摘要:

Recent concern over toxic effects of drugs in newborns, infants and children have stressed the need for better knowledge of drug kinetics during development. The present review focuses on the available data on clinical pharmacokinetics in the neonate. Despite the lack of systematic approaches on drug disposition during the first month of life, the body of data currently available indicates profound differences in drug disposition between neonates and older infants, children and adults.In terms of physiological and anatomical factors the neonate has to be considered as a ‘unique drug recipient’. For all the specific variables which govern the drug kinetic pattern (absorption, blood esterase activity, plasma protein binding, metabolic degradation and renal excretion), there are clear differences between neonates and older infants and children. Such differences are not always unidirectional. In the case of absorption, they depend on the maturational stage, but more on the physico-chemical properties of the individual compound. Esterase activity and renal excretion are also related to the physico-chemical properties of the drug, but are more clearly linked with the developmental stage.Plasma protein binding is generally reduced, and depends on several factors, not all of which are as yet clearly identified and understood. Biotransformation activities are usually very low, but may be increased several-fold by exposure to inducing agents. Hydroxylating activity and conjugation with glucuronic acid appear to be the two metabolic pathways which are most defective at birth, while sulphate and glycine conjugation, and dealkylation activities are close to the adult pattern.The material reviewed is fragmentary and does not always permit a comparison of the data obtained in newborns with those reported for adults. Differences in the methodology used and in the kinetic criteria further complicate the matter. It is, however, clearly emerging that drug disposition may vary greatly in the newborn in relation to its developmental age. The reported differences may be relevant for clinical practice and stress the need for more detailed information on drug kinetics in the neonate. Such information may be achieved by carefully planned clinical trials, but more meaningfully, and more profitably for the individual patient, by a very carefully, well integrated monitoring of the neonate at risk. By such an approach, where drug plasma levels are related to drug effects and to the pathophysiological condition, the significance of various factors on drug dispostion during development will be better clarified, thus allowing a more rational and safer therapy in the newborn.

ISSN:0312-5963    

出版商:ADIS    

年代:1976

数据来源: ADIS

摘要:

Patients with renal insufficiency often react abnormally to a number of drugs. Small doses that are safe under normal conditions may cause severe and even fatal side-effects. As a consequence, modification of the usual drug dosage of these drugs is required in renal insufficiency. Since the risk of retention concerns only those drugs which are mainly excreted by the kidney, it is possible to establish a mathematical relationship between glomerular filtration rate and the rate of drug elimination. These relationships serve as a basis for the determination of the proper dosage regimen for the individual patient. Such dosage adaptation for intermittent drug administration can be obtained by two methods and a series of compromises between them: (1) increase of the dosage interval without changing the dose, and (2) reduction of the dose without changing the frequency of administration.One must however, not only consider inadequate drug elimination but also a number of other factors. Some of these modify the behaviour of the drug, such as hypoalbuminaemia, which causes an increase of the unbound portion of the drug; anomalies of the volume of distribution, as found in patients with oedema; metabolic disturbances; alteration of absorption from the gastro-intestinal tract, etc. Other factors are related only indirectly to the pharmacokinetic behaviour of the drug. Frequently, there is an increased sensitivity to the undesirable side-effects of certain drugs in patients with renal insufficiency, causing the level of tolerance to be lowered compared with normal patients. Such an effect probably involves functional or morphological modifications of the drug receptors, or interaction with substances retained in renal insufficiency. Furthermore, drugs may accentuate the consequences of the nephropathy or have increased nephrotoxicity for those with diseased kidneys.It is with these important reservations that a critical analysis of the proposed methods of adapting drug dosage in renal insufficiency is presented. An appendix tabulates the effects of renal insufficiency on the behaviour of 117 drugs.Irrespective of the method used to calculate drug dosage, all patients with renal disease must be monitored closely, particularly for signs of unexpected drug toxicity.

ISSN:0312-5963    

出版商:ADIS    

年代:1976

数据来源: ADIS

摘要:

Plasma from patients with renal failure has decreased binding of many drugs. The decreased binding of anionic drugs is pronounced and is apparently due to occupation of protein binding sites by non-dialysable endogenous acidic compounds. Organic bases seem to bind normally, particularly if hypoproteinaemia or hypoalbuminaemia are not present. This modification of drug binding to plasma proteins from uraemic patients must be considered when plasma concentrations of acidic drugs are measured.

ISSN:0312-5963    

出版商:ADIS    

年代:1976

数据来源: ADIS

摘要:

Based on the well known linear relationship between the overall drug elimination rate constant and the endogenous creatinine clearance, it is shown how individual drug elimination parameters in patients with renal disease can be estimated from the patient's creatinine clearance or serum creatinine concentration.By means of a simple nomogram the elimination rate fraction is determined which describes the elimination rate of the drug as a fraction of its normal elimination rate constant. Based on the estimated elimination rate fraction the dosage regimen in the patient with renal disease is individually modified according to pharmacokinetic principles. At present the described method can be used with 45 different drugs.

ISSN:0312-5963    

出版商:ADIS    

年代:1976

数据来源: ADIS

摘要:

For some drugs, delivery to the liver by the hepatic circulation is an important determinant of removal by this organ. Classical pharmacokinetic analyses cannot predict the changes produced by altering any of the biological determinants of drug elimination by the liver; hepatic blood flow, metabolic enzyme activity, drug binding and route of administration. However, with the use of a physiological model of hepatic drug elimination, such predictions can be made. This model has been tested experimentally and appears to be valid.Hepatic blood flow can vary over about a 4-fold range from half normal flow to twice normal flow. These variations are produced by physiological, pathological or pharmacological changes affecting the circulation. For drug clearance to be affected significantly by these changes in flow, the drug must be avidly removed by the liver as reflected in a high hepatic extraction ratio and intrinsic hepatic clearance. This latter term is a useful way to characterise the ability of the liver to irreversibly remove drug from the circulation in the absence of any flow limitation. The clearance of drugs with low intrinsic clearances will not be affected significantly by changes in liver blood flow.

ISSN:0312-5963    

出版商:ADIS    

年代:1976

数据来源: ADIS

ISSN:0312-5963    

出版商:ADIS    

年代:1976

数据来源: ADIS