Chloramphenicol disposition in infants and children

Tissue Penetration of Antimicrobials in Intensive Care Unit Patients: A Systematic Review-Part II

In patients that are admitted to intensive care units (ICUs), the clinical outcome of severe infections depends on several factors, as well as the early administration of chemotherapies and comorbidities. Antimicrobials may be used in off-label regimens to maximize the probability of therapeutic concentrations within infected tissues and to prevent the selection of resistant clones. Interestingly, the literature clearly shows that the rate of tissue penetration is variable among antibacterial drugs, and the correlation between plasma and tissue concentrations may be inconstant. The present review harvests data about tissue penetration of antibacterial drugs in ICU patients, limiting the search to those drugs that mainly act as protein synthesis inhibitors and disrupting DNA structure and function. As expected, fluoroquinolones, macrolides, linezolid, and tigecycline have an excellent diffusion into epithelial lining fluid. That high penetration is fundamental for the therapy of ventilator and healthcare-associated pneumonia. Some drugs also display a high penetration rate within cerebrospinal fluid, while other agents diffuse into the skin and soft tissues. Further studies are needed to improve our knowledge about drug tissue penetration, especially in the presence of factors that may affect drug pharmacokinetics.

Pharmacokinetics of antibacterial agents in the CSF of children and adolescents

The adequate management of central nervous system (CNS) infections requires that antimicrobial agents penetrate the blood-brain barrier (BBB) and achieve concentrations in the CNS adequate for eradication of the infecting pathogen. This review details the currently available literature on the pharmacokinetics (PK) of antibacterials in the CNS of children. Clinical trials affirm that the physicochemical properties of a drug remain one of the most important factors dictating penetration of antimicrobial agents into the CNS, irrespective of the population being treated (i.e. small, lipophilic drugs with low protein binding exhibit the best translocation across the BBB). These same physicochemical characteristics determine the primary disposition pathways of the drug, and by extension the magnitude and duration of circulating drug concentrations in the plasma, a second major driving force behind achievable CNS drug concentrations. Notably, these disposition pathways can be expected to change during the normal process of growth and development. Finally, CNS drug penetration is influenced by the nature and extent of the infection (i.e. the presence of meningeal inflammation). Aminoglycosides have poor CNS penetration when administered intravenously. Intrathecal gentamicin has been studied in children with more promising results, often exceeding the minimum inhibitory concentration. There are very limited data with intrathecal tobramycin in children. However, in the few patients that have been studied, the CSF concentrations were highly variable. Penicillins generally have good CNS penetration. Aqueous penicillin G reaches greater concentrations than procaine or benzathine penicillin. Concentrations remain detectable for ≥ 12 h. Of the aminopenicillins, both ampicillin and parenteral amoxicillin reach adequate CNS concentrations; however, orally administered amoxicillin resulted in much lower concentrations. Nafcillin and piperacillin are the final two penicillins with pediatric data: their penetration is erratic at best. Cephalosporins vary greatly in regard to their CSF penetration. Few first- and second-generation cephalosporins are able to reach higher CSF concentrations. Cefuroxime is the only exception and is usually avoided due to its adverse effects and slower sterilization of the CSF than third-generation agents. Ceftriaxone, cefotaxime, ceftazidime, cefixime and cefepime have been studied in children and are all able to adequately penetrate the CSF. As with penicillins, concentrations are greatest in the presence of meningeal inflammation. Meropenem and imipenem are the only carbapenems with pediatric data. Imipenem reaches higher CSF concentrations; however, meropenem is preferred due to its lower incidence of seizures. Aztreonam has also demonstrated favorable penetration but only one study has been completed in children. Both chloramphenicol and sulfamethoxazole/trimethoprim (cotrimoxazole) penetrate into the CNS well; however, significant toxicities limit their use. The small size and minimal protein binding of fosfomycin contribute to its favorable CNS PK. Although rarely used, it achieves higher concentrations in the presence of inflammation and accumulation is possible. Linezolid reaches high CSF concentrations; however, more frequent dosing might be required in infants due to their increased elimination. Metronidazole also has very limited information but it demonstrated favorable results similar to adult data; CSF concentrations even exceeded plasma concentrations at certain time points. Rifampin (rifampicin) demonstrated good CNS penetration after oral administration. Vancomycin demonstrates poor CNS penetration after intravenous administration. When combined with intraventricular therapy, CNS concentrations are much greater. Of the antituberculosis agents, isoniazid, pyrazinamide and streptomycin have been studied in children. Isoniazid and pyrazinamide have favorable CSF penetration. Streptomycin appears to produce unpredictable CSF levels. No pediatric-specific data are available for clindamycin, daptomycin, macrolides, tetracyclines, and fluoroquinolones. Daptomycin, fluoroquinolones, and tetracyclines have demonstrated favorable CNS penetration in adults; however, data are limited due to their potential pediatric-specific toxicities and newness within the marketplace. Macrolides and clindamycin have demonstrated poor CNS penetration in adults and thus have not been studied in pediatrics.

Association of treatment for bacterial meningitis with the development of sequelae

BACKGROUND

Bacterial meningitis continues to be a serious, often disabling infectious disease. The aim of this study was to assess the possibility that treatment influences the development of sequelae in childhood bacterial meningitis.

METHODS

Two thousand four hundred and seventy-seven patients aged 1 month to 14 years with acute bacterial meningitis over a 32-year period were enrolled in the study. Data were collected prospectively from the Meningitis Registry of a tertiary university teaching hospital in Athens, Greece. Treatment was evaluated through univariate and multivariate analysis with regard to sequelae: seizure disorder, severe hearing loss, ventriculitis, and hydrocephalus.

RESULTS

According to the multinomial logistic regression analysis, there was evidence that penicillin, an all-time classic antibiotic, had a protective effect on the occurrence of ventriculitis (odds ratio (OR) 0.17, 95% confidence interval (CI) 0.05-0.60), while patients treated with chloramphenicol had an elevated risk of ventriculitis (OR 17.77 95% CI 4.36-72.41) and seizure disorder (OR 4.72, 95% CI 1.12-19.96). Cephalosporins were related to an increased risk of hydrocephalus (OR 5.24, 95% CI 1.05-26.29) and ventriculitis (OR 5.72, 95% CI 1.27-25.76). The use of trimethoprim/sulfamethoxazole increased the probability of seizure disorder (OR 3.26, 95% CI 1.08-9.84) and ventriculitis (OR 8.60, 95% CI 2.97-24.91). Hydrocortisone was associated with a rise in hydrocephalus (OR 5.44, 95% CI 1.23-23.45), while a protective effect of dexamethasone (OR 0.82, 95% CI 0.18-3.79) was not statistically significant.

CONCLUSIONS

Current study findings suggest that the type of antimicrobial treatment for childhood bacterial meningitis may influence in either a positive or a negative way the development of neurological sequelae.

Chloramphenicol toxicity revisited: a 12-year-old patient with a brain abscess

Chloramphenicol, a broad-spectrum antibiotic, is rarely used in the United States due to its well-described adverse effects. Because of its limited use, many clinicians are unfamiliar with its indications, spectrum of activity, and potential adverse drug effects. We describe a 12-year-old patient who presented after two craniotomies for a persistent brain abscess complicated by long-term chloramphenicol administration. Findings for this patient were consistent with many of the adverse drug effects associated with chloramphenicol, including elevated chloramphenicol serum concentrations, anemia, thrombocytopenia, reticulocytopenia, and severe metabolic acidosis. Rare manifestations of chloramphenicol toxicity that developed in this patient included neutropenia, visual field changes, and peripheral neuropathy. Chloramphenicol administration was discontinued, and hemodialysis was initiated for severe metabolic acidosis. The patient recovered with severe visual field deficits. Although chloramphenicol is rarely indicated, it remains an effective antibiotic. Healthcare providers should become familiar with the pharmacology, toxicology, and monitoring parameters for appropriate use of this antibiotic.

Multispectroscopic Study of the Interaction of Chloramphenicol with Human Neuroglobin

The interaction between chloramphenicol (CHL) and neuroglobin (Ngb) has been investigated by using fluorescence, synchronous fluorescence, UV-Vis and circular dichroism (CD) spectroscopy. It has been found that CHL molecule can quench the intrinsic fluorescence of Ngb in a way of dynamic quenching mechanism, which was supported by UV-Vis spectral data. Their effective quenching constants (KSV) are2.2×104,2.6×104,and 3.1×104 L⋅mol−1at 298 K, 303 K, and 308 K, respectively. The enthalpy change (ΔH) and entropy change (ΔS) for this reaction are 26.42 kJ⋅mol−1and 171.7 J⋅K−1, respectively. It means that the hydrophobic interaction is the main intermolecular force of the interaction between CHL and Ngb. Synchronous fluorescence spectra showed that the microenvironment of tryptophan and tyrosine residues of Ngb has been changed slightly. The fluorescence quenching efficiency of CHL to tyrosine residues is a little bit more than that to tryptophan residues of Ngb. Furthermore, CD spectra indicated that CHL can induce the formation of α-helix of Ngb.

Overton's rule helps to estimate the penetration of anti-infectives into patients' cerebrospinal fluid

In 1900, Ernst Overton found that the entry of anilin dyes through the cell membranes of living cells depended on the lipophilicity of the dyes. The brain is surrounded by barriers consisting of lipid layers that possess several inward and outward active transport systems. In the absence of meningeal inflammation, the cerebrospinal fluid (CSF) penetration of anti-infectives in humans estimated by the ratio of the area under the concentration-time curve (AUC) in CSF (AUC(CSF)) to that in serum (AUC(CSF)/AUC(S)) correlated positively with the lipid-water partition coefficient at pH 7.0 (log D) (Spearman's rank correlation coefficient r(S) = 0.40; P = 0.01) and negatively with the molecular mass (MM) (r(S) = -0.33; P = 0.04). The ratio of AUC(CSF) to the AUC of the fraction in serum that was not bound (AUC(CSF)/AUC(S,free)) strongly correlated with log D (r(S) = 0.67; P < 0.0001). In the presence of meningeal inflammation, AUC(CSF)/AUC(S) also correlated positively with log D (r(S) = 0.46; P = 0.002) and negatively with the MM (r(S) = -0.37; P = 0.01). The correlation of AUC(CSF)/AUC(S,free) with log D (r(S) = 0.66; P < 0.0001) was as strong as in the absence of meningeal inflammation. Despite these clear correlations, Overton's rule was able to explain only part of the differences in CSF penetration of the individual compounds. The site of CSF withdrawal (lumbar versus ventricular CSF), age of the patients, underlying diseases, active transport, and alterations in the pharmacokinetics by comedications also appeared to strongly influence the CSF penetration of the drugs studied.

Penetration of drugs through the blood-cerebrospinal fluid/blood-brain barrier for treatment of central nervous system infections

The entry of anti-infectives into the central nervous system (CNS) depends on the compartment studied, molecular size, electric charge, lipophilicity, plasma protein binding, affinity to active transport systems at the blood-brain/blood-cerebrospinal fluid (CSF) barrier, and host factors such as meningeal inflammation and CSF flow. Since concentrations in microdialysates and abscesses are not frequently available for humans, this review focuses on drug CSF concentrations. The ideal compound to treat CNS infections is of small molecular size, is moderately lipophilic, has a low level of plasma protein binding, has a volume of distribution of around 1 liter/kg, and is not a strong ligand of an efflux pump at the blood-brain or blood-CSF barrier. When several equally active compounds are available, a drug which comes close to these physicochemical and pharmacokinetic properties should be preferred. Several anti-infectives (e.g., isoniazid, pyrazinamide, linezolid, metronidazole, fluconazole, and some fluoroquinolones) reach a CSF-to-serum ratio of the areas under the curves close to 1.0 and, therefore, are extremely valuable for the treatment of CNS infections. In many cases, however, pharmacokinetics have to be balanced against in vitro activity. Direct injection of drugs, which do not readily penetrate into the CNS, into the ventricular or lumbar CSF is indicated when other effective therapeutic options are unavailable.

Successful treatment of vancomycin-resistant Enterococcus faecium ventriculitis with combined intravenous and intraventricular chloramphenicol in a newborn

Vancomycin-resistant Enterococcus faecium (VRE) infection is a rare event in paediatric patients and often occurs under immunosuppression or after surgical intervention. We report what we believe to be the first paediatric case of ventriculitis due to VRE (in a 2-month-old infant) to be successfully treated with combined intravenous (i.v.) and intraventricular chloramphenicol after failure of i.v. linezolid and intraventricular gentamicin.

Parenteral antibiotics for the treatment of serious neonatal bacterial infections in developing country settings

BACKGROUND

A number of special issues must be considered when selecting simple, safe, inexpensive, and effective antimicrobial regimens for treatment of neonatal sepsis in developing country community settings.

METHODS

We reviewed available data regarding pharmacologic profiles of parenteral antibiotics with specific attention to properties relevant to their use in the treatment of neonatal infections in developing country communities.

RESULTS

For community-based management of neonatal infections, particularly attractive properties include efficacy and safety of extended-interval, intramuscular dosing regimens. The penicillins and cephalosporins have relatively favorable efficacy and safety profiles. Although the aminoglycosides have narrow therapeutic indices, when used appropriately, they are safe and effective. Although inexpensive and effective, the potential for significant life-threatening toxicity among neonates associated with chloramphenicol makes it the least preferred of the parenteral agents for empiric therapy.

CONCLUSIONS

The preferred parenteral regimens for community and first-level facility use are a combination of procaine penicillin G and gentamicin, or ceftriaxone given alone, which are safe and retain efficacy when dosed at extended intervals (> or =24 hours) by intramuscular administration.

Pharmacokinetic optimisation of the treatment of bacterial central nervous system infections

Central nervous system (CNS) infections caused by bacteria with reduced sensitivity to antibacterials are an increasing worldwide challenge. In successfully treating these infections the following conditions should be considered: (i) Antibacterials do not distribute homogeneously in the central nervous compartments [cerebrospinal fluid (CSF), extracellular space of the nervous tissue, intracellular space of the neurons, glial cells and leucocytes]. Even within the CSF, after intravenous administration, a ventriculo-lumbar concentration gradient is often observed. (ii) Valid parameters of drug entry into the CSF are the CSF: serum concentration ratio in steady state and the CSF: serum ratio of the area under the concentration-time curves (AUCCSF/AUCS). Frequently, the elimination half-life (t1/2 beta) in CSF is longer than t1/2 beta in serum. (iii) For most antibacterials, lipophilicity, molecular weight and serum protein binding determine the drug entry into the CSF and brain tissue. With an intact blood-CSF and blood-brain barrier, the entry of hydrophilic antibacterials (beta-lactam antibacterials, glycopeptides) into the CNS compartments is poor and increases during meningeal inflammation. More lipophilic compounds [metronidazole, quinolones, rifampicin (rifampin) and chloramphenicol] are less dependent on the function of the blood-CSF and blood-brain barrier. (iv) Determination of the minimal inhibitory concentrations (MIC) of the causative organism is necessary for optimisation of treatment. (v) For rapid sterilisation of CSF, drug concentrations of at least 10 times MIC are required. The minimum CSF concentration: MIC ratio ensuring successful therapy is unknown. Strategies to achieve optimum antibacterial concentrations in the presence of minor disturbances of the blood-CSF and blood-brain barrier include, the increased use of low toxicity antibacterials (e.g., beta-lactam antibiotics), the use of moderately lipophilic compounds, and the combination of intravenous and intraventricular administration. Antibacterials which do not interfere with bacterial cell wall synthesis delay and/or decrease the liberation of proinflammatory bacterial products, delay or inhibit tumour necrosis factor release, and may reduce brain oedema in experimental meningitis. Conclusive evidence of the reduction of neuronal damage by this approach, however, is lacking.

Decrease in the placental transfer of chloramphenicol when administered in albumin microspheres into rats

Chloramphenicol is an antibiotic which can pass across the human placenta and has teratogenic effects in the foetus. When this antibiotic is entrapped in albumin microspheres and administered to pregnant rats intravenously its placental transport is significantly lowered when compared with that of free drug. Drug modifications such as entrapment are suggested as an alternative way to prevent harmful effects of drugs in case of consumption during pregnancy.

Chloramphenicol clearance in typhoid fever: implications for therapy

We prospectively studied the pharmacokinetics of intravenous Chloramphenicol succinate (CS) in children (age 6 months-14 years) with culture proven typhoid fever (n = 30) and non typhoidal illnesses (n = 10). CS was administered in three different dosage regimens (50, 75 and 100 mg/kg/d-q 6 hourly). Liver function tests were monitored. Plasma trough and peak chloramphenicol concentrations were measured by HPLC analysis after 42 hrs. The 50 mg/kg/day dosage schedule was terminated midway through the study, as blood levels were consistently low and two patients with typhoid relapsed, children with typhoid had significantly lower clearance of CS in comparison with those with non-typhoidal illness (0.29 +/- 0.1 versus 0.5 +/- 0.37 1/kg/hr, P 0.05). There was no significant difference between mean peak and trough concentrations of chloramphenicol on 100 mg/kg/day and 75 mg/kg/day in children with typhoid. However, two children on 100 mg/kg/day dosage developed trough concentrations greater than 20 mcg/ml. No correlation was found between CS clearance and serum bilirubin, SGPT (alanine transaminase) and alkaline phosphatase. Our data show altered clearance of CS in children with typhoid and suggests that 75 mg/kg/day may be a safer dose in children with hepatic dysfunction in typhoid.

Antibiotic treatment of community acquired bacterial meningitis

Community acquired meningitis is predominantly caused by three agents: Haemophilus influenzae, Streptococcus pneumoniae and Neisseria meningitidis Four physical properties of available drugs--molecular size, protein binding, lipid solubility and ionization--affect drug entry to the central nervous system (CNS). These factors, coupled with acute changes in blood-brain barriers and intrinsic bactericidal activity, have a bearing on the success of treatment with all agents. Third generation cephalosporins have largely supplanted older regimens due to their intrinsic qualities of greater bactericidal activity, optimal cerebrospinal fluid pharmacokinetics, and low toxicity. The pharmacological principles of treatment of CNS bacterial infections, pharmacology of available drugs, and current treatment recommendations are reviewed.

Lack of predictability of chloramphenicol toxicity in paediatric patients

We studied 45 patients (new-born to 12 year olds) who received 50-100 mg/kg/day chloramphenicol sodium succinate i.v. over 2-49 days for the treatment of central nervous system infections. Multiple blood samples were obtained to measure serum concentrations of chloramphenicol and its succinate ester by high pressure liquid chromatography (HPLC). Haematological parameters (haemoglobin, white cell, neutrophil, eosinophil and platelet counts) were also determined. Chloramphenicol therapy was effective in all patients. Anaemia was present in 10, leukopenia in four, neutropenia in four, and eosinophilia in 16 patients. These adverse effects occurred between 3 and 34 days after the initiation of therapy. Chloramphenicol therapy had to be discontinued only in three patients, who had absolute neutrophil counts less than 800/mm3. All adverse effects were reversible. Demographic factors, daily dose, duration of therapy, steady-state peak and trough serum concentrations, area under the serum concentration-time curve normalized for dose, and the elimination half-life were not correlated with the occurrence of adverse effects of chloramphenicol. The mean cumulative dose of chloramphenicol succinate was the only factor always higher but not statistically different in patients with adverse effects compared to those without. The mean cumulative dose of chloramphenicol succinate ranged from 1.2 to 1.8 g/kg in patients with adverse effects and 0.9-1.1 g/kg in those without. These data suggest that the adverse effects of chloramphenicol may not be predictable in paediatric patients. However, a high cumulative dose may possibly be an important factor in predisposing some patients to certain chloramphenicol toxicity.

Absence of a pharmacokinetic interaction between chloramphenicol and acetaminophen in children

The pharmacokinetics of chloramphenicol (CAP; administered intravenously as chloramphenicol succinate, CAPS) was studied in 26 acutely ill febrile children 3 to 58 months of age who either did (n = 18) or did not (n = 8) receive acetaminophen (APAP) for antipyresis. CAP pharmacokinetics were evaluated after the first dose and at steady state. CAP serum levels were quantitated by high-performance liquid chromatography. There were no significant differences between groups (APAP vs non-APAP) or between first dose and steady-state evaluations for the elimination rate constant, serum half-life, apparent volume of distribution, and serum clearance of CAP. Likewise, there were no statistically significant differences when the APAP group was evaluated according to the presence or absence of APAP in serum before the first dose of CAP. Elimination of CAP in subjects with serum CAPS level less than 1 microgram/ml was similar in the first dose and steady-state evaluations and in the APAP and non-APAP groups. The presence or absence of CAPS or APAP did not affect the estimation of CAP elimination. Thus a pharmacokinetic interaction between CAP and APAP was not demonstrated in acutely ill febrile children during concomitant therapy.

Current therapy of acute bacterial meningitis in children: Part II

Despite many advances in the past decade in the development of new antimicrobials, acute bacterial meningitis continues to have significant morbidity and mortality in infants and children. Regardless of the effectiveness of the antibiotic preparations, future improvements in outcome is most likely to occur because of more rapid diagnosis and initiation of therapy. The standard penicillins, chloramphenicol, and the aminoglycosides continue to hold an important place in treatment. The recent introduction of new extended spectrum penicillins, including piperacillin and mezlocillin, in addition to the development of the third generation cephalosporins, have expanded alternatives for treating bacterial meningitis. The most appropriate and effective antibiotic or combination of antibiotics must first be selected; thereafter, its use must be monitore to identify its beneficial effects as well as possible adverse effects.

Clinical pharmacokinetics of chloramphenicol and chloramphenicol succinate

In recent years there has been a renewal of interest in chloramphenicol, predominantly because of the emergence of ampicillin-resistant Haemophilus influenzae, the leading cause of bacterial meningitis in infants and children. Three preparations of chloramphenicol are most commonly used in clinical practice: a crystalline powder for oral administration, a palmitate ester for oral administration as a suspension, and a succinate ester for parenteral administration. Both esters are inactive, requiring hydrolysis to chloramphenicol for anti-bacterial activity. The palmitate ester is hydrolysed in the small intestine to active chloramphenicol prior to absorption. Chloramphenicol succinate acts as a prodrug, being converted to active chloramphenicol while it is circulating in the body. Various assays have been developed to determine the concentration of chloramphenicol in biological fluids. Of these, high-performance liquid chromatographic and radioenzymatic assays are accurate, precise, specific, and have excellent sensitivities for chloramphenicol. They are rapid and have made therapeutic drug monitoring practical for chloramphenicol. The bioavailability of oral crystalline chloramphenicol and chloramphenicol palmitate is approximately 80%. The time for peak plasma concentrations is dependent on particle size and correlates with in vitro dissolution and deaggregation rates. The bioavailability of chloramphenicol after intravenous administration of the succinate ester averages approximately 70%, but the range is quite variable. Incomplete bioavailability is the result of renal excretion of unchanged chloramphenicol succinate prior to it being hydrolysed to active chloramphenicol. Plasma protein binding of chloramphenicol is approximately 60% in healthy adults. The drug is extensively distributed to many tissues and body fluids, including cerebrospinal fluid and breast milk, and it crosses the placenta. Reported mean values for the apparent volume of distribution range from 0.6 to 1.0 L/kg. Most of a chloramphenicol dose is metabolised by the liver to inactive products, the chief metabolite being a glucuronide conjugate; only 5 to 15% of chloramphenicol is excreted unchanged in the urine. The elimination half-life is approximately 4 hours. Inaccurate determinations of the pharmacokinetic parameters may result by incorrectly assuming rapid and complete hydrolysis of chloramphenicol succinate. The pharmacokinetics of chloramphenicol succinate have been described by a 2-compartment model. The reported values for the apparent volume of distribution range from 0.2 to 3.1 L/kg.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacokinetics of chloramphenicol in the neonatal horse

Chloramphenicol sodium succinate was administered as an intravenous bolus (50 mg/kg) to eight foals which weighed 49-57 kg (mean +/- 1 standard deviation = 53.19 +/- 2.66) each, and were 1-9 days (4.5 +/- 2.56) of age. The drug was rapidly distributed and followed first-order elimination. Mean pharmacokinetic values were: zero-time serum concentration (C0) = 36.14 microgram/ml (+/- 14.80); apparent specific volume of distribution (Vd) = 1.614 1/kg (+/- 0.669); and elimination rate constant (K) = 0.7295 h-1 (+/- 0.3066) which corresponds to a biological half-life (t1/2) = 0.95 h. These values do not differ greatly from those reported for adult horses and ponies. A suspension of chloramphenicol was administered by nasogastric tube (50 mg/kg) to a second group of seven foals which weighed 49 to 57 kg (51.34 +/- 2.82) each and were 1 to 7 days (4.43 +/- 1.90) of age. A mean peak serum chloramphenicol concentration of 23.97 microgram/ml (+/- 7.06) was achieved 1.14 h (+/- 0.63) after administration. The bioavailability of this preparation was 83.27 percent.

Chloramphenicol pharmacokinetics in Ethiopian children of differing nutritional status

The pharmacokinetics of i.v. chloramphenicol succinate and oral chloramphenicol palmitate were studied in Ethiopian children with different nutritional states. In children with kwashiorkor the plasma clearance of chloramphenicol was significantly lower than in children of normal weight (4.16 ml/min/kg versus 7.53 ml/min/kg). In consequence the mean half-life was prolonged (3.76 h versus 2.85 h) and this led to somewhat higher plasma levels in the kwashiorkor children. The influence of the pathophysiological changes offset one another so that plasma concentrations within the therapeutic range were obtained in children with kwashiorkor given recommended standard i.v. doses. The absorption of chloramphenicol after oral administration in severely malnourished children was erratic, which suggests that this route should be avoided in such patients.

Initiation of chloramphenicol therapy in the newborn infant

To evaluate the ability of a loading dose of chloramphenicol succinate to rapidly, achieve adequate serum concentrations of chloramphenicol, we compared two intravenously administered dosages of chloramphenicol succinate given to initiate treatment. Thirteen premature neonates received an initial dose of 12.5 mg/kg; 26 received a loading dose of 20 mg/kg. Capillary blood samples were obtained at two, four, and 12 hours after the first dose. After the dose of 12.5 mg/kg, 45% of the neonates did not achieve serum concentrations greater than 10 mg/L. After the loading dose of 20 mg/kg, all neonates achieved concentrations greater than 10 mg/L. The peak chloramphenicol concentrations after the 12.5 mg/kg dose was 8.8 +/- 11.2 mg/L (+/- SEM) and after the 20 mg/kg loading dose, 15.9 +/- 0.7 mg/L. The disposition of chloramphenicol was age dependent. Chloramphenicol concentration peaked at four hours in neonates less than or equal to 2 days postnatal age and at two hours in neonates 3 to 55 days postnatal age. Chloramphenicol succinate concentrations were greater in younger than in older neonates at both two and four hours after the dose. We conclude that a loading dose is appropriate when using chloramphenicol succinate in neonates.

Chloramphenicol: new perspectives on an old drug

Chloramphenicol is an old antibiotic being used with increasing frequency in serious childhood infections largely due to the emergence of ampicillin-resistant Hemophilus influenzae type b. Because of this renewed popularity and the recent availability of accurate analytical techniques for measurement of chloramphenicol, there have been many recent articles examining the pharmacokinetics of chloramphenicol and its two major prodrug esters, chloramphenicol succinate and chloramphenicol palmitate. New data from these studies include the incomplete bioavailability of chloramphenicol succinate, the possible superior bioavailability of chloramphenicol palmitate vs. chloramphenicol succinate, and the wide interpatient variability in chloramphenicol clearance. These observations, coupled with the known serious hematologic toxicity (reversible bone marrow suppression or irreversible aplastic anemia) and metabolic toxicity (gray baby syndrome) associated with chloramphenicol use, require that initial antibiotic doses be selected by age and be carefully individualized by measurement of peak serum chloramphenicol concentrations.

Chloramphenicol clearance in infants

Chloramphenicol clearance was evaluated over one dosing interval in 10 infants after at least 24 hours of therapy to evaluate dosage guidelines using a specific chemical assay. Serum samples were obtained prior to and at 1, 2, 4, and 6 hours after the start of a 20-minute infusion of 24 mg/kg chloramphenicol as the sodium succinate. The chemical assay used is technically simple and is specific for unesterified chloramphenicol. Peak serum concentrations ranged from 20.9 to 94.0 microgram/ml and occurred from 1 to 4 hours after infusion. Clearances ranged from 0.058 to 0.236 l./kg . hr and paralleled previously reported results using different assay methodology. The 4-hour serum chloramphenicol concentrations were significantly lower (P less than 0.05) in infants on phenobarbital. The currently recommended dose of chloramphenicol for severe infections, 100 mg/kg per day, is excessive in some infants. Widely divergent clearance rates prohibit uniform dosage guidelines so that serum level monitoring with an assay specific for chloramphenicol is essential.

Oral chloramphenicol in the treatment of Haemophilus influenzae meningitis

We conducted a prospective, randomized evaluation of oral chloramphenicol administration for completion of therapy of Haemophilus influenza type b meningitis in 44 children: 21 received drug by this route after the second day of therapy, the remainder continued to receive the drug intravenously. Resolution of clinical manifestations and cerebrospinal fluid indicators of meningitis was equivalent with both routes in 43 patients. One infant failed to achieve efficacious serum concentrations by either route of administration. Paired analysis of the area under the serum concentration versus time curve in 13 patients after oral and intravenous administration indicated equivalent bioavailability. Neutropenia was the only observed drug-related toxicity and correlated with the highest observed serum concentration. We conclude that: (1) chloramphenicol can be used by the oral route to complete treatment of H. influenzae type b meningitis; (2) a dose of 75 mg/kg/day is effective and less likely than higher doses to cause neutropenia; and (3) the measurement of serum chloramphenicol concentrations is important, regardless of route of administration.

Relative bioavailability of intravenous chloramphenicol succinate and oral chloramphenicol palmitate in infants and children

The relative bioavailability of intravenously administered chloramphenicol succinate and orally administered chloramphenicol palmitate was compared in 18 children, age 2 months to 14 years. The area under the serum concentration vs time curve of chloramphenicol and urinary excretion of chloramphenicol succinate were determined in each child under steady-state conditions while receiving chloramphenicol succinate and again while receiving chloramphenicol palmitate. The mean AUC was significantly greater during oral therapy compared to intravenous therapy (110 vs 78 mg hr/L, P less than 0.001). The relative bioavailability of chloramphenicol succinate was 70% compared to chloramphenicol palmitate. This could be explained by the mean loss of 36% of the intravenous dose in the urine as unhydrolyzed chloramphenicol succinate. The intravenous dose of chloramphenicol succinate did not correlate with AUC (r = 0.193). However, there was a significant correlation between the oral dose of chloramphenicol palmitate and AUC (r = 0.429, P = 0.025). The bioavailability of orally administered chloramphenicol palmitate is superior to that of chloramphenicol succinate given intravenously. Furthermore, there is a greater correlation between dose and amount of active drug in the body when the oral preparation is used. Oral administration of chloramphenicol palmitate appears to offer significant therapeutic advantages in patients who can tolerate medication given orally.

Effect of intravenous flow rate and injection site on in vitro delivery of chloramphenicol succinate and in vivo kinetics

The delivery rates of chloramphenicol succinate from a standard pediatric intravenous infusion set were studied in vitro at varying flow rates and injection sites of the infusion set. The pharmacokinetic properties of CAPS and chloramphenicol were then studied in 15 children given intravenous injections of CAPS via the infusion set at the flashball and Buretrol sites in a crossover fashion on successive days. In vitro, the actual times required for 95% delivery of CAPS from the infusion set were two- to fourfold longer than the predicted infusion times at flow rates of 5, 15, and 29 ml/min and at all three available injection sites. In vivo, flashball injections vs Buretrol injections resulted in significantly higher mean peak serum concentrations of CAPS and CAP, with peaks occurring significantly sooner after the beginning of the intravenous infusion. These results suggest a need for considering characteristics of CAPS infusion when monitoring and interpreting serum concentration values.

Susceptibility of Haemophilus influenzae to chloramphenicol and eight beta-lactam antibiotics

We examined the minimal inhibitory concentrations and minimal bactericidal concentrations of chloramphenicol, ampicillin, ticarcillin, cefamandole, cefazolin, cefoxitin, cefotaxime, ceforanide, and moxalactam for 100 isolates of Haemophilus influenzae, 25 of which produced beta-lactamase. Susceptibility was not influenced by the capsular characteristic of the organism. The mean minimal inhibitory concentrations of cefamandole, ticarcillin, and ampicillin for beta-lactamase-producing strains were 3-, 120-, and 400-fold higher than their respective mean minimal inhibitory concentrations for beta-lactamase-negative strains. No such difference was noted for the other antibiotics. We performed time-kill curve studies, using chloramphenicol, ampicillin, cefamandole, cefotaxime, and moxalactam with two concentrations of the antimicrobial agents (4 or 20 times the minimal inhibitory concentrations) and two inoculum sizes (10(4) or 10(6) colony-forming units per ml). The inoculum size had no appreciable effect on the rate of killing of beta-lactamase-negative strains. The rates at which beta-lactamase-producing strains were killed by chloramphenicol, cefotaxime, and moxalactam was not influenced by the inoculum size. Whereas cefamandole in high concentrations was able to kill at 10(6) colony-forming units/ml of inoculum, it had only a temporary inhibiting effect at low drug concentrations. Methicillin and the beta-lactamase inhibitor CP-45,899 were able to neutralize the inactivation of cefamandole by a large inoculum of beta-lactamase-producing H. influenzae.

Antimicrobial penetration into cerebrospinal fluid

The complex physiology of the blood-brain barrier and the characteristics of an antimicrobial which govern its distribution into the brain are poorly understood. Likewise, available data regarding CSF antimicrobial concentrations after extra-CNS administration, as tabulated in this review, are inadequate. Because of the potentially dire consequences that result from inappropriately treated CNS infections, large cooperative studies using standardized methodology are needed. Suggestions for such methods are outlined.

Treatment of bacterial infections of the central nervous system

Antimicrobial agents for the treatment of bacterial meningitis and other pyogenic intracranial infections have now been in use for approximately 45 years. The last decade, however, has been a period of tremendous advances in knowledge of the pharmacokinetics and other characteristics of the available drugs. The identification of factors that affect their in vivo metabolism and excretion, the importance of drug interactions, and the development of methods for estimation of serum and cerebrospinal fluid levels have added both complexity and sophistication to the clinical utilization of the antimicrobial agents. The number of available antimicrobials has expanded greatly during recent years, although the penicillins, chloramphenicol, and the aminoglycosides remain the mainstay of antibiotic treatment in the majority of cases of bacterial infection of the central nervous system.

Pharmacokinetics of chloramphenicol and chloramphenicol succinate in infants and children

The metabolism and elimination of chloramphenicol-3-monosuccinate was studied in 45 infants and children, ages 3 days to 16 years, during intravenous administration. The apparent half-life of chloramphenicol was extremely variable, ranging from 1.7 to 12.0 hours with a mean of 5.1 hours. Apparent half-lives were inversely correlated with age. Chloramphenicol-S serum concentration declined biexponentially in most patients, with an estimated mean initial half-life of 0.7 hours and a subsequent longer mean half-life of 2.2 hours. Chloramphenicol-S persisted in serum up to six hours after a dose, and comprised a significantly larger fraction of total chloramphenicol in the serum of infants under one month of age than in older infants and children. A widely variable fraction of the administered chloramphenicol-S dose, with a mean of 33%, was excreted in the urine unchanged and was, therefore, not bioavailable in active form. Mean renal clearance of chloramphenicol-S was 259.5 ml/minute/1.73 M2, four times the mean creatinine clearance, indicating active tubular secretion. Variable hydrolysis and renal elimination of nonhydrolyzed chloramphenicol-S reduces the bioavailability of the antibiotic and appears to contribute substantially to the wide variation in apparent half-life and poor correlation between dose and serum concentration of free chloramphenicol.