Indication:
Opioid Induced Constipation
Adverse Reaction:
CNS- dizziness 7%
GI- abdominal pain 28% diarrhea 5% flatulence 13% nausea 11%
Contra-Indications:
In patients with known or suspeceted mechanical GI obstruction
Special Precautions-
Severe or persistent diarrhea- if severe or persistent diarrhea occurs advice patients
to discontinue therapy and consult the doctor
Peripheral catheters- use of methynaltexone has not been studied with peripherl catheters
Renal function impairment- dose reduction of one-half is recommended in patients with
severe renal function impairment (CrCl less than 30mL/min)
Pregnancy- use methylnatrexone only if absolutely needed
Lactation- excercise caution when methynatrexone is administered to breast-feeding
woman.
Children- Safety for use in children have not establishd
Dosages/ Overdosage Etc:
Indication-
Opioid Induced constipation
Dosage-
8mg for patients weighing 38 or less than 62kg (84 to less than 136 lb) or
12mg for patients weighing 62 to 114kg (136 to 251 lb)
The usual schedule is 1 dose every other day as needed but no more frequently than
1 dose in a 24 hour period.
Patients falling outside this range should be dosed at 0.15mg/kg
Patient Information:
1. Instruct patients the usual schedule of 1 dose every other day as needed, but no
more frequently than 1 dose in 24 hours period
2.In about 30% of patients in clinical trials, laxation was reported within 30 minutes of
administering the drug. Advice patients to be within close proximity of toilet facitites
once the drug is administered
3.Advice patients not to continue taking the drug if they experience severe or persistent
diarrhea
4. Instruct patients to discontinue mthylnatrexone if they stop taking their opioid
pain medication
Pharmacology/ Pharmacokinetics:
Ref - Drug Facts and Comparison (2010)
Pharmacology-
Methylnatrexone is a selective antagonist of opioid binding the muopioid receptor.
As a quaternary amine , the ability of methylnatrexone to cross the blood-brain barier
is restricted. This allows methynaltrexone to function as peripherally acting mucopioid
receptor antagonist in tissues such as GI tract, thereby decreasing the constipating
effects of opioid without impacting opioid mediated analgesic effects on the CNS
Pharmacokinetics
Following subcutaneous admin methylnaltrexone is absorbed rapidly with peak
concentration Cmax acheived at approx 0.5 hrs . Across the range of doses evaluated
peak concentration and area under curve (AUC) increase in a dose proportional
manner as indicated-
Pharmacokinetic Parameters of Methynaltrexone
following single Subcutaneous doses
Parameter 0.15mg/kg 0.3mg/kg 0.5mg/kg
Cmax 9ng/mL) 117(32.7) 239(62.2) 392(147.9)
Tmax (hours) 0.5(0.25 to 0.75) 0.5(0.25 to 0.75) 0.5 (0.25 to 0.75)
AUC 9ng*h/mL) 175(36.6) 382(63.8) 582(111.2)
Pregnancy and lactation:
Pregnancy- use methylnatrexone only if absolutely needed
Lactation- excercise caution when methynatrexone is administered to breast-feeding
woman.
Children- Safety for use in children have not establishd
Manufacturer Details