Regulation for the radiopharmaceuticals should be reasonably different from that of other drugs. Radiopharmaceuticals are always used by compounding based on the doctor's order, have short half life and very low administration dose. Its pharmacological effect is not from its chemical effect but from radiation. The background for exploratory IND (Investigational New Drug) explained by the FDA was to reduce the time and resources expended on candidate products that are unlikely to suceed, new tools are needed to distinguish earlier in the process those candidates that hold promise from those that do not. In this review, basic concept for exploratory IND and RDRC guideline is summarized and various suggestions for improving and expediting procedure for new radiopharmaceutical development would be described.
Half-Life ; Korea* ; Radiopharmaceuticals

This tutorial defines the principles of the concentration - effect relationship which are the basis of pharmacodynamics. The two key parameters of pharmacodynamics are the maximum response (Emax) and the concentration producing 50% of Emax (C₅₀). The time course of effect is illustrated under the assumption that drug effects are immediately related to concentration in the central compartment e.g. plasma. The related idea of duration of drug action and its relationship to dose is shown to have a simple relationship with drug half-life.
Half-Life ; Plasma

Authors have developed highly reproducible calibration method for the Micro-Selection HDR Ir-192 system(Nucletron, Netherland). The new jig has a 10cm radius circular hole in the 30cm x 30cm x 0.2cm acrylic plate, and 5F flexible bronchial tubes are attached around the hole. The source moves along the circle in the tubes an? the ionization chamber is placed vertically at the center of the circular hole(center of the jig). Dose distribution near the center was derived theoretically, and measured with the film dosimetry system. Theoretical calculation and measurement show the error margin below 0.1% for 1mm or 2mm position deviation. We have measured at 12 and 24 points of circle with 1, 6, 11 and 21 second dwell time of source in order to calculate the activity of the source. Measurements have been repeated daily for 50 days. The accuracy and the reproducibility are below 1% error margin. The half life of the source from our measurement is estimated 73.4+/-0.4 days.
Calibration* ; Film Dosimetry ; Half-Life ; Radius

Pharmacokinetics is the study of the rate and degree of drug transport to various tissues in the human body. Pharmacokinetic parameters summarize drug kinetics and ideally predict a clinical situation. A single kinetic profile may be summarized by peak concentration, peak time, half-life and area under the curve. Dosage regimens are designed to confer the maximum desired effects for the required time period with minimal toxicity. Target-controlled infusions use pharmacokinetic models to titrate intravenous anesthetic administration to achieve a desired drug concentration. Context-sensitive half time is used to predict the clinical time course, rather than terminal half-life. It is important that anesthesiologists understand the basic pharmacological principles and apply them in their daily clinical practice. This review discusses the ways in which anesthesiologists can design a patient-specific dosage regimen of intravenous anesthetics by utilizing basic concepts of pharmacokinetics and pharmacodynamics using pharmacokinetic simulations.
Anesthetics, Intravenous ; Half-Life ; Human Body ; Pharmacokinetics*

The effects of CYP1A enzyme on the pharmacokinetics of p-acetaminophen were studied in Bactrian camel. Twelve Bactrian camels were divided into 2 groups, then given a single dose of p-acetaminophen only or with the enzyme inhibitor lomefloxacin. Blood samples were collected after different intervals, and p-acetaminophen concentration was determined by high-performance liquid chromatography. Pharmacokinetic parameters were analyzed by Phoenix WinNonLin v.7.0. The results show that lomefloxacin can significantly inhibit Bactrian camel CYP1A enzyme, as evidenced by the prolonged elimination half-life, increased maximum plasma concentration and area under the curve values and the shortened time to peak concentration for p-acetaminophenol in the substrate with inhibitor group. The results lay a foundation for revealing the particular characteristics of the CYP1A enzyme in Bactrian camels.
Camels ; Chromatography, Liquid ; Half-Life ; Pharmacokinetics ; Plasma

Drugs of the benzodiazepine family pharmacologically have superior anti-anxiety, sedative, anti-convulsant, and muscle relaxant effect resulting in its popular use not only in psychiatry but in other field of medicine. However, the long term use of benzodiazepines may cause to question the efficacy and may amount to dependence, tolerance, and withdrawal symptoms thus leading to sociologic problems. The treatment strategies of benzodiazepine dependence consist of gradual dosage reduction, the substitution to a long half-life benzodiazepine, and providing psychological support. We present two treatment experiences of high dose lorazepam dependence along with the review of corresponding literature.
Benzodiazepines ; Half-Life ; Humans ; Lorazepam* ; Substance Withdrawal Syndrome

Etretinate, an effective retinoid in the treatment of pustular, erythrodermic and chronic plaque type psoriasis, has the disadvantage of a long terminal elimination half-life. On the other hand, acitretin, the active metabolite of etretinate, has much shorter terminal elimination half-life and is being reported as an agent with good antipsoriatic activity by several authors. To evaluate the clinical efficacy of acitret.in in comparison with etretinate, we treated 10 patients wit,h acitretin at a dose of 30mg per day and 11 patients with etretinate at a same dose for 12 weeks. The PASI score at 12 week was significantly reduced in each group as compared with baseline PASI score. In the acitretin treated group the initial PASI score of 14.5 reduced to 3.9, while the etretinate group PASI score reduced from 12.0 to 3.1. The PASI score differ ences between the acitretin and etretinate groups at each time during therapy and the end of therapy were not statistically significant. The severity of adverse reactions with acitretin was similar to those with etretinate but their incidence was higher. The change in laboratory parameters in the acitretin group was simlar to that of the etretinate group. In view of these results and the known pharmacokinetic advantage of acitretin, that is the short terminal elimination half-life, it is conceivable that acitretin may be a useful alternative to etretinate in the treatment of psoriasis.
Acitretin* ; Etretinate* ; Half-Life ; Hand ; Humans ; Incidence ; Psoriasis*

This tutorial deals with basic concepts of volume of distribution, the second most important parameter in pharmacokinetics but often challenging for students in clinical pharmacology. Its relationships with dose, concentration and amount in the body are discussed using a physical model and examples of commonly used drugs, as well as its physiological aspects pertaining to the physical volume of differing organs. Finally, application of volume of distribution to the calculation of loading dose and half-life is used to show how it is essential in pharmacotherapy and clinical pharmacology.
Drug Therapy ; Half-Life ; Humans ; Pharmacokinetics ; Pharmacology, Clinical

Riboflavine tetrabutyrate is a fat soluble riboflavine derivative. It was synthesized by esterification of riboflavine with fatty acid chloride or by esterification of riboflavine with fatty acid anbydride. The advantage of riboflavine tetrabutyrate is prolongation of its biologic half life and as a result enhancing effectivity of riboflavine, This riboflavine tetrabutyrate has been used for treatment of various dermatoses of which Pathogenesis are believed to be related with abnorma1 Iipid rnetabolism. Receatty, there were many case reports showing markedly improved clinical synptoms ofpsoriatic patients who had been administered oral riboflavine tetrabutyrate for more than one month in Japan. In this clinical trial, we have also experienced effectiveness in 4 of 7 psoriatic pztients who was given oral riboflavine t trabutyrate for more than 3 months.
Esterification ; Half-Life ; Humans ; Japan ; Psoriasis* ; Riboflavin* ; Skin Diseases

The pharmacokinetics of intravenously adminstrered lidocaine were studied in 5 normal patients withno renal disease and 4 patients with end-stage renal failue during anesthesia. In both group of patinets, the half life, the volume of distribution and clearance were not significantly different. However, valuses were altered in comparison with those of subjuc without anesthesia. This alteration of parameters is thought to be the effect of reduced hepatic blood flow due to potent anestheics grugs. Our understanding of lidocaine pharmacokinetics in patients with chronic renal failure during anesthesia suggests that these patients can safely receive a normal loading and maintenanece dose with close monitoring for signs of lidocaine toxicity. even though the total plasma concentration may be within the therapeutic range.
Anesthesia* ; Half-Life ; Humans ; Kidney Failure, Chronic ; Lidocaine ; Pharmacokinetics ; Plasma