Dangers of dextropropoxyphene.
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Biomedical subjects
Publications and source records attributed to P Crome.
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Charcoal haemoperfusion used to treat a 56-year-old woman who had taken a very large overdose of meprobamate was followed by fully recovery. The plasma clearance of meprobamate was 153 ml/min and this compares favourably with values obtained for haemodialysis. The indications for haemoperfusion are reviewed.
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30 patients at risk of hepatic damage from paracetamol (acetaminophen) ingestion were given 2-5 g oral methionine every four hours up to a total dose of 10 g. The first dose was given within ten hours of the overdose. There were no deaths and no reports of hepatic encephalopathy or other complications. In 21 patients plasma aspartate-aminotransferase remained within normal limits. These results suggest that methionine may be effective in reducing the frequency and severity of paracetamol-induced liver damage and may provide an effective non-toxic alternative to cysteamine.
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Tricyclic antidepressants are among the commonest causes of both non-fatal and fatal drug poisoning in the world. Their toxicity is due to effects on the brain, the heart, the respiratory system and the parasympathetic nervous system. Symptoms usually appear within 4 hours of an overdose and all but the most seriously poisoned patients recover within 24 hours. The most common clinical features are dry mouth, blurred vision, dilated pupils, sinus tachycardia, pyramidal neurological signs, and drowsiness. In severe poisoning, there may be coma, convulsions, respiratory depression, hypotension and a wide range of electrocardiographic (ECG) abnormalities. The most frequent findings on the ECG are prolongation of the PR and QT intervals; the tracing may resemble bundle branch block or supraventricular or ventricular tachycardias. Treatment of poisoning due to the tricyclic antidepressants is essentially supportive, there being insufficient evidence at present to recommend the use of methods to increase elimination of the drug from the body. Gastric aspiration and lavage should be performed if more than 750 mg of drug have been taken. There must be regular monitoring for hypoxia, acidosis and hypokalaemia and these complications should be corrected enthusiastically. Convulsions should be treated with diazepam or chlormethiazole. Muscular paralysis and artificial ventilation should be employed if anticonvulsants are ineffective. Hypotension should be treated firstly by fluid replacement and then with sympathomimetic agents (dopamine or dobutamine). Antiarrhythmic drugs should only be employed if there is evidence of circulatory failure which fails to respond to correction of hypotension. Sodium bicarbonate infusions should be given to cardiotoxic patients who are acidotic and are worth trying even if the patient is not acidotic. Although physostigmine salicylate will reverse most of the features of tricyclic antidepressant poisoning, its effects are short-lived in serious toxicity and it can produce dangerous side effects; physostigmine should therefore be reserved for those patients who have complications of coma or who have resistant cardiotoxicity or convulsions. Drug screening and quantitative determination of tricyclic antidepressant serum concentrations are useful in a minority of patients who have severe, unusual or prolonged symptoms.
Over the last decade a number of antidepressants have been introduced which differ either chemically, pharmacologically or toxicologically from established tricyclic and monoamine oxidase drugs. Of those presently available, maprotiline is similar in toxicity to tricyclic antidepressants perhaps causing convulsions more frequently. Lofepramine is metabolised to desmethylimipramine, but the limited clinical experience so far suggests that toxicity is less severe than with other tricyclic antidepressants. Amoxapine causes coma, convulsions and less frequently renal failure, but electrocardiographic abnormalities are uncommon. Mianserin and trazodone both cause drowsiness and more infrequently deeper grades of coma. Alprazolam produces the typical benzodiazepine overdose symptoms of drowsiness and floppiness. There is as yet insufficient clinical data to comment on the specific toxicity of fluoxetine and fluvoxamine. There are many more new antidepressants in various stages of development and it is likely that several of these will be marketed. Since their individual toxicities differ it is essential that monitoring of their overdose effects should be undertaken.
Healthy elderly people aged 70 or more should receive a starting dosage of the anxiolytic drug suriclone half that recommended for younger people; frail or ill elderly people may require further dosage reduction. These conclusions were based on a study of the pharmacokinetics and tolerability of orally administered suriclone after a single dose of 0.2mg and after multiple doses of 0.2mg 3-times daily in 8 male and 8 female healthy elderly volunteers. Informal comparisons of the pharmacokinetic data from this study with studies in younger volunteers showed a 53% decrease in clearance and an 84% increase in elimination half-life. Area under the plasma concentration-time curve (AUC) for suriclone and total antigenic products in the elderly were twice the values in younger volunteers when adjusted for different dosage. There were no significant changes in pulse rate or blood pressure during the study. One person showed a change from sinus rhythm to atrial fibrillation. Six people had transient adverse events including unsteadiness, vomiting, difficulty in reaching for objects, urinary incontinence and sedation.
A single oral dose of 75mg nortriptyline was given to a group of 20 depressed elderly patients in hospital. Subsequent plasma nortriptyline concentrations were used to calculate the half-life and clearance of the drug. These measurements were compared with those made previously in 17 healthy young volunteer subjects. Plasma nortriptyline half-life was longer and clearance slower (p < 0.002) in the elderly group than in the volunteers. There was no correlation of age with either of these parameters within the 2 groups, and no differences in nortriptyline pharmacokinetics could be detected between the male and female volunteer subjects. The possible reasons for these findings and their clinical consequences are discussed.
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