THE DOSAGE OF ALFENTANIL USED DEPENDS ON WHETHER THE PATIENT HAS SPONTANEOUS RESPIRATION OR ASSISTED VENTILATION AND ON THE EXPECTED DURATION OF ANAESTHESIA. DOSES ARE ADJUSTED ACCORDING TO THE NEEDS OF THE PATIENT. CHILDREN MAY REQUIRE HIGHER OR MORE FREQUENT DOSES THAN ADULTS, WHEREAS THE ELDERLY OR DEBILITATED PATIENTS MAY REQUIRE LOWER OR LESS FREQUENT DOSES. OBESE PATIENTS MAY REQUIRE DOSES BASED ON THEIR IDEAL (LEAN) BODY-WEIGHT.
WHEN USED AS AN ADJUNCT IN THE MAINTENANCE OF GENERAL ANAESTHESIA THE INITIAL LICENSED DOSE IN THE UK IS AS FOLLOWS:
IN ADULTS WITH SPONTANEOUS RESPIRATION, UP TO 500 MICROGRAMS GIVEN SLOWLY OVER ABOUT 30 SECONDS; SUPPLEMENTARY DOSES OF 250 MICROGRAMS MAY BE GIVEN.
VENTILATED ADULTS AND CHILDREN MAY BE GIVEN 30 TO 50 MICROGRAMS/KG WITH SUPPLEMENTS OF 15 MICROGRAMS/KG. (THE BNFC SUGGESTS DOSES AS LOW AS 20 MICROGRAMS/KG MAY BE APPROPRIATE IN NEONATES.) WHEN GIVEN BY INFUSION TO VENTILATED ADULTS AND CHILDREN INCLUDING NEONATES THERE IS AN INITIAL LOADING DOSE OF 50 TO 100 MICROGRAMS/KG GIVEN AS A BOLUS OR BY INFUSION OVER 10 MINUTES, AND THIS IS FOLLOWED BY INFUSION AT A RATE OF 0.5 TO 1 MICROGRAM/KG PER MINUTE.
TYPICAL DOSES THAT HAVE BEEN USED IN THE USA ARE AS FOLLOWS:
FOR PROCEDURES LASTING LESS THAN 30 MINUTES IN ADULTS WITH SPONTANEOUS RESPIRATION OR ASSISTED VENTILATION, THE DOSE IS 8 TO 20 MICROGRAMS/KG; THIS MAY BE FOLLOWED BY SUPPLEMENTARY DOSES OF 3 TO 5 MICROGRAMS/KG EVERY 5 TO 20 MINUTES OR AN INFUSION OF 0.5 TO 1 MICROGRAM/KG PER MINUTE.
WHEN THE EXPECTED DURATION OF ANAESTHESIA IS LONGER THAN 30 MINUTES, THE INITIAL DOSE FOR ADULTS WITH ASSISTED VENTILATION IS 20 TO 75 MICROGRAMS/KG, FOLLOWED BY EITHER SUPPLEMENTARY DOSES OF 5 TO 15 MICROGRAMS/KG OR AN INFUSION OF 0.5 TO 3 MICROGRAMS/KG PER MINUTE. IF ALFENTANIL HAS BEEN GIVEN IN ANAESTHETIC DOSES (SEE BELOW) FOR THE INDUCTION OF ANAESTHESIA, INFUSION RATES MAY NEED TO BE REDUCED BY 30 TO 50% DURING THE FIRST HOUR OF MAINTENANCE.
MAINTENANCE INFUSIONS OF ALFENTANIL SHOULD BE STOPPED 10 TO 30 MINUTES BEFORE THE ANTICIPATED END OF SURGERY.
THE DOSE FOR THE INDUCTION OF ANAESTHESIA IN PATIENTS WITH ASSISTED VENTILATION UNDERGOING PROCEDURES OF AT LEAST 45 MINUTES IS 130 TO 245 MICROGRAMS/KG, FOLLOWED BY AN INHALATION ANAESTHETIC OR MAINTENANCE DOSES OF ALFENTANIL OF 0.5 TO 1.5 MICROGRAMS/KG PER MINUTE.
IN INTENSIVE CARE VENTILATED ADULTS MAY BE GIVEN ALFENTANIL INITIALLY AT AN INFUSION RATE OF 2 MG/HOUR OR A LOADING DOSE OF 5 MG MAY BE GIVEN IN DIVIDED DOSES OVER 10 MINUTES OR MORE SLOWLY IF HYPOTENSION OR BRADYCARDIA OCCUR. THEREAFTER A SUITABLE RATE OF INFUSION SHOULD BE DETERMINED FOR EACH PATIENT (RATES OF 0.5 TO 10 MG/HOUR HAVE BEEN USED); PATIENTS SHOULD BE CAREFULLY MONITORED AND THE DURATION OF TREATMENT SHOULD NOT GENERALLY EXCEED 4 DAYS. DURING CONTINUOUS INFUSION ADDITIONAL BOLUS INJECTIONS OF 0.5 TO 1 MG MAY BE GIVEN IF REQUIRED TO PROVIDE ANALGESIA FOR SHORT PAINFUL PROCEDURES THAT MAY BE CARRIED OUT IN INTENSIVE CARE.