摘要:

At present, the most widely used inhalational anaesthetics are the halogenated, inflammable vapours halothane, enflurane, isoflurane and the gas nitrous oxide. The anaesthetic effect of these agents is related to their tension or partial pressure in the brain, represented at equilibrium by the alveolar concentration. The minimum alveolar concentration for a specific agent is remarkably constant between individuals. The uptake and distribution of inhalational anaesthetics depends on inhaled concentration, pulmonary ventilation, solubility in blood, cardiac output and tissue uptake. Inhalational anaesthetics are mainly eliminated by pulmonary exhalation, but significant amounts of halothane are removed by hepatic metabolism. Inhalational agents currently in use have acceptable pharmacokinetic characteristics, and clinical acceptance depends on their potential for adverse effects.Induction of anaesthesia with halothane is rapid and relatively pleasant and it is the agent of choice for paediatric anaesthesia. Between 20 and 50% is metabolised, and the parent drug is a potent inhibitor of drug metabolism. Post-operatively enzyme induction may follow. The major disadvantages of halothane are myocardial depression, propensity to evoke cardiac arrhythmias and the rare but serious halothane hepatitis.Induction and recovery from enflurane anaesthesia is rapid. Metabolism accounts for 5 to 9% of the elimination. The metabolic product inorganic fluoride may in rare cases cause renal toxicity. Enflurane is a weak inhibitor of drug metabolism at anaesthetic concentrations. Enflurane depresses circulation more than halothane by reducing both myocardial contractility and systemic vascular resistance, but cardiac rhythm is stable. Enflurane anaesthesia may, unlike the other agents, induce epileptic activity. Enflurane is widely used as replacement for halothane in adults.Despite its low blood-gas solubility, the airway irritability of isoflurane precludes a faster induction of anaesthesia than with halothane. Isoflurane is almost resistant to biodegradation. Myocardial contractility is maintained during isoflurane anaesthesia and cardiac rhythm is stable except for the occurrence of tachycardia in some patients. Isoflurane is the inhalational agent of choice for neurosurgical operations.Sevoflurane is an experimental ether vapour: induction and recovery is fast and pleasant. It is metabolised to the same extent as enflurane and subnephrotoxic concentrations of inorganic fluoride may result. Sevoflurane has fewer respiratory and cardiovascular depressant effects than halothane and may be a future alternative for paediatric anaesthesia.Nitrous oxide is the only anaesthetic gas widely used today. A rapid induction and recovery follows from its low blood-gas solubility. No metabolism occurs and the cardiovascular effects are small compared with the volatile agents. Nitrous oxide reacts chemically with vitamin B12and signs of megaloblastic bone marrow are present after 6 hours of anaesthesia.

ISSN:0312-5963    

出版商:ADIS    

年代:1987

数据来源: ADIS

摘要:

Interpatient pharmacokinetic variability normally observed in adults is often of even greater magnitude in paediatric patients because of age-related maturation of physiological processes responsible for drug disposition. Several antineoplastic agents have shown age-related changes, including alterations in volume of distribution, hepatic (doxorubicin, cyclophosphamide), and renal (bleomycin, methotrexate) clearances. These differences in pharmacokinetics as a function of age alter systemic exposure to chemotherapy, and may alter the efficacy and toxicity profile for standard doses of antineoplastic drugs.The relationship of systemic exposure to toxicity has been most clearly defined for methotrexate. Clinical monitoring of methotrexate serum concentrations, and adjustment of folinic acid dosages and duration of rescue based on methotrexate disposition is now routine. More recently, pharmacodynamic data have been published for high-dose methotrexate, epipodophyllotoxins, cisplatin, and cytarabine (cytosine arabinoside), indicating a relation between drug disposition and toxicity or efficacy. Collectively, these data suggest that the pharmacokinetics of many anticancer drugs in children is different from adults, and that variability in drug disposition may have an important influence on toxicity or efficacy.

ISSN:0312-5963    

出版商:ADIS    

年代:1987

数据来源: ADIS

摘要:

The pharmacokinetics of ketoprofen were evaluated in 29 patients suffering from acute renal colic following a single intravenous administration as a bolus or short infusion (1.5 and 2 hours), and after a loading dose and a 24-hour infusion. Serum concentrations of ketoprofen were measured by high pressure liquid chromatography. The mean (± SD) values of clinical parameters were as follows: distribution half-life = 0.34 ± 0.19h; elimination half-life = 2.05 ± 0.58h; kel= 0.968 ± 0.282h−1; k21= 0.943 ± 0.425 h−1; k12= 1.004 ± 0.708 h−1; volume of central compartment = 5.58 ± 1.67L; volume of tissue compartment = 5.14 ± 2.12L; plasma clearance = 5.10 ± 1.14L/h. These results concur with previously published data obtained after oral or intramuscular administration.According to clinical observations, administration of a ketoprofen bolus suppressed pain within 5 to 30 minutes; the administration of a loading dose and a 24-hour infusion is almost never followed by a recurrence of pain, and this regimen was proposed as the dosage schedule of ketoprofen to treat renal colic.

ISSN:0312-5963    

出版商:ADIS    

年代:1987

数据来源: ADIS