on drug-induced euphoria and there is no reason why

Transcription

1 Br. J. clin. Pharmac. (1978), 5, DGR OF TOLRANC AND TH RLATIONSHIP BTWN PLASMA MORPHIN CONCNTRATION AND PUPIL DIAMTR FOLLOWING INTRAVNOUS HROIN IN MAN KATHLN H. TRSS & A.A. L-SOBKY Neuropsychology Unit, Friern Hospital, London Ni 1 3BP and Department of Clinical Pharmacology, University College Hospital Medical School, London WC1 WYNN AHRN & VLYN PIALL Division of Clinical Biochemistry, Department of Biochemistry, University of Surrey, Guildford, Surrey GV2 5XH 1 After doses of heroin to tolerant (heroin-dependent) persons and non-tolerant (non-dependent) persons, pupil diameter varies with the degree of physical dependence and the plasma concentration of the drug. 2 The linear regression slopes of pupil diameter on plasma drug concentration correlate with daily prescription of opiates. That is, the greater the degree of physical dependence the higher the plasma drug concentration that is required for a given degree of miosis. 3 It is suggested that these observations might provide the basis of a test to estimate the drug requirements of drug dependent patients attending treatment clinics. Introduction Tolerance to the effects of opiate drugs such as morphine and heroin is a well-known consequence of the repeated use of these drugs. For instance, when morphine is administered for pain relief, increasing doses are required to maintain adequate relief over time. The heroin dependent subject is another example. He needs more and more heroin for his 'kick' or 'buzz' (the euphoric effects of the drug) as tolerance develops. However, despite these well known and obvious examples there is often confusion about what constitutes tolerance. Goodman & Gilman (197) define tolerance as occurring '... when increasingly larger doses (of drug) must be administered to obtain the effects observed with original dose.' This is an adequate definition of tolerance covering the two examples quoted above, i.e. pain relief and euphoria which require increasing doses of drug to obtain effective treatment or results. However the same authors (Goodman & Gilman, 197) when discussing the effect of morphine on pupil size state that 'tolerance to the miotic effect of morphine is not priminent, and the morphine addict continues to have constricted pupils,' implying that there is little or no tolerance to the effect of morphine on pupil diameter. This, of course, is an unjustifiable conclusion in that the morphine-dependent subject is already adjusting his dose of drug to overcome the effects of tolerance on drug-induced euphoria and there is no reason why this dose should not also overcome any tolerance effects on the miosis induced by morphine. To establish that tolerance does not develop to the miotic effect of opiates it would be necessary to determine that the same dose of opiate produced the same degree of miosis in all people regardless of their daily intake of opiates. This would be one way to investigate the degree of tolerance developed to the miotic effect of heroin. A second way is to compare the degree of miosis with a measure which shows no tolerance. A measure which shows no tolerance is one that varies only with the dose of drug given. For example if a dose of 1 mg heroin gives a response of x in all subjects regardless of whether their daily intake of heroin is or 5 mg heroin then the measure of this response shows no tolerance. One such measure is plasma morphine concentration (heroin is measured as morphine) which has been shown to be related to the dose of heroin administered and not affected by the daily dose of heroin or heroin plus methadone prescribed to the subjects (Tress, Aherne, l-sobky, Piall & Marks, 1977). If there is no tolerance to the miotic effect of morphine then pupil diameter will vary with the plasma morphine concentration alone. However, tolerance will be demonstrated if pupil diameter varies

2 3 KATHLN H. TRSS, A.A. L-SOBKY, WVYNN AHRN & VLYN PIALL with both plasma morphine concentration and with daily intake of opiates. In the following report plasma morphine levels and pupil diameters were measured before and after an intravenous dose of heroin in both dependent and nondependent volunteers in order to determine to what extent tolerance develops to the miotic effect of heroin. Methods The five non-tolerant male subjects were volunteers from among the clinical and scientific staff involved in the project. They were given intravenous doses of 2.5 and 5 mg heroin and a saline placebo each separated by at least 1 week. Stringent precautions were taken to minimize any risk of initiating addiction in these volunteers. A consultant psychiatrist interviewed each volunteer prior to the first test and if, in his opinion, there was any reason for it, the volunteer was excluded from the trial. If, after a dose, a subject expressed any doubts or concern about his own reaction to the injection he was excluded from further tests. These procedures had the approval of the thics Committees of both Friem Hospital and University College Hospital. The eighteen tolerant subjects (twelve male and six female) were volunteers from London Drug Dependency Clinics. Only volunteers receiving prescriptions of heroin or heroin plus methadone (where the quantity of methadone did not exceed half the weight of prescribed drug) were accepted. Dependent subjects were admitted to the Unit for 5 days. The first 2 days were used to check that the drug dosage was as prescribed and to allow for the dissipation of any effects from other drugs taken before being admitted. Testing took place on the remaining 3 days. On test days the subjects were allowed a small injection of heroin (1 mg for those prescribed 65 mg per day or less and 2 mg for those prescrbed more than 65 mg per day) early in the morning, 3-4 h prior to the experimental dose. Methadone, when this was a part of the prescription, was always administered in the evening so that there were at least 12 h in between taking the methadone and receiving the experimental dose of heroin. During the tests each subject received three different intravenous doses of heroin in random order, one dose per day. The doses were i, J and I of the daily prescribed dose but on the second test day a saline placebo (of which the subject was unaware) was administered 4 min before heroin dose. All subjects were interviewed to ascertain their usual drug taking habits, i.e. how much drug was usually bought in addition to prescription. It is known that the drug dependent subject's normal daily intake of drugs may be less than or more than the prescribed daily dose of drug. However, as the prescribed drug is known and patients are maintained on the prescribed dose during their stay at the Unit, this is the dose used in any calculations throughout this report. All subjects were tested in a soundproof room in constant dim illumination. The pupil diameter measure was made by photographing the subject's eye and a 1 mm scale using colour reversal film. The camera was effectively fixed focus with a telephoto lens and bellows preset to standard magnification. The photograph was taken with the aid of an electronic ring flash. The resulting colour transparencies were put in a photographic enlarger and the horizontal diameter of the pupil measured using the photographed scale. Blood samples were taken from an arm vein via an intravenous cannula where practicable. Where it was not possible to insert a cannula due to the lack of adequate superficial veins in some dependent subjects, samples were taken by repeated venepuncture. Blood samples of 5 ml were taken and spun in a centrifuge for 2 min to obtain plasma which was then kept frozen until it was assayed. The plasma samples were assayed for heroin (diacetylmorphine) and its breakdown products monoacetylmorphine and morphine using a radioimmunoassay for morphine (Aherne, Piall, Robinson, Morris & Marks, 1975). The antibodies used in this assay cross-react with heroin, monoacetylmorphine and morphine and the results expressed as morphine equivalents. The presence of methadone does not interfere with the measurement of morphine. Blood samples and pupil measures were taken at 2 min intervals for 4 min before intravenous injection of a dose of heroin and for 2 h after injection (seven samples and seven measures in all). Where repeated venepuncture was necessary the number of blood samples taken was reduced owing to the difficulty of this procedure. Results Cannulation was possible in all the non-tolerant subjects and measurements of plasma morphine and pupil diameter were made on the two doses of heroin and placebo in four subjects. The results from the remaining subject were available only for one dose (2.5 mg) of heroin. Cannulation was achieved in six dependent subjects and results for the three doses of drug obtained. In a further four subjects blood samples were by repeated venepuncture but in only one of these subjects were results available from all three doses of heroin. The remaining eight subjects had superficial veins so badly damaged by repeated injections of barbiturates etc, that no blood samples were obtained and in four subjects even the heroin injection had to be given

3 HROIN TOLRANC, PLASMA MORPHIN AND PUPIL DIAMTR 31 a) C'c o ='- m.' X _ v - L - a 1 9 \ _ t Heroin 5mg Heroin 13mg Time (min) b I cn O- 3 Xa).5 C Pupil diameter (mm) Figure 2 The same data as shown in Figure 1 displaying the linear regression of pupil diameter on plasma morphine concentration. Figure 1 (a) Plasma morphine concentrations and pupil diameters before and after an intravenous dose of 5 mg heroin in a non-dependent subject (N4 436). (b) Plasma morphine concentrations and pupil diameters before and after an intravenous dose of 13 mg heroin (I prescribed dose) in a dependent subject (D5 43) prescribed 8 mg heroin per day. before heroin injection, * after heroin injection. Broken horizontal line-limits of accuracy of the assay, 5 ng morphine equivalents. Table 1 Regression slopes of pupil diameter on plasma morphine for dependent and non-dependent subjects with daily prescription of opiates (where applicable) Subject Ni N2 N3 N4 N5 Dl D2 D3 D4 D5 D6 D7 D8 D9 D1 Prescribed dose of opiates (mg/day) Heroin Methadone Regression slope -5.92*** ** *** *** ** *** *** *** *** *** *** *** *** * *P<.; **P<.25; ***P<.5. N, non-dependent subject; D, dependent subject. intramuscularily. AU except one dependent subject stayed for the whole 5-day period. Testing of this one subject was discontinued when it was discovered that she had left the Unit in the evening to buy extra heroin and amphetamines. Figure la shows time response curves for pupil diameter and plasma morphine concentration for a non-dependent subject given 5 mg of heroin intravenously. It can be seen that there is an inverse relationship between plasma morphine concentration and pupil diameter. An injection of 5 mg of heroin resulted, 25 min later in a plasma concentration of 34.6 ng morphine equivalents/ml with a decrease of 2.25 mm in pupil diameter. Figure lb shows the time response curves for pupil diameter and plasma morphine concentrations for a heroin dependent subject (prescribed 8 mg/day) after an intravenous injection of 13 mg (j of daily prescription) heroin. Again it can be seen that there is an inverse relationship between pupil diameter and plasma morphine concentration. However in this case a decrease in pupil diameter of 2 mm after 2 min is associated with an increase of 82 ng morphine equivalents/ml in plasma morphine concentration. The relationships between plasma morphine concentration and pupil diameter in these two subjects as shown in Figure 1 are represented as linear regression lines in Figure 2. The regression slope for the nondependent subject (N4436) is for points before and after 5 mg heroin whereas the regression slope for the dependent subject (D543) is before and after 13 mg heroin. Both these regressions give significant correlation coefficients (r=.98, P<.5 and r=.88, P <G.G5 respectively). Regression slopes and daily prescription of opiates for all subjects are displayed in Table 1. It can be seen that whereas

4 32 KATHLN H. TRSS, A.A. L-SOBKY, WYNN AHRN & VLYN PIALL a( 2 16 a) 12 _ C (D.L Daily dose of opiates (mg/day) Figure 3 Linear regressions of daily prescription of opiates on regression slope of pupil diameter on plasma morphine concentration. The regression analysis represented by the solid line uses all the data points. The regression analysis represented by the broken line uses the mean for the non-dependent subjects and omits the data point at 34 mg heroin/day. control pupil diameters were calculated for each group of subjects: non-dependent subjects: 6.13 mm, n= 5, dependent subjects prescribed heroin: 7.66 mm, n=11 and dependent subjects prescribed heroin and methadone: 6.9 mm, n= 6. The result from a pilot study with unmedicated control subjects gave a mean pupil diameter of 7. mm, n =7 under the same lighting conditions. There are no significant differences between groups and so it appears that the prior methadone medication has not affected the pupil diameter measures. At interview four of the ten dependent subjects admitted to purchasing regularly extra heroin to supplement their prescription. These were subjects D2, D3, D5 and D9. The first three of these subjects presented with opiate withdrawal symptoms on at least one occasion while staying at the Unit thus confirming their statement that they were underprescribed. These subjects also showed regression slopes somewhat higher than might be expected from the daily dose alone (Table 1). the non-dependent subjects show regression slopes of -5.9 to , the dependent subjects show slopes of to -21 with the slope varying with the daily dose of heroin and methadone prescribed. A Spearman rank correlation corrected for ties performed on these data shows that regression slopes of pupil diameter on plasma morphine are correlated with the daily dose of opiates (heroin or heroin plus methadone in mg) -r=.91, P<.1. These data are displayed in Figure 3. A linear regression performed on all these data gives the solid line on this figure (r=.94, P<.5, slope=.55). However, the data are obviously not homogenous for variance and it might be argued that the slope of the regression is largely determined by the five points from the nondependent subjects and the one point from the dependent subject D 1. A second regression, represented by the broken line, was therefore performed taking the mean of non-dependent subjects as one point and omitting the data for D 1. Again the results were significant (r=.61, P<.5, slope=.32). Thus it seems that the regression slope of pupil diameter on plasma morphine concentration is a function of daily dose of opiates. Following placebo injection no non-dependent subject showed an increase in plasma morphine or a decrease in pupil diameter but some dependent subjects did show a fall in plasma morphine accompanied by an increase in pupil diameter. It was thought possible that the methadone given to some dependent subjects might be affecting the pupil diameters although the methadone was given at 12 h prior to the experimental dose. Accordingly mean Discussion This study shows that tolerance develops to the miotic effects of repeated heroin administration, i.e. pupil diameter varies with both plasma morphine concentration and daily prescription of heroin. The slope of the regression of pupil diameter on plasma morphine correlates well with daily prescription of heroin. Thus it should be possible to predict the daily dose of heroin to which a person is accustomed by the regression slope of pupil diameter on plasma morphine following a test dose of heroin. It would be of great assistance to Drug Clinics in prescribing opiates for their dependent patients if it were possible to estimate accurately the daily dose of heroin a person normally used. The prescribing of opiates has many pitfalls which could be avoided if the need of the patient were reliably known so that over-and underprescribing were avoided. One danger of overprescribing is that the patient will sell excess heroin to other dependent persons or even initiate new users. Also, patients who have been buying 'Chinese' heroin, which is heroin diluted with other substances may not know their real dose of heroin. In this case overprescribing may result in a lethal overdose being taken by the patient. Again a person who considers that he is underprescribed will often buy extra heroin to supplement and this may interfere with treatment or rehabilitation. In the cases of the patient who does not know his accustomed dose and the patient who knows he is being underprescribed it would be of advantage to both the patient and the clinician to have an objective test of the patient's normal daily intake of heroin. Again, where

5 HROIN TOLRANC, PLASMA MORPHIN AND PUPIL DIAMTR 33 the patient is selling excess heroin it would assist the clinician to have an objective test to adjust the patient's dose to prevent this occurring. The results presented in this paper lay the foundations for the development of such a test of physical dependence in the heroin-dependent patient. We wish to acknowledge the financial assistance of the Medical Research Council (Contract A86/4), the Leukaemia Research Fund and the Cancer Research Campaign. We also thank Dr M. Mitcheson and Dr J Willis for their help in obtaining dependent subjects for this study. References AHRN, G.W., PIALL,.M., ROBINSON, J.D., MORRIS, B.A. & MARKS, V. (1975). In Radioimmunoassay and related techniques in clinical biochemistry. Heydon Press. GOODMAN, L.S. & GILMAN, A. (197). The pharmacological basis of therapeutics, pp. 277, 242. London & New York: MacMillan. TRSS, K.H., AHRN, G.W., L-SOBKY, A.A., PIALL,.M. & MARKS, V. (1977). Measurement of serum morphine levels following diamorphine administration in dependent and non-dependent humans. In Clinical Toxicology: Proc. ur. Soc. Tox., 18, Amsterdam and London: xcerpta Medica. (Received April 7, 1977)