1126
`
`Journal of Phurmaceutual Sciences
`
`condition randomly. Group I-E received 250 mg.
`each of potassium and magnesium aspartate every
`12 hours starting within the first hour of the ex-
`pcriment. The drug was administered suspendcd
`iii 5 ml. distilled water directly into the stomach
`with a No. 18 catheter and syringe. (The potassiuin,
`but not the magnesium aspartate. would dissolve
`in the quantity of water used; for this reason only
`potassium aspartate was administered to groups
`11-E and 111-E.) Group 11-E received 200 mg.
`of potassium aspartate intraperitoneally in 1 ml.
`distilled water every 12 hours. Group 111-E re-
`ceived 50 mg. of potassium aspartate i.p. every 12
`hours in 0.5 ml. of distilled water. Each control
`group received an equal amount of distilled water
`administered by the same route as its experimental
`group.
`The rats were placed in individual 5.5 X 9.5-in.
`cubicles, on wheels, two-thirds submerged in water,
`which rotated at a constant speed of approximately
`2 r.p.m. Food trays were placed in each cubicle
`so that the animals could feed at any time. The
`animals remained on these wheels continuously
`except when they were removed twice a day for the
`drug administration. The total distance covered
`by an animal during the day was 0.7 mile. The
`rats, when exhausted, fell from the wheel into the
`water and were unable to remount the wheel.
`Animals were removed from the experiment when
`they fell into the water after being replaced on the
`wheel three times during a 15-minute period.
`This procedure is the same as that employed by
`Webb and Agnew.
`
`RESULTS
`Figure 1 shows for the experimental and control
`groups at each age the mean hours at which the
`criterion of exhaustion was reached. Data for
`only 34 animals are included in the analysis be-
`cause six did not learn to walk on the wheel (one
`in Group I-C, two in Group I-E, one in Group 111-C,
`and two in Group 111-E). Three animals were
`removed from the wheel at 136 hours at they seemed
`
`3
`
`I40
`
`30
`
`I50
`
`175
`AGE
`IOAYSI
`
`Fig. 1.-Mean
`hours until ex-
`haustion for the
`control and ex-
`p e r i m e n t a l
`groups at three
`ages.
`Key:
`t - -0. control ;
`0-0, e x p e r i -
`255 mental.
`
`to be interminable walkers (one in Group I-C,
`one in Group 11-E, and one in Group 11-C).
`DISCUSSION
`An analysis of variance resulted in a significant
`age difference ( p < .01) and a significant drug
`effect ( p < .05).
`First i t should be recognized that the design is
`flawed by the changed dosage procedures in the
`three age groups. Despite this flaw. the consistency
`of the results across all three conditions supports
`certain general conclusions.
`The previously reported relationship between
`age and exhaustion time was confirmed for both
`the experimental and the control groups. On the
`other hand, the results of the aspartate group (a)
`showed no differential age effect (when compared
`with the control groups) and (b) were contrary to
`the results reported by Rosen el al. (1).
`The latter finding suggests a dserential action
`of aspartic acid in a chronic exhaustion situation
`such as used here in contrast to the acute exhaustion
`procedure involved in the swim test. It is possible
`that aspartic acid may result in an overexpenditure
`of energy in a low requirement situation which
`reduces the possibility of resisting terminal ex-
`haustion.
`
`REFERENCES
`(1) Rosen H. Blumentbal A,, and Agenborg. H. P. K..
`THIS J O U R N ~ L , $1. 692(1982):
`(2) Webb. W. B.. and Agnew, H. W., Jr.. Science. 136,
`I122( 1962).
`
`Mineral Acid Salts of Lidocaine
`and JOHN J. HEPFERREN
`By HENRY M. KOEHLER
`. ,
`
`A ceptions are marketed as hydrochloride salts.
`
`Some physicochemical pro erties of the
`h drobromide, hydcochlori$
`nitrate, per-
`chorate, phosphate, and sulfate salts of hdo-
`caine are reported.
`LL LOCAL anesthetic agents with one or two ex-
`Since these agents are generally available in aqueous
`or glycol solutions or ointments for parenteral or
`topical administration, physical properties such as
`hygroscopicity are not so important as those of a
`drug normally formulated as a tablet or capsule.
`Keceived August 30 1963 from the Division of Chemistry,
`American Dental hdciatidn. Chicago, Ill.
`Accepted for publication January 8, 1964.
`A portion of this paper was presented at the 40th General
`meeting of the International Association for Dental Research,
`St. Louis. Mo., March 1962.
`The lidocaine base used in this study was generously sup-
`plied by Astra Pharmaceutical Products, Inc.
`
`For example, aqueous solutions of lidocaine hydro-
`chloride for pharmaceutical dosage forms are pre-
`pared by adding lidocaine base U.S.P. XVI (1) to a
`slight molar excess of dilute hydrochloric acid, rather
`than by dissolving the hydrochloride salt in water
`(2).
`In his dissertation about the synthesis and
`characteristics of anilide-type
`local anesthetics,
`Lofgren listed the melting points of four salts of lido-
`caine and the solubility of the hydrochloride salt
`in the common organic solvents (3). Except for this
`work, there is little or no published information on
`the hydrochloride (4) or other salts of lidccaine.
`This, coupled with the general feeling that lidocaine
`hydrochloride was difficult to prepare and somewhat
`hard to handle ( 5 ) led to the preparation and study
`of the mineral acid salts of lidocaine.
`The hydrobromide and hydrochloride salts were
`
`Merck Exhibit 2247, Page 1
`Mylan v. Merck, IPR2020-00040
`
`

`

`Vol. 53, No. 9, September 1964
`TABLE I.-%LUBILITY OF LIDOCAINE SALTS Gm./100 ml. Arr 25" C.
`
`1127
`
`Water
`Methanol
`Ethanol
`Acetone
`Chloroform
`Carbon disulfide
`Ether
`Carbon tetrachloride
`
`HCl
`100
`67
`11
`1 . 8
`4
`<0.01
`<0.01
`0.01
`
`HBr
`100
`67
`40
`2 . 2
`2 . 5
`<0.01
`<o. 01
`0.01
`
`H NOS
`17
`40
`4
`1.2
`20
`0.01
`<0.01
`<0.01
`
`HrSO4
`25
`0 . 8
`0 . 6
`<0.01
`0.02
`<o. 01
`<0.01
`0.01
`
`HsPOa
`29
`25
`0 . 7
`<0.01
`<0.01
`<0.01
`0.06
`<o. 01
`
`HClOa
`1.7
`10
`1.1
`14
`0.03
`<0.01
`<o. 01
`<0.01
`
`prepared in a dry box with a nitrogen atmosphere by
`passing dry hydrogen bromide and hydrogen chloride
`into anhydrous ether solutions of lidocaine base.
`The salts precipitated immediately and were washed
`thoroughly with ether. After removal of the ether,
`monohydrates of the halides were obtained in essen-
`tially quantitative yield. The anhydrous salts were
`prepared by drying overnight at 40' in a pumping
`vacuum. The nitrate. perchlorate, phosphate, and
`sulfate salts were prepared by adding a slight molar
`excess of the concentrated mineral acid or an abso-
`lute ethanolic solution of the acid to a well-stirred
`anhydrous ether solution of lidocaine base. The sul-
`fate was an equimolar salt, whereas the phosphate
`contained 1 mole of base per 2 moles of phosphoric
`acid. The salts, which were obtained in excellent
`yield and purity, could be recrystallized from an
`absolute methanol-ether mixture. The melting
`HBr - HzO, 94-103' : HCI, 127-132'. HCI . H20. 74-
`points of the lidocaine salts were: HBr, 127-132';
`
`78'; HNG, 131-133'; HC104. 204-205'; 2HsPO4.
`182c184'; and H801. 210-212'. Lijfgren (3) re-
`ported values of HCI, 128-129'; HNOa. 133-134';
`Hcl04,205'. The HC1. HIO was reported as 77-80'
`(4).
`All the lidocaine salts prepared were white, odor-
`less, crystalline solids. The solubilities of these salts
`are tabulated in Table I. All the salts, with the pos-
`sible exception of the perchlorate. are highly soluble
`in water and fairly soluble in polar solvents. Unlike
`most amine halide salts, lidocaine hydrobromide and
`hydrochloride are relatively soluble in chloroform.
`The stability of the salts in atmospheres of vafious
`relative humidities was determined by placing the
`powdered salts in tared aluminum moisture pans in
`three large desiccators, maintained at 52.9, 71.2,
`and 93.0yo relative humidities. These relative
`humidities were obtained by placing saturated solu-
`tions of Mg( NO*)*. 6H20, NH4Cl. KNOa, and NHI
`H2P04, respectively, in the bottom of the desicca-
`tors (6). The aluminum pans were weighed at 12
`and 24-hour intervals until constant weight was ob-
`tained. The gain in weight of the salts expressed as
`moles of water per mole of salt is given in Table 11.
`In the 93% relative humidity chamber, the halide
`salts liquified within 12 hours.
`In contrast, the
`monohydrates of
`the halide salts wcre relatively
`stable a t the lower humidities.
`
`TABLE II.-HYDRATION CHARACTERISTICS OF LIDO-
`CAINE SALTS
`-Relative Humidities at 25" C.-
`93.0%
`52.9%
`71.2%
`> 20
`1'1
`l a
`>2
`1
`1
`0
`0
`0
`0
`0
`0
`0
`0
`0
`0
`0
`0
`
`Hydrochloride
`Hydrobromide
`Nitrate
`Perchlorate
`Phosphate
`Sulfate
`
`a Increase in weight upreased as ratio of moles of water
`per moles of salt.
`The infrared absorption of the lidocaine salts was
`determined in KBr pellets and in chloroform when
`the solubility was adequate, The carbonyl band
`at about 6p offered an excellent peak for analysis.
`The base was extracted with chloroform from an
`aqueous alkaline solution and the chloroform extract
`dried, evaporated to a convenient volume, and then
`In a 1-mm. sodium
`diluted to known volume.
`chloride cell, the absorbance a t 6 p of the lidocaine
`base was linear from 1 to 7 mg./ml. Perchloric acid
`titration of the salt in glacial acetic acid or a chloro-
`form extract of the base was also a convenient
`analytical method.
`The mineral acid salts of lidomine base seemed to
`be characteristic of the salts of a number of thera-
`peutic agents containing basic nitrogen moieties.
`I t would appear that lidocaine hydrochloride mono-
`hydrate would present few problems in essentially
`dry pharmaceutical dosage forms. If extremes of
`humidity were anticipated, other salts such as the
`phosphate could be considered. Thus, with lidocaine
`as well as any basic drug, the potential availability
`of other mineral and carboxylic acid salts which
`may have more desirable physical properties should
`be considered before limiting work to the hydro-
`chloride salt.
`
`REFERENCES
`(1). "United States Pharmocopeia " 16th rev., Mack
`Printing Co.. Easton, Pa., 1960.p. 381:
`(2) "Accepted Dental Rcmediea," America Dental Asso-
`(3) iAlfgren. i., * * ~ y l A e ? i n a u g u r ~ Dissertation. Uni-
`ciation Chicago Ill. 1963
`versity of Stockholm, 1948. reprinted by the Morin Press.
`Inc.. Wornstet, Mass., 1948, p. 60.
`(4) Brown, C. L. M. Poole, B.. and Poole, A., W. S. pat.
`2,797,241 (June 25, 195'r).
`5) Cooper R Phavm.J 171 68(1953).
`[6) Lange,'N:"A.. "H.nciboo& of Chemistry." 9th ed..
`Handbook Publshers, hc., SPnduslry. Ohlo. 1956. p . 1420.
`
`Merck Exhibit 2247, Page 2
`Mylan v. Merck, IPR2020-00040
`
`