Myocardial cyclic AMP augmentation with high-dose PDEIII inhibitor in terminal warm blood cardioplegia.

PURPOSE: Phosphodiesterase (PDE) III inhibitors have been reported in various cellular protective activities via the cyclic adenosine monophosphate (cAMP) pathway. We investigated the effects of amrinone on ischemia/reperfusion injury and intracellular calcium (Ca2+) handling if utilized as a component of terminal warm blood cardioplegia (TWBCP). METHODS: Anesthetized pig hearts were subjected to 90-min global ischemia with single-dose crystalloid cardioplegia, followed by 30-min reperfusion under cardiopulmonary bypass. The animals were divided into three groups according to the contents of TWBCP (n = 5 each): Control, no TWBCP; TWBCP, no additive; Amrinone, TWBCP with amrinone. The time course of cardiac function and biochemical samples were measured. Further, coronary perfusion and ventricular arrhythmia were evaluated during reperfusion. RESULTS: Cardiac function improved with amrinone. Specifically, the amrinone group showed an increase of myocardial cAMP (p <0.05) and a suppression of creatine kinase, troponin-T, and lipid peroxide after reperfusion (p <0.05); many cases also showed much improvement of coronary perfusion and spontaneous resuscitation after global ischemia. CONCLUSION: Ischemia and/or reperfusion deplete myocardial cAMP, leading to impaired Ca2+ handling and further to cardiac dysfunction. High-dose PDEIII inhibitor in TWBCP may replenish myocardial cAMP and promote rapid and sustained cardiac functional recovery with various cellular protective effects after open-heart surgery.

Possible contribution of acetylamrinone and its enhancing effects on platelet aggregation under shear stress conditions in the onset of thrombocytopenia in patients treated with amrinone.

BACKGROUND: Thrombocytopenia is recognized as one of the most common complications when the patients with severe heart failure are treated with cardiotropic phosphodiesterase (PDE)-3 inhibitors. To understand the mechanism of the onset of this complication, we focused on the effects of various PDE-3 inhibitors and its stable metabolite of acetylamrinone on platelet aggregation occurring under physiological shear stress conditions. METHOD: Blood specimens were obtained from eight apparently healthy adult donors. Platelet-rich plasma was separated after anticoagulation by citrate. The effects of PDE-3 inhibitors of amrinone and olprinone, as well as the stable metabolite of the former of acetylamrinone, on platelet aggregation induced by its exposure to a shear rate of 1200 and 10,800 s(-1) were determined by optically modified cone-plate viscometer. RESULTS: Both olprinone and amrinone inhibited platelet aggregation at 10,800 s(-1) in a dose-dependent manner with the IC(50) value of 14 +/- 1 and 61 +/- 8 microM (mean +/- S.D.), respectively, while amrinone significantly inhibited platelet aggregation at 1200 s(-1) only at highest concentration tested (100 microM). Contrary to the effects shown with PDE-3 inhibitors, acetylamrinone did not inhibit platelet aggregation at all. Moreover, it even enhanced the aggregation at 1200 s(-1) when used with 5 microM. CONCLUSIONS: Our results demonstrate possible contribution of the enhancing effects of acetylamrinone on platelet aggregation occurring under blood flow conditions, which reduced the platelet count when occurring in real circulation, to the higher incidence of thrombocytopenia in patients treated with amrinone.

High-dose amrinone is required to accelerate rewarming from deliberate mild intraoperative hypothermia for neurosurgical procedures.

BACKGROUND: Since the time available to provide the cooling and rewarming is limited during deliberate mild hypothermia, the technique to accelerate the cooling and rewarming rate of core temperature has been studied. Amrinone has been reported to accelerate the cooling rate but not the rewarming rate of core temperature during deliberate mild hypothermia. The failure of amrinone effect on the rewarming rate might be due to an insufficient dose of amrinone during hypothermic conditions. The authors therefore tested whether higher doses of amrinone can accelerate the rewarming rate of core temperature during deliberate mild hypothermia for neurosurgery. METHODS: After institutional approval and informed consent, 30 patients were randomly assigned to one of three groups. Patients in the control group (n = 10) did not receive amrinone; patients in the AMR 15 group (n = 10) received 15 microg x kg(-1) x min(-1) amrinone with a 1.0-mg/kg loading dose of amrinone at the beginning of cooling; and patients in the ReAMR group (n = 10) received 5 microg x kg(-1) x min(-1) amrinone with 1.0-mg/kg loading and reloading doses of amrinone at the beginning of cooling and rewarming, respectively. Administration of amrinone was started just after the induction of cooling and continued until the end of anesthesia. Anesthesia was maintained with nitrous oxide in oxygen, propofol, and fentanyl. After induction of anesthesia, patients were cooled, and tympanic membrane temperature was maintained at 34.5 degrees C. After completion of the main surgical procedures, patients were actively rewarmed and extubated in the operating room. RESULTS: The cooling and rewarming rates of core temperature were both significantly faster in both amrinone groups than in the control group. During the cooling and rewarming periods, forearm minus fingertip temperature gradient was significantly smaller in both amrinone groups than in the control group. During the rewarming period, heart rate and mean arterial pressure in the AMR 15 group were significantly faster and lower, respectively, than in the control group. Systemic vascular resistance in the AMR 15 group was smaller than in the control group throughout the study; on the other hand, only the value after the start of rewarming in the ReAMR group was smaller than in the control group. CONCLUSIONS: Amrinone at an infusion rate of 15 or 5 microg x kg(-1) x min(-1) with a reloading at the beginning of rewarming accelerated the rewarming rate of core temperature during deliberate mild hypothermia. This suggests that high-dose amrinone is required to accelerate rewarming from deliberate mild intraoperative hypothermia for neurosurgical procedures.

[Endothelial-derived nitric oxide mediates the peripheral vasodilatory effects of amrinone in humans].

Amrinone, which is used for the treatment of acute congestive heart failure, has vasodilatory and positive inotropic effects through the increment of intracellular cyclic adenosine monophosphate. Recent in vitro investigations have shown that amrinone has an endothelium-dependent vasodilatory effect. The present study examined whether amrinone shows this endothelium-dependent vasodilatory effect in human peripheral vessels. Forearm blood flow during intra-arterial infusion of graded doses (12.5, 25, 50, 100, 200 micrograms/min) of amrinone was measured using plethysmography in 10 healthy subjects without organic vascular disease before and after nitric oxide synthase blocking with NG-monomethyl-L-arginine (L-NMMA, 400 mumol). The graded dose of amrinone produced progressive increases in amrinone plasma concentrations, and a dose over 100 micrograms/min caused amrinone plasma concentrations of more than 1.0 microgram/ml. The increase in forearm blood flow in response to amrinone was significantly depressed after L-NMMA doses of less than 100 micrograms/min, but the increase in forearm blood flow during infusion of higher doses (100, 200 micrograms/min) was not affected by L-NMMA. These results suggest that endothelial-derived nitric oxide may partially contribute to amrinone-induced vasodilation in humans. Thus, the vasodilatory effect of amrinone might be impaired in patients with endothelial dysfunction.

Amrinone improves lung compliance in patients receiving mechanical ventilation for cardiogenic pulmonary edema.

BACKGROUND: Decrease in lung compliance is one of the major causes of respiratory failure. We investigated whether amrinone could improve lung compliance. METHODS: We selected 20 consecutive patients with respiratory failure due to severe cardiogenic pulmonary edema to receive mechanical ventilation. Patients were administered a bolus injection (1 mg.kg-1) over 10 min followed by continuous intravenous infusion (10 micrograms.kg-1.min-1) of amrinone. Lung compliance, blood gas values, hemodynamic parameters, and sample plasma amrinone levels were assessed over a 120-min period after the onset of the continuous infusion of amrinone. RESULTS: Ten min following amrinone infusion, dynamic compliance (Cdyn) and static compliance (Cst) increased from 30 +/- 11 to 36 +/- 12 ml/cm H2O and from 37 +/- 12 to 42 +/- 13 ml/cm H2O, respectively (P < 0.01). Plasma amrinone levels reached a therapeutic level as vasodilator and positive inotropic effects at 10 min after amrinone infusion. The significant change in mean pulmonary artery pressure and pulmonary artery wedge pressure occurred later than the change in compliance of respiratory system. However, there were significant correlations between the mean pulmonary artery pressure and Cdyn (r = 0.36, P < 0.01) and Cst (r = 0.44, P < 0.01), as well as between plasma amrinone levels and Cdyn (r = 0.30, P < 0.05) and Cst (r = 0.41, P < 0.01). CONCLUSIONS: Amrinone-induced improvement in lung compliance was considered mainly to be due to an increase in the number of functioning lung units by improvement of the hemodynamics and a direct positive effect of amrinone on respiratory muscle contraction.

Hemodynamic effects of N-acetylamrinone in a porcine model of group B streptococcal sepsis.

High plasma concentrations of N-acetylamrinone, a primary metabolite of amrinone, are measured in some children during prolonged amrinone infusion. The purpose of this investigation was to determine if N-acetylamrinone has direct hemodynamic effects independent of amrinone. Twenty neonatal piglets received an infusion of 6 x 10(9) colony-forming units/kg of group B Streptococcus to induce sepsis. Subsequently, they were divided into 1 of 3 groups and received a 1-hr infusion of either normal saline (N = 4); 8 mg/kg amrinone, followed by 20 micrograms/kg/min (N = 9); or 8 mg/kg N-acetylamrinone, followed by 20 micrograms/kg/min (N = 7). Hemodynamic measurements and arterial/venous blood-gas determinations were obtained every 30 min during the study. Systemic vascular resistance and pulmonary vascular resistance were calculated. One milliliter of blood was obtained every 30 min during drug administration to determine plasma amrinone and N-acetylamrinone concentrations. The mean amrinone plasma concentrations measured at 30 and 60 min during the infusion time in the group receiving amrinone were 8.8 +/- 1.1 and 6.9 +/- 0.7 micrograms/ml, respectively. These animals experienced a significant decrease in mean pulmonary artery pressure and pulmonary vascular resistance, compared with saline controls after a 30-min infusion of amrinone. The mean N-acetylamrinone plasma concentrations measured at 30 and 60 min during the N-acetylamrinone infusion were 7.3 +/- 0.8 and 5.7 +/- 0.6 micrograms/ml, respectively. There was no difference between any hemodynamic parameter measured in these animals, compared with saline controls at any time during the infusion. We conclude that amrinone, but not N-acetylamrinone, causes pulmonary vasodilation in a porcine model of sepsis and that the parent drug is the sole active component in amrinone.

HPLC micromethod for amrinone and metabolites in patients receiving concurrent cephalosporin therapy.

Amrinone (AMR), a bipyridine derivative, is receiving increasing use in postoperative cardiac patients as an inotrope and vasodilator. The hemodynamic response to amrinone in adults is linearly related to AMR concentrations, warranting therapeutic drug monitoring. We report a rapid microsample HPLC method for monitoring AMR and its principal metabolites, N-acetyl (N-ac) and N-glycolyl (N-gly) AMR. Serum was precipitated with acetonitrile, and the supernatant fluid was then injected into a C18 narrow-bore column. The mobile phase consisted of a 0.1 mol/L sodium phosphate buffer (pH 6) with a gradient of acetonitrile going from 50 to 100 mL/L of eluent. Detection with a diode-array detector (DAD) concurrently monitored the absorbances at 320 and 345 nm. Monitoring 320 nm allows optimal quantification of AMR, N-gly, and N-ac. Patients often receive concurrent cephalosporin therapy, which is detectable at 320 nm but not 345 nm. Because cephalosporins coelute with AMR or metabolites, monitoring at 345 nm allows separation of these antibiotics from AMR and metabolites while retaining a detection limit of 0.5 mg/L.

Amrinone reverses bupivacaine-induced regional myocardial dysfunction.

Amrinone has been shown to have therapeutic effects on bupivacaine-induced cardiovascular toxicity, but its exact effects on the heart are not well understood. This study evaluated the regional myocardial effect of amrinone on bupivacaine-induced cardiovascular toxicity in in situ beating hearts in 10 dogs using a selective coronary perfusion and sonomicrometry. In the control group, bupivacaine was administered into the left anterior descending coronary artery (LAD) for 15 min at four steps: baseline, step 1, step 2 and step 3, (calculated LAD plasma concentrations; 0, 5, 5 and 10 mu g center dot ml-1, respectively). In the amrinone group, amrinone (5 mu g center dot ml-1) was simultaneously infused at steps 2 and 3 in addition to bupivacaine infusions. Regional myocardial function of the LAD supplied area was evaluated by analysis of the left ventricular pressure-segment length loop. In the control group, systolic shortening decreased from the baseline (10.5 +/- 1.3%, mean +/- SEM) to step 3 (0.1 +/- 1.3%), and post-systolic shortening increased from the baseline (18.0 +/- 3.7%) to step 3 (52.3 +/- 5.5%) dose-dependently. In contrast, with amrinone infusion at steps 2 and 3, both variables returned to near baseline values. These results indicate that amrinone reverses bupivacaine-induced regional myocardial dysfunction.

Beneficial effect of amrinone on murine cardiac allograft survival.

Amrinone is a non-glycoside positive inotropic agent with an inhibitory effect on a cyclic adenosine monophosphate (AMP) phosphodiesterase isoenzyme. In the present study, we examined the immunosuppressive action of amrinone, since several other cyclic AMP-elevating agents have been shown to suppress T lymphocyte activation. First, the in vivo effects of amrinone were investigated. Oral amrinone treatment, at 40 mg/kg per day, significantly prolonged median cardiac allograft survival compared with non-treated controls (22.0 days versus 10.5 days, P < 0.01) when DBA/2 mouse hearts (H-2d) were heterotopically transplanted into C57B1/6 mice (H-2b). Histopathological examination showed that there was less prominent cellular infiltration in the amrinone-treated than in the non-treated allografts. Plasma amrinone concentrations of mice after a single oral dose of 40 mg/kg were within the range of clinical relevance. To clarify the mechanism of action, in vitro studies were done. The generation of specific cytotoxic T lymphocytes after mixed lymphocyte culture was significantly suppressed by addition of amrinone to the culture medium at 5 micrograms/ml. The production of IL-2 and the interferon-gamma during mixed lymphocyte culture was also suppressed by amrinone at 5 micrograms/ml. However, the level of intracellular cyclic AMP in mouse splenic lymphocytes was not affected significantly by the same dose of amrinone. In conclusion, amrinone has immunosuppressive actions at the therapeutic doses, and it may be a beneficial agent for therapy against acute cardiac allograft rejection.

Amrinone loading during cardiopulmonary bypass in neonates, infants, and children.

OBJECTIVES: To determine whether amrinone is bound to cardiopulmonary bypass circuits. When amrinone is administered to children during cardiopulmonary bypass, determine whether measured amrinone concentrations differ from those predicted based on a reported volume of distribution of 1.6 L/kg. DESIGN: In vitro study: Uptake of amrinone by cardiopulmonary bypass circuits was determined. Clinical study: Prospective, open label investigation. SETTING: University-affiliated tertiary children's hospital. PARTICIPANTS: Clinical study: 27 children participated, including 5 neonates and 9 infants. INTERVENTIONS: In vitro study: Waste blood was circulated within seven pediatric cardiopulmonary circuits. Amrinone was administered, and blood was serially assayed for amrinone levels. Clinical study: Amrinone (mean dose 4.9 mg/kg) was loaded during cardiopulmonary bypass and amrinone concentrations in pump blood were determined at termination of bypass. Amrinone measured by high-performance liquid chromatography. MEASUREMENTS AND MAIN RESULTS: Cardiopulmonary bypass circuit uptake reduced amrinone concentrations to 79% of predicted. After correcting for circuit uptake, serum amrinone levels in patients were significantly higher than predicted. The levels, expressed in the ratio of measured: predicted amrinone concentration, did not differ among neonates, infants, and children older than 1 year of age. CONCLUSIONS: When amrinone is administered to children during cardiopulmonary bypass, about 20% of the dose becomes bound to the circuit. Available drug is distributed within a smaller volume than predicted. This may be the consequence of the physiologic perturbations of hypothermic cardiopulmonary bypass.

Elimination of amrinone during continuous veno-venous haemofiltration after cardiac surgery.

We studied the elimination of amrinone during continuous veno-venous haemofiltration (CVVHF) in three anuric patients after cardiac surgery. The patients had developed low cardiac output followed by acute prerenal failure. Plasma amrinone levels measured by HPLC were fitted to a two-compartment model. We found significant amrinone clearance, with a mean sieving coefficient (S) of 0.44%, which correlates with the protein-unbound, pharmacologically effective fraction of amrinone. The AUC of the arterial plasma concentration-time curve was decreased by 49.8%. All pharmacokinetic parameters showed wide interindividual variation. To ensure the therapeutic effect of amrinone and to avoid toxic adverse effects monitoring of plasma amrinone levels is necessary.

Effect of intracoronary infusions of amrinone and dobutamine on segment shortening, blood flow, and oxygen consumption in in situ canine hearts.

Previous in vivo studies assessing the effects of amrinone on myocardial contractility used intravenous infusions, and thus were complicated by varying cardiac loading conditions. Accordingly, the present study was performed in 15 open-chest, anesthetized (fentanyl and midazolam) dogs using infusions of amrinone and dobutamine directly into the left anterior descending artery (LAD). In the LAD bed, percentage of segment shortening (%SS), an index of local myocardial contractility, was assessed with ultrasonic crystals. Coronary blood flow was measured electromagnetically and used to calculate myocardial oxygen consumption and infused drug concentrations. Amrinone and dobutamine were infused separately into the LAD at rates yielding calculated arterial blood concentrations in the clinical range (100, 150, and 200 micrograms/min, and 2.5, 5.0, and 7.5 micrograms/min, respectively). A mixture of amrinone and dobutamine was also infused into LAD and changes in %SS compared with the sum of the their individual effects. In six of the dogs, an extracorporeal system was used to maintain constant coronary blood flow during amrinone infusions. Amrinone and dobutamine caused individually increases in %SS that were comparable (range, 20%-45%). Myocardial oxygen consumption increased in parallel with %SS for both amrinone and dobutamine. For amrinone, coronary blood flow increased more than myocardial oxygen consumption, resulting in a modest (at highest dose approximately 10%) decrease in oxygen extraction; whereas for dobutamine, coronary blood flow increased in proportion to myocardial oxygen consumption, resulting in no change in oxygen extraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermogenic effect of amrinone in healthy men.

OBJECTIVES: The thermogenic effect of amrinone is unknown and its utilization in patients with severe cardiac failure could potentially increase oxygen requirements and therefore aggravate oxygen debt. Consequently, the present study was undertaken to assess the thermogenic response to amrinone at three different plasma concentrations under controlled conditions and to analyze amrinone's effects on various biochemical variables. DESIGN: A prospective, unblinded, controlled study. The initial control period was followed by three sequential, experimental treatments. SUBJECTS: Ten young, healthy, male volunteers with normal body weight. INTERVENTIONS: Three experimental periods. Amrinone was administered intravenously in progressive doses: a) 0.5 mg/kg followed by 5 micrograms/kg/min; b) 0.5 mg/kg followed by 10 micrograms/kg/min; and c) 1.0 mg/kg followed by 10 micrograms/kg/min. MEASUREMENTS AND MAIN RESULTS: Oxygen consumption (VO2) and CO2 production were continuously measured by means of a computerized indirect calorimeter. At the highest dose, amrinone produced a slight and significant (p < .01) increase in VO2 and in resting metabolic rate (+4.5% and +3.7%, respectively), while no change in CO2 production or in respiratory quotient occurred throughout the study. At the medium and high doses, amrinone increased plasma free fatty acid concentrations by 38% and 53%, respectively (p < .05). No variation in plasma glucose, lactate, insulin, norepinephrine, or epinephrine concentrations was observed during the study. CONCLUSIONS: Amrinone administered intravenously at therapeutic doses has minimal thermogenic and metabolic effects in humans without cardiac failure.

Amrinone and N-acetylamrinone assay in human plasma using solid-phase extraction and reversed-phase chromatography.

A simple and sensitive liquid chromatographic assay for simultaneous quantitation of amrinone and N-acetylamrinone in human plasma was developed. The method involves extraction of samples via activated solid-phase extraction Bond Elut C18 disposable columns, followed by chromatographic separation on a reversed-phase phenyl column using isocratic condition and UV detection. The assay can measure concentrations of both compounds over the range 0.075-10 micrograms ml-1. The injection interval is 11 min. The inter-day relative standard deviation (RSD) for replicate analysis of spiked samples is less than 10% and the accuracy more than 94% for both compounds over the standard curve range. The assay has been successfully applied to pharmacokinetic studies in humans.

Effect of continuous arteriovenous haemofiltration on pharmacokinetics of amrinone.

This case report details the pharmacokinetic adjustments of an amrinone infusion in a paediatric patient who developed multiorgan system failure with anuric renal failure and was prescribed continuous arteriovenous haemofiltration. A significant proportion of clearance of amrinone is nonrenal. Near normal amrinone clearance can occur in patients with hepatic and renal dysfunction if continuous arteriovenous haemofiltration is used. Hepatic dysfunction with renal failure may require a reduction in the continuous amrinone infusion rate as previously reported for neonates.

Amrinone-associated thrombocytopenia: pharmacokinetic analysis.

Amrinone-associated thrombocytopenia is thought to result from nonimmune-mediated peripheral platelet destruction. Platelet destruction may be a concentration-dependent toxic effect of amrinone or its principal metabolite N-acetylamrinone. Eighteen children receiving amrinone after heart surgery were prospectively evaluated to correlate the pharmacokinetics of amrinone and N-acetylamrinone with thrombocytopenia. Amrinone and N-acetylamrinone plasma concentrations were determined by HPLC during loading, infusion, and terminal elimination, with concurrent monitoring of platelet counts. Thrombocytopenia developed in eight patients (platelet count, 66 +/- 17 x 10(9) platelets/L [mean +/- SD]). Peak and steady-state amrinone plasma concentration, amrinone total dose, duration of amrinone exposure, and amrinone area under curve (AUC) were similar between patients with and without thrombocytopenia. N-Acetylamrinone peak concentration, steady-state concentration, N-acetylamrinone AUC, and ratio of N-acetylamrinone to amrinone were greater in patients with thrombocytopenia. This association suggests that N-acetylamrinone, and not amrinone, may be the mediator of thrombocytopenia in children receiving amrinone.

Pharmacokinetics of amrinone during cardiac surgery.

Amrinone is a nonglycosidic noncatecholamine with both vasodilator and positive inotropic effects that may be administered to patients undergoing cardiac surgery. As an initial step toward elucidating the optimal dosage of amrinone for cardiac surgical patients we studied the pharmacokinetics of amrinone during and after cardiac surgery requiring cardiopulmonary bypass. The study population comprised 35 adult patients, each receiving a single dose of amrinone (0.75, 1.5, 2.0, or 2.5 mg/kg) administered into the venous reservoir near the end of cardiopulmonary bypass. Additionally, 15 of the 35 patients also received intravenous infusions of either 5 or 10 micrograms.kg-1.min-1. Arterial blood was sampled over the next 22 h, and plasma concentrations of amrinone were determined by high-performance liquid chromatography. Protein binding of amrinone, assayed by equilibrium dialysis, was 21.6 +/- 2.5%. The decay of amrinone concentrations in plasma over time was fit to a biexponential equation by nonlinear least-squares regression. The manufacturer's recommended dose of 0.75 mg/kg followed by an infusion of 10 micrograms.kg-1.min-1 was inadequate to maintain the plasma concentration within the therapeutic range based on the pharmacodynamics of amrinone in patients with chronic congestive heart failure. This was due to significant redistribution of amrinone in the body after the loading dose. To maintain a therapeutic plasma concentration of 1.5-2.0 micrograms/ml, a larger loading dose or a supplemental loading dose as well as a continuous infusion is required.