86
`
`VOLUME 1: FORMULA(ION AND PACKAGING
`
`glycol (PG), propylene glycol monoester of medium chain fatty acids (Capmul PG),
`dimethylsulfoxide (DMSO), and in different combinations of these cosolvents at four different
`temperatures. The degradation of the drug was monitored by HPLC and was fotmd to be
`catalyzed not only by general but also by specific acid and base and followed first-order
`kinetics. The t911 (time for 90% of the drug remaining intact) in pure cosolvent was 25 50 times
`higher than that in water or semi-aqueous vehicles. Figure 4 shows an Arrhenius plot of
`the observed rate constants of SarCNU in the solvent mixtures. There was no significant
`difference in the slopes for the different solvents, suggesting similar degradation mechanism of
`SarCNU in all solvent mixtmes. Furthermore, the order of stabilization by these solvents was
`Capoml PG> /EtOH> /PE> /PG> /WPE> /water, which was in agreement with decreasing
`the polarities of the vehicles. The greatest SarCNU stability, as measured by the degradation
`rate constant derived t9<l, was observed with Capmul PG as shown in Table 4. Another example
`where the degradation was significantly reduced in the nonaqueous solvents is described for
`Eptifibatide, a peptide compound used as an inhibitor of platelet receptor glycoprotein (42).
`The use of cosolvent to help in solubilization may not, however, lead to favorable stability
`outcome at all the times. Trivedi, et al, (43) showed that as the fraction of organic solvents was
`increased, the degradation of zi1euton also increased because of the solvolysis of the drug by
`the cosolvents used.
`
`0.1
`
`• PG
`
`• PE
`
`0.01 ~~ • CPG
`
`, EtOH
`
`s Water
`
`• DMSO
`
`+WPE
`
`.. <>.:~:.;
`
`~ · .
`·~.
`.
`... ...
`,.....
`..
`..
`'·
`·=,..
`.... . · ...
`. ... "!..
`• .. \,
`·<::~~::~; .. ·· .... ~:--
`
`••
`
`-;:-
`,E
`~
`.><:
`
`0.001
`
`0.0001
`
`0.00001
`
`0.000001 +---.--r----.-----.--,----.--.----.-----.--,----,
`2.9 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4
`1000fT
`
`Figure 4 Stability behavior of
`SarCNU in the presence of vari
`ous cosolvent.
`
`Table 4 Degradation of SarCNU in the Presence of Various Cosolvent Mixtures
`
`Solvent
`
`Water
`Water + propylene glycol + EtOH
`DMSO
`Propylene glycol
`Propylene glycol + EtOH
`EtOH
`Capmul PG
`
`Source: From Ref. 41.
`
`/90 (days)
`
`Room temperature
`(25' C)
`
`Refrigeration
`WC)
`
`0.25
`0.50
`1.14
`2.92
`3.64
`7.29
`12.50
`
`5.90
`8.96
`19.03
`77.78
`89.50
`199.52
`242.57
`
`Regeneron Exhibit 1015.101
`
`

`

`FORMULATION DEVELOPMENT OF SMALL AND LARGE VOLUME INJECTIONS
`
`87
`
`Table 5 Examples of Marketed Injectable Products Containing Cosolvent Mixtures
`
`Generic name
`
`Trade name
`
`Predominant cosolvent(s) in marketed vehicle
`
`Carmustine
`Diazepam
`
`Digoxin
`
`Melphalan
`
`Methocabamol
`Oxytetracycline
`Paricalcitol
`
`Phenobarbital Na
`
`Phenytoin Na
`
`Teniposide
`
`BiCNU
`Valium
`
`Lanoxin
`
`Alkeran
`
`Robaxin
`Terramycin
`Zemplar
`
`Nembutal
`
`Dilantin
`
`Vumon
`
`Docetaxel
`
`Taxotere
`
`Source. From Refs. 44 and 45.
`
`100% ethanol
`Propylene glycol 40%
`Ethyl alcohol 10%
`Propylene glycol 40%
`Ethyl alcohol 10%
`Propylene glycol 60%
`Ethyl alcohol 5%
`Polyethylene glycol 50%
`Propylene glycol 67 75%
`Propylene glycol 30%
`Ethyl alcohol 20%
`Propylene glycol 40%
`Ethyl alcohol 10%
`Propylene glycol 40%
`Ethyl alcohol 10%
`N,N dimethylacetamide 6%
`Cremophor 50%
`Ethyl alcohol 40%
`Polysorbate 80 t 00%
`
`Examples of drttgs marketed in water-miscible systems include digoxin, phenytoin,
`diazepam and others as shown in Table 5 (44,45). These injections are formulated in a water(cid:173)
`miscible system containing glycols and alcohol and adjusted to a suitable pH. Other cosolvents
`used in the past included glycerin in deslanoside, dimethylacetamide in reserpine and
`dimethylsulfoxide in chemotherapeutic agents undergoing clinical testing. Propylene glycol is
`used most frequently as a cosolvent, generally in concentrations of 40%. Although such
`systems are stable in individual vials, care must be exercised on administration. For example,
`phenytoin is dissolved as the sodium salt in a vehicle containing 40% propylene glycol and
`10% ethanol and adjusted to a pH of 12 with sodium hydroxide. However, if this solution is
`added to a large-volume IV solution and the pH is lowered to a value close to the pK, of the
`drug (pK" = 8.3), precipitation of the drug can occur. This is due to the fact that in aqueous
`systems at pH below 11, the amount of undissociated phenytoin exceeds its solubility.
`To be used as solubility/ stability enhancer in injectable products, the cosolvent must
`have certain attributes such as it should be nontoxic, compatibile with blood, nonsensitizing,
`nonirritating and above all physically and chemically stable and inert. Many cosolvent
`formulations contain high concentrations of organic solvent and most are diluted prior to
`injection, however, some may be injected directly and in that case, care must be taken that the
`rate of injection remains slow.
`
`Surfactants as solubilizers The ability of surfactants to enhance the solubility of otherwise
`poorly water-soluble compounds in aqueous solution is widely known and used in many
`injectable formulations. Surfactants ar-e effective solubilizing agents because of their wetting
`properties and association tendencies as they are able to disperse water-insoluble substances.
`Surfactants are also used ve1y widely in the biotechnology area for otherwise water-soluble
`monoclonal antibodies and other proteins and polypeptides, but the primary goal of using
`surfactant in these products is to minimize hydrophobic interaction related aggregation and
`not necessarily for the enhancement of solubility. This aspect wil1 be discussed in detail in
`other chapters.
`Surfactants can be either nonionic or ionic (i.e., the ability to lower surface tension rests
`with the anion or cation in the molecuJe). In nonionic surfactants, the head groups contain no
`charged moieties and their hydrophilic properties are due to the presence of hydroxyl groups.
`Nonionic surfactants are most frequently used in pharmaceutical systems because of their
`compatibility with other surfactants, stability, and relatively low toxicity. Some examples of
`
`Regeneron Exhibit 1015.102
`
`

`

`88
`
`VOLUME 1: FORMULA(ION ANO PACKAGING
`
`water-soluble nonionic surfactants include long-chain fatty acid analogs such as fatty alcohols,
`glyceryl esters, and fatty acid esters. Among the most widely used water-soluble nonionic
`surfactants in injectable products are polyethylene oxide (PEO) sorbitan fatty acid esters, or
`Polysorbates.
`In anionic surfactants, the head groups are negatively charged. The most widely used
`anionic surfactants are those containing carboxylate groups, such as soaps, sulfonates, and
`sulfate ions. In cationic surfactants, the head groups are positively charged. Some examples
`include amine and quaternary ammonium salts. Cationic surfactants are not used in
`pharmaceutical systems because of their toxicity since they adsorb readily to cell membrane
`structures in a nonspecific manner, leading to cell lysis (46).
`As shown in Figure 5, surfactants typically orient themselves at polar/nonpolar
`interfaces because of the presence of discrete hydrophobic and hydrophilic regions. As the
`bulk concentration of surfactant in solution_ is increased, the surfactant molecules begin to
`associate into small aggregates called micelles, whereby their hydrophobic regions are
`shielded from aqueous contact by their hydrophilic regions. All surfactant molecules in excess
`of that concentration associate into micelles, while the concentration of nonassociated
`surfactant molecules remains nearly constant. The concentration at which such association
`occurs is called critical miceJle concentration (CMC). Usi11g soap as a micelle forming
`substance, Lawrence proposed in 1937 that poorly soluble hydrophobic molecules locate in the
`hydrocarbon core of the micelle, while polar molecules would associate with the polar
`end (47). Molecules that contain polar and nonpolar groups align themselves between the
`chains of the micelle with the nonpolar part directed into the central region and the polar end
`extending out into the hydrophilic chains (Fig. 6).
`
`t:
`0
`
`Polyoxyethylene
`Chains
`Nonionic
`
`Polar
`Region
`
`Ionic
`
`Figure 5
`Illustration of spherical orien
`tations of nonionic and ionic micelles.
`
`Surfactant Molecules
`
`~?/P/
`/J~
`
`c:,.,-7~~
`
`Nonpolar Drugs
`(I)
`
`Semipolar Drugs
`<I>
`
`Figure 6 Schematic representation of mechanisms of miceller solubilization.
`
`Regeneron Exhibit 1015.103
`
`

`

`t:
`0
`
`FORMULATION DEVELOPMENT OF SMALL AND LARGE VOLUME INJECTIONS
`
`89
`
`Table 6 Effect of Surfactants on the Solubility of Furosemide
`
`Distilled water
`
`0.1 N hydrochloric acid
`
`Total solubility
`(µg/mL)
`
`Miceller solubility
`(µg/mL)
`
`Total solubility
`(µg/mL)
`
`Miceller solubility
`(1,g/ml)
`
`41.2
`
`31.2
`45.0
`57.0
`167.0
`705.0
`
`32.5
`45.0
`112.5
`143.7
`792.5
`
`43.7
`43.7
`141.2
`205.0
`980.0
`
`15.0
`
`40.0
`41.1
`50.0
`145.0
`670.0
`
`25.0
`22.5
`72.5
`137.5
`887.0
`
`15.9
`18.7
`74.0
`160.0
`808.0
`
`26.1
`35.0
`130.0
`655.0
`
`7.5
`57.5
`122.5
`872.0
`
`0.9
`3.7
`59.0
`145.0
`793.0
`
`3.7
`15.7
`125.7
`663.7
`
`3.7
`71.2
`102.4
`751.2
`
`2.4
`2.4
`100.0
`163.7
`938.7
`
`Surfactant % (w/v)
`
`0
`Polysorbate 20 (C12)
`0.005
`0.05
`0.5
`1.0
`5.0
`Polysorbate 40 (C16)
`0.005
`0.05
`0.5
`1.0
`5.0
`Polysorbate 80 (C18)
`0.005
`0.05
`0.5
`1.0
`5.0
`
`Source: From Ref. 49.
`
`Generally, the solubiJization capacity of a same amount of surfactant is high for those
`with lower CMC value. The solubilizing ability of nonionic surfactant toward water-insoluble
`drugs has been extensively studied (48). Akbuga and Gursoy (49) showed how the solubility of
`furosemide, a very insoluble compound commonly used as diuretic, was dramatically affected
`by the surfactant concentration and alkyl chain length (Table 6).
`The CMC can be measured by a variety of techniques, for example, surface tension, light
`scattering, osmometry, all of which show a characteristic break point in the plot of the
`operative property as a function of concentration. Figure 7, a plot of surface tension against
`concentration of surfactant shows a break in the linearity of the cmve, indicating the CMC (50).
`Many factors such as temperature, pH of the solution, electrolytes, and other ingredients affect
`mice!Jization and hence solubilization (51,52). For nonionic smfactants, the CMC value
`decreases with increasing temperature whereas for ionic surfactants, it increases as the
`temperature increases (53). Since the pH can affect the equilibrium between ionized and
`nonionized solute species, it can have an effect on the capacity of micellar solubility as shown
`by Castro et al, for atenolol, nadolol, midazolam and nitrazepam (54). For ionic surfactant
`micelles, electrolyte addition causes a decrease in the CMC resulting in an increase in the
`micellar solubilization capacity (55), whereas i11 the case of nonionic surfactru1t, polysorbate 80,
`the solubility of furosemide increases in the presence of soditun chloride because of increased
`micellar packing and micelle volume (56). Other ingredients present in the formulation can
`also have a profound effect on the solubilizing capacity of surfactants. Surfactants may
`precipitate in the presence of some organic additives or micellization may be abolished if high
`enough concentrations of, for example, alcohols are present. Excipients such as phospholipids
`also affect the CMC. Many water-soluble drugs themselves are remarkably surface active: they
`lower the surface and interfacial tension of water, promote foaming, and associate into
`micelles, such as antibacterial (hydrochlorides of acridines, benzalkonium chloride, cetylpyr(cid:173)
`idinium chloride) tranquilizers (hydrochlorides of reserpine and phenothiazine derivatives),
`local anesthetics (hydrochlorides of procaine, tetracaine, dibucaine, and lidocaine), nonnarcotic
`analgesic (propoxyphene hydrochloride) and narcotic analgesic (morphine sulfate and
`meperidine hydrochloride), antimuscarinic drttgs (propautheline bromide, methantheline
`bromide, methixene hydrochloride), cholinergic agents (pilocarpine hydrochloride, and other
`
`Regeneron Exhibit 1015.104
`
`

`

`90
`
`VOLUME 1: FORMULA(ION AND PACKAGING
`
`40
`
`1s ............................................................................................. -.
`-uo
`-,.oo
`-2.50
`-2.00
`-1.50
`-MO
`LOO CONCENTRATION, lftOO ml
`
`Figure 7 Surface tension versus concentration of
`surfactant. Break in the curve denotes CMC.
`Source: From Ref. 50.
`
`alkaloidal salts), antihistamines (pyrilamine maleate, tripelennamine hydrochloride, chlorcy(cid:173)
`clizine hydrochloride, diphenhydramine hydrochloride), anthelmintics (lucanthone hydro(cid:173)
`chloride), and antibiotics (sodium fusidate, some penicillins, and cephalosporins) (46).
`Selection of surfactant in the injectable products should be based on its safety and
`toxicology profile (LD50, tissue tolerance, hemolysis, etc.), solubility of the drug in the i11
`surfactant, and drug-surfactant compatibility. Since surfactants act as nonspecific solubilizers,
`stabilizers, emulsifiers and wetting agents, they can also cause toxicity and disrupt normal
`membrane structure. As mentioned earlier, only nonionic surfactants are generally used in
`parenterals because of their relative less destruction to biological membranes. Table 7 lists
`some commonly used surfactants, their properties, and examples of marketed injection
`prodttcts that contain surfactants for the purpose of solubility enhancement. Polysorbate 80 is
`
`Table 7 List of Some Surfactants in Injectable Products and Their Properties
`
`Surfactant
`
`Chemical name
`
`HLB" value CMC (% w/w)
`
`Cremophor
`
`Polyoxyethylated
`castor oil
`
`12 14
`
`0.02
`
`Solutol HS
`
`Pluronic F68
`
`Polyethylene glycol
`660 hydroxystearate
`Polaxomer
`
`Polysorbates
`
`Tween 80
`
`14 16
`
`> 24
`
`15
`
`Sodium desoxycholate
`Sodium dodecyl sulfate
`
`16
`40
`
`"Hydrophilic Lipophilic Balance
`
`0.03
`
`0.1
`
`0.0014
`
`0.08
`0.03
`
`Injection product (chemical/
`brand/% surfactant)
`
`Paclitaxel/taxol/52. 7
`Tenoposide/vumon/55
`Cyclosporine/sandimmune/65
`Vttamin K /Ao,ua mephyton/25
`
`Recombinant Growth
`hormone/accretropin/0.2
`Amiodorone/cordarone/10
`docetaxel/laxotere/100
`Vitamin A palmitate/aquasol A/12
`Amphotericin/fungizone/0.4
`Aldesleukin/proleukin/0.018
`
`Regeneron Exhibit 1015.105
`
`

`

`FORMULATION DEVELOPMENT OF SMALL AND LARGE VOLUME INJECTIONS
`
`91
`
`the most commonly used surfactant and is used. in the range from fraction of percent in many
`products to 100% in the case of taxotere injection.
`
`Cyclodextrins as solubilizers Cyclodextrins are oligomers of glucose produced by enzymatic
`degradatiou of starch. The number of ot-1,4-linked glucose units determine the classification
`into ot, p, or 'Y cyclodextrins haviJ1g six, seven, or eight glucose units, respectively (57 59). The
`cydodextrins exert their solubilizing effect by fonning soluble inclusion complexes in aqueous
`solutions. The cyclod.extrins are amphipathic (i.e., the exterior is hydrophilic due to the
`hydroxy groups oriented on the exterior while the interior is hydrophobic) and can form
`soluble, reversible inclusion complexes with water-insoluble compounds. The unsubstituted
`cyclodextrins are too toxic for parental use but the chemically modified cyclodextrins appear to
`be well tolerated when administered parenterally and have been shown to effectively enhance
`the solubility of several drugs including steroids and proteins (60,61). The solubility of
`alfaxalone, an insoluble anesthetic, was increased by 5000 times to 19 mg/mL in 20%
`hydroxypropyl-P-cyclodextrin (62). Some other examples of injectables that are currently in the
`market which contain chemically modified cyclod.extrin for the pu.rpose of enhancement of
`solubility are: Aripiprazole (AbiJify'll-) (63), ziprasid.one (Geodon'E) (64) and voriconazole
`(Vfend"1) (65) containing sulfobutylether p cyclod.extri11 (SBECD), itraconazole (Sporanox't )
`(66) contaiJ1iJ1g bydroxypropyl-P-cyclodextrm, and others.
`Having reviewed the factors that govern solubility and solubilization during the
`formulation development of injectable products, the next considerations are the elements of
`formulations.
`
`Types of vehicles
`Aqueous The vast majority of injectable products are administered as aqueous solutions
`because of the physiological compatibility of water with body tissues. Additionally, the high
`DC of water makes it possible to dissolve ionizable electrolytes, and its hydrogen-bonding
`potential facilitates the solution of alcohols, aldehydes, ketones, and amines. The current USP
`(1) has monographs for purified water, sterile purified water, WFI, sterile WFI, bacteriostatic
`WF[, sterile water for inhalation, and sterile water for irrigation.
`WFJ is the solvent of choice for making parenterals. It must be prepared fresh and be
`pyrogen-free. lt must meet all the chemical requirements for sterile purified water and in
`addition the requirements for bacterial endotoxins. The tests required for WFI are generally the
`same among the various phannacopeias but differences do exist with regards to limits. WFI may
`be prepared by either distillation or reverse osmosis but the distillation method is by far the most
`common and accepted method. Because of the excellent solvent properties of water, it is both
`difficult to purify and maintain purity. Microorganisms, dissolved gases, organic and inorganic
`substances, and foreign particulate matter are the most common contaminants of water.
`Prior to distillation, the water used as the source for WFI is usually subjected to
`chlorination, carbon treatment, deionization, and, sometimes, reverse osmosis treatment (forced
`passage through membrane materials). After distillation, it is filtered and then stored in a
`chemically resistant tank (stainless steel, glass, or blocked tin) at a cold temperature around 5"C
`or at an elevated temperature between 65"C and 85' C to inhibit microbial growth and prevent
`pyrogen formation. Generally, the hot water is continually circulated in the manufacturing areas
`during storage and usually filtered again prior to use. Sterile WFI and Bacteriostatic WFI are
`permitted to contain higher levels of solids than WFI because of the possible leaching of glass
`container constituents into the water during sterilization and storage. Bacteriostatic WFI, which
`generally contain 0.9% (9 mg/mL) of benzyl alcohol as a bacteriostatic preservative, should not
`be sold in containers larger than 30 mL to preve11t injection of unacceptably large amounts of
`bacteriostatic agents (such as phenol and thimerosal).
`
`Other wate r-miscible cosolvents These have been discLtssed earlier.
`
`Nonaqueous vehicles Drngs that are insoluble in aqueous systems are often incorporated in
`metabolizable oils. Steroids, hormones, and vitamins are incorporated i11 vegetable oils such as
`peamtt, sesame, corn, olive, and cottonseed. Oil injections are only administered intra(cid:173)
`muscularly. There are strict specifications for the vegetable oils used in manufacturing
`
`Regeneron Exhibit 1015.106
`
`

`

`92
`
`VOLUME 7: FORMULA(ION ANO PACKAGING
`
`Table 8 Official Injections Containing Oils as Vehicles
`
`USP (1)
`
`Desoxycorticosterone acetate
`Diethylstilbestrol
`Dimercaprol (suspension)
`Estradiol cypionate
`Estradiol valerate
`Estrone
`Ethiodized iodine
`Fluphenazine decanoate
`Fluphenazine enanthate
`Hydroxyprogesterone caproate
`Menadione
`Nandrolone decanoate
`Nandrolone phenpropionate
`Penicillin G procaine (combinations)
`Propyliodone (suspension)
`Testosterone cypionate
`Testosterone enanthate
`Testosterone propionate
`
`Oil commonly used
`
`Sesame
`Sesame, cottonseed
`Peanut
`Cottonseed
`Sesame
`Sesame
`Poppyseed
`Sesame
`Sesame
`Sesame
`Sesame
`Sesame
`Sesame
`Vegetable
`Peanut
`Cottonseed
`Sesame
`Sesame
`
`intramuscular injections. Storage of these preparations is important if stability is to be
`maintained. For example, they should not be subjected to conditions above room temperature
`for extended periods of time. Although the oils used for injections are of vegetable origin,
`federal regulations require that the specific oil be listed on the label of a product, because some
`patients have exhibited allergic responses to certain vegetable oils.
`Sesame oiJ is the preferred oil for most of the compendia! injections formulated with oil.
`It is the most stable of the vegetable oils (except to light), because it contains natural
`antioxidants. Sesame oil has also been used to obtain slow release of fluphenazi.ne esters given
`intramuscularly (67). Excessive tmsaturation of oil can produce tissue irritation. In recent
`years, tJ,e use of injections in oil has diminished somewhat in preference to aqueous
`suspensions, which generally have less irritating and sensitizing properties. Benzyl benzoate
`may be used to enhance steroid solubility in oils if desired. Table 8 lists the oil injections official
`in the current USP (1).
`
`Added Substances
`Added substances such as buffers, antioxidants, antimicrobial preservatives, tonicity adjusting
`agents, bulking agents, chelating agents, solubilizing agents, and surfactants must frequently
`be incorporated into parenteral formulas in order to provide safe, efficacious, and elegant
`parenteral dosage forms. However, any such additive may also produce negative effects such as
`loss of dmg solubility, activity, and/ or stability. Any additive to a formulation must be justified
`by a dear purpose and function. No coloring agent may be added, solely for the purpose of
`coloring the finished preparation, intended for parenteral administration (1). The reader is
`encouraged to refer to a number of publications that provide comprehensive listing of
`formulation components used in all marketed injectable products (1,68 74). Hospital
`pharmacists who are involved in IV additive programs should be aware of the types of
`additives present in products that are being combined. Commonly used parenteral additives
`and their usual concentrations are listed in Table 9.
`Pharmacopeias often specify the type and amount of additive substances that may be
`included in injectable products. These requirements often vary from compendia to compendia,
`so it is important to refer to the specific pharmacopeia that applies to the product in question.
`USP (1) specifies following maximum limits in preparations for injection that are administered
`in a volume exceeding 5 mL: for agents containing mercury and the cationic surface-active
`compounds, 0.01 %; for chlorobutanol, cresol, phenol, and similar types of substances, 0.5%;
`and for sulfur dioxide, or an equivalent amount of the sulfite, bisulfite, or metabisulfite of
`
`Regeneron Exhibit 1015.107
`
`

`

`~
`:::i
`
`~
`0
`"' 0
`.€
`11 .a
`C
`::>
`6
`~-t
`>,O
`J:;.,
`e :fl
`o-
`0
`"'
`0 C
`~ 0 a~
`68..
`~~
`€ ,0
`]
`e 0
`-0 .,
`"' 0
`~ 0
`0
`
`,i.
`
`"O
`
`FORMULATION DEVELOPMENT OF SMALL AND LARGE VOLUME INJECTIONS
`
`93
`
`Table 9 Commonly Used Parenteral Additives and Their Usual Concentration
`
`Added substance
`
`Usual concentrations (%)
`
`Antibacterial preservatives
`Benzalkonium chloride
`Benzethonium chloride
`Benzyl alcohol
`Chlorobutanol
`Chlorocresol
`Metacresol
`Phenol
`Phenylmercuric nitrate and acetate
`Methyl p hydroxybenzoate
`Propyl p hydroxybenzoate
`Butyl p hydroxybenzoate
`Thimerosal
`Antioxidants
`Acetone sodium bisulfite
`Asoorbic acid
`Asoorbic acid esters
`Butylhydroxyanisole (BHA)
`Butylhydroxytoluene (BHT)
`Cysteine
`Nordihydroguaiaretic acid (NOGA)
`Monothioglycerol
`Sodium bisulfite
`Sodium metabisulfite
`T ooopherols
`Glutathione
`Chelating agent
`Ethylenediaminetetraacetic acid salts
`DTPA
`Buffers
`Acetic acid and a salt, pH 3.5 5.7
`Citric acid and a salt. pH 2.5 6
`Glutamic acid., pH 8.2 10.2
`Phosphoric acid salts, pH 6 8.2
`Tonicity adjustment
`Dextrose
`Sodium chloride
`Mannitol
`
`0.01
`0.01
`1 2
`0.25 0.5
`0.1 0.3
`0.1 0.3
`0.5
`0.002
`0.18
`0.02
`0.015
`0.01
`
`0.2
`0.01
`0.015
`0.02
`0.02
`0.5
`0.01
`0.5
`0.15
`02
`0.5
`0.1
`
`0.01 0.075
`0.01 0.075
`
`2
`5
`1 2
`0.8 2
`
`4 5.5
`0.5 0.9
`4 5
`
`potassium or sodium, 0.2%. Ethylenediaminetetraacetic acid derivatives and salts are
`sometimes used to complex and thereby inactivate trace metals that may catalyze oxidative
`degradation of drugs. The properties and fttnction of these added substances will be reviewed
`next, except solubilizing agents and surfactant, which have been reviewed earlier.
`
`Buffers. Maintenance of appropriate pH of the formulation is essential .for proper solubility
`and stability. Changes in the pH of a formulation may occur during storage because of
`degradation reactions within the product, interaction with container components (i.e., glass or
`rubber), and absorption or evolution of gases and vapors. Buffers are added to many products
`to resist a change in pH. Excellent reviews on pH control within pharmaceutical systems by
`Fly1.1n (75) and Nema et al (76) are recommended to the reader. A suitable buffer system should
`have an adequate buffer capacity to maintain the p H of the product at a stable value during
`storage, while permitting the body fluids to adjust the pH easily to that of the blood following
`administration. Therefore, the ideal pH to select would be 7.4, the pH of the blood. Extreme
`deviation from this pH can cause complications. Tissue necrosis often occurs above pH 9,
`while extreme pain and phlebitis are experienced below pH 3. The acceptable range for IV
`injections is 3 to 9 because blood itself is an excellent buffer and can very quickly neutralize the
`
`Regeneron Exhibit 1015.108
`
`

`

`94
`
`VOLUME 1: FORMULArtON ANO PACKAGING
`
`•
`
`II
`
`~
`IO ~
`i=
`
`n "' 0
`I")
`
`.. ~ ...
`I
`11 t
`• i
`•
`
`\
`\
`
`'
`
`,1
`
`pH
`
`Figure 8 Solubility/stability pH profile of pro
`caine penicillin. Source: From Ref. 77.
`
`pH outside of 7.4. Parenterals administered by other routes are generally adjusted to a pH
`between 4 and 8.
`A suitable buffer system can be selected from knowledge of a solubility/ stability pH
`profile of the drug in solution. A typical pH profile of both solubility and stability is shown
`in Figure 8 for procaine penicillin G (77). By following the degradation over a given pH range
`and plotting the rate constants versus pH, the pH of maximum stability (pH 6.6) can be
`determined. In the case of procaine penicillin G, the solubility is lowest between the pH 6
`and 7, which is desirable since the product is formulated as a suspension. Once the desired pH
`is determined, a buffer system that provides sufficient buffer capacity can be selected. The
`buffer capacity, p, is an indication of the resistance to change in pH upon the addition of either
`basic or acid substances and can be represented by the following expression:
`
`p = dB = 2.303C KaH '
`(K. +WJ
`dpH
`
`(11)
`
`where
`
`dB = change in concentration of base or acid,
`dpH = change in pH,
`C = molar concentration of buffer system, and
`Ka = dissociation constant of the buffer.
`A hypothetical plot of P versus p H-p.K. is illustrated in Figure 9 for a monobasic acid. A
`maximum value at zero indicates that the greatest buffer capacity occurs at a pH equal to the
`pK0 of the buffer system and further Sttggests that a buffer system with a p.1<0 within ±1.0 unit
`of the desired pH should be selected.
`Buffer systems for parenterals generally consist of either a weak base and the salt of a
`weak base or a weak acid and the salt of a weak acid. Figure 10 shows the effective range of
`typical pharmaceutical buffers. The distance indicated by the arrows represents the effective
`buffer range for each system and the dashed lines represent the pK0 for the system. Commonly
`used buffers are phosphates, citrate, acetate, and gluk1mates.
`The Henderson-Hasselbach relationship is used to calculate the quantities of buffer
`species required to provide a desired pH .
`
`Csalt
`P = p .+ og -c
`K
`H
`I
`add
`
`(12)
`
`Regeneron Exhibit 1015.109
`
`

`

`FORMULATION DEVELOPMENT OF SMALL AND LARGE VOLUME INJECTIONS
`
`95
`
`OMu: 0.576C
`
`0,6
`
`0.4
`
`o.z
`
`.3
`
`·1
`
`0,0
`·I
`pH-pka
`
`+I
`
`+2
`
`+)
`
`Figure 9 Theoretical buffer capacity curves
`of a monobasic acid.
`
`t:
`0
`
`Figure 10 Effective range of pharma
`ceutical buffers, indicated by the arrows.
`The dashed line represents the pKa
`value.
`
`-
`t
`_GLUTAJ\1AT£
`·········-·
`pK8 (J): 9.67
`-
`+
`-
`t
`PHOSPHATE
`............
`- P".(I): 7..2
`t
`............
`CAIUONATE
`+
`•
`P"1,(I) :6A
`t
`..............
`t
`CITRATE
`- ACETATE
`t
`·····-··· ··
`·----- -- -----
`pK•, 4.1
`p"1, 0): 3.14
`···-·····-·
`-
`P"1, (2): 4JI
`GLUTA.MAT.£
`P"1, (1): Z.19
`.••• p"1, (3): 5.1 • •
`·-
`pl<,, (l.): 4,15
`
`11.0
`
`10.0
`
`9.0
`
`8.0
`
`7.0
`
`i 6.0
`s.o
`
`4.0
`
`3.0
`
`2.0
`
`1.0
`
`--
`
`TRIEl'HANbLAMINE
`
`·----------·-
`P"a: &O
`!
`
`. . . . . . . . . . .
`
`•
`
`Where C,,,,11 and C,.~;d are the molar concentrations of the salt form and the acid form,
`respectively. As shown from the following calculation, an acetate buffer system (pK,. = 4.8)
`consisting of 0.1 M acetic acid and 0.05 M sodium acetate would result in a pH of 4.5.
`0·05
`I
`p = 4. + og-
`8
`H
`. 1
`0
`Although buffers assure the stability of pH of solution, the buffer system itself can affect other
`properties such as reaction kinetics and solubility aspects. Buffers can act as general acid or
`genera 1 base catalysts and ca use degradation of some d mg substances. Such a mec11a nism occurs
`with a number of amine and amine derivative drugs in systems containing polycarboxylic
`acids (e.g., citric, tartaric, and succinic). In one such case, as shown in Figure 11, the degradation
`of vitamin 8 1 increases with increase in citrate buffer concentration (78).
`The ionic strength contributions of the buffer system can also affect both isotonicity and
`stability. For example, H adjustment of pH is made with sodium hydroxide, say of a solution
`
`5
`8 0 3
`= 4.
`. = 4 .
`
`Regeneron Exhibit 1015.110
`
`

`

`96
`
`0.1 00
`
`0.075
`
`-.... .c
`u.. i -....
`
`u.i u..
`0 .050
`~
`
`0.025
`
`VOLUME 1: FORMULA(ION ANO PACKAGING
`
`+- 4.60
`
`+- 4.40
`
`+- 4.00
`
`- - 3.60
`
`+- 3.00
`
`- - 2.50
`
`0.000 ,__ _ __., __ ...._ _ _._ _ __.. __ ..__
`0.04 0.08 0.1 2 o. 16
`0.20
`0
`TOTAL CITRATE (mol/llter)
`
`Figure 11 Effect of citrate buffer concentration
`on thiamine hydrolysis (vitamin B1) at 96.4"C at
`constant ionic strength and at different pH values.
`Source: From Ref. 78.
`
`containi11g monosodium phosphate, the effect of the generation of disodium salt on isotonidty
`2 must be taken into account (79,80).
`and the effect of HP04 -
`
`Antioxidants. Many drugs in solution are subject to oxidative degradation. Such reactions are
`mediated either by free radicals or by molecular oxygen and often involve the addition of
`oxygen or the removal of hydrogen. For products in which oxygen is directly involved in the
`degradation, protection can be afforded by displacing oxygen (air) from the system. This is
`accompl.ished by bubbling nitrogen, argon, or carbon dioxide through the solution p rior to
`filling and sealing in the final container. Oxidative decomposition is catalyzed by metal,
`hydrogen, and hydroxyl ions. Drugs possessiJ1g a favorable oxidation potential will be
`especially vulnerable to oxidation. For example, a great number of drngs are formulated in
`the reduced form (e.g., epinephrine, morphine, ascorbic acid, menadione, etc.) and are easily
`oxidized. Oxidation can be minimized by increasing the oxidation potential of the drug.
`As illustrated in Figure 12 (81), lowering the pH of the solution will increase the oxidation
`potential. This occurs because according to a simplified version of the Nernst equation:
`E __ Eo RT 1 IH+J · IOxJ
`-
`+ 2 og
`(Rd)
`
`(13)
`
`an increase in hydrogen ion concentration causes an increase in the actual oxidation potential,
`E. In this equation E0 is the standard oxidation potential, R the gas constant, T the absolute
`temperature, and constant 2 represents the number of electrons taking part in the oxidation(cid:173)
`reduction reaction.
`Agents that have a lower oxidation potential than the drug in qttestio11, and thus can be
`preferentialJy oxidized, are called antioxidants. Such agents are added to paren teral solutions
`either alone or in combination with a chelating agent or other antioxidant and fw1ction in at
`least two ways: (i) by being preferentially oxidized and thereby gradually consumed or (ii) by
`blocking an oxidative chain reaction in which they are not usually consumed.
`Morphine in aqueous solution undergoes a pH-dependent oxidative degradation. The
`rate is slow and constant between pH 2 and 5, where