IN THE UK, RECOMMENDED DOSES FOR PERNICIOUS ANAEMIA AND OTHER MACROCYTIC ANAEMIAS WITHOUT NEUROLOGICAL INVOLVEMENT ARE HYDROXOCOBALAMIN (OR CYANOCOBALAMIN) 250 TO 1000 MICROGRAMS INTRAMUSCULARLY ON ALTERNATE DAYS FOR 1 TO 2 WEEKS, THEN 250 MICROGRAMS WEEKLY UNTIL THE BLOOD COUNT RETURNS TO NORMAL. MAINTENANCE DOSES OF 1000 MICROGRAMS OF HYDROXOCOBALAMIN ARE GIVEN EVERY 2 TO 3 MONTHS (OR MONTHLY FOR CYANOCOBALAMIN). IF THERE IS NEUROLOGICAL INVOLVEMENT, HYDROXOCOBALAMIN OR CYANOCOBALAMIN MAY BE GIVEN IN DOSES OF 1000 MICROGRAMS ON ALTERNATE DAYS AND CONTINUED FOR AS LONG AS IMPROVEMENT OCCURS. FOR THE PROPHYLAXIS OF ANAEMIA ASSOCIATED WITH VITAMIN B12 DEFICIENCY RESULTING FROM GASTRECTOMY OR MALABSORPTION SYNDROMES HYDROXOCOBALAMIN MAY BE GIVEN IN DOSES OF 1000 MICROGRAMS INTRAMUSCULARLY EVERY 2 OR 3 MONTHS OR CYANOCOBALAMIN IN DOSES OF 250 TO 1000 MICROGRAMS INTRAMUSCULARLY EACH MONTH. FOR VITAMIN B12 DEFICIENCY OF DIETARY ORIGIN, CYANOCOBALAMIN 50 TO 150 MICROGRAMS MAY BE TAKEN DAILY BY MOUTH BETWEEN MEALS.
LOWER DOSES OF BOTH CYANOCOBALAMIN AND HYDROXOCOBALAMIN ARE RECOMMENDED IN THE USA. FOR THE TREATMENT OF DEFICIENCY, THE USUAL INTRAMUSCULAR DOSE OF CYANOCOBALAMIN IS 100 MICROGRAMS DAILY FOR 7 DAYS, THEN ON ALTERNATE DAYS FOR 7 FURTHER DOSES, THEN EVERY 3 TO 4 DAYS FOR 2 TO 3 WEEKS. FOR HYDROXOCOBALAMIN THE DOSE IS 30 TO 50 MICROGRAMS DAILY FOR 5 TO 10 DAYS. FOR MAINTENANCE, BOTH CYANOCOBALAMIN AND HYDROXOCOBALAMIN ARE GIVEN AT A DOSE OF 100 TO 200 MICROGRAMS MONTHLY, BASED ON HAEMATOLOGICAL MONITORING. AN INTRANASAL PREPARATION OF CYANOCOBALAMIN IS ALSO AVAILABLE FOR MAINTENANCE THERAPY, THE RECOMMENDED DOSE BEING 500 MICROGRAMS ONCE WEEKLY. ORAL DOSES OF UP TO 1000 MICROGRAMS OF CYANOCOBALAMIN HAVE ALSO BEEN USED. IN PATIENTS WITH NORMAL GASTROINTESTINAL ABSORPTION, DOSES OF 1 TO 25 MICROGRAMS DAILY ARE CONSIDERED SUFFICIENT AS A DIETARY SUPPLEMENT.
TREATMENT USUALLY RESULTS IN RAPID HAEMATOLOGICAL IMPROVEMENT AND A STRIKING CLINICAL RESPONSE. HOWEVER, NEUROLOGICAL SYMPTOMS RESPOND MORE SLOWLY AND IN SOME CASES REMISSION MAY NOT BE COMPLETE.
HYDROXOCOBALAMIN MAY ALSO BE GIVEN IN THE TREATMENT OF TOBACCO AMBLYOPIA AND LEBER'S OPTIC ATROPHY; INITIAL DOSES ARE 1000 MICROGRAMS DAILY FOR 2 WEEKS INTRAMUSCULARLY FOLLOWED BY 1000 MICROGRAMS TWICE WEEKLY FOR AS LONG AS IMPROVEMENT OCCURS. THEREAFTER, 1000 MICROGRAMS IS GIVEN EVERY 1 TO 3 MONTHS.