The pharmacokinetic assessment of sodium cromoglycate

The plasma concentration of sodium cromoglycate (SCG) was measured in four healthy subjects by radioimmunoassay after a 4 mg intravenous dose and after inhaling from 20 mg capsules, and from 10 and 30 mg ml^?1 nebulizer solutions. The mean absorption constant (K₁) after inhalation was 0·43 h^?1. The mean elimination constant from the plasma (K_elim) after intravenous administration was 11·5 h^?1, and that after inhalation was similar. The apparent volume of distribution of SCG (V_dβ) was 0·2 litre kg^?1 and the mean plasma clearance was 0·35 litre h^?1kg^?1. The amount of SCG absorbed after inhalation varied according to the method of inhalation and dose. After the inhalation of powder from 20 mg capsules, 1·30–3·96 mg reached the plasma, after inhalation of SCG produced by nebulizing a 10 mg ml^?1 solution for 5 min at 10 psi using a Minineb nebulizer 0·19—0·31 mg reached the plasma and when the solution was increased to 30 mg ml^?1 the figure was 0·33—0·45 mg.     

Glucuronidation Metabolic Kinetics of Valproate in Guinea Pigs: Nonlinear at Clinical Concentration Levels

Purpose. Nonlinear conjugation metabolic rate of valproic acid (VPA) has been speculated previously from plasma elimination and liver concentration of VPA in guinea pigs. The purposes of the present study were to assess our speculation by direct measurement of VPA glucuronidation rate in vitro. Methods. VPA at various concentrations (10–200 µg/ml) was incubated with guinea-pig liver-homogenate, mitochondria or microsome in the presence of cofactor, uridine 5-diphosphoglucuronic acid (UDPGA). The maximum glucuronidation rate (V_max) and Michaelis-Menten constant (K_m) of VPA were determined. Results. On a body weight basis, the V_max and the K_m values of VPA glucuronidation estimated from liver homogenate were 1.8 µmol/min/kg and 0.3 µmol/ml, respectively; and that from microsome suspension were 1.2 µmol/min/kg and 0.16 µmol/ml, respectively. These data are comparable with the primary metabolic parameters observed from previous in vivo study. The glucuronidation clearance calculated from these parameters was 0.10–0.48 fraction of total clearance, which was in agreement with the reported data observed from clinical and animal urinary recoveries of VPA-G. The glucuronidation reaction was not detectable in mitochondria suspension. Conclusions. The glucuronidation kinetics of VPA is nonlinear and saturable within clinical concentration range. Estimation of in vivo VPA glucuronidation kinetics from in vitro kinetic parameters is feasible.     

Effect of infusion duration on valproate pharmacokinetics

The pharmacokinetics of intravenously administered valproic acid (VPA) were investigated in 16 healthy male volunteers in a single-dose, fasting, four-period, randomized, double-blind, placebo-controlled, parallel design study. Subjects were randomly assigned to be infused a single dose of sodium valproate equivalent to 1000 mg VPA or placebo over each of four different time periods. Valproate concentrations in plasma were determined using gas chromatography with flame ionization detection. The pharmacokinetic parameters were determined by both non-compartmental and model-dependent techniques. Analyses of variance (ANOVAs) were performed to detect any statistical differences among the regimens. Overall, the pharmacokinetics of valproate were similar after infusions of 5, 10, 30, and 60 min, with an average terminal-phase half-life of 15.9 h. There were modest differences in overall clearances among the regimens, with the 5 min infusion producing a mean area under the plasma concentration-time curve (AUC; 1877 μg·h ml^?1) that was significantly (13 to 16 per cent) higher than the means for the longer infusions (1614–1656 μg·h ml^?1). Differences in distribution were also noted as a function of infusion duration. The shortest duration produced a significantly smaller terminal volume of distribution (12.8 vs 14.2–15.1 l) and more rapid tissue equilibration. The α-phase rate constant declined from a mean of 5.1 h^?1 after the 5 min infusion to a mean of 0.9 h^?1 after the 60 min infusion. The distributional differences are almost certainly related to the saturable protein binding of valproate. However, the lower clearance after the 5 min infusion indicates that there may have also been partial saturation of one of the metabolic pathways of valproate during the distributive phase, and that the increase in f_u was smaller than the decrease in CL′_int, such that the product of f_u·CL′_int showed a net decrease.     

Pharmacokinetic study of a tripeptide HIV-1 protease inhibitor,KNI-174, in rats after intravenous and intraduodenal administrations

Recently, as a new type of anti-AIDS drug, an HIV-1 protease inhibitor, KNI-174, has been synthesized; it shows a potent and selective HIV-1 protease inhibitory activity in vitro. In this study, we developed an HPLC assay system for KNI-174 in rat plasma and examined the pharmacokinetics of KNI-174 in rats using this assay method after both intravenous (i.v.) and intraduodenal (i.d.) administrations to obtain the disposition characteristics and bioavailability of this new anti-AIDS drug. This HPLC assay method is specific to KNI-174 and the standard curve was linear from 0.02 to 30 μg ml^?1 plasma. After i.v. administration, 10.0 mg kg^?1, KNI-174 disappeared from the rats' plasma in a three-exponential decay. The mean terminal elimination half-life, t_1/2ÀZ, was 3.97 ± 0.19 (S.E.)h, the total body clearance, CL_tot, was 9.53 ± 1.08 ml min^?1 and the distribution volume at steady state, V_{d, ss}′ was 7070 ± 960 ml kg^?1. In the case of the i.d. administration, 10.0 mg kg^?1, the mean peak plasma concentration, C_max, and the peak time, t_max, were 0.196 ± 0.076 μg ml^?1 and 0.444 ± 0.193 h, respectively. The bioavailability of KNI-174 till infinity, BA^(0-infinity), was 5.37 per cent. Because the IC₅₀ of KNI-174 against HIV-1 in PHA-PBM was 138 ng ml^?1, the time needed for maintaining the concentrations above IC₅₀ after a single i.d. administration of KNI-174 is estimated to be 0.350 ± 0.184 h.     

Pharmacokinetics of 14C-DMPS (sodium-1,3 14C-2,3-dimercaptopropane-l-sulphonate) in beagle dogs

The pharmacokinetics of labelled DMPS (sodium-1,3 ¹⁴C-2,3-dimercaptopropane-1-sulphonate) have been studied in four beagle dogs following bolus intravenous injection (65-7 μmolkg^?1) and oral administration (197μmol kg^?1). Following intravenous injection the main kinetic parameters were t_1/2 = 43min, V_β = 160 ml kg^?1, and plasma clearance Cl_p = 2.6ml min^?1 kg^?1. Following oral administration ¹⁴C-DMPS is rapidly absorbed with peak concentrations (478 ± 25 umol 1^?1) measured after 30–45 min. About 60 per cent of the oral dose was absorbed. Estimates of t_1/2, V_β, and Cl_p after oral administration were in close agreement with the values obtained in the intravenous study. ¹⁴C-DMPS is eliminated from the body by the kidneys. About 70 per cent of ¹⁴C-DMPS in dog plasma are bound to proteins. Binding is even higher in plasma from rat and man.     

Pharmacokinetics and metabolism of NO-1886, a lipoprotein lipase-promoting agent,in cynomolgus monkey

1. The study was conducted to investigate the pharmacokinetics and metabolism of NO-1886 (diethyl 4-[(4-bromo-2-cyanophenyl) carbamoyl] benzylphosphonate) in cynomolgus monkeys.

2. After single intravenous administration of NO-1886 at a dose of 3?mg?kg^?1, the total clearance (CL_tot), area under the plasma concentration–time curve (AUC_0–t), half-life (t_1/2), and volume of distribution (V_d) in cynomolgus monkeys were 531?ml?h^?1?kg^?1, 5.63?µg?h?ml^?1, 0.96?h and 679?ml?kg^?1, respectively. The AUC_0–t for oral administration of NO-1886 (3?mg?kg^?1) was 4.23?µg?h?ml^?1 and the bioavailability was 75%.

3. M-2 (ethyl 4-[(4-bromo-2-cyanophenyl) carbamoyl] benzylphosphonate) and M-3 (4-[(diethoxy-phosphoryl) methyl)] benzoic acid) were present as metabolites in plasma and urine. In faeces, M-2 was present but M-3 was not.

4. The major metabolite of NO-1886 in liver S9 or microsomes was M-2 in the presence of NADPH. On the other hand, M-3 was formed in the absence of NADPH in liver S9 or microsomes and its formation was inhibited by bis-(?p-nitrophenyl) phosphate (BNPP) in liver S9, suggesting that the formation of M-3 was catalysed by carboxylesterase.

5. The findings suggest that the main metabolic pathway of NO-1886 in cynomolgus monkeys is the O-deethylation of NO-1886 to M-2, as in rats and humans, and that the hydrolysis of the amide bond is a minor metabolic pathway.     

Alterations in Renal Uptake Kinetics of the Xanthine Derivative Enprofylline in Endotoxaemic Mice

The pharmacokinetics and renal uptake of enprofylline, which is primarily excreted into the urine by an active tubular secretion mechanism, were investigated in endotoxaemic mice by lipopolysaccharide isolated from Klebsiella pneumoniae. Lipopolysaccharide (1 mg kg^?1) was infused 2 h before starting the examination, thereby inducing a decrease in the systemic clearance and an increase in the steady-state volume of distribution of enprofylline while inducing no changes in the urinary recovery (> 90%). The protein binding of enprofylline significantly decreased in the presence of lipopolysaccharide. Both the systemic clearance for unbound enprofylline and glomerular filtration rate decreased in the treated mice. A nonlinear relationship was found in both groups between the steady-state unbound plasma concentration and renal uptake of enprofylline after constant infusion for 1 h. The renal uptake rate of enprofylline decreased in the treated mice. Lipopolysaccaharide caused increases in the apparent maximum capacity for renal uptake (V_max) from 17.3 to 32.2 μg h^?1 g^?1 of kidney and in the Michaelis–-Menten constant (K_m) from 2.7 to 21.7 μg mL^?1 and decrease in the nonsaturable uptake rate constant (K_d) from 0.87 to 0.43 mL h^?1 g^?1 of kidney. These results indicate that lipopolysaccharide decreases the renal tubular secretion of enprofylline by inducing a decrease in the renal uptake ability.     

Influence of Age on the Disposition and Renal Handling of Enprofylline in Rats

Abstract— The effects of ageing on the pharmacokinetics, renal handling and protein binding of enprofylline were investigated in 6-, 13- and 18-month-old male Fischer 344 rats. Concentrations of enprofylline in plasma and urine were determined by HPLC, and pharmacokinetic parameters were estimated by model-independent methods. No significant differences in the volume of distribution, systemic clearance of enprofylline or urinary recovery of unchanged enprofylline (> 85%) were observed among any of the groups of rats. The dissociation constant and free fatty acid concentration in plasma increased with age. Age-dependent decreases in the systemic clearance for unbound drug were observed, and the volume of distribution for unbound drug tended to decrease with age. The ratio of systemic clearance for unbound drug to the glomerular filtration rate (GFR) decreased with ageing. Ageing was associated with decreases in the apparent maximum capacity of transport (V_max) (223·33,160·24 and 142·98 μg min^?1 kg^?1 for 6-, 13- and 18-month-old rats, respectively) and in the tubular secretory intrinsic clearance (V_max/K_m) of enprofylline (75·45, 51·03 and 44·13 mL min^?1 kg^?1, respectively), while a slight change in the Michaelis-Menten constant (K_m) was observed. These results indicate that the mechanism responsible for age-related changes in the disposition and renal handling of enprofylline may be responsible for a decrease in the ability of the tubular anion transport system.     

Plasma pharmacokinetics and urinary and biliary excretion of a new potent tripeptide HIV-1 protease inhibitor,KNI-272, in rats after intravenous administration

The pharmacokinetic (PK) characteristics of KNI-272, a potent and selective HIV-1 protease inhibitor, were evaluated in rats after intravenous (IV) administration. The effect of dose on KNI-272 plasma kinetics, and the urinary and biliary elimination kinetics of KNI-272, were examined. After IV administration of 10.0 mg kg^?1 KNI-272, the mean terminal elimination half-life, t_1/2λz, was 3.49 ± 0.19 (SE) h, the total plasma clearance, CL_tot, was 15.1 ± 1.2 mL min^?1 and the distribution volume at steady state, V_d,ss, was 3790±280 mL kg^?1. On the other hand, after 1.0mg kg^?1 IV administration, t_d,ss, was 3.04±0.11 h, CL_tot was 15.9±0.2mL min^?1, and V_d,ss was 6950±600 mL kg^?1. The PK parameters of KNI-272 after IV administration showed that the disposition of KNI-272 in the rat plasma is linear within the dose range from 1.0 to 10.0mg kg^?1. Using an equilibrium dialysis method, the plasma binding of KNI-272 was measured in vitro. The free fractions were 17.7 ± 0.6%, 12.1±1.5%, and 13.8 ± 1.4% at the total concentration ranges of 9.898 ± 0.097 μg mL^?1, 0.888 ± 0.008 μg mL^?1, and 0.470±0.55 μg mL^?1, respectively. The percentages of the dose excreted into the urine and bile as the unchanged form were 1.20 ± 1.06% and 1.61 ± 0.32% at 1.0mg kg^?1 dose, and 0.164 ± 0.083% and 1.42 ± 0.26% at 10.0 mg kg^?1 dose, respectively. The renal clearance (CL_R) and the biliary clearance (CL_B) were calculated to be 0.191 and 0.256mL min^?1 for 1.0mg kg^?1, and 0.0248 and 0.215 mL min^?1 for 10.0 mg kg^?1, respectively. When comparing these values with the CL_tot values, the urinary and biliary excretion of KNI-272 are minor disposition routes.     

Midazolam α-Hydroxylation by Human Liver Microsomes in vitro: Inhibition by Calcium Channel Blockers,Itraconazole and Ketoconazole

Abstract: The inhibitory effects of five calcium channel blockers (diltiazem, isradipine, mibefradil, nifedipine and verapamil) and three azole antifungal agents (itraconazole, hydroxyitraconazole and ketoconazole) on the α-hydroxylation of midazolam, a probe drug for CYP3A4-mediated interactions in humans, were studied in vitro using human liver microsomes. IC₅₀ and K_i values were determined for each inhibitor. The kinetics of the formation of α-hydroxymidazolam were best described by simple Michaelis-Menten kinetics. The estimated values of V_max and K_m were 696 pmol min.^?1 mg^?1 and 7.46 μmol l^?1, respectively. All the compounds studied inhibited midazolam α-hydroxylation activity in a concentration-dependent manner, but there were marked differences in their relative inhibitory potency. Ketoconazole was the most potent inhibitor of midazolam α-hydroxylation (IC₅₀ 0.12 μmol l^?1), being 10 times more potent than itraconazole (IC₅₀ 1.2 μmol l^?1). The inhibitory effect of hydroxyitraconazole (IC₅₀ 2.3 μmol l^?1) was almost as large as that of itraconazole. Among the calcium channel blockers, mibefradil was the most potent inhibitor of the α-hydroxylation of midazolam, with an IC₅₀ value (1.6 μmol l^?1) similar to that of itraconazole. The other calcium channel blockers were much weaker inhibitors than mibefradil: verapamil exhibited a modest inhibitory effect with an IC₅₀ of 23 μmol l^?1, while isradipine, nifedipine and diltiazem, with IC₅₀ values ranging from 57 to >100 μmol l^?1, were weak inhibitors. This rank order of potency against the α-hydroxylation of midazolam was verified by the K_i values. With the exception of diltiazem, these in vitro results conform with the observed interaction potential of these agents with midazolam and many other CYP3A4 substrates in vivo in man.     

The Metabolic Fate of the Anti-HIV Active Drug Carrier Succinylated Human Serum Albumin after Intravenous Administration in Rats

The pharmacokinetics and metabolic fate of the intrinsically active (anti-HIV) drug carrier succinylated human serum albumin (Suc-HSA) was studied in rats. Suc-HSA was prepared by derivatizing HSA with 1,4-[¹⁴C]-succinic anhydride, a modification by which all available εNH₂-groups in HSA were converted into carboxylic groups.

After iv injections of 0.3, 1.0, 3.0 and 10.0 mg/kg in freely moving rats, Suc-HSA showed a dose dependent elimination pattern, indicating a saturable elimination pathway. The Michaelis-Menten parameters V_max and K_m were 98.7 μg.min^?1.kg^?1 and 8.5 μg.ml^?1 respectively. The kinetics of Suc-HSA was influenced by anaesthesia. In anaesthetised animals, V_max and K_m were found to be 26.9 μg.min^?1.kg^?1 and 0.26 μg.ml^?1, respectively. This implies an intrinsic clearance of 100ml.min^?1.kg^?1, which is about 10-fold higher as compared to 12 ml.min^?1.kg^?1 in freely moving animals.

Intravenous administration of a sub-saturable dose of 3.0mg.kg^?11,4-[¹⁴C]-Suc-HSA to freely moving rats resulted in a biphasic elimination with an initial t1/2 of 20 min and a terminal t1/2 of 40 hrs. Excretion of metabolites in urine and faeces lasted for at least 48 hours. About 70% of the radioactive dose was excreted in urine, whereas maximally 2% was detected in faeces. Suc-HSA was degraded to its individual amino acids including succinylated lysine (the only radioactive product formed). Succinylated lysine was not further metabolised and mainly excreted via the urine. Immunohistochemical staining showed that even after 48 hrs Suc-HSA could be detected in livers. Together with the urinary excretion patterns, this points to a gradual degradation of Suc-HSA.     

Comparison of a new orally potent tripeptide HIV-1 protease inhibitor (anti-aids drug) based on pharmacokinetic characteristics in rats after intravenous and intraduodenal administrations

Recently, a series of KNI compounds such as KNI-227 and KNI-272 has been synthesized and shows potent and selective HIV-1 protease inhibitory activity in vitro. In this study, we developed an HPLC assay system for KNI-227 and KNI-272 in rat plasma and examined the pharmacokinetic characteristics in rats after both intravenous (i.v.) and intraduodenal (i.d.) administrations to obtain the disposition characteristics and bioavailabilities of these new anti-AIDS drugs. After i.v. administration of KNI-227, 10.0mg kg^?1, the mean terminal elimination half-life, t_1/2λz, was 0.808±0.161(SE)h, the total body clearance, CL_tot, was 11.7±3.3 ml min^?1 and the distribution volume at steady state (V_d,ss) was 1410.460 ml kg^?1. On the other hand, after i.v. administration of KNI-272, 10.0mg kg^?1, t_1/2λz was 2.86±0.78 h, CL_tot was 15.3±1.4 ml min^?1 and V_d,ss was 3440.670 ml kg^?1. In the case of the i.d. administration of drugs, the mean peak plasma concentrations, C_max, of KNI-227 and KNI-272 were 0.374±0.110μg ml^?1 and 0.900±0.093 μg ml^?1, respectively. The bioavailabilities (BA) of KNI-227 and KNI-272 to infinity, BA^(0-∞), were 5.90% and 42.3%, respectively. As compared with the lead compound, KNI-174, the BA of KNI-272 was improved about 10 times. Although the anti-AIDS virus activity of these two drugs has not been investigated in vivo, KNI-272 is expected to be a better candidate for oral anti-AIDS therapies.     

Pharmacokinetics and pharmacodynamics of morphine-3-glucuronide in rats and its influence on the antinociceptive effect of morphine

In this study the pharmacokinetics and pharmacodynamics of morphine-3-glucuronide (M3G) were investigated in rats after i.v. administration as a bolus dose (86.7 μmol kg^?1) and as a constant rate infusion (2.9 μmol h^?1) over 5 days. After the bolus dose, the clearance (Cl) was 12.1 ± 0.6 ml min ^?1* kg, the volume of distribution at steady state (V_ss) 1.68 ± 0.89 1 kg^?1, the half-life of the first phase 13.2 ± 1.8 min and the halflife of the second phase 11.6 ± 7.7 h. After the constant rate infusion, Cl was 10.5 ± 1.7 ml min^?1*kg. The antagonistic effect of M3G on the antinociceptive effect of a bolus dose of morphine (35 μmol kg^?1) was tested during steady state concentrations of M3G on day 4 and to M3G naïve rats. No antinociceptive, hyperalgesic or withdrawal effects were observed as a result of M3G administration, but a significantly lower antinociceptive effect of morphine was found in the M3G infusion group compared to the control group. Systemically administered M3G antagonized the antinociceptive effect of morphine, but this cannot be the only explanation to the tolerance development observed after morphine administration.     

Intravenous verapamil kinetics in rats: Marked arteriovenous concentration difference and comparison with humans

The pharmacokinetics of verapamil, a calcium channel blocker, were studied in male Sprague—Dawley rats following i.v. administration at a dose of 1 mg kg^?1. Both arterial and venous blood were collected and the plasma drug concentrations were determined by reversed-phase high-performance liquid chromatography. Verapamil was distributed to the extravascular tissues very rapidly as indicated by the large V_dss (2.99±0.57 1 kg^?1) and V_dβ (5.08 ± 0.541 kg^?1). The apparent terminal plasma T_1/2, MRT_iv, and CL_p were 1.59 ± 0.46, 1.26 ± 0.12 h, and 40.4 ± 9.73 ml min^?1 kg^?1, respectively. Marked arterial/venous differences were found with a considerable influence on the MRT and V_dss, and the terminal phase venous levels were higher than arterial levels by 103, 69, and 90%, respectively, for the three rats studied. The distribution of verapamil between plasma and erythrocytes occurred very rapidly and was identical in vitro and in vivo. The average blood to plasma and plasma to blood cell concentration ratios were 0.85 and 1.47, respectively. In contrast to propranolol, blood data rather than plasma data should be used to predict the hepatic extraction ratio of verapamil (0.87). The plasma protein binding of verapamil in humans (90%) and rats (95%) were quite similar and constant over the wide concentration range studied. A comparison of some pharmacokinetic parameters between rats and humans is presented and the potential shortcomings of using T_1/2 or CL_p and the advantage of using CL_u (unbound plasma clearance) in interspecies scaling is also discussed.     

Prediction of clinical pharmacokinetic parameters of linezolid using animal data by allometric scaling: applicability for the development of novel oxazolidinones

1.?Allometric scaling has previously been used as an effective tool for the prediction of human pharmacokinetic data. The pharmacokinetic data for linezolid, a novel oxazolidinone to treat Gram-positive pathogens, in mice, rats and dogs were subjected to simple allometric scaling. Generated allometric equations for parameters such as clearance (CL), volume of distribution (V_ss) and elimination rate constant (K₁₀) were used to predict human pharmacokinetic parameters including elimination half-lives. In addition, the human plasma concentration–time curve was simulated using a one-compartmental model.

2.?Application of simple allometry (Y?=?aW^b) for animal parameters such as CL, V_ss, and K₁₀ showed excellent allometric fit (r?≥?0.98). The allometric equations for CL, V_ss, and K₁₀ were??0.5465W^0.6595,??0.1369W^0.9246, and??0.4117W^–0.3139, respectively. The confidence in predictability of CL and V_ss parameters was particularly high since the allometric exponents of CL and V_ss almost approached the suggested values of 0.75 and 1.00, respectively.

3.?Animal pharmacokinetic parameters generated in the present authors’?laboratories for linezolid were in close agreement with reported literature values. The predicted human values for CL (4.68?l?h^?1), V_ss (37.07 litres), and K₁₀ (0.10?h^?1) were within the range observed for linezolid in the literature (CL?=?4?10.5 l?h^?1; V_ss?=?21???53 litres; K₁₀?=?0.09???0.3?h^?1). The human half-life (t_1/2) predicted using allometry (6.9?h) was similar to reported values in humans of 5?h. In summary, the retrospective analysis for linezolid suggests that allometric scaling can be used as a prospective tool for predicting human pharmacokinetic parameters of novel oxazolidinones.     

The pharmacokinetics of methotrexate after intravenous administration of methotrexate-loaded proliposomes to rats

The pharmacokinetics and tissue distribution of methotrexate (MTX) were investigated after intravenous (i.v.) injection of free MTX (treatment I), MTX-loaded proliposomes (treatment II), and empty proliposomes mixed manually with free MTX (treatment III), 8 mg kg^?1, to rats using an HPLC assay. After i.v. infusion in 1 min, the plasma concentration of MTX (C_p), the area under the plasma concentration-time curve (AUC, 639 versus 913 μg min mL^?1), the terminal half-life (t_1/2, 48.8 versus 397 min), the mean residence time (MRT, 8.40 versus 325 min), and the apparent volume of distribution at steady state (V_ss, 98.1 versus 2800 mL kg^?1) were significantly higher; however, the total body clearance (CL, 12.5 versus 8.76 mL min^?1 kg^?1), renal clearance (CL_R, 4.49 versus 2.78 mL min^?1 kg^?1), non-renal clearance (CL_NR, 7.50 versus 5.99 mL min^?1kg^?1), and the amount of MTX excreted in urine (X_u, 808 versus 685 μg, p < 0.0948) were significantly lower from treatment II than from treatment I. This could be due to the fact that some of the MTX-loaded liposomes (formed immediately after hydration of MTX-loaded proliposomes) are entrapped in tissues and the rest are present in the plasma (higher MRT and V_ss from treatment II), and MTX is slowly released from MTX-loaded liposomes (higher t_1/2 from treatment II). In the present HPLC assay, the concentrations of MTX represent the sum of free MTX and MTX loaded in liposomes (higher C_p and AUC, slower CL from treatment II). After i.v. infusion in 1 min, some pharmacokinetic parameters, such as t_1/2, MRT, and V_ss, were significantly different between treatments I and III; however, the differences seemed to be smaller than those between treatments I and II. After 30 min from i.v. infusion, the tissue to plasma (T/P) ratios of MTX in kidney and stomach from treatment II were significantly lower than those from treatment I. This suggested that the i.v. administration of MTX-loaded proliposomes might have fewer side effects in the organs than that of free MTX. The mean amount of MTX loaded in MTX-loaded proliposomes was 2.54 mg/g proliposomes and the MTX was released slowly from hydrated MTX-loaded proliposomes when incubated with phosphate-buffered saline (PBS), rat plasma, or rat liver homogenate.     

A New Method for the Measurement of Nitrosoureas in Plasma: an H.P.L.C. Procedure for the Measurement of Fotemustine Kinetics

1. An analytical method for a novel nitrosourea, fotemustine, has been developed using solid-phase extraction and?h.p.l.c. with u.v. detection. As part of the development, different methods for stabilising fotemustine after sample collection have been investigated. The method has been successfully applied to pharmacokinetic studies in monkeys and man.

2. Providing plasma was separated immediately from blood and frozen within 3?min of collection, negligible degradation of fotemustine occurred. The samples could then be stored at —20°C in the dark for up to six days particularly if thawing prior to analysis was accelerated using a 50°C water-bath so that it was complete within 3?min. Equivalent results were also obtained with samples stabilised with 0·1?m citric acid immediately after the preparation of plasma.

3. The analytical method showed good precision with a within-day variation ranging between ±10.7% at the lowest concentration investigated (0.1 μg ml^?1) to 2.0% at 50.0 μgml^?1. The accuracy of measurement was from 108.9% to 97.6% at 0.1 and 50.0 μg ml^?1 respectively and the response was linear up to 50 μg ml^?1. The minimum level of quantitation was 20 ng ml^?1.

4. After a single intravenous bolus dose of [¹⁴C]fotemustine (100mg m^?2) to Cynomolgus monkeys, intact drug levels rapidly declined (t_1/2 12.6±0.5?min) although the halflife of radioactivity (approx 100?h) was much longer. The plasma clearance of fotemustine was 225±63 ml min^?1 with a volume of distribution based on area of 4.1±1.2 litres.

5. As with monkey, plasma levels of intact fotemustine in a patient given [¹⁴C]-drug as a 1?h constant rate intravenous infusion (approx. 100?mg m^?2), declined rapidly but with a half-life of 23.2?min. Again, the half-life for total radioactivity was considerably longer (30.8?h). The plasma clearance was 1426 ml min^?1 and the volume of distribution based on area was 47.71.     

Disposition kinetics of hepp in rats after intravenous,oral, and intraperitoneal administration. Correlation of plasma and brain levels with the anticonvulsant effects

D, L-3-hydroxy-3-ethyl-3-phenylpropanamide (HEPP) is a synthetic drug with anticovulsant effects in a variety of seizure models. HEPP pharmacokinetics was studied after single 50 mg kg^?1 intravenous (IV), intraperitoneal (IP), and oral (PO) administration in male albino Wistar rats. The plasma concentration against time curves showed a biphasic decay pattern with a similar distribution phase and the same terminal rate constant (β = 0.22 h^?1) by all three routes. The apparent volume of distribution at steady state (V_SS = 0.80 L kg^?1) indicates that HEPP is extensively distributed in extracellular tissues. This finding agrees very well with its low binding to plasma protein (mean bound fraction = 19.3 ± 1.1%). The systemic clearance (Cl) was very low (3.30mL min^?1 kg^?1). The bioavailability after IP and PO administration was 0.80 and 0.60 respectively. In the pharmacokinetic-pharmacodynamic studies a direct relationship was found between the protective effect of HEPP against pentylenetetrazole (PTZ) induced seizures and its concentration in plasma and/or brain. The concentrations at half-maximal effect (EC₅₀) with 95% confidence interval (Cl) were 70.6 (66–75.5) μg mL^?1 in serum and 60.1 (55.4–65.1) μg g^?1 in brain. There was a rapid uptake of HEPP into the brain, and after the distributive phase, the disappearances in plasma and brain were almost parallel [C_serum = 109 e^?0.25t, r² = 0.95; C_brain = 38 e^{2.53t + 91 e}?0.21t, r² = 0.93], with a C_brain/C_plasma ratio of 1.1.     

Inhibition of rat hepatic mitochondrial aldehyde dehydrogenase isozymes by repeated cyanamide administration: Pharmacokinetic-pharmacodynamic relationships

The inhibition of rat hepatic mitochondrial aldehyde dehydrogenase (ALDH) isozymes was studied in apparent steady-state conditions after repeated intra-peritoneal cyanamide administration. The low-K_m mitochondrial ALDH isozyme was more susceptible to cyanamide-induced inhibition (DI₅₀ = 0.104 mg kg^?1) than the high-K_m isozyme (DI₅₀ = 8.52 mg kg^?1), with almost complete inhibition occurring at 0.35 mg kg^?1 total cyanamide administered for the low-K_m isozyme. The relationships between plasma and liver cyanamide concentrations and the inhibition of high-K_m ALDH were established by means of the sigmoid I_max model. The effect of dosing rate on the plasma concentration of cyanamide at apparent steady-state showed non-linearity, indicating that clearance or first-pass metabolism of cyanamide during its absorption after intraperitoneal administration did not remain constant throughout the range of doses studied.     

Pharmacokinetics of methotrexate after intravenous and intramuscular injection of methotrexate-bearing positively charged liposomes to rats

The pharmacokinetics and tissue distribution of methotrexate (MTX) were investigated after intravenous (IV) and intramuscular (IM) injection of free MTX (treatment I), freshly prepared MTX-bearing positively charged liposomes (large unilamellar vesicles), PLUVs (treatment II), and empty PLUVs mixed manually with free MTX (treatment III), 4 mg kg^?1 as free MTX to rats, using HPLC assay. After 1 min IV infusion, the plasma concentrations of MTX (C_p), the area under the plasma concentration—time curve (AUC, 173 against 314 μg mL min^?1), the terminal half-life (t_1/2, 24.0 against 412 min), the mean residence time (MRT, 13.0 against 324 min), and the apparent volume of distribution at steady state (V_SS, 289 against 3370 mL kg^?1) were significantly larger, but the total body clearance (CL, 23.1 against 12.8 mL min^?1 kg^?1), the renal clearance (CL_R, 8.38 against 3.09 mL min^?1 kg^?1), the non-renal clearance (CL_NR, 14.6 against 9.56 mL min^?1 kg^?1), and the amount of MTX excreted in urine (X_u, 415 against 275 μg) were significantly lower in treatment II than in treatment I. This could be due to the fact that some of the MTX-bearing PLUVs were entrapped in tissues and the rest were present in plasma (larger MRT and V_ss in treatment II), and MTX is slowly released from MTX-bearing PLUVs (longer t_1/2 in treatment II). In the present HPLC assay, the concentrations of MTX represent the sum of free MTX and MTX in MTX-bearing PLUVs (larger C_p and AUC and slower CL in treatment II). Saturable formation of 7-hydroxymethotrexate from MTX was reported in rabbit blood and non-linear disposition of MTX was also reported in rats and rabbits (lower X_u and CL_R in treatment II). After 1 min IV infusion, some pharmacokinetic parameters of MTX, such as AUC, CL, CL_R, CL_NR, and X_u, were significantly different between treatments I and III, but nonetheless the differences were smaller than those between treatments I and II. After both IV and IM administration, the amount of MTX remaining per gram of tissue or organ in the kidney, stomach, small intestine, and large intestine was significantly smaller in treatment II than in treatment I. Such tissue results imply that the side-effects of MTX on kidney and GI tract could be reduced after both IV and IM administration of MTX-bearing PLUVs rather than free MTX. The encapsulation efficiency of MTX in MTX-bearing PLUVs was 5.47%, and MTX was released slowly from MTX-bearing PLUVs when incubated in phsophate buffered saline, rat plasma and rat liver homogenates.