IGPHARM: interactive graphic package for pharmacokinetic analysis

Pharmacokinetics of Iopentol in Patients with Chronic Renal Failure

Iopentol 350 mg I/ml was injected in doses of 265 to 533 mg I/kg b.w. (mean 417 mg I/kg b.w.) in 10 patients with advanced nondiabetic chronic renal failure (S-creatinine 672 ± 259 μmol/l (mean ± SD)). Urine (10 patients) and feces (7 patients) were collected at 24 h intervals for 5 days after the injection. The elimination of iopentol was delayed. Five days after injection a mean of 54% (range 35–79%) of the dose was recovered in urine, and 11% (0–20%) in feces. Mean elimination half-life was 28.4 h, about 14 times the half-life found in healthy volunteers. The apparent volume of distribution was 0.27 1/kg b.w., indicating distribution only to extracellular fluid. Using renal iopentol clearance as reference value, GFR was overestimated by 40 to 60% with iopentol total clearance, showing extrarenal elimination of iopentol. The difference was most pronounced in patients with low GFR. In conclusion, this study shows an extrarenal elimination of iopentol and demonstrates a substantial increase in the fecal elimination in patients with severe renal failure.

Pharmacokinetic Study of Gadolinium-DOTA in Control and Streptozocin Diabetic Rats

The pharmacokinetics of gadolinium tetraazacyclododecanetetraacetic acid (Gd-DOTA), a contrast agent used in magnetic resonance imaging, have been evaluated in control and streptozocin-diabetic rats of different ages. In control rats, an age-related decrease in the Gd-DOTA elimination rate was noted, supported by a significantly lower apparent total body clearance and a significantly higher mean residence time. In diabetic rats, a similar but less important age-related change in the mean residence time and the apparent total body clearance was observed. Regardless of age-related differences in the pharmacokinetic parameters, a diabetic state induced several alterations in the Gd-DOTA pharmacokinetic parameters. The apparent total body clearance was significantly higher and the mean residence time significantly lower in diabetic rats indicating a higher elimination rate of Gd-DOTA. An important age-related increase in the volume of distribution at steady-state was noted in diabetic rats.

Absolute bioavailability, pharmacokinetics, and urinary excretion of the novel antimigraine agent almotriptan in healthy male volunteers

Absolute bioavailability, pharmacokinetics, and urinary excretion of almotriptan, a novel 5-HT(1B/1D) receptor agonist, were studied in 18 healthy males following single intravenous (i.v.) (3 mg), subcutaneous (s.c.) (6 mg), and oral (25 mg) doses. Volunteers received each dose in a randomized sequence separated by a 7-day washout. Blood and urine samples for pharmacokinetic evaluations were taken for up to 24 hours after dosing. The disposition kinetics of almotriptan after i.v. and s.c. administration showed biphasic decline described by a two-compartment model. The fastest disposition phase was well observed, although estimates of the rate constant showed high variability. After s.c. administration of almotriptan, the bioavailability was 100% with a time to maximum plasma concentration (tmax) of 5 to 15 minutes, whereas after oral administration, the bioavailability was about 70% with a tmax of 1.5 to 3.0 hours. No significant differences were observed between administration routes in the elimination half-life (t(1/2), obtaining mean values ranging from 3.4 to 3.6 hours. The volume of distribution, total clearance, and t(1/2) indicated that almotriptan was extensively distributed and rapidly cleared from the body irrespective of dose or route of administration. The primary route of elimination was renal clearance (approximately 50%-60% of total body clearance). About 65% of the i.v. and s.c. dose and 45% of the oral dose were excreted unchanged in urine in 24 hours, with nearly 90% of this in the first 12 hours. Renal clearance was approximately 2- to 3-fold that of the glomerular filtration rate in man, suggesting that almotriptan is eliminated in part by renal tubular secretion.

Levodopa therapy monitoring in patients with Parkinson disease: a kinetic-dynamic approach

The authors assessed differences in both therapeutic and dyskinesia-matched concentrations of levodopa by kinetic-dynamic modeling in a large cohort of patients with Parkinson disease grouped by severity of symptoms. The goal was to provide a kinetic-dynamic approach to levodopa therapy monitoring to assist treating physicians in rationalizing patients' drug schedules in line with disease progression. Eighty-six patients, grouped according to Hoehn & Yahr (H&Y) clinical stage (H&Y I, n = 23; II, n = 25; III; n = 25; IV, n = 13) enrolled in the study. After a 12-hour levodopa washout each patient was examined using a standard oral levodopa test, based on simultaneous serial measurements of plasma levodopa concentrations, finger-tapping motor effects, and dyskinesia ratings. The kinetic-dynamic modeling for both effects was carried out according to the "link" effect compartment model and sigmoidal pharmacodynamic model. Levodopa plasma kinetics did not differ among patient groups. Duration of motor response was significantly (p < 0.001) curtailed in patients in advanced clinical stages whereas dyskinesia duration showed minor changes among the three affected groups (H&Y II, III, and IV). Median effective concentrations (EC 50 ) were increased at the more advanced clinical stage (p < 0.001), from a median 0.2 microg/mL in patients at H&Y stage I to 0.9 microg/mL in patients at H&Y stage IV, whereas the maximum effect showed less consistent changes among the four groups. Intrasubject levodopa therapeutic concentrations were lower than values for dyskinesias in patients at the moderate stage of the disease, equaling dyskinesia-matched drug concentrations in the more affected patients. These findings are in line with previous observations of major changes in levodopa concentration-effects relationship with disease progression and support a stratification of patients with Parkinson disease according to kinetic-dynamic modeling. From a practical point of view, knowledge of individual patients' kinetic-dynamic variables can help the physician assess patients' clinical needs objectively and optimize levodopa dosing according to disease progression.

Multiple-dose pharmacokinetics and safety of two regimens of quinupristin/dalfopristin (Synercid) in healthy volunteers

Quinupristin/dalfopristin (Q/D) is a novel streptogramin antibiotic for the treatment of severe gram-positive infections. The purpose of this open, nonrandomized, parallel-group, phase I trial was to evaluate Q/D pharmacokinetics after single and repeated doses under the two different dosing regimens corresponding to the effective doses and to evaluate tolerability. Two groups of 10 healthy volunteers received multiple 1-hour intravenous infusions of 7.5 mg/kg Q/D either every 8 or 12 hours for 4 or 5 days, respectively. Plasma concentrations of Q, D, and metabolites were determined using high-performance liquid chromatography and selective microbiological assays. The two regimens q8h and q12h lead to the same disposition profile after single and repeated administration. Single-dose data confirmed the high plasma clearances of Q and D (about 0.90 l/h/kg) obtained previously. Unchanged drugs were the main components in plasma, with each of the three metabolites representing about 20% (in terms of the AUC ratio) of the parent drugs. Comparable steady-state concentrations were reached from day 2 of both regimens. A similar moderate increase in Cmax and AUC (about 20%) of parent drugs was observed between the first and last day of treatment. This phenomenon, which was also observed for the metabolites, was not expected considering the short terminal disposition half-lives of the parent drugs and trough plasma concentrations of all components mostly below the limits of quantitation at steady state, whatever the dosing regimen. The clearances of parent drugs at steady state were about 20% lower as compared with that observed following the first drug administration (statistically significant difference). No trend suggesting a treatment effect on any laboratory parameter, vital signs, or electrocardiographic parameters was identified. However, 80% of subjects reported venous adverse events probably related to treatment.

Absorption and bioavailability of oestradiol from a gel, a patch and a tablet

OBJECTIVES

To compare oestradiol and oestrone concentrations and bioavailability after a single dose and at a steady state during oral oestradiol valerate, transdermal oestradiol gel and transdermal oestradiol patch treatments.

METHODS

Two open, randomised, cross-over studies were conducted. In the first study, 12 healthy postmenopausal women received 1.5 mg oestradiol as a transdermal gel or a 2 mg oestradiol valerate tablet daily for 14 days. In the second study, 15 postmenopausal women were treated for 18 days with 1.5 mg oestradiol gel or a transdermal patch releasing oestradiol 50 microg/24 h (replaced every 72 h). Venous blood samples for serum oestradiol and oestrone measurements with RIA were taken until 24 or 72 h after the first and last doses.

RESULTS

The tablet and the transdermal gel yielded similar serum oestradiol profiles with a peak concentration 4-5 h after administration. The patch resulted in relatively stable oestradiol levels during the mid third of the wearing time whereas much lower levels were observed in the beginning and towards the end. There was no difference in the fluctuation between the peak and trough oestradiol levels between the gel (56 or 67%) and the tablet (54%) while the fluctuation was greater with the patch (89%). The bioavailability of oestradiol from the gel was 61% as compared with the tablet and 109% as compared with the patch. The gel was not bioequivalent with the tablet or the patch.

CONCLUSIONS

The doses used of the transdermal gel and the patch roughly corresponded to each other with regard to the amount of oestradiol absorbed whereas the bioavailability from the tablet was significantly higher than from the gel. The lack of bioequivalence, the different serum oestradiol profiles and the large intersubject variability suggest that individual dose adjustments may be needed when changing administration form.

Interaction between pefloxacin and aminophylline in genetically epilepsy-prone rats

The effects of a chronic treatment with pefloxacin on aminophylline-induced seizures in genetically epilepsy-prone rat have been investigated. Two series of experiments were performed. In the first, animals received pefloxacin orally twice a day for five days, then were administered aminophylline intraperitoneally and the occurrence of seizures was evaluated. In the second series of experiments, theophylline serum concentration was evaluated in rats subject to the same experimental protocol. Pefloxacin significantly, and in a dose-dependent manner, increased the occurrence of seizure phases induced by aminophylline, but did not influence theophylline serum levels measured at different times after the injection of aminophylline. We suggest that additive neurotoxic effects of both pefloxacin and aminophylline might contribute to the increased severity of seizure score. The possible role of GABA-benzodiazepine, excitatory amino acid and purinergic mechanism, and the role of pharmacokinetic factors are discussed.

Half-life of intracameral gentamicin after phacoemulsification

PURPOSE

To determine the half-life of intracameral gentamicin administered during phacoemulsification.

SETTING

Southampton Eye Unit, Southampton General Hospital, England.

METHODS

Thirty-one patients having scleral tunnel phacoemulsification were given intracameral gentamicin in the irrigation fluid. Samples of fluid were taken from the anterior chamber at the end of the operation and at various times postoperatively. The concentration of gentamicin in the samples was determined by fluorescence polarization immunoassay and the half-life calculated for a single compartment model using a peeling algorithm.

RESULTS

The concentration of gentamicin in the anterior chamber after phacoemulsification decreased by half every 51 minutes (95% confidence interval, 42 to 66 minutes).

CONCLUSION

Intracameral gentamicin was cleared from the anterior chamber after phacoemulsification at a rate that prevents the maintainance of the bactericidal levels required for reliable antibiotic prophylaxis.

Comparison of the pharmacokinetics of dolasetron and its major active metabolite, reduced dolasetron, in dog

Dolasetron mesilate (Anzemet) ((2 alpha, 6 alpha, 8 alpha, 9a beta)-octahydro-3-oxo-2,6-methano-2H-quinolizin-8-yl-1 H-indole-3-carboxylate monomethane-sulfonate) is a 5-HT3 receptor antagonist, which is in development for the treatment of chemotherapy-induced emesis. The ketone moiety of dolasetron is rapidly reduced by carbonyl reductase to form an alcohol, reduced dolasetron (red-dolasetron), which is the major pharmacologically active metabolite in humans. The pharmacokinetics of dolasetron and red-dolasetron were compared in dog, after single intravenous (i.v.) (2 mg/kg) and oral (p.o.) (5 mg/kg) administration of [14C]dolasetron or [14C]red-dolasetron. Pharmacokinetic parameters of dolasetron showed a terminal elimination half-life (t1/2) of 0.1 h, total body plasma clearance (Cltot) of around 109 mL/min/kg, apparent volume of distribution (aVd beta) of 0.83 L/kg, and bioavailability (F) of 7%. Pharmacokinetic parameters of red-dolasetron, calculated after dolasetron or red-dolasetron administration, were very similar. The t1/2 was around 4.0 h, Cltot 25 mL/min/kg, aVd beta 8.5 L/kg, and F around 100%. The apparent first-order formation rate constant (ki) of red-dolasetron was 7 h-1, which was similar to the first-order elimination rate constant (kel) of dolasetron. Cmax of red-dolasetron was similar, after po administration of either compound, but the median Tmax was 0.33 h after dolasetron, compared with 1.5 h after red-dolasetron. The first-order absorption rate constants (ka) of dolasetron and red-dolasetron were 14 h-1 and 2 h-1, respectively. Dolasetron transport across Caco-2 cell monolayers was also higher than that of red-dolasetron. Thus dolasetron was more quickly absorbed than red-dolasetron, and its administration led to the more rapid appearance of red-dolasetron in plasma. There appears to be no advantage in the direct administration of the metabolite, especially as in humans oral administration of dolasetron, 30 min before chemotherapy, has been shown to be effective in preventing emesis.

5-(m-Benzyloxybenzyl)barbituric acid acyclonucleoside, a uridine phosphorylase inhibitor, and 2',3',5'-tri-O-acetyluridine, a prodrug of uridine, as modulators of plasma uridine concentration. Implications for chemotherapy

5-(m-Benzyloxybenzyl)barbituric acid acyclonucleoside (BBBA), the most potent inhibitor known of uridine phosphorylase (UrdPase, EC 2.4.2.3), the enzyme responsible for uridine catabolism, and 2',3',5'-tri-O-acetyluridine (TAU), a prodrug of uridine, were used to investigate the possibility of improving the bioavailability of oral uridine in mice. Oral BBBA administered at 30, 60, 120, and 240 mg/kg increased the concentration of plasma uridine (2.6 +/- 0.7 microM) by 3.2-, 4.6-, 5.4-, and 7.2-fold, respectively. After administration of 120 and 240 mg/kg BBBA, plasma uridine concentration remained 3- and 6-fold, respectively, higher than the plasma concentration at zero time (C0) for over 8 hr. On the other hand, BBBA did not change the concentration of plasma uracil. TAU was far more superior than uridine in improving the bioavailability of plasma uridine. The relative bioavailability of plasma uridine released from oral TAU (53%) was 7-fold higher than that (7.7%) obtained by oral uridine. Oral TAU at 460, 1000, and 2000 mg/kg achieved area under the curve (AUC) values of plasma uridine of 82, 288, and 754 mumol.hr/L, respectively. Coadministration of BBBA with uridine or TAU further improved the bioavailability of plasma uridine resulting from the administration of either alone and reduced the Cmax and AUC of plasma uracil. Coadministration of BBBA at 30, 60, and 120 mg/kg improved the relative bioavailability of uridine released from 2000 mg/kg TAU (53%) by 1.7-, 2.7-, and 3.9-fold, respectively, while coadministration of the same doses of BBBA with an equimolar dose of uridine (1320 mg/kg) increased the relative bioavailability of oral uridine (7.7%) by 4.1-, 5.3-, and 7.8-fold, respectively. Moreover, the AUC and Cmax of plasma uridine after BBBA (120 mg/kg) coadministration with TAU were 3.5- and 11.5-fold, respectively, higher than those obtained from coadministration of BBBA with an equimolar dose of uridine. The exceptional effectiveness of the BBBA plus TAU combination in elevating and sustaining high plasma uridine concentration can be useful in the management of medical disorders that are remedied by administration of uridine as well as to rescue or protect from host-toxicities of various chemotherapeutic pyrimidine analogues.

Rat tissue concentrations of chlorimipramine, chlorpromazine and their N-demethylated metabolites after a single oral dose of the parent compounds

A single oral dose of 90 mg kg-1 chlorimipramine or chlorpromazine, corresponding to 54.5 or 55.9 mumol, respectively, was given to male Sprague-Dawley rats and concentrations of parent drugs and their N-desmethyl metabolites measured by gas chromatography in plasma and major organs (brain, liver, lung, kidney, heart, spleen and peritoneal fat). In the case of chlorimipramine, N-desmethyl metabolite levels were consistently higher than those of the parent drug for the entire observation period of 24 h in all tissues except fat, while lower N-desmethyl metabolite/parent compound ratios were observed for chlorpromazine. N-Desmethyl metabolite kinetics of chlorimipramine appeared to be elimination-rate limited, while those of chlorpromazine were formation-rate limited. In all analysed organs, the maximu detectable drug+metabolite concentrations accounted for only 2.3 and 4.6% of the initial dose of chlorimipramine and chlorpromazine. Chlorpromazine treatment gave rise to an area under the total amount-time curve (AUC0-24) for parent drug+metabolites, 3.9-fold that for chlorimipraine. Closer scrutiny discloses a conversion ratio of parent compound to N-desmethyl metabolite of 1.1 for chlorpromazine and of 2.2 for chlorimipramine, indicating the greater efficiency of chlorimipramine metabolism in all compartments. The expected high conversion index found in the liver (2.3) reaches its maximum of 5.4 in the lung. Fractional data analysis of chlorimipramine and chlorpromazine distribution patterns revealed greater organ transfer for the N-desmethyl metabolites than for the more stably-located parent compounds. The N-desmethyl metabolites of chlorimipramine apparently moved from liver to lung, kidney and spleen, whereas N-desmethylchlopromazine moved preferentially to the brain and lung tissue. This single dose study of chlorimipramine and chlorpromazine kinetics, highlights the two distinct dispositional processes at work in the rat in all likelihood, attributable to different absorption patterns, to a slower metabolism and, thus, to the longer persistence of chlorpromazine.

Effects of 5-benzylacyclouridine, an inhibitor of uridine phosphorylase, on the pharmacokinetics of uridine in rhesus monkeys: implications for chemotherapy

The effects of subcutaneous administration of 5-benzylacyclouridine (BAU), a uridine phosphorylase (UrdPase, EC 2.4.2.3) inhibitor, on uridine concentration in plasma and urine were evaluated in rhesus monkeys. Administration of BAU at 50, 100 and 250 mg/kg increased the plasma uridine baseline concentration 1.5-, 2.9-, and 3.2-fold, respectively. The basis for this moderate perturbation of plasma uridine by BAU was investigated using a tracer dose of 500 microCi 3H-uridine. Administration of 3H-uridine alone led to its rapid catabolism to uracil and dihydrouracil. Administration of 83.3 mg/kg BAU with 500 microCi 3H-uridine resulted in a 2.5-fold enhancement of 3H-uridine plasma levels and a substantial decrease in the plasma levels of uridine catabolites, suggesting inhibition of UrdPase activity by BAU in rhesus monkeys. Coadministration of 83.3 mg/kg BAU with 83.3 mg/kg uridine also reduced the plasma concentration of uracil and dihydrouracil, but it did not increase plasma uridine concentration above that of control animals receiving 83.3 mg/kg uridine alone. In animals receiving uridine alone at 83.3 or 25 mg/kg, approximately 10% of the administered dose was recovered in the urine within 6 h, with unchanged uridine being the major component. In contrast, administration of 83.3 mg/kg BAU increased the excretion of unchanged uridine to more than 32% of the total dose administered, even when the urinary excretion ratio of uracil to uridine was reduced ten-fold. Administration of multiple doses (three times per day) of BAU alone (83.3 mg/kg) or in the presence of uridine (83.3 mg/kg) did not enhance plasma uridine concentration further. In addition, uridine pharmacokinetics were associated with a time-dependent relationship as evidenced by an increased total plasma clearance, renal clearance and volume of distribution, resulting in a substantial decrease in uridine peak concentration with time. These results indicate that administration of BAU inhibits UrdPase activity in rhesus monkeys as manifested by decreased uracil and dihydrouracil plasma levels, as well as a lower urinary excretion ratio of uracil to uridine, as compared to control animals. However, plasma levels of unchanged uridine were not substantially enhanced by BAU in spite of the large increase in urinary excretion of unchanged uridine. This phenomenon was also observed when uridine was coadministered with BAU, suggesting that plasma uridine concentration in monkeys may be strongly regulated by the renal system as evidenced by the "spillover" of excess plasma uridine into urine. In addition, the pharmacokinetics of uridine were dose-independent, but time-dependent.(ABSTRACT TRUNCATED AT 400 WORDS)

Repeated dose pharmacokinetics of pancopride in human volunteers

The aim of this study was to assess the pharmacokinetic profile of pancopride after repeated oral dose administration of 20 mg pancopride in tablet form once a day for 5 d in 12 healthy male volunteers. Plasma levels were measured by HPLC using a solid phase extraction method and automated injection. The minimum quantification limit of pancopride in plasma was 2 ng mL-1. The maximum plasma concentration (mean +/- SD) after the first dose was 92.5 +/- 41.5 ng ML-1 and tmax was 1.7 +/- 0.9 h. The elimination half-life (t1/2) was 14.3 +/- 6.9 h. The area under the concentration-time curve from zero to infinity (AUC) was 997 +/- 396 ng h mL-1. The maximum plasma concentration (mean +/- SD) at steady state (day 5) was 101.8 +/- 36.9 ng mL-1 and tmax was 2.2 +/- 1.2 h. The elimination half-life (t1/2) was 16.3 +/- 2.7 h and the minimum plasma concentration (Cssmin) was 16.6 +/- 6.9 ng mL-1. The area under the concentration-time curve during the dosing interval (AUCss tau) was 995 +/- 389 ng h mL-1. The average plasma concentration at steady state (Cssav) was 43.3 +/- 16.1 ng mL-1 and the experimental accumulation ratio (RAUC) was 1.34 +/- 0.19, whereas the mean theoretical value (R) was 1.40 +/- 0.29. The results obtained showed a good correlation between the experimental plasma levels and the expected values calculated using a repeated dose two-compartment model assessed by means of the Akaike value. It is concluded that the pharmacokinetics of pancopride are not modified after repeated dose administration.(ABSTRACT TRUNCATED AT 250 WORDS)

A non-linear fitting program in pharmacokinetics with Microsoft Excel spreadsheet

We propose a new approach of pharmacokinetics patterns of drugs by use of spreadsheets. We have developed a software program using Microsoft Excel (version 3.0) to determine initial poly exponential parameter values for 1-3 compartment open models and to make non-linear regression with many optimisation procedures. Results are compared with 2 other programs: Nonlin and Rugfit.

Pharmacokinetics of thymoxamine in rabbits after ophthalmic and intravenous administration

The pharmacokinetics of thymoxamine hydrochloride were studied in rabbits by the assessment of its ocular and systemic absorption after instillation of thymoxamine hydrochloride 0.5% eye drops. Plasma levels were compared with those observed after i.v. bolus administration of thymoxamine hydrochloride at 2.5 mg/kg. Deacetylthymoxamine is the main metabolite of thymoxamine, generated by esterase hydrolysis. It was evaluated, as an indication of the parent drug, in aqueous humor and plasma by an HPLC method with fluorescence detection (detection limit = 5 ng/ml). Thymoxamine was found to permeate the cornea and to be hydrolysed very quickly, showing very good absorption with a maximum aqueous humor concentration of deacetylthymoxamine of 2329 ng/ml 15 min after eye drop instillation. The study of the systemic absorption of thymoxamine allowed the exclusion of the possibility of systemic side effects following ocular treatment. In fact, considering the detection limit of the method, the plasma levels of deacetylthymoxamine are certainly more than 100-times lower than those observed with intravenous treatment.

Effect of entacapone, a COMT inhibitor, on the pharmacokinetics of levodopa and on cardiovascular responses in patients with Parkinson's disease

In an open, randomised, cross-over study we investigated the effect of a single 200 mg oral dose of entacapone, a novel catechol-O-methyltransferase (COMT) inhibitor, on the pharmacokinetics and metabolism of levodopa/carbidopa, and on the cardiovascular responses (blood pressure and pulse rate variation to standard stimuli) in eight parkinsonian patients. Entacapone significantly increased the mean area under the plasma concentration curve (AUC) of levodopa by 46%, from 3620 to 5280 h.ng.ml-1 and prolonged its elimination half-life (t1/2el) from 1.5 h to 2.0 h. The mean AUC of 3,4-dihydroxyphenylacetic acid (DOPAC), the monoamine oxidase-dependent metabolite of levodopa, was significantly increased from 122 to 343 h.micrograms.ml-1 by entacapone. A small decrease in the AUC of homovanillic acid (HVA), the COMT dependent metabolite of levodopa, was observed (from 455 to 303 h.ng.ml-1). Entacapone also decreased the excretion of HVA but not that of 3-methoxytyramine in the urine. Cardiovascular autonomic responses to sympathetic and parasympathetic stimuli were not changed by entacapone. We conclude that a single dose of entacapone moderately increases the AUC and prolongs the t1/2el of levodopa in man and that that does not affect cardiovascular autonomic regulation.

Effects of a subacute treatment in rats by a fresh cola extract on EEG and pharmacokinetics

The compared effects of an acute and subacute treatment by fresh cola extract and caffeine on the caffeine pharmacokinetics and on cortical activities by spectral analysis of the electroencephalogram (EEG) are studied in rats. After acute cola administration, we observed an increase in half-life elimination of caffeine and a stabilization of its plasma/erythrocyte ratio. Chronic administration revealed differences in cola-caffeine penetration in erythrocytes and a reduction of the area under the curve (AUC) and plasma/erythrocyte ratio. We also noted a significant difference in the binding of the caffeine on plasma proteins after subacute administration of cola seed extract. Cola seed treatment induces an increase in the cortical activity with a widening of the dominant frequency spectrum 7- to 10-Hz band of EEG, whereas caffeine alone induces a shift of the dominant frequency band toward higher frequencies. The observed delay to obtain the greatest EEG effect related to the caffeine contained in cola seeds can be partially explained by the pharmacokinetic data.

Pharmacokinetics and hematologic response to subcutaneous administration of recombinant human erythropoietin in children undergoing long-term peritoneal dialysis: a multicenter study

For a study of the pharmacokinetics and hematologic response of subcutaneously administered recombinant human erythropoietin (rHuEPO), 24 children (mean age, 10 years 3 months; range, 3 months to 18 years) maintained by peritoneal dialysis and with anemia caused by end-stage renal failure (mean hemoglobin level, 6.5 gm/dl; range, 4.7 to 7.9) were treated with rHuEPO administered subcutaneously at an initial dose of 25 IU/kg twice per week. After a 4-week interval, in the case of no response (hemoglobin increase < or = 1 to 1.5 gm/dl per month) the rHuEPO dosage was increased every 4 weeks according to the following schedule: 50, 75, 100, and 150 IU/kg twice per week. The administration of rHuEPO produced a rapid increase in serum concentration with a mean peak level of 59.8 mU/ml after 9 hours. Mean area under the curve to 72 hours was 2020 mU/ml per hour (range, 568 to 6609); mean elimination half-life and mean residence time were, respectively, 25.2 hours (range, 6.2 to 58.7) and 42.0 hours (range, 10.9 to 96). Of 24 children entered in the study, six had the drug suspended early because of renal transplantation (n = 1), lack of compliance (n = 4), or severe worsening of hypertension (n = 1). Eighteen patients had increased hemoglobin levels (to 9.4 +/- 1.7 gm/dl after 24 weeks of treatment). No correlation was found between the increase in hemoglobin concentration and any of the pharmacokinetic data or the peak erythropoietin level reached during the kinetic profile. Eight children required an increase of antihypertensive medications to maintain satisfactory blood pressure values. We conclude that low doses of subcutaneously administered rHuEPO slowly release the drug into the blood and satisfactorily increase hemoglobin levels with very few side effects.

Extended least squares curve fitting: a comparison of SIPHAR and MKMODEL

SIPHAR and MKMODEL in their extended least squares modes have been compared when fitting a triexponential declining function to simulated data. The data were simulated on SAS incorporating normally distributed random error, having coefficients of variation (CV) of 5, 10, 15, and 25 per cent. At each error level 100 data sets, consisting of 21 data pairs, were simulated. Non-parametric tests were used to compare the accuracy and precision of the estimates produced by the packages. The comparison was repeated with two different sets of exponent values incorporating error at the 15 per cent level. MKMODEL was also compared to ELSFIT and ELSMOS at the same error level. SIPHAR was consistently less accurate and less precise than MKMODEL in estimating the structural model parameters. SIPHAR was also sensitive to the concentration units used for the input data. Estimates of the variance model power produced by SIPHAR were very variable while those from MKMODEL covered a much tighter range. For both packages there was generally a linear increase in the CV on each mean parameter estimate with increase in the CV on the error model. Good agreement was observed between MKMODEL, ELSFIT, and ELSMOS. The presence of an additive constant in the variance model used in SIPHAR was shown to be responsible for its poorer accuracy and precision.

Disposition of exogenous tritium-labelled GM1lactone in the rat

The disposition of labelled [3H]GM1lactone, the inner ester of ganglioside GM1, was studied in the rat. After i.v. administration [3H]GM1lactone was quickly converted to its corresponding open form most likely by plasma esterases, and then displayed a pharmacokinetic profile identical to [3H]GM1. Following intramuscular administration of [3H]GM1lactone [3H]GM1 levels in plasma and in tissues were higher than those obtained after the administration of an equivalent dose of [3H]GM1. This increased bioavailability means that GM1lactone can be considered as a potential prodrug of GM1.

Kinetic-dynamic relationship of oral levodopa: possible biphasic response after sequential doses in Parkinson's disease

The potential difference in the concentration-effect relationship of oral sequential doses of levodopa was explored in six Parkinsonian patients with complex fluctuating response. These patients showed "wearing-off phenomena" characterized by a transient worsening of motor function at the end of the first morning dose response to below baseline values and complained of a progressive reduction of levodopa effect during the day. A first standard levodopa dose was given in the morning, after an overnight fast and levodopa withdrawal. A second equal levodopa dose was administered immediately at the end of the first dose deterioration phase. Postimprovement worsening of motor response was also observed after the second levodopa dose in all patients. No significant difference in the pharmacokinetics of levodopa or in duration or magnitude of motor response could be appreciated between the two doses. These results further support the suggestion that, under controlled dietary conditions, plasma levodopa levels and effects relationship is reproducible between doses. Moreover, even when transient deterioration of motor function occurs between levodopa doses, the central dopaminergic system appears to remain responsive to the drug.

Pharmacokinetics of chlormezanone in elderly patients

The pharmacokinetics of Chlormezanone (CM) has been determined after a single oral dose of 400 mg CM in 5 young volunteers (28 y) and in 8 elderly patients (79 y). In the young subjects, CM was rapidly absorbed and distributed, and was slowly eliminated with a half-life of 38 h major metabolites were not detected in plasma or urine. Only 3% of CM was excreted unchanged in urine. In elderly patients absorption was delayed but not reduced; the Cmax and AUC did not differ from those in younger subjects, the elimination rate was reduced compared to the younger subjects (mean 54 h). The increase was in part related to the reduction in renal function and metabolism observed in aging. However, the change in pharmacokinetics was moderate and no adjustment in dosage seems necessary for treatments of limited duration in elderly patients.

Pharmacokinetics of an indomethacin pro-drug: apyramide after intravenous administration in dog

The pharmacokinetics of apyramide, an ester of indomethacin and acetaminophen (paracetamol), were determined after intravenous administration to nine beagle dogs. Indomethacin and its pro-drug, apyramide, were extracted from acetonitrile-precipitated plasma by a solvent-demixing procedure and the concentration of these two drugs was measured by a reversed-phase liquid chromatographic assay. The kinetic evolution with time of plasma levels of apyramide and of indomethacin resulting from enzymatic hydrolysis was compared with values obtained for indomethacin injected in equimolar dose. Plasma levels of apyramide quickly decreased and the mean (+/- SD) half life was 0.15 +/- 0.08 h. For metabolic indomethacin, the mean (+/- SD) area under curve was 12.36 +/- 4.80 mg.h/l and the mean (+/- SD) half life of terminal phase was 16.71 +/- 9.46 h. After administration of indomethacin, these values were 17.60 +/- 4.12 mg.h/l and 7.89 +/- 2.20 h, respectively.

Pharmacokinetics of tinidazole in dogs and cats

Pharmacokinetics of tinidazole in dogs and cats after single intravenous (15 mg/kg) and oral doses (15 mg/kg or 30 mg/kg) were studied in a randomized crossover study. Tinidazole was completely absorbed at both oral dose levels in cats and dogs. Peak tinidazole concentration in plasma was 17.8 micrograms/ml in dogs and 22.5 micrograms/ml in cats after 15 mg/kg p.o. The oral dose of 30 mg/kg resulted in peak levels of 37.9 micrograms/ml in dogs and 33.6 micrograms/ml in cats. The apparent total plasma clearance of the drug was about twofold higher in dogs than in cats, resulting in an elimination half-life that was twice as long in cats (8.4 h) as in dogs (4.4 h). The apparent volume of distribution was 663 ml/kg in dogs and 536 ml/kg in cats. Therapeutic plasma drug concentrations higher than the MIC values of most tinidazole-sensitive bacteria were achieved for 24 h in cats and for 12 h in dogs after a single oral dose of 15 mg/kg. From the pharmacokinetic standpoint tinidazole seems to be well-suited to clinical use in small animal practice.

The pharmacokinetics of dermatan sulphate MF701 in healthy human volunteers

1. The pharmacokinetics of dermatan sulphate MF701 were studied in 12 healthy males after administration of single intravenous bolus (200 mg), intramuscular (100 and 300 mg) and oral (1 g) doses. The study was conducted according to a within-subject crossover design in two paired blocks. 2. Plasma drug concentrations were measured using a competitive binding assay and a range of biological activity assays, including a sensitive catalysed thrombin inhibition test. 3. Following intravenous administration, plasma concentrations of dermatan sulphate determined by competitive binding assay were described by a two-compartment open model with an initial t1/2, in of 0.6 h and a t1/2,z of 7.5 h. Biological activity assays were insufficiently sensitive to detect the second phase, and therefore yielded apparent monoexponential kinetics. 4. After intramuscular injection the apparent bioavailability of dermatan sulphate was 16-20%. Plasma drug concentrations increased in proportion to dose when measured by competitive binding assay. Low concentrations persisted for more than 24 h at the higher dose, and these may prove therapeutically relevant on chronic administration. 5. We confirm that dermatan sulphate is the only glycosaminoglycan known to generate significant plasma concentrations following oral administration. Oral bioavailability was estimated to be 7%.

Pharmacokinetic modeling of plasma and cerebrospinal fluid methotrexate after high-dose intravenous infusion in children

A pharmacokinetic study was performed in plasma and cerebrospinal fluid (CSF) of patients suffering from brain tumors to describe the disposition of methotrexate. An open three-compartment model was developed to fit together the data obtained in plasma and CSF. The pharmacokinetic parameters obtained by the model agreed with those obtained with classical analysis and the fitting correctly depicted the plasma and CSF concentration decays. According to the results, such a model could be applied to other anticancer drugs.

Pharmacokinetics of 3'-azido-3'-deoxythymidine and its catabolites and interactions with probenecid in rhesus monkeys

The pharmacokinetics and metabolism of 3'-azido-3'-deoxythymidine (AZT) were investigated in rhesus monkeys after subcutaneous administration of 33.3 mg of AZT per kg of body weight alone or in the presence of 100 mg of probenecid per kg. In addition to unchanged drug, two catabolites, 5'-O-glucuronide (GAZT) and 3'-amino-3'-deoxythymidine (AMT), were detected in plasma within 30 min. GAZT exhibited a kinetic profile similar to that of AZT, with an elimination half-life of approximately 1 h, while AMT was more variable, with an apparent half-life of 1.6 +/- 1.5 h. Approximately 90% of the total administered dose was recovered in urine within 24 h as AZT, GAZT, AMT, and the 5'-O-glucuronide of AMT. AZT and AMT demonstrated similar cerebrospinal fluid (CSF) penetration 1 h after AZT treatment, while GAZT poorly crossed the blood-brain barrier. Concomitant administration of probenecid greatly altered the pharmacokinetics of AZT, GAZT, and AMT, resulting in prolongation of their apparent elimination half-lives, increased concentrations in plasma, and marked reduction in renal clearances. In addition, the CSF/plasma concentration ratios for AZT and its catabolites were greatly increased, suggesting that probenecid inhibits efflux of AZT and its catabolites from CSF to plasma. The substantial levels of AMT in plasma suggest that this catabolite affects the pharmacodynamic properties of AZT in relation to its activity against human immunodeficiency virus replication and cytotoxicity to host cells. Enhanced AMT levels in plasma in the presence of probenecid may decrease the therapeutic efficacy of the AZT-probenecid combination.

Reversed-phase high-performance liquid chromatography method for the determination of bemegride in serum and brain tissue: pharmacokinetics and brain distribution of an intraperitoneal subconvulsive dose in rats

A simple and rapid HPLC method has been developed for the quantification of bemegride in serum and brain tissue, using p-methylphenobarbital as an internal standard. Serum and brain tissue homogenate samples were extracted with ethyl acetate and the evaporated and redissolved extracts injected into a reversed-phase column. The compounds were eluted with an acetonitrile-phosphate buffer mixture and monitored at 200 nm. A linear response was obtained in the range 1-40 micrograms ml-1 for serum and 1-40 micrograms g-1 for brain tissue. Within-day and between-day precisions were less than 5% and the analytical recovery greater than 76.4%. This method has been used to investigate the kinetic profiles of the drug in serum and discrete areas of rat brain after intraperitoneal administration of a subconvulsive dose of bemegride (10 mg kg-1). Peak concentrations occurred in the brain and serum at the same time (30 min), followed by a biphasic decay. The results also indicated the accumulation of the drug in the brain, with no significant differences (p greater than 0.05) in the impregnation of the different brain areas investigated.

Pharmacokinetics and toxicity of two modalities of etoposide infusion in metastatic non-small-cell lung carcinoma

The pharmacokinetics and toxicity of two schedules of etoposide administration were studied in 19 patients suffering from metastatic non-small-cell lung cancer. Ten subjects received a 72-h continuous venous infusion (CVI) of 360 mg/m2 etoposide, and nine were given a daily dose of 120 mg/m2 for 3 consecutive days. In the two groups 80 mg/m2 cis-diamminedichloroplatinum (II) (CDDP) was infused on day 1. With CVI, the steady-state plasma concentration was reached 12-24 h after the start of the treatment. The plasma elimination rate showed a biexponential decay curve in both groups. No significant difference between total body clearance and the beta-phase volume of distribution was noted between the two modalities of administration. No relationship was found between biological and pharmacokinetic parameters.

Effect of phenobarbital on carbamazepine and its major metabolites in serum, different brain areas, and urine after acute and chronic administration to rats

The influence of coadministration of phenobarbital (PB) on disposition of carbamazepine (CBZ) and carbamazepine-10,11-epoxide (CBZ-E) in serum and in discrete areas of rat brain, together with its effects on urinary excretion of CBZ, CBZ-E, and trans-10,11-dihydro-10,11-dihydroxycarbamazepine (CBZ-DIOL) were investigated after both acute and chronic administration. Acute coadministration of PB resulted in increased serum CBZ levels, whereas serum CBZ-E levels were initially lower and then higher. In daily urinary excretion, a reduction in both CBZ-E/CBZ ratio and CBZ-DIOL/CBZ ratio was observed. Chronic (30 day) coadministration of PB led to a decrease in serum CBZ levels after the first hour, whereas serum CBZ-E levels were initially higher and then lower. In daily urinary excretion, a decrease in CBZ-E/CBZ ratio and an increase in CBZ-DIOL/CBZ ratio were noted. These results are consistent with an inhibitory interaction and a metabolic induction on both CBZ epoxidation and CBZ-E metabolism in acute and chronic administration, respectively. However, effects on CBZ epoxidation were preferential. In the various brain areas, the effects observed were similar to those noted in serum. In addition, a relevant increase in brain/serum CBZ ratios was observed with chronic coadministration of PB.

Comparative bioavailability of diclofenac hydroxyethylpyrrolidine vs diclofenac sodium in man

A phamacokinetic study in man has been made of a new dosage form of diclofenac hydroxyethylpyrrolidine (DIEP); soluble salt packed in sachets was compared with diclofenac sodium as enteric coated tablets. Oral DIEP 2 X 50 mg showed a significant difference in absorption kinetics (ka, lag time and tmax) as compared to oral diclofenac sodium 2 X 50 mg. A relevant plasma concentration of diclofenac was detected just 15 min after DIEP, while diclofenac sodium produced a measurable plasma concentration only 0.5-1 h after the treatment. Cmax and t1/2 after DIEP and diclofenac sodium were comparable. Comparison of the two AUC values showed that DIEP was bioequivalent to diclofenac sodium (Q = 100%).

Pharmacokinetics of (-)-folinic acid after oral and intravenous administration of the racemate

1. A pharmacokinetic study of the natural (-)-isomer of folinic acid ((-)-5 CHOTHF) and of total (-)-folates was performed in 12 healthy subjects after i.v. and oral administration of the racemic form of folinic acid. 2. After a 25 mg i.v. injection, (-)-5 CHOTHF kinetics were described by a biexponential function. The mean steady state volume of distribution (Vss) was 161; systemic and renal clearances averaged 335 and 53 ml min-1, respectively. After the same oral dose, (-)-5 CHOTHF was rapidly absorbed. Plasma concentrations of unchanged drug were much lower than those achieved after i.v. administration but in nine subjects, the disposition kinetics were also biexponential. Absolute bioavailability was only 4% as a consequence of a significant intestinal first pass effect. 3. AUC and t1/2Z values for total (-)-folates were similar after both routes of administration, indicating that the drug was fully absorbed. However the AUC of the active metabolite after i.v. dosage was only half that after oral dosage. 4. The amounts of total (-)-folates excreted in urine after both routes of administration were not significantly different and averaged one third of the dose after 24 h, whereas excretion of (-)-5 CHOTHF was three times less after oral treatment than after parenteral treatment. 5. Oral administration is a more suitable route for folinic acid therapy because more of the active metabolite is produced than after parenteral injection.

Simultaneous determination of the two components of picrotoxin in serum by reversed-phase high-performance liquid chromatography with application to a pharmacokinetic study in rats

A reversed-phase HPLC method is reported which allows the quantification of picrotin and picrotoxinin in serum. A linear response was obtained for both drugs in the range 0.2-20 micrograms ml-1. The within-day and between-day precisions were 0.8-3.7% and 1.3-4.9%, respectively. The mean recoveries were greater than 94.2%. The method was applied to a pharmacokinetic study following intraperitoneal (i.p.) administration of 3 mg kg-1 of picrotoxin in rats. The obtained data suggest a relatively slow absorption after i.p. administration followed by a rapid elimination from the central compartment according to a one-compartment open model. The elimination half-lives were 0.340 +/- 0.0308 h for picrotin and 0.312 +/- 0.0241 h for picrotoxinin.

The pharmacokinetics of bendazac-lysine and 5-hydroxybendazac, its main metabolite, in patients with hepatic cirrhosis

We have studied the pharmacokinetics of bendazac and its major metabolite, 5-hydroxybendazac, in 11 patients with hepatic cirrhosis after the oral administration of a single 500 mg tablet of bendazac-lysine, and compared them with those obtained from 10 healthy adults. The rate of absorption of bendazac, as assessed by tmax and Cmax, is similar in patients and in healthy subjects. The drug is eliminated mostly by metabolism in healthy adults, more than 60% of the dose being excreted in the urine as 5-hydroxybendazac and its glucuronide. Hepatic insufficiency impairs this metabolism, a two-fold decrease in apparent plasma clearance (CL/f) being observed in the patients. Although the plasma unbound fraction of bendazac is increased in patients (the drug is highly bound to plasma albumin), the apparent volume of distribution (V/f) is unchanged. In consequence, the half-life of bendazac is increased two-fold in the patients. Impairment of metabolism decreases the formation of 5-hydroxybendazac, but metabolism remains the main route of its elimination. Renal excretion of bendazac accounts for about 10% of the dose in both patients with cirrhosis and healthy subjects. We conclude that in patients with severe hepatic insufficiency the daily dose of bendazac-lysine should be halved.

High-performance liquid chromatographic procedure for quantitative determination of pentylenetetrazol in serum and discrete areas of rat brain

A precise and reproducible high-performance liquid chromatographic method for the determination of pentylenetetrazol in serum and brain tissue is described. The procedure employs reversed-phase chromatography, monitoring the eluant at 202 nm. Quantification is based on peak-height ratio of the drug to the internal standard (p-methylphenobarbital). A linear response is obtained to 100 micrograms/ml (serum) or micrograms/g (brain tissue). Within-day and between-day precision are smaller than 5%, and analytical recovery is greater than 95%. Numerous drugs tested do not interfere with the assay. The method has been used to investigate the kinetics of pentylenetetrazol distribution in serum and in discrete areas of rat brain.

Chloroquine excretion following malaria prophylaxis

Urinary excretion of chloroquine and its desethyl-metabolite was monitored for up to 395 days after the last dose of oral chloroquine (300 mg base) taken once weekly for 10 weeks as malaria prophylaxis. Concentrations in plasma could be followed for up to 70 days after the last dose. A three exponential decay was applied to the urinary excretion data. The half-life of the terminal phase varied from 45 to 55 days for chloroquine and from 59 to 67 days for the metabolite. Mean residence time was approximately 20 days for the parent compound and 35 days for the metabolite, indicating that the terminal phases are of less importance for the effective half-lives.

Pharmacokinetics of bendazac-lysine and 5-hydroxybendazac in patients with renal insufficiency

The pharmacokinetics of bendazac and its major metabolite, 5-hydroxybendazac, have been investigated in 15 patients with moderate to severe renal insufficiency and renal failure following a single oral dose of 500 mg bendazac-lysine. The pharmacokinetic parameters were compared to those obtained in 10 healthy adult volunteers. The rate and the extent of absorption of bendazac was not modified in the patients with moderate and severe renal insufficiency, nor was there any change in plasma tmax, Cmax, apparent elimination t1/2 and AUC. There was a significant increase in the unbound fraction of bendazac in renal failure patients undergoing haemodialysis, with a consequent increase in the apparent volume of distribution (V/F) and apparent plasma clearance (CL/F), and a decrease in plasma Cmax and AUC. Simultaneous changes of V/F and CL/F lead to an unchanged plasma t1/2 in these patients. Renal clearance (CLR) was decreased, but CL/F was not affected, since renal excretion is a minor route of elimination of bendazac. Bendazac is mostly eliminated by metabolism to 5-hydroxybendazac, in healthy subjects greater than 60% of a dose being excreted in urine as 5-hydroxybendazac and its glucuronide. In patients with renal insufficiency urinary excretion of 5-hydroxybendazac was decreased and the systemic availability of the metabolite (AUC), was increased about three-fold, irrespective of the degree of renal failure. Plasma 5-hydroxybendazac glucuronide accumulated according to the degree of renal insufficiency. Overall it can be assumed that the pharmacological effect of the drug will not be enhanced in renal failure and that the dosage regimen of bendazac-lysine in such patients need not be modified.

Oral pharmacokinetics and ascitic fluid penetration of pefloxacin in cirrhosis

Plasma and ascitic fluid concentrations of pefloxacin in 10 cirrhotic patients and 8 healthy volunteers were determined following administration of a single oral dose of 400 mg. The mean elimination half-life was significantly increased in the patients (29.0 h) compared to in 8 healthy volunteers (12.3 h). In patients, the total plasma clearance (2.71 vs 6.85 l/h) and volume of distribution (1.12 vs 1.67 l/kg) were decreased. Estimated by the ratio of the AUC in peritoneal fluid and plasma, ascitic fluid penetration was 68% after one oral dose, and pronounced accumulation of pefloxacin in ascites was found after repeated doses. Oral pefloxacin would seem to be a convenient and useful treatment of spontaneous, gram-negative, bacterial peritonitis in cirrhosis. However, the decreased hepatic metabolism of the drug leads to a marked accumulation in plasma and ascites after repeated doses, and a reduced dose is required in these patients.

Discontinuous oral absorption of cimetropium bromide, a new antispasmodic drug

The pharmacokinetic profiles of cimetropium bromide, after either intravenous injection of 10 mg or oral ingestion of 200 mg, were determined in eight healthy volunteers. After intravenous administration, the plasma levels and urinary excretion indicated that the drug is distributed and eliminated at a rapid rate (terminal half-life, 50 +/- 8 min) and that urinary excretion is not the exclusive route of elimination (46 +/- 2%) of the administered dose). After oral administration, a low percentage of the drug is absorbed (1-4% of the administered dose), however, the amount is sufficient for therapeutic effect. The absorption is discontinuous, with two distinct phases, and ends abruptly during the second phase.

Steady-state dosage regimen calculations in linear pharmacokinetics

This paper describes a general approach to compute steady-state dosage regimens. The method deals with individual linear compartmental mammillary pharmacokinetic models and requires estimated values of model parameters. It is based on the linearity principle and computes dosage regimens to achieve and maintain specified steady-state plasma concentrations, e.g. mean value or minimum effective and maximum safe levels. An interactive computer program performing the calculations has been developed.

Effects of di-(2-ethylhexyl) phthalate and five of its metabolites on rat testis in vivo and in in vitro

In an attempt to establish which compound or compounds are responsible for the testicular damage observed after administration of di-(2-ethylhexyl) phthalate (DEHP) in rats, the effects of the parent compound and five of its major metabolites (mono-(2-ethylhexyl) phthalate (MEHP), 2-ethylhexanol (2-EH), mono-(5-carboxy-2-ethylpentyl) phthalate, mono-(2-ethyl-5-oxohexyl) phthalate and mono-(2-ethyl-5-hydroxyhexyl) phthalate) were investigated in vivo and in vitro. The concentrations of MEHP and the three MEHP-derived metabolites in plasma were determined after single and multiple oral doses of DEHP. The plasma concentrations and areas under the plasma concentration-time curves (AUC's) of each of the MEHP-derived metabolites were considerably lower than those of MEHP both after single and after repeated administration of 2.7 mmol of DEHP/kg body weight. The mean elimination half-life of MEHP was significantly shorter in animals given repetitive doses than in those given a single dose, but there was no statistically significant difference between the mean AUC values. No testicular damage was observed in young rats given oral doses of 2.7 mmol of DEHP or 2-EH/kg body weight daily for five days. In animals which received corresponding doses of MEHP the number of degenerated spermatocytes and spermatids was increased, whereas no such effects were found in animals given the MEHP-derived metabolites. MEHP was also the only compound that enhanced germ cell detachment from mixed primary cultures of Sertoli and germ cells.

Pharmacokinetics of terbutaline during pregnancy

Terbutaline in plasma was determined in three groups of women by gas chromatography-mass spectrometry. Eight women received a single i.v. dose of 0.25 mg terbutaline sulphate during pregnancy and 3-6 months after delivery. Mean plasma clearance was 29% higher during pregnancy than after delivery. There was a subsequent decrease in mean terminal half-life from 5.3 to 3.7 h and in mean residence time from 5.3 to 3.4 h. There was no change in volume of distribution. A second group of pregnant women in premature labour (n = 8) received oral terbutaline 5 mg t.d.s. The dosing was repeated after delivery. The mean steady state plasma concentration of terbutaline was about 30% lower during pregnancy than after delivery. A third group of women in preterm labour (n = 8) was treated with an i.v. infusion of terbutaline. The concentrations of terbutaline found on cessation of uterine contractions ranged between 12.8 and 31.5 ng/ml. At present there is no basis for formulation of a "therapeutic plasma level" of terbutaline for the treatment of preterm labour.

Plasma and erythrocyte concentrations of mercaptopurine after oral administration in children

Plasma and erythrocyte concentrations of 6-mercaptopurine (6-MP) were determined by gas chromatography-mass spectrometry. Eleven children (9 with acute lymphatic leukemia) were studied after oral intake of 6-MP doses ranging between 31 and 128 mg/m2 body surface area. The concentrations of 6-MP in plasma were found to vary considerably between patients even after dose normalization to 75 mg/m2. After dose normalization the mean peak plasma concentration was 0.68 microM (range 0.12-1.38) and the area under the plasma concentration-time curve (AUC) was 1.37 microM.h (range 0.12-3.04). The mean time taken to reach the peak concentration was 1.3 h (range 1-2), and the half-life of elimination was 1.8 h (range 0.6-2.5). No patient had detectable 6-MP concentrations 12 h after dose intake. The concentrations of 6-MP tended to be higher in erythrocytes than in plasma. The mean peak concentration in erythrocytes was 131% and the AUC 145% of that found in plasma. The mean half-life of elimination from erythrocytes was 2.0 h (range 0.7-2.8). These data indicate that 6-MP can pass through all membranes rapidly to reach intracellular concentrations equal to or even higher than in plasma. In summary, marked interindividual differences in pharmacokinetics were found, probably due to highly variable bioavailability of oral 6-MP. Further studies are needed to determine whether measurements of plasma concentrations of 6-MP can be used to optimize maintenance treatment of childhood leukemia.

Dispositions of di- and mono-(2-ethylhexyl) phthalate in newborn infants subjected to exchange transfusions

The dispositions of the plasticizer di-(2-ethylhexyl) phthalate (DEHP) and its primary metabolite mono-(2-ethylhexyl) phthalate (MEHP) were studied in newborn infants subjected to exchange transfusions. During a single exchange transfusion the amounts of DEHP and MEHP infused ranged from 0.8-3.3 and 0.05-0.20 mg kg-1 body weight, respectively. There were indications that about 30% of the infused DEHP originated from parts of the transfusion set other than the blood bag. Approximately 30% of the infused amount of DEHP was withdrawn during the course of each transfusion. Immediately after the transfusions the plasma levels of DEHP ranged between 5.8 and 19.6 micrograms ml-1, and subsequently they declined rapidly. This decline, probably reflecting distribution of DEHP within the body, was followed by a slower elimination phase. The half-life of this phase was approximately 10 h. The maximal plasma levels of MEHP were about 5 micrograms ml-1. In one pre-term infant the elimination of MEHP was slower than its formation, whereas in one full-term newborn the formation appeared to be rate-limiting for the elimination.

Toxicokinetic and metabolic study of dimethylnitrosamine and diethylnitrosamine in crayfish Austropotamobius pallipes

The acute toxicities of dimethylnitrosamine and diethylnitrosamine have been evaluated in adult male crayfish Austropotamobius pallipes; LD50 values are 2250 mg/kg and 230 mg/kg, respectively. Toxicokinetic studies of 14C-dimethylnitrosamine and 14C-diethylnitrosamine in crayfish, administered by i.v. injection, show high concentrations of 14C in abdominal muscle and hepatopancreas. Excretion is greater with dimethylnitrosamine, and retention in the tissues, especially the hepatopancreas, is greater with diethylnitrosamine. Metabolites identified in excreta include monomethylnitrosamine from dimethylnitrosamine, and hydroxyethyl-ethyl-, bishydroxyethyl- and carboxyethyl-ethylnitrosamine from diethylnitrosamine.