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.

[Measuring linezolid in biological fluids using high-efficiency liquid chromatography]. / Determinación de linezolid en fluidos biológicos mediante cromatografía líquida de alta eficacia.

OBJECTIVE: Evaluation of an analytic method for determining linezolid concentrations in biological fluids including plasma, vitreous humour and cerebrospinal fluid using high-efficiency liquid chromatography and subsequent ultraviolet detection. METHOD: The method was validated by studying the following parameters: accuracy, precision, sensitivity, linearity and recovery. The drug was extracted from the biological matrix by means of a protein precipitation with perchloric acid. Chromatographic separation was performed by eluting linezolid with a mobile phase consisting of 80% K2HPO4 buffer solution (15 mM; pH=5) and 20% acetonitrile, and a stationary phase, NOVAPAK C18 150x3.9 mm with precolumn. The wavelength reading was 254 nm and the working flow rate was 1 ml/min. RESULTS: We obtained values with accuracies between 94.4 and 106.1%, and precisions between 0.88-6% and 3.7-5.6% for intra-and inter-day variability, respectively. Recovery obtained after analysing the plasma samples was at 93%. The method showed itself to be linear for the concentration levels under study. DISCUSSION: The method's behaviour can be described as linear, precise and accurate. Furthermore, the method is fast, sensitive, and inexpensive. It is useful for determining linezolid concentrations in multiple biological matrices. It can also be used as a basis for further clinical pharmacokinetic studies.

Evaluation of antimicrobial regimens in a guinea-pig model of meningitis caused by Pseudomonas aeruginosa.

To compare the efficacy of meropenem, ceftazidime, tobramycin and ceftazidime+tobramycin in a guinea-pig model of P. aeruginosa meningitis. After anesthesia, the atlanto-occipital membrane was punctured with a butterfly needle and 100 microl of a solution containing 10(6)CFU/ml of P. aeruginosa were injected directly into the cisterna magna. Four h later, therapy was initiated with saline or antibiotics given im for 48 h in doses that obtained CSF levels as in human meningitis: ceftazidime 200 mg/kg/8h, meropenem 200 mg/kg/8h, tobramycin 30 mg/kg/24h. Tobramycin was also given intracisternally. Animals were sacrificed at different time points. CSF and blood samples were collected and a meningeal swab was performed. Four hours after inoculation, bacterial concentration in CSF was 4 to 5log10CFU and mean WBC was 16,000/-l. All control animals died in 24h with a 12% increase in cerebral edema. All blood-cultures were negative. Ceftazidime, ceftazidime+tobramycin and meropenem reduced the CSF bacterial concentration at 8h by 2.5log10. At 48 h all CSF cultures were sterile but meningeal swab cultures remained positive in 30%. Our results suggest that meropenem may be at least as effective as ceftazidime and that the addition of tobramycin to ceftazidime may improve its efficacy.

The contribution of pharmacokinetic-pharmacodynamic modelling with Monte Carlo simulation to the development of susceptibility breakpoints for Neisseria meningitidis.

This study used pharmacokinetic-pharmacodynamic (PK-PD) modelling and MICs of 15 antimicrobial agents, derived from testing a large international culture collection, to assist in the development of interpretative criteria, i.e., breakpoints, for Neisseria meningitidis. PK parameters, protein binding, percentage penetration into cerebrospinal fluid (CSF), and the variability of these values, were extracted from the published literature for the 15 agents. PK-PD parameters have not been developed specifically for N. meningitidis in animal or human studies. Thus, it was necessary to invoke PK-PD targets from other organisms that cause infections at similar sites. The PK-PD targets utilised were: time above the MIC for at least 50% of the dosing interval for all beta-lactams, chloramphenicol, sulphafurazole and trimethoprim-sulphamethoxazole; an AUC/MIC ratio of >or=25 for the tetracyclines and macrolides; and an AUC/MIC ratio of >or=125 for the fluoroquinolones. A 10 000-subject Monte Carlo simulation was designed with the usual dosing regimens of each antimicrobial agent at MIC values of 0.03-64 mg/L in both serum and CSF. The PK-PD breakpoint was defined as the MIC at which the calculated target attainment was >or=95%. Using these assumptions, the proposed PK-PD breakpoints were: azithromycin, 0.125 mg/L; doxycycline, 0.25 mg/L; cefotaxime, ciprofloxacin and levofloxacin, 0.5 mg/L; penicillin G, meropenem, rifampicin, tetracycline and minocycline, 1 mg/L; chloramphenicol and sulphafurazole, 2 mg/L; and ampicillin, ceftriaxone and trimethoprim-sulphamethoxazole, 4 mg/L. Proposed PK-PD breakpoints applicable to CSF were: penicillin and cefotaxime, 0.06 mg/L; rifampicin, 0.125 mg/L; ceftriaxone, meropenem and trimethoprim-sulphamethoxazole, 0.25 mg/L; ampicillin, 0.5 mg/L; and chloramphenicol, 1 mg/L.

Levels of antimicrobial molecules defensin and lactoferrin are elevated in the cerebrospinal fluid of children with meningitis.

OBJECTIVE: To measure levels of defensins and lactoferrin in the cerebrospinal fluid (CSF) of children with meningitis. STUDY DESIGN. Prospective descriptive study involving children undergoing lumbar puncture during evaluation for meningitis. METHODS: CSF concentrations of defensins and lactoferrin were determined using enzyme-linked immunosorbent assays on 19 children with bacterial meningitis, 31 children with aseptic meningitis, and 32 control children found to have normal CSF during evaluation for meningitis. Pertinent clinical and laboratory data were gathered on all children. RESULTS: CSF concentrations of both defensins and lactoferrin were elevated markedly in children with bacterial and aseptic meningitis, compared with control children. No control subject had detectable levels of defensins in the CSF. Lactoferrin was undetectable in the CSF of 31 of 32 control subjects. Defensin and lactoferrin levels were significantly higher in the CSF of children with bacterial meningitis than in those with aseptic meningitis. Defensin levels in the CSF of children with bacterial meningitis ranged from 128 ng/mL to 99 430 ng/mL with a mean of 30 311 ng/mL (SD +/- 28 865) and a median of 23 042 ng/mL. Defensin levels in the CSF of children with aseptic meningitis ranged from 0 ng/mL to 1675 ng/mL with a mean of 227 ng/mL (SD +/- 433) and a median of 23 ng/mL. A significant correlation was found between defensin levels in the CSF and the total leukocyte count and the absolute neutrophil count in the CSF of children with bacterial meningitis. Lactoferrin levels in the CSF of children with bacterial meningitis ranged from 184 ng/mL to 31 412 ng/mL with a mean of 13 209 ng/mL (SD +/- 9644) and a median of 10 382 ng/mL. Lactoferrin levels in the CSF of children with aseptic meningitis ranged from 0 ng/mL to 2715 ng/mL with a mean of 1042 ng/mL (SD +/- 878) and a median of 852 ng/mL. No correlation was found between lactoferrin level in the CSF and the total leukocyte count or the absolute neutrophil count in the CSF of children with bacterial meningitis. In our study population, the sum total of CSF defensins and lactoferrin was found to be highly sensitive and specific in delineating bacterial from aseptic meningitis when compared with standard CSF studies. CONCLUSIONS: Significant elevations of defensins and lactoferrin, indicative of endogenous local antimicrobial peptide and polypeptide release, are found in the CSF of children with meningitis. We speculate that elevations in these antimicrobial molecules may reflect the intensity of the host response. Defensins seem to parallel neutrophil activation more closely than lactoferrin. Cumulative levels of CSF defensins and lactoferrin clearly distinguished bacterial meningitis from aseptic meningitis and control patients. Further investigation is warranted to determine the usefulness of measuring defensins and lactoferrin as a diagnostic tool and therapeutic monitor in the evaluation of children with meningitis.

Clinical pharmacokinetics of cerebrospinal fluid.

The distribution of drugs into the cerebrospinal fluid has long been considered a challenging field of investigation in 2 major respects: (a) understanding how the physicochemical properties (molecular weight, pKa, plasma protein binding) of various molecules influence their movements across such a specific structure as the blood-brain barrier; and (b) defining the relationship between cerebrospinal fluid concentrations of various drugs and their central (side) effects. An attempt has been made to review the very dispersed information presently available to offer a clinically orientated picture of this area of pharmacokinetics. Drugs acting on the central nervous system (benzodiazepines, tricyclic antidepressants, anticonvulsants, opioids), antibacterial agents, cardiovascular drugs (beta-adrenoceptor blockers and digoxin), antineoplastic drugs (mainly methotrexate), and other miscellaneous agents (corticosteroids, cimetidine, methylxanthines) are reviewed. The available evidence seems to support the conclusion that only for methotrexate and antibacterial agents does knowledge of cerebrospinal fluid pharmacokinetics have direct therapeutic implications, while the mosaic of information available for other drugs does little more than provide a partially satisfactory picture.

Bacterial meningitis. Rational selection and use of antibacterial drugs.

Bacterial meningitis is a continuing challenge. This applies especially to infections in the neonate and the elderly, and to those which are hospital acquired. Factors which maintain the high morbidity and significant mortality from this disease include microbial virulence, a limited host response to infection within the cerebrospinal fluid (CSF), where phagocyte function is often impaired and complement and opsonic antibody activity are deficient, as well as delays in diagnosis and treatment. Added to these adverse factors is the pharmacokinetic hurdle of the 'blood-brain barrier', which limits drug concentrations achievable within the CSF. Inflammatory changes certainly improve the penetration of many agents, especially the penicillins and cephalosporins, but it must be remembered that with resolution of inflammation, achievable concentrations decline. Hence, the necessity for continuing parenteral administration of antibiotics throughout the treatment period. Although penicillin G (benzylpenicillin) remains the drug of choice for both pneumococcal and meningococcal infections, increasing resistance to ampicillin among Haemophilus influenzae has lead to greater reliance on alternative agents. Chloramphenicol is widely used, yet is potentially toxic, so that therapy with cefuroxime and the newer cephalosporins has been increasingly advocated. The advent of these potent, broad spectrum cephalosporins has induced a reappraisal of the treatment of Gram-negative bacillary meningitis, where ampicillin resistance and poor CSF penetration by the aminoglycosides have contributed to an unsatisfactory impact on outcome. Agents such as cefotaxime and ceftazidime have proved effective, although greater controlled experience is required. Finally, the contagious nature of meningococcal and H. influenzae infections justifies offering chemoprophylaxis to selected contacts, with rifampicin (or minocycline for contacts of patients with meningococcal infections).

Dapsone penetrates cerebrospinal fluid during Pneumocystis carinii pneumonia prophylaxis.

Dapsone has been proposed as a prophylactic agent for both Pneumocystis carinii pneumonia (PCP) and reactivation cerebral toxoplasmosis. To determine whether dapsone penetrates the central nervous system, cerebrospinal fluid (CSF) and serum samples were drawn from patients taking dapsone for PCP prophylaxis. These samples were quantitatively assayed using high-performance liquid chromatography. Five AIDS patients and one cardiac transplant patient had CSF assayed for dapsone. Only one had evidence of CSF inflammation, resulting from a paraspinal abscess. Doses ranged from 50 mg 3 days/week to 100 mg/day, and levels were 0.30-1.61 mu g/ml, which are in the range of inhibition of Toxoplasma gondii tachyzoites. This is the first report to demonstrate that dapsone enters the CSF, and supports preliminary clinical evidence that dapsone may have protective activity against cerebral toxoplasmosis when used for PCP prophylaxis.

The influence of indomethacin co-administration on ofloxacin levels in plasma and cerebrospinal fluid in rats.

The possible increase of ofloxacin levels in serum and cerebrospinal fluid (CSF) by concomitant indomethacin administration was investigated in 120 healthy adult rats. The animals were administered intramuscular doses of ofloxacin 30 mg/kg alone (Group A, n = 60) or with indomethacin 2 mg/kg (Group B, n = 60). Blood and CSF samples were obtained from both groups at 30, 45, 60 and 90 min post-administration. Concentrations of ofloxacin were estimated using a microbiological assay. Co-administration of indomethacin did not affect plasma levels of ofloxacin significantly; however, higher levels were found in all CSF samples after co-administration with indomethacin, particularly after 90 min with 0.59 microg/ml versus zero median values when only ofloxacin was administered (P = 0.05). No central nervous system adverse effects were observed clinically. No correlation between levels of ofloxacin in plasma and CSF could be established either in rats administered only ofloxacin or in rats administered both drugs. The presented pharmacokinetic findings revealed that co-administration of ofloxacin and indomethacin may result in protracted quinolone levels in the CSF. However, the absence of significant correlation between concentrations of ofloxacin in plasma and CSF upon co-administration of indomethacin, as well as of central nervous system adverse effects, make the probability of an epileptogenic interaction between them unlikely. These results merit further clinical evaluation.

Pharmacokinetics of sulfadiazine/trimethoprim in neonatal male calves: effect of age and penetration into cerebrospinal fluid.

Sulfadiazine (SDZ)/trimethoprim (TMP; 30 mg of SDZ/TMP/kg of body weight) was given IV to the same 6 male calves at 1, 7, and 42 days of age and to 2 additional calves at 7 days of age. Serum concentrations of SDZ and TMP were best represented by a 2-compartment open model, but in 42-day-old calves, CSF concentrations of both drugs were best represented by a 1-compartment open model with first-order input. Between 1 and 42 days of age, the elimination half-life (t1/2(beta)) of SDZ decreased from 5.7 to 3.6 hours, and total body clearance (CLtot) increased from 1.43 to 1.88 ml/min/kg; the area under the curve (AUC0----infinity) decreased from 291.5 to 225.4 mg/L.h. The distribution coefficient (Vd(area)/kg of body weight) decreased with age, changing from 0.72 to 0.59 L/kg, between 1 and 42 days of age. Therapeutic concentrations of SDZ in serum (greater than 2 micrograms/ml) were maintained for 24 hours in 1-day-old calves and for about 15 hours in 7- and 42-day-old calves. The elimination rate of TMP increased about 9-fold; t1/2(beta) was 8.4, 2.1, and 0.9 hours, respectively, at 1, 7, and 42 days of age. Other values also reflected an increase in TMP elimination rate with age: CLtot increased from 2.8 to 12 to 28.9 ml/min/kg, k13 increased from 0.336 to 0.654 to 1.664/h and AUC0----infinity decreased from 32.8 to 7.9 to 3.1 mg/L.h, respectively. Therapeutic concentrations (greater than 0.1 microgram/ml) were maintained for 15 hours, 8 hours, and about 6 hours in 1-, 7-, and 42-day-old calves, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and body fluid and endometrial concentrations of trimethoprim-sulfamethoxazole in mares.

Six healthy adult mares were each given a single IV injection of trimethoprim (TMP)-sulfamethoxazole (SMZ) at a dosage of 2.5 mg of TMP/kg of body weight and 12.5 mg of SMZ/kg. Serum concentrations of each drug were measured serially over a 24-hour period. For TMP, the mean overall elimination rate constant (K) was 0.43/hr and the elimination half-life (t1/2) was 1.9 hours. The apparent volume of distribution (at steady state) was 1.62 L/kg and TMP clearance was 886 ml/hr/kg. For SMZ, K was 0.22/hr and t1/2 was 3.53 hours. The apparent volume of distribution at steady state was 0.33 L/kg and SMZ clearance was 78.2 ml/hr/kg. Each mare was then given 5 consecutive oral doses of TMP-SMZ at a rate of 2.5 mg of TMP/kg and 12.5 mg of SMZ/kg at 12-hour intervals. Trimethoprim and SMZ concentrations were measured in serum, synovial fluid, peritoneal fluid, CSF, urine, and endometrium. Although both mean TMP and SMZ serum concentrations were higher after the 5th dose than after the 1st dose, only the mean TMP concentration was significantly (P less than 0.05) different. After the 5th oral dose, concentrations of TMP and SMZ attained in body fluids (except CSF) and endometrial tissue were equal to or exceeded reported minimum inhibitory concentrations for Corynebacterium pseudotuberculosis, Staphylococcus sp, Streptococcus zooepidemicus, and several obligate anaerobes. Absorption of both drugs was variable after oral administration.

[Determination of levofloxacin in plasma and cerebrospinal fluid with HPLC and its pharmacokinetics in patients undergoing neurosurgical operations].

A RP-HPLC method was developed to determine the concentrations of levofloxacin in plasma and cerebrospinal fluid and its pharmacokinetics were studied in patients undergoing neurosurgical operations. C18H37 column was eluted with the mobile phase consisting of 10 mmol.L-1 KH2PO4-10 mmol.L-1(C4H9)4Br-CH3CN(45:45:10, pH 3.0) and the utraviolet absorbance was monitored at 295 nm. Ciprofloxacin was used as internal standard. The mean recoveries were 74.76% in plasma and 82.43% in cerebrospinal fluid, with the lowest detectable limits of 10 micrograms.L-1 and 6 micrograms.L-1, respectively. The RSD for the intra-day and inter-day were all less than 5%. A single oral administration of 300 mg levofloxacin tablet was given to 10 patients undergoing neurosurgical operations. The pharmacokinetic parameters in blood and in cerebrospinal fluid could be described by one compartment open model. The pharmacokinetic parameters were: blood Ke 0.12 +/- 0.04 h-1, T1/2 6.05 +/- 1.68 h, Tmax 1.05 +/- 0.29 h, Cmax 3.67 +/- 0.42 mg.L-1, AUC 33.43 +/- 7.32 mg.h.L-1, CLs 9.46 +/- 2.53 L.h-1, Vd 77.49 +/- 7.39 L; cerebrospinal fluid Ke 0.11 +/- 0.04 h-1, T1/2 6.95 +/- 1.88 h, Tmax 3.56 +/- 1.24 h, Cmax 1.68 +/- 0.25 mg.L-1, AUC 23.70 +/- 5.62 mg.h.L-1, CLs 13.70 +/- 5.11 L.h-1, Vd 126.61 +/- 13.20 L.

Successful treatment and cerebrospinal fluid penetration of oral linezolid in a patient with coagulase-negative Staphylococcus ventriculitis.

OBJECTIVE: To describe a case of coagulase-negative Staphylococcus ventriculitis successfully treated with oral linezolid, for which good cerebrospinal fluid (CSF) penetration was observed. CASE SUMMARY: A 69-year-old man had an extraventricular drain inserted following a right cerebellar infarct. On day 6, the CSF culture was positive for coagulase-negative staphylococci; intravenous vancomycin 1 g daily was initiated to treat ventriculitis. A ventriculoperitoneal shunt, inserted on day 35 to manage communicating hydrocephalus, was subsequently removed as symptoms suggesting infection presented. Coagulase-negative Staphylococcus was isolated from shunt reservoir aspirate, and intrathecal vancomycin 10 mg daily was added to the treatment regimen. On day 61, vancomycin was stopped and oral linezolid 600 mg twice daily was started. Linezolid was discontinued 22 days later, with no evidence of ongoing infection. Four blood samples were collected around the seventh dose of linezolid and 5 CSF samples were collected on separate days during treatment. Linezolid concentrations were measured in plasma and CSF by HPLC. Using an ADAPT II maximum a priori Bayesian estimator module, a 2 compartment pharmacokinetic model was fitted to the plasma linezolid concentration data and CSF:predicted plasma concentration ratios (ranging from 0.27 to 1.02) were derived. All CSF concentrations exceeded the reported 90% minimum inhibitory concentration of 2 mg/L for linezolid against coagulase-negative staphylococci. DISCUSSION: Evidence of the effectiveness of linezolid against central nervous system infections is growing; however, limited data exist describing its CSF penetration. Oral linezolid exhibited good CSF penetration in this patient, which corresponded to positive clinical response. CONCLUSIONS: Oral linezolid may play a valuable role in the treatment of multiresistant gram-positive central nervous system infections.