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Biomedical subjects

L F Prescott

Publications and source records attributed to L F Prescott.

At least 109 records · Page 6Linked to original sources
PubMed1980

Mefenamic acid nephropathy.

Non-oliguric renal failure developed in six elderly women who had been prescribed 1--2 g of mefenamic acid daily for 2--6 weeks for the relief of musculoskeletal pain.

Aged↗
PubMed1980

Paracetamol pharmacokinetics in thyroid disease.

The absorption, distribution and elimination of oral paracetamol have been studied in patients before and after treatment of thyrotoxicosis (n = 7) and hypothyroidism (n = 4). Absorption was faster in patients with untreated thyrotoxicosis than when subsequently euthyroid. The peak paracetamol concentration, however, was lower in thyrotoxic patients due to an apparent increase in the total body clearance and a shorter plasma half-life. Both absorption and elimination rates were reduced in hypothyroid patients, but were not significantly different from the euthyroid results. When estimated using a two compartment model the total volume of distribution and the hybrid distribution rate constants were unrelated to thyroid status, but the apparent volume of the central compartment was significantly greater in the thyrotoxic group. These changes in drug disposition may contribute to differences in drug response seen in thyroid disease.

Acetaminophen↗
PubMed1980

Failure of alkaline diuresis to enhance diflunisal elimination.

1 The effects of alkaline diuresis on the elimination of a single oral dose of 750 mg diflunisal were studied in six healthy male volunteers. 2 The plasma concentrations and half-life of diflunisal were not reduced by alkaline diuresis. 3 The 72 h urinary recovery of unchanged diflunisal was more than doubled with alkaline diuresis, but even so, only 5-7% of the administered dose was excreted unchanged. 4 With alkaline diuresis there was a significant increase in the mean renal clearance of diflunisal from 0.27 to 0.46 ml/min, but there was no significant correlation between the renal clearance of diflunisal and urine flow or pH. 5 However, there was a significant increase in the overall mean renal clearance of diflunisal from 0.22 ml/min over the period 0-24 h to 0.73 ml/min from 48-72 h. 6 Forced alkaline diuresis is unlikely to be of value in diflunisal poisoning.

Adult↗
PubMed1980

Kinetics and metabolism of paracetamol and phenacetin.

1 The rate of absorption of oral paracetamol depends on the rate of gastric emptying and is usually rapid and complete. The mean systemic availability is about 75%. 2 Paracetamol is extensively metabolized and the plasma half-life is 1.5-2.5 hours. About 55% and 30% of a therapeutic dose is excreted in the urine as glucuronide and sulphate conjugates, respectively, whereas mercapturic acid and cysteine conjugates (representing conversion to a potentially toxic intermediate metabolite) each account for some 4% of the dose. Paracetamol metabolism is age- and dose-dependent. 3 With hepatotoxic doses, paracetamol metabolism is impaired and the half-life prolonged. Sulphate conjugation is saturated and the proportion excreted as mercapturic acid and cysteine conjugates is increased. 4 The renal clearance of paracetamol depends on urine flow rate by not pH. The renal clearances of the glucuronide and sulphate conjugates often exceed the glomerular filtration rate and are independent of urine flow and pH. 5 Phenacetin absorption depends on formulation. It is extensively metabolized to paracetamol and minor metabolites are probably responsible for toxicity.

Acetaminophen↗
PubMed1980

Hepatotoxicity of mild analgesics.

1 Hepatotoxicity is rare when mild analgesics are used in normal therapeutic doses. 2 The potential of aspirin and salicylates to cause hepatotoxicity has been only recently recognized. 3 Salicylate hepatitis is often asymptomatic, and may only be revealed by finding elevated levels of aminotransferases. 4 Most cases have occurred in children or young adults with connective tissue diseases, who take high doses of salicylates for long periods. 5 Hepatic injury is not recognized as a complication of acute aspirin poisoning. 6 Following overdosage of paracetamol, a toxic intermediate metabolite causes acute hepatic necrosis which may be fatal. 7 Cysteamine, methionine and N-acetylcysteine confer protection against this severe liver damage, but the time between overdosage and treatment is critical. 8 The chronic therapeutic use of paracetamol should be considered a potential but very rare cause of active chronic hepatitis. 9 There is no clear evidence of phenacetin hepatotoxicity in man. 10 Phenylbutazone may cause liver injury and other analgesics can cause hypersensitivity reactions in which the liver is involved.

Acetaminophen↗
PubMed1979

Intravenous N-acetylcystine: the treatment of choice for paracetamol poisoning.

One hundred cases of severe paracetamol poisoning were treated with intravenous N-acetylcysteine (acetyl-cysteine). There was virtually complete protection against liver damage in 40 patients treated within eight hours after ingestion (mean maximum serum alanine transaminase activity 27 IU/1). Only one out of 62 patients treated within 10 hours developed severe liver damage compared with 33 out of 57 patients (58%) studied retrospectively who received supportive treatment alone. Early treatment and acetylcysteine also prevented renal impairment and death. The critical ingestion-treatment interval for complete protection against severe liver damage was eight hours. Efficacy diminished progressively thereafter, and treatment after 15 hours was completely ineffective. Intravenous acetylcysteine was more effective than cysteamine and methionine and noticeably free of adverse effects. It is the treatment of choice for paracetamol poisoning.

Acetaminophen↗
PubMed1979

Effect of gel fibre on gastric emptying and absorption of glucose and paracetamol.

To determine the part played by altered gastric emptying in the modification of glucose absorption by gel fibres, glucose tolerance tests were done in seven healthy volunteers with and without the addition of pectin to the ingested glucose solution and after pharmacological inhibition of gastric emptying with propantheline. Compared with the controls, pectin significantly reduced blood-glucose. Propantheline had a similar but more pronounced effect. Pectin and guar gum did not substantially alter glucose tolerance in a patient who had had total gastrectomy. In a further investigation, gastric emptying and paracetamol absorption were studied simultaneously in fourteen subjects. In eight of these the study was repeated after addition of guar gum and pectin to the ingested paracetamol. Both gastric emptying and paracetamol absorption were slower after gel fibre but the total absorption of the drug, reflected in urinary recovery, was not significantly reduced. The results suggest that the effects of guar gum and pectin on glucose tolerance and paracetamol absorption could be due simply to alteration in the rate of gastric emptying.

Absorption↗
PubMed1979

Paracetamol metabolism in chronic liver disease.

The plasma concentrations and urinary excretion of paracetamol and its glucuronide, sulphate, cysteine and mercapturic acid conjugates were measured in eight normal subjects, eight patients with mild liver disease and seven patients with severe liver disease following an oral dose of 1.5 g of paracetamol. The mean plasma paracetamol half-life was similar in normal subjects (2.43 h +/- 0.19) but was significantly prolonged in all patients with severe liver disease (4.25 h +/- 1.15:p = less than 0.001). Prolongation of the paracetamol half-life was related to reduced plasma albumin and increased prothrombin time. The mean ratios of plasma concentrations of unchanged paracetamol to paracetamol glucoronide and sulphate were significantly greater in patients with sever liver disease than the normal subjects. There were no significant differences in the overall 24-h urinary excretion of paracetamol and its glucuronide, sulphate, cysteine and mercapturic acid conjugates in the three groups. The glutathione conjugation of paracetamol did not seem to be impaired in patients with severe liver disease as evidence by the production of normal amounts of the cysteine and mercapturic acid conjugates. There is thus no evidence that they are at increased risk of hepatotoxicity when given a single therapeutic dose of paracetamol.

Acetaminophen↗
PubMed1979

The disposition of intravenous doxapram in man.

The pharmacokinetics of intravenous doxapram in healthy individuals is consistent with a three-compartment open model. Doxapram was administered by bolus injection (1.5 mg . kg-1) and by intravenous infusion (6.5 mg . kg-1 for 2 h) to 5 subjects on separate occasions. There was no significant difference in mean terminal plasma half-lives (355 and 448 min) or in mean total body clearances 5.9 and 5.6 ml . min-1 . kg-1) following i.v. bolus injection or infusion respectively. In 3 subjects plasma doxapram concentrations during and after i. v. infusion agreed with those predicted from pharmacokinetic values obtained from the bolus injection study. Since mean steady-state concentrations (9.9 microgram . ml-1) would be reached only after an extended interval (mean 15.2 h), a variable-rate infusion regimen was calculated to produce and maintain a concentration of 2 microgram . ml-1 from 15--25 min onwards. A regimen in which the infusion rate is reduced step-wise is recommended to achieve early near-constant plasma doxapram concentrations.

Adult↗
PubMed1979

A pharmacokinetic study of doxapram in patients and volunteers.

1. Following intravenous bolus injections or brief infusions in healthy volunteers, plasma concentrations of doxapram declined in a multi-exponential fashion. The mean half-life from 4-12 h was 3.4 h (range 2.4-4.1h), the mean apparent volume of distribution was 1.5 1 kg-1 and the whole body clearance was 370 ml min-1. 2. Enteric-coated capsules of doxapram base were absorbed rapidly after an initial delay, and the systemic availability was about 60%. 3. Doxapram is extensively metabolized and less than 5% of an i.v. dose was excreted unchanged in the urine in 24 h. A metabolite (AHR 5955) was present in plasma in amounts comparable to the parent compound and had a similar half-life. 4. The disposition of doxapram appears to be similar in healthy volunteers and patients with respiratory failure. 5. The previously held belief that plasma concentrations fall rapidly when an infusion is stopped is only true following short duration infusions. The pharmacokinetic properties of doxapram are such that steady-state plasma concentrations will not be achieved for many hours with the recommended constant rate infusion régime.

Administration, Oral↗
PubMed1979

Treatment of severe 2,4-D and mecoprop intoxication with alkaline diuresis.

1 Self-poisoning with a selective weedkiller containing 2,4-D and mecoprop in a 39 year old man resulted in prolonged deep coma, pyrexia, hyperventilation, hypoxaemia, myotonia, skeletal muscle damage and electrocardiographic changes consistent with cardiomyopathy. 2 The admission plasma concentrations of 2,4-D and mecoprop were 400 and 751 microgram/ml respectively. The patient remained gravely ill with no signs of improvement for 2 days with supportive therapy and there was no fall in the 2,4-D level. 3 Alkaline diuresis greatly increased the renal clearance of 2,4-D, and there was a rapid fall in plasma concentration (T1/2 3.7 h) with corresponding clinical improvement. The effect on the elimination of mecoprop was similar, but less dramatic. 4 Forced alkaline diuresis may improve the otherwise very poor prognosis in severe intoxication with 2,4-D and related weedkillers.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1979

Inappropriate methods for the emergency determination of plasma paracetamol.

Methods for the estimation of plasma paracetamol which depend on acid hydrolysis to p-aminophenol without a prior extraction step also measure inactive metabolites which are present in high concentrations. The extent of the overestimate obtained with such methods was determined using 24 samples from patents after paracetamol overdosage. There was a positive error of between 40 and 700% compared with a high-performance liquid chromatography reference method which measured only unchanged paracetamol. These non-specific methods should not be used to determine the need for specific therapy in patients with paracetamol poisoning.

Acetaminophen↗