Acute Opioid Physical Dependence in Humans: Effect of Varying the Morphine-Naloxone Interval. I

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1 /89/ $.OO/O THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Copyright ( 1989 by The American Society for Pharmacology and Experimental Therapeutics Vol. 25. No.2 Printed in U.S.A. Acute Opioid Physical Dependence in Humans: Effect of Varying the Morphine-Naloxone Interval. I STEPHEN J. HEISHMAN, MAXINE L. STITZER, GEORGE E. BIGELOW and IRA A. LIEBSON Department of Psychiatry and Behavioral Sciences, The Johns Hopkins University School of Medicine (S.J.H., M.L.S., G.E.B., l.a.l.) and Department of Psychiatry, Francis Scott Key Medical Center (M.L.S., G.E.B., l.a.l.), Baltimore, Maryland Accepted for publication April 21, 1989 ABSTRACT Acute opiold physical dependence refers to the ithdraal symptoms precipitated by an oploid antagonist administered after a single dose or short-term infusion of an opioid agonist. This phenomenon is particularly interesting given that the abstinence syndrome has generally been thought to develop only after chronic exposure to oploid agonists. The purpose of this study as to determine the minimum time after agonist administration hen antagonist-precipitated ithdraal could be observed. Naloxone (1 mg/7 kg) as administered i.m. either, 1 5, 45 or 9 mm after single i.m. injections of morphine (1 8 mg/7 kg) in five nondependent male opiate users. Physiological and subjective report measures revealed no effect of morphine or naloxone at the and 1 5 mm morphine-naloxone interval conditions; Acute opioid physical dependence refers to the ithdraal syndrome precipitated by administration of an opioid antagonist after either a single dose or a short-term infusion of an opioid agonist (Martin and Eades, 1964; Martin and Sloan, 1977). It is generally thought that physical dependence develops only after chronic exposure to opiates. This state of chronic physical dependence is characteried by a ell-defined abstinence syndrome upon discontinuation of the opiate (Himmelsbach, 1941; Jaffe and Martin, 1985; Wikler, 198). Hoever, conclusions from studies of acute opioid physical dependence in animals (Eisenberg and Sparber, 1979; Wikler and Carter, 1953) and humans (Bickel et a!., 1988; Heishman et at., 1989) suggest that the adaptational changes underlying physical dependence begin ith the first exposure to an opiate. Such changes could be inferred through studies of the early developmental course of physical dependence. Although acute opioid physical dependence has been demonstrated in various species, fe studies have systematically investigated the effect of varying the temporal interval beteen agonist and antagonist administration. Typically, agonist-antagonist intervals of beteen 1 and 24 hr have been used to Received for publication October 7, This ork as supported by U.S. Public Health Service Research Grant DA and Research Training Grant DA-729 from the National Institute on Drug Abuse. A preliminary report of this research as presented at the 5th Annual Scientific meeting of the Committee on Problems of Drug Dependence, Inc., June, 1988, North Falmouth, MA. hoever, before the naloxone challenge 45 and 9 mm postmorphine, agonist effects (e.g., miosis, respiratory depression and good drug effect subjective ratings) ere dearly evident. Naloxone reversed these effects to premorphine levels and simultaneously precipitated subjective symptoms and observer rated signs of opiate ithdraal. Thus, this study shoed that antagonist-precipitated ithdraal in humans as first observed 45 mm after agonist administration. Further, the onset of naloxone-precipitated ithdraal effects closely paralleled the onset of morphine agonist effects. The results of this study suggest that adaptational changes underlying the development of physical dependence begin ithin minutes after acute exposure to an opiate. demonstrate antagonist-precipitated ithdraal responses in mice (Cheney and Goldstein, 1971; Way et at., 1969), rats (Meyer and Sparber, 1977; Eisenberg and Sparber, 1979), dogs (Jacob and Michaud, 1974; Martin and Eades, 1961, 1964; Wikler and Carter, 1953), monkeys (Krystal and Redmond, 1983) and humans (Bickel et a!., 1988; Heishman et at., 1989; Higgins et a!., 1988; Jones, 198, 1981). Other studies have demonstrated antagonist-precipitated ithdraal effects ithin 1-3 mm after acute agonist administration as measured by the jumping response in mice (Jacob et a!., 1974; Kosersky et at., 1974; Ritmann, 1981; Smits, 1975; Yano et at., 1979) or increased plasma corticosterone levels in rats (Eisenberg, 1982). These data suggest that the adaptive mechanisms underlying antagonist-precipitated ithdraal begin to develop ithin minutes after acute opioid administration. Observational research ith humans has shon that ithdraal symptoms, including nausea, vomiting, tachycardia, seating and hypertension, occurred after administration of naloxone to reverse opioid anesthesia during surgery (Aar and Turndorf, 1979; Johnstone et a!., 1974; Longnecker et at., 1973). In experimental research ith nondependent former opiate addicts, Nutt and Jasinski (1974) reported the occurrence of physiological and subjective ithdraal responses precipitated by the second administration of a methadone/naloxone mixture 1 eek after a previous administration of that same mixture. Jones (198, 1981) observed antagonist-precipitated ithdraal effects in opiate-naive subjects ho received naloxone 485 Donloaded from jpet.aspetjournals.org at ASPET Journals on September 18, 216

2 486 Heishman et al. Vol or 24 hr after a single dose of morphine. Three recent studies (Bickel et a!., 1988; Heishman et a!., 1989; Higgins et at., 1988) have investigated antagonist-precipitated ithdraal by administering naloxone 6 hr after single morphine doses in nondependent humans ith a history of opiate use. These studies found that the intensity of the naloxone-precipitated ithdraal syndrome, hich included physiological, subjective report and observer-rated measures, varied directly ith the sie of the morphine pretreatment dose (Bickel et at., 1988; Higgins et at., 1988) and the naloxone challenge dose (Heishman et at., 1989). To our knoledge, no human data exist on the early developmental course of acute opioid physical dependence; such data ould provide a comparative extension of existing animal research (e.g., Jacob et at., 1974; Smits, 1975). In the present study, e manipulated the temporal interval beteen single doses of morphine and naloxone from to 9 mm in nondependent opiate users. The purpose of the study as to determine the minimum duration of agonist exposure necessary to observe antagonist-precipitated ithdraal. Methods Subjects. Participants ere five male community volunteers in good physical health ith documented histories of drug abuse but ithout other significant psychiatric disorder, as assessed by the National Institute of Mental Health Diagnostic Intervie Schedule (Robins et at., 1981). Subjects ranged in age from 23 to 41 years (mean 34.6), in history of i.v. opiate use from 3 to 2 years (mean 16) and in current i.v. opiate use from 6 to 14 times per month (mean 11.6). To subjects had previously participated in opiate detoxification programs; one subject reported to treatment episodes, the other three. All subjects reported having experienced some degree of opiate ithdraal sickness in the past; hoever, none considered themselves currently dependent, nor ere any seeking treatment for opiate addiction. Most subjects also reported current use of five drugs: tobacco (1% of participants), caffeine (1%), alcohol (8%), cocaine (8%) and marijuana (8%). One subject reported using barbiturates or tranquiliers once per eek. Subjects gave ritten informed consent before the study and ere paid for participation. General procedures. During the 4-eek study, subjects lived on an eight-bed behavioral pharmacology research ard that has been described (Griffiths et at., 198). After admission to the research ard, subjects ere observed for ithdraal symptoms for 3-4 days, and they provided a drug-free urine sample before the start of the study. No ithdraal symptoms ere observed in any subject as assessed by clinical observation and monitoring of vital signs by the nursing staff. The participation of each subject in the study generally overlapped ith another subject s participation. When this occurred, experimental test sessions ere scheduled on different days to maximie the independence of each subject s data. Other residents on the research ard also had histories of drug abuse and participated in different behavioral experiments involving the administration of opioid agonists and antagonists, stimulants or sedatives. Before the protocol, subjects ere informed that the purpose of the study as to gain a better understanding of ho physical dependence develops to opiate drugs and that they should expect to experience mild ithdraal sickness after some drug injections. Subjects ere also told the general plan of drug administration and that the drugs to be administered ould include an opiate agonist, an opiate antagonist and placebo. Hoever, subjects and research staff ere blind to the nature of individual drug injections. Before the study, subjects received detailed instructions concerning experimental session procedures and ere familiaried ith the various measurement techniques. Drugs. Commercially available morphine (15 mg/ml) as diluted in bacteriostatic saline to the desired concentration for injection. The constant morphine dose as 18 mg/7 kg. Naloxone hydrochloride (Dupont, Wilmington, DE) as eighed as the salt and dissolved in bacteriostatic saline to a concentration of 1 mg/ml, hich as then diluted in saline to desired concentrations. The constant naloxone challenge dose as 1 mg/7 kg. Placebo injections consisted of bacteriostatic saline. Morphine, naloxone and placebo ere administered i.m. under double-blind conditions in a constant volume of 1.5 ml in the right or left deltoid muscle. The i.m. route of drug administration as chosen over the i.v. route so that the onset of antagonist effects ould be relatively gradual and therefore more readily measurable. Experimental procedures. Subjects participated in six experimentel sessions conducted tice eekly and separated by at least 72 hr. On the first to sessions only, subjects ere tested in our standard 6-hr morphine-naloxone interval paradigm, in hich i.m. morphine or morphine placebo as administered at 9: A.M. on the research ard; 5.5 hr after morphine injection, subjects ere seated in a quiet experimentel room located off the ard and connected to physiological recording equipment. At 3: P.M. (6 hr postmorphine), subjects received an i.m. injection of naloxone and ere monitored for 6 mm. During the first experimental session, subjects received morphine placebo folloed 6 hr later by naloxone challenge (1 mg/7 kg). The purpose of this session as to verify further the absence of opioid physical dependence by testing for naloxone-precipitated ithdraal signs and symptoms; none ere observed in any subject. During the second experimental session, subjects received 18 mg/7 kg morphine folloed 6 hr later by 1 mgi 7 kg naloxone. The purpose of this session as to determine each subject s sensitivity to the antagonist challenge. Five subjects reported symptoms and exhibited signs of naloxone-precipitated ithdraal after 18 mg/7 kg morphine pretreatment and continued testing at this dose. Three subjects ere insensitive to the antagonist challenge after 18 mg/7 kg morphine and ere dimissed from the study after session 2. On sessions 3-6, subjects ere seated in the experimental room at 9: A.M. and connected to the recording equipment. Physiological measurements ere alloed to stabilie for 15 mm; premorphine baseline measures ere then recorded for 1 mm. During the next 5 mm, a base-line pupil photograph as taken, subjective forms completed and objective signs of ithdraal observed. At 9:3 A.M., subjects received an i.m. injection of 18 mg/7 kg morphine. Naloxone (1 mg/7 kg) as administered i.m. either immediately ( mm condition) or 15, 45 or 9 mm after morphine injection, and subjects ere then monitored for 6 mm. The measurement battery of pupil photographs, subjective reports and observer-rated ithdraal signs as repeated just before naloxone challenge (prenaloxone base-line) and at 5, 15, 3, 45 and 6 mm postnaloxone. The four morphine-naloxone interval conditions ere presented in random order, and subjects ere blind to the specific interval conditions. Physiological measures. Systolic and diastolic blood pressure, mean arterial pressure, heart rate, respiration rate and skin temperature ere recorded continuously throughout experimental sessions as previously described (Heishman et a!., 1989). Pupil photographs ere taken in ambient room lighting using a Polaroid camera ith 3x magnification. Subjective report measures. At each measurement point subjects completed opioid symptom, ithdraal symptom and drug effect questionnaires. The opioid and ithdraal symptom forms each contained 15 items describing typical opioid or ithdraal effects (see table 1). The drug effect questionnaire assessed six items: 1) drug high, 2) any drug effect, 3) good drug effect, 4) bad drug effect, 5) drug liking, and 6) ithdraal sickness. On all questionnaires, subjects rated the extent to hich they currently experienced each symptom or effect on a 1- point scale from (not at all) to 9 (most strongly). A Composite score as obtained for the ithdraal and opioid symptom questionnaires by summing across the 15 items. Each drug effect questionnaire item as scored separately. Observer rated measures. Tearing eyes, runny nose, perspiration, gooseflesh, yaning and restlessness ere observed as previously described (Heishman et al., 1989) by a research technician ho as blind Donloaded from jpet.aspetjournals.org at ASPET Journals on September 18, 216

3 1989 TABLE 1 Items comprising the subjective questionnaires Opiold Symptom Questionnaire: rush, flushing, seating, nodding, dry mouth, turning of stomach, itchy skin, relaxed, coasting or spaced out, talkative, pleasant sickness, drive, nervous, floating, good mood Withdraal Symptom Questionnaire: muscle cramps, painful joints, yaning, hot or cold feelings, upset stomach, irritable, runny nose, sneeing, atery eyes, restless, abdominal cramps, backache, chills or goose flesh, bothered by noises, skin dammy and damp to drug. These ithdraal signs ere rated on the same 1-point scale used for subjective report measures. A composite observer rating score as obtained by summing the individual item scores. Data analysis. Measures analyed included pupillary diameter, respiration rate, heart rate, akin temperature, systolic and diastolic blood pressure, mean arterial pressure, composite score on the opioid and ithdraal symptom questionnaires, individual ithdraal symptorn and drug effect questionnaire items, and individual and composite scores of observer-rated ithdraal signs. The data consisted of the 1 mm before naloxone injection (prenaloxone base line) and the 6-mm test after naloxone (postnaloxone session). The continuously recorded physiological measures ere averaged over the base line and test session. The subjective report and observer-rated base-line data consisted of the single prenaloxone observation; the session data ere an average of the five postnaloxone measurements. All data ere analyed by to-ay, repeated-measures ANOVA ith condition (morphinenaloxone interval) and time (prenaloxone base line versus postnaloxone session) as the factors. Huynh-Feldt adjustments of repeated-measure degrees of freedom ere used to correct for violation of the sphericity assumption. Data from the prenaloxone base line indicated onset of agonist drug effects, hereas data from the postnaloxone session reflected antagonist-precipitated ithdraal effects. A condition main effect could indicate that morphine-naloxone interval affected the magnitude of agonist effects, antagonist effects or both. A significant condition x time interaction ould indicate that morphine-naloxone interval influenced either agonist or antagonist effects, but not both. We predicted that interaction effects ould be observed on most measures. In general, here significant interactions are reported, there ere also significant condition main effects. To assess more specifically the influence of morphine-naloxone interval on agonist and antagonist drug effects, results from the 15-, 45- and 9-mm conditions ere compared ith data from the -mm condition using Tukey post hoc tests. Post hoc analysis as also used to assess differences beteen prenaloxone and postnaloxone values for each morphine-naloxone interval condition. For all statistical tests, effects ere considered significant if P <.5. Onset of Agonist Effects Results Figure 1 shos to physiological and to subjective report measures as a function of morphine-naloxone interval. These graphs illustrate the gradual onset of morphine agonist effects, as indicated by the prenaloxone base-line assessment, and the reversal of these effects during the postnaloxone session. Regarding the onset of agonist effects (prenaloxone data), significant condition x time interactions ere observed for pupillary diameter [F (3, 12) = 15.62, P <.1], respiration rate [F (3, 12) = 7.68, P <.1], good drug effect item [F (3, 12) = 4.53, P <.5] and drug liking item [F (3, 12) = 3.95, P <.5] from the drug effect questionnaire. Morphine significantly constricted pupils from a normal diameter of -5.5 mm, as measured before the -mm naloxone challenge session, to mm, as measured before the 45- and 9-mm naloxone challenge sessions. Acute Opioid Physical Dependence 487 Similarly, morphine produced a significant decline in respiration rate from about 16 breaths/mm before the -mm condition to 13 breaths/mm at 45 and 9 mm postmorphine. Subjective ratings of good drug effect and drug liking ere increased by morphine. Post hoc analysis indicated that responses obtained before the 45- and 9-mm naloxone challenge sessions ere significantly greater than those before the -mm condition for both measures. Maximum subjective effects on both items ere observed before the 45-mm naloxone challenge, ith no further increases at 9 mm postmorphine. A similar pattern of subjective effects as observed on the 15-item opiate symptom questionnaire (data not shon). A significant condition main effect [F (3, 12) = 7.11, P <.5] as observed for this scale, but the interaction failed to reach statistical significance. Other physiological measures that revealed significant condition X time interactions ere diastolic blood pressure [F (3, 12) = 16.87, P <.1], mean arterial pressure [F (3, 12) = 5.82, P <.5], heart rate [F (3, 12) = 6.79, P <.5] and skin temperature [F (3, 12) = 5.84, P <.5]. A significant condition effect as observed for systolic blood pressure [F (3, 12) = 6.13, P <.51. Post hoc analysis revealed small but significant increases in the prenaloxone base-line value of diastolic blood pressure and mean arterial pressure at 15, 45 and 9 mm postmorphine compared ith that before the -mm condition. Systolic pressure as significantly increased only at 15 mm postmorphine compared ith the -mm condition. No significant agonist effects ere observed for heart rate or skin temperature in the prenaloxone base-line data. In general, the observed agonist effects ere completely reversed after naloxone administration. Examination of the postnaloxone session data for each measure in figure 1 revealed no significant differences beteen the 15-, 45- and 9-mm conditions compared ith the -mm condition. Naloxone-induced reversal of agonist effects ould be more specifically indicated by significant differences beteen prenaloxone base line and postnaloxone session data for each morphine-naloxone interval condition (fig. 1). Pupillary diameter measured before and after naloxone as significantly different at both 45 and 9 mm, indicating reversal of miosis by naloxone. Respiration rate differed significantly before and after naloxone at 45 but not 9 mm postmorphine. Subjective ratings of good drug effect observed 45 and 9 mm postmorphine ere reversed after naloxone, as indicated by significant pre- versus postnaloxone scores. Drug liking scores ere significantly different only during the 45-mm session. Examination of the ithin-session course of naloxone-induced reversal of agonist effects (data not shon) revealed that miosis and subjective effects ere fully reversed ithin 5 mm after naloxone administration, hereas maximal reversal of respiratory depression as evident 1-15 mm postnaloxone. Antannnist-Prcinitated Withdraal Subjective effects. Figure 2 shos average responses during the postnaloxone session as a function of morphine-naloxone interval for the 15-item ithdraal symptom questionnaire. Included for comparison are data from the 6-hr (36 mm) morphine-naloxone interval (session 2, see Methods ), hich each subject experienced at the beginning of their protocol. Because this condition as not randomly ordered ith the other four conditions, these data ere not included in the analysis. Prenaloxone base-line scores ere omitted from the figure because post hoc analysis indicated that no data point as significantly different from one another. Essentially, the Donloaded from jpet.aspetjournals.org at ASPET Journals on September 18, 216

4 488 Heishmen et ai. Vol. 25 I- o Prenaloxone I #{149} Posrnabxj U) 6 5 Puplllary Diameter Good Drug Effect 4 3-.( I- F- 2 -J -J I-. a- Cl) I I I- I RespIration Rate -) #{163} C/, I- 2 F #{163} 6-2 ) 4 U) MORPHINE - NALOXONE INTERVAL (minutes) Withdraal Symptom QuestIonnaire I I, -1 -r MORPHINE - NALOXONE INTERVAL (minutes) Fig. 1. Onset of morphine (18 mg/7 kg) agonist effects (open circles) and reversal by naloxone (1 mg/7 kg) challenge (filled circles) for to physiological measures (pupillary diameter and respiration rate) and to subjective report measures (good drug effect and drug liking) as a function of morphine-naloxone interval. Points are means ± S.E. of prenaloxone base line and postnaloxone sessions as described in text for five subjects. If S.E. is not visible, Drug Liking it as less than the radius of the symbol. Significant differences from the -mm condition: <.5, P < Fig. 2. Antagonist-precipitated ithdraal effects of naloxone (1 mg/ 7 kg) on 1 5-item ithdraal symptom questionnaire as a function of morphine-naloxone interval. Points are means ± S.E. of postnaloxone session for five subjects pretreated ith 1 8 mg/7 kg morphine. If S.E. is not visible, it as less than the radius of the symbol. Withdraal symptoms ere assessed at 5, 1 5, 3, 45 and 6 mm postnaloxone for each morphine-naloxone interval condition. Data from the 36 mm (6 hr) condition ere not induded in data analysis but are shon for comparison. Significant differences from the -mm condition: <.5, and ** <.1. prenaloxone data revealed a function of ero slope and magmtude across the four times. Figure 2 shos that subjective ithdraal scores ere significantly increased after naloxone in an orderly condition-dependent manner, as indicated by a significant condition x time interaction [F(3, 12) = 7.75, P <.5]. Post hoc analysis revealed that subjective ratings of ithdraal during the 45- and 9- mm sessions sere significantly increased compared ith the -mm condition. Withdraal scores from the 6-hr naloxone challenge session ere similar to those obtained during the 9- mm condition. Naloxone produced similar significant condition-related increases in subjective responses on the bad drug effect item [F (3, 12) 6.7, P <.5] and ithdraal sickness item [F (3, 12) = 6.6, P <.5] from the drug effect questionnaire. Results of the ithdraal symptom questionnaire item analysis revealed significant condition x time interactions for hot or cold feelings [F (3, 12) = 19.78, P <.1J, irritable (F (3, 12) = 9.5, P <.5], atery eyes [F (3, 12) = 5.8, P <.5] backache [F (3, 12) = 17.85, P <.1] and significant condition main effects for yaning [F (3, 12) = 5.69, P <.5], upset stomach [F (3, 12) = 7.57, P <.1] and clammy and damp skin [F (3, 12) = 4.34, P <.5]. For all these symptoms, postnaloxone ratings ere negligible or very lo at and 15 mm, increasing in intensity at 45 and 9 mm. Post hoc analysis revealed that ratings ere significantly elevated at 45 and 9 mm compared ith mm for hot or cold feelings, irritability, atery eyes and backache. Ratings of upset stomach ere significantly elevated at 9 mm; post hoc tests ere nonsignificant for the yaning and clammy skin items. Similar to the reversal of agonist effects, the onset of naloxone-precipitated ithdraal effects as rapid. Responses on the ithdraal symptom questionnaire ere clearly increased 5 mm postnaloxone during the 45- and 9-mm conditions. Maximal responses ere observed 3 mm postnaloxone, and scores remained elevated at 6 mm postnaloxone. The course Donloaded from jpet.aspetjournals.org at ASPET Journals on September 18, 216

5 1989 of naloxone effects as similar for the bad drug effect and ithdraal sickness items from the drug effect questionnaire. Observer-rated effects. Figure 3 shos the composite observer rating of objective ithdraal signs and the to individual signs, yaning and restlessness, that shoed the most robust change as a function of morphine-naloxone interval condition. Data from the 6-hr morphine-naloxone interval data condition are included for comparison. An orderly condition-dependent increase in composite observer ratings as obtamed after naloxone administration, indicated by a significant condition X time interaction [F (3, 12) = 21.53, P <.1]. Post hoc analysis revealed significant increases at the 45- and 9- mm conditions compared ith -mm condition. Significant condition X time interactions ere observed for yaning [F (3, 12) = 21.13, P <.1], restlessness [F (3, 12) = 13.79, P <.1], perspiration IF (3, 12) = 3.85, P <.5] and goose flesh [F (3, Cl) #{163} Cl) #{163} Yaning - 3. I- 2 1 Cl, o 4 ComposIte Observer RatIng I I I I Restlessness MORPHINE - NALOXONE INTERVAL (minutes) Fig. 3. Antagonist-precipitated ithdraal effects of naloxone (1 mg/ 7 kg) on composite observer-rated signs of ithdraal and to individual signs, yaning and restlessness, as a function of morphine-naloxone interval. Points are means ± SE. of postnaloxone scssion for five subjects pretreated ith 18 mg/7 kg morphine. Observer ratings ere made at 5, 15, 3, 45 and 6 mm postnaloxone for each morphinenaloxone interval condition. Data from the 36 mm (6 hr) condition ere not included in data analysis but are shon for comparison. Significant differences from the -mm condition: *f < 5, P <.1. Acute Opioid Physical Dependence ) = 3.57, P <.5]. A significant condition main effect as observed for tearing eyes [F (3, 12) = 6.13, P <.5]. Ratings of yaning and restlessness increased in an orderly conditiondependent manner, ith the 45- and 9-mm conditions significantly different from the -mm condition. Goose flesh shoed a significant increase during the 9-mm condition. Post hoc tests ere nonsignificant for perspiration and tearing eyes. Observer ratings obtained during the 6-hr naloxone challenge session ere similar to those obtained during the 9-mm condition. During the naloxone challenge session, composite observer ratings and yaning ere first elevated from base line at 15 mm postnaloxone, reached a peak at 3 mm, and declined during the remainder of the session. This contrasts ith the course of subjective effects, hich ere apparent by 5 mm postnaloxone and remained elevated throughout the 6-mm session. Physiological effects. Significant condition x time interactions ere observed for diastolic blood pressure, mean arterial pressure, skin temperature and heart rate as described above. Hoever, skin temperature as the only physiological measure that revealed an unambiguous ithdraal effect. Skin temperature declined in an orderly condition-related manner; post hoc analysis indicated that the 9-mm condition average (8.6#{176}F) as significantly different from that of the -mm condition (85.4#{176}F). Additionally, at the 9-mm condition, skin temperature as significantly loer during the postnaloxone challenge session than during prenaloxone base line, indicating a naloxone-induced effect. Blood pressure measures shoed small but orderly increases as a function of morphine-naloxone interval, but there ere no differences beteen prenaloxone base line and postnaloxone session values, indicating the absence of any specific naloxone-precipitated ithdraal effect. Heart rate changes ere unrelated to morphine-naloxone interval in any systematic ay. Discussion This study investigated the early developmental course of acute opioid physical dependence and shoed that ithdraal symptoms ere precipitated by naloxone challenge as early as 45 mm after a single dose of morphine in nondependent opiate users. This extends the human research of Bickel et at. (1988), Higgins et a!. (1988) and Heishman et at. (1989), ho documented naloxone-precipitated ithdraal 6 hr after acute morphine administration in similar subject populations. The profile of subjective report symptoms and observer-rated signs of opioid ithdraal observed in the present study as very similar to that of these recent reports. In this study, simultaneous administration of morphine and naloxone (-mm interval) produced no agonist or antagonistprecipitated ithdraal effects. This condition thus served as an appropriate control for agonist and antagonist effects observed after longer morphine-naloxone intervals. This absence of effect as expected and consistent ith previous animal research demonstrating that the coadministration of morphine and naloxone abolished subsequent naloxone-precipitated ithdraal responses in mice (Smits, 1976; Tremblay et at., 1976; Yano and Takemori, 1977) and the increased plasma corticosterone response in rats (Eisenberg and Sparber, 1979). Thus, previous research ith animals and no ith humans has shon that the development of physical dependence as Donloaded from jpet.aspetjournals.org at ASPET Journals on September 18, 216

6 49 Heishman et al. prevented by complete blockade of the opiate receptor by naloxone at the time of morphine administration. In the present study, antagonist-precipitated ithdraal responses ere observed at 45 mm, but not 15 mm, postmorphine, indicating that a relatively short duration of opiate receptor occupancy by the agonist as necessary for the development of acute physical dependence in humans. This is consistent ith the short (1-3 mm) time for the development of physical dependence observed in animals (Eisenberg, 1982; Jacob et at., 1974; Kosersky et at., 1974; Ritmann, 1981; Smits, 1975; Yano et at., 1979). Our study extends and emphasies the cross species generality of parameters associated ith acute opioid physical dependence, in this case, the relatively short duration of agonist exposure needed to observe antagonist-precipitated ithdraal. The course of effects in the present study as based on the i.m. route of agonist and antagonist administration; time course effects might be altered if a different route (e.g., i.v.) ere used. The second major finding as that the onset of morphine agonist effects closely paralleled that of naloxone-precipitated ithdraal effects, both occurring at 45 mm postmorphine. In terms of agonist effects, miosis, respiratory depression, and subjective reports of good drug effect and drug liking ere first significantly altered at the base-line assessment before the 45- mm interval session (fig. 1). Simultaneously, subjective responses on the ithdraal symptom questionnaire (fig. 2) and the composite observer rating of ithdraal signs (fig. 3) ere first significantly elevated after naloxone challenge 45 mm postmorphine. This concurrent onset of agonist and antagonist effects suggest that the occurrence of antagonist-precipitated ithdraal is intimately related to receptor occupancy by the agonist and its subsequent abrupt displacement from the receptor by the competitive antagonist. There as one difference beteen the agonist and antagonist effects, hoever. All measures reflecting agonist effects (fig. 1) revealed a maximal effect at 45 mm postmorphine, hich did not increase at 9 mm. In contrast, there as a trend for subjective report and observerrated measures of ithdraal to continue increasing in intensity to the 9-mm condition. Withdraal intensity may continue to increase if naloxone challenges ere presented at postmorphine intervals greater than 9 mm. Hoever, this seems unlikely given that e observed a similar magnitude of naloxone-precipitated ithdraal responses at 9 and 36 mm postmorphine (figs. 2 and 3). In addition to subjective reports of general dysphoria and sickness, subjects consistently reported experiencing specific ithdraal symptoms, hich included yaning, hot or cold feelings, upset stomach, irritability, atery eyes, backache and clammy skin. The reported occurrence and intensity of this cluster of ithdraal symptoms agreed closely ith that observed in past human studies of acute dependence that used a morphine-naloxone interval of 6 hr (Bickel et at., 1988; Heishman et at., 1989) and ith reports of naloxone-induced ithdraal symptoms after opioid surgical anesthesia (Aar and Turndorf, 1979; Johnstone et a!., 1974; Longnecker et at., 1973). In the present study, there as no indication of differential appearance of ithdraal symptoms as a function of the temporal interval beteen agonist and antagonist administration, as has been observed after antagonist challenge in chronically dependent rats (Linseman, 1977). This discrepancy is most readily explained by methodological differences, in that Linseman (1977) as using an animal model of chronic opioid dependence and observed precipitated ithdraal up to 22.5 hr Vol. 25 after the last maintenance dose of morphine, the time hen several ithdraal symptoms (et dog shakes, teeth chattering, diarrhea) ere most frequently observed. The observer-rated ithdraal signs in the present study ere, for the most part, consistent ith the subjective ithdraal symptoms after naloxone challenge. Yaning as clearly the most consistently observed ithdraal sign in addition to restlessness and perspiration. The entire constellation of ithdraal symptoms and signs observed in this study as consistent ith previous reports of antagonist-precipitated ithdraal in humans after acute (Bickel et a!., 1988; Heishman et a!., 1989; Higgins et a!., 1988; Jones, 198; Nutt and Jasinski, 1974) and chronic (Jasinski, 1977; Wikler et a!., 1953) exposure to opiates. The fact that the ithdraal effects observed in the present study ere also similar to the abstinence syndrome associated ith chronic opioid dependence (Himmelsbach, 1941; Martin and Sloan, 1977) suggests that naloxone as indeed precipitating true opioid ithdraal ithin minutes after a single morphine dose. The major distinction in the ithdraal syndrome beteen acute and chronic physical dependence appears to be quantitative rather than qualitative. Martin and Eades (1964) reported more intense and longer ithdraal effects after nalorphine challenge in dogs made chronically dependent on morphine compared ith those receiving a 7-hr infusion of morphine, but the ithdraal symptoms and signs of both groups ere qualitatively similar. A similar comparative study in humans has not been conducted. The antagonist-precipitated ithdraal effects observed in this study ere demonstrated in humans ith histories of chronic opiate use. As a result, the magnitude of ithdraal effects may have been influenced by some degree of residual tolerance and/or dependence. There is evidence of increased antagonist sensitivity in animals formerly dependent on morphine (Brase et a!., 1976; Goldberg and Schuster, 1969). Hoever, the significance of heightened responsivity to naloxone challenge in the present study is mitigated by the observations that our research volunteers ere not physically dependent upon entering the study and that similar naloxone-precipitated ithdraal has been documented in opiate-naive humans (Jones, 198, 1981). The fact that e observed no precipitated ithdraal in three opiate-experienced subjects suggests that individual differences, in some form, are important in the development of acute opioid physical dependence. This ould be a very interesting problem for future research. In summary, this study has shon that the course of onset of morphine effects closely paralleled that of naloxone-precipitated ithdraal effects and that precipitated ithdraal as first observed 45 mm after agonist administration. We therefore conclude that adaptational changes underlying the development of opioid physical dependence begin ithin minutes after acute morphine exposure, are closely associated ith the onset of other agonist effects and do not require chronic opioid administration. Acknoledgments The authors thank Beverly Banks for assistance in conducting the study and Linda Felch for consultation and assistance ith data analysis and graphics. References AZAR, I. AND TURNDORF, H.: Severe hypertension and multiple atrial premature contractions folloing naloxone administration. Anesth. Analg. 58: , BICKEL, W. K., STITZER, M. L., LIEBSON, I. A. AND BIGELOW, G. E.: Acute physical dependence in man: Effects of naloxone after brief morphine exposure. J. Pharmacol. Exp. 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