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

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

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

BACKGROUND: Darbepoetin alfa is a new erythropoietic agent with a three fold longer terminal half-life than recombinant human erythropoietin (r- HuEPO). The aim of this randomized, open-label study is to determine whether darbepoetin alfa is as effective as r-HuEPO for the treatment of anemia in hemodialysis patients when administered at a reduced dosing frequency. METHODS: A total 74 Korean hemodialysis patients receiving r-HuEPO therapy by either the intravenous (IV) or subcutaneous (SC) route were randomized to continue r-HuEPO or to receive an equivalent dose of darbepoetin alfa at a reduced dosing frequency. Patients receiving r-HuEPO once weekly changed to once every other week darbepoetin alfa, and those receiving r-HuEPO two or three times weekly changed to once-weekly darbepoetin alfa. The initial dose of darbepoetin alfa was based on the r-HuEPO dose at the time of entry into the study, using a formula equating the peptide mass of the two molecules (200 IU r-HuEPO=1 microgram darbepoetin alfa). The doses of r-HuEPO and darbepoetin alfa were titrated to maintain hemoglobin concentrations within -1.0 to +1.5 g/dL of patients' baseline values and within a range of 8.0 to 13.0 g/ dL for up to 20 weeks (16-week dose-titration period followed by a 4-week evaluation period). The primary end point was change in hemoglobin level between baseline and the evaluation period. RESULTS: The mean change in hemoglobin from baseline to the evaluation period was similar in the darbepoetin alfa (-0.03+/-0.19 g/dL) and r-HuEPO (0.27+/-0.20 g/dL) groups, and the difference between the two treatments was -0.30 g/dL (95% CI, -0.84 to 0.23). This was not a statistically significant or clinically relevant difference, despite the reduced frequency of darbepoetin alfa administration. The safety profiles of darbepoetin alfa and r-HuEPO were similar. CONCLUSION: This study suggests that darbepoetin alfa maintains hemoglobin as effectively as r- HuEPO, but with reduced dose frequency.
Anemia* ; Erythropoietin ; Half-Life ; Hemoglobin A ; Humans ; Renal Dialysis* ; Darbepoetin alfa

BACKGROUND: Radioiodine treatment is effective for the removal of remnant thyroid tissues after thyroidectomy in patients with differentiated thyroid carcinoma. To induce the elevation of serum TSH level which facilitates the uptake of radioiodine into remnants, a 4 to 6 week interval between thyroidectomy and radioiodine administration has been established. During the period of preparation, most patients have experienced overt symptoms of hypothyroidism which have led to the development of alternative strategies. Some reports have suggested that the interval could be reduced to about 3 weeks with less symptoms. We reevaluated the adequate time needed for the elevation of serum TSH level above 30microU/mL after thyroidectomy. METHODS: Forty five patients who had undergone total thyroidectomy for differentiated thyroid carcinoma were investigated. Serum TSH and free T4 levels were measured one or more times within 3 weeks after operation(total 97 blood samples). Eighty nine blood samples were obtained within 15 days. RESULTS: In 41 patients (91.1%) serum TSH levels increased to 30 microU/mL until 15 days after operation. Until postoperative 21 days, serum TSH levels in all the other patients reached 30microU/mL. In linear equation, the daily increment of serum TSH levels was 2.62microU/mL for the first 8 days after operation and 5.34micorU/mL for the next 7 days. The half-life of serum free T4 levels showed marked individual variations. CONCLUSION: Measurement of serum TSH level at about 15 days after total thyroidectomy for differentiated thyroid carcinoma may be useful in determining the time of radioiodine administration.
Half-Life ; Humans ; Hypothyroidism ; Thyroid Gland* ; Thyroid Neoplasms* ; Thyroidectomy ; Thyrotropin

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

This tutorial deals with basic concepts of absorption processes and links previous tutorials on clearance and volume of distribution to introduce the concept of half-life. The time course of both absorption and elimination are commonly described using a half-life. Half-life can also be used to describe drug accumulation. Understanding the principles underlying the time course of absorption and elimination are essential in pharmacotherapy and clinical pharmacology.
Absorption* ; Drug Therapy ; Half-Life* ; Pharmacokinetics ; Pharmacology, Clinical

PURPOSE: The purposes of the authors' analysis were to assess the values that plastic surgery journals demonstrate in terms of the standardized measures created by the Korea Medical Citation Index, and to assess the relationship between these values and the turnaround time of these journals. METHODS: The overall indexes of J Korean Soc Plast Reconstr Surg(JKSPRS), J Korean Soc Aesthetic Plast Surg(JKSAPS), J Korean Cleft Palate-Craniofac Assoc (JKCPRA) were compared with those of journals related with Korean plastic surgery using the following parameters: impact factor, cited half-life, total articles, and the number of journals. Korean plastic surgery journals were compared with journals from relative fields. In addition, an evaluation of all original articles published in 2007, assessing the time intervals from submission to publication was conducted for Korean plastic surgery journals and various journals which were related with plastic surgery. RESULTS: The number of articles for Korean plastic surgery journals for 2006 ranged from 19 for JKCPRA to 149 for JKSPRS. The time interval from submission to publication of an article among Korean plastic surgery journals for 2007 ranged from 73.7 days for JKSAPS to 176.2 days for JKSPRS. The variation in impact factor of JKSPRS for the period from 2002 to 2005 increased from 0.084 in the year 2002 to 0.168 in 2005. But the impact factor in 2006 has fallen to 0.112. CONCLUSION: JKSPRS demonstrated comparatively high overall index values and a short turnaround time in comparison to relative journals. To improve the status of Korean plastic surgery journals, members of Korean plastic surgeons should quate Korean plastic surgery journals and adjust key word to MeSH. The title written down in Korean should use medical terminology published by Korean medical association.
Half-Life ; Korea ; Publications ; Serial Publications ; Surgery, Plastic