Pharmacokinetics of erythromycin ethylsuccinate and estolate in infants under 4 months of age

Antibiotics and Antifungals in Neonatal Intensive Care Units: A Review

The incidence of infections is higher in the neonatal period than at any time of life. The basic treatment of infants with infection has not changed substantially over the last years. Antibiotics (with or without supportive care) are one of the most valuable resources in managing sick newborn babies. Early-onset (ascending or transplacental) or late-onset (hospital acquired) infections present different chronology, epidemiology, physiology and outcome. Some classes of antibiotics are frequently used in the neonatal period: penicillins, cephalosporins, aminoglycosides, glycopeptides, monobactams, carbapenems. Other classes of antibiotics (chloramphenicol, cotrimoxazole, macrolides, clindamycin, rifampicin and metronidazole) are rarely used. Due to emergence of resistant bacterial strains in Neonatal Intensive Care Units (NICU), other classes of antibiotics such as quinolones and linezolid will probably increase their therapeutic role in the future. Although new formulations have been developed for treatment of fungal infections in infants, amphotericin B remains first-line treatment for systemic Candida infection. Prophylactic antibiotic therapy is almost always undesirable. Challenges from pathogens and antibiotic resistance in the NICU may warrant modification of traditional antibiotic regimens. Knowledge of local flora and practical application of different antibiotic characteristics are key to an effective and safe utilization of antibiotics and antifungals in critical newborns admitted to the NICU, and especially in very low birth weight infants.

Prediction of drug clearance in children 3 months and younger: an allometric approach

BACKGROUND

Sometimes it might not be possible to conduct a pharmacokinetic (PK) study in neonates and infants. Under these circumstances, one would like to predict PK parameters in this age group. Because drug clearance is the most important PK parameter, the objective of this study was to describe an allometric method to predict drug clearance in children ≤3 months.

METHODS

In total, 43 drugs (107 observations) were randomly selected for this study. The age of the children ranged from 0 to 1 year. Children were divided into two groups: ≤3 months and ≥3 months to 1 year. Drug clearance (CL) in children was predicted using the following equation: CL in the child=adult CL×(weight of the child/70)(0.75 or 1.0 or 1.2).

RESULTS

The results of the study indicated that the exponent 1.2 performs better in the prediction of drug clearance than exponent 1.0 or 0.75 for children ≤3 months. By contrast, exponent 1.0 provided better prediction for children ≥3 months to 1 year than exponent 1.2. Exponent 0.75 provided the worst results leading to substantial prediction error in children 0-1 year (in many instances more than 1000% prediction error).

CONCLUSIONS

Overall, it appears that exponent 1.2 is the best method out of three methods for reasonably accurate prediction of drug clearance in children ≤3 months old. However, exponent 1.2 will underpredict drug clearance in children older than 3 months. The suggested approach could be used to support the choice of the initial dose in clinical trials for children ≤3 months old.

Pharmacokinetics of erythromycin after intravenous, intramuscular and oral administration to cats

The aim of this study was to characterise the pharmacokinetic properties of different formulations of erythromycin in cats. Erythromycin was administered as lactobionate (4 mg/kg intravenously (IV)), base (10mg/kg, intramuscularly (IM)) and ethylsuccinate tablets or suspension (15 mg/kg orally (PO)). After IV administration, the major pharmacokinetic parameters were (mean ± SD): area under the curve (AUC)((0-∞)) 2.61 ± 1.52 microgh/mL; volume of distribution (V(z)) 2.34 ± 1.76L/kg; total body clearance (Cl(t)) 2.1 0 ± 1.37 L/hkg; elimination half-life (t(½)(λ)) 0.75 ± 0.09 h and mean residence time (MRT) 0.88 ± 0.13 h. After IM administration, the principal pharmacokinetic parameters were (mean ± DS): peak concentration (C(max)), 3.54 ± 2.16 microg/mL; time of peak (T(max)), 1.22 ± 0.67 h; t(½)(λ), 1.94 ± 0.21 h and MRT, 3.50 ± 0.82 h. The administration of erythromycin ethylsuccinate (tablets and suspension) did not result in measurable serum concentrations. After IM and IV administrations, erythromycin serum concentrations were above minimum inhibitory concentration (MIC)(90)=0.5 microg/mL for 7 and 1.5h, respectively. However, these results should be interpreted cautiously since tissue erythromycin concentrations have not been measured and can reach much higher concentrations than in blood, which may be associated with enhanced clinical efficacy.

Challenges for drug studies in children: CYP3A phenotyping as example

A paucity of data exists on the disposition and effect of drugs in young children. This information gap can be reduced by elucidating developmental principles of absorption, distribution, metabolism and excretion (ADME) in vivo. Such knowledge might enable the prediction of the disposition of individual drugs in children over the whole pediatric age range. CYP3A, the most abundant human drug metabolizing enzyme, is involved in the metabolism of more than 50% of all marketed drugs. Hence, elucidating the developmental pattern of CYP3A in relation to genetic background, disease and comedications might greatly enhance our knowledge on drug disposition in children. Several methods have been used to determine in vivo CYP3A activity in human adults, while similar studies in children face several ethical, practical and scientific challenges. The aim of this review is to identify these challenges and offer feasible solutions for studying drugs in young children, with an emphasis on CYP3A phenotyping as an example.

Efficacy of oral erythromycin for treatment of feeding intolerance in preterm infants

OBJECTIVE

To determine the efficacy and safety of oral erythromycin (EM) for feeding intolerance in preterm infants < 35 weeks gestation.

STUDY DESIGN

In this randomized, double-blinded, placebo-controlled trial, preterm infants with feeding intolerance were randomly allocated to a treatment group given EM ethyl succinate 10 mg/kg every 6 hours for 2 days, followed by 4 mg/kg every 6 hours for another 5 days, or to a control group given placebo. The primary outcome was time to full feeding (150 mL/kg/day) after the start of treatment.

RESULTS

Each group comprised 23 preterm infants, almost all of whom were < 32 weeks gestation. Baseline characteristics were similar between the 2 groups. Times to full feeding were significantly shorter and the number of withheld feeds were significantly less in the EM group than the control group; the respective medians (interquartile ranges) were 7 days (6 to 9 days) versus 13 days (9 to 15 days) (P < .001) and 1 episode (0 to 2 episodes) versus 9 episodes (2 to 13 episodes) (P < .001). No significant differences in episodes of sepsis, necrotizing enterocolitis, and cholestasis were observed.

CONCLUSIONS

Oral EM was effective and safe for treatment of feeding intolerance in preterm infants.

Mycoplasmas and ureaplasmas as neonatal pathogens

The genital mycoplasmas represent a complex and unique group of microorganisms that have been associated with a wide array of infectious diseases in adults and infants. The lack of conclusive knowledge regarding the pathogenic potential of Mycoplasma and Ureaplasma spp. in many conditions is due to a general unfamiliarity of physicians and microbiology laboratories with their fastidious growth requirements, leading to difficulty in their detection; their high prevalence in healthy persons; the poor design of research studies attempting to base association with disease on the mere presence of the organisms in the lower urogenital tract; the failure to consider multifactorial aspects of diseases; and considering these genital mycoplasmas only as a last resort. The situation is now changing because of a greater appreciation of the genital mycoplasmas as perinatal pathogens and improvements in laboratory detection, particularly with regard to the development of powerful molecular nucleic acid amplification tests. This review summarizes the epidemiology of genital mycoplasmas as causes of neonatal infections and premature birth; evidence linking ureaplasmas with bronchopulmonary dysplasia; recent changes in the taxonomy of the genus Ureaplasma; the neonatal host response to mycoplasma and ureaplasma infections; advances in laboratory detection, including molecular methods; and therapeutic considerations for treatment of systemic diseases.

The association of erythromycin and infantile hypertrophic pyloric stenosis: causal or coincidental?

The safety profile of erythromycin is notable for the frequent occurrence of intolerable gastrointestinal effects. One of the more serious of these is infantile hypertrophic pyloric stenosis (IHPS). A recent cluster of IHPS cases prompted an epidemiological investigation which identified oral erythromycin chemoprophylaxis of pertussis as the major risk factor. Evidence suggests an association between early postnatal erythromycin exposure and IHPS. There is no substantive evidence of a risk associated with prenatal exposure, with the single published case-control study to date producing negative findings. The epidemiological investigations of the association with early postnatal exposure have reported significantly elevated odds ratios but have a variety of methodological limitations that prevent definitive conclusions being made. Nevertheless, the concordance of findings across studies increases the strength of evidence favouring an association. The prominent gastrokinetic properties of erythromycin have been postulated as the mechanism behind this phenomenon. A comprehensive assessment of this potential adverse effect should consider its biological plausibility in light of known gastrointestinal physiology, its modulation by erythromycin, and the known pathophysiology of IHPS. Gastrointestinal motor activity in the fasted mammal consists of three phases, phase III being large amplitude contractions called migrating motor complexes (MMC) that can be initiated by motilin and erythromycin. The gastrokinetic effects of erythromycin are variable and complex and include effects on the timing, duration, amplitude and distribution of MMCs. It has been speculated that the motilinomimetic effects of erythromycin on antral smooth muscle function, such as the MMC, may mediate the effect via work hypertrophy. Although intuitively plausible and consistent with hypertrophic obstructive changes similar to IHPS observed in hyperplastic rat ileum after artificially induced mechanical obstruction, there is no direct evidence of this phenomenon. Further complicating the association is the limitations of our knowledge about the pathophysiology of IHPS, including numerous genetic abnormalities, increased parietal cell mass, and gastric hyperacidity. The implications of the reported findings with erythromycin on the benefit-risk profiles of newer macrolides and azalides must be considered. The available data on the comparative gastrokinetic properties of macrolides are significant for the potent gastrokinetic properties and its acid degradation products, the marked variation in gastrokinetic properties associated with macrolide ring size, and the requirement for specific glycosidic linkages at the C-3 and C-5 carbons of the macrolide ring. The variation in gastrokinetic properties associated with variations in molecular structure suggests that if the association between erythromycin and IHPS is causal it may not be a class effect.

Pharmacology for the gastrointestinal tract

A variety of drugs are used in the neonatal nursery for the management of feeding intolerance, gastroesophageal reflux, and acid-related disease. Although the pharmacokinetics of some of these drugs have been described in infants and older children, further data are needed, particularly for preterm infants. No data are available characterizing the disposition of the proton pump inhibitors, which will likely be used in infants with refractory, acid-related disease. Further data are also needed to characterize fully the pharmacodynamics, or efficacy, of many of the commonly used drugs.

Antibiotics in neonatal infections: a review

The bacteria most commonly responsible for early-onset (materno-fetal) infections in neonates are group B streptococci, enterococci, Enterobacteriaceae and Listeria monocytogenes. Coagulase-negative staphylococci, particularly Staphylococcus epidermidis, are the main pathogens in late-onset (nosocomial) infections, especially in high-risk patients such as those with very low birthweight, umbilical or central venous catheters or undergoing prolonged ventilation. The primary objective of the paediatrician is to identity all potential cases of bacterial disease quickly and begin antibacterial treatment immediately after the appropriate cultures have been obtained. Combination therapy is recommended for initial empirical treatment in the neonate. In early-onset infections, an effective first-line empirical therapy is ampicillin plus an aminoglycoside (duration of treatment 10 days). An alternative is ampicillin plus a third-generation cephalosporin such as cefotaxime, a combination particularly useful in neonatal meningitis (mean duration of treatment 14 to 21 days), in patients at risk of nephrotoxicity and/or when therapeutic monitoring of aminoglycosides is not possible. Another potential substitute for the aminoglycoside is aztreonam. Triple combination therapy (such as amoxicillin plus cefotaxime and an aminoglycoside) could also be used for the first 2 to 3 days of life, followed by dual therapy after the microbiological results. In late-onset infections the combination oxacillin plus an aminoglycoside is widely recommended. However, vancomycin plus ceftazidime (+/- an aminoglycoside for the first 2 to 3 days) may be a better choice. Teicoplanin may be a substitute for vancomycin. However, the initial approach should always be modified by knowledge of the local bacterial epidemiology. After the microbiological results, treatment should be switched to narrower spectrum agents if a specific organism has been identified, and should be discontinued if cultures are negative and the neonate is in good clinical condition. Penicillins and third-generation cephalosporins are generally well tolerated in neonates. There is controversy regarding whether therapeutic drug monitoring of aminoglycosides will decrease toxicity (particularly renal damage) in neonates, and on the efficacy and safety of a single daily dose versus multiple daily doses of these drugs. Toxic effects caused by vancomycin are uncommon, but debate still exists over the need for therapeutic drug monitoring of this agent. When antibacterials are used in neonates, accurate determination of dosage is required, particularly for compounds with a low therapeutic index and in patients with renal failure. Very low birthweight infants are also particularly prone to antibacterial-induced toxicity.

Pharmacokinetics of anti-infective agents in paediatric patients

Various differences in drug disposition exist between children and adults. For example, the volume of distribution (Vd) for many drugs is larger in children than in adults. Other parameters, including excretion and elimination may be altered in children compared with adults. The penicillins and cephalosporins are used commonly for the treatment of infection in paediatric patients. The increased Vd in children contributes to the increased elimination half-life of these agents. Clearance of the acylureido-penicillins is increased in children with cystic fibrosis, a disease that decreases the elimination half-life for these drugs. Aminoglycosides distribute into extracellular fluid and their pharmacokinetic profile is affected by changes in Vd. The Vd for aminoglycosides is slightly higher in children than in adults. Children with cystic fibrosis, burns, or cancer have higher clearance rates and larger Vd values for aminoglycosides. Few data in the literature address the pharmacokinetics of other anti-infective agents, including vancomycin, teicoplanin, erythromycin, metronidazole, chloramphenicol, and cotrimoxazole (trimethoprim-sulfamethoxazole), in children. Similarly, there is little information regarding the pharmacokinetic profile of antivirals and antifungals in children. Dosage guidelines are available to enable the clinician to initiate anti-infective therapy in children. Subsequent dosage requirements may change based on the patient's current clinical condition. Although several studies have investigated the pharmacokinetics of anti-infectives in neonates and adults, data for children are limited. Therefore, further studies are required so that the ever growing arsenal of anti-infectives can be administered appropriately to children.

Clinical pharmacokinetics of antibacterial drugs in neonates

Neonatal patients are surviving longer due to the rapid advances in medical knowledge and technology. Our understanding of the developmental physiology of both preterm and full term neonates has also increased. It is now apparent that differences in body composition and organ function significantly affect the pharmacokinetics of antibacterial drugs in neonates, and dosage modifications are required to optimise antimicrobial therapy. The penicillins and cephalosporins are frequently used in neonates. Although ampicillin has replaced benzylpenicillin (penicillin G) for empirical treatment of neonatal sepsis, many of the other penicillins may be used in neonates for the management of various infections. Increased volume of distribution (Vd) and decreased total body clearance (CL) affect the disposition of penicillins and cephalosporins. Decreased renal clearance (CLR) due to decreased glomerular filtration and tubular secretion is responsible for the decreased CL for most of the beta-lactams. Aminoglycoside Vd is affected by the increased total body water content and extracellular fluid volume of neonates. The increased Vd, in part, accounts for the extended elimination half-life (t1/2) observed in neonates. Aminoglycoside CL is dependent on renal glomerular filtration which is markedly decreased in neonates, especially those preterm. These drugs appear to be less nephrotoxic and ototoxic in neonates than in older patients, and the role of serum concentration monitoring should be limited to specific neonatal patients. Other antibiotics such as vancomycin, teicoplanin, chloramphenicol, rifampicin, erythromycin, clindamycin, metronidazole and cotrimoxazole (trimethoprim plus sulfamethoxazole) may be used in certain clinical situations. The emergence of staphylococcal resistance to penicillins has increased the need for vancomycin. With the exceptions of vancomycin and chloramphenicol, the efficacy and safety of these other agents in neonates have not been established. The need for serum vancomycin concentration monitoring may be limited, as with aminoglycosides, while safety concerns warrant the routine monitoring of serum chloramphenicol concentrations in neonates. Dosing guidelines are provided, based on the pharmacokinetics of the drugs and previously published recommendations. These dosing guidelines are intended for initial therapy, and close therapeutic monitoring is recommended for maintenance dose requirements to optimise patient outcome. There has been an enormous increase in our knowledge of neonatal physiology and drug disposition. Fortunately, many of the antibacterial drugs used in neonates (e.g. penicillins and cephalosporins) are relatively safe. It will be important to evaluate all newly developed antibiotics in neonates to assure their maximum efficacy and safety.

Levels of erythromycin in tear fluid and serum in infants with conjunctivitis

38 newborns with purulent conjunctivitis were treated with oral erythromycin ethylsuccinate 25 mg/kg every 12 h for 14 days. 3-4 days after initiation of therapy, erythromycin levels in serum and tear fluid were measured 1 and 12 h after the administration of erythromycin. The level of erythromycin in tear fluid was significantly higher than that in serum 1 and 12 h after administration of the antibiotic. On both occasions the concentrations of erythromycin in tear fluid and in serum exceeded the minimum inhibitory concentration (MIC) in vitro for Chlamydia trachomatis.

Bioinequivalence of erythromycin ethylsuccinate and enteric-coated erythromycin pellets following multiple oral doses

Bioequivalence comparisons between erythromycin ethylsuccinate and an enteric-coated erythromycin base pellet product were made following multiple-dose, oral administration. Twenty-four volunteers participated in a ten-dose protocol (one dosage unit every six hours) using a complete crossover design. Plasma samples were assayed using a microbiological method specific for erythromycin base in the presence of the ester. Without correcting for the differences in doses administered, the amount of active erythromycin base absorbed from the enteric-coated pellet (250 mg base) was five to seven times that absorbed from the erythromycin ethylsuccinate product (400 mg base equivalent) at steady state. Erythromycin ethylsuccinate is not bioequivalent to an enteric-coated erythromycin base pellet product. The lower bioavailability of the ethylsuccinate may be due to instability in the acidic medium of the stomach.