Circulatory shock following intravenous propoxyphene poisoning. An experimental study of cardiac function and metabolism in pentobarbital-anesthetized pigs

Membrane toxicity of opioids measured by protozoan motility

The acute toxicity of some opioid drugs cannot solely be explained by a specific interaction with the opioid receptor. The anaesthetic-like membrane effect of 10 opioid agents and the antagonist naloxone was determined and correlated with their hydrophobicity. The inhibitory effect of drugs on protozoan motility was used as a measure of their membrane toxicity, measured by the reduction in swimming speed of Tetrahymena pyriformis using an image analysis system. Hydrophobicity was determined as the n-octanol/water partition coefficient, at pH 7.4, 37 degrees C. Opioid agents dose-dependently reduced the swimming speed of Tetrahymena pyriformis with a wide range of IC50 values. Some weak opioid agents were shown to have high protozoan immobilising potency comparable to quinidine, an agent with known membrane stabilising activity. Norpropoxyphene, the metabolite of dextropropoxyphene, with little affinity for the opioid receptor, also had a high potency. The inhibition of protozoan motility by these opioid agents was not antagonised by the opioid receptor antagonist naloxone; moreover an additive inhibitory action was demonstrated when opioid agents were combined with naloxone. The effect of opioid agents on protozoan motility was closely correlated with their partition coefficient but not with their known affinity for opioid receptors. These results suggest that opioid agents possess differing degrees of membrane depressant action independent from their interaction with the opioid receptor, and have a potential for causing depressant effects on excitable tissues.

Methadone block of K+ current in squid giant fiber lobe neurons

Voltage-dependent ionic currents were recorded from squid giant fiber lobe neurons using the whole-cell patch-clamp technique. When applied to the bathing solution, methadone was found to block IK, I Na and I Ca. Both I Na and I Ca were reduced without apparent change in kinetics and exhibited IC(50)'s of 50-100 and 250-500 mu M, respectively, at +10 mV. In contrast, IK was reduced in a time-dependent manner that is well fit by a simple model of open channel block (K(D)= 32+/- or 2 mu M, +60 mV, 10 degrees Celsius). The mechanism of I(K) block was examined in detail and involves a direct action of methadone, a tertiary amine, on K channels rather than an opioid receptor-mediated pathway. The kinetics of I(K) block resemble those reported for internally applied long chain quaternary ammonium (QA) compounds; and recovery from I(K) block is QA-like in its slow time course and strong dependence on holding potential. A quaternary derivative of methadone (N-methyl-methadone) only reproduced the effects of methadone on I(K) when included in the pipette solution; this compound was without effect when applied externally. I(K) block thus appears to involve diffusion of methadone into the cytoplasm and occlusion of the open K channel at the internal QA blocking site by the protonated form of the drug. This proposed mode of action is supported by the pH and voltage dependence of block as well as by the observation that high external K+ speeds the rate of drug dissociation. In addition, the effect of methadone on I(K) evoked during prolonged (300 ms) depolarizations suggests that methadone block may interfere with endogenous K+ channel inactivation. The effects of temperature, methadone stereoisomers, and the methadone-like drugs propoxyphene and nor-propoxyphene on IK block were examined. Methadone was also found to block I(K) in GH3 cells and in chick myoblasts.

Adverse cardiac manifestations following dextropropoxyphene overdose: can naloxone be helpful?

Dextropropoxyphene overdose may be complicated by serious cardiovascular manifestations, including conduction abnormalities and collapse. We report two patients in whom cardiac toxicity developed. Cardiovascular depression seemed to be improved after naloxone infusion in these two cases. Possible mechanisms are briefly discussed.

Propoxyphene-induced wide QRS complex dysrhythmia responsive to sodium bicarbonate--a case report

Propoxyphene overdose is known to cause widening of the QRS complex on ECG. We report a case of a 54-year-old female who ingested approximately 100 propoxyphene hydrochloride tablets in a suicide attempt. She developed a wide complex dysrhythmia which responded to sodium bicarbonate therapy. Propoxyphene-induced wide complex dysrhythmia responsive to sodium bicarbonate therapy has not been previously reported in the literature.

Dopamine and dobutamine reduce myocardial d-propoxyphene content in experimentally intoxicated rats

The effect of sympathomimetic intervention with dopamine or dobutamine on the myocardial uptake of d-propoxyphene was investigated experimentally in rats. The d-propoxyphene (19 mg kg-1 h-1) was continuously infused, intravenously, over 45 min. After 20 min of infusion the rats were given either dopamine (12.5 micrograms kg-1 min-1 or 25 micrograms kg-1 min-1), dobutamine (25 micrograms kg-1 min-1 or 45 micrograms kg-1 min-1) or normal saline (control). Each group consisted of eight rats. The myocardial d-propoxyphene content was significantly lower in the two groups given dopamine and in the group given dobutamine 45 micrograms kg-1 min-1 than in the control group (P less than 0.05). This finding indicates the benefit of early sympathomimetic intervention with either dopamine or dobutamine in d-propoxyphene intoxication.

Cardiovascular function measured by ultrasound Doppler in healthy young men after ingestion of dextropropoxyphene napsylat

In a double blind cross-over study 10 healthy male volunteers were given either 300 mg dextropropoxyphene napsylat (DP) or placebo daily for 16 days. The serum levels of DP and the metabolite nordextropropoxyphene were measured on day 3, 6 and 16. Haemodynamic measurements were made on day 1 and day 16, both at rest and during exercise. The measurements were made non-invasively, with a pulsed ultrasound Doppler. Blood pressure, heart rate, velocity, cardiac output, left cardiac work, increased during work, but showing no significant differences between the groups. The systolic time intervals were also measured by the ultrasound Doppler. The preejection period increased significantly in the DP-group, whereas the ratio preejection period/left ventricular ejection time which reflects the contractility of the heart did not differ significantly. It is concluded that DP taken daily in a normal dose for 16 days did not affect the heart function in healthy young men.

Effects of prenalterol on central hemodynamics and myocardial metabolism in experimental propoxyphene-induced shock

The hemodynamic and cardiometabolic effects of prenalterol were evaluated in propoxyphene-induced circulatory shock in 10 pentobarbital-anesthetized pigs. Circulatory shock (i.e. a systolic arterial blood pressure below 60 mmHg (8 kPa) and/or a cardiac index of less than 2.0 1 X min-1 X m-2) was induced by intravenous propoxyphene chloride 15 mg X min-1. Circulatory shock occurred after 26 +/- 3 mg X kg-1 of propoxyphene. During continuous infusion of propoxyphene, consecutive doses of prenalterol 0.5, 1.0, 2.0 and 4.0 mg i.v. were injected with an interval between increments of 8 min. The maximum effect of prenalterol was seen following the 2 mg dose. Increases were observed in mean arterial blood pressure, cardiac index, stroke volume index, left ventricular stroke work index, right ventricular stroke work index, maximum rate of rise of ventricular pressure, and total body oxygen consumption. Decreases were observed in pulmonary artery occlusion pressure, mean right atrial pressure and systemic vascular resistance, whereas heart rate and pulmonary vascular resistance remained unchanged. The cardiometabolic parameters: coronary sinus flow, coronary vascular resistance, myocardial oxygen consumption and extraction, remained low. Due to profound vasodilation, normal perfusion pressures were not reestablished. In conclusion, prenalterol improved cardiac performance by a significant positive inotropic action. However, pure inotropic stimulation was not sufficient to counteract the circulatory shock state during severe propoxyphene intoxication.

Severe acute propoxyphene overdose: plasma concentrations of propoxyphene and norpropoxyphene and the effect of dopamine on circulatory failure

Twelve patients with cardiovascular failure because of propoxyphene self-poisoning were treated with dopamine. The patients responded favourably to dopamine infusion (2-17 micrograms/kg/min) with a dose-dependent rise in systolic arterial blood pressure and a fall in central venous pressure and copious urinary output. Side effects during infusion were few, and in periods where dopamine infusion exceeded 10 micrograms/kg/min no tachyarrhythmias were seen. Eleven of the patients were treated on a respirator. Two patients were discharged from the ICU with signs of hypoxic brain damage, one of whom recovered completely after 2 weeks. Serum propoxyphene and norpropoxyphene were measured in nine patients. All but one patient had either propoxyphene or norpropoxyphene concentrations above 3 mumol/l.

The effects of naloxone on central hemodynamics and myocardial metabolism in experimental propoxyphene-induced circulatory shock

The courses of the hemodynamic and cardiometabolic effects of naloxone were evaluated in propoxyphene-induced shock in eight pentobarbital-anesthetized pigs. Circulatory shock was induced by an infusion of propoxyphene chloride 15 mg . min-1 i.v. At shock, i.e. MAP less than 60 mmHg and/or CI less than 2.0 l . min-1 . m-2, naloxone was administered at 0.75, 1.5 and 3.0 mg . kg-1 with an interval between increments of 8 min. The propoxyphene infusion of 15 mg . min-1 was continued throughout the study. Following the injection of naloxone 0.75 mg . kg-1, increases were observed (% of baseline value) in MAP (41%), i.e. deficit to baseline 59%, HR (66%), CI (67%) and SVI (108%), whereas MPAP and MPAOP were unchanged. dP/dt increased (34%). In the coronary circulation naloxone initiated the following changes: CSF increased (69%) as did MVO2 (48%) with unchanged MO2-extraction, but CVR decreased further (36%). The maximum effects of naloxone were registered 2-3 min after 0.75 mg . kg-1. Following 1.5 and 3.0 mg . kg-1, no changes in hemodynamics were observed other than those caused by progressing propoxyphene intoxication.

The effects of cardiac pacing on central hemodynamics in experimental propoxyphene-induced cardiac failure

Coronary sinus pacing was evaluated in 10 pigs during propoxyphene-induced cardiac failure. From baseline, propoxyphene chloride 15 mg . min-1 was infused until circulatory shock developed. Cardiac pacing was evaluated at different dose levels expressed as % of the shock dose of propoxyphene: at intoxication levels below 50% of the shock dose, cardiac pacing improved cardiac performance. At dose levels above 50% of the shock dose cardiac performance deteriorated further during pacing. The results are consistent with a severe negative inotropic effect of propoxyphene in overdose.

The effects of dopamine on central hemodynamics and myocardial metabolism in experimental propoxyphene-induced shock

The hemodynamic and cardiometabolic effects of dopamine were evaluated in propoxyphene-induced circulatory shock in eight pentobarbital anesthetized pigs. Circulatory shock was induced by an infusion of propoxyphene chloride 15 mg . min-1 i.v. At shock, i.e. CI less than or equal to 2.0 l . min-1 . m-2 and/or MAP less than or equal to 60 mmHg, dopamine was infused at 10, 20, 40, 80 and 160 micrograms . kg-1 . min-1 with an interval between increments of 8 min. After 30 min at 160 micrograms . kg-1 . min-1, the infusion rate was reversibly decreased. The propoxyphene infusion of 15 mg . min-1 was continued throughout the study. Dopamine improved the circulation in seven animals; one animal died in refractory shock during dopamine infusion. Dopamine infusion at shock level resulted in an increase of the following variables (% of baseline value): MAP (69%), HR (109%), CI (138%) and SVI (129%). Normalisation was seen in MRAP (120%) and in MPAOP (100%). A profound decrease in systemic vascular resistance was unchanged. Increases were seen in left and right ventricular stroke work index, to 88% and 176% of baseline, respectively. Left ventricular dP/dt increased (170%). In the coronary circulation myocardial blood flow increased (133%) as did myocardial oxygen consumption (65%) concomitant with a decrease in myocardial oxygen uptake (41%), but coronary vascular resistance progressively decreased (38%). The myocardial propoxyphene extraction changed from +54% to -86% during peak dopamine infusion. In conclusion, dopamine reversed cardiac failure in propoxyphene overdose by a marked positive inotropic stimulation restoring contractility. A marked positive chronotropic stimulation maintained a sufficient cardiac index and a normal blood pressure in spite of a profound vasodilatation which was unresponsive to dopamine.

Severe, acute propoxyphene overdose treated with dopamine

Six patients suffering from cardiovascular failure due to acute propoxyphene overdose, were treated with dopamine infusion in doses of 2-17 microgram/kg/min. All patients responded with increased systolic arterial blood pressure, increased urinary output and decreased central venous pressure. The two most severely poisoned patients showed no increase in heart rate in spite of dopamine infusion in positively chronotropic doses. In two out of three patients the initially abnormal ECGs normalised during treatment. It is concluded that dopamine seems suitable for reversal of propoxyphene induced circulatory failure.

Cardiac pacing and central hemodynamics in experimental propoxyphene induced shock

Coronary sinus pacing was evaluated in 10 pigs with propoxyphene induced cardiac failure. During the early phase of intoxication cardiac pacing improved cardiac function slightly but significantly worsened it in severely intoxicated animals. The results are consistent with marked negative inotropic action of propoxyphene in overdose.