a 52-year - old male patient with a height of 163 cm and a weight of 65 kg was admitted to the hospital due to right femoral edema , and following a diagnosis of right femoral abscess , an incision and drainage procedure was performed . with regard to medical history ,
the patient was paraplegic from the level of the fourth thoracic vertebra due to a t2-level spinal cord injury from a car accident 4 years previously . due to tetany symptoms in both lower limbs
, he had been regularly taking an oral dantrolene formula of 50 mg ( anorex cap .
25 mg , yooyoung pharmaceutical , seoul , korea ) every night for the previous 3 years .
prior to the operation , the patient 's blood pressure was 100/60 mmhg , and his heart rate was 94 beats per minute .
there was a systemic inflammation response due to the right femoral abscess , accompanied by an increase in body temperature ( 38.3 ) ; in addition , the prothrombin time was outside the normal range ( inr 1.21 ) .
when the patient entered the operating room , the standard anesthetic monitoring devices were applied , and the blood pressure and heart rate were 123/78 mmhg and 86 beats per minute , respectively . the neuromuscular monitoring device ( tof - watch
, organon , boxtel , netherlands ) was attached to the ulnar nerve of the left forearm flap .
propofol 2 mg / kg was intravenously administered for induction of anesthesia , and i.v .
rocuronium 0.3 mg / kg ( ed95 ) was administered while ventilating with 5 l / min of oxygen and 4 vol% of sevoflurane .
the tof ratio did not fall under 0.25 2 minutes after rocuronium administration , and 10 mg ( 0.15 mg / kg ) of i.v .
after 2 minutes , the tof count still had not decreased to 0 , and 0.15 mg / kg of i.v .
thereafter , the tof count decreased to 0 , and endotracheal intubation was carried out .
the mandible was sufficiently relaxed at the time of endotracheal intubation ; there was no movement of the vocal cord , and coughing or movement was not observed after intubation .
the anesthesia was maintained with 1.2 - 1.5 vol% of sevoflurane and 50% n2o during the operation .
the tof ratio was 0.37 at the end of the operation , which was 35 minutes after the last dose of the muscle relaxant had been administered .
intravenous pyridostigmine 0.15 mg / kg and glycopyrrolate 0.003 mg / kg were administered as antagonists of the muscle relaxant .
extubation was carried out ; the tof ratio was maintained above 0.9 at around 55 minutes after the last dose of the muscle relaxant had been administered .
no sign of respiratory depression was observed after extubation , and no particular signs and symptoms were observed in the recovery unit .
three months later , the patient was diagnosed with chronic osteomyelitis , and an incision and drainage operation was planned .
it was decided to perform general anesthesia in consideration of the state of systemic inflammation and the patient 's preference . as pretreatment for anesthesia , 0.2 mg of i.m .
when the patient entered the operating room , the standard anesthetic monitoring devices and the neuromuscular monitoring device were applied in the same manner as in the previous operation .
the blood pressure was 112/70 mmhg , and the heart rate was 93 beats per minute .
the neuromuscular monitoring device ( tof - watch sx , organon , netherlands ) was attached to the ulnar nerve of the right forearm flap .
after the loss of consciousness , stabilization and calibration were carried out to establish the initial value of the spasm height prior to the administration of rocuronium .
for the calibration of the spasm reaction , a 50 hz tetanic stimulation was conducted for 5 seconds , which was then changed to a 2 hz tof stimulation with 15-second intervals , and the calibration was initiated by pressing the cal switch on the tof - watchsx ( cal 2 mode ) .
the tof response change was within 10% 2 minutes after the calibration , and this was considered as the stabilization of the spasm response .
administration of rocuronium 0.3 mg / kg ( ed95 ) , a block of more than 80% of t1 failed ; therefore , additional i.v .
rocuronium 0.3 mg / kg was administered , and a 100% block of t1 was achieved at just past 300 seconds .
the anesthesia was maintained with 1.5 - 2.0 vol% of sevoflurane and 50% of n2o during the operation .
the time taken to recover t1 to 25% after the administration of the second dose of the muscle relaxant was 4 minutes and 36 seconds .
twenty - five minutes after endotracheal intubation , t1 had recovered more than 25% ; hence , an additional 7.5 mg of rocuronium was administered . with
the recovery of the muscle relaxation , the time taken for t1 to recover from 25% to 75% was 9 minutes and 1 second .
the tof ratio was 0.33 5 minutes after ceasing sevoflurane administration on completion of the operation .
neostigmine 0.05 mg / kg and glycopyrrolate 0.005 mg / kg were administered to antagonize the muscle relaxation . at 5 minutes and 30 seconds after administration of the antagonist ,
t1 had recovered more than 95% , and the tof ratio had recovered to more than 0.9 . therefore , extubation was carried out .
the authors confirmed that long - term administration of oral dantrolene for the treatment of spasticity does not significantly affect the muscle relaxant action of rocuronium . regarding the induction of muscle relaxation in the second operation ,
t1 did not decrease more than 84% 3 minutes and 30 seconds after the administration of 0.3 mg / kg of rocuronium .
hence , an extra dose of 0.3 mg / kg of rocuronium was administered . a more than 95% reduction in t1
was observed 5 minutes after the administration of the first dose of the muscle relaxant . in both of the operations , the total amount of rocuronium required for endotracheal intubation was twice the ed95 ( 0.6 mg / kg ) . for the maintenance of muscle relaxation , the clinical duration ( the time taken from the administration of the intubating dose until 25% recovery of t1 ) was 24 minutes and 36 seconds , which was not extended any further . for the recovery of muscle relaxation ,
the recovery index ( the time taken for t1 recover from 25 to 75% ) in the second operation was 9 minutes and 1 second , and the time taken for the tof ratio after the last dose of the muscle relaxant to be greater than 0.9 was 22 minutes and 30 seconds , which was not extended any further .
reported the case of an 8-year - old patient who had been taking oral dantrolene 20 mg daily for the treatment of spasticity for 2 years prior to an operation .
when 75 g / kg of vecuronium was administered for general anesthesia , the recovery index was 7 minutes , and the recovery time of t1 to 90% was 25 minutes , which was not extended .
after the operation , neostigmine and atropine were used as antagonists of the muscle relaxant when t1 had recovered to 25% .
flewellen et al .   evaluated the dose - dependent effect of dantrolene on the muscle relaxant action in adults without a particular medical history , and 75% twitch depression was observed when 2.4 mg / kg was intravenously administered with the additional administration of 0.1 mg / kg of dantrolene every 5 minutes . however , there was no significant change in maximum expiratory flow rate , lung capacity , or respiratory rate per minute .
driessen et al .   reported the case of a 60-year - old female patient who was administered 350 mg ( 5.3 mg / kg ) of dantrolene for 28 hours prior to an operation for the prevention of malignant hyperthermia .
when 45 g / kg of vecuronium was administered for general anesthesia , the spasm response of the 90% recovery time on the electromyogram was extended to 47 minutes .
furthermore , watson et al .   described the case of a 5-year - old female patient who was administered 2 doses of 1 mg / kg oral dantrolene every 6 hours for the prevention of malignant hyperthermia .
after the second dose , the patient manifested muscle weakness and partial obstruction of the soft tissue of the upper respiratory tract under respiration .
the patient in this case had been administered 50 mg of oral dantrolene once a day , and in both operations , the total dose of muscle relaxant ( 0.6 mg / kg ) required for endotracheal intubation was not particularly different from the dose required in other patients .
these results can be attributed to the fact that the patient was taking 0.76 mg / kg of dantrolene , and the elimination half life of dantrolene is 15.8  6.0 h. as the first operation was at 4 p.m. and the second operation was at 1 p.m. , the operations were carried out 21 hours and 18 hours after the administration of dantrolene , respectively . therefore , the reduction in the serum concentration of dantrolene that was administered the day before the operation is considered to be one of the factors influencing the results .
the perioperative administration of dantrolene may cause a delay in the recovery of muscle relaxation in a dose - dependent manner , and the timing of preoperative administration is especially important as it is associated with the serum dantrolene concentration .
therefore , for patients taking a high dose of dantrolene , it is helpful to consider the half life of the medication when making decisions about the timing of medication discontinuation .
however , there are individual differences in pharmacokinetics . for the use of a muscle relaxant , neuromuscular monitoring
 oral dantrolene causes a dose - dependent depression of skeletal muscle contractility . a 52-year - old man treated with oral dantrolene for spasticity after spinal cord injury was scheduled to undergo irrigation and drainage of a thigh abscess under general anesthesia . 
 he had taken 50 mg oral dantrolene per day for 3 years . under standard 
 neuromuscular monitoring , anesthesia was performed with propofol , rocuronium , and sevoflurane . 
 a bolus dose of ed95 ( 0.3 mg / kg ) of rocuronium could not depress t1 up to 95% . 
 an additional dose of rocuronium depressed t1 completely and decreased the train - of - four ( tof ) count to zero . 
 there was no apparent prolongation of the neuromuscular blocking action of rocuronium . 
 the tof ratio was recovered to more than 0.9 within 40 minutes after the last dose of rocuronium . a small dose of oral dantrolene 
 does not prolong the duration of action and recovery of rocuronium . 