Home About us Contact
|
Home About us Contact | ||
|
|
||
I.v. Doses (i.v + dose)
Selected AbstractsPharmacokinetics and pharmacodynamics of clemastine in healthy horsesJOURNAL OF VETERINARY PHARMACOLOGY & THERAPEUTICS, Issue 2 2003K. Törneke Clemastine is an H1 antagonist used in certain allergic disorders in humans and tentatively also in horses, although the pharmacology of the drug in this species has not yet been investigated. In the present study we determined basic pharmacokinetic parameters and compared the effect of the drug measured as inhibition of histamine-induced cutaneous wheal formation in six horses. The most prominent feature of drug disposition after intravenous dose of 50 ,g/kg bw was a very rapid initial decline in plasma concentration, followed by a terminal phase with a half-life of 5.4 h. The volume of distribution was large, Vss = 3.8 L/kg, and the total body clearance 0.79 L/h kg. Notably, oral bioavailability was only 3.4%. There was a strong relationship between plasma concentrations and effect. The effect maximum (measured as reduction in histamine-induced cutaneous wheal formation) was 65% (compared with controls where saline was injected) and the effect duration after i.v. dose was approximately 5 h. The effect after oral dose of 200 ,g/kg was minor. The results indicate that clemastine is not appropriate for oral administration to horses because of low bioavailability. When using repeated i.v. administration, the drug has to be administered at least three to four times daily to maintain therapeutic plasma concentrations because of the short half-life. However, if sufficient plasma concentrations are maintained the drug is efficacious in reducing histamine-induced wheal formations. [source] Gliclazide: pharmacokinetic,pharmacodynamic relationships in ratsBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 5 2007tinová Abstract The relationship between the pharmacokinetics of gliclazide and its antidiabetic efficacy were evaluated on the basis of experimental determination of changes with time in the plasma levels of this antidiabetic agent and those of glucose. The experiment included rats with both initial normal glycaemia and alloxan-induced hyperglycaemia (glycaemia increased by a minimum of 30%). Pharmacokinetic and pharmacodynamic parameters were examined in the interval of 30 to 180 min after p.o. administration of a single dose of 25 mg/kg of gliclazide. The drug was administered on day 4, following a single i.v. dose of either 50 mg/kg of alloxan (hyperglycaemic group) or the injection vehicle (control group). Even though the biological availability of gliclazide was similar in both normoglycaemic and hyperglycaemic animals, the gliclazide-induced hypoglycaemizing response was not uniform: until 60 min, the decrease of glycaemia was smaller in animals with alloxan hyperglycaemia (23% decrease at 60 min) in contrast to the normoglycaemic animals (36% decrease at 60 min), at later times, the intensity of this hypoglycaemizing effect of gliclazide persisted in the hyperglycaemic animals, while in the normoglycaemic ones, a reversal of the hypoglycaemizing effect occurred. Copyright © 2007 John Wiley & Sons, Ltd. [source] Dose-dependent pharmacokinetics of 1-(2-Deoxy- , - D - ribofuranosyl)-2,4-difluoro-5-iodobenzene: A potential mimic of 5-iodo-2,-deoxyuridineBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 9 2003Panteha Khalili Abstract The dose-range pharmacokinetics of l-(2-deoxy- , - D -ribofuranosyl)-2,4-difluoro-5-iodobenzene (5-IDFPdR), a C -aryl nucleoside mimic of IUdR, were studied in male Sprague-Dawley rats following single intravenous (i.v.) and oral doses. After i.v. administration, the blood clearance decreased from ,32 ml/min/kg at a dose of 15 mg/kg, to ,19 ml/min/kg when dosed at 54 mg/kg, and the elimination half-life increased from 8.4 min to 21.5 min, for the respective doses. While the dose-normalized area under the concentration-time curve (AUCnorm) remained practically unchanged (0.132 kg min ml,1) upon increasing the i.v. dose from 5 to 15 mg/kg, it increased by about 44% (,0.19 kg min ml,1) when the i.v. dose was increased from 15 to 54 mg/kg. Similarly, there was a dose-dependent increase in AUCnorm with increasing oral doses: AUCnorm increased by 49% as the oral dose increased from 20 to 40 mg/kg, and further by 55% as the oral dose was increased from 40 mg/kg to 54 mg/kg. For the respective oral doses, the elimination half-life increased from 24.5 min to 176 min, while blood clearance was reduced from ,37 ml/min/kg to ,17 ml/min/kg. The urinary recoveries of unchanged 5-IDFPdR and its glucuronides (as percent of the dose) were somewhat increased at higher doses. This increase was more pronounced following the highest oral dose. The total biliary recovery of 5-IDFPdR (as percent of the dose) was, however, decreased with increasing doses. The overall kinetic profile of 5-IDFPdR based on these data is suggestive of dose-dependent pharmacokinetics. Decreased elimination of 5-IDFPdR with increasing dose, as supported by longer elimination half-lives at higher doses, is one likely mechanism contributing to the dose-dependent behaviour of this compound. Saturable non-renal metabolism might explain the reduced total body clearance of 5-IDFPdR at higher doses, despite the unchanged or increased urinary clearance. For drugs exhibiting nonlinear kinetics, the dosage regimens may need to be carefully designed to avoid potential unpredictable toxicity and/or lack of pharmacological response associated with the disproportional changes in steady state drug concentrations on changing dose. Manifestation in the rat of nonlinear kinetics at doses of 5-IDFPdR, which may be of therapeutic relevance, warrants extended dose-range evaluations of this compound in future preclinical and clinical studies, to establish safe and efficacious dosage regimens. Copyright © 2003 John Wiley & Sons, Ltd. [source] ADME Investigations of Unnatural Peptides: Distribution of a 14C-Labeled ,,3 -Octaarginine in RatsCHEMISTRY & BIODIVERSITY, Issue 7 2007Markus Weiss Abstract The highly positively charged, cell-penetrating ,,3 -octaarginine has been prepared with a radioactive label by acetylation at the N-terminus with a doubly 14C-labeled acetyl group (14CH314CO). With the radioactive compound, an ADME study (Absorption, Distribution, Metabolism, Excretion) was performed in male rats following an intravenous or oral dose of 1,mg/kg. Sampling was carried out after periods ranging from 5,min to 4,d or 7,d for blood/excretia and quantitative whole-body autoradioluminography (QWBA), respectively. After p.o. dosing, no systemic exposure to peptide-related radioactivity was observed, and the dose was completely excreted in the feces within 24,h suggesting the absence of relevant absorption; less than 3% of the i.v. dose was excreted from the animals within 4,d. Blood levels, after i.v. dosing, dropped within 4,d to less than 2% of Cmax and decreased afterwards only very slowly. No metabolites were observed in the systemic circulation. QWBA Data indicated that the distribution of the acetyl- , -octaarginine-related radioactivity in the organs and tissues shifted over time. Notably, after 7,d, the highest concentration was measured in the lymph nodes, and the largest amount was found in the liver. A comparison with the results of two previous ADME investigations of , -peptides (cf. Table,1) reveals that the distribution of the compounds within the animals is structure-dependent, and that there is a full range from oral availability with rather rapid excretion (of a tetrapeptide) to essentially complete lack of both oral absorption and excretion after i.v. administration (of a highly charged octapeptide). A discussion is presented about the in vivo stability and ,drug-ability' of peptides. In general, , -peptides bearing proteinogenic side chains are compared with peptides consisting entirely of D - , -amino acid residues (the enantiomers of the ,natural' building blocks), and suggestions are made regarding a possible focus of future biomedical investigations with , -peptides. [source] The novel N -substituted benztropine analog GA2-50 possesses pharmacokinetic and pharmacodynamic profiles favorable for a candidate substitute medication for cocaine abuseJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2008Ahmed A. Othman Abstract GA2-50 is a novel N -substituted benztropine analog with improved potency and selectivity for the dopamine transporter. The pharmacokinetic and pharmacodynamic properties of GA2-50 were characterized as a part of its preclinical evaluation as a substitute medication for cocaine abuse. In vitro transport and metabolism studies as well as pharmacokinetic studies in rats were conducted. Effect of GA2-50 on the extracelluar nucleus accumbens (NAc) dopamine levels and on cocaine's induced dopamine elevation was evaluated using intracerebral microdialysis. GA2-50 showed high transcellular permeability despite being a P-glycoprotein substrate. GA2-50 was a substrate of human CYP2D6, CYP2C19, CYP2E1, rat CYP2C11, CYP2D1, CYP3A1, and CYP1A2; with low intrinsic clearance values. In vivo, GA2-50 showed high brain uptake (Ri,,,10), large volume of distribution (Vss,=,37 L/kg), and long elimination half-life (t˝,=,19 h). GA2-50 resulted in 1.6- and 2.7-fold dopamine elevation at the 5 and 10 mg/kg i.v. doses. Dopamine elevation induced by GA2-50 was significantly reduced, slower and longer lasting than previously observed for cocaine. GA2-50 had no significant effect on cocaine's induced dopamine elevation upon simultaneous administration. Results from the present study indicate that GA2-50 possesses several attributes sought after for a substitute medication for cocaine abuse. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci [source] Pharmacokinetics of intravenous ceftiofur sodium and concentration in body fluids of foalsJOURNAL OF VETERINARY PHARMACOLOGY & THERAPEUTICS, Issue 4 2009S. MEYER The objectives of this study were to determine pharmacokinetics of intravenous (i.v.) ceftiofur in foals, to compare ultra-high performance liquid chromatography tandem mass spectometry (UPLC-MS/MS) and microbiologic assay for the measurement of ceftiofur concentrations, and to determine the minimum inhibitory concentration (MIC) of ceftiofur against common equine bacterial pathogens. In a cross-over design, ceftiofur sodium was administered i.v. to six foals (1,2 days-of-age and 4,5 weeks-of-age) at dosages of 5 and 10 mg/kg. Subsequently, five doses of ceftiofur were administered i.v. to six additional foals between 1 and 5 days of age at a dose of 5 mg/kg q 12 h. Concentrations of desfuroylceftiofur acetamide (DCA), the acetamide derivative of ceftiofur and desfuroylceftiofur-related metabolites were measured in plasma, synovial fluid, urine, and CSF by use of UPLC-MS/MS. A microbiologic assay was used to measure ceftiofur activity for a subset of plasma samples. Following i.v. administration of ceftiofur at a dose of 5 mg/kg to 1,2 day-old foals, DCA had a t˝ of 7.8 ± 0.1 h, a body clearance of 74.4 ± 8.4 mL/h/kg, and an apparent volume of distribution of 0.83 ± 0.09 L/kg. After multiple i.v. doses at 5 mg/kg, DCA concentrations in CSF were significantly lower than concurrent plasma concentrations. Ceftiofur activity using a microbiologic assay significantly underestimated plasma concentrations of DCA. The MIC of ceftiofur required to inhibit growth of 90% of isolates of Escherichia coli, Pasteurella spp, Klebsiella spp, and ,-hemolytic streptococci was <0.5 ,g/mL. Intravenous administration of ceftiofur sodium at the rate of 5 mg/kg every 12 h would provide sufficient coverage for the treatment of susceptible bacterial isolates. [source] The effect of tamoxifen on the pharmacokinetics of letrozole in female ratsBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 7 2006X. Tao Abstract The effects of single doses of tamoxifen (TAM; 0.5,5 mg/kg, i.v.) and chronic pretreatment with TAM (0.1,5.0 mg/kg/day, i.p. for 7 consecutive days) on letrozole (0.5 mg/kg, i.v.) pharmacokinetics were evaluated in female Sprague-Dawley rats. The plasma concentration-time profiles of letrozole (0.1,2.0 mg/kg) after single i.v. doses were analysed by the non-compartment model with terminal half-lives (t1/2,,z) ranging from 34.3 to 37.5 h. The volume of distribution at the terminal phases (Vd(,z)) ranged from 1.9 to 2.1 l/kg and clearance (CL) varied from 0.036 to 0.042 l/(h·kg). After co-administration of TAM and letrozole intravenously, the t1/2, Vd(,z) and CL of letrozole were not significantly altered. Chronic pretreatment with TAM significantly decreased the t1/2 of letrozole by about 33%, and increased its clearance by an average of 40%. However, TAM pretreatment did not significantly affect the Vd((,z) of letrozole in female rats. Co-administration of letrozole and TAM orally increased the absorption half-life of letrozole threefold although the absolute bioavailability remained unchanged. These observations suggest that single oral doses of TAM delay the absorption of letrozole while chronic pretreatment with TAM accelerates the elimination of letrozole, probably due to induction of cytochrome P450 enzymes in rats. Copyright © 2006 John Wiley & Sons, Ltd. [source] Proarrhythmic potential of halofantrine, terfenadine and clofilium in a modified in vivo model of torsade de pointesBRITISH JOURNAL OF PHARMACOLOGY, Issue 4 2002Andrew J Batey This study was designed to compare the proarrhythmic activity of the antimalarial drug, halofantrine and the antihistamine, terfenadine, with that of clofilium a K+ channel blocking drug that can induce torsade de pointes. Experiments were performed in pentobarbitone-anaesthetized, open-chest rabbits. Each rabbit received intermittent, rising dose i.v. infusions of the ,-adrenoceptor agonist phenylephrine. During these infusions rabbits also received increasing i.v. doses of clofilium (20, 60 and 200 nmol kg,1 min,1), terfenadine (75, 250 and 750 nmol kg,1 min,1), halofantrine (6, 20 and 60 ,mol kg,1) or vehicle. Clofilium and halofantrine caused dose-dependent increases in the rate-corrected QT interval (QTc), whereas terfenadine prolonged PR and QRS intervals rather than prolonging cardiac repolarization. Progressive bradycardia occurred in all groups. After administration of the highest dose of each drug halofantrine caused a modest decrease in blood pressure, but terfenadine had profound hypotensive effects resulting in death of most rabbits. The total number of ventricular premature beats was highest in the clofilium group. Torsade de pointes occurred in 6 out of 8 clofilium-treated rabbits and 4 out of 6 of those which received halofantrine, but was not seen in any of the seven terfenadine-treated rabbits. These results show that, like clofilium, halofantrine can cause torsade de pointes in a modified anaesthetized rabbit model whereas the primary adverse effect of terfenadine was cardiac contractile failure. British Journal of Pharmacology (2002) 135, 1003,1012; doi:10.1038/sj.bjp.0704550 [source] The experimental Alzheimer drug phenserine: preclinical pharmacokinetics and pharmacodynamicsACTA NEUROLOGICA SCANDINAVICA, Issue 2000N. H. Greig Phenserine, a phenylcarbamate of physostigmine, is a new potent and highly selective acetylcholinesterase (AChE) inhibitor, with a >50-fold activity versus butyrylcholinesterase (BChE), in clinical trials for the treatment of Alzheimer's disease (AD). Compared to physostigmine and tacrine, it is less toxic and robustly enhances cognition in animal models. To determine the time-dependent effects of phenserine on cholinergic function, AChE activity, brain and plasma drug levels and brain extracellular acetylcholine (ACh) concentrations were measured in rats before and after phenserine administration. Additionally, its maximum tolerated dose, compared to physostigmine and tacrine, was determined. Following i.v. dosing, brain drug levels were 10-fold higher than those achieved in plasma, peaked within 5 min and rapidly declined with half-lives of 8.5 and 12.6 min, respectively. In contrast, a high (>70%) and long-lasting inhibition of AChE was achieved (half-life >8.25 h). A comparison between the time-dependent plasma AChE inhibition achieved after similar oral and i.v. doses provided an estimate of oral bioavailability of 100%. Striatal, in vivo microdialysis in conscious, freely-moving phenserine-treated rats demonstrated >3-fold rise in brain ACh levels. Phenserine thus is rapidly absorbed and cleared from the body, but produces a long-lasting stimulation of brain cholinergic function at well tolerated doses and hence has superior properties as a drug candidate for AD. It selectively inhibits AChE, minimizing potential BChE side effects. Its long duration of action, coupled with its short pharmacokinetic half-life, reduces dosing frequency, decreases body drug exposure and minimizes the dependence of drug action on the individual variations of drug metabolism commonly found in the elderly. [source] | |||||||||||||