CONTINUOUS INTRAVENOUS INFUSION OF ADENOSINE TO HUMAN PATIENTS, A UNIT DOSAGE FORM OF ADENOSINE AND USE OF ADENOSINE FOR THE MANUFACTURE OF MEDICAMENTS

Abstract: Adenosine is administered to human patients by continuous intravenous infusion at levels at which the heart blocking action of adenosine is not detected, to modify the hemodynamic properties of the patient. Specific indications of use are induction of controlled hypotension, control of hypertensive crisis, effecting preferential coronary vasodilation, increasing blood flow in a coronary artery graft, increasing cardiac output, reducing platelet loss during coronary bypass surgery and facilitation of the induction of cardioplegia. A unit dosage form of adenosine and use of adenosine for the manufacture of medicaments for certain medical indications are further disclosed.

Description: Continuous intravenous infusion of adenosine to human patients, a unit dosage form of adenosine and use of adenosine for the manufacture of medicaments This invention is concerned with the use of adenosine as an agent for the treatment of human beings. More particularly, this invention is concerned with the administration of adenosine to human patients by continuous intravenous infusion for, inter alia, control of blood pressure, use as a selective vasodilator and for preservation of platelets during cardiovascular surgery. Adenosine is a naturally occurring nucleoside composed of the purine, adenine, and the sugar, D-ribose. Normal basal plasma levels of adenosine are from about (..1 to about 0.2 μ mol per liter. In addition, it is commonly present in the body in the form of adenosine monophosphate (AMP), adenosine diphosphate (ADP) and adenosine triphosphate (ATP). Adenosine has been reported to have a variety of biological effects, depending on whether the adenosine is endogenous or exogenously administered, including sedative and anti-epileptic effects on the central nervous system and inhibitory effects on respiration, cardio-vascular effects including prolongation of atrio-ventricular conduction time and impulse formation in the sinus node, vasodilation, antiaggregatory effect, decreased release of free fatty acids, anti-secretory effect in the stomach, and anti-diuretic effect. As a general rule, however, adenosine and its biological effects have been largely of physiological interest. To the extent adenosine was of interest as a pharmaceutical product, that interest has centered primarily on its phosphate derivative, which now is known to be rapidly metabolized to yield adenosine and phosphate in the circulation. See Sollevi et a]_, Acta. Physio! . Scand. 120:171-6 (1984). However, phosphate may cause undesired side effects. For example, high levels of phosphate may cause arrhythmias secondary to chelation of magnesium and calcium. (See Dedrick, et al., Anesthesiology, 57:3A, 66 (1982)).. Furthermore, adenosine is known to produce heart block through blockage of the atrioventricular (A-V) node. As a consequence, methylxanthines such as theophylline have been proposed by Berne, et al . , in U.S. Patent IT TE SH ET No. 4364922 for use in preventing heart block caused by adenosine, in particular adenosine released as a consequence of cardiac ischemia or hypoxia. In addition, it has been proposed to take advantage of adenosine's ability to block atrioventricular conductance by using it to treat tachyarrhythmias. For such use, adenosine is administered as an injectable intravenous bolus containing from about 37.5 micrograms/kg up to about 450 micrograms/kg of adenosine. In such a use, the adenosine has little detectable vasodilating action. Adenosine has a very short plasma half-life, of the order of 10-20 seconds (see, Fredholm and Sollevi.J. Physiol., 313:351-62 (1981)), and thus the concentration of injected adenosine is rapidly reduced to normal serum levels (about 0.15 μ mol per liter). The transitory presence of the injected adenosine precludes all but the most transitory vasodilation. Accordingly, for adenosine to be of practical value for use as a vasodilator, it must be administered continuously to maintain plasma levels sufficiently high to achieve vasodilation. The problem, however, is that such continuous administration could lead to undesired side effects, such as the above noted heart blockage. It also should be noted that compounds commonly used as vasodilators, such as sodium nitroprusside, nitroglycerine, isoflurane, hydralazine, prazosin and the like, have various side effects. For example, sodium nitroprusside has the drawbacks of tachyphylaxis and rebound hypertension, apparently caused by autogenous generation of angiotensin to counteract the hypotensive effect of nitroprusside. As a consequence, the dosage of nitroprusside must be progressively increased with continued use to overcome the hypertensive effect of angiotensin, and there is a risk of rebound due to the presence of residual excess angiotensin. Nitroglycerine and prazosin suffer from the drawbacks of slow onset and unpredictable action. Isoflurane and sodium nitroprusside both have a tendency to reduce cardiac blood flow, while nitroprusside, hydralazine and prazosin increase heart rate. SUBSTITUTE SHEΞET Accordingly, there remains a need for a vasodilator suitable for administration by continuous intravenous infusion. The present invention is based upon the discovery that adenosine can be administered to human patients under conditions such that significant vasodilation is achieved without the occurrence of significant heart blockage. It is based on the further discovery that adenosine has a unique, and heretofore unappreciated, activity profile in humans which differs significantly from the profiles of heretofore commonly used vasodilators. As a consequence of this descovery, it has been discovered that adenosine may be employed for the treatment of a variety of conditions by continuous intravenous infusion techniques. In particular, and as will be illustrated in greater detail below, adenosine has been found to have the following characteristics: 1. It has selective vasodilation activity, in that its effect is limited to a cardiac after-load effect. That is, its activity is limited to dilation of arteries and it has little or no effect on cardiac pre-load, i.e. as a dilator of veins. 2. Although adenosine has significant action in blocking atrio-ventricular (A-V) conductance by bolus injection, it can be administered by continuous infusion and have significant useful vasodilating action at dosages below those at which it has significant A-V activity. 3. Adenosine has significant hypotensive activity without the occurrence of significant tachyphylaxis, apparently because adenosine blocks the renin-angiotensin system of the kidney, thus preventing hypertension due to the formation of angiotensin in response to hypotension. 4. Adenosine's effect is readily controlled bbecause it is active at relatively small doses and because of its short plasma half-life (10-20 seconds). In addition, its activity quickly ceases when adenosine administration is terminated. -. ,..-.—- ~ * -" 5. Adenosine is capable of significantly increasing cardiac output without significantly increasing cardiac work. 6. Adenosine, in the amounts used in accordance with the invention, is essentially non-toxic. It is rapidly taken up by the body to form ATP, and upon degradation its metabolites are present at or below levels normally resulting from physical exercise. The foregoing activity profile permits continuous infusion of adenosine for controlled hypotension during surgery, for control of various forms of hypertensive crisis, to improve coronary circulation during surgery in patients with ischemic heart disease, for reducing the incidence of coronary graft occlusion by increasing graft flow following coronary bypass surgery, and for after-load reduction in low cardiac output states. It also has been found that continuous infusion of adenosine during cardiac bypass surgery is able to reduce platelet loss during such surgery. In accordance with this invention, adenosine may be administered to human patients by continuous intravenous infusion to provide significant vasodilation and without significant heart blockage under two conditions. First, the heart blocking action of adenosine is not detected during anesthesia when the rate of administration is 0.35 milligrams of adenosine per kilogram of body weight per minute or less. Second the heart blocking action of adenosine is not detected, even in conscious patients, at rates of administration of about 0.10 milligram of adenosine per kilogram of body weight per minute or less. For purposes of this invention, adenosine can be administered to the patient in any pharmaceutically acceptable form suitable for use in continuous, intravenous infusion. A preferred form is an aqueous solution of adenosine, and more preferably adenosine in isotonic saline. The concentration of adensine in the solution is not narrowly critical, although concentrations of at least 5 millimol (or about 1.5 milligrams per milliliter) of solution are desired to avoid the need for excessive infusion rates to achieve desired serum levels. The concentration can be up to the solubility limit of adenosine (about 20 millimols per liter or SUBSTITUTESHEET 5.5 to 6 milligrams per milliliter) if desired. When used for continuous infusion in accordance with this invention, the unit dosage form typically has a volume of at least 250 milliliters, and preferably in the range of 250 to 500 milliliters, to provide an adequate supply of adenosine. Consequently, the unit dosage form generally will contain from about 0.4 to about 3 grams of adenosine. Of course, the adenosine solution should be sterile and free from fungi and bacteria. Such solutions have been found to be stable at room temperature for at least two years. Such solutions are prepared by mixing adenosine with the aqueous carrier, e.g. water or an isotonic solution, and other desired ingredients, to achieve a solution having the desired concentration, and thereafter sterilizing the solution. Continuous infusion can be achieved by any technique known to the art. Because adenosine has such a short plasma half-life and it is active at relatively low concentrations, it is desired that the method be one which minimizes or avoids fluctuations of serum adenosine levels. Accordingly use of high precision roller pumps is preferred. As is noted above, the present invention has numerous specific applications, depending upon adenosine dosage levels and whether or not adenosine is administered to anesthesized or conscious patients. The first general category of applications is that in which adenosine is continuously administered to a patient undergoing surgery under general anesthesia at doses that do not induce heart block. Specific applications include controlled hypotension during surgery, in particular dissection and clipping of cerebral arterial aneurysms; control of hypertension crisis during surgery, for example due to release of catecholamines in the course of pheochomocytoma surgery; and improved coronary circulation and after-load reduction during abdominal aortic aneurysm surgery, especially in patients with ischemic heart disease. For such uses, dosage rates of the order of 0.05 to about 0.3 milligrams per kilogram of body weight per minute are effective amounts. SURSTITI JTP « .H£=F-T The second general category of continuous adenosine infusion applications is that in which adenosine is administered to conscious patients, also at levels below which adenosine exhibits significant heart blocking action. These levels are typically achieved at administration rates of 0.05 milligram of adenosine per kilogram per minute or less. Specific examples of conditions which may be treated with adenosine in conscious patients include prevention of occlusion of cardiac bypass grafts following bypass surgery, increased cardiac output in patients with low cardiac output, and use of adenosine as an adjunct to dopamine treatment for shock. The following examples illustrate in greater detail specific applications of continuous intravenous infusion of adenosine in accordance with this invention. Example 1 Controlled hypotension during anesthesia It is frequently desired to reduce the blood pressure of patients during surgery. For example, in the case of dissection and clipping of cerebral arterial aneurysms, controlled hypotension is desired to reduce the aneurysm wall tension in order to minimize the risk of rupture and bleeding. Controlled hypotension is also used to reduce bleeding during other forms of surgery. Prior to this invention, vasodilators, such as sodium nitroprusside and nitroglycerine, were used for this purpose, but both have drawbacks. For example, sodium nitroprusside suffers from tachyphylaxis, or the need to increase the dose of nitroprusside with time due to the release of angiotensin. In addition, rebound hypertension also has been observed following use of nitroprusside. Nitroglycerine is characterized by slow onset of action and unpredictable action. Adenosine has been found to be a remarkably effective agent for inducing controlled hypotension during surgery. Adenosine, when administered in SUBSTITUTESHSET effective amounts, has a very rapid hypotensive effect which can be rapidly terminated due to its short half-life. Moreover, adenosine does not cause tachyphylaxis, apparently because it blocks the renin-angiotensin system of the kidney, thereby preventing formation of angiotensin which tends to counteract the hypotension. For the same reason, rebound hypertension is avoided after discontinuation of infusion. For this indication, adenosine typically is administered intravenously via the left basilic vein or via a central vein in an amount (or at a rate) sufficient to achieve the desired hypotensive effect. It has been found that lowering of mean arterial blood pressure to as low as 40 millimeters of mercury, as measured by a cannula in the left radial artery, is readily achieved without significant side effects. In particular, so long as the patient is under anesthesia, no blockage of atrio-ventricular conductance is observed. The actual plasma levels of adenosine employed for controlled hypotension will vary, depending upon such factors as the particular patient, the age of the patient and the desired degree of hypotension. As a general rule, however, a reduction of mean arterial blood pressure to 40 to 50 mm HG is achieved by administration of adenosine at a rate of from about 0.2 to about 0.35 milligrams of adenosine per kilogram of body weight per minute. The amount of adenosine required to achieve a given degree of hypotension can be reduced if adenosine uptake inhibitors, such as dipyridamole, are also administered to the patient. The possibility that adenosine might be useful for inducing controlled hypotension in humans was suggested by Kassell et al., J. Neurosurg., 58: 69-76 (1983), based upon tests in dogs. However, this study was performed during the administration of dipyridamole, another vasodilator that potentiates the effect of adenosine by inhibiting cellular uptake of adenosine. The dose of dipyridamole (1 mg/kg) was high, " tiand it in fact induced a 20 % reduction of the mean arterial blood pressure. The hypotensive effect of adenosine was then studied upon this hypotensive dose of dipyridamole. It was reported that hypotension to a mean arterial pressure of 40 mm/Hg could be induced and maintained with an infusion of 0.4 gram of adenosine per 100 milliliters of normal saline, " at a dose of 50 μg/kg/ inute. When dipyridamole was excluded in a pilot study, as much as 5-10 mg/kg/minute was required for the induction of hypotension, thereby creating an excessive fluid load. Kassel et al. noted that induction of hypotension in dogs is difficult, and speculated that "adenosine alone, without the potentiating effects of dipyridamole, may be sufficient to produce hypotension in man without excessive volumes of fluid". As noted above, effective induction of hypotension in man is achieved at adenosine dose levels of only 0.2 to 0.35 mg/kg/minute, or 30 to 50 times lower levels than effective levels in the dog. Such low rates are hardly predictable from the information of Kassel et al . In a study intended to demonstrate use of continuous infusion of adenosine to effect controlled hypotension in man, ten patients with no known history of cardiopulmonary diseases (seven men and three women, ages 35-58 years), schedeled for intracerebral aneurysm surgery, were selected. One hour before the operation the patients were premedicated orally with diazepam (10-20 mg) Atropine (0.5 mg) and droperidol (0.1 mg per kg) were given intravenously before induction of anesthesia. Induction was started with thiopental (5 mg per kg) followed by phenoperidine (1-2 mg), a synthetic opiate with pharmacodyna ics resembling fentanyl but with a longer duration of action and 1/10 of its analgesic potency. Pancuronium bromide (0.1 mg per kg) was given to facilitate endotracheal intubation. Anesthesia was maintained by supplementary doses of phenoperidine and droperidol, as required. The total dose of droperidol did not exceed 0.2 mg per kg and was administered within the first 2 hours of anesthesia. Phenoperidine was supplemented regularly to prevent the blood pressure from exceeding the preanesthetic level (approx. 1 mg/30-60 min). Controlled hyperventilation was employed with a humidified gas mixture of 60 % N^O in oxygen to maintain PaCO values at approximately 30 mπiHg (+ 1.5/SEM). Mannitol (1-1.5 g per kg) was given routinely at the start of the operation (e.g., 1-2 hours prior to the controlled hypotension). The patients were operated on in the horizontal supine position. A 1.2-mm plastic cannula was introduced into the left radial artery to monitor systemic arterial blood pressure (MABP) and collect arterial blood. A balloon-tipped, flowdirected, quadruple lumen Swan-Ganz catheter (Model 93A-831-7.5 F, VIP) was inserted percutaneously via the left basilic vein, and its correct position in the pulmonary artery was determined by pressure tracings. The catherer was used for the monitoring of mean right atrial pressure (RAP), mean pulmonary artery pressure (PAP), and mean pulmonary capillary wedge pressure (PCWP) for the determination of cardiac output and collection of mixed venous blood and for the infusion of adenosine. Another plastic cannula was introduced percutaneously, in a retrograde direction, into the right jugular bulb for the collection of blood. The correct position was verified by x-ray. The ECG was monitored with a standard chest (V5) lead. Heart rate was determined from the R-R interval. Blood pressures were measured by transducers placed at the midthoracic level. Cardiac output (QT) was determined in triplicate according to the ther odilution technique with a cardiac output computer (Edwards Lab, model 9510). Isotonic glucose, 10 ml at 1°C, was used as a thermal indicator. The ECG, heart rate, blood pressures, and thermodilution curves were recorded on a Grass^ polygraph. Blood gases were measured with appropriate electrodes for pH, PCO ^ , and P0 (Radiometer, Copenhagen). The hemoglobin concentration was determined spectrophotometrically. Samples for the determination of adenosine and its metabolites were collected as described by Sollevi et al., Acta Physiol. Scand., 120: 171-76 (1984). Adenosine and inosine were purified and analyzed by HPLC as described by Fredholm and Sollevi., J. Physiol. (London), 313: 351-67 (1981). Hypoxanthine, xanthine, and uric acid were analyzed by HPLC according to the method of Schweinsberg and Loo., J. Chromatogr., 181: 103-7 (1980). Arterial levels of dipyridamole were determined by HPLC. J Chromatogr., 162: 98-103 (1979). Blood lactate was measured according to Tfelt-Hansen and Siggard-Andersen. Scand. Clin. Lab. Invest., 27: 15-19 (1971). SUBSTITUTE SHξET Measurements and blood samplings were performed immediately before hypotension, as late as possible during hypotension (1-5 min before terminating the infusion) and approximately 30 min after the hypotensive period. Dipyridamole (5 mg per ml) was infused iv (0.3-0.4 mg per kg over a period of 5-10 min) approximately 20 minutes prior to the induction of controlled hypotension. This dose of dipyridamole produced clinically relevant drug levels in the plasma (1.2 + 0.3 μM, SEM) during the hypotensive periods. (See Pedersen, J. Chromatogr., 162: 98-103 (1979)). Adenosine (5mM, 1.34 mg per ml in isotonic saline) was administered by continuous infusion (Critikon roller pump, 2102A, superior vena cava) for 12-71 minutes (x = 33 + 3 SEM) at a rate of 0.01-0.32 mg per kg per min (x = 0.14 + 0.04 SEM, corresponding to 8.0 + 2.7 mg per min). The infusion was started at a rate of 0.01 mg per kg per minute, which was doubled at 15 second intervals until the desired MABP level of 40-50 mmHg was reached. The corresponding volume of infused adenosine solution ranged from 0.5 to 17 ml per min (x = 6 + 2 SEM). The mean hypotensive period was 32 + 8 min. The total adenosine dose did not exceed 1.5 grams. Serum creatinine was determined before and on two consecutive days afterOperation. The standard ECG was recorded the day before and the day after operation. Systemic vascular resistance (SVR) was derived from the formula SVR (mmHg per liter min) = MABP - RAP and pulmonary vascular resistance QT (PVR) from the formula PVR = PAP - PCWP QT Oxygen content was derived from the formula S0 2 * x 1.34 x Hb + P0 2 x 0.03. Foex et al., Br. J. Anesth., 42: 803-4 (1970). The arteriovenous oxygen content difference (AVDOp) was determined and used to calculate total oxygen consumption (VO as the product of AVDO- and QT. The results of this work are summerized in Tables I-IV, in which data are presented as means + SEM. The statistical significance (control 1 SUBSTITUTE SHEET vs. adenosine and control 1 vs. control 2) was determined by Student's t- test for paired data. A P value of < 0.05 was regarded as significant. The purine levels of nine of the patients were determined prior to, during and after adenosine-induced controlled hypotension. The results are summarized in Table 1. *S0 = Oxygen saturation. Table I Purine levels (μM) in arterial plasma before, during, and after adenosine- induced controlled hypotension in nine patients. After hypotension Control 1 Hypotension 3-9 min 20-40 min Adenosine 0.15 + 0.02 2.45 + 0.65 0.24 + 0.06 0.19 + 0.03 (9) ' (9) (6) (7) Inosine 0.04 + 0.01 3.01 + 1.48 0.69 + 0.26 0.29 + 0.15 (8) (8) (5) (7) Hypoxanthine 1.94 + 0.55 6.28 + 2.33 3.25 + 1.00 (9) (9) (8) Xanthine 5.93 + 2.04 6.10 + 1.67 5.49 + 1.58 (7) (7) (7) Uric Acid 185.2 + 14.2 198.1 + 22.7 199.5 + 28.8 (9) (9) (8) * p<0.01 ** p<0.05, denotes significantly different from the control 1 levels. Number of observation in parentheses. As is evident from Table I, adenosine is present in the 10 M range durin basal conditions. Continuous infusion of adenosine increased the arterial SUBSTITUTESHEET adenosine level to 2.45 + 0.65 μM. The adenosine metabolites inosine and hypoxanthine were increased during the infusion, whereas xanthine and uric acid levels were unaffected. Once the desired blood pressure level was reached, the infusion rate could be kept constant throughout the hypotensive period. After termination of the infusion, the arterial adenosine levels returned to control values within 3-9 min. Inosine was eliminated more slowly from the circulation and remained slightly above basal levels 20-40 minutes after the infusion. The central hemodynamic variables were measured in all 10 patients before, during and 30 minutes after controlled hypotension and are summarized in Table II. Table II Central hemodynamic variables before, during and 30 min after adenosine- induced controlled hypotension in ten patients. Control 1 Adenos-ine Control 2 Systolic blood pressure (mmHg) 115 + 6 78 + 6* 130 + 7** Diastolic blood pressure (mmHg) 61 + 3 34+ 2* 71 + 3** Mean arterial blood pressure (mmHg) 82 + 3 46 + 2* 91 + 4** Right atria! pressure (mmHg) 6.8 + 1.1 7.2 + 0.7 5.6 + 0.8 Pulmonary artery pressure (mmHg) 14.4 + 1.0 16.5 + 0.9 14.7 + 1.4 Pulmonary capillary wedge pressure (mmHg) 9.6 + 1.1 11.0 + 1.0 9.9 + 1.4 Heart rate (beats per min) 54 + 2 63 + 3* 58 + 3 Cardiac output (liters per min) 4.93 + 0.51 6.86 + 0.71* 5.17 + 0.54 Systemic vascular resistance (mmHg per min) 16.65 + 1.95 6.22 + 0.60* 17.70 + 1.72 Pulmonary vascular resistance (mmHg per liter min) 0.97 + 0.15 0.82 + 0.08 0.97 + 0.15 * p 0.01 ** p 0.05, denotes significantly different from control 1 " » ! "?"" The infusion of dipyridamole decreased MABP by approximately 10 mmHg in five of the patients. At the start of the adenosine infusion, MABP was not significantly different from the predipyridamole level (82 + 3 vs. 86 + 3 mmHg) as shown in Table II. Adenosine induced a decrease in MABP to 46 mmHg (43 ± 3 %) within 1-2 minutes. The decrease in MABP was caused by a parallel decrease in both systolic and diastolic pressure. The MABP was stable throughout the hypotensive period. Cardiac output increased from 4.9 to 6.9 liter per minute (44 + 9 %) in parallel with a small increase in heart rate of 9 + 2 beats per minute. The SVR decreased from 16.7 to 6.2 m Hg per liter a minute, corresponding to a decrease of 61 + 3 . , whereas PVR was unchanged. RAP, PAP and PCWP were not influenced by adenosine. After discontinuation of the infusion, MABP was restored within 1-5 minutes. Rebound hypertension did not occur, although the MABP was persistently approximately 10 mmHg higher after hypotension than during the control period. However, the posthypotensive MABP was not significantly higher than the MABP before administration of dipyridamole. Heart rate, QT and SVR returned rapidly to control levels concurrently with the restoration of MABP. Oxygen contents, consumptions and lactate concentrations in nine patients before, during and 30 minutes after controlled hypotension are summerized in Table III. : Table III Total arteriovenous oxygen content difference (AVDT02), jugular arteriovenous oxygen content difference (AVDJ02, total oxygen concumption(V T 0 2 ), arterial oxygen tension (PaO , arterial lactate concentration (La) and jugular arteriovenous lactate content differences (AVDjLa) before, during and after adenosine-induced hypotension in nine patients. Control 1 Adenosine Control 2 AVD T 0 2 (ml per liter) 46.3 + 2.3 29.3 + 2.5* 46.8 + 3.2 AVD.0 2 (ml per liter) 85.2 + 10.5 58.1 + 14.1** 74.9 + 7.7 τ 0 2 (ml per mm) 220 + 15 193 + 16** 235 + 16 Pa0 2 (mmHg) 111.0 + 9.8 97.5 + 9.0 93.0 + 5.2 La ( mol per liter) 1.46 + 0.17 1.73 + 0.20 1.82 + 0.20** AVD.La (mmol per liter) 0.02 + 0.04 -0.05 + 0.05 -0.06 + 0.04 J ** p 0.05, denotes significantly different from control 1. From Table III, it can be seen that arterial oxygen tension remained unchanged during adenosine-induced hypotension. V0 2 was decreased by 13 + 4 %, with a decrease in AVD0 2 of 37 + 5 %. The arterial lactate concentration was not affected by hypotension. The cerebral AVD0 2 decreased similarly by 37 + 13 %, while the arterio-jugular lactate content difference was unaltered. After the hypotensive period, the metabolic variables returned to the control levels, except for a minor increase in the arterial lactate concentration. The ECG the day after the operation was unchanged. The mean serum creatinine level was 83 + 4 μM before operation and 70 + 3 and 71 + 4 μM on the first 2 postoperative days. •-—- » < 15 Adenosine infusion rate was constant during the hypotension, which suggests the absence of tachyphylaxis. Subsequent to the tests described above, a 20 mM solution of adenosine in isotonic saline was administered to 50 surgical patients employing techniques similar to those described, except that pretreatment with dipyridamole was omitted. Hemodynamic effects similar to those described above were observed at adenosine dosages of 0.2 - 0.35 mg per kg per minute. The enhanced cardiac output obtained with adenosine, in combination with the maintained right and left heart filling pressures, is in contrast with the hemodynamic effects of controlled hypotension with sodium nitroprusside or nitroglycerine, as is shown in Table IV. Table IV Hemodynamic effects of adenosine and nitroglycerine-(TNG), and nitroprusside-(SNP) induced controlled hypotension during cerebral aneurys surgery with similar anesthetic techniques (data presented as per cent from control ). ADENOSINE SNP** TNG*** n=10 n=17 n=20 MABP -43* -36* -36* RAP +6 -39* -45* PAP +15 -27* -34* PCWP +14 -44* -45* HR +9* +22* +19* QT +44* -15* -24* SVR -61* -29* -16* PVR -15 +11 +12 * P <0.01 ** Data from Lagerkranser et al . , Acta. Anesth. Scand., 24: 426-32 (1980). *** Data from Lagerkranser, Acta. Anesth. Scand., 26: 453-7 (1982) r\. ~ζ? From the foregoing it is evident that continuous infusion of adenosine during anesthesia is capable of significatly reducing blood pressure without evidence of tachyphylaxis while, at the same time, causing a decrease in peripheral vascular resistance, an increase in cardiac output and a moderate increase in heart rate. This suggests that adenosine acts as a hypotensive agent through dilation of the arterial resistance vasculature. In contrast, sodium nitroprusside and nitroglycerine induce hypotension by both pre- and post-capillary dilatation. In addition, controlled hypotension with adenosine better preserves oxygen tissue pressures than hypotension induced by nitroprusside. It should be noted that, at the levels of adenosine used, blockage of atrio-ventricular conductance does not occur in these persons during anesthesia. Indeed, adenosine is used in bolus form specifically to block A-V conductance. Apparently the peak plasma concentration of adenosine is considerably higher when giving bolus injections than the steady state levels obtained during these continuous infusions. Example II Control of " hypertensive crisis Continuous infusion of adenosine can also be employed to control hypertensive crises occurring during surgery. Such crises can occur, for example, as a result of release of catecholamines during surgery on pheochromocytoma - a tumor characterized by the presence of catecholamine - which can cause pulmonary edema and death. At present, this situation is treated prophylactically by pre-ad inistration of alpha- and beta-adrenoceptor blockers or vasodilators, but the effect is often insufficient. It has now been found that, in the case of a catecholamine-induced hypertensive crises, prompt infusion of adenosine will rapidly restore blood pressure to normal, and will easily maintain normal pressure until the crisis has passed. Amounts of adenosine which are effective in controlling such hypertensive crises will depend on the degree of hypertension. However, as a general rule they are about half of the amounts found useful for controlled hypotension, i.e., in the range of from about 0.1 to about 0.2 mg adenosine per kilogram of body weight per minute. Example III Improved coronary circulation in ischemic heart disease Patients requiring abdominal vascular surgery, such as surgery for an aortic aneurysm, frequently also suffer from ischemic heart disease, or insufficient blood flow to the heart tissue, which may present undesirable complications in such surgery. Accordingly, drugs with vasodilator properties, such as isoflurane and nitroprusside, have bεsn investigated for possible use to increase myocardial blood flow and to reduce peripheral vascular resistance (after-load reduction) during such surgery; however, they have been found to have no beneficial effect with respect to coronary flow and, indeed, may reduce coronary blood flow. In contrast, adenosine administered by continuous infusion has been found very effective in increasing myocardial blood flow and, in such use, is . accompanied by an increase in cardiac output. For such application, the rate of adenosine administration should be such that there is no more than a 10-20 per cent reduction in blood pressure. As a general rule, this is achieved by use of rate of administration of the order of 0.05 to about 0.1 mg adenosine per kilogram per minute. In such a case myocardial blood flow has been found to be doubled, cardiac output has been increased by 10 to 20 per cent, and blood pressure has been reduced by 10 to 20 per cent, all without change in oxygen consumption and without ECG signs of ischemia. Example IV Coronary vasodilation It has been further found that when adenosine is administered by infusion at rates which do not induce significant hypotension, it has clinically useful regional effects in unanesthetized and anesthetized patients. For example, adenosine at dosages of the order of 10 to 15 per cent of hypotensive levels (e.g. 0.02 to 0.05 mg per kg per minute) can be a useful adjunct to coronary by-pass surgery, apparently due to a preferential coronary vasodilation. It has been reported that coronary artery grafts occulade more frequently during the postoperative period when low graft-flow values are obtained during surgery. See Groudin et al, Circulation, 42: Suppl 3: 106-111 (1970). It has been found that low doses of adenosine administered postoperatively increase graft blood flow without significant effect on atrio-ventricular conductance. The administration of low doses of adenosine for this purpose can be carried out for as long as is necessary to afford appropriate graft flows and reduce risk of occlusion, but ordinarily the period need not exceed 48 hours following surgery. In a study designed to investigate the use of adenosine to inhibit occlusion of coronary grafts, nine patients (age 45-65, all taking beta-blockers) were studied during coronary artery surgery. After premedication, morphine (10-15 mg) and scopolamine (0.4-0.6 mg), anesthesia was induced by fentanyl (30 mcg/kg b.w.). Pancuronium (0.1 mg/kg b.w.) was given to facilitate endotracheal intubation. Anesthesia was maintained with fentanyl 0.5 mg/hour, N 2 0 (50 %) in oxygen and droperidol (0.1 mg/kg b.w.). During bypass thiomebumal (5 g/kg-b.w.) was given. Nitrous oxide was not used after bypass. Extracorporeal circulation (ECC) was performed with a roller pump and a Shiley buddle oxygenator primed with crystalloid solution. ECG (modified V g ), an arterial line and a Swan-Ganz Catheter were used for monitoring and for hemodynamic measurements. Blood flow in bypass grafts (n=15, internal mammary and venous grafts), was measured with appropriate sized square wave electromagnetic flow probes (Nycotron 732). The study was performed 20-30 minutes after the termination of ECC. After a control period (5 min), adenosine (5.3 mg/ml clinical solution) was continuously infused in a central vein in order to induce approximately 10 % reduction of mean arterial blood pressure (about 30 to 50 μg per kg per min). Graft flow was continuously measured before and during a 10 or 30 minute infusion of adenosine and finally during the following 5 minute control period. Data are expressed as mean + SEM and differences were tested with Student's paired t-test against the preceding period. ι The results of thi s study are summarized in Table V. Table V Control Control Before Adenosin After Mean Arterial Pressure (mmHg) 84 + 3 74 + 3 85 ± 3 p « 0.01 p «i 0.01 Heart Rate (beats/min) 82 + 5 82 + 15 81 ± 6 Cardiac Output (1/min) 4.8 + 0.4 5.6 + 0.3 5.3 + 0.3 p : 0.05 n .s . Pulmonary Artery Pressure (mean) (mmHg) 16.7 + 1 .2 18.8 + 1.2 19.9 + 1 .0 RAP (mean) (mmHg) 4.7 + 0.5 5.3 + 0.4 5.8 + 0.7 2 Stroke Index (ml/m ) 35.6 + 2.6 38.8 + 2.0 39.6 + 2.5 Left Ventricular Stroke Index (Joule/n 2 ) 0.44 + 0.03 0.41 + 0.03 0.49 + 0.04 Graft flow ml/min (n=15) 40 + 5 77 + 7 39 + 5 p _. 0.001 p < 0.001 As is evident from Table V, adenosine in a dose of 49 + 4 μg/kg/minute, a level which reduced mean arterial pressure 12 %, increased cardiac output 12 %, and doubled graft flow. At the same time, heart rate, mean pulmonary artery pressure, central venous pressure, stroke index and left ventricular stroke work index remained essentially unchanged. Graft flow rate was restored to its original value on termination of adenosine. No arrhythmias were observed. This demonstrates that i.v. adenosine at low rates (30-50 μg per kg per min) induces a marked and reproducible increase in graft flow without increased myocardial work, apparently due to preferential vasodilatory effect of adenosine in the coronary vasculature. SUBSTITUTE SHEET Exampl e V Increased cardiac output As is evident from the foregoing data, intravenously infused adenosine has the ability to increase cardiac output without increasing heart work. This is in contrast to other vasodilators, such as sodium nitroprusside, which may reduce cardiac output, depending on the hemodynamic status of the patient. As a consequence, adenosine can be used to stimulate cardiac output in patients with low cardiac output states due, for example, to heart surgery, infarct and the like. This apparently is due to adenosine's ability to reduce after-load, without having significant effect on pre-load. In contrast, nitroprusside reduces both after-load and pre-load, and nitroglycerine is effective principally (90 %) on reducing pre-load, and has only a marginal effect on after-!oad. For this application, effective dosages are intermediate those used for increased graft flow and controlled hypotension. Typically the effective dose is of the order of 40-80 μg/kg/per minute. The duration of treatment can be as long as required to support the heart. It also has been found that, on termination of the adenosine, cardiac output, although less than that during treatment with adenosine frequently remains above the cardiac output prior to treatment. In this respect, adenosine is of value as an adjunct to dopamine treatment for cardiogenic shock. Dopamine is frequently given to patients in shock to stimulate heart action and thereby increase blood pressure. Adenosine can be administered with dopamine to modulate peripheral resistance without compromising systemic blood pressure, and thus increase cardiac output. Adenosine is unique in its activity in this respect, because it is able to reduce after-load without significantly increasing heart rate. In contrast, agents previously used to reduce cardiac after-load, for example, hydralazine and prazosin, increase heart rate. Example VI Platelet protection during cardiopulmonary bypass Continuous infusion of adenosine also has been found of use in protecting platelets during cardiopulmonary bypass. For such use, it is desired to maintain the adenosine dosage below that affording significant vasodilation, and a rate of about 100 μg/kg/min has been found effective. In contrast, prostacyclin, a prostaglandin used to inhibit platelet aggregation, is associated with severe systemic vasodilation and hypotension during coronary bypass surgery. Twenty-five patients scheduled for coronary artery bypass surgery were randomly assigned to two groups, one with adenosine infusion (n=13) and the other with placebo infusion (n=12). Routine tests of coagulation status were normal in all patients, and none was taking drugs known to affect platelet function. Intravenous anesthesia was used, either high-dose fentanyl (100-150 μg/kg) or balanced anesthesia (thiopental, fentanyl diazepam and N 2 0/0 2 ). During cardiopulmonary bypass (CPB), mean arterial blood pressure (MABP) above 70 mmHg was treated with the vasodilator sodium nitroprusside (SNP), except in the final phase or rewarming. CPB was performed with SARN roller pump and a Shiley oxygenator (100A) primed with 2000 ml crystalloid solution (75 mg heparin). The perfusion rate was kept at 2 approximately 1.8 ml/m body surface.. Moderate hypothermia (25°C) was induced. Cardioplegia was obtained with Ringer's solution (with added potassium up to 20 mM/1). Heparin (3 mg/kg) was administered as a bolus injection before cannulation. The heparin effect was controlled by measurements of activated clotting time. (Hemocron^Int. Technidyne Corp, USA). This time (ACT) was > 400 seconds in all patients during CPB. At the termination of CPB, the heparin effect was antagonized with protamine (c. 1.3 mg/mg heparin). ACT was checked 10-20 min after the protamine injection. ACT values 120 sec were considered satisfactory. en .ςτ'7"""^ ,υcpτ u PC .SE85/0 Platelet count (Linson 431 A cell counter) and hematocrit were determined in arterial samples before anesthesia, after thoracotomy, during CPB at 10, 20, 40, 60, 80 and 100 min, 30 min after CPB and on the postoperative day. Platelet counts were expressed in percentage of preanesthesia levels and were corrected for hemodilution. MABP was monitored continuously via a catheter introduced in the radial artery. All patients received hypertonic mannitol (1-1.5 g/kg) during CPB and urine production was calculated as ml/min of CPB (table VI). Peroperative blood loss and blood transfusions could not be compared between the groups, due to the smallness of the series and the involvement of many surgeons in the study. Postoperative bleeding was measured as the blood loss from the tube drainage from the end of operation until the postoperative morning. One patient in the adenosine group was excluded because of reoperation for surgical reasons (for massive bleeding due to suture insufficiency in a graft anastomosis) within 6 hours after CPB. Adenosine (5.3 mg/ml, clinical solution) was infused at a rate of 100 μg/kg/min into the superior vena cava throughout CPB. The adenosine dose was based on five pilot cases in which a vasodilation dose-response was observed. The highest infusion rate that did not induce systemic vasodilation was chosen for this study. In six cases the plasma adenosine levels were determined by high performance liquid chromotography (HPLC) (Fredholm and Sollevi, J. Physiol. (London), 313: 351-67 (1981) in arterial and in venous (venous lines to the oxygenator) blood. The adenosine metabolites inosine, hypoxanthine and uric acid were also determined by HPLC. The samples were collected as previously described (Sollevi, Acta. Physiol. Scand., 121: 165-72 (1984) at the intervals of 10, 20, 40 and 80 minutes during CPB and 20 minutes after CPB. Results are summerized in Tables VI and VII, below in which data are presented as means + SEM. Statistical significance (controls v. adenosine group) was determined with Student's t-test for unpaired data. For significance within the groups the Wilcoxon Rank Sum test was used, p <0.05 was regarded as significant. Table VI Patient data Adenosine (mg per kg per min) 0.1 Age, years 57 (range 47-66) 57 (range 42-74) Males/females n/i 12/1 CPB-time (min) 95 + 10 120 + 10 preoperative platelet counts (x 10 9 cells/1) 162 (range 107-235) 158 (range 106-251) Peroperative urine production (ml /min CPB) 9.7 (2.1-20) 4.1 (1.1-9.5) Postoperative blood loss (ml) 630 + 60 640 ' 80 Table VII Arterial and venous concentrations (μM) of adenosine and its metabolites (n=6), before, during and after adenosine infusion (0.1 mg x kg-1 x min-1) CPB CPB 20' pre-CBP 10 1 20' 40' 80' post Vein Adenosine 0.3+0.2 3.7+1.3* 5.7+2.1* Inosine 0.2+0.1 0.9+0.3* 2.4+1.2* 1.6+0.5* 1.6+0.4* 0.4+0.1 Artery Adenosine 0.3+0.1 0.7+0.3 0.8+0.4* 0.6+0.3 0.4+0.2 0.3+0.1 Inosine 0.2+0.1 1.3+0.7* 2.5+1.0* 1.2+0.3* 1.4+0.4* 0.4+0.1 Hypoxanthine 3.2+0.8 5.3+1.2 7.7+1.4* 5.3+1.0 5.0+0.9 4.2+0.9 Uric Acid 250+30 260+32 269+35 250+32 249+30 260+34 ''Significantly different from pre-CPB val ue. ι !T"™ tr i . Table VIII Platelet count; % of Awake count Time of count Control Adenosine Awake 100 100 Pre CPB 95 97 During CPB (Duration 100 minutes) 10 minutes 80 96 20 minutes 75 87 40 minutes 65 85 60 minutes 80 91 80 minutes 78 100 100 minutes 77 97 Post CPB, time after infusion of CPB - 30 minutes 70 88 24 hours 60 60 As shown in Table VIII, platelet count was similar in the two groups before anesthesia and was unaltered by anesthesia and thoracotomy. In the control group the platelet count fell rapidly and markedly during the first 40 minutes of CPB and remained significantly reduced during and after CPB. During adenosine infusion the initial platelet reduction was small, and was significant only at 20 and 40 minutes on CPB. From 60 minutes to the end of CPB and at 30 minutes after CPB the platelet counts were not significantly different from those before anesthesia. Throughout CPB and 30 minutes after CPB there was significant intergroup difference in platelet counts. On the day after operation the platelet counts were markedly reduced in both groups, with no significant intergroup difference. As shown in Table VII, the arterial and venous adenosine levels were in the normal range of 0.3 μM prior to CPB. The adenosine infusion raised the venous plasma concentration to 2-10 μM, while the arterial levels were approximately doubled during the initial CPB period. Only the first adenosine metabolite, inosine, was consistently elevated during the infusion. All parameters had returned to control levels within 20 minutes after CPB. The mean arterial blood pressure (MABP) did not differ significantly between the two groups during CPB. In the placebo group, however, seven patients required sodium nitroprusside infusion ( 5 μg/kg/min) to keep MABP below 70 mmHg. No patient in the adenosine group required vasodilator treatment. After CPB the patients in the adenosine group had slightly lower MABP, but at the end of operation there was no intergroup difference. The urine production during CPB was 250 ml/h in the adenosine group and 500 ml/h in the controls (p *-.0.01, Table VI). Transient elevation of serum creatinine levels (10-20 . above normal range) was found in two patients in the adenosine group and one control patient during two postoperative days. The postoperative blood loss did not differ between the groups. All patients were extubated within 24 hours after the operation and all recovered normally. There were no clinical signs of neurologic complications and all the patients were discharged from the hospital. Example VII Addition of adenosine to cardioplegia solution Cardioplegia is induced during open heart surgery in order to arrest the heart and to reduce myocardial oxygen consumption during cardiopulmonary bypass. This is at present generally obtained by ice-cooled solution containing high concentration of potassium (20 mmol/liter, four times the normal serum level) that is infused into the coronary vessels. It is well known that high concentrations of potassium effectively induce asystole, but also cause damage on vascular endothelium. The latter may lead to permanent stenosis of coronary vessels. The foregoing data has clearly demonstrated in human patients that adenosine is effective as coronary vasodilator and preserves circulating ' n. ^ ,«,„_, 26 PCT/SE85/00 platelets. Adenosine is also known to be incorporated into high energy phosphates (ATP) in various tissues. In addition, it is well known since the early work of Drury and Szent Gyorgyi (J. Physiol (London) 68:213 (1929)) that high concentration of adenosine can produce heart block. These four effects of adenosine are all useful during the induction of cardioplegia in human patients. First, the vasodilatory effect can counteract the vasoconstrictor effect of potassium and thereby reduce the time required for administration of cardioplegia solution. This will give a more rapid cooling and thereby more rapid asystoli. Secondly, the inhibitory effect of adenosine on platelet activation can prevent platelet aggregation in the coronary circulation during this cooling phase. Third, adenosine can serve as a substrate and be incorporated into myocardial ATP during this condition, when the heart is beating without obtaining adequate oxygen supply. Finally, the well known A-V blocking effect of high concentrations of adenosine can be used for the induction of asystoli. Then, the potassium concentration of the cardioplegia solution can be reduced to a level that do not damage the vascular endothelium. These four effects of adenosine can all be achieved with a cardioplegia solution containing 0.5-1.5 mg/ml of adenosine, administered into the coronary circulation during the induction of cardioplegia. Ordinarily, when adenosine is administered for this purpose through the aortic root, the cardioplegia solution will be administered at the rate of 50 to 150 ml/min over a period of about 10 to about 20 minutes. -■a i—™ pijrj*

Claims: 2/ 5/0 CLAIMS 1. Method for modifying the hemodynamic properties of a human patient comprising continuously administering into the blood stream of said patient adenosine in an amount sufficient to have a hemodynamic effect on said patient under conditions such that atrio-ventricular block is avoided. 2. Method according to claim 1 in which adenosine is administered to an anesthetized patient undergoing surgery. 3. Method according to claim 2 in which adenosine is administered to said patient in an amount effective to induce controlled hypotension in said patient. 4. Method according to claim 3, wherein said adenosine is administered at a rate of from about 0.2 to about 0.35 mg of adenosine per kilogram of body weight per minute. 5. Method according to claim 2, wherein adenosine is administered in an amount effective to control a hypertensive crisis. 6. Method according to claim 5, wherein said adenosine is administered at a rate of from about 0.1 to about 0.2 mg of adenosine per kilogram of body weight per minute. 7. Method according to claim 1 in which adenosine is administered to a conscious patient in an amount below that sufficient to cause significant blockage of atrio-ventricular conductance. 8. Method according to claim 7, wherein adenosine is administered to said patient in an amount effective to provide preferential coronary vasodilation. 9. Method according to claim 8, wherein adenosine is administered to effect increased blood flow in a coronary artery graft and thereby reduce incidence of occlusion of said graft. 10. Method according to claim 9, wherein said adenosine is administered at a rate of from about 0.03 to about 0.05 mg per kilogram per minute. 11. Method according to claim 7 in which adenosine is administered to said patient in an amount sufficient to increase cardiac output. 12. Method according to claim 11, wherein said adenosine is administered at a rate of from about 0.03 to about 0.05 mg per kilogram per minute. 13. Method for preventing platelet loss during coronary bypass surgery of a patient which comprises continuously into the blood stream adenosine to said patient in an amount effective to reduce platelet loss during said surgery. 14. Method according to claim 13 in which said adenosine is administered to said patient at a rate of from about 0.05 to about 0.15 mg per kilogram per minute. 15. Method according to claim 1 which comprises continuously introducing adenosine into the coronary circulation of said patient in amount sufficient to facilitate the induction of cardioplegia. 16. Method according to claim 15 in which said adenosine is administered to said patient at a concentration of from about 1 to about 1.5 mg per ' milliliter at a rate from about 50 to about 150 milliliter per minute. 17. A unit dosage form of adenosine suitable for continuous intravenous infusion into a human patient comprising a physiologically acceptable aqueous solution containing from about 0.4 to about 3 grams of adenosine at a concentration of at least 1 milligram of adenosine per milliliter. 18. A unit dosage form according to claim 15, wherein said adenosine is in isotonic saline. 19. Use of adenosine for the manufacture of a medicament for controlling a hypertensive crisis in a human patient. 29 20. Use of adenosine for the manufacture of a medicament to provide preferential coronary vasodilation in a human patient. 21. Use of adenosine for the manufacture of a medicament to effect increased blood flow in a coronary artery graft of a human patient. 22. Use of adenosine for the manufacture of a medicament to increase cardiac output of a human patient. 23. Use of adenosine for the manufacture of a medicament to prevent platelet loss during coronary bypass surgery in a human patient. 24. Use of adenosine for the manufacture of a medicament to facilitate induction of cardioplegia in a human patient. Q5 A im-m i

Inventors: SOLLEVI ALF, SOLLEVI, ALF
Applicants: HAESSLE AB, AKTIEBOLAGET HAESSLE
Application year: 1985
Main classification: A61K31
IPC codes: A61K31, A61P9, C07H19