Role of modelling and simulation in Phase I drug development.

Although the use of pharmacokinetic/pharmacodynamic modelling and simulation (M&S) in drug development has increased during the last decade, this has most notably occurred in patient studies using the population approach. The role of M&S in Phase I, although of longer history, does not presently have the same impact on drug development. However, trends such as the increased use of biomarkers and clinical trial simulation as well as adoption of the learn/confirm concept can be expected to increase the importance of modelling in Phase I. To help identify the role of M&S, its main advantages and the obstacles to its rational use, an expert meeting was organised by COST B15 in Brussels, January 10-11, 2000. This article presents the views expressed at that meeting. Although it is clear that M&S occurs in only a minority of Phase I clinical trials, it is used for a large number of different purposes. In particular, M&S is considered valuable in the following situations: censoring because of assay limitation, characterisation of non-linearity, estimating exposure-response relationship, combined analyses, sparse sampling studies, special population studies, integrating PK/PD knowledge for decision making, simulation of Phase II trials, predicting multiple dose profile from single dose, bridging studies and formulation development. One or more of the following characteristics of M&S activities are often present and severely impede its successful integration into clinical drug development: lack of trained personnel, lack of protocol and/or analysis plan, absence of pre-specified objectives, no timelines or budget, low priority, inadequate reporting, no quality assurance of the modelling process and no evaluation of cost-benefit. The early clinical drug development phase is changing and if these implementation aspects can be appropriately addressed, M&S can fulfill an important role in reshaping the early trials by more effective extraction of information from studies, better integration of knowledge across studies and more precise predictions of trial outcome, thereby allowing more informed decision making.

Structure-function relationship of recombinant follicle stimulating hormone (Puregon).

After separation by means of preparative isoelectrofocusing, the isohormones of a Chinese hamster ovary (CHO)-derived recombinant follicle stimulating hormone (rFSH, Puregon) were characterized with respect to structural and functional features. A carbohydrate analysis revealed that rFSH isohormones with a low isoelectric point (pl) have a high sialic acid/galactose ratio and are rich in tri- and tetra-antennary N-linked carbohydrate chains in comparison with the high pl isohormones. The relative basic isohormones exhibit receptor binding activity and intrinsic bioactivity 2-3-fold higher than the relative acidic isohormones. However, due to their lower clearance rate these acidic isohormones displayed a 20-fold higher in-vivo bioactivity in the rat. A comparison of the isohormone profile of rFSH and urinary FSH (Metrodin) revealed that rFSH contains about 2-fold more basic isohormones with pl > or = 4.7 and 2-fold less acidic isohormones with pl < 4.1. In-vitro studies showed that the receptor binding affinity and intrinsic bioactivity of both FSH preparations are similar. Also the in-vivo efficacy and the pharmacokinetic behaviour of rFSH and urinary FSH in the rat were similar, which is not surprising since both preparations were compared in terms of in-vivo bioactivity calibrated in the rat Steelman-Pohley assay. However, in dogs the bioavailability of rFSH was lower than that of urinary FSH, which is in agreement with the higher percentage of relative basic isohormones in rFSH. This suggests that the pharmacokinetic behaviour of FSH in rats and dogs is different, which is supported by the much longer elimination half-life of rFSH and urinary FSH in dogs (27.9 and 30.4 h respectively) compared with rats (11.4 and 10.4 h respectively) for rFSH and urinary FSH respectively. The observed differences in pharmacokinetic behaviour in dogs and rats indicate that the rat Steelman-Pohley assay might not be a valid model for the prediction of the FSH bioactivity in species other than rat.

Clinical profiling of recombinant follicle stimulating hormone (rFSH; Puregon): relationship between serum FSH and efficacy.

Single-dose and multiple-rising dose studies of recombinant follicle stimulating hormone (rFSH) in hypogonadotrophic male and female volunteers demonstrated that the rate of FSH absorption after i.m. injection is higher in men than in women. In the absence of endogenous FSH, a correlation between serum FSH and body weight became apparent. The elimination half-life of rFSH was not different between the sexes and was comparable with urinary FSH. However, the in-vitro bio:immuno ratio of serum FSH was significantly higher after the administration of rFSH than after urinary FSH. When rFSH was administered daily with a fixed dose, steady state levels were reached within 3-5 days. Serum FSH concentrations increased in a dose-dependent manner when the daily dose was increased weekly over 3 weeks from 75 to 225 IU. In hypogonadotrophic women, rFSH induced normal follicular growth whereas oestrogen synthesis was impaired. In women pituitary suppressed by a high-dose oral contraceptive, the daily administration of 150 IU rFSH for 1 week induced more and larger antral follicles than the same regimen with urinary FSH, whereas the serum immunoactive FSH concentrations measured 24 h after each dosing were similar. It is concluded that even though equal or lower serum immunoactive FSH concentrations were obtained following the administration of rFSH compared with urinary FSH, circulating bioactive FSH concentrations were higher. Therefore, the conventional idea that serum immunoreactive FSH correlates positively with the magnitude of the ovarian response should be reconsidered.

A bioequivalence study of two urinary follicle stimulating hormone preparations: Follegon and Metrodin.

The purpose of this study was to demonstrate bioequivalence between two follicle stimulating hormone (FSH)-only gonadotrophin preparations (Follegon(R) and Metrodin(R)) after a single i.m. injection of IU FSH in-vivo bioactivity. A total of 16 healthy normally cycling females were treated for 7 weeks with a high-dose oral contraceptive containing 50 microg ethinyl oestradiol plus 2.5 mg lynestrenol (Lyndiol(R)) to suppress endogenous gonadotrophin production. After 3 and 5 weeks or oral contraceptive treatment, each subject received 300 IU Follegon or Metrodin in a random order. Frequent blood sampling was performed to measure immunoreactive FSH for pharmacokinetic analysis. After normalization for the immunodose administered, Follegon and Metrodin were bioequivalent with respect to the extent and the rate of absorption, the elimination half-life and plasma clearance per kg. The time taken to reach peak plasma FSH concentrations was shorter with Follegon than with Metrodin. Because bioequivalence was proved for the major pharmacokinetic variables, it can be assumed that Follegon and Metrodin are also equally effective inovulation induction, in-vitro fertilization and embryo transfer programmes and the treatment of male infertility.

Pharmacokinetics of two human menopausal gonadotrophin preparations after single intravenous administration during pituitary suppression.

A randomized study was performed in nine healthy women, to investigate pharmacokinetic parameters and bioequivalence of two human menopausal gonadotrophin preparations after i.v. administration. Endogenous gonadotrophin activity was suppressed by triptorelin administration. Humegon and Pergonal (225 IU of each) were injected i.v. in a cross-over way with an interval of 1 week. Blood samples were collected frequently and serum concentrations of follicle stimulating hormone (FSH), luteinizing hormone (LH), specific LH, and human chorionic gonadotrophin (HCG) were determined by fluoroimmunoassays assays. Serum LH bioactivity was measured by an in-vitro bioassay. The area under curve (AUC) and half-life of FSH were respectively 431.5 IU h/l and 22.20 h for Humegon, and 402.6 IU h/l and 21.33 h for Pergonal. For both preparations, the (total) LH immunoactivity and in-vitro bioactivity of serum LH were very similar, and appeared to be a composite of specific LH and HCG activity. The AUC data of specific LH were 17.50 IU h/l for Humegon and 21.79 IU h/l for Pergonal respectively. The AUC and half-life of HCG were 153.7 IU h/l and 14.80 h for Humegon, and 134.1 IU h/l and 12.11 h for Pergonal. The two preparations were bioequivalent with respect to FSH and HCG immunoreactivity. Bioequivalence could not be proven for LH activity because of the small number of subjects.

Single-dose pharmacokinetics and pharmacodynamics of recombinant human follicle-stimulating hormone (Org 32489*) in gonadotropin-deficient volunteers.

OBJECTIVE: To assess safety, pharmacokinetic, and pharmacodynamic properties of recombinant human follicle-stimulating hormone (FSH; Org 32489, Organon International, Oss, The Netherlands) after a single intramuscular injection in the buttock. DESIGN: In a prospective study, safety variables, serum FSH, luteinizing hormone, inhibin, estradiol (females only), and testosterone (males only) were evaluated up to a maximum of 11 days after injection of 300 IU recombinant FSH. SETTING: Four specialist Reproductive Endocrinology and Infertility units. VOLUNTEERS: Fifteen men and women exhibiting all pituitary gonadotropin deficiency. RESULTS: A single bolus of 300 IU recombinant FSH was well tolerated, and no drug-related adverse effects were noted. Comparison of before and after treatment safety variables, including serum antirecombinant FSH antibodies, showed no changes of clinical relevance. Analysis of serum FSH levels revealed comparable elimination half-lives of 44 +/- 14 (mean +/- SD) and 32 +/- 12 hours in women and men volunteers, respectively. In contrast, peak FSH concentrations were significantly lower in women than in men volunteers (4.3 +/- 1.7 versus 7.4 +/- 2.8 IU/L), and the time required to reach peak levels of FSH was significantly longer in women than in men (27 +/- 5 versus 14 +/- 8 hours). The area under the serum level versus time curve tended to be smaller in women than in men volunteers (339 +/- 105 versus 452 +/- 183 IU/L x hours), but the difference did not reach statistical significance. Together these data suggest that recombinant FSH is absorbed from its intramuscular depot to a lower rate and extent in women than in men. In both sexes a relationship between serum FSH levels and body weight was apparent. During the experimental period, other hormones remained low at baseline levels or were only slightly increased. CONCLUSION: Our findings indicate that recombinant FSH is well tolerated and that it is absorbed from its intramuscular depot to a higher rate and extent in men than in women. After intramuscular administration, its half-life is in good agreement with that previously reported for natural FSH.

Pharmacokinetics of steroidal muscle relaxants in isolated perfused rat liver.

Both in humans and animals hepatic elimination is an important factor determining the duration of action of non-depolarizing neuromuscular blocking drugs. To elucidate the hepato-biliary disposition of muscle relaxants the pharmacokinetics of several structurally related but physicochemically distinct steroidal neuromuscular blocking drugs were studied in isolated perfused rat livers. Pharmacokinetics analysis with the DIFFIT computer program enabled the simultaneous fitting of independently measured perfusate disappearance and biliary excretion rate curves using a numerical approach. The hepatic disposition of the steroidal muscle relaxants could be adequately described by a three compartment model with elimination from the peripheral compartment V2 (biliary excretion) and storage in a deep compartment (V3) connected to V2. In addition, for vecuronium only slow ester hydrolysis occurring in V2 and V3 was included in the model. The lipophilicity rather than the relative mobility of the muscle relaxants showed a positive relationship with biliary clearance (Cl20) and the initial hepatic uptake (Cl12), indicating that hepato-biliary transport of these organic cations is highly dependent on the hydrophobic character of the compounds. In addition, net hepatic uptake of the steroidal cations was influenced markedly by transport from the liver to perfusate (hepatic efflux). This hepatic efflux (k21) decreased with increasing lipophilicity. In contrast, the extent of intracellular sequestration into deep compartments, indicated by high k23/k32 ratios, seemed to be inversely related to the lipophilicity of the muscle relaxants and might explain the observed prolonged hepatic storage of some of these compounds. In combination with data from subfractionation studies the results indicate that the pharmacokinetic analysis of the hepatic disposition of steroidal muscle relaxants may be used to evaluate actual transport phenomena participating in the hepatic disposition of these drugs.