Pharmacokinetics of tobramycin in pregnant women. Safety and efficacy of a once-daily dose regimen

The Pharmacokinetics and Target Attainment of Antimicrobial Drugs Throughout Pregnancy: Part III Non-penicillin and Non-cephalosporin Drugs

INTRODUCTION

Understanding the pharmacokinetics (PK) of antimicrobial drugs in pregnant women is crucial to provide effective and safe treatment. This study is part of a series that systematically reviews literature on the PK and analyzes if, based on the changed PK, evidence-based dosing regimens have been developed for adequate target attainment in pregnant women. This part focusses on antimicrobials other than penicillins and cephalosporins.

METHODS

A literature search was conducted in PubMed according to the PRISMA guidelines. Search strategy, study selection, and data extraction were independently performed by two investigators. Studies were labeled as relevant when information on the PK of antimicrobial drugs in pregnant women was available. Extracted parameters included bioavailability for oral drugs, volume of distribution (Vd) and clearance (CL), trough and peak drug concentrations, time of maximum concentration, area under the curve and half-life, probability of target attainment, and minimal inhibitory concentration (MIC). In addition, if developed, evidence-based dosing regimens were also extracted.

RESULTS

Of the 62 antimicrobials included in the search strategy, concentrations or PK data during pregnancy of 18 drugs were reported. Twenty-nine studies were included, of which three discussed aminoglycosides, one carbapenem, six quinolones, four glycopeptides, two rifamycines, one sulfonamide, five tuberculostatic drugs, and six others. Eleven out of 29 studies included information on both Vd and CL. For linezolid, gentamicin, tobramycin, and moxifloxacin, altered PK throughout pregnancy, especially in second and third trimester, has been reported. However, no target attainment was studied and no evidence-based dosing developed. On the other hand, the ability to reach adequate targets was assessed for vancomycin, clindamycin, rifampicin, rifapentine, ethambutol, pyrazinamide, and isoniazid. For the first six mentioned drugs, no dosage adaptations during pregnancy seem to be needed. Studies on isoniazid provide contradictory results.

CONCLUSION

This systematic literature review shows that a very limited number of studies have been performed on the PK of antimicrobials drugs-other than cephalosporins and penicillins-in pregnant women.

Safety of Antimicrobials During Pregnancy: A Systematic Review of Antimicrobials Considered for Treatment and Postexposure Prophylaxis of Plague

BACKGROUND

The safety profile of antimicrobials used during pregnancy is one important consideration in the decision on how to treat and provide postexposure prophylaxis (PEP) for plague during pregnancy.

METHODS

We searched 5 scientific literature databases for primary sources on the safety of 9 antimicrobials considered for plague during pregnancy (amikacin, gentamicin, plazomicin, streptomycin, tobramycin, chloramphenicol, doxycycline, sulfadiazine, and trimethoprim-sulfamethoxazole [TMP-SMX]) and abstracted data on maternal, pregnancy, and fetal/neonatal outcomes.

RESULTS

Of 13 052 articles identified, 66 studies (case-control, case series, cohort, and randomized studies) and 96 case reports were included, totaling 27 751 prenatal exposures to amikacin (n = 9), gentamicin (n = 345), plazomicin (n = 0), streptomycin (n = 285), tobramycin (n = 43), chloramphenicol (n = 246), doxycycline (n = 2351), sulfadiazine (n = 870), and TMP-SMX (n = 23 602). Hearing or vestibular deficits were reported in 18/121 (15%) children and 17/109 (16%) pregnant women following prenatal streptomycin exposure. First trimester chloramphenicol exposure was associated with an elevated risk of an undescended testis (odds ratio [OR] 5.9, 95% confidence interval [CI] 1.2-28.7). Doxycycline was associated with cardiovascular malformations (OR 2.4, 95% CI 1.2-4.7) in 1 study and spontaneous abortion (OR 2.8, 95% CI 1.9-4.1) in a separate study. First trimester exposure to TMP-SMX was associated with increased risk of neural tube defects (pooled OR 2.5, 95% CI 1.4-4.3), spontaneous abortion (OR 3.5, 95% CI 2.3-5.6), preterm birth (OR 1.5, 95% CI 1.1-2.1), and small for gestational age (OR 1.6, 95% CI 1.2-2.2). No other statistically significant associations were reported.

CONCLUSIONS

For most antimicrobials reviewed, adverse maternal/fetal/neonatal outcomes were not observed consistently. Prenatal exposure to streptomycin and TMP-SMX was associated with select birth defects in some studies. Based on limited data, chloramphenicol and doxycycline may be associated with adverse pregnancy or neonatal outcomes; however, more data are needed to confirm these associations. Antimicrobials should be used for treatment and PEP of plague during pregnancy; the choice of antimicrobials may be influenced by these data as well as information about the risks of plague during pregnancy.

Evaluation of Once Daily Tobramycin Versus the Traditional Three Time Daily for the Treatment of Acute Pulmonary Exacerbations in Adult Cystic Fibrosis Patients

Once daily tobramycin is convenient to use and achieves higher tissue levels that should kill Pseudomonas aeruginosa more rapidly. Small trials of OD compared with TDS aminoglycosides in CF patients have shown no dif-ference in efficacy or toxicity. No one has looked in detail at the impact on sputum microbiology. In a prospective, randomized study at Papworth Hospital, UK, we compared OD with TDS tobramycin, each plus a second anti-pseudomonal, for the treatment of acute infective exacer-bation in 15 adult cystic fibrosis patients colonized with Pseudomonas aeruginosa. Using the patients as their own control, the same individuals received the alternate treat-ment regime for the next exacerbation. We aimed to com-pare the clinical and bacteriological efficacy, toxicity>, and the effects on susceptibility of the organism among patients in both treatment groups. Isolates were identified, and the Minimum Inhibitory Concentration (MIC) of the antibi-otic in each patient was performed. Patients were assessed for clinical improvement, toxicity and the total viable count in their sputum on days 0\ 7 and 14. In both treatment groups there was a significant clinical improvement, and toxicity did not occur in either group. There was no differ-ence in clinical outcome, adverse events, or time to the next exacerbation. No difference was seen in the selection of antibiotic resistance. OD tobramycin appeared more ef-fective in reducing the number of bacteria in the group overall at day 7 and in two individuals, at day 14.

Drug Transfer and Metabolism by the Human Placenta

The major function of the placenta is to transfer nutrients and oxygen from the mother to the foetus and to assist in the removal of waste products from the foetus to the mother. In addition, it plays an important role in the synthesis of hormones, peptides and steroids that are vital for a successful pregnancy. The placenta provides a link between the circulations of two distinct individuals but also acts as a barrier to protect the foetus from xenobiotics in the maternal blood. However, the impression that the placenta forms an impenetrable obstacle against most drugs is now widely regarded as false. It has been shown that that nearly all drugs that are administered during pregnancy will enter, to some degree, the circulation of the foetus via passive diffusion. In addition, some drugs are pumped across the placenta by various active transporters located on both the fetal and maternal side of the trophoblast layer. It is only in recent years that the impact of active transporters such as P-glycoprotein on the disposition of drugs has been demonstrated. Facilitated diffusion appears to be a minor transfer mechanism for some drugs, and pinocytosis and phagocytosis are considered too slow to have any significant effect on fetal drug concentrations. The extent to which drugs cross the placenta is also modulated by the actions of placental phase I and II drug-metabolising enzymes, which are present at levels that fluctuate throughout gestation. Cytochrome P450 (CYP) enzymes in particular have been well characterised in the placenta at the level of mRNA, protein, and enzyme activity. CYP1A1, 2E1, 3A4, 3A5, 3A7 and 4B1 have been detected in the term placenta. While much less is known about phase II enzymes in the placenta, some enzymes, in particular uridine diphosphate glucuronosyltransferases, have been detected and shown to have specific activity towards marker substrates, suggesting a significant role of this enzyme in placental drug detoxification. The increasing experimental data on placental drug transfer has enabled clinicians to make better informed decisions about which drugs significantly cross the placenta and develop dosage regimens that minimise fetal exposure to potentially toxic concentrations. Indeed, the foetus has now become the object of intended drug treatment. Extensive research on the placental transfer of drugs such as digoxin and zidovudine has assisted with the safe treatment of the foetus with these drugs in utero. Improved knowledge regarding transplacental drug transfer and metabolism will result in further expansion of pharmacological treatment of fetal conditions.

Effects of antibacterials on the unborn child: what is known and how should this influence prescribing

Antibacterials are among the most commonly prescribed drugs worldwide. In general, infections occur in pregnant women at much the same rate as in the general population. However, as a result of physiological changes brought about by pregnancy, some infections, such as those of the urinary tract, may have an increased incidence. It is important to remember that almost every drug crosses the placenta, ensuring that the unborn fetus is also exposed. When prescribing an antibacterial agent to a pregnant woman, it is important that the mother is treated appropriately while at the same time protecting the unborn child. Certain factors need to be addressed, such as the possible teratogenic risk, changes in pharmacokinetics and the potential toxicity of the drug. In this paper we have reviewed various classes of antibacterials which are commonly used during pregnancy, including penicillins, beta-lactam inhibitors, cephalosporins, macrolides, aminoglycosides, tetracyclines, lincosamides, fluoroquinolones, sulfonamides, nitrofurans, and anti-tubercular agents. Some of these drugs have been on the market for many years, whereas others are relatively new and increasingly popular, despite the fact that the older drugs remain very effective. After reviewing the evidence-based information from epidemiological studies, it appears that most antibacterial agents can be used relatively safely during pregnancy. Women who are pregnant should not be denied appropriate antibacterial therapy because of a lack of information. It is possible to treat the mother, while protecting the unborn child, by prescribing an agent that the causative bacteria is sensitive to, rather than a perceived 'safer' option that may not effectively treat the infection and which may also add to the growing problem of bacterial resistance.

Techniques to study human placental transport

Pregnancy in the 20th century involves women of many age groups from early teens to the fourth or fifth decade. Modern medicine and in vitro fertilization techniques have increased options for pregnancy and childbirth. Pregnancy is a dynamic state, and medical concerns may involve disorders of the fetus and mother requiring medications and special nutrients. Therefore, different techniques have been developed to evaluate the placental transfer of drugs and nutrients using tissues and cells derived from human placenta. These include (a) isolated tissues and cells to study placental transport, (b) primary and malignant trophoblast cell cultures and (c) biophysical methods for studying placental transport. Also, convenient study models have been developed to evaluate placental transfer of safe drugs in pregnant women. Some of the drugs studied by these techniques and models include (a) anesthetics and pain medications used during delivery, (b) antibiotics and anti-bacterials used to cure infections, (c) drugs abused by pregnant women and (d) nutrients required for proper fetal growth. Placental transfer and exchange mechanisms are complicated processes, and in vitro models reflect only partially the equilibria that exist among mother, placenta and fetus. The perfused cotyledon model is elegant and simple but gives only restricted information. Isolated placental tissues give useful information about the pharmacological effects of drugs. Metabolic studies using human placental models provide information on the metabolism of a drug during placental transfer and accumulation of the drug or its metabolite in the placenta or fetal circulation. Several studies on the transplacental passage of drugs exist but many questions regarding the transfer of drugs between the maternal and fetal circulations and clearance of drugs from fetal circulation have yet to be answered. This article reviews in vitro and in vivo methods for evaluation of transplacental transport of drugs and their current effectiveness to obtain clinically useful data.

Factors influencing the protein binding of azosemide using an equilibrium dialysis technique

Various factors most likely to influence the plasma protein binding of azosemide to 4% human serum albumin (HSA) were evaluated using equilibrium dialysis at the initial azosemide concentration of 10 micrograms mL-1. It took approximately 8 h of incubation to reach an equilibrium between 4% HSA and isotonic phosphate buffer of pH 7.4 containing 3% dextran (the 'buffer') using a Spectra/Por 2 membrane (molecular weight cut-off, 12000-14000) in a water bath shaker kept at 37 degrees C and a rate of 50 oscillations min-1. Azosemide was fairly stable both in 4% HSA and in the 'buffer' for up to 24 h. The binding of azosemide to 4% HSA was constant (95.5 +/- 0.142%) at azosemide concentrations ranging from 5 to 100 micrograms mL-1. However, the extent of binding was dependent on HSA concentration: the values were 88.4, 91.0, 92.2, 94.2, 94.9, 94.9, and 94.9% at albumin concentrations of 0.5, 1, 2, 3, 4, 5, and 6%, respectively. The binding was also dependent on incubation temperature: the binding values were 97.0, 94.9, and 94.9% when incubated at 6, 28, and 37 degrees C, respectively. The binding of azosemide was also influenced by buffers containing various chloride ion concentrations and buffer pHs. The binding values were 95.3, 94.9 and 93.6% for the chloride ion concentrations of 0, 0.249, and 0.546%, respectively, and the unbound values were 6.8, 5.1, 3.8, 3.4, and 3.3% for buffer pHs of 5.8, 6.4, 7.0, 7.4, and 8.0, respectively. The binding of azosemide was independent of the quantity of heparin (up to 40 U mL-1), AAG (up to 0.16%), sodium azide (NaN3, up to 5%), its metabolite, M1 (up to 10 micrograms mL-1), and anticoagulants (EDTA and citrate).

Auditory effect of kanamycin given to newborn guinea pigs whose mothers received kanamycin during pregnancy

Clinical and experimental data indicate that aminoglycoside ototoxicity occurs more frequently in individuals previously exposed to ototoxic drugs. This study investigated the auditory effect of repetitive administration of kanamycin on newborn guinea pigs that had previously been exposed, in utero, to kanamycin administered to their mothers. Sixteen pregnant guinea pigs in the late stages of gestation were divided into two groups, one receiving kanamycin 500 mg/kg per day intramuscularly for 8 days, and the other acting as a control. After birth, the mothers and their newborns in both groups were examined for auditory brain stem response (ABR) and then treated with kanamycin 500mg/kg per day for 4 days. The results from the second examination demonstrated that the group receiving prior treatment with kanamycin, despite their good ABR responses during the first measurement, showed significantly elevated auditory thresholds compared to the control group. Therefore, any ototoxic drugs should be used with extreme caution in newborns having had prior exposure to the drugs in utero, even if they have a "normal" auditory response after birth.

Pharmacokinetics and protein binding of ceftriaxone during pregnancy

The purpose of the present work was to study the pharmacokinetics and the protein binding (free fraction of the drug) of ceftriaxone (CTX) during pregnancy. Nine pregnant women (ages, 20 to 34 years) whose gestational ages ranged from 28 4/7 to 40 5/7 weeks were included. The diagnosis of infection was established in all cases; i.e., four women had chorioamnionitis and five women had pyelonephritis. The following triple antibiotic therapy was infused with the aim of achieving cure: CTX, 2 g once every 24 h (constant rate over 60 min); tobramycin, 3 mg/kg of body weight once every 24 h; and ornidazole, 1 g/day. Two series of blood samples were collected, i.e., during the first day of treatment (on day 1), to establish the primary pharmacokinetic profile of CTX, and at the plateau (on day 7), to evaluate a possible accumulation of the drug. This was an open, noncompartmental study, with each patient serving as her own control. Concentrations of total and unbound CTX in serum were measured by a high-performance liquid chromatographic method. Pharmacokinetic analysis was done by a noncompartmental method. Data were compared by a Wilcoxon t test (a P value of < or = 0.05 was considered significant). Data were also compared with those obtained for healthy subjects who received similar treatments. (i) The tolerance to treatment was excellent, and in all cases patients had a complete remission without premature delivery. (ii) No accumulation of CTX was noted during the treatment, and the profiles of the drug determined at days 1 and 7 were not significantly different.(iii) The pharmacokinetic parameters measured in pregnant patients during the third trimester of pregnancy were similar to those measured in healthy subjects. (iv) Residual concentrations of total and unbound CTX measured at 24 h were greater than the MICs for allegedly susceptible organisms, both on day 1 and at steady state. (v) During the final 3 months of pregnancy, the dosage schedule of CTX (2-g infusion per day) required no particular adjustment (i.e., neither a loading dose nor any increase in the maintenance dose.)