the present invention is directed at methods for preventing and treating opioid - induced dysphoria , opioid - induced pruritus , opioid - induced urinary retention , opioid - or nonopioid - induced inhibition of gastric emptying by enteric feeding , and opioid - or nonopioid - induced constipation . when used as a treatment for these opioid - and nonopioid - induced side effects , orally administered , particularly if enteric coated , methylnaltrexone ( mntx ) or other quaternary derivatives of noroxymorphone ( qdmn ) provides prolonged relief of the side effects . furthermore , for treatment or prevention of delayed gastric emptying from enteric feeding and constipation , whether caused by extrinsic or endogenous opioids , enteric coating surprisingly allows for equal or better efficacy despite lower plasma levels . idiopathic constipation , i . e ., that due to causes other than exogenous administration of opioids , may be mediated by opioid sensitive mechanisms . endogenous opioid receptors have been identified in the gut , and these receptors may modulate gut motility . thus , administration of an opioid antagonist with peripheral action , such a methylnaltrexone or other quaternary derivatives of noroxymorphone , would block the effects of endogenous opioids . quaternary derivatives of noroxymorphone are described in full in goldberg et al ., ( supra ), and in general are represented by the formula : wherein r is allyl or a related radical such as chlorallyl , cyclopropyl - methyl or propargyl , and x is the anion of an acid , especially a chloride , bromide ,. iodide or methylsulfate anion . the presently preferred quaternary derivative of noroxymorphone is methylnaltrexone . methylnaltrexone is a quaternary amine derivative of naltrexone . methylnaltrexone has been found to have only 2 to 4 % of the opiate antagonistic activity of naltrexone in vivo due to its inability to pass the blood - brain - barrier and bind to the opiate receptors in the central nervous system . opioids are typically administered at a morphine equivalent dosage of : 0 . 005 to 0 . 15 mg / kg body weight for intrathecal administration ; 0 . 05 to 1 . 0 mg / kg body weight for intravenous administration ; 0 . 05 to 1 . 0 mg / kg body weight for intramuscular administration ; 0 . 05 to 1 . 0 mg / kg body weight / hour for transmucosal or transdermal administration . by “ morphine equivalent dosage ” is meant representative doses of other opioids which equal one milligram of morphine , for example 10 mg meperidine , 1 mg methadone , and 80 . mu . g fentanyl . in accordance with the present invention , methylnaltrexone is administered at a dosage of : 0 . 03 to 1 . 0 mg / kg body weight for intravenous administration ; 0 . 03 to 1 . 0 mg / kg body weight for intramuscular administration ; 0 . 03 to 1 . 0 mg / kg body weight for transmucosal administration and 1 . 0 to 40 . 0 mg / kg body weight for oral administration . in accordance with the present invention , enteric coated methylnaltrexone , is administered at a dosage of 1 . 0 to 80 . 0 mg / kg body weight for oral administration . the administration of the methylnaltrexone is preferably commenced prior to administration of the opioid to prevent opioid - induced dysphoria , pruritus , urinary retention , inhibition of gastric emptying with enteric feeding , or constipation . it is desirable to commence administration of methylnaltrexone about 5 minutes for parenteral mntx administration and 20 minutes for enteral mntx administration prior to administration of opioids in order to prevent these opioid - induced side effects . it is also preferable to administer the methylnaltrexone prior to the onset of nonopioid - induced gastric dysfunction symptoms , inhibition of gastric emptying with enteric feeding or constipation , in order to prevent these symptoms from manifesting . while the prevention of symptoms is preferred , methylnaltrexone administration may also be commenced after the administration of the opioid or after the onset of opioid induced symptoms as a treatment for those symptoms . methylnaltrexone is rapidly absorbed after oral administration from the stomach and bowel . initial plasma levels of the drug are seen within 5 - 10 minutes of the administration of non - enteric coated compound . addition of an enteric coating which prevents gastric absorption is associated with lower plasma levels of the methylnaltrexone . surprisingly , the addition of an enteric coating ( i . e ., a coating which will prevent degradation or release in the stomach , but will release drug in the small and large bowel ) appears to enhance the efficacy of methylnaltrexone in the prevention of decreases in gut motility by intravenously administered opioids ( morphine ). for intravenous administration , methylnaltrexone is formulated with saline or other physiologically acceptable carriers ; for intramuscular administration , the methylnaltrexone is formulated with saline or other pharmacologically acceptable carriers ; for transmucosal administration the methylnaltrexone is formulated with a sugar and cellulose mix or other pharmacologically acceptable carriers known in the art ; and for oral administration , the methylnaltrexone is formulated with pharmacologically acceptable binders to make a tablet or capsule with or without an enteric coating . methods for such formulations are well known to those skilled in the art . in a preferred embodiment for the prevention and / or treatment of constipation , the mntx is enterically coated and administered orally . the enteric coating may be made of any suitable composition . suitable enteric coatings are described , for example , in u . s . pat . nos . 4 , 311 , 833 to namikoshi , et al . ; 4 , 377 , 568 to chopra ; 4 , 385 , 078 to onda , et al . ; 4 , 457 , 907 to porter ; 4 , 462 , 839 to mcginley , et al . ; 4 , 518 , 433 to mcginley , et al . ; 4 , 556 , 552 to porter , et al . ; 4 , 606 , 909 to bechgaard et al . ; 4 , 615 , 885 to nakagame , et al . ; 4 , 670 , 287 to tsuji ; 5 , 536 , 507 to abramowitz , et al . ; 5 , 567 , 423 to ying , et al . ; 5 , 591 , 433 to michael , et al . ; 5 , 597 , 564 to ying , et al . ; 5 , 609 , 871 to michael , et al . ; 5 , 614 , 222 to kaplan ; 5 , 626 , 875 to rodes , et al . ; and 5 , 629 , 001 to michael , et al ., all of which are incorporated herein by reference . preferred enteric coating compositions include alkyl and hydroxyalkyl celluloses and their aliphatic esters , e . g ., methylcellulose , ethylcellulose , hydroxyethylcellulose , hydroxypropylcellulose , hydroxybutylcellulose , hydroxyethylethylcellulose , hydroxyprophymethylcellulose , hydroxybutylmethylcellulose , hydroxypropylcellulose phthalate , hydroxypropylmethylcellulose phthalate and hydroxypropylmethylcellulose acetate succincate ; carboxyalkylcelluloses and their salts , e . g ., carboxymethylethylcellulose ; cellulose acetate phthalate ; cellulose acetate trimellitate , polycarboxymethylene and its salts and derivatives ; polyvinylalcohol and its esters : polyvinyl acetate phthalate ; polycarboxymethylene copolymer with sodium formaldehyde carboxylate ; acrylic polymers and copolymers , e . g ., methacrylic acidmethyl methacrylic acid copolymer and methacrylic acid - methyl acrylate copolymer ; edible oils such as peanut oil , palm oil , olive oil and hydrogenated vegetable oils ; polyvinylpyrrolidone ; polyethyleneglycol and its esters : natural products such as shellac , and zein . other preferred enteric coatings include polyvinylacetate esters , e . g ., polyvinyl acetate phthalate ; alkyleneglycolether esters of copolymers such as partial ethylene glycol monomethylether ester of ethylacrylate - maleic anhydride copolymer or diethyleneglycol monomethylether ester of methylacrylate - maleic anhydride copolymer , n - butylacrylatemaleic anhydride copolymer , isobutylacrylate - maleic anhydride copolymer or ethylacrylate - maleic anhydride copolymer ; and polypeptides resistant to degradation in the gastric environment , e . g ., polyarginine and polylysine . mixtures of two or more of the above compounds may be used as desired . the presently preferred enteric coating comprises cellulose acetate phthalate . the enteric coating material may be mixed with various excipients including plasticizers such as triethyl citrate , acetyl triethyl citrate , diethyl phthalate , dibutyl phthalate , dibutyl subacute , dibutyl tartrate , dibutyl maleate , dibutyl succinate and diethyl succinate and inert fillers such as chalk or pigments . the composition and thickness of the enteric coating may be selected to dissolve immediately upon coated with the digestive juice of the intestine . alternatively , the composition and thickness of the anterior coating may be selected to be a time - release coating which dissolves over a selected period of time , as is well known in the art . the amount of enteric coating depends on the particular enteric coating composition used and is preferably sufficient to substantially prevent the absorption of mntx in the stomach . hydroxyalkyl celluloses and their aliphatic esters , carboxyalkyl celluloses and their salts , polycarboxymethylene and its salts and derivatives , polyvinyl alcohol and its esters , polycarboxymethylene copolymer with sodium formaldehyde carboxylates , polyvinylpyrrolidone , and polyethylene glycol and its esters can be applied as enteric coatings by first dissolving the compound in a minimum amount of water . alcohol is then added to the point of incipient cloudiness . the mixture can then be applied by conventional techniques . application of cellulose acetate phthalate may be accomplished by simply dissolving the cellulose acetate phthalate in a minimum amount of alcohol and then applying by conventional techniques . hydrogenated vegetable oils may be applied by first dissolving the oil in a minimal amount of a non - polymer solvent , such as methylene chloride , chloroform or carbon tetrachloride , then adding alcohol to the point of incipient cloudiness and then applying by conventional techniques . in a particularly preferred embodiment , the mntx is coated with eudragit l100 or s100 , a methacrylic acid copolymer enteric coating , at a 50 % coating level to provide stability at gastric ph and dissolution at gut ph per a us pharmacopeia ( usp ) standard for enteric coatings . any art - known transdermal application may be used , but transdermal administration is preferably via a patch applied to the skin with a membrane of sufficient permeability to allow diffusion of mntx at a fixed rate in the range of 1 . 0 to 10 . 0 mg / hr . the rate of administration may be varied by varying the size of the membrane contact area and / or applying an electrical wiring potential to a drug reservoir . the patch preferably holds 25 mg to 1 gram of available drug in the reservoir plus additional drug as needed for the mechanics of the system . in the above description , methylnaltrexone is used as an example of a particularly effective qdnm . it is apparent that other qdnm &# 39 ; s may be used as desired . the following examples are intended to illustrate aspects of the invention and are not to be construed as limitations upon it . the methylnaltrexone used in the following examples was manufactured by mallinckrodt pharmaceuticals , st . louis , mo . the enteric coating was manufactured by coating place , inc ., verona , wis . ten patients were treated with morphine sulfate administered directly to the central nervous system or intravenously . the morphine sulfate was administered at 0 . 1 mg / kg body weight . the patients in the study had been treated for pain resulting from surgery . all the patients exhibited pruritus as a side effect of the morphine sulfate administration . subsequent to the onset of the pruritus , methylnaltrexone , at a dosage of 0 . 3 mg / kg of body weight was administered intravenously as a saline solution containing methylnaltrexone in a concentration of 5 mg / ml to each of the patients . eighty percent of the 10 patients exhibited relief from the pruritus sixty minutes after receiving methylnaltrexone . in a control group , 8 patients were treated with morphine sulfate administered directly to the central nervous system or intravenously . the morphine sulfate was administered at 0 . 1 mg / kg body weight . the patients in the study had been treated for pain resulting from surgery . all the patients exhibited pruritus as a side effect of the morphine sulfate administration . a placebo , saline at a volume equivalent to the volume administered to patients receiving active drug , was administered intravenously to each of the patients . only 50 % of the patients exhibited relief from the pruritus within sixty minutes . the study indicates that methylnaltrexone was effective in treating pruritus induced by morphine sulfate . morphine ( 0 . 05 ) mg / kg intravenous ) was administered to three volunteers after the oral administration of placebo , methylnaltrexone ( 6 . 4 mg / kg ) in a gelatin capsule ( which dissolves readily in the stomach ), or methylnaltrexone after enteric coating ( 12 . 8 mg / kg of substance to yield a mass of 6 . 4 mg / kg methylnaltrexone incorporated ) which has decreased release and absorption in the stomach . oral - cecal transit time was measured using the lactulose - hydrogen breath test . plasma levels of methylnaltrexone were measured and after the enteric coated preparation were lower . in each subject morphine alone increased the oral - cecal transit time by 20 - 70 minutes , methylnaltrexone blocked this effect , and enteric coated methylnaltrexone blocked the effect to a similar or greater extent than the uncoated methylnaltrexone . two patients receiving morphine ( 375 mg / day and 18 mg / day ) and receiving enteric tube feedings of 200 ml every four ( 4 ) hours were studied . the first patient had residual stomach contents of 50 cc to 100 cc , or 22 . 0 - 58 . 8 % of administered feedings measured every 4 hours during a 24 hour control period . prior to drug administration the residual volume had increased to 260 cc or & gt ; 100 % of previous feeding volume . methylnaltrexone , 0 . 45 mg / kg , was administered intravenously every 4 hours for 24 hours , after the control period . after the first dose ( 4 hours ) of mntx , the residual was 150 cc or 58 % of the previous bolus feed , after the 3rd dose ( 12 hours ) the residual was 75 cc or 30 % of the previous feed , after the 5th dose ( 20 hours ) the residual was 22 cc or 13 % of the previous feed and after the 6th and final dose ( 24 hours ) the residual was 8 cc or 5 . 5 % of previous feed . the follow - up residual sampling after the final drug - tube feed interval had increased to 50 cc or 38 % or previous feed . the second patient had greater than 200 cc residual or 100 % of previous feedings on two consecutive samplings , that is 8 hrs and 4 hrs before drug administration . after initiation of methylnaltrexone , 0 . 45 mg / kg , administered intravenously every 4 hours , the first residual ( 4 hrs ) was 0 cc , the second residual ( 8 hrs ) was 24 cc or 15 % of previous bolus feed . subjects receiving morphine at a variety of doses ( via patient controlled analgesia — pca ) who experience urinary retention are administered methylnaltrexone 0 . 45 mg / kg intravenously or a placebo . those treated with methylnaltrexone have resolution of their symptoms , while those administered placebo go on to require additional therapy ( usually urinary catheterization ). in a double - blind randomized placebo - controlled study , we evaluated the efficacy of oral methylnaltrexone to decrease subjective effects after administering morphine to 10 normal human volunteers . after intravenous morphine injection ( 0 . 05 mg / kg ), significant increases in subjective ratings were obtained on “ nauseous ”, “ skin itch ”, “ stimulated ”, and “ flushing ”. compared to baseline , significant increases were obtained on “ nauseous ”, “ skin itch ”, “ stimulated ”, and “ flushing ” ratings after placebo and morphine administration ( p & lt ; 0 . 05 , p & lt ; 0 . 05 , p & lt ; 0 . 01 and p & lt ; 0 . 01 , respectively ). oral methylnaltrexone ( 19 . 2 mg / kg ) significantly decreased these four ratings ( p & lt ; 0 . 05 , p & lt ; 0 . 05 , p & lt ; 0 . 01 and p & lt ; 0 . 01 , respectively ) compared to placebo and morphine and resulted in no change when compared to baseline . plasma methylnaltrexone concentrations were also measured and correlation between pharmacological effects of the compound and its plasma levels was shown . our results indicate that methylnaltrexone decreases dysphoria and some other undesirable subjective effects associated with opioid medications . the preceding description and examples are intended to be illustrative . those skilled in the art to which the invention pertains will appreciate that alterations and changes in the described protocols may be practiced without departing from the meaning , spirit , and scope of this invention . therefore , the foregoing description should be read consistent with and as support to the following claims , which are to have their fullest and fair scope .
a method of for preventing or treating gastrointestinal dysfunction and constipation caused by endogenous opioids in a patient who has been chronically taking opioids . the method comprises administering methylnaltrexone or another quaternary derivative of noroxymorphone most preferably by parenteral , intramuscular , intravenous or oral route .