Human dolasetron pharmacokinetics: II Absorption and disposition following single-dose oral administration to normal male subjects

Dolasetron is a 5-hydroxytryptamine antagonist active at type III receptors; it is presently undergoing clinical evaluation for the reduction/prevention of cancer chemotherapyinduced nausea and vomiting. A previous study demonstrated that following intravenous administration to healthy male subjects, dolasetron disappeared extremely rapidly from plasma, and less than 1 per cent of the dose appeared in the urine. A major plasma metabolite, reduced dolasetron, peaked rapidly in the plasma. In this study, dolasetron was administered orally to healthy male subjects at doses ranging from 50 to 400 mg (mesylate monohydrate). Plasma concentrations of dolasetron were low and sporadic, and there was little excreted in urine; this prevented dolasetron pharmacokinetic analysis. Reduced metabolite concentrations peaked rapidly, with a median value of 1.00 h. The median terminal disposition half-life was 7.80 h. Median values for fraction of dose excreted in urine and renal clearance were 22.2 per cent and 2.56 ml min^?1 kg^?1. Whereas areas under the plasma concentration—time curves were proportional to dose, renal clearance increased with dose (p < 0.05). However, given dose proportionality to AUC, this is probably of little therapeutic consequence. Since reduced dolasetron has significant anti-emetic activity in the ferret model, it appears that this metabolite may play a significant role in pharmacodynamic activity.     

Unterschiedliche Flüssigkeits- und Substanzbewegungen durch die Mucosa der verschiedenen Abschnitte des Intestinaltraktes beim Kaninchen

Zusammenfassung Die Schleimhaut des Duodenums beim Kaninchen sezerniert eine blutisotone Flüssigkeit, deren Hauptcharakteristikum ihr HCO₃ ^–-Gehalt von fast 100 mMol/l ist. Auf die Instillation einer Lösung, die wie das duodenale Sekret zusammengesetzt ist, reagiert das Jejunum mit einer isotonen Absorption bei nur geringfügigen Konzentrationsänderungen der Konstituenten der Instillationslösung. Das Ileum reagiert analog dem Jejunum, nur sind die Absorptionsraten für Flüssigkeit und die geprüften Solute größer als im Jejunum. Im Colon kommt es zu einer Enterosorption von Flüssigkeit mit teilweise beträchtlichen Konzentrationserniedrigungen der in der Installationslösung enthaltenen Solute.Auf die Instillation einer blutisotonen NaCl-Lösung reagiert das Jejunum stets mit einer Absorption von Flüssigkeit. Na⁺ und Cl^– werden absorbiert, während HCO₃ ^–, K⁺ und Harnstoff netto sezerniert werden. Im Colon kommt es unter den Bedingungen des 30 min-Versuches zur enterosorption von Flüssigkeit, zur Absorption von osmotisch aktivem Material, Na⁺ und Cl^–, während HCO₃ ^–, K⁺ und Harnstoff sezerniert werden.Auf die Instillation reinen Wassers reagiert das Jejunum mit einer Absorption von Flüssigkeit sowie einer Enterosorption aller geprüften Solute in das Jejunum hinein, daß fast Konzentrationsgleichheit mit dem Plasma eingestellt wird. Im Colon kommt es im 30 min-Versuch teils zur Enterosorption, teils zur Absorption von Flüssigkeit. Nach 60 min wird in allen Fällen eine Absorption von Flüssigkeit beobachtet. Die Gleichgewichtskonzentrationen im Jejunum sind: Osmolarität 296,0 mOsmol/l, Na⁺ 78,6 mMol/l, Cl^– 24,6 mMol/l, HCO₃ ^– 54,8 mMol/l, K⁺ 2,2 mMol/l, Harnstoff 59,9 mg/100 ml. Die analogen Werte für das Colon lauten: Osmolarität 184,0 mOsmol/l, Na⁺ 11,6 mMol/l, Cl^– 12,9 mMol/l, HCO₃ ^– 25,9 mMol/l, K⁺ 16,4 mMol/l, Harnstoff 18,8 mg/100 ml.     

Influence of disodium ethane-1-hydroxy-1,1-diphosphonate on vitamin D metabolism in rats

Summary The metabolism and the organ distribution of double labelled vitamin D₃ (1,2-³H-4-¹⁴C-cholecalciferol) has been studied in rats in which the bone mineralization and the intestinal calcium absorption have been inhibited by a large pose (10 mg P/kg s.c. for 7–14 days) of disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP). The most striking difference found was a reduced accumulation of radioactive cholecalciferol and its metabolites in the kidney of EHDP-treated rats. It is unlikely that this effect was due to an unspecific alteration of the functional renal tissue since blood urea, glomerular filtration rate and renal plasm a flow remained unaltered by this dose of EHDP. The EHDP-treated rats were able to form the metabolite eluted with peak IV of the silicic acid chromatographic system, that is 25-hydroxycholecalciferol. In these vitamin D repleted rats fed a high calcium diet, the tritium deficient metabolite eluted with peak V (1,25-dihydroxycholecalciferol) was only found in the intestinal mucosa of both control and EHDP groups three days after the injection of radioactive cholecalciferol, and this in a very small amount. Therefore no definitive conclusion can be drawn as to a possible interference of EHDP treatment on the production of 1,25-dihydroxycholecalciferol. The change in the renal metabolism of vitamin D in rats treated with a rachitogenic dose of EHDP may be caused by the modifications of the calcium metabolism brought about by the diphosphonate. Its relation, if any, with the decreased calcium absorption remains to be established.     

Segmental heterogeneity of swelling-induced Cl transport in rat small intestine

The effect of cell swelling induced by hypotonic media was studied in segments of rat small intestine. In the Ussing chamber, exposure to a hypotonic medium caused a decrease in short-circuit current (I _sc) and potential difference (V ^ms) in the jejunum, whereas the ileum responded with an increase in I _sc and V ^ms. The transition from one pattern to the other was located about in the middle of the small intestine. Tissue conductance decreased in both segments, probably due to a reduction of paracellular shunt conductance induced by the cell swelling. Voltage scanning experiments revealed that the observed decrease in total tissue conductance in the ileum was caused solely by a decrease in local conductance in the villus region while the crypt conductance did not change, suggesting that the decrease in paracellular conductance of the crypts is compensated by an increase in cellular conductance. The response in both segments was dependent on the presence of Cl⁻ and was blocked by the Cl⁻ channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB). It was not affected by the neurotoxin tetrodotoxin. In the jejunum the swelling-induced decrease in I _sc was reduced in the presence of the cyclooxygenase inhibitor, indomethacin, or the lipoxygenase inhibitor, nordihydroguaiaretic acid. In the ileum the Cl⁻ secretion induced by hypotonicity was blocked by the K⁺ channel blocker quinine and was reversed into a decrease in I _sc when serosal Ca²⁺ was zero. We conclude that the observed volume regulatory changes are initiated in the jejunum by an eicosanoid-mediated opening of basolateral Cl⁻ channels and in the ileum by a Ca²⁺-mediated opening of K⁺ channels which enhances apical Cl⁻ efflux. Received: 27 June 1995/Received after revision: 8 December 1995/Accepted: 28 December 1995     

Gemfibrozil absorption and elimination in kidney and liver disease

Summary The disposition of the lipid-lowering drug gemfibrozil was studied in patients with either renal (n= 8) or hepatic disease (n= 8) and compared to those of healthy volunteers (n= 6). Gemfibrozil was determined in plasma and urine by means of a HPLC method. Urine was also analyzed for gemfibrozil conjugates.Following oral administration of 900 mg gemfibrozil, maximal plasma levels of the parent drug were 46.1±15.8 g/ml, attained after 2.2±1.1 h. In chronic renal failure and in liver cirrhosis the plasma concentrations of gemfibrozil did not significantly differ from that of controls except in those patients who were comedicated with antacids. These patients had significantly lower C_max and AUC values. The elimination half-life of the drug was 1.5 h in controls, 2.4 h in renal failure, and 2.1 h in liver disease. In healthy volunteers, only 0.02 to 0.15% of the given dose was recovered in the urine as parent gemfibrozil, while conjugates made up 7–14%. In patients with renal failure also, only traces of parent gemfibrozil could be detected, and conjugates accounted for 0.5–9.8%. In those with liver disease, however, about 0.1–0.2% were recovered in urine as parent gemfibrozil and up to 50% as conjugates. Strikingly, the amount of excreted conjugates in the urine was positively correlated to the direct bilirubin plasma concentration. It can be concluded that the elimination of gemfibrozil is not significantly influenced by renal failure. However, comedication with antacids markedly reduced plasma disposition of the drug. Patients with severe liver disease excreted more conjugated gemfibrozil via the kidney than did healthy controls. Thus, transfer across the canalicular cell membrane to the bile duct, rather than drug metabolization, is primarily disturbed in liver disease. Gemfibrozil accumulation is unlikely to occur in either kidney or liver disease.Abbreviations Cl_r creatinine clearance (ml/min) - HPLC high pressure liquid chromatography - C_max maximal plasma concentration (g/ml) - t_max time (h) after which C_max is attained - k_e elimination rate constant (h^–1) - t_1/2 elimination half-life (h) - A_e amount of drug excreted into the urine (% of given dose) - MRT mean residence time (h) - AUMC area under the first moment curve (g h²/ml) - AUC area under the plasma level time curve (g·h/ml) - ANOVA analysis of variance The paper is gratefully dedicated to G.W. Löhr     

Characteristics of the transport of oxalate and other ions across rabbit proximal colon

In order to characterize oxalate handling by the P2 segment of the rabbit proximal colon, the fluxes of [¹⁴C]oxalate, ²²Na⁺, and ³⁶Cl^– were measured in vitro using conventional short-circuiting techniques. In standard buffer the proximal colon exhibited net secretion of Na⁺ (–2.31±0.64 equiv cm^–2 h^–1), negligible net Cl^– transport, and net secretion of oxalate (–12.7±1.6 pmol cm^–2 h^–1). Replacement of buffer Na⁺ or Cl^– abolished net oxalate secretion, while HCO ₃ ^– -free media revealed a net absorption of oxalate (19.3±4.2 pmol cm^–2 h^–1) and stimulated NaCl absorption. Mucosal amiloride and dimethylamiloride (1 mM) significantly reduced the unidirectional fluxes of oxalate and enhanced sodium secretion by decreasing J _ms ^Na . The anion exchange inhibitor 4,4-diisothiocyanatostilbene-2,2-disulfonic acid (DIDS; 0.1 mM, both sides) reduced the unidirectional fluxes of oxalate and chloride. Serosal epinephrine (50 M) stimulated oxalate absorption (21.3±6.3 pmol cm^–2 h^–1) and sodium absorption (5.71±1.20 equiv cm^–2 h^–1), whereas dibutyryl-cAMP enhanced oxalate secretion (–43.4±6.9 pmol cm^–2 h^–1) and stimulated chloride secretion (–7.27 ±0.64 equiv cm^–2 h^–1). These results indicate that the P2 segment of the proximal colon possesses (a) secretory as well as absorptive capacities, (b) oxalate fluxes that are mediated by pathways involving Na⁺, Cl^–, HCO ₃ ^– transport and (c) a net oxalate flux that is sensitive to absorptive and secretory stimuli.     

A pharmacokinetic approach to the establishment of biopharmaceutic characteristics of different acetylsalicylic acid formulations in man

Eleven acetylsalicylic acid (ASA) formulations were administered to 26 healthy volunteers in a cross-over design. The properties of the preparations differed from conventional, effervescent, buffered to buccal. The objectives of this study were:

• 1 Consideration of the general aspects of a biopharmaceutical study: which parameter for which biopharmaceutic characteristic?
• 2 Measurement of the kinetic parameters of ASA: first-pass effect, mean residence time, mean appearance time, total body clearance, apparent volume of distribution, half-lives, etc.
• 3 Comparison of the formulations.

Most of the formulations yield mean residence times for ASA of 0.3–1.0h, which do not differ significantly (p > 0.05). For most of the products the first-pass effect is about 40 per cent; the average values of the apparent volume of distribution and whole body clearance, corrected for the first-pass effect, are about 201 and 650 ml min^?1, respectively. Peak levels are reached slowly for the buccal formulations, and rapidly for the buffered products. It is difficult, especially for ASA, to characterize the gastro-intestinal absorption with pharmacokinetic model parameters, because the first-pass effect is large and often elimination of ASA is faster than absorption. The model-independent approach has the special advantages of calculating reliable pharmacokinetic parameters, and creating theoretical possibilities to characterize the absorption patterns of the different formulations in a quantitative way. No significant differences in the values of the parameters are found between most of the formulations. The ASA first-pass effect is reasonably constant and buccal application has no advantage. Enteric coating of the outer layer of ASA formulations causes inconsistent absorption and may be categorized under ‘artificial mistakes’.     

氟尿嘧啶对大鼠小肠的损伤作用研究

目的：探讨氟尿嘧啶对大鼠小肠的损伤作用,方法：通过胃管连续2d给予大鼠尿嘧啶125mk/kg.d,观察给药后第1天－第7天大鼠每日饮食量的变化,给药前和给药后的第8天分别称大鼠体重,给药后第8天测定门静脉血流量及门静脉压,分析小肠形态学变化,观察小肠对色氨酸吸收能力,测定动脉血谷氨酰胺的浓度,结果：给药后第1天－第7天大鼠饮食量均明显低于正常,尤其是第2天－第4天最为严重,第8天大鼠体重下降,小肠结构有明显损伤,门静脉血流量减少,门静脉压下降,小肠对色氨酸的吸收及动脉血谷氨酸胺浓度明显下降,与对照组相比的均有显著差异,结论：氟尿嘧啶可导致大鼠小肠结构和功能的明显障碍。     

In vivo differences between Asian, Black and White in the stratum corneum barrier function

The stratum corneum barrier function of Blacks, Caucasians and Asians were compared in vivo. A noninvasive technic, laser doppler velocimetry (LDV), was used to evaluate the cutaneous penetration of nicotinates by the determination of the lag time before vasodilatation induced by the application of those local vasodilatator drugs. The study was performed on untreated skin and after removal of the stratum corneum by 12 strips. The influence of molecular weight and solubility of different nicotinates (methyl, ethyl, hexyl and vitamin E) were also studied on Japanese skin. Vasodilatation lag times assessed by LDV, with methyl nicotinate (MN), showed that skin permeability was more important in Asians (P < 0.01)=" and=" in=" caucasians=">P < 0.05)=" than=" in=" blacks.=" moreover=" asian=" skin=" was=" significantly=" more=" sensitive=" to=" stripping=">P < 0.05)=" than=" black=" skin.=" a=" significant=" shorter=" lag=" time=" was=" obtained=" with=" small=" and=" hydrophilic=" nicotinates=" (methyl=" and=" ethyl)=">P < 0.01)=" compared=" to=" a=" lipophilic=" one=" (hexyl).=" the=" alteration=" of=" the=" stratum=" corneum=" barrier=" function=" by=" stripping=" showed=" a=" more=" important=" modification=" with=" mn=">P < 0.05)=" than=" with=" hexyl=" nicotinate.=" consequently,=" this=" noninvasive=" method=" can=" evaluate=" the=" modifications=" of=" the=" stratum=" corneum=" barrier=" function=" and=" racial=" origin=" has=" to=" be=" taken=" into=" account=" in=" the=" determination=" of=" skin=">     

EDTA-NaOH吸收液--分光光度法测定空气中硫化氢的研究

本文对EDTA -NaOH作为硫化氢吸收液进行探讨和研究。试验表明 :当空气中硫化氢含量为国家最高允许液度 0 .6～ 6倍时 ,吸收液采样效率为 98.2～ 10 0 % ,催化剂与显色剂混合使用 ,可降低空白值 ,提高方法灵敏度。本法准确度 ( p)为 93 .0 % ,精密度合并变异系数 (cv)为 3 .93 % ;检出限、测量限分别为 7× 10 -2 μg/5ml和1.7× 10 -1μg/5ml;规定采气量为 0 .5L时 ,则最小检出浓度为 0 .6 8mg/m3。