Metabolism intravenous infusion

The recommended dose of pemetrexed is 500 mg/m2 administered as an intravenous infusion over 10 min on Day 1 of each 21-day cycle. Pemetrexed is not metabolized to an appreciable extent and is primarily eliminated in the urine, with 70-90% of the dose recovered unchanged within the first 24 h following administration. Pemetrexed has a steady-state volume of distribution of 16.1 L. Pemetrexed is highly bound (approximately 81%) to plasma proteins. Binding is not affected by the degree of renal impairment. Plasma... 

Little is known regarding the pharmacokinetic properties of volatile nitrites in humans, particularly isobutyl nitrite and its primary metabolite, isobutyl alcohol. In rodents, after an intravenous infusion of isobutyl nitrite, blood concentrations peaked rapidly and then declined, with a half-life of 1.4 minutes and blood clearance rate of 2.9 L/min/kg (Kielbasa and Fung 2000). Approximately 98% of isobutyl nitrite is metabolized rapidly to isobutyl alcohol, concentrations of which also decline rapidly, with a half-life of 5.3 minutes. Bioavailability of inhaled isobutyl nitrite at a concentration of 300-900 ppm is estimated to be 43%. 

Dopamine, a vasodilator, has been widely used for treatment of acute circulatory failure. However, since dopamine is rapidly metabolized when administered orally, its use has been limited to intravenous infusion. Murata et al., studied the bioavailability and the pharmacokinetics of orally administered dopamine (DA). The oral administration of DA to dogs resulted in an absolute bioavailability of approximately 3%. To minimize the extensive first-pass metabolism of DA, a dopamine prodrug, V-(/V-acetyl-l-mcLhionyl)-o,o-bis(cLhoxycarbonyl)dopamine (TA-870), was synthesized [28] (Fig. 6). Since DA is a substrate for both mono-... 

No specific antidote has been shown to be effective in treating 1,2-dibromoethane intoxication once absorption into the bloodstream has occurred (Ellenhorn and Barceloux 1988). Intravenous infusions of glucose may limit the hepatotoxicity of 1,2-dibromoethane (ERA 1989b). During the recovery phase, a diet rich in vitamin B and carbohydrates may limit liver damage (Dreisbach and Robertson 1987 Lawrence and Michaels 1984). Hemodialysis may be needed to regulate extracellular fluid and electrolyte balance and to remove metabolic waste products if renal failure occurs (ERA 1989b). 

These studies suggest that there are substance(s) in tobacco smoke, as yet unidentified, that inhibit the metabolism of nicotine. Because nicotine and cotinine are metabolized by the same enzyme, the possibility that cotinine might be responsible for the slowed metabolism of nicotine in smokers was examined. In a study in which nonsmokers received an intravenous infusion of nicotine with and without pretreatment with high doses of cotinine, there was no effect of cotinine on the clearance of nicotine (Zevin et al. 1997). Also, carbon monoxide at levels and in patterns similar to those experienced during smoking had no effect on nicotine and cotinine clearance (Benowitz and Jacob 2000). 

Animal experiments have shown (A3) that equilibration of lignocaine between blood and brain occurs relatively slowly. This may explain why plasma levels of lignocaine that can readily be tolerated, without cerebral side effects, after intravenous bolus injection nevertheless are associated with serious toxic symptoms when produced by constant intravenous infusion or when resulting from impaired metabolic degradation. 

Amsacrine (m-AMSA) is a synthetic aminoacri-dine which intercalates into DNA and inhibits DNA topoisomerase II. m-AMSA is not cross-resistant to anthracyclines and has been particularly active in acute non-lymphocytic leukemia. Amsacrine is administred by intravenous infusion. It is metabolized in the liver and eliminated in the bile with an elimination half-life of 6-9 hours. Its major toxicity is bone marrow depression. Gastrointestinal disturbances are frequent. Neurotoxicity and cardiotoxic-ity may occur. 

Gemcitabine (Gemzar), an antimetabolite, undergoes metabolic activation to difluorodeoxycytidine triphosphate, which interferes with DNA synthesis and repair, ft is the single most active agent for the treatment of metastatic pancreatic cancer, and it is used as a first-line treatment for both pancreatic and small cell lung cancer. It is administered by intravenous infusion. The dose-limiting toxicity is bone marrow suppression. 

Esmolol is a -selective blocker that is rapidly metabolized via hydrolysis by red blood cell esterases. It has a short half-life (9-10 minutes) and is administered by constant intravenous infusion. Esmolol is generally administered as a loading dose (0.5-1 mg/kg), followed by a constant infusion. The infusion is typically started at 50-150 mcg/kg/min, and the dose increased every 5 minutes, up to 300 mcg/kg/min, as needed to achieve the desired therapeutic effect. Esmolol is used for management of intraoperative and postoperative hypertension, and sometimes for hypertensive emergencies, particularly when hypertension is associated with tachycardia. 

Fenoldopam is rapidly metabolized, primarily by conjugation. Its half-life is 10 minutes. The drug is administered by continuous intravenous infusion. Fenoldopam is initiated at a low dosage (0.1 mcg/kg/min), and the dose is then titrated upward every 15 or 20 minutes to a maximum dose of 1.6 mcg/kg/min or until the desired blood pressure reduction is achieved. 

The rate of fructose metabolism is more rapid than that of glucose because the trioses formed from fructose 1 -phosphate bypass phosphofructokinase—the major rate-limiting step in glycolysis (see p. 97). [Note Loading the liver with fructose, for example, by intravenous infusion, can significantly elevate the rate of lipogenesis, caused by the enhanced production of acetyl CoA.]... 

Transdermal delivery is a noninvasive intravenous infusion of drug to maintain efficacious drug levels in the body for predictable and extended duration of activity. Diffusion-controlled transdermal systems are designed to deliver the therapeutic agent at a controlled rate from the device to and through the skin into the systemic circulation. This route of administration avoids unwanted presystemic metabolism (first-pass effect) in the GI tract and the liver. Patient satisfaction has been realized through decreased... 

A. Roskey, and S. Agrawal. 1998. Pharmacokinetics and metabolism of an oligodeoxynucleotide phosphorothioate (GEM91) in cynomolgus monkeys following intravenous infusion. Antisense Nucleic Acid Drug Dev. 8 43—52. 

Pharmacokinetics Slow intravenous infusion is employed for treatment of systemic infections or for prophylaxis. Because vancomycin is not absorbed after oral administration, this route is only employed for the treatment of antibiotic-induced colitis due to Q difficile. Inflammation allows penetration into the meninges. Metabolism is minimal 90-100 % is excreted by glomerular filtration. [Note Dosage must be adjusted in renal failure since the drug will accumulate. Normal half-life is 6-10 hours compared to over 200 hours in end-stage renal disease.]... 

Orally administered isosorbide dinitrate shows clear hemodynamic and anti-anginal effects, but it undergoes a rapid hepatic first-pass metabolism, with a plasma half-life of ca. 40 min. Its major metabolites are isosorbide-2-mononitrate and isosorbide-5-mononitrate, with half-lives of 2 and 4 h, respectively [16]. A transdermal spray of isosorbide dinitrate can be administered in order to avoid the first-pass effect, and the unchanged drug penetrates through the skin within 20 min so that it is slowly released into the capillaries in therapeutically effective amounts [24]. A very recent study showed intravenously infused isosorbide dinitrate to be ideal anti-anginal agent, especially in acute conditions [25]. 

Metabolic blood parameters are assayed in anesthetized male rats using a modified method of glucose clamp studies in rodents (Terrettaz and Jeanrenaud 1983). Four to 6 rats per group (vehicle control and one dose of the candidate compound) are used. Rats are anesthetized with an intraperitoneal injection of pentobarbital sodium (60 mg/kg), tracheotomized, and one jugular vein per rat is cannulated for intravenous infusion the other vein is prepared for collection of blood samples. Anesthesia is maintained for up to 7 hours by subcutaneous infusion of pentobarbital sodium (adjusted to the anesthetic depth of the individual animal about 24 mg/kg/h). Body temperature is monitored with a rectal probe thermometer, and temperature is maintained at 37 °C by means of a heated surgical table. Blood samples for glucose analysis (10 il) are obtained from the tip of the tail every 15 minutes, and for lactate analysis (20 p.1) every... 

Reaction rate parameters required for the distributed pharmacokinetic model generally come from independent experimental data. One source is the analysis of rates of metabolism of cells grown in culture. However, the parameters from this source are potentially subject to considerable artifact, since cofactors and cellular interactions may be absent in vitro that are present in vivo. Published enzyme activities are a second source, but these are even more subject to artifact. A third source is previous compartmental analysis of a tissue dosed uniformly by intravenous infusion. If a compartment in such a study can be closely identified with the organ or tissue later considered in distributed pharmacokinetic analysis, then its compartmental clearance constant can often be used to derive the required metabolic rate constant. 

Diagnosis is based upon hyperammonaemia, which is detectable either spontaneously or after the oral intake of proteins - or, most obviously, following intravenous infusion of amino acids. The respective amino acids are increased in the serum prior to the disturbed metabolic reaction. Argininosuccinate is only detectable in the urine. A striking feature in these patients is their thin, brittle hair. With defective ornithine transcarbamylase, there is an increase in orotic acid, uridine and uric acid in the urine, while the respective citrulline concentration is decreased. The determination of OTC activity in liver tissue verifies the diagnosis and facilitates a genomic analysis. (172) The allopurinol test can be applied for the identification of heterozygosity (or the mild form of OTC deficiency). The liver shows steatosis, portal inflammation and portal fibrosis. 

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