Comparative efficacy of triptorelin pamoate and leuprolide acetate in men with advanced prostate cancer.

OBJECTIVE: To compare the efficacy of monthly administrations of the luteinizing hormone-releasing hormone agonists triptorelin pamoate and leuprolide acetate to induce and maintain castrate levels of serum testosterone in men with advanced prostate cancer. PATIENTS AND METHODS: Men with advanced prostate cancer were randomly assigned to receive triptorelin 3.75 mg or leuprolide 7.5 mg. The agent was injected intramuscularly every 28 days for nine injections. Primary endpoints were the percentages of men whose serum testosterone concentrations declined to and were maintained at or below castrate levels (

Pharmacokinetics and pharmacodynamics of recombinant human chorionic gonadotrophin in healthy male and female volunteers.

The pharmacokinetics and pharmacodynamics of recombinant human chorionic gonadotrophin (rHCG) were investigated in three studies of healthy volunteers. After single intravenous doses of 25, 250 and 1000 microg, rHCG and urinary HCG (uHCG) showed linear pharmacokinetics described by a bi-exponential model, although the area under the curve (AUC) for uHCG was ~29% lower than for rHCG. After intramuscular or subcutaneous administration (absolute bioavailability, 40-50% for both), rHCG pharmacokinetics could be described by a first-order absorption, one-compartment model. During multiple subcutaneous dosing, the amount of HCG increased by approximately1.7-fold. A comparison of liquid and freeze-dried rHCG and freeze-dried uHCG showed pharmacokinetic bioequivalence. In down-regulated male subjects, single doses of 125 microg rHCG, given intravenously, intramuscularly or subcutaneously, produced comparable increases in serum testosterone, inhibin and 17beta-oestradiol, with little further increase during repeated subcutaneous administration (in female subjects, this produced a sustained comparable increase in serum androstenedione and testosterone concentrations). In conclusion, the pharmacokinetics and pharmacodynamics of rHCG are similar to those of uHCG and are not affected by the use of different formulations. In healthy subjects, rHCG produces pharmacodynamic responses consistent with HCG physiology and is suitable for use in the same clinical indications as uHCG. The secured source and high purity of rHCG may offer important advantages.

Down-regulation models and modeling of testosterone production induced by recombinant human choriogonadotropin.

Chorionic gonadotropin (CG) is a glycoprotein hormone, whose action is mediated by the luteinizing hormone/CG receptor. Testosterone concentrations from six pituitary-desensitized, healthy male volunteers were obtained after four different administrations of recombinant-human CG (rhCG). We present a modeling study to provide a possible explanation for the observations that increased exposure to rhCG induces higher and then lower testosterone concentrations and that marked rebound effects are observed at the end of repeated administration of rhCG. We used semimechanistic models (in which flexible functions represent unknown parts of the models) to identify the relationship of rhCG concentrations to the testosterone levels. Based on the results obtained with the semimechanistic models, different mechanistic down-regulation models were devised and tested. The final model uses a one-compartment model to describe the endogenous production rate of testosterone; rhCG affects the production rate with a mechanism consistent with a two-site binding site, with effect proportional to one-site bound concentration. The modeling results indicate that when rhCG concentration increases, the testosterone production rate increases to 45 times the baseline value. However, at an rhCG concentration of more than about 30 IU/liter, the production rate decreases. Simulations showed that both dose and dosing interval profoundly influence testosterone response to rhCG.

Clinical pharmacology of recombinant human luteinizing hormone: Part I. Pharmacokinetics after intravenous administration to healthy female volunteers and comparison with urinary human luteinizing hormone.

OBJECTIVE: To assess the pharmacokinetics after i.v. administration of a recombinant human LH and to compare them to those of a reference hMG preparation containing urinary human LH. DESIGN: Prospective, dose-escalating, cross-over study. SETTING: Phase I clinical research environment. PATIENT(S): Twelve healthy pituitary down-regulated females. INTERVENTION(S): Subjects received single i.v. doses of 300, 10,000, and 40,000 IU of recombinant human LH, followed by a single i.v. dose of 300 IU of hMG, all separated by 1 week. MAIN OUTCOME MEASURE(S): Pharmacokinetic parameters. RESULTS: For both preparations, LH serum levels were well described by similar biexponential models. The pharmacokinetics of recombinant human LH were linear over the 300 to 40,000 IU range. After a rapid distribution phase with an initial half-life of 1 hour, both recombinant human LH and urinary human LH were eliminated with a terminal half-life of 10-12 hours. Total serum clearance was 1.7 L/h with < 4% and 30% of the dose being eliminated in the urine for recombinant human LH and urinary human LH, respectively. The volume of distribution at steady-state was approximately 10 L. Irrespective of the dose, recombinant human LH was well tolerated. CONCLUSION(S): The pharmacokinetics of recombinant human LH are linear with dose and similar to those of urinary human LH.

Clinical pharmacology of recombinant human luteinizing hormone: Part II. Bioavailability of recombinant human luteinizing hormone assessed with an immunoassay and an in vitro bioassay.

OBJECTIVE: To assess the single-dose pharmacokinetics of a recombinant human LH preparation administered by the i.v., i.m., and s.c. route. DESIGN: Prospective, randomized cross-over study. SETTING: Phase I clinical research environment. PATIENT(S): Twelve healthy pituitary down-regulated females. INTERVENTION(S): Subjects received single i.v., i.m., and s.c. doses of 10,000 IU of recombinant human LH, each separated by 1 week. MAIN OUTCOME MEASURE(S): Pharmacokinetic parameters. RESULT(S): After single i.v. administration, the pharmacokinetics were described by a two-compartment model, after i.m. or s.c. administration, by a one-compartment model with zero order absorption and a lag time. Using the immunoassay, after i.v. administration initial half-life was 1 hour and terminal half-life was 10 hours (half-life was prolonged after extravascular administration, suggesting rate-limiting absorption). Total serum clearance was 2.6 L/h, and steady, state volume of distribution was 14 L. Observed Cmax, after i.m. and s.c. administration, was 43 IU/L with median tmax of 9 hours (i.m.) and 5 hours (s.c.). Bioavailability was 0.54 (i.m.) and 0.56 (s.c.). The pharmacokinetics of LH are comparable using an in vitro bioassay. CONCLUSION(S): The terminal half-life of recombinant human LH is around 12 hours and is slightly prolonged after extravascular administration. The pharmacokinetics are similar after i.m. and s.c. injection, and one-half the administered dose is available systemically.

Pharmacokinetic and pharmacodynamic interactions between recombinant human luteinizing hormone and recombinant human follicle-stimulating hormone.

OBJECTIVE: To assess the pharmacokinetics of a recombinant human LH preparation and its pharmacokinetic and pharmacodynamic interactions with recombinant human follicle-stimulating hormone (FSH). DESIGN: Prospective, randomized cross-over study. SETTING: Phase I clinical research environment. PATIENT(S): Twelve healthy pituitary down-regulated females. INTERVENTION(S): Subjects received 150 IU of s.c. recombinant human LH and FSH, either alone or in combination, followed by recombinant human LH and FSH once daily for 7 days. MAIN OUTCOME MEASURE(S): Pharmacokinetic parameters, ovarian follicle development. RESULT(S): No pharmacokinetic interaction between recombinant human LH and FSH was observed, with no significant difference in baseline-corrected maximal observed concentration over baseline, area under the concentration-time curve from t = 0 to t = 24 hours, or time to maximal concentration after single doses alone or in combination. After daily administration, the mean accumulation ratio was 1.6 for LH and 2.9 for FSH, with absorption and terminal phase half-life estimates of 4 and 11 hours for LH and 8 and 16 hours for FSH, respectively. Combined administration of FSH and LH for 7 days was effective in stimulating ovarian follicular development and steroidogenesis, with large interindividual variability related to ovarian sensitivity. CONCLUSION(S): A new recombinant human LH preparation has a low accumulation ratio at steady-state and no pharmacokinetic or pharmacodynamic interactions with recombinant human FSH.

Pharmacokinetics of triptorelin after intravenous bolus administration in healthy males and in males with renal or hepatic insufficiency.

AIMS: Triptorelin is a gonadotropin-releasing hormone (GnRH) analogue with enhanced affinity for GnRH receptors and a prolonged half-life due to its resistance to enzymatic degradation. The sustained-release formulation of this molecule is advantageous in conditions requiring chronic hormone suppression. METHODS: This was an open study to determine the pharmacokinetics of a single i.v. bolus dose of 0.5 mg triptorelin acetate in four groups of six male subjects; namely in healthy subjects (Group I), in patients with varying degrees of renal insufficiency (Groups II and III), and in patients with hepatic insufficiency (Group IV). RESULTS: The maximum concentrations of triptorelin were found to be similar for all four study groups (geometric mean Cmax between 41.6 mg ml(-1) and 53.9 mg ml(-1)). The total clearance of triptorelin decreased with increasing renal impairment, and was even lower in patients with hepatic insufficiency (geometric mean CLtot: 210 ml min(-1), 113 ml min(-1), 86.8 ml min(-1) and 57.3 ml min(-1) for Groups I, II, III and IV, respectively). Serum triptorelin concentrations in all four groups were adequately described by a three-compartment model. The elimination half-life for patients with hepatic impairment was similar to that of patients with renal impairment (geometric mean t(1/2, z): 6.6 h, 7.7 h and 7.6 h for Groups II, III and IV, respectively), but significantly longer than in healthy volunteers (2.8 h for Group I). The first and second distribution half-lives were similar for the four groups studied, with geometric mean distribution half-lives of about 0.1 h (6 min) and 0.75 h (45 min), respectively. CONCLUSIONS: Although both renal and hepatic function are important for the clearance of triptorelin, the liver plays the predominant role in subjects suffering from some degree of renal impairment.

Modeling a bivariate control system: LH and testosterone response to the GnRH antagonist antide.

A pharmacodynamic analysis of the input-response relationship between the gonadotropin-releasing hormone antagonist antide and luteinizing hormone (LH) and testosterone concentrations is presented. A control compartmental model is developed using pharmacokinetic and pharmacodynamic data from experiments in which different short intravenous antide infusions were given to healthy male volunteers. Because of the control interdependence between serum LH and testosterone a separation principle similar to one we have used previously to analyze physiological pharmacokinetic data is used for model exploration: testosterone and LH are first modeled separately, conditioning on the other observed response. This reveals that the LH effect on testosterone depends on previous LH exposure and that LH depends not on current but on previous testosterone exposure, resulting in an LH overshoot after antide-induced suppression. Both submodels are combined into one global model, which in addition includes a model for testosterone circadian variation. This model describes the data well and can be used to predict responses for some nonstudied antide dosages. However, the sensitivity of predictions to model assumptions limits the range of valid extrapolation, and this, too, is illustrated.

Comprehensive pharmacokinetics of urinary human follicle stimulating hormone in healthy female volunteers.

PURPOSE: The study determined the pharmacokinetics of urinary human follicle stimulating hormone (u-hFSH) in 12 down-regulated healthy female volunteers. METHODS: Following pituitary desensitization, baseline FSH serum levels were measured over a 24-hour period. Then each subject received, in random order, single doses of u-hFSH (Metrodin), 75 IU, 150 IU and 300 IU iv, and 150 IU im on four occasions separated by washout periods of one week. Blood and urine samples were collected at preset times. FSH levels were measured by a immuno-radiometric assay and an in vitro rat granulosa cells aromatase bioassay. RESULTS: All doses of u-hFSH were well tolerated. After an iv bolus, the pharmacokinetics of FSH were well described by a two-compartment open model. Immunoassay data showed that the total exposure to FSH was proportional to the administered dose. Mean total clearance of FSH was approximately 0.5 L.h-1 and renal clearance was 0.14 L.h-1. The volume of distribution at steady-state was around 8 liters. The distribution half-life was 2 h and the terminal half-life nearly one day. After im injection, almost two thirds of the administered dose was available systemically. The in vitro bioassay confirmed this pharmacokinetic analysis. CONCLUSIONS: The estimation of the elimination half-life of around one day indicates that the maximal effect of a given dose of u-hFSH administered daily cannot be observed until 3 to 4 days of repeated administration. This indicates that, on a pure pharmacokinetic basis, physicians should wait at least 4 days to assess the efficacy of a given dose of u-hFSH and that they should not modify dosage too frequently.

Pharmacokinetics of recombinant human luteinizing hormone after intravenous, intramuscular, and subcutaneous administration in monkeys and comparison with intravenous administration of pituitary human luteinizing hormone.

To assess the pharmacokinetics of recombinant human LH (rhLH) in monkeys, we measured serum LH levels after single iv injection and after single and repeated doses by the im or sc route. A single iv bolus of 400 IU/kg rhLH or pituitary hLH (phLH) in six cynomolgus monkeys resulted in parallel concentration-time curves. The initial and terminal half-lives of rhLH (0.8 and 11 h) were comparable to those of phLH (0.6 and 10 h). The serum levels of phLH were consistently higher due to the fact that the immunological dose of phLH was higher. Administration of increasing iv doses of rhLH (10, 63, and 400 IU/kg) to six monkeys showed that the pharmacokinetics are linear over this dose range. The total clearance for the two higher doses was 0.03 L/h.kg. Systemic bioavailability was 50% after a single sc injection of 400 IU/kg and 61% after a single im injection of the same dose. The peak concentration (180 IU/L) after im injection was reached after 2.7 h. This was higher and sooner than after sc injection (110 IU/L after 5.3 h). The terminal half-life by both routes was similar to that seen after iv injection (11 h). Daily sc or im administration of 63 IU/kg for 7 days confirmed these findings. There was no accumulation of rhLH. Some monkeys developed antibodies, especially after repeated administration. They were excluded from the analysis. No significant local or systemic adverse events occurred.

Clinical pharmacology of recombinant human follicle-stimulating hormone (FSH). I. Comparative pharmacokinetics with urinary human FSH.

OBJECTIVE: To assess and compare the pharmacokinetics of recombinant human FSH with those of a reference preparation of urinary human FSH. DESIGN: Urinary human FSH and recombinant human FSH (Metrodin and Gonal-F; Laboratoires Serono, Aubonne, Switzerland) were administered in a balanced, random order, crossover sequence as a single i.v. dose of 150 or 300 IU separated by 1 week of washout to 12 pituitary down-regulated, healthy female volunteers. Serum FSH concentrations were measured by an immunoradiometric assay (IRMA) and by an in vitro rat granulosa cell aromatase bioassay. Urine FSH concentrations were measured by IRMA. RESULTS: The mean concentration-time profiles after 150 IU of urinary human FSH and recombinant human FSH were superimposed, and the mean profile after 300 IU of recombinant human FSH was double that of the 150 IU dose. The data for both FSH preparations were well described by a biexponential equation. Total clearance of the preparations was comparable, judging from immunoassay and bioassay data (0.5 and 0.15 L/h, respectively). Based on the immunoassay, renal clearance of urinary human FSH was 0.1 L/h, whereas for recombinant human FSH it was slightly lower at 0.07 L/h, indicating that less than one fifth of the administered dose was excreted in the urine. Immunoassay showed that the two preparations were similar in terms of initial and terminal half-lives (2 and 17 hours, respectively). The volumes of distribution at steady state (11 L) were similar. The results of the in vitro bioassay confirmed this pharmacokinetic analysis. Just after i.v. administration, an initial decrease in the serum bioassay:immunoassay ratio was observed because of dilution of urinary human FSH or of recombinant human FSH in the residual endogenous FSH pool. Then the ratio increased progressively with time, suggesting either metabolic selection or activation of both types of injected human FSH toward forms with greater in vitro bioactivity. The bioassay:immunoassay ratio returned to baseline by day 7. CONCLUSION: The results obtained in this study indicate that the following [1] the pharmacokinetic characteristics of recombinant human FSH are similar to those of urinary human FSH; [2] the terminal half-life of human FSH is approximately 1 day; [3] after a single i.v. injection of human FSH a progressive increase in FSH bioassay: immunoassay ratio is observed; and [4] clinical use of recombinant human FSH could follow protocols and treatment regimens currently applied to urinary human FSH.

Clinical pharmacology of recombinant human follicle-stimulating hormone. III. Pharmacokinetic-pharmacodynamic modeling after repeated subcutaneous administration.

OBJECTIVE: To investigate the respective role of the pharmacokinetic and of the pharmacodynamic characteristics in individual variability and to reassess the time course and the informative value of FSH pharmacodynamic markers by applying a combined pharmacokinetic-pharmacodynamic modeling analysis. DESIGN: After a 1-week SC administration of 150 IU/d of recombinant human FSH (Gonal-F; Laboratoires Serono, Aubonne, Switzerland) to 12 healthy down-regulated female volunteers, inhibin and E2 serum level and total follicular volume were recorded at preset times during 2 weeks. RESULTS: Good correlations were obtained between inhibin maximal levels and maximal total follicular volumes and between E2 maximal serum level increases and maximal total follicular volumes. In contrast, no correlation was found between maximal serum concentration of FSH and any of the recorded effects. Pharmacodynamic effects started to increase significantly later than FSH serum concentration, especially for E2 serum level and total follicular volume. Inhibin serum level was the first pharmacodynamic marker to increase. A full pharmacokinetic-pharmacodynamic model was developed to determine the relationship between drug concentrations and FSH pharmacological effects. This approach provides a better understanding of the concentration-effect relationship and should allow a rational design for recombinant human FSH dose regimen. The average equilibration half-life between serum concentrations and theoretical effect-compartment concentrations is approximately 2 days for inhibin and approximately 4 days for E2, indicating that inhibin serum levels are tracking FSH concentrations more closely than E2 serum levels. CONCLUSIONS: [1] Recombinant human FSH alone is effective to stimulate ovarian follicular development and steroidogenesis in women pretreated with a GnRH agonist despite complete LH suppression; [2] there is a large interindividual variability in the response to recombinant human FSH; [3] this variability is mainly related to ovarian sensitivity to FSH rather than difference in pharmacokinetics; [4] inhibin is an early index of follicular development, further supporting its role as a putative tool to monitor FSH therapy; and [5] a slow stepwise increase in FSH dose is recommended if FSH overexposure and excessive ovarian stimulation are to be minimized. These observations suggest that recombinant human FSH will in the near future replace urinary human FSH in the clinics.

Clinical pharmacology of recombinant human follicle-stimulating hormone. II. Single doses and steady state pharmacokinetics.

OBJECTIVE: To assess the single-dose pharmacokinetics of a recombinant human FSH preparation (Gonal-F; Laboratoires Serono, Aubonne, Switzerland), administered by i.v., IM, and SC routes and its pharmacokinetics at steady state after multiple dosing by the SC route. DESIGN: Twelve healthy down-regulated female volunteers received in random order three single doses of recombinant human FSH (150 IU, i.v., IM, and SC), with each administration separated by 1 week. The volunteers then received multiple recombinant human FSH doses by the SC route (150 IU one time per day) for 7 days. Follicle-stimulating hormone concentrations were measured by an immunoradiometric assay and an in vitro granulosa cell aromatase bioassay. RESULTS: After a single administration, the pharmacokinetics of recombinant human FSH were well-described by a two-compartment model after i.v. administration and by a one-compartment model with first order absorption after IM or SC administration. The mean total clearance of FSH was approximately 0.6 L/h, and renal clearance accounted for one tenth of the total elimination after i.v. administration. The distribution half-life was close to 2 hours. The terminal half-life was nearly 1 day when estimated either by modeling the i.v. data set or from analysis of the terminal phase of the steady state pharmacokinetic curve or from the time taken to reach steady state after repeated SC administrations. After single IM and SC injection, two thirds of the administered dose was available systemically. The cumulation factor for repeated SC administration was approximately 3 when steady state was reached. The in vitro bioassay data confirmed these estimations. The temporal evolution of the bioassay:immunoassay ratio suggests either metabolic selection or activation of recombinant human FSH toward forms with greater in vitro bioactivity. CONCLUSION: The estimation of the elimination half-life of approximately 1 day indicates that the maximal effect of a given dose of recombinant human FSH administered daily cannot be observed until 3 to 4 days of repeated administration. This indicates that, on a pure pharmacokinetic basis, physicians should wait at least 4 days to assess the efficacy of a given dose of recombinant human FSH and that they should not modify dosage too frequently.

Comparative pharmacokinetics of two urinary human follicle stimulating hormone preparations in healthy female and male volunteers.

These studies were designed to compare the pharmacokinetic characteristics of a very highly purified urinary human follicle stimulating hormone (FSH-HP) preparation (sp. act. approximately 9000 IU FSH/mg of protein), Metrodin HP, with a standard urinary FSH preparation Metrodin (FSH). The two preparations were administered in a balanced, random-order, cross-over sequence as single doses of 150 IU, separated by 1 week of washout to 12 female volunteers by i.v. injection and to 12 male volunteers by i.m. and s.c. routes. FSH concentrations were measured by immunoradiometric assay and by an in-vitro rat granulosa cell aromatase bioassay. After an i.v. bolus, the pharmacokinetics of the two FSH preparations were identical. Total clearance was 0.5 and 0.15 l/h respectively for immunoassay and bioassay data. Immunoassay showed that the two preparations were similar for renal clearance (0.1 l/h), volumes of distribution at steady state (9 l), distribution and terminal half-lives (2 and 17 h, respectively). After parenteral administrations, the absorption half-life of FSH was approximately 3 h and the apparent terminal half-life was approximately 1.5 days. Both preparations had relative bioavailabilities close to 100% for i.m. and s.c. administrations. Immunopurification, which results in a very highly purified FSH-HP, does not modify the pharmacokinetic properties of FSH. This study also confirmed that s.c. and i.m. doses of FSH-HP are equivalent from the pharmacokinetic and pharmacodynamic points of view.

Central analgesic effects of desipramine, fluvoxamine, and moclobemide after single oral dosing: a study in healthy volunteers.

The antinociceptive effect of three antidepressants with different postulated modes of action, 75 mg desipramine, 225 mg fluvoxamine, and 450 mg moclobemide, was evaluated after single oral dosing in a randomized, double-blind, placebo-controlled crossover study in 10 healthy volunteers. Experimental pain thresholds (polysynaptic R-III reflex and subjective pain rating) were monitored over 23 hours. Compared with placebo, all drugs induced significant subjective pain threshold increases (maximal increase: desipramine, +20%; fluvoxamine, +17%; moclobemide, +13%). However, only desipramine (maximal increase, +25%) and moclobemide (maximal increase, +14%) displayed a significative effect on R-III threshold. Antidepressants thus exert an antinociceptive effect after a single oral dose. The level of their action apparently relies on the postulated mode of action.

Pharmacokinetics of recombinant human follicle stimulating hormone after intravenous, intramuscular, and subcutaneous administration in monkeys, and comparison with intravenous administration of urinary follicle stimulating hormone.

Recombinant human follicle stimulating hormone (r-hFSH; Gonal-F) is a new human FSH produced by a genetically engineered mammalian cell line (Chinese Hamster Ovary cells). To assess and compare its pharmacokinetics with urofollitropin (u-hFSH; Metrodin), extracted from the urine of postmenopausal women, we performed a cross-over study in 12 monkeys. They received 10 IU/kg iv of u-hFSH and r-hFSH. Then all received a single 10 IU/kg dose im and sc of r-hFSH. In the third phase, six monkeys received 10 IU/kg/day im of r-hFSH for 7 days when the six others received the same regimen subcutaneously. Blood was withdrawn at predetermined time points, and FSH serum concentrations were measured by an immunoenzymetric assay. Data were analyzed individually by fitting a two-compartment pharmacokinetic model for the intravenous routes and a one-compartment first-order absorption model for the intramuscular and subcutaneous routes. After intravenous administration of u-hFSH and r-hFSH, mean FSH concentration-time curves were almost parallel. AUC0-infinity was significantly smaller after r-hFSH (846 IU.hr-1/liter +/- 125) than after u-hFSH (1377 IU.hr-1/liter +/- 236) (p < 0.005; analysis of variance), because the u-hFSH immunological dose was greater (8.77 IU/kg) than the r-hFSH immunological dose (6.94 IU/kg). Thus total clearance for r-hFSH (0.008 liter/hr/kg +/- 0.001) and for u-hFSH (0.007 liter/hr/kg +/- 0.001) was almost similar. Distribution half-lives (1.5 hr +/- 0.1 and 1.8 hr +/- 0.4) and terminal half-lives (15.3 hr +/- 3.8 and 15.5 hr +/- 5.1) for r-hFSH and u-hFSH were similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and tissue distribution of human urinary tumor necrosis factor binding protein in mice.

Iodinated natural human urinary tumor necrosis factor binding protein I (125I-uTBP) was iv injected into BALB/c mice, and its pharmacokinetics and tissue distribution were assessed during a short-term (0-1 hr) and for a long-term (0-24 hr) period. The blood 125I-uTBP concentration displayed a biphasic pattern that was adequately described by a biexponential function with estimated half-lives of 0.1 and 3.8 hr. The apparent volume of distribution (Vc) of the central compartment was 3 ml, which approximated the mouse blood volume. The clearance (CL) derived either from a model-dependent or a model-independent method of analysis was 2.5 and 2.9 ml/hr, respectively. One hr after the iv administration of 125I-uTBP, the radioactivity accumulated in the major organs and tissues. The highest concentrations in terms of pg per organ were seen in the skin and in the liver. When expressed as pg 125I-uTBP per mg organ, the distribution was the highest in the gallbladder, bladder, kidneys, and lungs. At 24 hr, the distribution of 125I-uTBP represented about 10% of the amount measured at 1 hr. The rank order of accumulation of the radiolabeled uTBP in the major organs, expressed as pg per organ at 24 hr was skin greater than liver greater than kidneys greater than lungs greater than gut greater than spleen greater than gallbladder.

Serum concentration-effect relationship of (+/-)-nicardipine and nifedipine in elderly hypertensive patients.

The concentration-effect relationships of (+/-)-nicardipine and nifedipine have been investigated in hypertensive geriatric patients. Following a parallel group, randomised, double blind trial design, they received either slow release nifedipine 20 mg b.d. (n = 9) or slow release (+/-)-nicardipine 50 mg b.d. (n = 10) for 7 days. On Days 1 and 7 serum (+/-)-nicardipine and nifedipine, blood pressure and heart rate were measured 6 and 12 h after drug administration. (+/-)-Nicardipine showed significant cumulation (ca 2 x) without a corresponding decrease in blood pressure or increase in heart rate. Concentration-effect plots indicated that (+/-)-nicardipine was more potent than nifedipine but that it showed apparently comparable efficacy in reducing the blood pressure. Compared to young healthy volunteers, both drugs had a more pronounced effect in elderly patients.

Pharmacokinetic-pharmacodynamic modeling of the effects of clonidine on pain threshold, blood pressure, and salivary flow.

Although clonidine analgesia appears to be mediated by the same central alpha 2-adrenoceptors that mediate its hypotensive effect, it is short-lasting when compared to the fall in blood pressure. This has been investigated by combined pharmacokinetic-pharmacodynamic analysis in 10 healthy volunteers who received (double-blind and crossover) clonidine 200 micrograms orally + placebo i.v. and clonidine orally + naloxone i.v. (2.8 mg/5 h). Analgesia was assessed by measuring the subjective (VAS) and objective (RIII) pain thresholds after transcutaneous electrical stimulations of the sural nerve; the mean arterial blood pressure (MAP), salivary flow (SF), and plasma clonidine concentrations were also monitored. A combined pharmacokinetic (first order absorption - 1 compartment) - pharmacodynamic (linear) model, including a hypothetical effect compartment with and without tolerance, were fitted to the data. Clonidine and clonidine + naloxone increased subjective and objective pain thresholds for 4 h. The concentration-effect plot for MAP showed distinct hysteresis. The t1/2s for effect compartment equilibration were 29 and 42 min for clonidine + naloxone and clonidine. The concentration-effect curves for RIII had the same shape as MAP but the starting hysteresis suddenly collapsed, suggesting acute tolerance. The best fit was obtained with a model where the linear relationship between concentration in the effect compartment and analgesia changed acutely after the third hour. The short-lived analgesia was probably related to an acute change in pain sensitivity induced by food, suggesting that it is not mediated solely by the alpha 2-adrenoceptors responsible for hypotension.

[Central analgesic effects of antidepressant drugs with various mechanisms of action: desipramine, fluvoxamine and moclobemide]. / Effet analgésique central d'antidépresseurs à mode d'action distinct: désipramine, fluvoxamine et moclobémide.

Analgesic properties of antidepressants are not yet well established. The aim of this study was to investigate the analgesic effect of three antidepressants after single oral dose administration to healthy volunteers. The late spinal R-III reflex threshold (objective pain threshold) and the subjective pain threshold (numerical categorical scale) were markers of analgesic effect. Desipramine induced significant increases in both thresholds. Fluvoxamine and moclobemide also exerted a significant analgesic effect, although displaying distinct patterns depending on the analgesic marker considered. Antidepressants exert a central analgesic effect independent of their antidepressive effect and, depending on their mode of action, already detectable at spinal level.