摘要:

Haemoperfusion has been used increasingly in treatment of patients with drug overdose. Blood is pumped from the patient through a column of adsorbent material and recirculated back to the patient. The adsorbent materials, activated charcoal and Amberlite XAD-4 resin, avidly bind particular drugs so that extraction from blood, including protein bound drug, is nearly complete. Activated charcoal removes both polar and nonpolar drugs and probably metabolites; Amberlite removes non-polar drugs better than charcoal but does not remove more polar drugs or polar metabolites.The haemoperfusion cartridge can be regarded as an extracorporeal clearance organ. Methodological issues in computing column clearance are discussed. The efficacy of haemoperfusion in removing a drug is determined by the relative magnitude of haemoperfusion and intrinsic body clearance, by volume of distribution, and by rate of movement of drug from peripheral tissues to the blood compartment. Haemoperfusion is most efficacious for drugs with low intrinsic clearance and a relatively small volume of distribution, such as phenobarbitone, theophylline, and tolbutamide. In contrast, haemoperfusion removes only a small fraction of drugs with high intrinsic clearance and large volumes of distribution, such as digoxin and amitriptyline. Drug overdose may influence pharmacokinetics of drugs such as salicylate, phenytoin, and ethchlorvynol, making predictions and evaluation of haemoperfusion difficult.Clinical reports of haemoperfusion treatment for drug overdose indicate that haemoperfusion can effectively remove certain drugs and potentially significantly influence the clinical outcome, although the latter remains to be proven. Haemoperfusion is quite effective in removing phenobarbitone. Short and intermediate acting barbiturates are also removed in substantial quantity, but because of a larger volume of distribution they demonstrate rebound increase in blood concentrations with possible associated clinical deterioration, after haemoperfusion is completed. Haemoperfusion appears to be less effective for glutethimide because of the drug's large volume of distribution, compared with barbiturates, and rebound appears to be an even more significant problem. Haemoperfusion may be useful in treating overdosage with ethchlorvynol or phenytoin, particularly with high blood concentrations of drug, when the intrinsic clearance of the drug may be quite low due to non-linear metabolism. Salicylate can be removed by charcoal haemoperfusion, but no more effectively than can be effected with haemodialysis. The latter has the advantage of providing a means for fluid and electroiyte control and not requiring systemic heparinisation. Haemoperfusion does not substantially remove digoxin and tricyclic antidepressants compared with the total body burden because of the extremely large volumes of distribution. However, clinical responses during haemoperfusion for these types of overdose have been reported. Temporary reduction in the concentrations of these drugs in the brain or heart or removal of active metabolites might account for a discrepancy. Haemoperfusion is quite effective for removing theophylline, a drug with a small volume of distribution and moderate intrinsic clearance, and results in substantial clinical benefit.The major complication of haemoperfusion is thrombocytopenia with the potential risk of haemorrhage. Platelet counts are commonly halved during haemoperfusion and return to normal levels over 1 to 2 days.

ISSN:0312-5963    

出版商:ADIS    

年代:1979

数据来源: ADIS

摘要:

Attention in recent years has focused upon the ability of lung to accumulate and/or to metabolise circulating hormones, drugs and other xenobiotic agents. Although often studied in broken cell preparations, such functions must be examined in intact lung before extrapolation to the situationin vivois possible.The role of lung in total body clearance of xenobiotic agents is often considered to be small, as compared with the liver it usually has much lower concentrations of degradative enzymes and a smaller mass. However, consideration of such factors as organ blood flow or stimulation of drug metabolising enzymes suggests that the contribution of the lung to total body clearance of some drugs is greater than previously recognised. This may explain some of the alterations in drug clearance seen clinically. For example, cigarette smoking may increase the clearance of certain xenobiotic compounds by stimulating pulmonary drug metabolising enzymes.Pulmonary drug disposition may also be altered by conditions affecting cardiac output, such as exercise, hypoxia, and circulatory shock, or those affecting acid-base balance, such as hyperventilation. In addition, pneumotoxicants may affect pulmonary clearance of circulating drugs and xenobiotics.

ISSN:0312-5963    

出版商:ADIS    

年代:1979

数据来源: ADIS

摘要:

Biliary excretion is an important route for the elimination of some drugs and drug metabolites in man. The factors which determine elimination via the biliary tract include characteristics of the drug such as chemical structure, polarity and molecular size as well as characteristics of the liver such as specific active transport sites within the liver cell membranes. A drug excreted in bile may be reabsorbed from the gastrointestinal tract or a drug conjugate may be hydrolysed by gut bacteria, liberating original drug which can be returned to the general circulation. Enterohepatic circulation may prolong the pharmacological effect of certain drugs and drug metabolites, but the quantitative importance of this in man appears to be less than in animals.Biliary elimination may play a role in the interindividual differences in drug response observed in healthy subjects and in patients with certain diseases. Cholestatic disease states, in which normal bile flow is reduced, will influence drug elimination by this route resulting in increased risk of drug toxicity. Bile may serve as an alternate route of elimination in renal failure, but this has not been determined in man.Lack of reliable information regarding the biliary excretion of drugs in man is partly due to the relative inaccessibility of the human biliary tract. Most studies of drug excretion in human bile have been performed in post-surgical patients with T-tube drainage. This method of bile collection is not ideal because bile flow and composition are often severely altered during the period of study, not all bile is collected and enterohepatic circulation is partially interrupted. Recent advances in the methods of collection of bile may improve future studies of drug excretion in human bile.

ISSN:0312-5963    

出版商:ADIS    

年代:1979

数据来源: ADIS

摘要:

Cyclosphosphamide is widely used for cancer chemotherapy and for immunosuppression. The parent compound is inactivein vitroand exerts its biological activities through metabolites generated by hepatic microsomal enzymes. The drug may be administered either parenterally or orally. Systemic availability after oral administration is greater than 75% at the low doses which have been studied. Cyclophosphamide is minimally protein bound but some of its metabolites are more than 60% protein bound.A linear 2-compartment model for the disposition of the parent compound has been formulated, but characteristics of the kinetics of disposition of the active metabolites have been delayed by analytical difficulties. Parameters vary widely between patients. Vc for this polar compound ranges from 0.32 to 0.34L/kg. Vd ranges from 0.60 to 0.64L/kg. T1/2&bgr;ranges from 3 to 12 hours.Modelling of the time course of specific cytotoxic metabolites (aldophosphamide, 4-hydroxy-cyclophosphamide and phosphoramide mustard) has not been systematically performed. When measured by various nonspecific techniques, the serum concentration of metabolites was found to be maximal about 2 hours after an intravenous dose and declined by only 25% during the next 6 hours. Mean t1/2was 7.7 hours in 1 study. Alkylating metabolites have been measured in the cerebrospinal fluid, but only a small fraction crosses the blood brain barrier.At least 80% of an administered dose of cyclophosphamide is eliminated by metabolism. Both cyclophosphamide and metabolites are principally excreted by the kidney. Renal clearance has been measured at 5 to 11ml/min, suggesting extensive tubular resorption; up to 25% of the administered dose is excreted unchanged in the first 24 hours. Only 60% of radiolabel can be recovered in the urine over 24 to 48 hours. An additional 1 to 4% can be collected as expired CO2or in the stool. Although elevated levels of metabolites have been described in patients with renal failure, a recent study did not demonstrate excess clinical toxicity in such patients. Unchanged cyclophosphamide has been shown to be extensively cleared by haemodialysis (78ml/min).Complex interactions are to be expected with agents modifying hepatic microsomal activation, and conflicting data have been obtained in several animal studies. No clear alteration of the effects of cyclophosphamide has been observed in patients after phenobarbitone administration. Synergistic haematopoietic toxicity may occur with concomitant use of allopurinol.Dose related efficacy has been demonstrated in animal models. Human data are available on dose related toxicity. One study demonstrated a direct relationship between metabolite AUC and depth of white blood count nadir. Clinical correlation between kinetic data and efficacy and/or toxicity awaits studies evaluating the time course of specific cytotoxic metabolites.

ISSN:0312-5963    

出版商:ADIS    

年代:1979

数据来源: ADIS

摘要:

Several recent publications have encouraged the use of haemoperfusion to remove digoxin from the body of overdosed patients. The usefulness of haemoperfusion in removing digoxin from the body has therefore been examined using pharmacokinetic simulation techniques and published data. Haemoperfusion for a period of 4 hours with a clearance of 100ml/min removes less than 7% of the amount of digoxin in the body (including that in the gastrointestinal tract at the beginning of haemoperfusion), regardless of the time after the dose that haemoperfusion is started. Dramatic therapeutic benefit in digoxin intoxication is unlikely to be a consequence of the amount of digoxin removed from the body by haemoperfusion. If therapeutic benefit is derived from a transient decline of digoxin concentration in plasma, it may be expected to be negated as the drug redistributes from tissues.

ISSN:0312-5963    

出版商:ADIS    

年代:1979

数据来源: ADIS

ISSN:0312-5963    

出版商:ADIS    

年代:1979

数据来源: ADIS