Pharmacokinetics of furosemide in gestosis of pregnancy

A Pilot Study of the Maternal-Fetal Pharmacokinetics of Furosemide in Plasma, Urine, and Amniotic Fluid of Hypertensive Parturient Women Under Cesarean Section

The third trimester of pregnancy is related to physiological changes that can modify the process of absorption, distribution, metabolism, and excretion and, consequently, the efficacy and toxicity of drugs. However, little is known about furosemide pharmacokinetics and placental transfer in pregnancy. This study evaluated the maternal-fetal pharmacokinetics and distribution to amniotic fluid of furosemide in hypertensive parturient women under cesarean section. Twelve hypertensive parturient women under methyldopa (250 mg/8 h) and/or pindolol (10 mg/12 h) treatment received a 40-mg single oral dose of furosemide 1 to 10 hours before delivery by cesarean section. Blood and urine samples were collected for 12 hours after furosemide administration. At delivery, samples were obtained from maternal and umbilical cord blood (n = 8) to assess the transplacental transfer. Amniotic fluid (n = 4) was collected at the time of delivery. The following furosemide pharmacokinetic parameters were obtained as median (interquartile range): C_max , 403 ng/mL (229 to 715 ng/mL); T_max , 2.00 hours (1.50 to 4.83 hours); elimination half-life (t_1/2 ), 2.50 hours (1.77 to 2.97 hours); AUC_{0-12 h} , 1366 ng⋅h/mL (927 to 2531 ng⋅h/mL); AUC_0-∞ , 1580 ng⋅h/mL (1270 to 2881 ng⋅h/mL); CL/F 25.3 L/h (13.8 to 31.4 L/h); CLR, 2.50 L/h (1.77 to 2.97 L/h); CLNR, 22.7 L/h (12.1 to 25.6 L/h); and V_d /F 82.8 L (34.4 to 173 L). The transplacental transfer of furosemide was 0.43 (0.10 to 0.73), and the amniotic fluid concentration was 11.0 ng/mL (5.51 to 14.6 ng/mL). From a clinical point of view, these results suggest that substrates of uridine diphosphate-glucuronosyltransferase isoenzymes such as furosemide may have increased clearance during pregnancy and could require dose adjustment in this population.

Physiologically Based Pharmacokinetic Modeling of Renally Cleared Drugs in Pregnant Women

BACKGROUND

Since pregnant women are considerably underrepresented in clinical trials, information on optimal dosing in pregnancy is widely lacking. Physiologically based pharmacokinetic (PBPK) modeling may provide a method for predicting pharmacokinetic changes in pregnancy to guide subsequent in vivo pharmacokinetic trials in pregnant women, minimizing associated risks.

OBJECTIVES

The goal of this study was to build and verify a population PBPK model that predicts the maternal pharmacokinetics of three predominantly renally cleared drugs (namely cefazolin, cefuroxime, and cefradine) at different stages of pregnancy. It was further evaluated whether the fraction unbound (f _u) could be estimated in pregnant women using a proposed scaling approach.

METHODS

Based on a recent literature review on anatomical and physiological changes during pregnancy, a pregnancy population PBPK model was built using the software PK-Sim^®/MoBi^®. This model comprised 27 compartments, including nine pregnancy-specific compartments. The PBPK model was verified by comparing the predicted maternal pharmacokinetics of cefazolin, cefuroxime, and cefradine with observed in vivo data taken from the literature. The proposed scaling approach for estimating the f _u in pregnancy was evaluated by comparing the predicted f _u with experimentally observed f _u values of 32 drugs taken from the literature.

RESULTS

The pregnancy population PBPK model successfully predicted the pharmacokinetics of cefazolin, cefuroxime, and cefradine at all tested stages of pregnancy. All predicted plasma concentrations fell within a 2-fold error range and 85% of the predicted concentrations within a 1.25-fold error range. The f _u in pregnancy could be adequately predicted using the proposed scaling approach, although a slight underestimation was evident in case of drugs bound to α₁-acidic glycoprotein.

CONCLUSION

Pregnancy population PBPK models can provide a valuable tool to predict a priori the pharmacokinetics of predominantly renally cleared drugs in pregnant women. These models can ultimately support informed decision making regarding optimal dosing regimens in this vulnerable special population.

Diuretics for preventing pre-eclampsia

BACKGROUND

Diuretics are used to reduce blood pressure and oedema in non-pregnant individuals. Formerly, they were used in pregnancy with the aim of preventing or delaying the development of pre-eclampsia. This practice became controversial when concerns were raised that diuretics may further reduce plasma volume in women with pre-eclampsia, thereby increasing the risk of adverse effects on the mother and baby, particularly fetal growth.

OBJECTIVES

To assess the effects of diuretics on prevention of pre-eclampsia and its complications.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (April 2005), the Cochrane Central Register of Controlled Trials (The Cochrane Library 2005, Issue 2) and EMBASE (2002 to April 2005).

SELECTION CRITERIA

Randomised trials evaluating the effects of diuretics for preventing pre-eclampsia and its complications.

DATA COLLECTION AND ANALYSIS

Three review authors independently selected trials for inclusion and extracted data. We analysed and double checked data for accuracy.

MAIN RESULTS

Five studies (1836 women) were included. All were of uncertain quality. The studies compared thiazide diuretics with either placebo or no intervention. There were no clear differences between the diuretic and control groups for any reported pregnancy outcomes including pre-eclampsia (four trials, 1391 women; relative risk (RR) 0.68, 95% confidence interval (CI) 0.45 to 1.03), perinatal death (five trials,1836 women; RR 0.72, 95% CI 0.40 to 1.27), and preterm birth (two trials, 465 women; RR 0.67, 95% CI 0.32 to 1.41). There were no small-for-gestational age babies in the one trial that reported this outcome, and there was insufficient evidence to demonstrate any clear differences between the two groups for birthweight (one trial, 20 women; weighted mean difference 139 grams, 95% CI -484.40 to 762.40). Thiazide diuretics were associated with an increased risk of nausea and vomiting (two trials, 1217 women; RR 5.81, 95% CI 1.04 to 32.46), and women allocated diuretics were more likely to stop treatment due to side-effects compared to those allocated placebo (two trials, 1217 women; RR 1.85, 95% CI 0.81 to 4.22).

AUTHORS' CONCLUSIONS

There is insufficient evidence to draw reliable conclusions about the effects of diuretics on prevention of pre-eclampsia and its complications. However, from this review, no clear benefits have been found from the use of diuretics to prevent pre-eclampsia. Taken together with the level of adverse effects found, the use of diuretics for the prevention of pre-eclampsia and its complications cannot be recommended.

Diuretic effect and disposition of furosemide in cystic fibrosis

The pharmacodynamics and kinetics of single oral and intravenous doses of furosemide were studied in 9 patients (mean age 18.5 y) with cystic fibrosis. The diuretic effect of furosemide lasted for 6 h after oral administration and 2 h following intravenous injection of the drug. The patients with cystic fibrosis had a more pronounced diuretic response both to the oral and intravenous treatments than that reported in normals. Furosemide caused a marked decrease in urine pH for 5 h following the oral dose and between the 2nd and 3rd h after i.v. injection. The baseline nocturnal urine flow rate in 7 of the 9 patients given furosemide orally was increased by 30.6% compared to that reported in healthy subjects. The bioavailability of furosemide, its mean absorption rate and the mean plasma and urinary elimination half-lives both of the oral and the intravenous drug were similar to those reported in normal subjects. The patients with cystic fibrosis showed, however, about double normal mean total clearance after both the oral and i.v. treatments, and its renal clearance was almost half the plasma clearance. Nonrenal clearance was markedly increased in the patients, which agreed with a considerable decrease in the renal excretion of the drug. The mean apparent volume of distribution was also markedly increased compared to data in the literature. Oral furosemide resulted in a moderate increase in haematocrit and haemoglobin levels in 7 of 9 patients with cystic fibrosis and marked hypokalemia developed in 6 of the 9 patients 6 h after dosing. Pulmonary function tests performed at that time were changed in an inconsistent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Disposition and response to bumetanide and furosemide

Bumetanide and furosemide are potent loop diuretics; the former is 40 to 50 times more potent than the latter on a weight basis. Bumetanide is absorbed more quickly than furosemide and is twice as bioavailable. Both drugs exhibit changes in elimination in the presence of renal insufficiency as well as changes in the time course of absorption in congestive heart failure. More data are needed to assess potential differences between them in various clinical conditions.

Bioavailability and diuretic effect of furosemide during long-term treatment of chronic respiratory failure

The bioavailability and diuretic effect of furosemide 40 mg administered orally for at least 6 months have been compared in patients with chronic respiratory failure and in healthy controls. The mean urinary recovery of unchanged drug was 11.5 mg and 9.41 mg in 24 h after pre- and postprandial administration to 10 patients, whereas the recovery was 14.4 mg in 10 healthy subjects. The diuretic effect, in terms of urine flow and sodium ion excretion in the 6 h after administration, was also less in patients than in healthy subjects. This was ascribed to the lower bioavailability of furosemide in patients, based on the urinary recovery of unchanged drug, and not to a lower level of response to furosemide than in healthy subjects. The mean absolute bioavailability of furosemide in 6 patients was 41.3% and 63.4%, respectively, calculated from unchanged drug and total drug (unchanged plus glucuronide conjugate). Approximately 53.9% of the dose of furosemide was excreted as the glucuronide conjugate after oral administration, and 34.2% after i.v. injection in the 6 patients. In 3 of the 6 patients studied, a distinct first-pass effect for glucuronidation of furosemide was observed after oral administration. In another study, the mean glucuronide fraction recovered in 24-h urine was 20.7% and 7.3% (p less than 0.01) in 38 patients and 12 healthy subjects, respectively. The fraction in urine was not affected by changing the dose of furosemide from 20 to 120 mg. The lower bioavailability in patients as compared to healthy subjects is ascribed to enhanced glucuronidation and incomplete drug absorption.

Placental transfer of etozolin and ozolinone during the first half of gestation in man

The placental transfer of etozolin and its pharmacologically active metabolite ozolinone was studied in 48 patients during the first (44 patients) and second (4 patients) trimester. 24 patients received a single oral dose of etozolin 400 mg 2-20 h prior to interruption of pregnancy by curettage or prostaglandin infusion. 24 other patients received 3 oral doses of etozolin 400 mg (11 patients) or 800 mg (13 patients) on 3 consecutive days, and pregnancy was terminated 2-10 h after the last dose. The fetal tissue/maternal serum and placental tissue/maternal serum ratios of etozolin and ozolinone were found to lie between 0.3 and 0.6. The serum levels were lower in pregnant than in non-pregnant patients. The low placental and fetal concentrations of etozolin and ozolinone suggest that these drugs may prove useful when a diuretic is indicated in the treatment of oedema and hypertension during pregnancy.

The treatment of hypertension in pregnancy

The drug treatment of hypertension occurring during pregnancy is described. Diagnostic problems and management are outlined, and the available literature regarding the use of standard hypotensive agents in pregnancy is reviewed by drug class. Based on currently published literature and opinion, the following drugs are recommended when needed during pregnancy (with proper monitoring) : methyldopa, hydralazine, and furosemide. Caution is recommended when the following drugs are used during pregnancy: propranolol, and thiazide diuretics. The following drugs are not recommended for use during pregnancy based on currently available information: reserpine, clonidine, chlorthalidone, prazosin, minoxidil, spironolactone, ethacrynic acid, metoprolol, nadolol, and guanethidine.