Indomethacin Pharmacokinetics and Pharmacodynamics in Pregnancies With Preterm Labor: The Need for Dose-Ranging Trials.

The use of indomethacin to delay delivery in preterm labor (PTL) is widely accepted; however, the optimal dosage of indomethacin in pregnancy is unknown. Here, we perform population pharmacokinetic (PK) and pharmacodynamic (PD) analyses, characterize the plasma disposition of indomethacin in pregnant women with PTL, and relate indomethacin exposure to delayed delivery and maternal/neonatal safety. We analyzed plasma and urine samples collected from a multicenter, prospective, opportunistic PK/PD study of indomethacin in pregnant women 12-32 weeks gestation admitted with PTL. Ninety-four participants with 639 plasma concentrations for indomethacin were included in the analysis. The final population PK (popPK) model for indomethacin was a 2-compartment structural model with first-order absorption and elimination and a covariate effect of body mass index on apparent oral clearance. We observed a 21%-60% increase in apparent oral clearance observed during pregnancy. There was no clear association between indomethacin exposure and maternal or neonatal safety outcomes, or with the magnitude of delayed delivery; however, 96.7% of women treated with indomethacin had a delivery that was delayed at least 48 hours. Given the changes to indomethacin apparent oral clearance during pregnancy, and the lack of relationship between indomethacin exposure and safety, dose-finding studies of indomethacin in pregnant women with PTL may help clarify the most safe and efficacious dosage and duration of indomethacin.

Coadministration of the prostaglandin F2α receptor antagonist preterm labour drug candidate OBE022 with magnesium sulfate, atosiban, nifedipine and betamethasone.

AIMS: To investigate presence or absence of clinically relevant drug interactions (pharmacokinetic and safety/tolerability) of OBE022 with standard-of-care medicines for preterm labour, enabling coadministration and further clinical development. METHODS: Part A: open-label, randomized, 3-period crossover assessing coadministration of single doses of OBE022 (1100 mg) and MgSO4 . Part B: open-label, single-sequence crossover assessing the interactions following administration of OBE022 (1000 mg/day) at steady state coadministered with single doses of atosiban, nifedipine and betamethasone. Twenty-five healthy nonpregnant women of reproductive age were enrolled (Part A: n = 12; Part B: n = 13). RESULTS: OBE022, alone or in combination with standard-of-care medications, was well tolerated. Headache and dizziness were the most frequently reported adverse events; dizziness occurred more often with the nifedipine/OBE022 combination. There were no clinically significant pharmacokinetic interactions when coadministered with MgSO4 . Co-administration had no notable effect on atosiban exposure. Atosiban reduced exposure to OBE002 (peak concentration [Cmax ] 22%, area under the concentration-time curve [AUC] 19%). Coadministration with betamethasone slightly increased betamethasone exposure (Cmax  + 18%, AUC +27%) and OBE002 exposure (Cmax  + 35%, AUC +15%). These changes were not considered clinically significant. Coadministration with nifedipine slightly increased OBE002 exposure (Cmax  + 29%, AUC +24%) and markedly increased nifedipine exposure (Cmax by 2-fold and AUC by 2-fold), which may be clinically significant. CONCLUSIONS: The use of OBE022, a PGF2α antagonist prodrug, in combination with standard-of-care medicines may provide new treatment alternatives for preterm labour. All tested combinations were well tolerated. Nifedipine doses could potentially be reduced or staggered when coadministered with OBE022.

Pharmacokinetics, safety and tolerability of OBE022, a selective prostaglandin F2α receptor antagonist tocolytic: A first-in-human trial in healthy postmenopausal women.

AIMS: Preterm birth remains a significant risk for later disability. The selective inhibition of the prostaglandin F2α receptor has significant advantages for a tocolytic. The prodrug OBE022 and its metabolite OBE002 are novel prostaglandin F2α receptor antagonists under development for treating preterm labour. METHODS: We performed a prospective, first in human, Phase I, dose escalation, placebo-controlled, randomized trial at a clinical trial site in the UK. Placebo, single ascending doses of 10, 30, 100, 300, 1000 or 1300 mg, and multiple ascending doses over 7 days of 100, 300 or 1000 mg day-1 ; were administered to postmenopausal female volunteers. Food interaction was additionally evaluated. RESULTS: Subjects tolerated OBE022 well at all single and multiple doses. No clinically relevant changes in safety parameters were shown and there were no serious adverse events. Observations showed that prodrug OBE022 was readily absorbed and rapidly converted into its equally active stable metabolite OBE002. The plasma level of OBE002 rose with increasing doses, reaching exposure levels that were anticipated to be clinically relevant within 1 h following administration. There was no clinically significant food interaction, with peak exposures reduced to 80% and area under the curve staying bioequivalent. The mean half-life of OBE002 ranged between 8 and 11 h following administration of a single dose and 22-29 h after multiple doses. CONCLUSIONS: Administration of OBE022 was safe and had favourable pharmacokinetic characteristics and no clinically relevant interaction with food. Our results allow further investigation of OBE022 in preterm labour patients.

Oxytocin Receptor Antagonist (Atosiban) in the Threat of Preterm Birth: Does It Have Any Effect on Breastfeeding in the Term Newborn?

AIM: Oxytocin is a hormone involved in the mechanism of breastfeeding, uterine contractions, and social relationships. Atosiban (competitive oxytocin antagonist) is one of the most commonly used tocolytics for the threat of preterm labor in Europe. The aim of this study is to determinate if the administration of atosiban has any influence in the type of feeding in the term newborn at discharge. The secondary objective is to verify its effectiveness for the prevention of preterm delivery and in the possibility of applying treatment to complete lung maturation. MATERIALS AND METHODS: Retrospective cohort study carried out in a tertiary University Hospital distinguished by WHO-UNICEF as a Baby-Friendly Hospital Initiative. The analysis included 264 women exposed to atosiban during a period of 4 years. One hundred met inclusion criteria. Unexposed infants born right after and before the exposed ones were selected as the not exposed subgroup (n = 200). RESULTS: Among women treated with atosiban, 82% maintained exclusively breastfed (EBF), 8% had mixed breastfeeding, and 10% had formula feeding at discharge. In the nonexposed group, 82% maintained EBF, 9.5% had mixed breastfeeding, and 8.5% had formula feeding at discharge (p = 0.84). 97.5% of pregnant women treated with atosiban received corticosteroid for lung maturation, and 49.5% completed gestation with term newborns. CONCLUSION: There were no significant differences in the type of feeding at discharge between the atosiban group and the nonexposed group. In most cases, the administration of tocolytic therapy allowed to complete lung maturation.

Treatment of spontaneous preterm labour with retosiban: a phase II pilot dose-ranging study.

AIMS: The aims of the present study were to investigate the maternal, fetal and neonatal safety and tolerability, pharmacodynamics and pharmacokinetics of intravenous (IV) retosiban in pregnant women with spontaneous preterm labour (PTL) between 340/7 and 356/7  weeks' gestation. METHODS: In parts A and B of a three-part, double-blind, placebo-controlled, multicentre study, women were randomized 3:1 (Part A) or 2:1 (Part B) to either 12-h IV retosiban followed by a single dose of oral placebo (R-P) or 12-h IV placebo followed by single-dose oral retosiban (P-R). RESULTS: A total of 29 women were randomized; 20 to R-P and nine to P-R. An integrated analysis found that adverse events were infrequent in mothers/newborns and consistent with events expected in the population under study or associated with confounding factors. Retosiban was rapidly absorbed after oral administration, with an observed half-life of 1.45 h. Efficacy analyses included 19 women. While not statistically significant, those receiving R-P more frequently achieved uterine quiescence in 6 h (R-P, 63%; 95% credible interval [CrI]: 38, 84; P-R, 43%; 95% CrI: 12, 78) and more achieved a reduction of ≥50% in uterine contractions in 6 h (R-P, 63%; 95% CrI: 38, 84; P-R, 29%; 95% CrI: 4, 64). The number of days to delivery was increased in women receiving R-P (median 26 days for R-P vs. 13 days for P-R). CONCLUSIONS: Intravenous retosiban has a favourable safety and tolerability profile and might prolong pregnancies in women with PTL. The study provides the rationale and dosing strategy for further evaluation of the efficacy of retosiban in the treatment of PTL.

Uterus-targeted liposomes for preterm labor management: studies in pregnant mice.

Preterm labor caused by uterine contractions is a major contributor to neonatal morbidity and mortality. Treatment intended to reduce uterine contractions include tocolytic agents, such as indomethacin. Unfortunately, clinically used tocolytics are frequently inefficient and cross the placenta causing fetal side effects. Here we show for the first time in obstetrics the use of a targeted nanoparticle directed to the pregnant uterus and loaded with a tocolytic for reducing its placental passage and sustaining its efficacy. Nanoliposomes encapsulating indomethacin and decorated with clinically used oxytocin receptor antagonist were designed and evaluated in-vitro, ex-vivo and in-vivo. The proposed approach resulted in targeting uterine cells in-vitro, inhibiting uterine contractions ex-vivo, while doubling uterine drug concentration, decreasing fetal levels, and maintaining the preterm birth rate in vivo in a pregnant mouse model. This promising approach opens new horizons for drug development in obstetrics that could greatly impact preterm birth, which currently has no successful treatments.

Pharmacokinetics and placental transfer of magnesium sulfate in pregnant women.

BACKGROUND: Magnesium sulfate is one of the most commonly prescribed intravenous medications in obstetrics. Despite its widespread use, there are limited data about magnesium pharmacokinetics, and magnesium is prescribed empirically without dose adjustment for different indications. OBJECTIVE: The aim of this study was to characterize the pharmacokinetics and placental transfer of magnesium sulfate in pregnant women and to determine key covariates that impact the pharmacokinetics. STUDY DESIGN: This is a prospective pharmacokinetic cohort study of pregnant women who were prescribed magnesium sulfate for preeclampsia, preterm labor, or extreme prematurity. Women received a 4-g loading dose and 2 g/h maintenance dose as clinically indicated. Maternal blood samples were obtained before and at multiple time points during and after magnesium administration. Cord blood also was sampled at delivery. A population pharmacokinetic approach that used a nonlinear mixed-effects modeling was used to characterize magnesium disposition. RESULTS: Pharmacokinetic profiles of 111 pregnant women were analyzed. Magnesium clearance was 3.98 L/h in preeclamptic women and 5.88 L/h non-preeclamptic women. Steady-state concentration of magnesium was 7.2 mg/dL in preeclamptic women compared with 5.1 mg/dL in non-preeclamptic women. Maternal weight significantly impacted time to steady state. The ratio of the mean umbilical vein magnesium level to the mean maternal serum magnesium level at the time of delivery was 0.94 ± 0.15. CONCLUSIONS: The study accurately characterizes the pharmacokinetics of magnesium administered to pregnant women. Preeclamptic status and maternal weight significantly impact serum magnesium levels. This pharmacokinetic model could be applied to larger cohorts to help tailor magnesium treatment and account for these covariates.

Pharmacokinetic interactions of OBE001 and betamethasone in healthy female volunteers.

WHAT IS KNOWN AND OBJECTIVE: To treat preterm labour, antenatal corticosteroids and tocolytics are often co-administered. OBE001 is an orally active oxytocin receptor antagonist under development for preterm labour treatment. METHODS: Co-administration of OBE001 and betamethasone to determine pharmacokinetic interactions was studied during an open-label, randomized, three-period crossover study. Twelve healthy post-menopausal volunteers received either two consecutive OBE001 administrations of 600 mg/day, two intramuscular injections of 12 mg/day betamethasone or the two drugs administered in combination. The area under the plasma concentration-time curve (AUC), the maximum plasma concentration (Cmax) and the time to Cmax (tmax) for OBE001 and betamethasone were measured. RESULTS AND DISCUSSION: There was no effect on geometric mean Cmax after the second administration and AUCs of OBE001 [geometric mean ratio point estimate (90% CI): Cmax (Day2) 1·05 (0·98-1·12) and AUC(0-24 h )1·11 (0·99-1·23)/AUC(24 h-∞) 0·99 (0·93-1·06), respectively]; Cmax after the first administration together with betamethasone was increased by 12% [geometric mean ratio point estimates (90% CI): Cmax (Day1) 1·12 (0·96-1·32)]. Tmax after concomitant administration with betamethasone occurred with a median delay of 1 h. Geometric mean Cmax and AUCs of betamethasone were not affected by concomitant OBE001 administration [geometric mean ratio point estimate (90% CI): Cmax (Day1) 1·02 (0·98-1·07)/Cmax (Day2) 1·03 (0·98-1·08) and AUC(0-24 h) 1·07 (1·04-1·11)/AUC(24 h-∞ )1·04 (1·01-1·08), respectively], with no effect on median tmax . No subject was discontinued from the study due to adverse events. WHAT IS NEW AND CONCLUSION: AUC and Cmax of the betamethasone and OBE001 combination did not differ significantly between treatments. Co-administration of OBE001 and betamethasone was well tolerated and resulted in a tmax median delay of 1 h for OBE001 but not for betamethasone. Co-administration of OBE001 and betamethasone in clinics is feasible and does not require any specific precaution or administration adaptation.

[Calcium channel blockers pharmacology and their use as tocolytics]. / Pharmacologie des inhibiteurs calciques et leur utilisation dans la menace d'accouchement prématuré.

Nifedipine and nicardipine are both calcium channel inhibitors, used off-label as tocolytics in preterm labour. Their use is related to their relaxing effects on uterin muscle by L-type voltage dependent calcium channels blockade. This article describes pharmacological effects, pharmacokinetics properties and tolerance of these drugs. It also discusses serious adverse effects, such as pulmonary edema, reported with both nifedipine and nicardipine in preterm labour.

Liposomes: a nanoscale drug carrying system to prevent indomethacin passage to the fetus in a pregnant mouse model.

OBJECTIVE: Indomethacin (IND) is a prostaglandin production inhibitor that reduces uterine contractions, but crosses the placenta leading to adverse fetal effects. Liposomes (LIP) are nanoscale systems clinically used to preferentially deliver a drug to the tissue of interest and simultaneously prevent distribution to unwanted locations. Our objective was to determine whether LIP could prevent the transfer of IND across the placenta to the fetus while preserving its pharmacological activity. STUDY DESIGN: Multilamellar LIP were designed with a 150- to 200-nm size, fluorescently labeled, and loaded with IND. Timed pregnant CD1 mice (n = 6/group) on gestational day 18 were administered LIP, LIP-IND (1 mg IND/kg), or saline (SAL) via tail vein injection, or IND (1 mg/kg) via oral gavage. After 4 hours, the uterus, placenta, and fetuses were retrieved. LIP levels were visualized using fluorescent microscopy and quantitatively assessed by National Institutes of Health image processing software. LIP brightness values (mean ± SEM) in arbitrary units (AU) were normalized to the autofluorescence of the same tissue (as measured in SAL group). IND and prostaglandin E2 levels were assessed using liquid chromatography-tandem mass spectrometry and enzyme-linked immunosorbent assay, respectively. RESULTS: The qualitative analysis of LIP distribution revealed that the system was primarily confined within the uterus, minimally detected within the placenta, and absent in the fetus. LIP fluorescence was greater in the uterus compared to placenta and fetus (uterus 15.3 ± 5.4 AU vs placenta 3.0 ± 3.5 AU vs fetus 4.4 ± 2.5 AU; P = .009). LIP-IND resulted in a 7.6-fold reduction in the IND levels in the fetus compared to IND alone (LIP-IND 10.7 ± 17.1 ng/g vs IND 81.3 ± 24.7 ng/g; P = .041). Prostaglandin E2 levels were significantly reduced in the uterus of animals given LIP-IND and IND compared to LIP and SAL. CONCLUSION: LIP localized within the uterus and did not cross the placenta to the fetus. IND within the fetus was reduced 7.6-fold while encapsulated within the LIP and the pharmacologic effects of IND were maintained. Thus, LIP provide a novel therapeutic approach to correct the primary clinical limitation of IND by reducing placental passage to the fetus.

Pharmacokinetics of nifedipine slow-release during sustained tocolysis.

OBJECTIVE: The pharmacokinetics of nifedipine as a tocolytic agent has not been studied in great detail in pregnant women and has instead focused on immediate release tablets and gastrointestinal therapeutic system (GITS) tablets. The aim of this study was to determine nifedipine slow-release half-life and distribution volume in pregnant women and to compare these with pharmacokinetic parameters of nifedipine in non-pregnant subjects described in the literature. MATERIALS: This is a study parallel to a trial studying women with threatened preterm labor between 26 + 0 and 32 + 2 weeks after initial tocolysis and a completed course of corticosteroids, who were randomly allocated to maintenance nifedipine (slow-release tablets 20 mg 4 times daily) or placebo. Exclusion criteria for the pharmacokinetic study were contra-indications for nifedipine, impaired liver function, and concomitant intake of inhibitors or inducers of the cytochrome P450 3A4 isoenzyme. Blood samples for measuring nifedipine plasma concentrations were drawn at t = 0, t = 12 hours, t = 24 hours, t = 48 hours, t = 72 hours, t = 7 days, and t = 9 days. METHODS: Pharmacokinetic parameters were estimated using iterative two-stage Bayesian population pharmacokinetic analysis by MWPharm© software. The study was designed to establish a correlation between body weight and nifedipine plasma level. RESULTS: The pharmacokinetic parameters of nifedipine slow-release tablets were determined from the data of 8 pregnant women. Nifedipine slow-release had a half-life of 2 - 5 hours, a mean distribution volume of 6.2 ± 1.9 L/kg (calculated while using a fixed biological availability of 0.45 taken from the literature due to lack of intravenous data in this population) compared to a half-life of 6 - 11 hours, and a distribution volume of 1.2 - 1.3 L/kg described in non-pregnant subjects in the literature. None of the women delivered during study medication. Study medication was continued for the duration of the pharmacokinetic study (9 days) in all women. A correlation between nifedipine plasma levels and maternal body weight was not demonstrated. This may have been caused by lack of power. CONCLUSION: Pregnant subjects in this study, using nifedipine slow-release tablets, showed a larger volume of distribution and a shorter elimination half-life than for non-pregnant subjects as published in the literature.

Preparation and evaluation of ritodrine buccal tablets for rational therapeutic use.

Ritodrine hydrochloride (RD-HCl) tablets containing alginate (AL) and lactose (LC) with or without microcrystalline cellulose (MC) as excipients were produced as a buccal dosage form. The RD-HCl (2 mg) tablets with AL/LC but no MC swelled and dissolved gradually in the in vitro dissolution test. The tablet showing the fastest dissolution and highest drug release rate, called Tablet A1, was selected as a tablet to show rapid and prolonged absorption. However, in the in vivo buccal absorption test using rats, it could not give a plasma concentration over the human minimal effective level (15 ng/mL). The modified tablet containing AL, LC, MC and RD-HCl (4 mg), named Tablet B/MC, showed better hardness and faster drug release. Tablet B/MC gave a plasma concentration over the human effective level within 15 min, and the plasma concentration was maintained at >15 ng/mL over 4 h. Moreover, the deconvolution analyses demonstrated that a prolonged high absorption rate could be achieved in vivo best with Tablet B/MC. Tablet B/MC improved the pharmacokinetic profile in comparison with Tablet A1 and the solution dosage form. The RD-HCl buccal tablets with AL, LC and MC as excipients are suggested to be possibly useful for the treatment of premature labor.

Pharmacokinetics of indomethacin in pregnancy.

BACKGROUND AND OBJECTIVES: Although indomethacin has been widely used for the treatment of preterm labor over the past 40 years, there are few reports regarding its pharmacokinetics in pregnant women. METHODS: This opportunistic study assessed the steady-state pharmacokinetics of indomethacin in pregnant subjects to whom an oral dose of 25 mg every 6 h was prescribed. Indomethacin concentrations in plasma and urine were analyzed by a validated high-performance liquid chromatography method with mass spectrometric detection. RESULTS: The mean area under the plasma concentration versus time curve at steady state (AUCss) was 1.91 ± 0.53 µg·h/mL, mean peak plasma concentration (C max) was 1.02 ± 0.49 µg/mL, and mean time to reach C max (t max) was 1.3 ± 0.7 h. The mean apparent clearance at steady state was 14.5 ± 5.5 L/h, which is higher than the apparent clearance reported in the literature for non-pregnant subjects. Indomethacin crosses the placenta; the mean fetal/maternal ratio from five sets of cord blood samples collected at delivery was 4.0 ± 1.1. CONCLUSIONS: Further studies are needed to determine whether any dose adjustments are necessary as a result of the increased clearance of indomethacin during pregnancy.

Nifedipine pharmacokinetics are influenced by CYP3A5 genotype when used as a preterm labor tocolytic.

OBJECTIVE: To characterize the pharmacokinetics and pharmacogenetics of nifedipine in pregnancy. STUDY DESIGN: Pregnant women receiving oral nifedipine underwent steady-state pharmacokinetic testing over one dosing interval. DNA was obtained and genotyped for cytochrome P450 (CYP) 3A5 and CYP3A4*1B. Nifedipine and oxidized nifedipine concentrations were measured in plasma, and pharmacokinetic parameters were compared between those women who expressed a CYP3A5*1 allele and those who expressed only variant CYP3A5 alleles (*3,*6, or *7). RESULTS: Fourteen women had complete data to analyze. Four women (29%) expressed variant CYP3A5; three of these women were also CYP3A4*1B allele carriers. The mean half-life of nifedipine was 1.68 ± 1.56 hours. The area under the curve from 0 to 6 hours for the women receiving nifedipine every 6 hours was 207 ± 138 µg·h /L. Oral clearance was different between high expressers and low expressers (232.0 ± 37.8 µg/mL versus 85.6 ± 45.0 µg/mL, respectively; p = 0.007). CONCLUSION: CYP3A5 genotype influences the oral clearance of nifedipine in pregnant women.

In vivo absorption study of ritodrine hydrochloride in the buccal administration to rats.

BACKGROUND: Although ritodrine (RD)-hydrochloride (HCl), named RD-HCl, is widely used in the treatment of premature labor by intravenous prolonged infusion or frequent oral dosing of tablets, those administrations often lower patients' quality of life (QOL) or cause undesirable side effects, such as tachycardia; therefore, in this study, the potential usefulness of buccal administration as a novel administration method was examined in vivo. METHOD: First, the HPLC method was assessed for the determination of plasma RD concentration. Then, after RD-HCl solution in saline was administered intravenously (1 mg/kg), intragastrically (10 mg/kg) or buccally (10 mg/kg) in rats, the plasma concentration-time profiles were investigated, and the absorption extent and rate compared. RESULTS: The present modified determination method by HPLC with fluorescence detection (Ex. 278 nm, Em. 306 nm) was suitable to analyze the plasma level at 8-200 ng/mL. Buccal administration gave the best plasma concentration-time profile for maintenance of an effective plasma level and fewer side effects. Absorption rates calculated by deconvolution also supported better sustained absorption in buccal dosing. CONCLUSION: Buccal application of RD-HCl was demonstrated to be a potentially useful dosing method in the treatment of premature labor with RD-HCl.

Use of non-steroidal anti-inflammatory drugs in pregnancy: impact on the fetus and newborn.

Non-steroidal anti-inflammatory drugs (NSAIDs) are commonly prescribed in pregnancy to treat fever, pain and inflammation. Indications for chronic use of these agents during pregnancy are inflammatory bowel or chronic rheumatic diseases. Since the seventies, NSAIDs have been used as effective tocolytic agents: indomethacin has been the reference drug, delaying delivery for at least 48 hours and up to 7-10 days. Additionally, self-medication with NSAIDs is practiced by pregnant women. NSAIDs given to pregnant women cross the placenta and may cause embryo-fetal and neonatal adverse effects, depending on the type of agent, the dose and duration of therapy, the period of gestation, and the time elapsed between maternal NSAID administration and delivery. These effects derive from the action mechanisms of NSAIDs (mainly inhibition of prostanoid activity) and from the physiological changes in drug pharmacokinetics occurring during pregnancy. Increased risks of miscarriage and malformations are associated with NSAID use in early pregnancy. Conversely, exposure to NSAIDs after 30 weeks' gestation is associated with an increased risk of premature closure of the fetal ductus arteriosus and oligohydramnios. Fetal and neonatal adverse effects affecting the brain, kidney, lung, skeleton, gastrointestinal tract and cardiovascular system have also been reported after prenatal exposure to NSAIDs. NSAIDs should be given in pregnancy only if the maternal benefits outweigh the potential fetal risks, at the lowest effective dose and for the shortest duration possible. This article discusses in detail the placental transfer and metabolism of NSAIDs, and the adverse impact of prenatal NSAID exposure on the offspring.

Veterinary treatment of cows with isoxsuprine for a caesarian section may temporarily lead to residues in hair of both cow and calf.

Isoxsuprine is a beta-agonist that can be used for growth promotion in cattle, but it is also used as registered veterinary medicine. To investigate if veterinary treatment of cows could lead to residues of isoxsuprine in the hair of their newborn calves, an animal experiment was performed. Four cows, treated on veterinary indication with isoxsuprine lactate (Duphaspasmin) before a caesarian section, were included in the experiment. Hair samples from cows and from their calves were analyzed. The animals were shaved every week for 16 weeks and levels of isoxsuprine were measured in hair. In the cows, the levels of isoxsuprine were highest (>15 µg/kg) just after administration of the isoxsuprine lactate. After two weeks in two cows, a sort of plateau was reached and then the levels decreased. After approximately 10-15 weeks the levels were around the CCα level of the method used (0.5 µg/kg). In calves, for the first two weeks after birth, no isoxsuprine was found above CCα level in three of the four animals. At about 20-30 days old, a maximum concentration of 4 µg/kg was found. Then the levels dropped again under the CCα level, after 60 days no levels above CCα level were found. In one animal, the levels never reached CCα level. We conclude that veterinary treatment of cows with isoxsuprine may temporarily lead to low levels of isoxsuprine in the hair of their newborn calves which can be measured for a maximum of 60 days after birth.

A pilot study of the impact of genotype on nifedipine pharmacokinetics when used as a tocolytic.

OBJECTIVE: To characterize the pharmacokinetics of nifedipine when used for tocolysis in preterm labor and to determine the impact of genetics on these parameters. STUDY DESIGN: Pharmacokinetic study performed on women given tocolytic nifedipine. Over one dosing interval, drug concentrations, clinical data, and genotype for Cytochrome P450 (CYP)3A5 polymorphisms were obtained. Non-compartmental pharmacokinetic analysis was used to estimate nifedipine exposure at steady state. RESULTS: The mean nifedipine area under the curve in 20 pregnant women was 86.1±61.1 ng/ml/h. The mean nifedipine exposure differed by expression of CYP3A5 (expressers [exp]: 139.5±97.3 ng/ml/h vs. nonexpressers[non]: 68.3 ± 31.8 ng/ml/h, p = 0.02). Four women consumed CYP3A inhibitors and this affected the nifedipine concentrations (p < 0.001). CYP3A5 expressers had less improvement in contraction frequency after the loading dose (p = 0.04), at steady state (p = 0.006), and at 0-1 h after the study dose (p < 0.001). CONCLUSIONS: CYP3A5 genotype plays a role in nifedipine concentration when used as a tocolytic.

Oxytocin antagonists for the management of preterm birth: a review.

Preterm birth, the leading cause of neonatal morbidity and mortality, is estimated at incidence of 12.7% of all births, which has not decreased over the last four decades despite intensive antenatal care programs aimed at high-risk groups, the widespread use of tocolytics, and a series of other preventive and therapeutic interventions. Oxytocin antagonists, namely atosiban, represent an appealing choice that seems to be effective with apparently fewer side effects than the traditional tocolytics. This article reviews the available literature on the pharmacokinetics, mode of administration, and clinical utility of oxytocin antagonists for acute and maintenance tocolysis with special emphasis on its safety profile.

Pharmacokinetics of ritodrine diastereomers in patients pregnant with singletons and twins.

OBJECTIVE: The chiral pharmacokinetics and pharmacodynamics of ritodrine in patients pregnant with singletons and twins were investigated to determine the optimal use of ritodrine. METHODS: Eight and 20 patients with threatened preterm delivery of singletons and twins, respectively, were infused with ritodrine diastereomers. Serum concentrations of the drug were then measured using a newly developed method of chiral high-performance liquid chromatography. RESULTS: Almost double the dosage of racemic ritodrine was required to prolong pregnancies with twins compared with those of singletons (2.20 +/- 1.06 vs. 1.24 +/- 0.36 microg/min per kilogram; p < 0.0001). The mean ratios of (-)-ritodrine to (+)-ritodrine in singleton and twin pregnancies were 1.17 +/- 0.10 and 1.16 +/- 0.10, respectively. However, the serum concentration and dosage ratio (C/D ratio) of (-)-ritodrine as significantly higher than that of (+)-ritodrine (p < 0.0001), whereas the clearance of (-)-ritodrine was significantly lower than that of (+)-ritodrine (p < 0.0001). A comparison of the gestation period (weeks) and diastereomer clearance did not reveal significant regression in the total analysis of the data obtained from singleton and twin pregnancies. CONCLUSION: These results indicate that the clinical effectiveness of ritodrine diastereomers should be evaluated and that administration guidelines should be established based upon serum concentrations so that ritodrine can be more effectively administered to pregnant patients carrying either singletons or twins.