Transplacental passage of ampicillin

Vertical transfer of antibiotics and antibiotic resistant strains across the mother/baby axis

Antibiotic resistance is a health and socioeconomic crisis recognized as a serious threat affecting humans worldwide. Overuse of antibiotics enhances the spread of multidrug-resistant bacteria, causing drug-resistant infections which can be difficult to treat. This resistance, mostly of the acquired type, is thus a major clinical issue. Acquired resistance can occur by horizontal transfer of genes between bacteria (community settings), by vertical transmission that can occur between mother and her offspring at birth and during lactation, or spontaneously due to antibiotic exposure. While there have been multiple studies about the horizontal transfer of antibiotic-resistance genes, not many studies have been conducted to study their vertical transmission. Vertical transmission is of importance as the early bacterial colonization of infants has an impact on their health and immune programming throughout life. This review discusses some possible mechanisms of mother-to-infant transmission of antibiotics and antibiotic-resistant strains and addresses the knowledge gaps for further studies.

Prophylaxis and treatment of anthrax in pregnant women

OBJECTIVE

To review the safety and pharmacokinetics of antimicrobials recommended for anthrax postexposure prophylaxis and treatment in pregnant women.

DATA SOURCES

Articles were identified in the PubMed database from inception through December 2012 by searching the keywords (["pregnancy]" and [generic antibiotic drug name]). Additionally, we searched clinicaltrials.gov and conducted hand searches of references from REPROTOX, TERIS, review articles, and Briggs' Drugs in Pregnancy and Lactation.

METHODS OF STUDY SELECTION

Articles included in the review contain primary data related to the safety and pharmacokinetics among pregnant women of 14 antimicrobials recommended for anthrax postexposure prophylaxis and treatment (amoxicillin, ampicillin, chloramphenicol, clindamycin, ciprofloxacin, doripenem, doxycycline, levofloxacin, linezolid, meropenem, moxifloxacin, penicillin, rifampin, and vancomycin).

TABULATION, INTEGRATION, AND RESULTS

The PubMed search identified 3,850 articles for review. Reference hand searching yielded nine additional articles. In total, 112 articles met the inclusion criteria.

CONCLUSIONS

Overall, safety and pharmacokinetic information is limited for these antimicrobials. Although small increases in risks for certain anomalies have been observed with some antimicrobials recommended for prophylaxis and treatment of anthrax, the absolute risk of these antimicrobials appears low. Given the high morbidity and mortality associated with anthrax, antimicrobials should be dosed appropriately to ensure that antibiotic levels can be achieved and sustained. Dosing adjustments may be necessary for the β-lactam antimicrobials and the fluoroquinolones to achieve therapeutic levels in pregnant women. Data indicate that the β-lactam antimicrobials, the fluoroquinolones, and, to a lesser extent, clindamycin enter the fetal compartment, an important consideration in the treatment of anthrax, because these antimicrobials may provide additional fetal benefit in the second and third trimesters of pregnancy.

Placental transfer of drugs administered to the mother

Drugs administered to mothers have the potential to cross the placenta and reach the fetus. Under particular circumstances, the comparison of the drug concentration in the maternal and fetal plasma may give an idea of the exposure of the fetus to the maternally administered drugs. In this review drugs are classified according to their type of transfer across the placenta. Several drugs rapidly cross the placenta and pharmacologically significant concentrations equilibrate in maternal and fetal plasma. Their transfer is termed 'complete'. Other drugs cross the placenta incompletely, and their concentrations are lower in the fetal than in maternal plasma. The majority of drugs fit into 1 of these 2 groups. A limited number of drugs reach greater concentrations in fetal than maternal plasma. It is said that these drugs have an 'exceeding' transfer. The impression prevails that suxamethonium chloride (succinylcholine chloride) and doxorubicin do not cross the placenta. However, a careful analysis of the literature suggests that this impression is wrong and that all drugs cross the placenta, although the extent transfer varies considerably. The following parameters were considered as possible factors determining the extent of placental transfer: (i) the molecular weight of the drug; (ii) the pKa (pH at which the drug is 50% ionised); and (iii) the extent of drug binding to the plasma protein. Drugs with molecular weights greater than 500D have an incomplete transfer across the human placenta. Strongly dissociated acid drug molecules should have an incomplete transfer, but this does not seem to be an absolute rule. For example, ampicillin and methicillin transfer completely and they are strongly dissociated at physiological pH. The extent of drug binding to plasma protein does not influence the type of drug transfer across the human placenta.

Transplacental ampicillin: inhibitory concentrations in neonatal serum

Concentrations of ampicillin were measured in maternal serum at delivery, in cord serum, and in neonatal serum sampled at 1, 4, and 8 hours after ampicillin had been administered prophylactically to 22 mothers who were undergoing cesarean section. The concentrations of ampicillin in maternal serum at delivery ranged from 4.6 to 50 micrograms per milliliter and were inversely related to the time between administration of the drug and delivery. Concentrations in cord serum ranged from 4.4 to 23 micrograms/ml and were lower than those in corresponding maternal samples in all but two cases. The ratios of cord/maternal concentrations of ampicillin ranged from 0.16 to 1.3 and were directly related to the time which had elapsed between administration of ampicillin and delivery. The mean concentration of ampicillin in cord and neonatal serum declined exponentially in the 8 hours after infusion; it exceeded the minimal inhibitory concentration against Escherichia coli for 4 hours and against Listeria monocytogenes and group B streptococcus for at least 8 hours.

Drug kinetics in childbirth

Drugs from a wide range of pharmacological classes are commonly given to women in childbirth, either for a maternal effect or a fetal/neonatal effect. A number of striking physiological and biochemical changes occur during labour and delivery that might alter drug kinetics. The rate of drug absorption from the gastrointestinal tract may be normal in labour provided that narcotic analgesics are not administered concurrently. Altered blood flow characteristics in the extremities could modify drug absorption from intramuscular injection sites. Drug distribution might be altered as a result of the presence of placental-fetal tissues, or as a consequence of changes in, for example, maternal blood volume, concentrations of proteins and other endogenous compounds, cardiac output or tissue perfusion. Although data are scanty on the status of the physiological determinants of drug clearance, that limited information available suggests that drug clearance could be altered in childbirth. The possibility of a placental and/or fetal contribution should not be overlooked when considering the clearance of drugs administered during labour and delivery. Uterine contractions, maternal posture and obstetric medication have been found to affect the extent of some of the physiological changes that occur. Consequently, drug disposition could be modified by these factors. All of the drugs given to women in childbirth are capable of crossing the placenta to some degree. This is a disadvantage in those cases where drugs are given for a maternal effect and may result in neonatal sequelae. The fetal exposure to, and neonatal burden at delivery of, drugs administered during labour and delivery may be influenced by many factors, including maternal posture, mode of drug administration, the drug administraton to delivery interval, fetal pH, and whether intravenous bolus drug administration coincides with the contraction or relaxation phase of uterine activity. Protracted elimination by the neonate may occur for those drugs acquired in utero. Realisation of this is of considerable importance in the clinical management of the newborn.

Clinical pharmacology of amikacin sulphate: blood, urinary and tissue concentrations in the terminal stage of pregnancy

Within a broad programme of research into the pharmacokinetics of various antimicrobials in gynaeco-obstetric patients, with a view of determining its concentrations in the different compartments and reproductive organs, we administered 7-5 mg/kg of amikacin sulphate to eleven women in the terminal stage of pregnancy one hour before collecting the specimens studies. The concentrations in the maternal blood and urine was similar to that obtained during the first weeks of gestation, and to that achieved outside pregnancy. The low determinations observed at the level of the foetal blood and urine and the anniotic fluid, as well as in the placenta and oviducts, is in our view due to the fact that the passage of this drug into the 'compartments' mentioned takes place slowly; this hypothesis is, however, subject to corroboration or refutation by further studies on this question. The concentration of this compound found was, nonetheless, bactericidal in all the parameters studied.

Influence of sex on drug kinetics in man

Very few investigations in man have been specifically devoted to the influence of sex on drug kinetics. Although the potential role of various factors such as the phase of the menstrual cycle, hormonal steroid contraceptive use, menopause or andropause is virtually never taken into account, sex-linked differences in drug kinetics do exist for a limited number of substances such as certain antibiotics, a few tricyclic antidepressants, lithium and aspirin. These sex-linked differences are relatively minor from a quantitative standpoint and appear to be due chiefly to differences in body composition and activity of circulating enzymes and hormones. On the basis of present knowledge, in general these differences in drug kinetics do not warrant modifying dosage as a function of sex.

Cephazolin: clinical studies in obstetrics

A clinical evaluation of a new cephalosporin, cephazolin, in obstetric patients is presented. Sixteen cardiac patients received the drug prophylactically as antibiotic cover during labour. Eighteen patients with miscellaneous antenatal and puerperal infections received the drug as primary treatment. The data obtained indicate adequate serum and tissue levels with the dose used, and corresponding clinical response. The impression is of a safe and efficaceous drug in the described obstetric situations requiring antibiotic therapy. It may be given prophylactically and with confidence to the cardiac patient in labour.

Gastro-intestinal absorption and transplacental transfer of amoxycillin during labour and the influence of metoclopramide

The absorption of amoxycillin from the gastro-intestinal tract, with or without oral metoclopramide, has been evaluated. Levels of amoxycillin in the maternal blood and liquor prior to the induction of labour were of a therapeutic level against many organisms. However, absorption during labour, as reflected by maternal blood levels at delivery and cord blood levels, suggests that amoxycillin is poorly absorbed and may not reach adequate therapeutic levels in the fetus. Oral metoclopramide did not improve the absorption of amoxycillin. Should a parenteral form of amoxycillin become available, a similar study of blood and liquor levels may indicate that, like ampicillin, intramuscular administration is required for adequate therapeutic use at this stage of pregnancy. Until an oral formulation of an appropriate antibiotic is available which gives rapid absorption may and a sustained level of the chemotherapeutic agent in this situation, parenteral administration of an appropriate antibiotic remains mandatory.

Pharmacological studies with lincomycin in late pregnancy

The placental transmission of lincomycin was studied in 60 patients in late pregnancy. A peak maternal blood level of 12.5 mug/ml was recorded 45 minutes after injection, and detectable levels were still present up to 42 hours after a single injection. A peak cord blood level of 2.7 mug/ml was recorded 55 minutes after injection; cord blood levels were about a quarter of the maternal blood levels, and in most cases no levels were detectable 24 hours after a single injection. The passage of lincomycin into and out of the liquor was slower and more variable, but some hours after injection the liquor levels were always higher than the maternal or cord blood levels, and detectable levels were still present in the liquor 52 hours after a single injection. Repeated injections did not lead to any significant accumulation of lincomycin. The only side effect was a possible case of neuromuscular block in a mother delivered by caesarean section. No infant was adversely affected.