Half-life ranges

Anhydrous, monomeric formaldehyde is not available commercially. The pure, dry gas is relatively stable at 80—100°C but slowly polymerizes at lower temperatures. Traces of polar impurities such as acids, alkahes, and water greatly accelerate the polymerization. When Hquid formaldehyde is warmed to room temperature in a sealed ampul, it polymerizes rapidly with evolution of heat (63 kj /mol or 15.05 kcal/mol). Uncatalyzed decomposition is very slow below 300°C extrapolation of kinetic data (32) to 400°C indicates that the rate of decomposition is ca 0.44%/min at 101 kPa (1 atm). The main products ate CO and H2. Metals such as platinum (33), copper (34), and chromia and alumina (35) also catalyze the formation of methanol, methyl formate, formic acid, carbon dioxide, and methane. Trace levels of formaldehyde found in urban atmospheres are readily photo-oxidized to carbon dioxide the half-life ranges from 35—50 minutes (36). 

Estramustine, an oral drug, also inhibits microtubule assembly and has weak estrogenic activity at the estradiol hormone receptors of the cell. Approximately 75% of a dose of estramustine is absorbed.15 The terminal half-life ranges between 20 to 24 hours, with nonrenal excretion as the major route of elimination. This drug is used primarily for the treatment of prostate cancer, but its use is limited by the side effects, which include nausea and vomiting, diarrhea, thromboembolic events, and gynecomastia. 

Hydroxyurea is an oral drug that inhibits ribonucleotide reductase, which converts ribonucleotides into the deoxyribuon-cleotides used in DNA synthesis and repair. The time to peak concentrations of hydroxyurea is 1 to 2 hours after oral administration. Approximately 50% is degraded by the liver to form urea and respiratory carbon dioxide. The remainder is excreted by the kidney. The half-life ranges from 3.5 to 4.5 hours. Hydroxyurea has shown clinical activity in the treatment of chronic myelocytic leukemia, polycythemia vera, and thrombocytosis. The major side effects are myelo-suppression, nausea and vomiting, diarrhea, and constipation. Rash, mucositis, and renal tubular dysfunction occur rarely. 

Lenalidomide was approved recently for the indication of myelodysplastic syndrome where the 5q deletion is present. Since lenalidomide is an analog of thalidomide, all the same precautions must be taken to prevent phocomelia. The time to maximum lenalidomide concentrations occurs 0.5 to 4 hours after the dose. The terminal half-life ranges from 3 to 9 hours. Approximately 65% of lenalidomide is eliminated unchanged in the urine, with clearance exceeding the glomerular filtration rate. To date, no pharmacokinetic studies have been done in patients with renal dysfunction. Lenalidomide is used in the treatment of myelodysplastic syndrome and multiple myeloma. Other side effects are neutropenia, thrombocytopenia, deep vein thrombosis, and pulmonary embolus. 

Caffeine is the most widely consumed psychoactive substance. Peak plasma caffeine is reached between 15 and 120 minutes after oral ingestion in humans at doses of 5-8 mg/kg. The caffeine half-life ranges from 0.7 to 1.2 h in rodents, from 3 to 5 h in monkeys, and from 2.5 to 4.5 h in humans (Nehlig 1999). 

The main rout of excretion of the drug and its metabolites is the kidney with a half-life of 9-18 h in human. In contrast to human, animal models have a lower elimination half-life ranging from 0.6-9 h [78]. The elimination half-life of valproic acid and some metabolites was found to be much longer in the neonates (40-50 h) than adult subjects (9-18 h) [78,81]. One study reported no difference between the elimination half-life between elderly and young subjects (15.4 and 13.0 h, respectively) while other found an increase in for older patients (14.9 versus 7.2 h for young patients) [78,90], Insignificant amounts of valproic acid are found in breast milk, approximately 3% of maternal drug levels [84]. 

PK For therapeutic range of 0.45. 5 tg/kg, maximum plasma concentration, half-life, and AUC are linear with respect to dose. Following subcutaneous injection, the absorption is slow and rate limiting. The half-life ranges from 27 to 89 hours. Peak plasma concentration is 34 hours after subcutaneous (SC) administration for CRF patients and 90 hours for cancer patients. 

Chloroform in humans tends to be eliminated in a biphasic manner. After ingesting 500 mg of chloroform orally, an initial (a) half-life in the blood of 9-21 minutes was reported, with the second (P) half-life ranging from 86 to 96 hoirrs. 

Soil In Hudson River, NY sediments, the presence of adsorbed /5,/7-DDD in core samples suggests it is very persistent in this environment. The estimated half-life ranged from 4.2 to 4.5 yr (Bopp et al, 1982). 

Biological. Strychnine degraded in sandy loam and sandy clay loam soils. The disappearance half-life ranged from 24 to 27 d (Starr et al., 1996). Initial degradation products (i.e., strychnine... 

The metabolism and elimination of TCAs takes several days to occur, the elimination half-life ranging from 20 hours for amitriptyline to 80 hours for protriptyline. The half-life values for the desmethylated metabolites such as desmethylimipramine and nortriptyline are approximately twice those of the parent compounds imipramine and amitriptyline. It is also well established that the half-life values of the TCAs are considerably greater in the elderly, which predisposes such patients to a greater possibility of severe side effects. 

The rapid elimination from plasma following intravenous administration of phosphorothioated AS-ODN can be explained by a two compartment model in all species, i.e. an initial plasma half-life of less than 1 h [111,113,114] and a slower elimination half-life ranging between 20 and 50 h [111,113]. 

Metabolism/Excretion - From 60% to 80% of a dose is metabolized via the liver into several metabolites. Quinidine is excreted unchanged (10% to 50%) in the urine within 24 hours. The elimination half-life ranges from 4 to 10 hours in healthy patients, with a mean of 6 to 7 hours. Urinary acidification facilitates quinidine elimination, and alkalinization retards it. In patients with cirrhosis, the elimination half-life may be prolonged and the volume of distribution increased. 

Absorption/Distribution - Oral absorption is nearly complete. Peak plasma levels are attained at approximately 3 hours. The plasma half-life ranges from 12 to 27 hours after multiple oral doses. Steady-state levels are approached in 3 to 5 days once at steady-state, no accumulation occurs during chronic therapy. Plasma levels are approximately proportional to dose. In patients with congestive heart failure (CHF NYHA class III), the rate of flecainide elimination from plasma is moderately slower than for healthy subjects. Plasma protein binding is about 40% and is independent of plasma drug level over the range of 0.015 to about 3.4 mcg/mL. 

The terminal half-life ranges from 6.9 to 8.1 hours. During dialysis, a 2-fold increase in clearance occurs. The drug is eliminated intact by the kidneys. Approximately 70% to 80% of an IM dose is excreted in the urine during the first 24 hours, with an additional 10% excreted over the next 3 days. 

Pharmacokinetics It is well absorbed from the Gl tract after oral administration (40% to 70%) peak plasma levels occur in 1 to 3 hours. Most (80%) of the plasma penicillamine is protein bound, primarily to albumin. Penicillamine is rapidly excreted in the urine 50% is excreted in the feces. Metabolites may be detected in the urine for up to 3 months after stopping the drug. Half-life ranges are 1.7 to 3.2 hours. 

The mean plasma half-life ranged from 2.7 to 5.5 hours in healthy young adults. 

Excref/on - Aprepitant is eliminated primarily by metabolism aprepitant is not renally excreted. The apparent plasma clearance of aprepitant ranged from approximately 62 to 90 mL/min. The apparent terminal half-life ranged from approximately 9 to 13 hours. 

Metaboiism/Excretion- Nefazodone is extensively metabolized after oral administration by less than 1% is excreted unchanged in urine. The mean half-life ranged between 11 and 24 hours. Nefazodone is extensively (more than 99%) bound to human plasma proteins in vitro. 

Metabolism/Excretion - Phenytoin is metabolized in the liver and excreted in the urine. The metabolism of phenytoin is capacity-limited and shows saturability. Elimination is exponential (first-order) at plasma concentrations less than 10 mcg/mL, and plasma half-life ranges from 6 to 24 hours. 

Metabolism/Excretion - Carbamazepine is metabolized in the liver to the 10,11-epoxide, which also has anticonvulsant activity. It may induce its own metabolism. Initial half-life ranges from 25 to 65 hours and decreases to 12 to 17 hours with repeated doses. 

Excretion - After oral dosing of two 333 mg acamprosate tablets, the terminal half-life ranges from approximately 20 to 33 hours. The major route of excretion is via the kidneys as acamprosate. 

CSF concentratons are less than 1% of plasma concentrations. Half-life ranged from 67 to 77.6 hours following the suspension. The long half-life is caused by presumed enterohepatic cycling and eventual fecal elimination. There is indirect evidence that atovaquone may undergo limited metabolism however, a specific metabolite has not been identified. 

L, volume of peripheral compartment is 3.4 L. The estimated terminal elimination half-life for the reference patient was 20 days (480 hours), which is similar to the terminal elimination half-life for human IgG (18 to 23 days). Bayesian estimates of terminal elimination half-life ranged from 11 to 38 days for the 123 patients included in the population analysis. 

Pharmacokinetics The absolute bioavailability after a 70 mg subcutaneous bolus injection in healthy subjects (n = 11) is 95%. In subjects with RA, maximum plasma concentrations occurred 3 to 7 hours after subcutaneous administration of anakinra at clinically relevant doses (1 to 2 mg/kg n = 18) the terminal half-life ranged from 4 to 6 hours. In RA patients, no unexpected accumulation was observed after daily subcutaneous doses for up to 24 weeks. The estimated clearance increased with increasing Ccr and body weight. 

Rifabutin is well absorbed orally, and peak plasma concentrations are reached in 2 to 3 hours. Because of its lipophiUcity, rifabutin achieves a 5- to 10-fold higher concentration in tissues than in plasma. The drug has a half-life range of 16 to 96 hours and is eliminated in urine and bile. 

Clonazepam reaches a peak plasma level in 1 to 4 hours. It is metabolized by acetylation, so the half-life ranges from 20 to 80 hours and is dependent on whether a person has a rapid or slow acetylatior phenotype (DeVane et ah, 1991). 

Peak blood levels occur within 15 minutes after smoking. The effects last for approximately 4 hours, although it may take more than 24 hours for an individual to return to a normal state. The drugs are stored in fatty tissue and released slowly. PCP has a long half-life ranging from many hours to days, and the PCP glucuronide metabolite can be found in urine for several days or weeks. PCP is found in breast milk. The half-life of ketamine is three to four hours, and metabolites of ketamine are excreted in urine. PCP and ketamine cross the placental barrier, and infants of chronic abusers have been born with cerebral palsy, facial deformities, and behavioral abnormalities. 

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