absorbed from the gastro-intestinal tract, but may be irregularly absorbed when given in large therapeutic doses. Absorption is impaired in patients with an absence of intrinsic factor, with a malabsorption syndrome or with a disease or abnormality of the gut, or after gastrectomy.

After injection of cyanocobalamin a large proportion is excreted in the urine within 24 hours; the body retains only 55% of a100-microgram dose and 15% of a 1000-microgram dose. Vitamin B12 is extensively bound to specific plasma proteins called transcobalamins; transcobalamin II appears to be involved in the rapid transport of the cobalamins to tissues. Vitamin B12 is stored in the liver, excreted in the bile, and undergoes extensive enterohepatic recycling; part of an administered dose is excreted in the urine, most of it in the first 8 hours; urinary excretion, however, accounts for only a small fraction in the reduction of total body stores acquired by dietary means. Vitamin B12 diffuses across the placenta and also appears in breast milk.

None stated.

Sodium chloride

Acetic acid

Water for injections

None.

18 months.

Protect from light. Do not store above 25° C

1ml clear, one-point cut (OPC) colourless glass Type 1 Ph Eur ampoules packed in cartons of 5 ampoules

None stated.