A new population pharmacokinetic model for recombinant factor IX-Fc fusion concentrate including young children with haemophilia B

AIMS

Recombinant factor IX Fc fusion protein (rFIX-Fc) is an extended half-life factor concentrate administered to haemophilia B patients. So far, a population pharmacokinetic (PK) model has only been published for patients aged ≥12 years. The aim was to externally evaluate the predictive performance of the published rFIX-Fc population PK model for patients of all ages and develop a model that describes rFIX-Fc PK using real-world data.

METHODS

We collected prospective and retrospective data from patients with haemophilia B treated with rFIX-Fc and included in the OPTI-CLOT TARGET study (NTR7523) or United Kindom (UK)-EHL Outcomes Registry (NCT02938156). Predictive performance was assessed by comparing predicted with observed FIX activity levels. A new population PK model was constructed using nonlinear mixed-effects modelling.

RESULTS

Real-world data were obtained from 37 patients (median age: 16 years, range 2-71) of whom 14 were aged <12 years. Observed FIX activity levels were significantly higher than levels predicted using the published model, with a median prediction error of -48.8%. The new model showed a lower median prediction error (3.4%) and better described rFIX-Fc PK, especially for children aged <12 years. In the new model, an increase in age was correlated with a decrease in clearance (P < .01).

CONCLUSIONS

The published population PK model significantly underpredicted FIX activity levels. The new model better describes rFIX-Fc PK, especially for children aged <12 years. This study underlines the necessity to strive for representative population PK models, thereby avoiding extrapolation outside the studied population.

Use of the novel combined contraceptive vaginal ring NuvaRing for ovulation inhibition

OBJECTIVE

To assess the effects of the combined contraceptive vaginal ring NuvaRing on ovarian function.

DESIGN

Randomized, open-label, crossover study.

SETTING

Clinical pharmacology unit.

PARTICIPANT(S)

Sixteen healthy female volunteers.

INTERVENTION(S)

Group 1: one cycle of combined oral contraceptive containing desogestrel (150 microg) and ethinyl estradiol (30 microg) (desogestrel/EE COC), followed by a NuvaRing treatment period. Group 2: NuvaRing treatment period followed by a cycle of desogestrel/EE COC.

MAIN OUTCOME MEASURE(S)

Follicular diameter, serum hormone concentrations (follicle-stimulating hormone, 17beta estradiol, luteinizing hormone, and progesterone), and endometrial thickness.

RESULT(S)

NuvaRing use for the recommended period of 3 weeks resulted in complete inhibition of ovulation, as assessed by vaginal ultrasound (follicular diameter) and by serum luteinizing hormone and progesterone concentrations. Inhibition of ovulation was maintained for an additional 2 weeks of NuvaRing use. Ovarian suppression between the groups was comparable. Furthermore, ovarian suppression after 3 weeks of NuvaRing use was comparable to that on day 21 of DGS/EE COC intake. NuvaRing was well tolerated.

CONCLUSION(S)

NuvaRing completely inhibited ovulation throughout the normal 3-week period and the extended period of use. Ovarian suppression was comparable to that with desogestrel/EE COC.

Efficacy, tolerability and acceptability of a novel contraceptive vaginal ring releasing etonogestrel and ethinyl oestradiol

A novel contraceptive vaginal ring releasing etonogestrel 120 microg and ethinyl oestradiol 15 microg daily over a period of 3 weeks was tested. Each ring was used for one cycle, comprising 3 weeks of ring use followed by a 1 week ring-free period. This 1 year, multicentre study assessed the contraceptive efficacy, cycle control, tolerability and acceptability of the contraceptive. Altogether, 1145 women were exposed to the vaginal ring for 12,109 cycles (928 woman-years). Six pregnancies occurred during treatment, giving a Pearl Index of 0.65 (95% confidence interval 0.24--1.41). Cycle control was very good, since irregular bleeding was rare (2.6--6.4% of evaluable cycles) and withdrawal bleeding (mean duration 4.7--5.3 days) occurred in 97.9--99.4% of evaluable cycles. Compliance to the prescribed regimen was high with criteria being fulfilled in 90.8% of cycles. The ring was well tolerated. The majority of women considered this new contraceptive method easy to use, and it offers an effective, convenient, well-accepted and novel method for hormonal contraception.

Desogestrel plus testosterone effectively suppresses spermatogenesis but also causes modest weight gain and high-density lipoprotein suppression

OBJECTIVE

To test the hypothesis that oral desogestrel (DSG) plus testosterone would uniformly and rapidly suppress sperm concentrations in young men as effectively as levonorgestrel (LNG) plus testosterone and cause less high-density lipoprotein (HDL) suppression and weight gain.

DESIGN

Single-blind, randomized trial.

SETTING

VA Puget Sound and University of Washington, Seattle, Washington.

PATIENT(S)

Twenty-four healthy young men, aged 20-49.

INTERVENTION(S)

Subjects were randomized to three groups of men who were administered 6 months of therapy with oral DSG plus im testosterone enanthate: 150 microg of DSG plus 50 mg of testosterone (DSG 150-T 50), 150 microg of DSG plus 100 mg of testosterone (DSG 150-T 100) or 300 microg of DSG plus 100 mg of testosterone (DSG 300-T 100). We compared these three groups to two groups of historical controls of 100 mg of im testosterone alone or 150 microg of oral LNG plus 100 mg of im testosterone (LNG 125-T 100 group) enrolled in similar studies.

MAIN OUTCOME MEASURE(S)

Suppression of sperm counts to severe oligoazoospermia (sperm counts <1 x 10(6)/mL) and azoospermia, weight gain, and serum high-density cholesterol (HDL) suppression.

RESULT(S)

Azoospermia was achieved in all eight men receiving DSG 150-T 100 and seven of the eight men in the DSG 300-T 100 group. DSG 150 or 300 plus T 100 suppressed spermatogenesis as effectively as LNG 125-T 100 and more effectively than DSG 50-T 100 or testosterone alone. All groups tended to gain weight compared with their baseline, but the weight gain was greatest (and statistically significant) in the DSG 150-T 100, DSG 300-T 100, and LNG 125-T 100 groups. Serum HDL levels were modestly suppressed in all groups, and this effect was greatest in the DSG 300-T 100 and LNG 125-T 100 groups.

CONCLUSION(S)

The combination of DSG plus testosterone is a very effective regimen for suppression of spermatogenesis and has acceptably low side effects.

Pharmacokinetics of etonogestrel and ethinylestradiol released from a combined contraceptive vaginal ring

OBJECTIVE

To assess the pharmacokinetics of etonogestrel and ethinylestradiol released from a novel combined contraceptive vaginal ring (NuvaRing) releasing etonogestrel 120microg and ethinylestradiol 15 microg per day and compare them with those of a combined oral contraceptive containing desogestrel 150 microg/ethinylestradiol 30 microg (DSG/EE COC).

DESIGN AND SETTING

This was a nonblind, randomised, crossover study in 16 healthy women.

METHODS

All volunteers received one cycle of DSG/EE COC before being randomised to 1 of 2 treatment groups. The participants in group 1 received 1 cycle of DSG/EE COC, a treatment period with NuvaRing and an intravenous bolus injection of etonogestrel/ethinylestradiol (150 microg/30 microg). Those in group 2 received a NuvaRing treatment period, 1 cycle of DSG/EE COC and the same intravenous bolus injection.

RESULTS AND CONCLUSIONS

After the insertion of NuvaRing, maximum serum concentrations of etonogestrel and ethinylestradiol were achieved in approximately 1 week. The concentrations subsequently showed a gradual linear decrease in time. The maximum serum concentrations of etonogestrel and ethinylestradiol were approximately 40 and 30%, respectively, of those for the DSG/EE COC. In comparison with the DSG/EE COC, the absolute bioavailability for NuvaRing was higher for etonogestrel (102.9 vs 79.2%) and similar for ethinylestradiol (55.6 vs 53.8%). Taking the difference in daily doses into account, systemic exposure to etonogestrel was similar for NuvaRing and the DSG/EE COC, whereas systemic exposure to ethinylestradiol with NuvaRing was only approximately 50% of that for the DSG/EE COC.

Oral progestogen combined with testosterone as a potential male contraceptive: additive effects between desogestrel and testosterone enanthate in suppression of spermatogenesis, pituitary-testicular axis, and lipid metabolism

The effects of a synthetic oral progestogen, desogestrel (DSG), administered with low dose testosterone (T) were investigated to determine the optimal combination for suppression of gonadotropins and spermatogenesis to targets compatible with effective male contraception. Twenty-four healthy male volunteers (33.2 +/- 0.9 yr) were randomly assigned to 3 groups (n = 8) to receive: 1) 300 microg DSG orally daily and 100 mg T enanthate, i.m., weekly; 2) 300 microg DSG and 50 mg T enanthate; or 3) 150 microg DSG and 100 mg T enanthate for 24 weeks. To investigate the individual contribution to the combined action, DSG was administered alone for the first 3 weeks, and T enanthate was added on day 22. After 24-week treatment, sperm density in 78% (18 of 23) of the subjects became azoospermic, whereas 91.7% (22 of 24) and 95.8% (23 of 24) suppressed to less than 1 million/mL and less than 3 million/mL, respectively. The 300 microg DSG with 50 mg T enanthate combination induced azoospermia in 8 of 8 subjects, and the suppression of sperm density was significantly greater than that in the 300 microg DSG/100 mg T enanthate group, but was not different from that in the 150 microg DSG/100 mg T enanthate group. DSG (300 or 150 microg daily) alone in the first 3 weeks suppressed LH, FSH, and T to 60.6%, 48.0%, and 35.4%, respectively, of the baseline. Addition of T enanthate (50 and 100 mg weekly) raised plasma T to the physiological range and induced a further fall in LH and FSH to the limits of assay detection. There was no consistent difference in mean LH and FSH levels among the three groups during treatment or recovery, except that FSH remained detectable in a higher proportion of samples from the group receiving 300 microg DSG with 50 mg T enanthate. Total cholesterol, high density lipoprotein cholesterol, and low density lipoprotein cholesterol decreased by 9.3 +/- 1.7%, 10.3 +/- 2.6%, and 7.7 +/- 2.8%, respectively, during treatment with DSG alone with no difference between 300 and 150 microg. Addition of T enanthate (both 50 and 100 mg weekly) induced a further fall only in high density lipoprotein cholesterol to 22.6 +/- 3.7% from the baseline. In summary, the combined actions of oral DSG with low doses of T enanthate were highly effective in suppressing pituitary-testicular functions in adult men. The optimal regimen for inducing azoospermia was 300 microg DSG daily with 50 mg T enanthate weekly. Oral DSG exerted discernible effects on lipid metabolism. We conclude that the combination of oral progestogens with low dose T is a promising approach to achieve effective reversible male contraception.

Safety, tolerability, and pharmacokinetics of a novel, selective antiprogestagen (Org 31710) in healthy male volunteers

The safety and tolerability as well as pharmacokinetics of a new selective antiprogestagen, Org 31710, were studied after oral administration of single doses of 10, 25, 50, or 75 mg to 24 healthy male volunteers. Per dose-group, five subjects received active and one subject received placebo treatment. In subjects receiving 75 mg, the effects of Org 31710 on serum levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone were also studied. No adverse or seriously adverse events were observed. All doses of Org 31710 were well tolerated. Characterization of the Org 31710 plasma pharmacokinetics revealed a statistically significant deviation from linearity: the dose normalized Cmax (nCmax) and dose normalized area under the curve (nAUC) values were significantly lower for the higher dosages (p < 0.05). Furthermore, tmax tended to decrease (from 1.6 to 0.9 h), whereas the elimination half-life (t1/2) tended to increase (from on average 45 to 57 h) with increasing dose. Org 31710 did not have any effect on serum levels of FSH, LH, and testosterone. In conclusion, Org 31710 appears to be a safe and well-tolerated compound in the dosage range studied.

Pharmacodynamics and pharmacokinetics after repeated subcutaneous administration of three gonadotrophin preparations

Recently, several new urinary gonadotrophin preparations have been developed, containing less luteinizing hormone (LH) activity than human menopausal gonadotrophin. Normegon is a gonadotrophin preparation with a follicle stimulating hormone (FSH)/LH ratio of 3:1; Follegon and Metrodin-HP are purified FSH preparations. The aim of the present randomized study was to compare pharmaco-dynamics, -kinetics and local tolerance of these preparations after repeated s.c. administration. Thirty-six healthy female subjects were treated with Lyndiol contraceptive pills for 5 weeks to suppress endogenous gonadotrophin concentrations. After 3 weeks of Lyndiol treatment, 150 IU of Normegon, Follegon or Metrodin HP were administered once daily, s.c. for 7 days. Blood samples were collected once daily during the fourth and fifth weeks of the study and assayed for FSH and oestradiol. After the last gonadotrophin injection, blood samples were collected more frequently to determine pharmacokinetic parameters of FSH. During the fourth and fifth study weeks, daily ultrasound measurements of follicular growth were performed. Endogenous FSH and LH values were extremely suppressed during Lyndiol treatment. Serum FSH values showed similar patterns in the three groups. The maximum FSH concentration was reached 9-11 h post-injection, the terminal half-life was 43-47 h. The preparations were bioequivalent with respect to FSH immunoreactivity. The number of follicles tended to be larger after Normegon than after Follegon and Metrodin HP treatment, though this was not statistically significant. Serum oestradiol concentrations were significantly higher after Normegon treatment. In general, s.c injections were well tolerated. In conclusion, the three preparations were bioequivalent with respect to FSH immunoreactivity. Nevertheless, the biological activity of Normegon tended to be higher than that of Follegon and Metrodin HP in Lyndiol-suppressed women.

Abnormal glutathione conjugation in patients with tyrosinaemia type I

Previous studies have suggested that tyrosinaemia type I may be associated with reduced glutathione availability due to conjugation of tyrosinaemia-associated reactive intermediates with glutathione. In the present study, the glutathione/ glutathione S-transferase system of two tyrosinaemia patients and three healthy controls were characterized by administering the racemic sedative drug bromisoval, a probe drug for assessing glutathione conjugation activity in vivo. Furthermore, concentrations of glutathione and glutathione S-transferase class alpha (GSTA) isoenzymes as well as the glutathione S-transferase class mu phenotype were assessed in the blood of six tyrosinaemia patients. The excretion of bromisoval mercapturates in healthy children was comparable to that observed in healthy adults. Tyrosinaemia patients were found to have a very high urinary recovery of bromisoval mercapturates (> or = 60% of the dose compared to about 30% for healthy, age-matched children and adults), which could be attributed mainly to a higher urinary excretion of the mercapturate derived from S-bromisoval. Healthy children and adults predominantly excrete the (R)-bromisoval mercapturate. The differences in amount excreted as well as in stereoselectivity of the urinary excretion of bromisoval mercapturates in tyrosinaemia patients are possibly related to an increased activity of specific glutathione S-transferase isoenzymes. Plasma glutathione and blood cell glutathione disulphide concentrations in tyrosinaemia patients were normal. Low blood cell glutathione concentrations were in general found only in two patients with a poor clinical condition. These results indicate that, in contrast to previous suggestions, reduced glutathione availability is not a generalized problem in (stabilized) tyrosinaemia patients.

Effect of ifosfamide treatment on glutathione and glutathione conjugation activity in patients with advanced cancers

Several studies have suggested that the glutathione/glutathione S-transferase (GSH/GST) system is involved in resistance of tumors toward ifosfamide and other cytostatic agents. Besides, ifosfamide metabolites (in vitro) as well as ifosfamide treatment (in vivo) have been shown to decrease cellular GSH availability. In the present study, the in vivo effects of three different ifosfamide treatment schedules on the GSH/GST system were studied in patients with advanced cancers (n = 24): continuous i.v. infusions of 1300 mg/m2 daily for 10 days and 5000 mg/m2/day for 24 h, as well as a 4-h infusion of 3000 mg/m2 daily for 3 days. The GSH/GST system was characterized by administering bromisoval, a probe drug to assess GSH conjugation activity in vivo, as well as by daily monitoring of GSH concentrations in blood cells and plasma. Bromisoval pharmacokinetics was assessed before and at the end of the ifosfamide treatment. Blood cell GSH levels decreased significantly (P < 0.05) during the 3- and 10-day ifosfamide treatment schedules; the 24-h treatment had no effect. The ifosfamide treatment schedules had only minimal effects on bromisoval pharmacokinetics. Assuming that the kinetics of the probe drug provide an accurate reflection of enzyme activity, this suggests that GST activity remains unchanged. Because GSH conjugation of bromisoval enantiomers requires both GST activity and GSH availability, these results also indicate that, despite the 35% decrease in GSH in blood cells of two patient groups, the GSH availability of the cancer patients was not rate-limiting for GSH conjugation of bromisoval enantiomers. If GSH levels in blood cells reflect those in tumors/other tissues, the present results indicate that ifosfamide may be used clinically to decrease GSH levels. However, whether a 35% decrease is sufficient to increase tumor sensitivity toward (other) cytostatics remains uncertain.

Stereoselectivity of human liver and intestinal cytosolic fractions as well as purified human glutathione S-transferase isoenzymes towards 2-bromoisovalerylurea enantiomers

Glutathione (GSH) conjugation of 2-bromoisovalerylurea (BIU) enantiomers is stereoselective in humans in vivo. Administration of racemic BIU results in a higher plasma elimination and urinary excretion of R-BIU and its mercapturate, respectively, than of S-BIU and its mercapturate. In order to relate the in vivo BIU pharmacokinetics to the activity of glutathione S-transferase (GST) isoenzymes, the GSH conjugation of BIU enantiomers was studied with human liver and intestinal cytosolic fractions as well as purified human class alpha (GSTA1-1, GSTA2-2), mu (GSTM1a-1a) and pi (GSTP1-1) GST isoenzymes. Stereoselective GSH conjugation of BIU enantiomers was observed for most human liver and intestinal cytosolic fraction. In general, the cytosolic fractions preferentially conjugated S-BIU. Stereoselective preference for GSH conjugation of S-BIU was also observed for GSTA2-2 and GSTM1a-1a, whereas GSTA1-1 was not selective for either of the BIU enantiomers. GSTP1-1 did not catalyse conjugation of R- and S-BIU. Quantification of the GST isoenzymes in the liver cytosolic fractions showed that the stereoselectivity towards S-BIU was related to the profile and amount of GST subunits in the cytosolic fractions. The discrepancy in stereoselectivity between the BIU pharmacokinetics in vivo and the GSH conjugation of BIU enantiomers in vitro is discussed. In addition, since in contrast to human GSTM1a-1a, rat class Mu isoenzymes prefer R-BIU, the present results indicate that related isoenzymes in different species may have a different stereoselectivity.

Characterization of glutathione conjugation in humans: stereoselectivity in plasma elimination pharmacokinetics and urinary excretion of (R)- and (S)-2-bromoisovalerylurea in healthy volunteers

Characterization of glutathione conjugation in vivo was performed in 12 healthy male volunteers by use of the racemic drug bromisovalum (bromisoval; 2-bromoisovalerylurea) as a model substrate. To study whether the pharmacokinetics of both bromisovalum enantiomers was related to the glutathione S-transferase class Mu phenotype, six subjects who were class Mu deficient and six subjects who were not class Mu deficient participated. After oral administration of 600 mg racemic bromisovalum, enantioselective measurement of unchanged bromisovalum (plasma and saliva) and the diastereomeric bromisovalum mercapturates (urine) showed a pronounced stereoselectivity in all subjects. The plasma clearance of R-bromisovalum was about 12 times higher than that of S-bromisovalum (9.3 +/- 3.7 and 0.78 +/- 0.38 L/min, respectively), which was in agreement with the higher urinary cumulative excretion for the mercapturate derived from R-bromisovalum: 26% +/- 4% of the dose versus 8% +/- 3% of the dose for the mercapturate derived from S-bromisovalum. Both the bromisovalum pharmacokinetics in general and the stereoselectivity in bromisovalum pharmacokinetics were not different for the subjects who were glutathione S-transferase class Mu deficient and the subjects who were not glutathione transferase class Mu deficient.

Stereoselective pharmacokinetics of oral felodipine and nitrendipine in healthy subjects: correlation with nifedipine pharmacokinetics

The pharmacokinetics of racemic (rac) felodipine, rac-nitrendipine and nifedipine (all given as an oral dose of 20 mg in solution) have been investigated in a randomised cross-over study in 12 healthy male subjects using stereoselective assays. Both felodipine and nitrendipine exhibited stereoselective pharmacokinetics. On average, the AUCs of the active (S)-enantiomers of felodipine and nitrendipine were 139% and 104% higher than those of their optical antipodes, but the elimination half-lives of the enantiomers of each racemate were not different. The AUCs of nifedipine, rac-felodipine, rac-nitrendipine and of their enantiomers were highly correlated (all r > 0.83), suggesting closely related rate limiting steps in the in vivo first-pass metabolism of these high-clearance drugs. Stereoselectivity was only a minor contributor to inter-individual variability in the oral pharmacokinetics of these compounds in healthy subjects.

Enantioselective determination of R- and S-(alpha-bromoisovaleryl)urea in plasma using high-performance liquid chromatography after solid-phase extraction

A stereoselective method has been developed for the determination of R- and S-(alpha-bromoisovaleryl)urea in plasma and saliva after oral administration. The chiral separation was carried out on Chiralcel OJ or OD columns with hexane--2-propanol as the mobile phase. The poor detection properties of the analyte required the development of an effective sample pretreatment procedure to enable ultraviolet detection at 210 nm. Solid-phase extraction using hydrophobic Amberlite XAD-2 in combination with washing steps at alkaline and acidic pH completely removed interfering components of the biological matrix and allowed the detection of the optical isomers at concentrations down to 10 ng/ml (0.05 microM). The method was validated by determining the recovery, linearity, accuracy and within-day and between-day repeatability at 50, 200 and 2000 ng/ml. Application to the analysis of plasma and saliva samples is demonstrated.

Prostate-specific antigen (PSA). A tissue-specific and sensitive tumor marker

Noninvasive methods for the diagnosis of prostatic cancer, its staging and evaluation of response to therapy are often not sufficiently sensitive or specific. Prostate-specific antigen (PSA) was identified in 1979 and has been evaluated since then as a marker, both at the serum and the tissue level. A review is presented in this article. PSA is an organ-specific glycoprotein presented in most prostatic carcinomas, but also in normal prostatic tissue and in benign prostatic hypertrophy (BPH). The monitoring of serum PSA concentrations by serial measurement can be used for the detection of residual or recurrent tumor after primary treatment and for the evaluation of response to systemic treatment of advanced disease. At the tissue level immunohistochemical detection of PSA may help to identify metastatic tumor of unknown origin. PSA serum assays have not been sufficiently sensitive and specific for staging of the primary tumor or for screening purposes. PSA is an equally specific, but more sensitive marker of prostatic carcinoma compared to prostatic acid phosphatase.