Pharmacokinetics of 5-aminofluorescein-albumin, a novel fluorescence marker of brain tumors during surgery.

In a phase I/II study, the new fluorescence marker 5-aminofluorescein covalently bound to human serum albumin (AFL-HSA) was intravenously administered to 10 patients with brain tumor 1 to 4 days before surgery, and AFL-HSA kinetics were determined to assess the optimum timing of dye administration. AFL-HSA was determined in serum and brain tissue by size exclusion chromatography with fluorescence detection. AFL-HSA disposition was quite similar to albumin kinetics with small volumes of distribution (volume of central compartment [V(c)] = 2.4 L; volume of distribution [Vd(ß)] = 6.8 L; volume at steady state [V(ss)] = 5.9 L), a low clearance (mean Cl = 16.85 mL/h), and a long elimination half-life (mean T(1/2;ß) = 307 hours). Predicted peak concentrations in the peripheral compartment occurred at 80.9 hours, the time point of optimal fluorescence intensity observed in brain tumors during surgery.

Intraoperative fluorescence staining of malignant brain tumors using 5-aminofluorescein-labeled albumin.

OBJECTIVE: The newly developed conjugate 5-aminofluorescein (AFL)-human serum albumin (HSA) was investigated in a clinical trial for fluorescence-guided surgery of malignant brain tumors to assess its efficacy and tolerability. METHODS: AFL, covalently linked to human serum albumin at a molar ratio of 1:1, was administered intravenously 0.5 to 4 days before surgery at 0.5 or 1.0 mg/kg of body weight to 13 patients aged 38 to 71 years who were suspected of having malignant gliomas. Fluorescence guidance using a 488-nm argon laser was performed during surgery at will. The extent of tumor resection was verified by early postoperative magnetic resonance imaging. Fluorescent and nonfluorescent samples were collected for neuropathology. Blood samples for laboratory and pharmacokinetic analyses were taken over the course of 4 weeks. RESULTS: Fluorescence staining of tumor tissue was bright in 11 patients (84%), resulting in complete resection of fluorescent tumor tissue in 9 patients (69%). In 2 patients, residual fluorescent tumor tissue was also confirmed by magnetic resonance imaging. Neither bleaching nor penetration of AFL-HSA into the surrounding brain edema or into necrotic tissue was seen. The agreement between fluorescence and histopathology in tumor samples and samples of the tumor border was 83.3%. There were no toxic side effects. The quality of fluorescence was independent of the dose administered. The optimal time for surgery is between 1 and 4 days after AFL-HSA administration. CONCLUSION: Tumor fluorescence using AFL-HSA made fluorescence-guided brain tumor resection possible, demonstrating that albumin is a suitable carrier system for selective targeting of aminofluorescein into malignant gliomas.

Significant pharmacokinetic and pharmacodynamic interaction of warfarin with the NO-independent sGC activator HMR1766.

HMR1766 is a new nitric oxide (NO)-independent activator of soluble guanylyl cyclase (sGC) in development for the treatment of cardiovascular diseases and chronic heart failure. A significant fraction of patients to be treated with HMR1766 is expected to be maintained on warfarin. Because HMR1766 is an inhibitor and warfarin a substrate of CYP2C9, the authors studied whether warfarin pharmacokinetics and pharmacodynamics are influenced by HMR1766. Eighteen healthy males were to receive a single oral dose of 20 mg warfarin each under steady-state conditions of HMR1766 or placebo. Plasma concentrations of HMR1766, (R)- and (S)-warfarin, and its 7-hydroxy-metabolites were determined using high-performance liquid chromatography and prothrombin time, and the international standardized ratio was determined by the nephelometric method. (S)-Warfarin AUC(inf) and t(1/2) were 106,471 h x microg/L and 82.92 hours versus 33,148 h x microg/L under HMR1766 and 31.72 hours under placebo, and the maximum decrease in prothrombin time values after warfarin dosing was 58.75% versus 39.94%. These data demonstrate a CYP2C9-mediated pharmacokinetic interaction with pharmacodynamic, clinically relevant consequences, which might require warfarin dose adjustment.

Potent cytochrome P450 2C19 genotype-related interaction between voriconazole and the cytochrome P450 3A4 inhibitor ritonavir.

OBJECTIVES: Cytochrome P450 (CYP) 2C19 and CYP3A4 are the major enzymes responsible for voriconazole elimination. Because the activity of CYP2C19 is under genetic control, the extent of inhibition with a CYP3A4 inhibitor was expected to be modulated by the CYP2C19 metabolizer status. This study thus assessed the effect of the potent CYP3A4 inhibitor ritonavir after short-term administration on voriconazole pharmacokinetics in extensive metabolizers (EMs) and poor metabolizers (PMs) of CYP2C19. METHODS: In a randomized, placebo-controlled crossover study, 20 healthy participants who were stratified according to CYP2C19 genotype received oral ritonavir (300 mg twice daily) or placebo for 2 days. Together with the first ritonavir or placebo dose, a single oral dose of 400 mg voriconazole was administered. Voriconazole was determined in plasma and urine by liquid chromatography-mass spectrometry, and pharmacokinetic parameters were estimated by noncompartmental analysis. RESULTS: When given alone, the apparent oral clearance of voriconazole after single oral dosing was 26%+/-16% (P > .05) lower in CYP2C19*1/*2 individuals and 66%+/-14% (P < .01) lower in CYP2C19 PMs. The addition of ritonavir caused a major reduction in voriconazole apparent oral clearance (354+/-173 mL/min versus 202+/-139 mL/min, P = .0001). This reduction occurred in all CYP2C19 genotypes (463+/-168 mL/min versus 305+/-112 mL/min [P = .023] for *1/*1, 343+/-127 mL/min versus 190+/-93 mL/min [P = .008] for *1/*2, and 158+/-54 mL/min versus 22+/-11 mL/min for *2/*2) and is probably caused by inhibition of CYP3A4-mediated voriconazole metabolism. CONCLUSIONS: Coadministration of a potent CYP3A4 inhibitor leads to a higher and prolonged exposure with voriconazole that might increase the risk of the development of adverse drug reactions on a short-term basis, particularly in CYP2C19 PM patients.

Reduction of saquinavir exposure by coadministration of loperamide: a two-way pharmacokinetic interaction.

OBJECTIVE: To assess any pharmacokinetic interactions between loperamide and saquinavir. DESIGN: Double-blind, double-dummy, randomised, placebo-controlled, three-way crossover trial. PARTICIPANTS: Twelve healthy male and female volunteers, aged 24-46 years. METHODS: Saquinavir and loperamide pharmacokinetics were determined over a 72-hour period after single dose administration of saquinavir 600mg and/or loperamide 16mg. Plasma and urine concentrations of loperamide, its metabolites, and saquinavir were analysed using a single liquid chromatography/tandem mass spectrometry method for all compounds. RESULTS: Saquinavir exposure was reduced by 54% when given with loperamide (median area under the concentration-time curve from zero to infinity [range], 1189 [243-2113] vs 550 [234-1468] pmol . h/mL; p = 0.016) with unchanged renal clearance. In contrast, loperamide concentrations increased and desmethylloperamide concentrations decreased during saquinavir coadministration, resulting in a reduced metabolic clearance of loperamide (median [range], 544 [224-1393] vs 443 [238-692] mL/min; p = 0.016). CONCLUSIONS: Whereas the effect of saquinavir on loperamide disposition is unlikely to be of clinical relevance, the reduced drug exposure of saquinavir when loperamide is coadministered is worrisome because a relationship between protease inhibitor drug exposure and antiviral response has been reported. Patients receiving saquinavir monotherapy should be advised not to combine these drugs, especially for prolonged periods of time because a reduction in therapeutic efficacy may result.

Assessment of levothyroxine sodium bioavailability: recommendations for an improved methodology based on the pooled analysis of eight identically designed trials with 396 drug exposures.

BACKGROUND: Assessment of dosage form performance in delivering endogenous compounds, such as hormones, in vivo requires a specific approach. OBJECTIVES: Assessment of relative bioavailability of levothyroxine sodium (L-T4) from eight solid preparations, compared with a liquid formulation, by using pharmacological doses, and critical evaluation of trial methodology based on the pooled analysis of individual data. DESIGN: Eight open-label, randomised, single-dose, crossover phase I studies using eight solid L-T4 dosage forms (25, 50, 75, 100, 125, 150, 175, 200 microg per tablet; administered total doses 600, 625 or 700 microg) and a liquid formulation; assessment of relative bioavailability by 90% confidence intervals for the relative area under the concentration-time curve (AUC) of total thyroxine (TT4), i.e. protein-bound plus free thyroxine, calculated by using the recommended log AUC four-way analysis of variance models for crossover designs. For the pooled analysis, general linear models were applied to assess the validity of model assumptions, to identify potential sources of effect modification, to discuss alternative modelling approaches with respect to endogenous hormone secretion and to give recommendations for future designs and sample sizes. PARTICIPANTS: One hundred and sixty-nine healthy males; 29 of these individuals participating in two studies. INTERVENTIONS: Single oral doses of L-T4 tablets and the liquid formulation administered after fasting, separated by at least 6 weeks; a total of 396 drug exposures. MAIN OUTCOME MEASURES: TT4 AUC from 0 to 48 hours and peak plasma concentration with and without baseline correction. RESULTS: Each study demonstrated equivalence of the tablets to the drinking solution, independent of the chosen analysis model. Sequence effects that could devalidate the chosen crossover approach were not found. Period effects with changing directions that could best be explained by seasonal variation were detected. While the pre-specified method of baseline correction of simply subtracting individual time-zero TT4 values was disadvantageous, the analysis of total AUC could be improved considerably by covariate adjustment for baseline TT4. With this approach, sample sizes could have been substantially reduced or, alternatively, the recommended equivalence ranges could be reduced to +/-6%. CONCLUSION: Using a single pharmacological dose of L-T4 in two-period crossover designs is a safe and reliable procedure to assess L-T4 dosage form performance. With an adequate statistical modelling approach, the design is efficient and allows general conclusions with moderate sample sizes.

Substantial pharmacokinetic interaction between digoxin and ritonavir in healthy volunteers.

BACKGROUND: Ritonavir is a potent in vitro inhibitor of several cytochrome P450 isozymes and ABC transporters including the efflux pump P-glycoprotein (P-gp). This study assessed the effect of repetitive ritonavir administration on digoxin distribution and total and renal digoxin clearance as a marker for P-gp activity in vivo. METHODS: In a randomized, placebo-controlled crossover study, 12 healthy male participants received oral ritonavir (300 mg twice daily) for 11 days. With the assumption that ritonavir steady state had been reached, 0.5 mg digoxin was given intravenously on day 3. Digoxin concentrations were determined in plasma and urine by radioimmunoassay, and plasma ritonavir concentrations were determined by liquid chromatography-tandem mass spectrometry. Digoxin kinetics was estimated by compartmental and noncompartmental analyses, by use of the area under the plasma concentration-time curve, and the corresponding digoxin amount excreted into urine was used for digoxin clearance calculations. RESULTS: Ritonavir significantly (P <.01) increased digoxin area under the plasma concentration-time curve from time 0 to infinity by 86% and its volume of distribution by 77% and decreased nonrenal and renal digoxin clearance by 48% and 35%, respectively. Digoxin terminal half-life in plasma increased by 156% (P <.01). CONCLUSION: This inhibition of renal digoxin clearance is likely caused by ritonavir inhibition of P-gp. Its extent is considerable and similar to the effect of other potent P-gp inhibitors on digoxin disposition such as quinidine. These findings may, therefore, indicate that the pharmacokinetics of P-gp substrates sharing the renal tubular elimination pathway will be affected when combined with therapeutic doses of ritonavir in antiretroviral treatment regimens. In addition and contrarily to quinidine, these data indicate that ritonavir promotes digoxin distribution in the body.

Pharmacokinetic and pharmaceutic interaction between digoxin and Cremophor RH40.

BACKGROUND: The pharmacokinetics of digoxin is modulated by the efflux pump P-glycoprotein. Cremophor EL (BASF Aktiengesellschaft, Ludwigshafen, Germany) (polyoxyl 35 castor oil), a castor oil derivative used to improve the solubilization of drugs and vitamins, has been shown to inhibit this membrane transporter in vitro and in vivo. So far, no study in humans has evaluated the effect of Cremophor RH40 (BASF Aktiengesellschaft) (polyoxyl 40 hydrogenated castor oil) on P-glycoprotein. METHODS: A randomized, double-blind, placebo-controlled crossover study in 12 healthy individuals was performed with a single oral dose of 0.5 mg digoxin in a hard gelatin capsule in combination with multiple doses of oral Cremophor RH40 (600 mg 3 times daily) or placebo. A digitized electrocardiogram with 12 standard leads was recorded to assess the pharmacodynamics of digoxin. RESULTS: Cremophor RH40 delayed and enhanced the absorption of digoxin in the first 5 hours after dosing. During Cremophor RH40 administration, digoxin lag time was significantly prolonged compared with placebo (0.53 +/- 0.25 hour versus 0.36 +/- 0.19 hour, P =.04). The peak concentration of digoxin increased by 22%, from 2.21 +/- 0.94 ng/mL to 2.69 +/- 1.28 ng/mL (P =.06). Similarly, the area under the plasma concentration-time curve from 0 to 5 hours significantly increased by 22% (5.23 +/- 1.63 h. ng/mL versus 4.30 +/- 1.12 h. ng/mL, P =.03). Digoxin did not cause a clinically significant change in the dynamic parameters during both periods. CONCLUSION: This study demonstrates a pharmacokinetic and pharmaceutic interaction between the emulgent Cremophor RH40 and digoxin, caused by P-glycoprotein inhibition and prolongation of the dissolution time of digoxin tablets by Cremophor RH40, respectively. Our in vivo study in humans supports the validity of in vitro observations on P-glycoprotein.

Dose-dependent increase of saquinavir bioavailability by the pharmaceutic aid cremophor EL.

AIMS: Bioavailability of orally administered drugs depends on several factors including active excretion, e.g. by P-glycoprotein (PGP), and presystemic metabolism, e.g. by cytochrome P450 3A (CYP3A), in both gastrointestinal tract and liver. Many drugs including saquinavir are substrates of both PGP and CYP3A. It was the aim of this study to test whether the extremely low bioavailability of saquinavir can be increased dose-dependently in vivo by cremophor EL, an 'inactive' pharmaceutic aid known to inhibit PGP in vitro. METHODS: In a randomized, placebo-controlled, double-blind, four phase cross-over design single doses of oral saquinavir (Invirase, 600 mg, without food) were administered with increasing single doses of oral cremophor EL (up to 5000 mg) to eight healthy, male individuals. Saquinavir plasma concentrations were determined by LC/MS/MS up to 48 h after intake. Main outcome measures were area under the plasma concentration time curve (AUC), peak concentration (Cmax), time to reach Cmax (tmax) and terminal elimination half-life (t(1/2)). RESULTS: Cremophor EL dose-dependently increased Cmax, AUC(0,4 h), and AUC(0,infinity) of saquinavir. As compared with placebo, the increment observed after 5000 mg cremophor EL was 13-fold for both Cmax and AUC(0,4 h) and 5-fold for AUC(0,infinity). The terminal half-life and the time to reach Cmax (tmax) were unchanged. CONCLUSIONS: Cremophor EL increased the systemic availability of saquinavir without affecting its elimination suggesting that cremophor EL is not devoid of pharmacological action and acts as a modulator of the absorption process, probably by inhibiting intestinal PGP.