stability of adrenalin in dental local anesthetics on the

Original Article

IJOMS Vol 19-2-14 IJOMS Vol 19-2-14

Int J Oral-Med Sci 19（2）:81–87, 2020 　81

Stability of Adrenalin in Dental Local Anesthetics on the Different Storage Condi-tions

Hidenori Yamaguchi,1,3 Masatoshi Suzuki,1,3 Mami Nakamura,1,3 Akio Uda,1,3 Airi Hori,1,3

Masatoshi Akiyama,1 and Hiroko Matsumoto2,3

Departments of 1Anesthesiology and 2Pharmacology, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271–8587, Japan3Research Institute of Oral Science, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271–8587, Japan

IntroductionLocal anesthetics are frequently used to anesthetize

the oral cavity before painful medical procedures. Howev-er, the injection of local anesthetics is itself painful and causes a burning or stinging sensation while being infil-trated into tissue（1）. The patients avoid dental treat-ments, because the pain and its experience of this injec-tion induce a feeling of fear on dental treatments（2）. The pain and feeling of fear of the patients have possibility to affect circulatory system such as blood pressure elevation

and tachycardia by fear, because a vasoconstrictor is add-ed in dental local anesthetics. The application of surface anesthesia, warming of local anesthetics, thin needle, and slow infusion without pressure are used to reduce a pain in the local anesthesia. Particularly, the warming of local anesthetics is effective to reduce pain undergoing local anesthetic infiltration into oral tissue. And also, it has re-ported that the use of warmed lidocaine improves the quality of local anaesthesia for knee arthroscopy（3）. Many studies have investigated warmed local anesthetics to reduce pain from infiltration（4–6）. A survey in the United Kingdom found that 34% of maxillofacial surgeons and 8% of general surgeons regularly warmed local anes-thetics to reduce pain（7）. On the other hand, it has re-

Correspondence to： Hidenori YamaguchiE-mail : [email protected]：10.5466/ijoms.19.81

Article History Abstract

Received 19 May 2020Accepted 23 June 2020

Local anesthetics are frequently used to anesthetize the oral cavity before painful medical procedures. However, the injection of local anesthetics is itself painful. The warming of local anesthetics is effective to reduce pain undergoing local anesthetic infil-tration into oral tissue. In the present study, the stability of adrenaline, a vasoconstric-tor in dental local anesthetics, on the different storage conditions was investigated. The cartridges of dental local anesthetics were kept in the fluorescent light（FL）or the cir-cumstances shielded from light（LS）at 37°C or room temperature（RT）for 1, 2, 3, 4, 8, 12, and 16 weeks. Adrenaline concentrations were measured by a reversed -phase high -performance liquid chromatography（RP -HPLC）. The concentrations of sulfite which is added as a stabilizer in dental local anesthetics were measured by ion chroma-tography（IC）. Adrenaline concentrations decreased at 37°C compared with RT for 12 and 16 weeks, and also decreased on FL compared with LS at 16 weeks. Sulfite ion

（SO32-）concentration decreased at 37°C compared with RT for 16 weeks. These results

suggest that the temperature influences adrenaline and SO32 - concentrations for 16

weeks, while adrenaline and SO32- concentrations are not affected by temperature and

light for less than 8 weeks. Adrenalin in the cartridge of dental local anesthetics is hard to be oxidized, since the cartridge is superior in air tightness. However, it is necessary to be careful of storage management for the cartridge of dental local anesthetics.

Keywords：dental local anesthetics,adrenaline, cartridge warmer,sodium pyrosulfite


82　 Int J Oral-Med Sci 19（2）:81–87, 2020

ported that there were no significant differences among these three groups with local anesthetic solution at re-frigerator temperature, room temperature, and normal body temperature. Temperature of local anesthetic de-pended upon the length of time from storage to oral cavi-ty and to touch a cartridge by the fingers（8）. A cool and dark area such as a refrigerator is recommended for the storage place of dental local anesthetic cartridge. Howev-er, the cartridges were stored in a place at room tem-perature and a thermal insulation box for warming. It is quite important to know the effect of storage condition on the quality of dental local anesthetics. The previous re-port showed a storage method by the special experimen-tal equipment which is difficult to use in a clinical field. There is only one model of cartridge warmer which can use in a clinical field.

In the present study, the stability of adrenaline, a vaso-constrictor in dental local anesthetics, on the different storage conditions by a cartridge warmer which a dental practitioner can use easily was investigated.

Materials and MethodsExperimental condition

The ingredients of dental local anesthetics（ORA Injec-tion Dental Cartridge 1.8mL, Showa Yakuhin Kako Co., Ltd, Tokyo, Japan）are shown in Table 1. The cartridges of dental local anesthetics were kept in the fluorescent light（FL）or the circumstances shielded from light（LS）at 37°C or room temperature（RT）for 1, 2, 3, 4, 8, 12, and 16 weeks. Dental local anesthetics kept in a refrigerator were used as control. Two fluorescent lamps were used for FL groups and the brightness of fluorescent lamps was 30 W and 690 lx. The distance of lamps and car-tridge warmer was 1.5m. Cartridge warmer CAPRI（Den-tronics Co., Ltd., Tokyo Japan）are shown in Fig. 1.

Measurement of adrenaline and sulfite concentrationsAdrenaline concentrations were measured by a re-

versed -phase high -performance liquid chromatography（RP -HPLC）. Operating conditions for RP -HPLC are shown in Table 2.

The concentrations of sulfite which is added as a stabi-lizer in the cartridges of dental local anesthetics were measured by ion chromatography（IC）. Sulfite ion（SO3

2-）and Sulfate ion（SO4

2 -）concentrations were obtained by the procedure described by Nagashima et al（9）and Asa-da et al（10）with a slight modification. Operating condi-tions for IC are shown in Table 3.

ResultsEffect of temperature and light on adrenaline concentra-tions

Representative images of peaks for adrenaline in the

Table 1．The ingredients of dental local anesthetics

Fig. 1． Cartridge warmers were showed during an experi-ment period. Cartridges were warmed at 37°C（A, B）and shielded from light（B）. Cartridges of RT groups were held and kept in cartridge warmer without turn-ing on power.


Int J Oral-Med Sci 19（2）:81–87, 2020 　83

absence or presence of lidocaine measured by RP-HPLC are shown in Fig. 2. In the absence of lidocaine（Fig. 2A）, the peak of adrenaline was completely separated from the other ingredients in this method. In the presence of lidocaine（Fig. 2B）, the peak of adrenaline also was selec-tively measured though the lidocaine of concentration of 800 times as large as adrenaline is included in dental local anesthetic solution.

Effect of temperature and light on adrenaline concen-trations are summarized in Fig. 3. Relative adrenaline concentration rate was calculated by dividing the peak area of experimental by the peak area of control. Adrena-line concentration decreased at 37°C compared with RT for 12 and 16 weeks, and also decreased on FL compared with LS for 16 weeks.

Effect of temperature and light on sulfite concentrationsRepresentative image of peaks for SO3

2 - and SO42 - in

dental local anesthetics measured by IC is shown in Fig. 4. The peaks of SO3

2- and SO42- were completely sep-

arated from the other ingredients in this method. Gener-ally, the separation of SO3

2 - and SO42 - measured by IC

was quite difficult, however SO32 - and SO4

2 - separated well by this column.

Effect of temperature and light on SO32- and SO4

2- con-

centrations is summarized in Fig. 5. Representative im-age of peaks of SO3

2- and SO42- on different conditions at

16 weeks are shown in Fig. 5a. Relative SO32- concentra-

tion rate was calculated by dividing the peak area of ex-perimental by the peak area of control（Fig. 5b）. 85% of SO3

2- and 15% of SO42- were detected in dental local anes-

thetics stored at a refrigerator. SO42 - concentration in-

creased at RT compared with control, and also increased at 37°C compared with RT for 16 weeks. On the other hand, SO3

2 - concentration decreased at RT compared with control, and also decreased at 37°C compared with RT for 16 weeks.

Table 2．Operating conditions for RP-HPLC

Table 3．Operating conditions for IC

Fig. 2． Representative image of peaks for adrenaline in the absence or presence of lidocaine measured by RP -HPLC. A, adrenaline bitartrate. B, adrenaline bitar-trate with lidocaine and additives.


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DiscussionAddition of vasoconstrictor to dental local anesthetics

is obtained a synergistic effect of anesthetic action to be able to enhance durability of local - anesthetic effect in oral cavity. The decrease of vasoconstrictor attenuates

anesthetic action. A vasoconstrictor which acts for a long time on the body has a great influence on blood pressure

（11）. Therefore, catecholamine which metabolized imme-diately in the body has been used as a vasoconstrictor. However, it is easy to be oxidized the hydroxyl group of

Fig. 3． Effect of temperature and light on relative adrenaline concentration rate in dental local anesthetics. Relative concentration rate was calculated by dividing the con-centration of experimental by the concentration of control. RT, room temperature. 37°C, warming. FL, flu-orescent light. LS, shield from light.

Fig. 4． Representative image of peaks for SO32 - and SO4

2 - in dental local anesthetics measured by IC. A, SO4

2- . B, SO32- .


Int J Oral-Med Sci 19（2）:81–87, 2020 　85

catechol nucleus, changes into a quinone type, and loses the affinity for the adrenergic receptor. The pH of local anesthetic solution is regulated to 3 -4 to maintain stabili-ty of lidocaine, though the oxidation of local anesthetics is promoted depending on a preservation condition（12）. When local anesthetics have been stored for a long time, the storage condition is an important factor for con-trolling the duration of local anesthesia effect. It is recom-mended to store local anesthetics in the cool and dark place, such as a refrigerator, which is not affected by air, light, and heat. It is necessarily to warm local anesthetics before injection, since the cold local anesthetics which was taken out of a refrigerator is painful. The warming of local anesthetics is effective to reduce pain undergoing local anesthetic infiltration into oral tissue（4）. The physi-ological mechanism of the temperature on pain reduction could be due to a synergic action on the permeabilization of Transient Receptor Potential Vanilloid -1 channels, al-

lowing the passage of anesthetic inside the nociceptors（6）.

Recently, cartridge warmer is frequently used at the dental clinic. However, the stability of local anesthetics in cartridge warmer is not examined. It is necessary to con-sider both of a local anesthetic and a vasopressor, when it is examined the influence on quality by warming dental local anesthesia cartridge. Local anesthetics such as lido-caine are hard to receive the influence by the warming, because it is a stable material for heat, light, acid, and al-kali（12–14）. On the other hand, the vasopressors such as adrenalin are disintegrated by ultraviolet rays and heat, and are easy to be oxidized by contacting with the rub-ber stopper of the cartridge（15, 16）.

In the present study, our data showed that adrenaline concentration decreased at 37°C compared with RT for 12 and 16 weeks, and also decreased on FL compared with LS for 16 weeks. Kawaguchi et al（16）reported that

Fig. 5． Effect of temperature and light on relative SO32- concentration rate in cartridge. Relative con-

centration rate was calculated by dividing the concentration of experimental by the concentra-tion of control. A, a representative image of peaks for SO3

2- and SO42- . B; relative SO3

2- concen-tration rate. RT, room temperature. 37°C, warming. FL, fluorescent light. LS, shield from light.


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adrenalin levels were remarkably decreased by 55% at the second month in the cartridge exposed to fluorescent or ultraviolet light. Temperatures of 23°C and 50°C had a little effect on alterations in adrenalin and noradrenalin, whereas a temperature of 50°C remarkably lowered the levels by 55%. They suggest that the plunger gum affect a decrease of adrenalin concentration, because it con-tained some heavy metals used for staining and polymer-izing. Small amounts of heavy metals are sufficient to cat-alyze the oxidation of catecholamine and enhance photochemical effects of fluorescent or ultraviolet light.

Several studies have investigated the effect of tempera-ture and light on adrenalin levels, however, did not con-sider the effect of temperature and light on sulfite levels contained as a stabilizer in dental local anesthetics. On the next step, we focused on the effect of temperature and light on sulfite concentrations. Sodium pyrosulfite is induced a chemical change by heating to high tempera-ture and produced sodium sulfite and sulfur dioxide, and then SO3

2- is oxidized to SO42- .

Na2S2O5 → Na2SO3+SO2

2SO32-+O2 → 2SO4

2-

In the present study, our data showed that SO32- con-

centration decreased at 37°C compared with RT for 16 weeks, while SO4

2- concentration increased at 37°C com-pared with RT for 16 weeks. The oxidation of SO3

2- may influence on the resolution of adrenalin, since the increase of SO4

2- concentration lower pH. In addition, sodium pyro-sulfite which is added to inhibit the oxidation of adrenalin, induce the racemization of adrenalin at pH values much below pH 4. The racemization of adrenalin is promoted under condition at low pH and high temperature. The re-sults suggest that the racemization reaction may prove to be an important route for loss of biological activity of adrenaline at pH values much below pH 4（17, 18）.

Miura et al（19）reported that no marked hemolytic ef-fects of the local anesthetics without adrenalin were ob-served. Slight hemolysis was noted when the local anes-thetics without adrenalin were stored for 10 weeks under ultraviolet irradiation in ambient temperature. On the other hand, an increase of hemolytic ability and a de-crease of pH value occurred when the adrenalin - contain-ing local anesthetics were stored under ultraviolet irradi-ation. Therefore, it is necessary to use cartridge warmer appropriately, because it may induce not only an attenua-tion of vasoconstrictor effect but also an increase of he-

molytic ability by adrenalin oxidation.Sakiyama（20）reported that the concentrations of lido-

caine on the different storage conditions showed no signif-icant difference at 12 month compared with the start of the experiment. On the other hand, the concentrations of adrenaline decreased at 30°C or room temperature with-out shade from the light for 12 month. Additionally, the duration of dental local anesthetic reduced to 80 min from 180 min after storage at 30°C or room temperature with-out shade from the light for 12 month. They suggest that there is a correlation between adrenalin concentrations and duration of anesthesia. Furthermore, Sasao et al（21）investigated that the different effects of infiltration anes-thesia induced by various concentrations of lidocaine and adrenaline by somatosensory evoked potentials in rats. They concluded that the duration is considered to be a direct reflection of differences of adrenaline concentra-tion. Therefore, it is important to know the change of adrenaline concentration.

In conclusion, we found that adrenaline concentrations decreased at 37°C compared with RT for 12 and 16 weeks and also decreased on FL compared with on LS at 16 weeks. SO3

2 - concentration decreased at 37°C com-pared with RT for 16 weeks. These results suggest that the temperature influences adrenaline and SO3

2- concen-trations, while adrenaline and SO3

2 - concentrations are not affected by temperature and light for less than eight weeks. Adrenalin in the cartridge of dental local anesthet-ics is hard to be oxidized, since the cartridge is superior in air tightness. However, it is necessary to be careful of safekeeping management of the cartridge of dental local anesthetics.

AcknowledgmentsThis study was supported by a grant from the Re-

search Institute of Oral Science, Nihon University School of Dentistry at Matsudo.

Conflict of InterestNone of the authors have any conflicts of interest asso-

ciated with this study.

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stability of adrenalin in dental local anesthetics on the

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