Karen I. Plaisance

Association of Vancomycin Serum Concentrations With Outcomes in Patients With Gram-Positive Bacteremia

We attempted to determine if an association exists between vancomycin serum concentrations resulting from traditional dosing regimens, and efficacy and toxicity outcomes. We reviewed the medical charts of 273 consecutive patients prescribed 273 courses of vancomycin therapy for documented, gram‐positive bacteremia. Of the 273 courses of therapy, 45 and 31 patients met all criteria and were evaluated for toxicity and efficacy, respectively. The duration of fever and abnormal white blood cell counts, length of hospital stay, overall mortality, serum creatinine, and serum vancomycin concentrations were evaluated retrospectively. No association between initial peak or trough levels with mortality was noted. However, patients were more likely to become afebrile within 72 hours if peak and trough concentrations were 20 μg/ml or greater and 10 μg/ml or greater, respectively (p<0.01). Patients were also more likely to have their white blood cell count return to normal within 72 hours if trough concentrations were 10 μg/ml or above (p<0.01). No statistically significant correlation between nephrotoxicity and initial serum creatinine, days of hospital stay, or days of vancomycin therapy were found. Serum concentrations of vancomycin, assessed before the development of nephrotoxicity, were significantly higher in patients who became nephrotoxic. Mean (SD) trough concentrations were 23.2 (2.5) μg/ml and 10.2 (3.8) μg/ml in nephrotoxic and nonnephrotoxic patients, respectively. Our results suggest that the commonly accepted therapeutic range for vancomycin trough concentrations (<10 μg/ml) may be too restrictive in patients receiving vancomycin therapy alone.

Plasma pharmacokinetics of butyrate after intravenous administration of sodium butyrate or oral administration of tributyrin or sodium butyrate to mice and rats

Purpose: To define the plasma concentrations of butyrate achieved and the profile of plasma butyrate concentrations versus time in mice and rats treated with tributyrin or sodium butyrate. Methods: Female CD2F1 mice were treated with tributyrin by oral gavage or with sodium butyrate by i.v. bolus or oral gavage. Oral tributyrin doses delivered to mice were 3.1, 5.2, 7.8, and 10.3 g/kg. Intravenous sodium butyrate doses were 0.31, 0.62, 0.94, and 1.25 g/kg. Oral sodium butyrate was given to mice at 5 g/kg. Subsequently, similar studies were performed in female Sprague-Dawley rats. Rats were given tributyrin by oral gavage at doses of 3.6, 5.2, or 10.3 g/kg or sodium butyrate i.v. at a dose of 500 mg/kg. Plasma butyrate concentrations were determined by gas chromatography. Results: In mice, oral dosing with tributyrin resulted in detectable plasma butyrate concentrations as early as at 5 min after treatment and produced peak plasma butyrate concentrations at between 15 and 60 min after dosing. Peak plasma butyrate concentrations increased proportionally with increasing tributyrin dose, but as the oral tributyrin dose increased there was a greater than proportional increase in the area under the curve of plasma butyrate concentrations versus time (AUC). At a tributyrin dose of 10.3 g/kg, plasma butyrate concentrations peaked at approximately 1.75 mM and remained ≥1 mM for between 10 and 60 min after dosing. However, approximately 10% of mice treated with this dose died acutely. At a tributyrin dose of 7.8 g/kg, plasma butyrate concentrations reached approximately 1 mM by 15 min after dosing and remained between 0.8 and 1 mM until 60 min after dosing. No mouse treated with this dose died acutely. Mice given tributyrin doses of 5.2 and 3.1 g/kg achieved peak plasma butyrate concentrations of approximately 0.9 and 0.5 mM, respectively, by 45 min after dosing. Plasma butyrate concentrations in these mice remained above 0.1 mM until 120 and 90 min after dosing, respectively. The four i.v. doses of sodium butyrate resulted in plasma concentration-time profiles that also indicated nonlinear pharmacokinetics and were well described by a one-compartment model with saturable elimination. Values recorded for the Michaelis-Menten constant (Km) and the maximal velocity of the process (Vmax) ranged between 1.02 and 5.65 mM and 0.60 and 1.82 mmol/min, respectively. Values noted for the volume of the central compartment (Vc) varied between 0.48 and 0.72 l/kg. At 1.25 g/kg, i.v. sodium butyrate produced peak plasma butyrate concentrations of 10.5–17.7 mM, and plasma butyrate concentrations remained above 1 mM for 20–30 min. Sodium butyrate delivered orally to mice at 5 g/kg produced peak plasma butyrate concentrations of approximately 9 mM at 15 min after dosing and plasma butyrate concentrations exceeding 1 mM for 90 min after dosing. In rats the 10.3-g/kg oral dose of tributyrin produced peak plasma butyrate concentrations of approximately 3 mM by 75 min after dosing and butyrate concentrations excedding 1 mM from 30 to 90 min after dosing. The plasma butyrate concentrations produced in rats by 5.2- and 3.6-g/kg doses were appropriately lower than those produced by the 10.3-g/kg dose, and there was no evidence of nonlinearity. The 500-mg/kg i.v. dose of sodium butyrate produced peak plasma butyrate concentrations in rats of approximately 11 mM, and the decline in plasma butyrate concentrations with time after dosing was consistent with saturable clearance. Conclusion: These studies document the ability to use oral administration of tributyrin to achieve pharmacologically relevant concentrations of butyrate in rodent plasma. They also document the nonlinear nature of butyrate clearance. These data are being used in the design of clinical trials of oral tributyrin in patients with malignancies and hemoglobinopathies.

Absolute oral bioavailability of ciprofloxacin.

We evaluated the absolute bioavailability of ciprofloxacin, a new quinoline carboxylic acid, in 12 healthy male volunteers. Doses of 200 mg were given to each of the volunteers in a randomized, crossover manner 1 week apart orally and as a 10-min intravenous infusion. Half-lives (mean +/- standard deviation) for the intravenous and oral administration arms were 4.2 +/- 0.77 and 4.11 +/- 0.74 h, respectively. The serum clearance rate averaged 28.5 +/- 4.7 liters/h per 1.73 m2 for the intravenous administration arm. The renal clearance rate accounted for approximately 60% of the corresponding serum clearance rate and was 16.9 +/- 3.0 liters/h per 1.73 m2 for the intravenous arm and 17.0 +/- 2.86 liters/h per 1.73 m2 for the oral administration arm. Absorption was rapid, with peak concentrations in serum occurring at 0.71 +/- 0.15 h. Bioavailability, defined as the ratio of the area under the curve from 0 h to infinity for the oral to the intravenous dose, was 69 +/- 7%. We conclude that ciprofloxacin is rapidly absorbed and reliably bioavailable in these healthy volunteers. Further studies with ciprofloxacin should be undertaken in target patient populations under actual clinical circumstances.

Dose ranging study and constant infusion evaluation of ciprofloxacin.

We evaluated the pharmacokinetics of 100- and 200-mg doses of ciprofloxacin, with the 200-mg dose administered either as a 30-min infusion or as a 100-mg loading dose followed by a 4-h constant infusion of 25 mg/h in six normal volunteers. No significant differences were seen in the dose-normalized area under the curve when the 100- and 200-mg 30-min administrations were compared. Differences that approached statistical significance were seen when data from either of these trials were compared with data from the constant-infusion arm. Serum clearances averaged 23.0 +/- 9.1 liters/h per 1.73 m2 for the 100-mg dose and 23.7 +/- 5.1 liters/h per 1.73 m2 for the 200-mg dose. Renal clearance accounted for approximately two-thirds of the serum clearance in each instance. Half-lives were slightly longer than 4 h. For the constant-infusion arm, serum clearance was 28.9 +/- 2.7 liters/h per 1.73 m2, with renal clearance accounting for 58% of serum clearance. Although no nonlinearities were apparent in the 100- to 200-mg dose range, larger doses, particularly in the multiple-dosing situation, may uncover nonlinearity in the disposition of ciprofloxacin.

Pharmacokinetics of intravenously administered ciprofloxacin in patients with various degrees of renal function.

We examined the pharmacokinetic behavior of 200 mg of ciprofloxacin administered intravenously to 32 volunteers whose renal function as measured by creatinine clearance ranged from 0 to 8.99 liters/h per 1.73 m2. Serum clearances (mean +/- standard deviation) were 26.8 +/- 5.7 and 15.4 +/- 4.3 liters/h per 1.73 m2 in normal and anephric volunteers, respectively. The half-life (mean +/- standard deviation) increased from 4.3 +/- 0.8 h in normal volunteers to 8.6 +/- 3.3 h in anephric volunteers. There was good correlation between normalized creatinine clearance and both normalized serum and renal clearance. The regression equation for serum clearance (CLS) versus creatinine clearance (CLCR) was CLS = 1.97 X CLCR + 13.23, where r = 0.697; for renal clearance versus creatinine clearance, the equation was CLR = 2.26 X CLCR, where r = 0.845. On the basis of these data, we recommend a maximum 50% reduction in dose when ciprofloxacin is instituted at a renal function of 1.2 to 1.8 liters/h per 1.73 m2 (20 to 30 ml/min per 1.73 m2). Because of the observed variation in ciprofloxacin half-life in our anephric volunteers, we also recommend that a schedule of administration every 12 h be maintained, even for patients without urine output.

Effect of dose size on bioavailability of ciprofloxacin.

We evaluated the bioavailability of ciprofloxacin at two dose sizes in eight healthy volunteers. Each volunteer was given 200 mg of ciprofloxacin both orally and intravenously in a randomized crossover fashion and 750 mg orally. Bioavailability at the two doses was similar: 69 and 69.1% for the 200- and 750-mg doses, respectively. However, the bioavailability observed with the 750-mg dose was significantly more variable than that observed with the 200-mg dose. Between 375 and 700 mg of ciprofloxacin reached the systemic circulation after administration of the 750-mg dose, with no evidence of adverse reactions.

Effect of antipyretic therapy on the duration of illness in experimental influenza A, Shigella sonnei, and Rickettsia rickettsii infections.

Study Objectives. To determine whether antipyretic therapy prolongs the course of experimental influenza A, Shigella sonnei, and Rickettsia rickettsii infections.

Toxicities of Drugs Used in the Management of Fever

Fever is frequently managed outside the purview of medical professionals, and antipyretic therapy, on the whole, is generally considered safe. However, each of the drugs used in the management of fever has significant toxicities. The purpose of this review is to examine the relative safety of such agents with a focus on the nonsteroidal anti-inflammatory drugs and acetaminophen. Toxicity to the gastrointestinal, renal, and hepatic systems are considered; the comparative safety profile of acetaminophen and ibuprofen as antipyretics are highlighted; and specific recommendations to improve the safe use of these therapies are advanced.

Pharmacokinetic evaluation of two dosage regimens of clindamycin phosphate.

Interpretation of the majority of data on the disposition of clindamycin is confounded by the presence of active metabolites, which may interfere with commonly employed bioassays. We undertook a multiple-dose study of the disposition of clindamycin phosphate and clindamycin, given either as 600 mg intravenously every 6 h or 1,200 mg intravenously every 12 h for five and three doses, respectively, in six healthy volunteers. Concentrations in serum and urine were analyzed by a specific gas chromatography assay. Maximum and minimum clindamycin concentrations in serum and the area under the serum concentration-time curve following the first dose were similar to those observed at the steady state. The mean and standard deviation of the maximum, 1-h postdose, and minimum concentrations in serum at steady state for the 600-mg dose given every 6 h were 16.8 +/- 6.0, 7.6 +/- 0.7, and 2.3 +/- 0.9 microgram/ml, whereas for the 1,200-mg dose given every 12 h they were 17.2 +/- 3.5, 9.8 +/- 1.5, and 0.6 +/- 0.3 microgram/ml, respectively. For the 12-h regimen, clindamycin concentrations in serum remained above 2 micrograms/ml for 7 h. The decay of clindamycin phosphate levels in serum was rapid, with virtually 100% of the phosphate eliminated within the first 1.5 h following the dose. Approximately 0.35 and 4.5% of the administered dose were recovered in the urine as clindamycin phosphate and clindamycin, respectively. Further pharmacokinetic evaluation of the 12-hourly dosage regimen should be done before clinical evaluation in infected patients is undertaken.

A prospective evaluation of optimal sampling theory in the determination of the steady-state pharmacokinetics of piperacillin in febrile neutropenic cancer patients

We examined the use of optimal sampling theory in the determination of the pharmacokinetics of piperacillin in febrile, neutropenic cancer patients. Patients were studied prospectively as part of a randomized, double‐blind clinical trial of piperacillin and amikacin versus imipenem and placebo. The results from the analysis of 5 optimal samples were compared with those derived from 15 concentration determinations (10 samples, with the 5 optimal samples assayed in duplicate). The use of a standard least‐squares estimator as opposed to a bayesian estimator, with normal prior distributions placed on beta and serum clearance, was also examined. Finally, the use of duplicate determinations in improving the precision of parameter estimation was studied. Plasma concentrations obtained at time points determined by optimal sampling theory, when analyzed with a bayesian estimator, produced estimates of pharmacokinetic parameter values that were in good agreement with those derived from the 15‐determination set. Duplicate assay did not improve the precision of parameter estimation. Estimation of plasma clearance was quite robust, irrespective of the estimator used, probably because this evaluation was performed at steady state. Optimal sampling theory is a promising technique that can be employed to determine patient‐specific estimates of pharmacokinetic parameter values in target populations.