Page 1
`
`RB Ex. 2021
`BDSI v. RB PHARMACEUTICALS LTD
`IPR2014-00325
`
`

`
`668 Bullinglzam er al.
`
`Clin. Phnrmacul. The-r.
`November I980
`
`Table I. Data of patient groups
`
`Phase 1],
`
`Phase II.
`
`Number of patients
`Age (yr 1- SEM)
`Sex distribution (malezfemale)
`Weight (kg i SEM)
`lntraoperative Pa. .,,
`(kPa :9: SEM)
`Surgery start to reversal time
`(min : SEM)
`394 1 58.8
`539 I 94 0
`487 t 53.6
`lntraoperative blood loss
`(ml 2 SEM)
`
`10
`67.5 ‘J: 6.5
`6:4
`67.5 1‘ 2.1
`5.35 i 0.16
`
`l I
`62.1 : 2.6
`7:4
`66.5 2‘: 3.6
`5.5 :1: 0.28
`
`24
`64.5 1* 1.6
`14:10
`67.7 i 2.4
`5.4 i 0.15
`
`96.3 1 5.8
`
`95.3 i 10.1
`
`88.6 : 6.5
`
`All patients received diazepam 10 mg orally
`2 to 4 hr preoperatively. Anesthesia was in-
`duced with intravenous thiopental 4 mg/kg, fol-
`lowed by pancuronium 0.1 mg/kg. After tra-
`cheal intubation,
`intermittent positive-pressure
`ventilation was instituted on the Bain circuit“ at
`
`a tidal volume of 10 ml/kg. The fresh gas flow
`of 70 ml/kg was chosen to achieve intraopera-
`tive normocapnia, and this was checked by ar-
`terial blood gas measurement. Fresh gas flow
`consisted of nitrous oxide and oxygen in a ratio
`of 2:1, with 0.5% halothane. Halothane was
`
`used to avoid awareness during this light anes-
`thesia and because quantitative information is
`available on its effect on hepatic blood flow.‘-" 7
`Radial artery cannulation was performed and
`then (phase I) 0.3 mg buprenorphine, diluted to
`10 ml with 0.154 M NaCl, was injected intra-
`venously over 1.0 min. All patients received
`this initial dose. Zero time was taken as the end
`
`of injection. Arterial samples were drawn in-
`traoperatively and into the postoperative period,
`at 2, 5, 7.5, 10, 15, 20, 30, 40, 60, 80, 100,
`120, 150, and 180 min. A basal venous blood
`
`sample was drawn before induction of anesthe-
`sia. All blood samples were taken into lithium
`heparin tubes, centrifuged, and the plasma
`separated at
`room temperature. Plasma was
`stored at 20” until required for analysis.
`Intraoperatively, all patients were kept hori-
`zontal on a warming blanket. Nasopharyngeal
`temperature, ECG, and direct arterial pressure
`were monitored throughout. Hartmann’s solu-
`tion was infused at 5 ml/kg/hr for 2 hr and then
`blood was transfused according to a standard
`formula.
`lntraoperative blood loss was moni-
`
`tored by weighing of swabs and calibrated auc-
`tion.
`
`No supplements of muscle relaxant were giv-
`en. Halothane was withdrawn about 10 min be-
`
`fore reversal. Reversal was with intravenous
`
`neostigmine 2.5 mg and atropine 1.2 mg. Post-
`operatively, patients breathed spontaneously,
`using controlled oxygen therapy (28% Ven-
`timask).
`
`Phase II started at 180 min. The patients were
`divided into two groups and a second dose of
`0.3 mg buprenorphine was given. One group
`again received the dose intravenously. The sec-
`ond group was given the dose intramuscularly
`into the vastus lateralis on the side opposite to
`the hip replacement. Arterial samples were
`drawn after the second dose at 2, 5, 10, 15, 20,
`40, 60, 80, 120, 150, and 180 min, and treated
`in the same way as the phase I samples.
`Analytical procedures. Buprenorphine was
`measured in whole heparinized plasma by a ra-
`dioimmunoassay procedure‘ using specific an-
`tibodies raised to N-hemisuccinyl-nor-bupre-
`norphine linked to bovine serum albumin in
`rabbits. Standard displacement curves were
`prepared by measuring the displacement of
`31-l-buprenorphine binding to antiserum by un-
`labeled buprenorphine in drug-free human plas-
`ma. Samples with high values were diluted with
`drug-free plasma, and those with low values
`reassayed in a system where the volume of plas-
`ma samples was increased from 100 to 300 pl.
`Nonspecific binding of plasma to “H-bu-
`prenorphine in the absence of antiserum was
`less than 5%. The precision of the assay was
`excellent, and the intra-assay and interassay
`Page2
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`Page 2
`
`

`
`Volume 28
`.Number 5
`
`:
`
`Buprenorphine kinetics
`
`669
`
`- Table II. Buprenorphine plasma levels (f i SD) (ng/ml)
`
`Sample Iime
`Phase II. intra-
`muscular (n =— II)
`
`
`
`Phase I
`(n = 24)
`
`Phase II, intru-
`venous (n = I0)
`
`(min)
`
`14.62 t 6.281”
`5.23 + 1.67
`
`3.56 i 2.8021.‘
`3.61 I 2.97
`
`18.62 i 5.60*
`2
`9.37 : 2.99
`5
`6.03 t 1.60
`7.5
`4.60 i 1.09
`10
`3.12 1: 0.85
`15
`2.30 : 0.56
`20
`1.59 1 0.40
`30
`1.13 :t 0.32
`40
`0.85 i 0.18
`60
`0.67 2*: 0.24
`80
`0.53 1- 0.16
`100
`0.49 i 0.15
`120
`0.49 i 0.27
`0.47 :t 0.17
`0.46 i 0.16
`150
`0.43 2*: 0.24
`0.42 t 0.18
`0.37 1 0.17
`180
`0.36 + 0.16
`0.38 .t 0.15
`
`‘n -— 23.
`+.n -' 9
`in =- 8
`
`3.15 2*: 0.92
`2.15 + 0.56
`1.77 + 0.43
`
`1.05 : 0.27
`0.77 1 0.17
`0.70 .+ 0.16
`
`3.31 ;2.52
`2.46 1- 1.60
`2.19 2*; 1.26
`
`1.22 :*:—0.76
`0.79 i 0.49
`0.64 t 0.36
`
`variation at various plasma levels was less than
`5%. In these short-term experiments, metabo-
`lite cross-reaction does not cause significant
`problems.‘
`Analysis of results. Plasma levels were fitted
`to a sum of exponentials curve, using a com-
`puter program based on a stripping method.”
`The quality of the fit was judged by a minimum
`least-squares criterion. Before analysis,
`the
`computed temiinal decay portion of the first
`dose of drug was removed from all plasma val-
`ues measured after the second dose of drug.
`Justification for this came from the close expo-
`nential fits obtained with the first dose, showing
`behavior corresponding to that of a linear ki-
`netic system.
`
`Kinetic parameters were calculated from the
`exponential fits.“ For calculation of percentage
`availability of the intramuscular dose, the area
`under the curve (AUC) from time 0 to 180 min
`in phase II was calculated using a numerical
`integration program.“ The AUC from 180 min
`to infinity was estimated by calculation using an
`exponential fitted to the last six points of the
`curve for the intramuscular dose. The total
`
`AUC could then be compared with one simi-
`larly calculated for patients who received their
`second dose of drug intravenously. Since these
`were different patients, two different methods
`were used for the comparison. In one method,
`
`in-
`second dose
`receiving the
`the patient
`tramuscularly was matched in terms of first-
`dose plasma levels of buprenorphine to all pa-
`tients receiving the second dose intravenously.
`The best match was taken as that with minimum
`
`sum of squared differences, and then that pa-
`tient’s second-phase data was used in the com-
`parison.
`In the second method,
`the averaged
`second-phase data for the intravenous group
`was used for comparison with each of the in-
`tramuscular patients.
`
`Results
`
`Three patients who completed the first phase
`subsequently did not complete the second phase
`because of arterial line failure. One patient who
`completed both phases subsequently did not
`complete the succeeding analgesia-measure-
`ment phase because of
`instrument
`failure.
`Plasma levels from these patients are included
`with those of the basic 20 who completed all
`phases. Patient data is shown in Table I. There
`was no significant difference between the
`groups with respect to age, weight, sex distri-
`bution, duration of anesthesia, or the total blood
`loss.
`
`Average buprenorphine plasma level data is
`given in Table II. The intravenous plasma data
`from individual patients fitted a mu1tiexponen-
`tial decay curve. In 27 of the total of 34 intrave-
`Page 3
`
`Page 3
`
`

`
`670 Bullingham er al.
`
`Clin. Pharmacal. Thar
`Notembcr I 980
`
`
`
`Phase II,
`intramus culur
`
`Phase II,
`imra venous
`
`Table III. Average kinetic parameters (.'t' 7!: SEM)
`
`
`
`— P
`
`arameter values are for the triexponential fit; Plasma concentration (ng. ml) ' Aexp - ul -1- Bexp - B! + Cexp
`Bexp
`31 + Cexp
`yt Other parameters are calculated fmm these fits
`
`yt. or biexpomntial fit:
`
`nous curves analyzed, the triexponential fit was
`better than the biexponential. In the remaining 7
`patients, although a biexponential fit was better
`than a triexponential, the difference was small,
`and a triexponential analysis was used on their
`data.
`
`The quality of the fit obtained for each patient
`was assessed by the following method. A sum
`of squared differences was calculated for each
`data point between a given patient and the cor-
`responding data points of every other patient,
`then the minimum value obtained from this
`
`match was compared with the sum of squares
`obtained for that patient from his best triexpo-
`nential
`fit. By this criterion, for 75% of the
`patients the differences in plasma levels be-
`tween patients were substantially greater than
`the differences between plasma level and com~
`puted fit within the patient. In the remaining
`patients, further analysis showed that the major
`source of error was caused by the 2-min sample
`point. The timing of the early samples always
`poses the greatest practical problems.
`Average kinetic parameters derived from in-
`dividual
`triexponential
`fits are presented in
`Table III, as values
`in plasma concentra-
`tion = Aexp - at + Bexp - [it + Cexp —
`'yt. Intramuscular uptake calculated by either
`method was very similar. Seven of eleven
`showed systemic availabilities of above 90%.
`The other four patients had poor availability of
`40% to 60% of the dose. One of these had had
`
`previous hip surgery on the side of injection.
`
`Plasma levels were correspondingly low and ir-
`regular in this group. A notable feature of those
`patients with good drug mobilization was the
`rapidity with which the peak level occurred.
`The data then showed an excellent fit to a biex~
`
`ponential curve. Average kinetic parameters
`derived from these individual biexponential fits
`are also shown in Table III, in the form plasma
`concentration = B exp — Bt + C exp
`yt.
`Fig.
`1 shows a plot of the average data of
`phase II for the inuamuscular and intravenous
`
`groups as given in Table II. The closeness of the
`plasma levels for these two routes is evident.
`
`Discussion
`
`The plasma level of intravenous buprenor-
`phine declines very rapidly, with a t‘/& of 2.0
`min, as expected for this very lipophilic drug.
`This is followed by a slow terminal phase
`with a W: of 2 to 3 hr.
`In view of the 3-hr
`duration of the experiment, this t‘/2 can only be
`considered to be an estimate.
`
`Plasma clearance under anesthesia is about
`900 ml/ min. The plasma/red blood cell ratio of
`buprenorphine is close to unity,* and so the
`blood clearance has a similar value. Buprenor—
`phine is almost completely metabolized in
`vivo.'1 The clearance obtained is thus very close
`to the expected hepatic blood flow under these
`anesthetic conditions.” ”’ Consequently,
`the
`
`‘Moon:-12A. Unpublished observations.
`Tknnce MJ: Personal communication.
`
`Page 4
`
`Number of patients
`A (ng/ml)
`tfiatmin)
`B (ng/ml)
`W35 (min)
`C (ng/ml)
`W2, (min)
`Plasma clearance (ml/min)
`Vdq, (I)
`Initial C (ng/ml)
`
`Phase I
`(in rraoperari re)
`
`24
`26.5 + 3.
`2.1 3: 0.
`5.8 + 0.
`11.2 + 0.
`1.1 + 0 08
`139.6 + 14.4
`901.3 :4: 39.7
`97.3 + 7.66
`33.5 -+.- 2.98
`
`10
`18.1 t 3.1
`2.2 1 0.29
`2.8 i 0.60
`18.7 i 3.16
`0.72 i 0.14
`183.6 :1: 37.0
`1,275 I 88.9
`187.8 1 35.26
`21.6 1- 3.54
`
`7
`-
`
`4.7 + 0.79
`16.5 + 2.46
`1.4 + 0.26
`138.5 + 418
`992.7 -*7 70 3
`148.1 + 51 '1
`
`Page 4
`
`

`
`Volume 28
`-:NumfW 5
`
`Buprenorphine kinetics
`
`671
`
`
`
`
`
`PlasmaBuprenorphinelnglmll
`
`100
`
`120
`
`140
`
`160
`
`180
`
`Time (min)
`
`Fig. 1. Plasma levels of buprenorphine in phase II by intravenous (o- -
`(.~.----- ) routes of administration.
`
`---0) and intramuscular
`
`_ extraction ratio is close to 1.0, and a very large
`first-pass effect is to be expected.
`Analysis of the plasma levels after a second
`dose, when a measurable plasma level is still
`present as a result of the first dose, requires that
`assumptions be made about the behavior of the
`drug. The assumption that the behavior is linear
`in this experiment is justified because of the
`good fit to a sum of exponential terms that was
`obtained. Removing the tail of the first dose
`from the total plasma level after the second dose
`will increase the total error in the phase 11 fit
`parameters. However, the plasma level of bup-
`renorphine from the first dose at the time of
`administration of the second dose is small
`
`the long terminal
`(about 0.4 ng/ml). Further,
`t‘/2 means that this value shows little absolute
`change during the time of measurement of the
`second dose. When the second dose is given
`intravenously with high initial plasma levels,
`the relative error is likely to be small. This is
`supported by the fits with data treated in this
`way, which were as good as those obtained for
`the first dose alone. The relative error will be
`
`greater with intramuscularly administered drug,
`
`especially if poor absorption should lead to little
`rise in plasma level.
`Comparison of the results from the same pa-
`tient, anesthetized and awake postoperatively,
`shows two interesting differences. Plasma lev-
`els awake were all lower (p < 0.025, paired t
`test) than the anesthetized values, up to 30 min.
`This arose mainly from higher initial plasma
`values in the anesthetized state, implying lower
`initial volumes of distribution when anes-
`
`thetized. This presumably reflects the lowered
`cardiac output known to occur in anesthesia,”
`
`even in the normocapnic situation achieved here.
`The second effect of anesthesia is to lower the
`
`clearance by a consistent 30% with respect to the
`awake patient. As shown, the drug is almost
`completely cleared by the liver, and this figure
`agrees well with the measured effect of
`halothane anesthesia on hepatic blood flown?’ 7
`The reported effects of anesthesia on meperidine
`kinetics“ are in the same direction and of the
`
`same magnitude as reported here. We believe
`sufficient attention has not been paid to the ef-
`fects of anesthesia on drug kinetics. There will
`be a predictable difference in the behavior of
`Page 5
`
`Page 5
`
`

`
`672 Bullingham et (:1.
`
`Clin. Plzannacal. Ther.
`November I980
`
`drugs used in the anesthetized and awake condi-
`tions, and failure to recognize this may lead to
`important clinical differences.
`
`A notable feature of buprenorphine given in-
`tramuscularly is its very rapid uptake. Peak
`plasma level was usually at 5 min after the dose,
`and in some patients had occurred by 2 min.
`Mean plasma levels of intramuscular and intra-
`venous buprenorphine differ little beyond 5
`min, although the variance is larger at a given
`level. Systemic availability is generally close to
`100%. Poor drug uptake presumably occurs
`with misplacement of the drug, an inherent risk
`with this route of administration.
`
`The clinical effects of these doses in this trial
`
`will be reported elsewhere. As anticipated,‘ the
`effect of the drug far outlasts the plasma level
`and there is no direct
`relationship between
`plasma level and pharmacologic effect. Fur-
`thermore, poor systemic availability by the in-
`tramuscular route does not imply correspond-
`ingly poor analgesia.
`
`We thank the surgeons of the Nuffield Orthopedic
`Centre for allowing us to study their patients, and the
`Anesthetic and Recovery staff for their help. Reckitt
`and Colman donated the drug and assay materials; we
`gratefully acknowledge their support.
`
`References
`
`l. Bartlett AJ, Lloyd-Jones JG, Rance MJ, Flock-
`hart
`IR, Dockray G, Bennett MRD, Moore
`RA: The radioimmunoassay of buprenorphine.
`Eur] Clin Pharmacol. (In press.)
`
`. Epstein RM, Deutsch S, Coopennan LH, Cle-
`ment AJ, Price HL: Splanchnic circulation dur-
`ing halothane anaesthesia and hypercapnia in
`normal man. Anesthesiology 27:654-661, 1966.
`. Greville TNE: Theory and application of spline
`functions. London, 1969, Academic Press, lnc.,
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`Hambrook JM. Rance MJ: The interaction of
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`. Heel RC, Brogden RN, Speight TM, Avery GS:
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`Ther 5:29-33, 1979.
`. Henville JD, Adams AP: The Bain anaesthetic
`
`system. Anaesthesia 31:247-256, 1976.
`. Juhl B, Einer-Jensen N: Hepatic blood flow and
`cardiac output during halothane anaesthesia: An
`animal study. Acta Anaesthiol Scand 18:114-
`l22, 1974.
`. Mather LE, Tucker GT, Pflug AE, Lindop MJ,
`Wilkerson C: Meperidine kinetics in man. CLIN
`PHARMACOL THER 17:21-30, 1975.
`. Perl W: A method for curve fitting by exponen-
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`1960.
`
`10.
`
`11.
`
`Prys—Roberts C, Kelman GR, Greenbaum R,
`Robinson RH: Circulatory influences of artificial
`ventilation during nitrous oxide anaesthesia in
`man. Br J Anaesth 39:533-548, 1967.
`Wagner JG: Linear pharmacokinetic equations
`allowing direct calculation of many needed
`pharmacokinetic
`parameters
`from the
`co-
`efficients and exponents of polyexponential
`equations which have been fitted to the data. J
`Pharmacokinet Biopharm 4:443-467, 1976.
`
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