Failure of naloxone to reverse the cardiotoxocity of Distalgesic overdose

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.

Marked QRS complex abnormalities and sodium channel blockade by propoxyphene reversed with lidocaine

The opiate analgesic propoxyphene produces cardiac toxicity when taken in overdose. We recently observed a patient with propoxyphene overdose in whom marked QRS widening was reversed by lidocaine. The reversal is apparently paradoxical as both agents block the inward sodium current (INa). We examined possible mechanisms of the reversal by measuring INa in rabbit atrial myocytes during exposure to propoxyphene and the combination of propoxyphene and lidocaine (60 and 80 microM, respectively). Propoxyphene caused use-dependent block of INa during pulse train stimulation. Block recovered slowly with time constants of 20.8 +/- 3.9 s. Block during lidocaine exposure recovered with time constants of 2-3 s. During exposure to the mixture, block recovered as a double exponential. The half time for recovery during exposure to the mixture was 1.6 +/- .9 s compared with a half-time of 14.3 +/- 2.9 s during exposure to propoxyphene alone. During pulse train stimulation, less steady-state block was observed during exposure to the mixture than during exposure to propoxyphene alone when the interval between pulses was greater than 0.95 s. Both drugs compete for a common receptor during the polarizing phase. The more rapid dissociation of lidocaine during the recovery period leads to less block during the mixture than during exposure to propoxyphene alone. The experiments suggest a mechanism for reversal of the cardiac toxicity of drugs which have slow unbinding kinetics.

Dextropropoxyphene overdose. Epidemiology, clinical presentation and management

This paper comprehensively reviews the worldwide situation regarding acute overdosage of dextropropoxyphene (propoxyphene). The changing epidemiology of this type of poisoning over the last 20 years is described with discussion of concurrent trends and, in particular, the effects of different preventive measures adopted in various countries. The clinical pharmacology of dextropropoxyphene relevant to the clinical toxic effects resulting from acute overdosage is described, and the management is detailed. In particular, the importance of early diagnosis and treatment is stressed in view of the potentially lethal complications that may suddenly occur with this poisoning. Recommendations for the correct use of the specific narcotic antagonist, naloxone, are made, together with other intensive supportive measures. As dextropropoxyphene is frequently taken together with other toxic agents, the concomitant effects of alcohol and sedative drugs are described and the treatment of paracetamol (acetaminophen) in combination with dextropropoxyphene is emphasised. The most effective preventive measures for the future are suggested, but caution is advised regarding the prescription for 'at risk' patients of alternative analgesics, which may be no safer in overdosage.

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.

Ethanol does not increase lethality due to propoxyphene in rats

Male Wistar rats (210-330 g) were used as test animals. Propoxyphene (175 mg/kg) and ethanol (2 g/kg) were administered by gastric intubation, naloxone (2 mg/kg) by subcutaneous injection. Four groups, each consisting of 19 rats received either of the following drug treatments: Propoxyphene; ethanol + propoxyphene; naloxone + propoxyphene; and naloxone + ethanol + propoxyphene. The drugs were given in the sequence mentioned at the beginning of the experiment. Naloxone was also given 45 and 90 min later. Mortality was reduced to 42% in the group that received ethanol and propoxyphene as compared to 73% in the group that received propoxyphene only. Naloxone protected against lethality in both groups. A rise in the propoxyphene/norpropoxyphene (P/N) ratio due to an increase in the absolute concentrations of propoxyphene and a decrease in the absolute levels of norpropoxyphene in blood, brain and heart tissues was observed in the ethanol + propoxyphene group, compared to the propoxyphene group. Although these pharmacokinetic data indicate impaired propoxyphene metabolism in the presence of ethanol, ethanol did not enhance propoxyphene induced lethality. This is also contrary to suggestions from previous studies. Our results demonstrate that at least in one species and at one dose ratio (ethanol/propoxyphene) ethanol might reduce the lethality caused by propoxyphene alone. This suggests antagonism between the two drugs, probably in the central nervous system.

Lack of evidence of increased lethality due to propoxyphene overdose in the presence of ethanol in male Wistar rats

The primary purpose of the present investigation was to evaluate if the presence of ethanol increased lethality induced by propoxyphene. A secondary aim was to study the effect of naloxone on propoxyphene lethality alone, and on the concomitant administration of propoxyphene and ethanol. Male Wistar rats (210-330 g) were used as test animals. Propoxyphene (175 mg/kg) and ethanol (2 g/kg) were administered by gastric intubation, naloxone (2 mg/kg) by subcutaneous injection. Four groups, each consisting of 19 rats, received either of the following drug treatments: Propoxyphene, ethanol + propoxyphene, naloxone + propoxyphene, and naloxone + ethanol + propoxyphene respectively. The drugs were given in the sequence mentioned at the beginning of the experiment. Naloxone was also given 45 and 90 min later. Mortality was reduced to 42% in the group that received ethanol and propoxyphene compared to 73% in the group that received propoxyphene only. Naloxone protected against lethality in both groups. Some animals died despite naloxone administration, possibly due to a nonopioid cardiotoxic effect of propoxyphene or its metabolite. An increase in the propoxyphene/norpropoxyphene (P/N) ratio due to an increase in the absolute concentrations of propoxyphene and a decrease in the absolute levels of norpropoxyphene in blood, brain, and heart tissues was observed in the ethanol + propoxyphene group, compared to the propoxyphene group. In the animals which died, the highest P/N ratio was observed in brain tissue and the lowest in heart muscle. Despite the pharmacokinetic data obtained in this investigation indicating impaired propoxyphene metabolism in the presence of ethanol, ethanol did not enhance propoxyphene-induced lethality.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute propoxyphene self-poisoning in 222 consecutive patients

The course of severe propoxyphene self-poisoning in 222 consecutive patients is presented. On admission, 73% of the patients had neurological symptoms, 10% had convulsions, 45% were in respiratory failure, and impaired circulation was present in 48%. A mortality rate of 8% was observed. Twelve patients arrived in asystole of whom six were resuscitated without sequelae. The overdose was accidental in 13 patients, one of whom died. Early medical intensive care was found mandatory for a good prognosis. Before discharge from the ICU we recommend an observation-period free of cardiovascular symptoms for 24 h.

Clinical features and management of Distalgesic overdose

'In our experience Distalgesic seems to have superseded barbiturates as the ingested agent principally responsible for deaths from self-poisoning and also as the drug that most often necessitates urgent resuscitation in poisoned patients.'

Dextropropoxyphene overdosage. Pharmacological considerations and clinical management

Dextropropoxyphene is a widely prescribed synthetic opiate-like drug of uncertain analgesic efficacy which, in acute overdosage, manifests all the features of opiate toxicity. It is rapidly absorbed and, in association with other central nervous system depressants such as alcohol or benzodiazepine drugs, may be rapidly fatal. Seriously overdosed patients are comatose with respiratory depression, vomiting, seizures and circulatory collapse; small pupils are a useful diagnostic marker. The first priority is to establish the airway and treat convulsions, if present. All the features of overdosage are then rapidly and safely reversed by the specific opiate antagonist naloxone given intravenously. High tissue concentrations and slow elimination of dextropropoxyphene metabolites make continued and intensive monitoring after resuscitation essential because sudden unpredictable deterioration may occur for up to 24 hours. Other more slowly toxic co-ingestants such as paracetamol (acetaminophen) are often present and should be detected and treated as necessary. Dextropropoxyphene poisoning is now probably one of the most common causes of self-poisoning death because, although there is an effective antidote, subjects frequently succumb before treatment can be made available.