ISSN:0312-5963    

出版商:ADIS    

年代:1995

数据来源: ADIS

摘要:

Meropenem is a recently developed carbapenem antibiotic, similar to imipenem, with a wide spectrum of activity against Gram-positive and Gramnegative bacteria. In comparison with imipenem, meropenem is relatively stable to hydrolysis by the enzyme dehydropeptidase I (DHP-I), thus precluding the need for coadministration with an inhibitor of DHP-I, such as cilastatin. Furthermore, meropenem may be less nephrotoxic and neurotoxic than imipenem.Plasma meropenem concentrations reach a peak (Cmax) of approximately 30 mg/L after administration of a standard dose of 1g intravenously. The elimination half-life (t½) is approximately 1 hour, and the area under the plasma concentration-time curve increases linearly in a dose-related manner.The volume of distribution is 21L, indicating predominantly extracellular distribution. Meropenem distributes partly into cerebrospinal fluid. The drug is eliminated both by metabolism and excretion. In normal volunteers, up to 70% is recovered in urine, and the remainder is accounted for by a &bgr;-lactam ring-opened form of the compound, ICI 213689.The t½of meropenem is prolonged in patients with renal insufficiency and correlates well with creatinine clearance. Dosage adjustments in people with decreased creatinine clearance can, thus, be made on the basis of creatinine clearance.

ISSN:0312-5963    

出版商:ADIS    

年代:1995

数据来源: ADIS

摘要:

Theophylline has been widely used as a bronchodilatory drug for the treatment of neonatal apnoea in premature newborns and patients with obstructive airways disease. The development of analytical equipment and procedures to determine the systemic concentration of theophylline renders it possible to improve the effectiveness of theophylline therapy and reduce the incidence of toxic and adverse effects. Since the beginning of the 1970s, endogenous and exogenous factors (e.g. age, blood pH, concomitant diseases and drug therapy, meal preparation procedures, nutritional habits, pregnancy, gender, smoking and, to a lesser extent, biorhythms), influencing nearly all parameters of theophylline pharmacokinetics have been described.Drug absorption depends on galenic formulation, drug delivery, nutritional habits and the chemical derivatives used. The mean plasma protein binding rates depend on the method of plasma protein determination: acidic blood pH values and advanced age may result in reduced plasma proteins. The volume of distribution depends primarily on age; it is 2-fold greater in newborns than in adults. Furthermore, changes in blood pH values, the plasma protein content and the administration of concomitant drugs may vary this parameter.Biotransformation is the most clinically important pharmacokinetic parameter. Hepatic metabolism accounts for 90% of the metabolism of theophylline. Essentially, 2 microsomal isoenzymes of the cytochrome P450 system appear to be responsible for theN-methylation and 8-hydroxylation of the drug. Age and concomitant disease are the major endogenous effectors influencing biotransformation of theophylline, whereas biorhythms, gender and pregnancy are of lesser importance. Exogenous factors, such as concomitantly administered drugs, smoking and nutritional factors, affect biotransformation by inducing or inhibiting the metabolising enzymes.Because of intra- and interindividual variability in the pharmacokinetics of theophylline, which may be increased by the presence of endogenous and/or exogenous effectors, it is necessary to supervise theophylline therapy by therapeutic drug monitoring if target concentrations are to be achieved.

ISSN:0312-5963    

出版商:ADIS    

年代:1995

数据来源: ADIS

摘要:

Thrombolytic agents are widely used for the treatment of acute thromboembolic diseases, especially acute myocardial infarction (AMI). These compounds include streptokinase, anistreplase, alteplase, urokinase and, although not commercially available yet, saruplase (prourokinase). The therapeutic window of these compounds is relatively small and subtherapeutic or toxic plasma concentrations may have serious clinical implications (insufficient thrombolysis, reocclusion and bleeding).Among the factors that affect the pharmacokinetics and pharmacodynamics of thrombolytic agents, comedication is especially relevant since these drug interactions are partly predictable and sometimes preventable. Based on knowledge of the pharmacology of thrombolytic agents and general mechanisms by which pharmacokinetic drug interactions occur, interactions with alteplase and saruplase are expected. The clearance of alteplase is dependent on hepatic blood flow (HBF), and scientific evidence is emerging that saruplase is also a highclearance compound. Each pharmacological agent that alters HBF and is given concurrently with one of these agents can change the plasma concentrations of those thrombolytics. Although there are no published data confirming druginduced changes in the metabolism of alteplase or saruplase by this mechanism in humans, indirect supportive evidence (clinical observations and animal experiments) is available.An overview is presented of the anticipated effects of compounds that are frequently coadministered with thrombolytic agents on the pharmacokinetics of the thrombolytics with high-clearance properties. Since the clearance of these thrombolytics may be strongly affected by hypoperfusion of the liver as a result of cardiogenic haemodynamic failure, the role of circulatory changes in potential drug-drug interactions is also discussed.Pharmacodynamic drug interactions are highly relevant in the treatment of acute thrombotic lesions and are still being evaluated to further optimise treatment strategies. As most of these treatments exist as combinations of thrombolytic, antithrombin and antiplatelet compounds, beneficial effects are partly offset by bleeding complications.Changes in the pharmacokinetics and/or pharmacodynamics of thrombolytic agents may have serious consequences. It becomes imperative for the practising physician to be aware of benefits and risks of interactions with thrombolytic agents and especially of the fact that the principal way by which the pharmacokinetics of alteplase and, presumably, saruplase can be affected is by drug- and/or haemodynamic failure-induced changes of HBF.

ISSN:0312-5963    

出版商:ADIS    

年代:1995

数据来源: ADIS

摘要:

Renewed interest in vancomycin over the past decade has led to an abundance of data concerning the pharmacokinetics of vancomycin, and its dosage selection and concentration-response relationships.No definitive data exist that correlate vancomycin serum concentrations with clinical outcomes. However, inconsistencies in sampling times for peak serum concentrations and differences in infusion times make interpreting vancomycin serum concentrations difficult. Furthermore, the evidence implicating vancomycin as a cause of oto- or nephrotoxicity is circumstantial, and these adverse effects may occur only in high-risk populations.Owing to the variability in its dose-serum concentration relationship and multicompartmental pharmacokinetics, several methodologies have been developed for instituting and adjusting vancomycin dosages. Nomograms rely on a fixed volume of distribution and the relationship between vancomycin clearance and creatinine clearance. Since both of these factors may be altered in certain populations, dosage methodologies (both traditional and Bayesian) that use population-or patient-specific pharmacokinetic data perform better than standard nomograms for initiating vancomycin therapy. Controversy still exists as to whether a 1- or a 2-compartment model is more appropriate for making dosage adjustments; however, steady-state rather than non-steady-state vancomycin serum concentrations should be used for dosage adjustments. Certain pathophysiological states such as age, bodyweight and renal function contribute to altered pharmacokinetics and may alter the design of the dosage regimen.Since no definitive relationship exists between vancomycin serum concentrations and either clinical outcome or adverse effects, considerable controversy surrounds the utility of monitoring serum vancomycin concentrations. Therefore, routine vancomycin serum concentration monitoring may be warranted only in specific populations, such as patients receiving concurrent aminoglycoside therapy or those receiving higher than usual dosages of vancomycin, patients undergoing haemodialysis and patients with rapidly changing renal function.

ISSN:0312-5963    

出版商:ADIS    

年代:1995

数据来源: ADIS