the present invention provides an oral pharmaceutical composition which contains an effective amount of nalbuphine , nalbuphine derivatives , or pharmaceutically acceptable nalbuphine salts thereof . a nalbuphine monoester prodrug has the following generic chemical formula ( ii ): in which r is r ′ co , wherien r ′ is a straight or branched alkyl group of 2 - 36 carbon atoms or a phenyl group . ( yoa - pu et al ., u . s . pat . no . 5 , 750 , 534 ). the preferred nalbuphine monoester prodrugs which include , but are not limited to , nalbuphine propionate , nalbuphine pivalate , nalbuphine enanthate , nalbuphine decanoate , nalbuphine behenate , nalbuphine erucicate , nalbuphine arachidate , and nalbuphine benzoate . a nalbuphine polyester prodrug has the following generic chemical formula ( iii ): wherein n is an integer from 2 to 4 and wherein r is a saturated or unsaturated , substituted or unsubstituted , aliphatic or aromatic group having 1 to 40 carbon atoms . ( hu et al ., u . s . pat . no . 6 , 225 , 321 ). the preferred nalbuphine polyester prodrugs include adipoyl dinalbuphine ester , sebacoyl dinalbuphine ester , 1 , 3 - cyclohexane diacid dinalbuphine ester , docosanodic dinalbuphine ester , 3 , 3 - dimethylglutaric diacid dinalbuphine ester , trinalbuphine trimesoyl ester , 1 , 3 , 5 - cyclohexane triacid trinalbuphine ester , pyromellitoyl tetranalbuphine ester . the most favorable nalbuphine polyester prodrug is sebacoyl dinalbuphine ester ( sdn ). the pharmaceutical composition of the present invention contains three major components : ( 1 ) an active ingredient ; ( 2 ) an oily substance ; and ( 3 ) a solubility - assisting agent . the active ingredient of the pharmaceutical composition includes nalbuphine , nalbuphine monoester , and nalbuphine polyester , or a pharmaceutically acceptable salts of nalbuphine , nalbuphine monoester , and nalbuphine polyester . the preferred active ingredient is nalbuphine polyester . among nalbuphine polyester , the most favorable one is sebacoyl dinalbuphine ester . the amount of nalbuphine or nalbuphine ester prodrug used in the pharmaceutical composition of the present invention is about 1 % to 15 % by weight of the composition . the preferred concentration of sebacoyl dinalbuphine ester in the pharmaceutical composition of the present invention is 100 mg / ml . the oily substance in the pharmaceutical composition of the present invention includes a vegetable oil . the vegetable oil used in the present invention include , but are not limited to , sesame oil , soybean oil , peanut oil , or an ethyl ester of sesame oil , soybean oil , or peanut oil . the preferred oily substance is sesame oil . the pharmaceutical composition contains about 30 % to 90 % by weight of vegetable oil . the solubility - assisting agent of the pharmaceutical composition is benzyl benzoate . the pharmaceutical composition contains about 5 % to 50 % by weight of the solubility - assisting agent . each and every one of these nalbuphine and / or nalbuphine ester prodrugs as listed above has been tested for suitability as an orally administered pharmaceutical composition for use in animals and humans . the efficacy and bioavailability of these nalbuphine ester prodrugs have been studied . the results indicate that the addition of the solubility - assisting agent to the nalbuphine and / or nalbuphine ester prodrugs and an oily substance substantially improves the bioavailability and half - life of nalbuphine in blood . among the nalbuphine active ingredient , sebacoyl dinalbuphine ester ( sdn ) appears to be the best in terms of longer half - life and greater bioavailability rate . the studies using sdn as an example are therefore provided below . please note that the following examples are illustrative only , and should not be viewed as limiting the scope of the present invention . reasonable variations , such as those occur to reasonable artisan , can be made herein without departing from the scope of the present invention . the pharmaceutical composition of the present invention is prepared as follows : 1 . mixing 5 . 5 ml sesame oil with 4 . 5 ml benzyl benzoate and stirring well to form an oily mixture . 2 . adding 1 g of sdn to 10 ml of the oily mixture with further stirring to produce a homogeneous pharmaceutical composition containing about 100 mg sdn per ml of the oily mixture . to assess the effects of various pharmaceutical compositions of the present invention on beagles . the compositions were orally administered into beagles , and the concentration of nalbuphine in vivo was monitored in the animals as follows : 1 . three pharmaceutical compositions were tested in this study , which include : ( 1 ) the pharmaceutical composition described in example 1 ( the “ complete sdn ” group ); ( 2 ) pure sebacoyl dinalbuphine ester powder without any oily substance or solubility - assisting agent ( the “ sdn powder ” group ); and ( 3 ) sebacoyl dinalbuphine ester with verapamil ( which is used as an oily substance ) ( the “ sdn + verapamil ” group ). 2 , in each study group , the pharmaceutical composition that contained 30 mg / kg of sdn were orally given to beagles . 3 . blood samples were taken from the forearm vein at 0 . 167 , 0 . 33 , 0 . 5 , 0 . 75 , 1 , 1 . 5 , 2 , 3 , 4 , 6 , 8 , 12 , 15 , 24 , 30 , and 48 hours after the oral administration . 4 . the blood samples were analyzed by high performance liquid chromatography ( hplc ) to determine the pharmacokinetics ( including the half - life and bioavailability of nalbuphine ) in vivo . as shown in fig1 the concentration of nalbuphine in the three groups peaked about 1 - 2 hours after oral administration of the pharmaceutical compositions . among the three groups , both the complete sdn group and the sdn + verapamil group had about the same concentration of nalbuphine in plasma 1 - 3 hours after the oral uptake of sdn . the concentration of nalbuphine in the sdn powder was much less than the other two groups . however , the concentration of nalbuphine in the sdn powder and the sdn + verapamil group decreased substantially whereas the concentration of nalbuphine in the complete sdn group still maintained at high percentage . verapamil is α -[ 3 -[[ 2 -( 3 , 4 - dimethoxyphenyl ) ethyl ] methylamino ] propyl ]- 3 , 4 - dimethoxy - α -( 1 - methylethyl )- benzeneacetonitrile . it is a viscous , pale yellow oil . verapamil is a well - known cytochrome p 450 3a ( cyp 3a ) inhibitor . cyp 3a is known to be responsible for metabolism of a large number of drugs in vivo , thus , reducing the bioavailability of drugs . the drugs that are know to be affected by cyp 3a include nifedipine , macrofide antibiotics such as erythromycin and troleandomycin , cyclosporin , fk506 , teffenadine , tamoxifen , lidocaine , midazolam , triazolam , dapsone , diltiazem , lovastatin , quinidine , ethylestradiol , testosterone , and alfentanil . a cyp 3a inhibitor can be used to inhibit the enzymatic activity of cyp 3a and thus improve the bioavailability of the drugs . assuming that the bioavailability of nalbupine is also affected by cyp 3a , an inclusion of verapamil ( the cyp 3a inhibitor ), together with sdn , should further improve the bioavailability of nalbupine ( if there is an synergistic effect between verapamil and sdn ). the results in fig1 suggest that without the solubility - assisting agent ( benzyl benzoate ), the addition of verapamil did not improve the bioavailability of nalbupine . table 1 shows the results of the pharmacokinetic studies of the three pharmaceutical compositions . as shown in table 1 , the nalbuphine half - life ( t 1 / 2 ) in the complete sdn group is 23 . 9 ± 3 . 0 hours , which was about 3 times longer than that of the sdn powder group and about 2 . 5 times longer than that of the sdn + verapamil group . the bioavailability of nalbuphine , as determined by auc ( area under curve ) and by % of decrease (% bioavailability ) also shows that the complete group is far much better than the rest of the two group ( auc - 171 [ complete group ] vs . 39 [ sdn powder group ] or 83 [ sdn + verapamil group ]; % bioavailability : 67 % [ complete group ] vs . 14 . 6 [ sdn powder group ] or 30 . 0 [ sdn + verapamil group ]). the results of fig1 and table 1 show that the addition of an oily substance to sdn greatly improve the half - life and bioavailability of nalbuphine in plasma ( as comparing the sdn powder group and sdn + verapamil group ). but the half - life and bioavailability rate of nalbuphine is far much greater when benzyl benzoate as a solubility - assisting agent is added to sdn with oil ( as comparing the complete sdn group with the sdn powder group and sdn + verapamil group ). while the invention has been described by way of examples and in terms of the preferred embodiments , it is to be understood that the invention is not limited to the disclosed embodiments . on the contrary , it is intended to cover various modifications as would be apparent to those skilled in the art . therefore , the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications .
the present invention provides orally administered pharmaceutical compositions which contains an effective amount of free base or pharmaceutcially acceptable salts of nalbuphine and / or nalbuphine ester , an oily substance , and a solubility - assisting agent . the oily substance is preferably sesame oil . the solubility - assisting agent is preferably benzyl benzoate . the pharmaceutical composition is useful as an analgesic . the compositions achieves a much higher bioavailability rate and yields much longer lasting effects on nalbuphine than other nalbuphine products currently in the market .