Drug Levels In Tissues Research Articles

Polymorphisms in the ABC drug transporter gene MDR1.

In addition to genetically variable metabolic enzymes such as Cyp p450 proteins, blood and tissue levels of many drugs are influenced by controlled transport across compartmental boundaries. Major determinants in these transport processes are ATP-dependent efflux pumps such as P-glycoprotein and related proteins (eg MRPs), which can influence the bioavailability and CNS concentrations, as well as disposition of drugs. In addition to its recognized role in the development of multiple chemotherapy resistances, experimental evidence for the relevant influence of the MDR1 gene encoded P-glycoprotein, on the pharmacology of many other drugs has been gathered by the analyses of knockout mice, as well as in clinical studies. Recently, functional genetic polymorphisms in the MDR1 gene have been identified which influence the distribution and bioavailability of PGP substrates.

EVALUATING THE EFFICACY OF AMIKACIN IN LOW-CLEARANCE UNILAMELLAR LIPOSOMES IN A S. AUREUS LOCAL INFECTION MODEL

Traditional therapies for Staphylococcal infections such as osteomyelitis or localized abscesses have a difficult time penetrating into tissue sites. To effectively ameliorate these infections, prolonged therapy and/or high doses of antibiotics are frequently required. Aminoglycosides, such as amikacin, are not routinely utilized for treating local infections due to poor efficacy associated with ineffective tissue penetration, toxicity, and poor penetration in an acid millieu. We postulated that a formulation of amikacin in small unilamellar liposomes might readily be engulfed by inflammatory macrophages facilitating drug delivery to the site of infection. This increased drug load to the site of bacterial infection may result in enhanced bactericidal action compared to conventional aminoglycosides. Tissue drug concentrations were determined for liposomal amikacin (L-AN) and conventional amikacin (AN). Plasma amikacin levels were determined for L-AN. The L-AN was very effective at concentrating at the site of infection compared to AN. Following confirmation of adequate tissue drug levels, a rodent subcutaneous abscess infection using S. aureus as the bacterial challenge agent was evaluated. Sprague-Dawley rats were intravenously administered L-AN every other day due to its prolonged half-life, while the comparator agent, AN, was administered daily. Abscess size, weights, severity, histology, and tissue colony counts were examined. In efficacy studies, L-AN was superior to AN in reducing colony counts.

Ocular delivery of flurbiprofen from ophthalmic liposomes dispersed in thermosensitive gel

In order to maintain adequate drug levels in ocular tissues, frequent drug instillation is necessary in treatment of ophthalmic disorders. Flurbiprofen, NSAIDs, was entrapped in EPC liposomes dispersed in thermosensitive polaxamer gel. The size and Zeta-​potential of the vesicles were analyzed. The in-​vitro leakage of the entrapped and free drug were carried out under sink condition, the t1​/2 for entrapped drug was 4.1 fold when compared to that of the free drug. The concns. of Flurbiprofen in the ocular tissues of the rabbits for both formulations (entrapped and free drug) were detd. by HPLC measurement. The in-​vivo study depicted that entrapment of the drug in liposomes enhanced the drug precorneal retention, drug penetration and consequently increased the drug levels in ocular tissues compared to free drug formulation. The study also revealed that, the highest drug level deposited in the cornea and sclera followed by aq. humor and vitreous body. The pharmacokinetic parameters (AUC and Cmax) and the significance t-​test levels (P values) for the difference between entrapped and free drug were calcd. It was found that the majority of differences were very highly to highly significant. These findings indicate that entrapment of drug in liposomes may be promising formulation, particularly when dispersed in highly viscous system, for ophthalmic therapeutic use.

Drug efflux transporters and antiviral drug therapy

It is now becoming increasingly clear that for a drug to become truly successful as a therapeutic agent it must be not only specific and potent, but also capable of reaching target sites at relevant concentrations. This is particularly important for anti-infectives since failure to fully eradicate the pathogen may mean persistence or progression of the infection, which may allow for the emergence of drug-resistant variants. A key process governing target tissue drug levels appears to be the presence of carrier-mediated processes or transporters. Moreover, in addition to their role in drug distribution into various tissues, expression of drug transporters in organs such as the intestine, liver and kidney also affects absorption and excretion of many drugs. Clearly, consideration of transport systems earlier in the drug screening/discovery process may lead to candidate compounds with greater likelihood of more favourable disposition and target tissue penetration profiles in vivo. Accordingly, this review wi...

Compartmental pharmacokinetics and tissue distribution of multilamellar liposomal nystatin in rabbits.

The plasma pharmacokinetics of multilamellar liposomal nystatin were studied in normal, catheterized rabbits after single and multiple daily intravenous administration of dosages of 2, 4, and 6 mg/kg of body weight, and drug levels in tissues were assessed after multiple dosing. Concentrations of liposomal nystatin were measured as those of nystatin by a validated high-performance liquid chromatography method, and plasma concentration data were fitted into a two-compartment open model. Across the investigated dosage range, liposomal nystatin demonstrated nonlinear kinetics with more than proportional increases in the AUC(0-24) and decreasing clearance, consistent with dose-dependent tissue distribution and/or a dose-dependent elimination process. After single-dose administration, the mean C(max) increased from 13.07 microg/ml at 2 mg/kg to 41.91 microg/ml at 6 mg/kg (P < 0.001); the AUC(0-24) changed from 11.65 to 67.44 microg. h/ml (P < 0.001), the V(d) changed from 0.205 to 0. 184 liters/kg (not significant), the CL(t) from 0.173 to 0.101 liters/kg. h (P < 0.05), and terminal half-life from 0.96 to 1.51 h (P < 0.05). There were no significant changes in pharmacokinetic parameters after multiple dosing over 14 days. Assessment of tissue concentrations of nystatin near peak plasma levels after multiple dosing over 15 days revealed preferential distribution to the lungs, liver, and spleen at that time point. Substantial levels were also found in the urine, raising the possibility that renal excretion may play a significant role in drug elimination. Liposomal nystatin administered to rabbits was well tolerated and displayed nonlinear pharmacokinetics, potentially therapeutic peak plasma concentrations, and substantial penetration into tissues. Pharmacokinetic parameters were very similar to those observed in patients, thus validating results derived from infection models in the rabbit and allowing inferences to be made about the treatment of invasive fungal infections in humans.

Dependency of cyclosporine tissue distribution and metabolism on the age and gender of rats after a single intravenous dose

In a previous study we demonstrated the dependency of cyclosporine (CyA) pharmacokinetics on the age and gender of Wistar rats given 10 mg/kg intravenously. The present study has been conducted under the same experimental conditions (10 mg/kg as a single intravenous dose) to identify the mechanisms behind such differences. On the one hand, drug distribution was studied by measuring the CyA levels in blood, liver, kidney, spleen, adipose tissue, skin and muscle at 48 h post-treatment by using a specific fluorescence polarization immunoassay ( m-FPIA, Abbott Laboratories). Drug blood and tissue levels in male rats were significantly higher than the female counterparts except for adipose tissue where the concentrations were 2-fold higher in females. In males, the highest CyA concentrations were observed in the liver, followed in rank order by kidney and spleen, fat, skin, muscle, then blood. On the contrary, females showed the highest drug levels in fat, followed by liver, kidney, spleen, skin, muscle and blood. Age exerted a significant influence on CyA tissue levels in males but no effect was observed in females. The potential differences in drug metabolism were established by measuring (HPLC) the amounts of CyA and its metabolites accumulated in faeces after hepatic biotransformation and biliary excretion. The amounts of circulating metabolites in blood as well as those accumulated and excreted in the liver and urine were also estimated by using specific ( m-FPIA) and non-specific fluorescence polarization immunoassay ( p-FPIA, Abbott Laboratories), respectively. The analysis of faeces revealed that AM9 was the major identified metabolite with females excreting lower amounts of unchanged CyA than males. In addition, the comparison of the AUC values corresponding to parent CyA and total CyA derivatives suggested that blood concentrations of CyA metabolites were higher in females indicating higher biotransformation rates. Therefore, both CyA distribution and metabolism are responsible for the sex-associated differences in drug pharmacokinetics previously found in rats.

Pharmacokinetic characterization of the indole alkaloid ibogaine in rats

To investigate the pharmacokinetic properties of ibogaine, a putatively anti-addictive alkaloid, levels of this drug were quantified in plasma and tissues for up to 3 h following i.v. infusion in rats. Immediately following a 31-35 min infusion (20 mg/kg), mean plasma ibogaine levels were 373 ng/ml; these values declined rapidly thereafter in a biexponential manner. The plasma time course in 5 of 7 animals demonstrated an excellent fit to a two-compartment pharmacokinetic model, with alpha and beta half-lives of 7.3 min and 3.3 h, respectively. Drug clearance was estimated to be 5.9 l/h (n = 7). Ibogaine levels in brain, liver and kidney 3 h after the end of drug infusion were 143-170 ng/g, close to simulated values for the peripheral pharmacokinetic compartment. However, 3-h drug levels in adipose tissue were much higher (3,328 ng/g), implying the need for a more complex pharmacokinetic model. Mechanisms for the initial, rapid disappearance of plasma ibogaine are thought to include metabolic demethylation as well as redistribution to body stores. The sequestration of ibogaine by adipose tissue probably contributes to a protracted persistence of drug in the body. This persistence may be underestimated by the beta half-life reported in the present study.

Colchicine Encapsulation within Poly(Ethylene Glycol)-Coated Poly(Lactic Acid)/Poly(?-Caprolactone) Microspheres-Controlled Release Studies

Smooth muscle cell proliferation plays a major role in the genesis of restenosis after angioplasty or vascular injury. Local delivery of agents capable of modulating vascular responses have the potential to prevent restenosis. However, the development of injectable microspheres for maintaining high tissue levels of drugs at the site of vascular injury is a major challenge. We demonstrated the possibility of entrapping an antiproliferative agent, colchicine, in polyethylene glycol (PEG)-coated biodegradable microspheres composed of poly(lactic acid)/poly(epsilon-caprolactone) blends, with a mean diameter of 3-6 microm. A solution of colchicine and blends of polylactic acid (PLA)/polycaprolactone (PCL) dissolved in acetone-dichloromethane mixture was poured into an aqueous solution of PEG (or polyvinyl alcohol) with stirring by a high-speed homogenizer to form microspheres. Colchicine recovery in microspheres ranged from 30-50% depending on the emulsification system and the ratio of polymer blends used for the preparations. Scanning electron microscopy revealed that the PLA/PCL microspheres were spherical in shape and had a smooth surface texture. Results of in vitro release studies showed that it is possible to control the colchicine release by choosing the appropriate particle size, loading, and PLA/PCL composition. Water permeability through the PLA membrane was greater, when compared with PCL blends. The amount of drug release also was much higher (58.3%) in PLA compared with PCL (39.3%) microspheres, for 30 days. Therefore, we concluded that the drug release from the microspheres followed a diffusion mechanism where bulk erosion and surface deposition were negligible. These PEG-coated PLA/PCL microspheres may have potential for targeting antiproliferative agents for prolonged periods to treat restenosis.

Drug retention and distribution after intratumoral chemotherapy with fluorouracil/epinephrine injectable gel in human pancreatic cancer xenografts.

Pancreatic cancer is widespread, associated with high mortality, and rapidly fatal. Most cases are diagnosed too late for surgical treatment, and the disease responds poorly to systemic chemotherapy. Nevertheless, pancreatic cancer cells are sensitive to fluorouracil (5-FU) in a time- and dose-dependent manner, suggesting that improved retention of drug in the tumor may improve patient prognosis. In this study, we evaluated a novel drug delivery system, 5-FU/epinephrine injectable gel (5-FU/epi gel), designed to improve drug retention in tumors. We used a BxPC-3 human pancreatic cancer xenograft model in athymic mice to examine drug levels in tumor, liver, and kidney tissue following administration of: (a) 5-FU/epi gel (30 mg 5-FU/ml) intratumorally (i.t.); (b) 5-FU solution i.t.; and (c) 5-FU solution intraperitoneally (i.p.). [(3)H]5-FU was added as a radiolabeled marker to all test formulations. Animals were sacrificed at designated times, and the tumor, liver, and one kidney from each animal were excised and processed for radioactivity analysis. Drug concentration was quantified by both storage-phosphor autoradiography (SPA) and liquid scintillation counting (LSC). Higher and sustained i.t. drug levels were achieved following i.t. administration of 5-FU/epi gel (SPA AUC 18.4 mM. h, LSC AUC 13.0 mM. h) compared with 5-FU solution i.t. (SPA AUC 2.02 mM. h, LSC AUC 1.92 mM. h) or 5-FU solution i.p. (SPA AUC 0.07 mM. h, LSC AUC 0.04 mM. h). Use of the 5-FU/gel system was associated with lower drug levels in liver and kidney, indicating that it produces far less systemic exposure. In the human pancreatic cancer xenografts, i.t. administration of 5-FU/epi injectable gel provided significantly higher drug and/or metabolite concentrations for extended periods than was possible with either i.t. or i.p administration of drug solution. This i.t. drug delivery system could potentially be used to treat patients with pancreatic cancer to increase tumor exposure to drug and improve the therapeutic index in comparison to systemic drug administration.

The placental transfer and fetal effects of levobupivacaine, racemic bupivacaine, and ropivacaine.

The purposes of this study were to assess the effects of levobupivacaine on uterine blood flow and fetal well-being and to compare its placental transfer with that of bupivacaine and ropivacaine. After a control period, pregnant ewes that were fitted with instruments for long-term monitoring were randomized to receive a two-step intravenous infusion of levobupivacaine, bupivacaine, or ropivacaine, in a blinded manner, for 1 h. Maternal and fetal hemodynamics were monitored during the study. Arterial blood samples were drawn at 30 and 60 min of infusion from the mother and fetus to determine the acid-base status (60 min only) and serum drug concentrations. The fetal brain, heart, liver, lungs, adrenal glands, and kidneys were obtained to measure tissue drug levels. Maternal blood pressure, central venous and intraamniotic pressures, acid-base status and uterine blood flow were unaffected by any drug infusion. In contrast to the other two local anesthetics, the infusion of bupivacaine was associated with a small but significant decrease in the ewe's heart rate. At the end of the study, the heart rate in the bupivacaine-treated animals was significantly less than in the animals treated with the other two drugs. All fetuses were in good condition at the start of study, and none of the local anesthetics affected fetal well-being. No significant differences were found among the three drugs in the maternal serum, fetal serum, fetal tissue concentrations, and tissue:serum concentration ratios. Levobupivacaine was similar to bupivacaine and ropivacaine in causing no important hemodynamic changes in the pregnant ewe and fetus. There were no significant differences in the fetal serum and tissue levels of the drugs.

Rapid Communication: Stability of the Fluorescence Measurement of Foscan® in the Normal Human Oral Cavity as an Indicator of its Content in Early Cancers of the Esophagus and the Bronchi

Photodynamic therapy (PDT) with Foscan (mTHPC) is used to cure early cancers of the esophagus or the tracheobronchial tree. However, fixed PDT parameters (drug dose, light dose, etc.) do not permit an accurate prediction of the tissue damage. Large interpatient fluctuations in tissue drug level, at the time of light application, suggest that the light dose must be adjusted to the drug dose shortly before the PDT. This drug dose can be measured endoscopically by light-induced fluorescence spectroscopy, but this measurement is inconvenient and somewhat difficult. A better test site, yielding comparable information, is needed. The oral cavity seems ideal. However, it first had to be established to what extent the estimation of the drug dose was dependent upon the location of the measurement and the pressure applied to the probe. These measurements prove to be not only correlated to similar measurements in the esophagus or the bronchi but also more consistent and less sensitive to the location and the applied pressure. The buccal mucosa is therefore recommended as a test site for measuring the Foscan fluorescence signal at the time of PDT in the esophagus or the bronchi. This measurement is accurate enough for use in light-dose adjustment.

EARLY SKIN BUT NOT WHOLE-BLOOD CYCLOSPORINE (CSA) LEVELS CORRELATE WITH REVERSIBILITY OF REJECTION IN A NOVEL SWINE COMPOSITE TISSUE ALLOGRAFT (CTA) MODEL

237 With an eye toward direct clinical application, we developed a porcine brachial artery-based radial forearm osteomyocutaneous flap allograft model to assess the antirejection efficacy of CSA/mycophenolate mofetil (MMF) treatment. Transplants were performed between size-matched, outbred donor-recipient pairs (n=5). A once-daily oral CSA/MMF/prednisone regimen was used: CSA dose was 40 mg/kg/d, adjusted to maintain 24 hr trough levels between 100-300 ng/ml by the EMIT assay; MMF dose was 1 g/d; and prednisone was tapered from 2.0 to 0.1 mg/kg/d over 30 days. Drug doses were not adjusted based on the clinical course. Graft skin biopsies were performed at 0, 2, 4, 7, 10, 14, 21, 30, 45, 60, and 90 days posttransplant. Histologic grading of skin rejection (I, mild-IV, severe) was based on the severity of vasculitis; dermal inflammation; folliculitis; and epidermal degeneration. CSA trough levels were determined daily for the first 3 weeks; then 3X/week for the next 3 weeks; and then weekly. Skin CSA levels were measured on days 2, 7, 14, 21, 30, 45, 60, and 90 using the EMIT assay. All 5 pigs developed grade I-II rejection by day 7. However, rejection reversed spontaneously in 3 pigs (#1-3), which remained rejection-free at 90 days, but progressed in 2 pigs (#4, 5), with graft loss from grade IV rejection on days 25 and 29. (Table)TableDespite lower mean blood [CSA] during the first week, pigs #1-3 were able to subsequently reverse established mild to moderate acute rejection occurring by day 7, presumably as a result of achieving higher local skin [CSA] within the allograft. Indeed, these pigs displayed higher Kp values on day 2, day 7, and overall during the first week (p=0.09, 0.09, and 0.01, respectively, by unpaired t-test vs #4,5), indicating that more CSA was being distributed to the skin relative to the blood in these animals in the early posttransplant period. There were no differences between the subgroups with regard to mean blood or skin [CSA] or Kp values during weeks 2 and 3. Skin [CSA] correlated significantly with blood [CSA] only in pig #3 (r = 0.97, p = 0.005 by Fisher's r to z test). Our preliminary data in a small number of animals suggests that (1) early attainment of adequate local [CSA] within CTA skin may be more important in inhibiting rejection than systemic blood levels and that this may be dependent upon the Kp; and (2) monitoring local tissue drug levels may be essential to proper immunosuppressive management of CTAs.

Effect of Emblica officinalis, Phyllanthus amarus and Picrorrhiza kurroa on N-nitrosodiethylamine induced hepatocarcinogenesis

Extracts of Emblica officinalis (EO), Phyllanthus amarus ( P. amarus) and Picrorrhiza kurroa ( P. kurroa) significantly inhibited hepatocarcinogenesis induced by N-nitrosodiethylamine (NDEA) in a dose dependent manner. The anticarcinogenic activity of these extracts were evaluated by their effect on tumour incidence, levels of carcinogen metabolizing enzymes, levels of liver cancer markers and liver injury markers. Animals treated with NDEA alone showed 100% tumour incidence and significantly elevated tissue levels of drug metabolizing enzymes such as glutathione S-transferase (GST) and aniline hydroxylase (AH). Treatment of extracts significantly reduced these levels. Levels of γ-glutamyl transpeptidase (GGT) were also found to be elevated both in serum and tissues of tumour bearing animals, while they were significantly reduced in the treated group. Similar reduction was seen in tissue levels of reduced glutathione. Serum levels of lipid peroxide (LPO), alkaline phosphatase (ALP) and glutamate pyruvate transaminase (OPT), which are markers of liver injury, were also elevated. Morphology of liver tissue and levels of marker enzymes indicated that these extracts offered protection against chemical carcinogenesis.

Stability of the Fluorescence Measurement of Foscan® in the Normal Human Oral Cavity as an Indicator of its Content in Early Cancers of the Esophagus and the Bronchi

Photodynamic therapy (PDT) with Foscan (mTHPC) is used to cure early cancers of the esophagus or the tracheobronchial tree. However, fixed PDT parameters (drug dose, light dose, etc.) do not permit an accurate prediction of the tissue damage. Large interpatient fluctuations in tissue drug level, at the time of light application, suggest that the light dose must be adjusted to the drug dose shortly before the PDT. This drug dose can be measured endoscopically by light-induced fluorescence spectroscopy, but this measurement is inconvenient and somewhat difficult. A better test site, yielding comparable information, is needed. The oral cavity seems ideal. However, it first had to be established to what extent the estimation of the drug dose was dependent upon the location of the measurement and the pressure applied to the probe. These measurements prove to be not only correlated to similar measurements in the esophagus or the bronchi but also more consistent and less sensitive to the location and the applied pressure. The buccal mucosa is therefore recommended as a test site for measuring the Foscan fluorescence signal at the time of PDT in the esophagus or the bronchi. This measurement is accurate enough for use in light-dose adjustment.

Intravitreal pharmacokinetics in rabbits of the foscarnet lipid prodrug: 1-O-octadecyl-sn-glycerol-3-phosphonoformate (ODG-PFA)

Purpose. To evaluate the intraocular distribution and metabolism of the lipid prodrug of foscarnet, 1- O -octadecyl- sn -glycerol-3-phosphonoformate (ODG-PFA), following intravitreal administration. Methods. Twenty rabbits received ODG-[14C]PFA intravitreal injection, yielding 0.632 mM resultant intravitreal concentration. Two animals per group were sacrificed at different intervals post-injection. The drug levels in ocular tissues were determined with counting the radioactivity by Tracor Mark III Liquid Scintillation Counter. Four rabbits were used for analysis of the drug metabolism in vitreous by lipid extraction technique. Results. The drug level in vitreous was 526 µM at day one and 227 µM at the fifth week. The vitreous half life was approximately four to five weeks. The retinal level of the drug was 292 µM at day one, 75 µM at the fifth week and 32 µM at the tenth week, which was still more than ten times higher than the IC90 against HCMV. Lipid extraction analysis showed that, in vivo, both ODG-PFA and PFA were present in vitreous, but in in vitro incubations with vitreous, ODG-PFA conversion to PFA was negligible. Conclusion. ODG-PFA possesses a long vitreous half life and sustained high drug level in retina. The vitreous did not metabolize drug but acted as a drug reservoir. Intravitreal liposomal ODG-PFA may be expected to be a long acting potent local therapy for CMV retinitis.

Ocular drug targeting by liposomes and their corneal interactions

Topical drug delivery is preferred in the eye to avoid under or over medication and undesired side effects of systemic administraion. In order to maintain adequate drug levels in ocular tissues, frequent drug installation is necessary in vision threatening conditions like glaucoma, corneal ulcers due to microbial infections, etc. Only apart of the installed drug reaches the aqueous humor and the rest of it is drained by the nasolacrimal duct. Positively charged liposomes have been found to enhance the penetration of drugs into the cornea. The present study was conducted to visualize the interaction of liposomes with the cornea. Briefly, positively charged liposomes entrapped with Carboxyfluorescein (CF), Propidium iodide (PI), Horseradish peroxidase (HRP), Biotin, Hydroxy benzimide (Hoechst No: 33258), and Ethoxy benzimide (Hoechst No: 33342) were prepared by sonication. Their size and shape were analysed by laser dynamic lightspectraand electron microscopy, respectively. The liposome encapsulated and free materials in buffer were instilled, in a volume of 20mul, into eyes of anesthetized albino rats. After 30min and 1h, the eyes were enucleated and quickly processed for cryosections of 3-5mum thickness. The interaction of liposome entrapped propidium iodide and HRPwas visualized on the outer epithelium of the cornea after specific processing.

Pharmacokinetics of Azithromycinin Rabbit Lacrimal Glands and Conjunctiv a

Purpose and Background: To measure azithromycin levels in rabbit lacrimal and Harder glands, conjunctiva and plasma after a single oral dose of 20 mg/kg. Drug levels in lacrimal gland tissue are significant in trachoma because the gland may be involved in the disease process and it is the source of tears by which the drug is carried to the external eye. Methods: Lacrimal and Harder glands, conjunctiva and plasma were collected from New Zealand white female rabbits at 24, 48, 72, 96 and 144 h following a single oral dose of azithromycin (20 mg/kg). Azithromycin levels in tissue and plasma were measured using high-performance liquid chromatography (HPLC) electrochemical detection. Results: Azithromycin levels peaked within the first 24 h in all tissues and plasma assayed. The highest concentration was in the lacrimal gland (6.2 µg/g, SD ± 0.8), followed by Harder gland (4.4 µg/g, SD ± 0.8), conjunctiva (0.9 µg/g, SD ± 0.5) and plasma (0.06 µg/g, SD ± 0.03). These concentrations reached their lowest measured levels at 120 and 144 h. Conclusion: Azithromycin levels measured throughout the 144 h after dosing were consistently above the minimum inhibitory range (MIC) for Chlamydia trachomatis (0.03–0.25 µg/ml) in the lacrimal glands, while the conjunctiva maintained a concentration above the MIC for 96 h and stayed within MIC levels for 144 h.

Compartmental pharmacokinetics and tissue drug distribution of the pradimicin derivative BMS 181184 in rabbits.

The pharmacokinetics of the antifungal pradimicin derivative BMS 181184 in plasma of normal, catheterized rabbits were characterized after single and multiple daily intravenous administrations of dosages of 10, 25, 50, or 150 mg/kg of body weight, and drug levels in tissues were assessed after multiple dosing. Concentrations of BMS 181184 were determined by a validated high-performance liquid chromatography method, and plasma data were modeled into a two-compartment open model. Across the investigated dosage range, BMS 181184 demonstrated nonlinear, dose-dependent kinetics with enhanced clearance, reciprocal shortening of elimination half-life, and an apparently expanding volume of distribution with increasing dosage. After single-dose administration, the mean peak plasma BMS 181184 concentration (Cmax) ranged from 120 microg/ml at 10 mg/kg to 648 microg/ml at 150 mg/kg; the area under the concentration-time curve from 0 to 24 h (AUC0-24) ranged from 726 to 2,130 microg . h/ml, the volume of distribution ranged from 0.397 to 0.799 liter/kg, and the terminal half-life ranged from 4.99 to 2.31 h, respectively (P < 0.005 to P < 0.001). No drug accumulation in plasma occurred after multiple daily dosing at 10, 25, or 50 mg/kg over 15 days, although mean elimination half-lives were slightly longer. Multiple daily dosing at 150 mg/kg was associated with enhanced total clearance and a significant decrease in AUC0-24 below the values obtained at 50 mg/kg (P < 0.01) and after single-dose administration of the same dosage (P < 0.05). Assessment of tissue BMS 181184 concentrations after multiple dosing over 16 days revealed substantial uptake in the lungs, liver, and spleen and, most notably, dose-dependent accumulation of the drug within the kidneys. These findings are indicative of dose- and time-dependent elimination of BMS 181184 from plasma and renal accumulation of the compound after multiple dosing.

Skin Necrosis due to Photodynamic Action of Benzoporphyrin Depends on Circulating Rather than Tissue Drug Levels: Implications for Control of Photodynamic Therapy

In an ideal world, photodynamic therapy (PDT) of abnormal tissue would reliably spare the surrounding normal tissue. Normal tissue responses set the limits for light and drug dosimetry. The threshold fluence for necrosis (TFN) was measured in normal skin following intravenous infusion with a photosensitizer, benzoporphyrin derivative monoacid ring A (BPD-MA) Verteporin as a function of drug dose (0.25-2.0 mg/kg), wavelength of irradiation (458 and 690 nm) and time interval (0-5 h) between drug administration and irradiation. The BPD-MA levels were measured in plasma and skin tissue to elucidate the relationship between TFN, drug kinetics and biodistribution. The PDT response of normal skin was highly reproducible. The TFN for 458 and 690 nm wavelengths was nearly identical and the estimated quantum efficiency for skin response was equal at these two wavelengths. Skin phototoxicity, quantified in terms of 1/TFN, closely correlated with the plasma pharmacokinetics rather than the tissue pharmacokinetics and was quadratically dependent on the plasma drug concentration regardless of the administered drug dose or time interval between drug and light exposure. This study strongly suggests that noninvasive measurements of the circulating drug level at the time of light treatment will be important for setting optimal light dosimetry for PDT with liposomal BPD-MA, a vascular photosensitizer.

COADMINISTERED NEORAL AND THE NEW RAPAMYCIN DERIVATIVE, SDZ RAD, FOR NONHUMAN PRIMATE LUNG TRANSPLANTATION: SYSTEMATIC PHARMCOKINETIC-BASED TRIALS TO MAXIMIZE EFFICACY AND TOLERABILITY

677 This is the first preclinical study to exploit blood drug levels (PK) to guide trial design and drug tissue levels to interpret adverse events. A stringent lung graft model combined with complex interactions between Neoral and RAD required a thorough understanding of the relationships among PK,efficacy and toxicity at each stage of the study to insure progressive improvements. Method: 39 cynomolgus monkeys were recipients of MLR-mismatched unilateral lung transplants (tx) and sacrificed either at the end of 28 daily PO drug treatments or earlier if clinically ill. Follow-up included serial trough blood drug levels (LC/MS), blood chemistries, chest radiographs and tissue drug levels and graft biopsies at necropsy. At each stage of the study, existing data from tx and nontx monkeys were used to design treatment regimens for subsequent groups. Results: Perioperative complications excluded 3 monkeys from analysis. Biopsies of grafts in vehicle treated monkeys (n=4) and those treated with Neoral (150 mg/kg, d 1-7; 100 mg/kg, d 8-28; n = 6; mean±SE trough level(MTL):276±17 ng/ml) or RAD (1.5 mg/kg; n = 6; MTL:13±1 ng/ml) monotherapy showed severe rejection. Combining Neoral (150/100mg/kg) and RAD(1.5 mg/kg) in 2 tx monkeys caused early death in both animals and produced a more than 4-fold increase in RAD trough levels (>80 ng/ml). A PK study in nontx monkeys on the same drug regimen confirmed equally elevated RAD trough levels (MTL:101±20 ng/ml). In nontx monkeys co-administration of Neoral and RAD required a 4-fold decrease in the RAD dose to achieve RAD levels of less than 25 ng/ml. In tx monkeys, Neoral (150/100 mg/kg; MTL:205±12 ng/ml) + RAD (0.3 mg/kg; MTL:21±2 ng/ml) improved graft outcome (mild rejection), but 3 monkeys were euthanized on days 21-23 due to renal failure(n=2) and seizures (n=1). In an attempt to improve efficacy and safety and reduce potential drug interaction staggered administration was compared to simultaneous treatment in nontx monkeys using a Neoral dose of 50 mg/kg (to limit CsA toxicity) and a RAD dose of 1.5 mg/kg (to maintain efficacy). Staggered treatment resulted in significantly lower RAD trough levels(MTL:40±6ng/ml) than simultaneous treatment(MTL:54±4ng/ml;p<0.04) while CsA-levels were comparable (MTL: sim. 171±14 ng/ml, stag: 179±23 ng/ml). The staggered regimen in tx monkeys resulted in no rejection in 4 grafts and minimal or mild rejection in 1 graft each. However, 5/6 monkeys had moderate or severe diarrhea (3 requiring euthanasia before d 28). These results led us to perform a concentration-controlled trial (CCT) of simultaneously administered Neoral and RAD in tx monkeys (target RAD MTL:20-40 ng/ml; CsA MTL:100-200 ng/ml). All 6 tx monkeys survived until study completion with improved drug tolerability and an average biopsy score of only mild rejection. Compared to RAD monotherapy, colon RAD tissue levels in the staggered and CCT group were 12x and 3x greater, respectively. Conclusion: 1) A combination of orally administered RAD and Neoral showed unprecedented efficacy of an immunosuppressive regimen in a stringent transplant model. 2) Complex Neoral-RAD drug interactions in monkeys necessitated the use of PK and drug tissue levels to guide trial design and interpret adverse events leading to improvements in efficacy and safety 3) The best balance of efficacy and tolerability was achieved in lung transplanted monkeys with a concentration-controlled, rather than fixed dose regimen. Funded by Novartis.