The influence of labour on the pharmacokinetics of intravenously administered amoxicillin in pregnant women

Pharmacokinetics and Target Attainment of Antimicrobial Drugs Throughout Pregnancy: Part I-Penicillins

BACKGROUND AND OBJECTIVE

Pharmacokinetics (PK) are severely altered in pregnant women due to changes in volume of distribution (Vd) and/or drug clearance (CL), affecting target attainment of antibiotics in pregnant women. This review is part of a series that reviews literature on the description of PK and target attainment of antibiotics in pregnant women with specific focus on penicillins.

METHODS

A systematic literature search was carried out in PubMed. Articles were labelled as relevant when information on PK of penicillins in pregnant women was available.

RESULTS

Thirty-two relevant articles were included, 8 of which discussed amoxicillin (with and without clavulanic acid), 15 ampicillin, 4 benzylpenicillin, 1 phenoxymethylpenicillin, and 4 piperacillin (with and without tazobactam). No studies were found on pheneticillin and flucloxacillin in pregnant women. Ten out of 32 articles included information on both Vd and CL. During the second and third trimester of pregnancy, a higher CL and larger Vd was reported than in non-pregnant women and in pregnant women during first trimester. Reduced target attainment was described in second and third trimester pregnant women. Only 7 studies reported dosing advice, 4 of which were for amoxicillin.

CONCLUSION

The larger Vd and higher CL in second and third trimester pregnant women might warrant a higher dosage or shortening of the dosing interval of penicillins to increase target attainment. Studies frequently fail to provide dosing advice for pregnant women, even if the necessary PK information was available.

Understanding the pharmacokinetics of antibiotics in pregnancy: Is there a role for therapeutic drug monitoring? A narrative review

PURPOSE

Antibiotics are commonly used during pregnancy. However, physiological changes during pregnancy can affect the pharmacokinetics of drugs, including antibiotics, used during this period. Pharmacokinetic evaluations have shed light on how antibiotics are affected during pregnancy and have influenced dosing recommendations in this context. Methods: A narrative review was conducted and included reports providing data reflecting drug distribution and exposure in the context of pregnancy. Results: Pharmacokinetic parameters of antibiotics in pregnancy and transplacental passage of antibiotics are comprehensively presented. Conclusion: Knowledge about the impact on pharmacokinetics and fetal exposure is especially helpful for complicated or severe infections, including intra-amniotic infection and sepsis in pregnancy, where both mother and fetus are at risk. Further studies are warranted to consolidate the role of therapeutic drug monitoring in complicated or severe infections in pregnant patients.

Population pharmacokinetics of cefazolin in maternal and umbilical cord plasma, and simulated exposure in term neonates

BACKGROUND

Intra-partum cefazolin is used to prevent group B Streptococcus (GBS) vertical transmission in mothers allergic to penicillin without a history of anaphylaxis.

OBJECTIVES

To investigate the maternal cefazolin dose-exposure relationship and subsequent maternal and neonatal target attainment at delivery.

METHODS

Data were obtained from 24 healthy, GBS-colonized pregnant women (20-41 years), undergoing vaginal delivery (gestational age ≥37 weeks). During labour, all women received a 2 g cefazolin IV infusion. Eight hours later, eight women received another 1 g in the event of delayed (>8 h) delivery. Next to maternal plasma concentrations (up to 10 per dosing interval, until delivery), venous and arterial umbilical cord concentrations were determined at delivery. Target attainment in maternal/neonatal plasma was set at 1 mg/L for 60% of the dosing interval (unbound cefazolin, worst-case clinical breakpoint). A population pharmacokinetic (popPK) model was built (NONMEM 7.4). ClinicalTrials.gov Identifier: NCT01295606.

RESULTS

At delivery, maternal blood and arterial umbilical cord unbound cefazolin concentrations were >1 mg/L in 23/24 (95.8%) and 11/12 (91.7%), respectively. The popPK of cefazolin in pregnant women was described by a two-compartment model with first-order elimination. Two additional compartments described the venous and arterial umbilical cord concentration data. Cefazolin target attainment was adequate in the studied cohort, where delivery occurred no later than 6.5 h after either the first or the second dose. PopPK simulations showed adequate maternal and umbilical cord exposure for 12 h following the first dose.

CONCLUSIONS

PopPK simulations showed that standard pre-delivery maternal cefazolin dosing provided adequate target attainment up to the time of delivery.

Anti-Infective Dosing in Special Populations: Pregnancy

Substantial anatomical and physiological changes occur during pregnancy and labor, which impact on drug absorption, distribution, metabolism, and elimination. Reduced maternal concentrations may have a clinically important impact on the efficacy of anti-infectives for mother, fetus, and neonate, with potential dosing implications. However, there is a paucity of pregnancy-specific data examining this. Existing data on the pharmacokinetics of anti-infectives in pregnancy are summarized and evaluated, with emphasis on agents that are used in treatment of HIV, tuberculosis, malaria, and common bacterial infections. Limitations and challenges in achieving ideal study designs in pregnant populations are highlighted, and key quality considerations for the generation of the highest quality evidence are outlined. PubMed was searched for each chosen anti-infective. Pharmacokinetic studies which either compared pharmacokinetics from pregnant women against nonpregnant controls, or which assessed concentrations against a known minimum inhibitory concentration were included. Two independent reviewers extracted data from each study and appraised them using the 24-point ClinPK Checklist. The main finding was that there is a lack of published data for anti-infectives in pregnancy, despite their clinical importance. Of the studies identified, only those investigating cobicistat-boosted antiretroviral regimens firmly concluded that these should not be used in pregnancy. Most studies concluded either that further research was needed, or that there were significant pharmacokinetic differences between pregnant and nonpregnant participants which had uncertain clinical significance. Challenges in applying existing quality grading systems to these studies were noted, suggesting a development of a refined system for appraisal of pharmacokinetic studies in "special populations" may be warranted.

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.

A pharmacokinetic-pharmacodynamic assessment of oral antibiotics for pyelonephritis

Antibiotic resistance to oral antibiotics recommended for pyelonephritis is increasing. The objective was to determine if there is a pharmacological basis to consider alternative treatments/novel dosing regimens for the oral treatment of pyelonephritis. A systematic review identified pharmacokinetic models of suitable quality for a selection of antibiotics with activity against Escherichia coli. MIC data was obtained for a population of E. coli isolates derived from patients with pyelonephritis. Pharmacokinetic/pharmacodynamic (PK/PD) simulations determined probability of target attainment (PTA) and cumulative fraction response (CFR) values for sub-populations of the E. coli population at varying doses. There are limited high-quality models available for the agents investigated. Pharmacokinetic models of sufficient quality for simulation were identified for amoxicillin, amoxicillin-clavulanic acid, cephalexin, ciprofloxacin, and fosfomycin trometamol. These antibiotics were predicted to have PTAs ≥ 0.85 at or below standard doses for the tested E. coli population including cephalexin 1500 mg 8 hourly for 22% of the population (MIC ≤ 4 mg/L) and ciprofloxacin 100 mg 12 hourly for 71% of the population (MIC ≤ 0.06 mg/L). For EUCAST-susceptible E. coli isolates, doses achieving CFRs ≥ 0.9 included amoxicillin 2500 mg 8 hourly, cephalexin 4000 mg 6 hourly, ciprofloxacin 200 mg 12 hourly, and 3000 mg of fosfomycin 24 hourly. Limitations in the PK data support carrying out additional PK studies in populations of interest. Oral antibiotics including amoxicillin, amoxicillin-clavulanic acid, and cephalexin have potential to be effective for a proportion of patients with pyelonephritis. Ciprofloxacin may be effective at lower doses than currently prescribed.

Population Pharmacokinetic Study of Amoxicillin-Treated Burn Patients Hospitalized at a Swiss Tertiary-Care Center

The objective of this study was to investigate the population pharmacokinetics (PK) of amoxicillin in ICU burn patients and the optimal dosage regimens. This was a prospective study involving 21 consecutive burn patients receiving amoxicillin. PK data were analyzed using nonlinear mixed-effects modeling. Monte-Carlo simulations assessed the influence of various amoxicillin dosage regimens with identified covariates on the probability to achieve a target (PTA) value of time during which free amoxicillin concentrations in plasma exceeded the MIC (fT>MIC). A two-compartment model best described the data. Creatinine clearance (CL_CR) and body weight (BW) influenced amoxicillin CL and central volume of distribution (V₁), respectively. The median CL_CR (Cockcroft-Gault formula) was high (128 ml/min), with 25% of patients having CL_CRs of >150 ml/min. The CL, V₁, and half-life (t_1/2) values at steady state for a patient with a CL_CR of 110 ml/min and BW of 70 kg were 13.6 liters/h, 9.7 liters, and 0.8 h, respectively. Simulations showed that a target fT>MIC of ≥50% was achieved (PTA > 90%) with standard amoxicillin dosage regimens (1 to 2 g every 6 to 8 h [q6-8h]) when the MIC was low (<1 mg/liter). However, increased dosages of up to 2 g/4 h were necessary in patients with augmented CL_Rs or higher MICs. Prolonging amoxicillin infusion from 30 min to 2 h had a favorable effect on target attainment. In conclusion, this population analysis shows an increased amoxicillin CL and substantial CL PK variability in burn patients compared to literature data with nonburn patients. Situations of augmented CL_CR and/or high bacterial MIC target values may require dosage increases and longer infusion durations. (This study has been registered at ClinicalTrials.gov under identifier NCT01965340.).

Inclusion of pregnant and breastfeeding women in research - efforts and initiatives

Pregnant and breastfeeding women have been rendered therapeutic orphans as they have been historically excluded from clinical trials. Labelling for most approved drugs does not provide information about safety and efficacy during pregnancy. This lack of data is mainly due to ethico-legal challenges that have remained entrenched in the post-diethylstilbestrol and thalidomide era, and that have led to pregnancy being viewed in the clinical trial setting primarily through a pharmacovigilance lens. Policy considerations that encourage and/or require the inclusion of pregnant or lactating women in clinical trials may address the current lack of available information. However, there are additional pragmatic strategies, such the employment of pharmacometric tools and the introduction of innovative clinical trial designs, which could improve knowledge about the safety and efficacy of medication use during pregnancy and lactation. This paper provides a broad overview of the pharmacoepidemiology of drugs used during pregnancy and lactation, and offers recommendations for regulators and researchers in academia and industry to increase the available pharmacokinetic and -dynamic understanding of medication use in pregnancy.

Non-linear absorption pharmacokinetics of amoxicillin: consequences for dosing regimens and clinical breakpoints

OBJECTIVES

To describe the population pharmacokinetics of oral amoxicillin and to compare the PTA of current dosing regimens.

METHODS

Two groups, each with 14 healthy male volunteers, received oral amoxicillin/clavulanic acid tablets on two separate days 1 week apart. One group received 875/125 mg twice daily and 500/125 mg three times daily and the other group 500/125 mg twice daily and 250/125 mg three times daily. A total of 1428 amoxicillin blood samples were collected before and after administration. We analysed the concentration-time profiles using a non-compartmental pharmacokinetic method (PKSolver) and a population pharmacokinetic method (NONMEM). The PTA was computed using Monte Carlo simulations for several dosing regimens.

RESULTS

AUC0-24 and Cmax increased non-linearly with dose. The final model included the following components: Savic's transit compartment model, Michaelis-Menten absorption, two distribution compartments and first-order elimination. The mean central volume of distribution was 27.7 L and mean clearance was 21.3 L/h. We included variability for the central volume of distribution (34.4%), clearance (25.8%), transit compartment model parameters and Michaelis-Menten absorption parameters. For 40% fT>MIC and >97.5% PTA, the breakpoints were 0.125 mg/L (500 mg twice daily), 0.25 mg/L (250 mg three times daily and 875 mg twice daily), 0.5 mg/L (500 mg three times daily) and 1 mg/L (750, 875 or 1000 mg three times daily and 500 mg four times daily).

CONCLUSIONS

The amoxicillin absorption rate appears to be saturable. The PTAs of high-dose as well as twice-daily regimens are less favourable than regimens with lower doses and higher frequency.

Pregnancy-related pharmacokinetic changes

The pharmacokinetics of many drugs are altered by pregnancy. Drug distribution and protein binding are changed by pregnancy. While some drug metabolizing enzymes have an apparent increase in activity, others have an apparent decrease in activity. Not only is drug metabolism affected by pregnancy, but renal filtration is also increased. In addition, pregnancy alters the apparent activities of multiple drug transporters resulting in changes in the net renal secretion of drugs.

Drug metabolism and transport during pregnancy: how does drug disposition change during pregnancy and what are the mechanisms that cause such changes?

There is increasing evidence that pregnancy alters the function of drug-metabolizing enzymes and drug transporters in a gestational-stage and tissue-specific manner. In vivo probe studies have shown that the activity of several hepatic cytochrome P450 enzymes, such as CYP2D6 and CYP3A4, is increased during pregnancy, whereas the activity of others, such as CYP1A2, is decreased. The activity of some renal transporters, including organic cation transporter and P-glycoprotein, also appears to be increased during pregnancy. Although much has been learned, significant gaps still exist in our understanding of the spectrum of drug metabolism and transport genes affected, gestational age-dependent changes in the activity of encoded drug metabolizing and transporting processes, and the mechanisms of pregnancy-induced alterations. In this issue of Drug Metabolism and Disposition, a series of articles is presented that address the predictability, mechanisms, and magnitude of changes in drug metabolism and transport processes during pregnancy. The articles highlight state-of-the-art approaches to studying mechanisms of changes in drug disposition during pregnancy, and illustrate the use and integration of data from in vitro models, animal studies, and human clinical studies. The findings presented show the complex inter-relationships between multiple regulators of drug metabolism and transport genes, such as estrogens, progesterone, and growth hormone, and their effects on enzyme and transporter expression in different tissues. The studies provide the impetus for a mechanism- and evidence-based approach to optimally managing drug therapies during pregnancy and improving treatment outcomes.

Antibiotic Treatment of Dogs and Cats during Pregnancy

The use of pharmacological agents in pregnant females poses a major clinical challenge due to the marked physiological changes that may modify the pharmacokinetics of drugs and to the potential effects on the fetus. The purpose of this paper is to review briefly our knowledge on the use of antibacterial drugs during pregnancy and to provide information for the judicious selection of an antimicrobial treatment for use in pregnant bitches and queens. The risk to the fetus is a result of the ability of a drug to reach the fetal circulation and to produce toxic effects. The placenta functions as a barrier that protects the fetus due to the presence of transporters and metabolising enzymes; however, during pregnancy, the presence and activity of both enzymes and transporters may change. Antimicrobial agents that have been shown to be safe for use during pregnancy include betalactams, macrolides, and lincosamides. Pharmacotherapy during pregnancy in all species may affect adversely the developing fetus; therefore, it should be avoided when possible.