Increase In Drug Levels Research Articles

Intensification with Intravenous Ustekinumab in Refractory Crohn’s Disease

Background: The rates of clinical and biochemical responses in Crohn’s disease (CD) patients treated with intravenous (IV) ustekinumab (UST) intensification are scarcely described. Methods: Patients with diagnosis of CD who were under intensified IV ustekinumab treatment (130 mg every 4 weeks) were retrospectively included, evaluating the clinical and biochemical response 12 weeks after the change in treatment regimen (switch from SC to IV), as well as the serum levels of the drug. Results: Twenty-seven patients, all of whom had transitioned to intensified intravenous ustekinumab treatment due to a secondary loss of response to the drug, were included in the retrospective analysis. At the baseline visit, prior to changing IV UST, differences in levels were observed between intensified and non-intensified patients (7216 vs. 2842 ng/mL, p = 0.00005). However, no significant differences were found between these two groups 12 weeks after IV intensification (7949 vs. 7937 ng/mL; p = 0.99). In patients with previous intensified UST SC, a decrease in fecal calprotectin was observed 12 weeks after starting IV intensification, going from a mean of 1463 ug/g to 751 ug/g, although the differences were not significant (p = 0.14). Conclusion: In our experience, intensifying treatment with IV UST leads to clinical and biochemical improvements in CD patients with a secondary loss of response to SC maintenance with this drug, and an increase in drug levels was observed 12 weeks after IV UST intensification.

P657 Persistence of subcutaneous infliximab after two years of the switch from intravenous infliximab to subcutaneous infliximab in Inflammatory Bowel Disease patients

Abstract Background Biosimilar infliximab (CT-P13) has been available for subcutaneous (SC IFX) administration since march 2021. It has shown to be equivalent to its every-8-week-intravenous formula (IV IFX), however, we do not have long term efficacy and safety data. Our aim was to evaluate medication persistence, efficacy and safety two years after switching from IFX IV to IFX SC Methods Multicentre, descriptive, and observational study, with prospective data collection, of Crohn’s Disease (CD) or Ulcerative Colitis (UC) patients who were going to be changed from IV IFX to SC IFX. All patients were on clinical and biological remission for at least 6 months. Clinical activity, analytical data, trough level determinations and adverse events were gathered. Baseline results were compared with those from week 108 after starting CT-P13 SC. Maintenance of the drug after two years and the reason for removal, if so, or of loss of follow-up, were evaluated. Results 41 patients were included. 24 of whom had intensified doses while 17 were on standard doses (5 mg/kg every 8 weeks). 51% were male; mean age 40.8. 63,4 % (n = 26) had CD. No PCR differences were observed at baseline (IV IFX) [median 0,17 mg/dL] and week 108 [median0,3 mg/dL]. Fecal calprotectin stayed under 200 ug/mg from baseline to 24 months. No changes in clinical indexes were observed. A considerable increase in drug levels was observed after switching to SC IFX at week 108 (6,8 vs 12.3; p < 0,001). 46% of the patients were also on immunosupressor when they switched to IFX SC, and 52% of these had removed it after 2 years of IFX SC. 85% of the patients were still on IFX SC after two years (only one was removed due to loss of response). There were only 3 adverse events, all of which were mild. Conclusion Persistence of IFX SC after two years was observed in 85% of the patients. Switching from IV IFX to SC IFX maintains remission in Inflammatory Bowel Disease (IBD) after a 2-year follow-up. Higher drug levels are obtained with the subcutaneous formulation, despite removing the immunosupressor in over 50% of the patients. Switching from IV IFX to SC IFX is safe in IBD.

Validation of a novel direct method to determine reduced adherence to atorvastatin therapy

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): Drammen hospital. Introduction Objective methods to monitor statin adherence may be a useful supplement to improve lipid management. We have recently established a test procedure with cut-off values that discriminate reduced adherence to atorvastatin therapy, defined by ≥2 doses omitted, by liquid chromatography–tandem mass spectrometry measurements of plasma drug concentrations. Purpose To validate our direct method for atorvastatin adherence in a larger sample, and to optimize previous cut-off values of reduced adherence according to pharmacokinetic variability. Methods We designed a clinical pharmacokinetic adherence study with 59 participants treated with atorvastatin 20 mg (N=20), 40 mg (N=20) and 80 mg (N=19). All were instructed to administer atorvastatin between 7 and 9 AM for at least seven days prior to study start to ensure steady-state drug concentrations. At the first study day, they met at the hospital outpatient clinic without having taken their morning dose. Two blood samples were collected with a one-hour interval (t24h and t25h) to detect any unscheduled morning dose. The participants temporarily stopped dosing and returned to the outpatient clinic the subsequent four days for blood samples for analyses of drug concentrations. Dose-normalized levels of atorvastatin plus all five major metabolites off statin treatment (t72h) were validated against the previously derived cut-off by calculating diagnostic sensitivity and specificity. Optimization of the cut-off value was sought by comparing dose-normalized concentrations off statin (t72h) with the adherence state at baseline (t24h). Results Mean age was 65.5 (SD 11.1) years, 31% women and 42% had atherosclerotic CVD. No participants had a significant increase in drug levels at baseline, confirming no ingestion of an unscheduled morning dose. The sum of parent drug and all major metabolites correlated moderately with the dose taken (Spearman’s rho= 0.40, 95% CI 0.15-0.60) at baseline (t24h). Hypo- or hyperthyroidism (β from linear regression 0.42, 95% CI 0.17–0.66) and diabetes (β 0.30, 95% CI 0.04–0.34) were associated with dose-normalized trough concentrations of atorvastatin plus metabolites in adjusted analyses, whereas age, gender, body weight, liver function or total number of drugs were not. Our previously suggested cut-off for reduced adherence (≥2 doses omitted), i.e. dose-normalized sum of atorvastatin plus metabolites <0.10 nM/mg, provided a sensitivity of 97% and a specificity of 95%. An alternative cut-off at <0.065 nM/mg provided a sensitivity of 90% and a specificity of 100%. With this alternative cut-off, no adherent participants would be misclassified with reduced adherence. Conclusion This validation study confirms that our direct method discriminate adherence from reduced adherence to atorvastatin therapy with high diagnostic accuracy. The method may be advantageous for the improvement of lipid management in clinical practice and serve as a useful tool in future studies.

P737 Intensification with intravenous ustekinumab in refractory Crohn′s disease

Abstract Background There is little scientific evidence available about the results in terms of clinical and biochemical response after intensification with intravenous (IV) ustekinumab (UST) as a therapeutic strategy to be used in patients with refractory Crohn’s disease (CD) who are receiving subcutaneous (SC) treatment with said drug. Methods Patients with CD in stable follow-up at Hospital Universitario La Paz (Madrid), who were undergoing intensified treatment with IV UST, were recruited. The objective of the study was to assess the clinical and analytical response and drug levels 12 weeks after the change from subcutaneous to intravenous UST. Results 27 patients were retrospectively included, all of them with previous treatment with UST SC. In Table 1 baseline characteristics are collected. Out of the 27 patients included, 4/27 were under treatment with UST in first line, 10/27 in second line, 9/27 in third line and 4/27 had failed to three biologics. The reason for intensification with IV UST was the lack of response to treatment in the 27 patients, 7 of them (25.93%) being found in the context of post-surgical recurrence. On the other hand, 10 patients (37.03%) were already under treatment with intensified SC UST, while the remaining 17 patients (62.96%) were under treatment with a standard schedule of SC UST every 8 weeks. At the baseline visit, prior to the change to IV UST, differences in levels were observed between intensified and non-intensified patients (7216 vs 2842, p=0,00005). However, no significant differences were appreciated between these two groups 12 weeks after IV intensification (7949 vs 7937; p=0,99). In patients with intensified UST SC was observed a decrease in fecal calprotectin 12 weeks after starting IV intensification, going from a mean of 1463 to 751, although the differences were not significant (p=0,14). In Figure 1 is shown improvement in fecal calprotectin levels and in Figure 2 improvement in UST levels in blood is reflected, both parameters quantified 12 weeks after intravenous intensification of the drug. In Table 2 data derived from the analysis of the clinical activity and determinations of CRP and calprotectin are collected, before performing the intensification with UST IV and 12 weeks after it. Conclusion In our experience, change to intravenous ustekinumab in maintenance led to an improvement in the clinical and biochemical response in patients with Crohn’s disease (even in patients already intensified). Likewise, an increase in drug levels was observed 12 weeks after the change from subcutaneous to intravenous treatment.

The effect of infliximab dose escalation in inflammatory bowel disease patients with antibodies to infliximab.

Infliximab dose escalation (DE) can be used in inflammatory bowel disease patient; however, the long-term benefit remains unclear, especially in those with antibodies to infliximab (ATI). The aim was to assess the effect of DE in patients with ATI on drug level, clinical response and ATI status. All patients undergoing infliximab DE (a reduction in dose interval between infusions <8 weeks ± an increase in dose up to 10 mg/kg) at a referral centre between April 2016 and August 2019 were included. Ninety-two patients were DE: 51 were men, 50 had CD and 63 were receiving immunosuppression. A total of 87 people received DE for a median of 44 weeks (range 4-176). Five stopped infliximab after 1 dose of DE: 2 for loss of response and 3 for infusion reaction. In patients with ATI ≤10 vs. >10 AU/mL, DE significantly increased drug levels: median infliximab levels of 1.4 and 0.9 at baseline, respectively, to 3.2 and 3.5 at week 24. After DE, 21/35 ATI-positive patients had a fall in ATI ≤10 AU/mL. At week 24 following DE 62/92 patients were in clinical remission. Duration of clinical remission was shorter in those with ATI >10 AU/mL (median 24 weeks, range 0-88) than in those with transient/ATI ≤10 AU/mL (median 36 weeks, range 0-126, P = 0.06). A strategy of DE for selected patients receiving infliximab is associated with an increase in drug levels and reduced ATI positivity. This is associated with clinical remission in approximately 70% of patients at 6 months.

CML-268: Study to Evaluate the Effect of Fatty Meals on Nilotinib Drug Levels in Patients with CML-CP

Context: Nilotinib is an oral tyrosine kinase inhibitor used in chronic myeloid leukemia (CML) and is known to have food interactions. It is recommended for administration in a fasting state (meals taken either 2 hours after dose or 1 hour before a dose). Food, especially fat-rich food, has been shown to increase the bioavailability of drugs. If the drug is allowed to be taken with food, it will be convenient for patients and also lower the dose needed to produce clinical benefit. This will decrease the cost of therapy and will improve the quality of life of patients. Objective: To assess the effect of fatty meals on nilotinib drug levels in patients with CML. Design/Setting/Patients/Intervention: It is a single-center, open-label, pharmacokinetic study. There were 5 cohorts with 6 patients enrolled in each. A total of 30 patients were included in the study. The patient population included patients of newly diagnosed CML (chronic phase). The dose of nilotinib in each cohort was 150 mg OD, 200 mg OD, 150 mg BD, 200 mg BD, and 300 mg BD, respectively. The drug was given an empty stomach for an initial 8 days, followed by fatty meals for the next 8 days. Fatty meals were defined as 2 slices of bread with 10 grams of butter. Two ml blood was withdrawn at specified time points at 0 hours, 1 hour, 2 hours, 3 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 16 hours, 20 hours, and 24 hours and on day 8 (0 hour and 3 hours). Nilotinib drug levels were estimated by liquid chromatography mass spectrometry. Main Outcome Measures: To assess serum drug levels of nilotinib in both fasting and post-meals statuses to determine an increase in drug levels with fatty meals. Results: Initial results of the study have shown the significant benefit of food on nilotinib drug levels. We will discuss the complete results at the SOHO conference. Acknowledgements: The study is funded by a research grant from the Indian Council of Medical Research, New Delhi (ICMR).

Investigation of 3′-debenzoyl-3′-(3-([124I]-iodobenzoyl))paclitaxel analog as a radio-tracer to study multidrug resistance in vivo

A study was carried out to identify a suitable radioactive paclitaxel analog and to use it to investigate tumor multidrug resistance in vivo. 3′-Debenzoyl-3′-(3-([124I]-iodobenzoyl))paclitaxel was prepared by aromatic iodination of 3′-debenzoyl-3′-(3-trimethylstannylbenzoyl)paclitaxel. Uptake of the labeled paclitaxel analog in nude mice bearing tumor with the paclitaxel sensitive cancer cell lines MCF7 and MDA-435/LCC6(WT), and multidrug resistant cell lines NCI/ADR-RES and MDA-435/LCC6(MDR), was studied. There was no difference in drug level between the sensitive and resistant MDA-435/LCC6 tumors at 6h post-injection. However, at 6h, there was a significant increase in drug level for the MCF7 tumor as compared with the NCI/ADR-RES tumor, presumably due to increased drug retention. At 24h, drug uptake/retention was significantly higher in both sensitive tumor cell lines as compared to their drug resistant counterparts. Pretreatment of mice with MDR transport modulators, Cyclosporine or tRA 96029, did not increase the level of labeled paclitaxel analog in the drug resistant MDA-435/LCC6(MDR) tumor. On the other hand, at 24h Cyclosporine apparently increased analog level in the drug sensitive MDA-435/LCC6(WT) tumor, aiding drug imaging studies.

Abstract 5537: GSH-conjugation improves efficacy of Doxil against intracranial xenografts

Abstract High-grade glioma is a uniformly fatal disease with an unmet need for better therapy. A major reason for this poor outcome is the invasive nature of gliomas. Novel therapies that target invasive brain tumor cells should be invented, but a major impediment to the delivery of adequate amounts of therapeutics is the blood brain barrier (BBB), which is largely intact in regions where invasive cells reside. Glutathione (GSH)-conjugated PEGylated liposomes (G-TechnologyTM) may be suitable vehicles for targeted delivery of small molecule cytotoxic drugs across the BBB. GSH is a natural anti-oxidant that is found at high levels in the brain and its active transporter is abundantly expressed at the BBB. Previous studies using microdialysis with an increasing % of GSH conjugated to liposomes carrying ribavirin have shown a %GSH-dependent increase of drug levels in brain interstitial fluid (up to 5-fold higher), and GSH-liposomes carrying endomorphin-1 were more effective in hot-plate tests when compared to unconjugated liposomes. We have now tested GSH-conjugated PEGylated liposomes containing doxorubicin (GSH-Doxil) for treatment of mice carrying intracranial U87 xenografts. In a first series, we compared 5%GSH-Doxil to conventional Doxil, free doxorubicin (Dx) and untreated controls. Mice were injected with 10^5 U87-luc cells and bioluminescence (BL) imaging was used for follow up. After 11 days, mice were stratified into control or test groups (n=9 / group). Mice received 3 consecutive weekly dosings of 5 mg/kg Dx-equivalents. The cohorts receiving Doxil and Dx showed a marginal growth delay relative to controls. The response with 5%GSH-Doxil was more promising but variable: two animals receiving 5%GSH-Doxil showed complete regression, which was not observed in any of the other cohorts, whereas other tumors in this cohort responded more similar to the other treatment groups. Since the treatment was well tolerated, we performed another more dose-intense series, administering biweekly 5 mg/kg Dx equivalents. Moreover, 5%GSH-Doxil and 3%GSH-Doxil were tested relative to Doxil and untreated controls. Treatment started at day 14 after tumor cell injection, stratifying only animals whose tumor BL signals increased relative to day 11. After day 25 the animals experienced weight loss that precluded further dosing. In this series, the variation in tumor response was small. There was again one complete regression in the cohort of 5%GSH and not in any of the other cohorts. Moreover, the growth delay in the other tumors in this 5%GSH-Doxil cohort was significantly longer than in any of the other groups. This growth delay translated into a significantly increased median survival of 32.5 days relative to 27 days for untreated controls. The response in the 3%GSH and Doxil cohorts was marginally better relative to controls. Overall these results warrant further preclinical and clinical investigation using 5%GSH-Doxil liposomes. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5537.

Abstract A218: Pharmacokinetic (PK) and pharmacodynamic (PD) data for MPC-3100, a fully synthetic HSP90 inhibitor, in cancer patients

Abstract Purpose: MPC-3100 is a fully synthetic, orally bioavailable, HSP90 inhibitor that recently entered Phase I clinical studies. We show updated xenograft data and preliminary PK/PD data in cancer patients. Experimental Design: MPC-3100 was dosed either daily or five out of every 7 days for a total of three weeks, as indicated, for most pre-clinical studies. Following acute and 28-day repeated dose toxicology studies in rats and cynomolgus monkeys, a human clinical study was initiated at a starting dose of 50 mg/m2. MPC-3100 is administered by mouth in tablet form for 21 consecutive days in a 28 day cycle to each enrolled subject. For determination of drug levels in humans, plasma was collected prior to drug administration and 0.5 , 1, 2, 3, 4, 6, 8, and 24 hours post-dosing on cycle 1 day 1, and cycle 1 day 21. Plasma was collected pre-dose only for cycle 1 day 8. Peripheral blood mononuclear cells (PBMCs) were collected prior to drug administration, and 8 and 24 hours post-dose on cycle 1 day 1 and cycle 1 day 21 in order to quantitate Hsp70 protein levels as an exploratory biomarker. Results: Animals implanted with a large number of cancer cell types (MV-4-11, HT29, DU145, NCI-H69, OVCAR-3, BT-474, NCI-N87, and OPM-2) as xenografts and dosed with 200 mg/kg of MPC-3100 displayed activity that ranged between 68% tumor growth inhibition and 44% regression. Animals showed no significant weight loss. We present preliminary PK and PD data from three patients with metastatic cancer who have been treated with MPC-3100. Hsp70 levels in PBMCs showed an increase 8 hours after the first dose which was sustained on Day 8 and Day 21. There was a more than proportional increase in drug levels with increasing dose. Plasma Cmax and AUC(0-24) in the patient dosed at 165 mg/m2 (11789 ng/mL and 199,749 hr*ng/mL at day 21) are comparable in magnitude to those achieved in tumor bearing mice after a single dose of 200 mg/kg (21841 ng/mL and 135,779 hr*ng/mL, respectively). The drug level achieved in humans has demonstrated anti-tumor activity in multiple mouse xenograft models. No dose limiting toxicities have been reported to date. Conclusion: MPC-3100 is orally bioavailable in cancer patients. The pharmacokinetic properties and drug concentration achieved in patients are similar to those observed in efficacious mouse experiments. Dose (mg/m2)/Total daily dose (mg) Cycle 1 Timepoints T ½ (hr)/ Cmax (ng/mL)/Cmin (ng/mL)/AUC (0–24) (hr*ng/mL) Hsp70* 50/100 day 1 8.5/1903.5/0.0/20636.0 104 50/100 day 8 N/A/N/A/162.0/N/A 85 50/100 day 21 13.4/1700.5/456.6/21992.0 63 100/160 day 1 9.8/2984.8/0.0/30230.0 16 100/160 day 8 N/A/N/A/914.3/N/A 53 100/160 day 21 11.2/3182.1/818.1/49805.0 −25 165/300 day 1 11.5/6869.2/0.0/91824 43 165/300 day 8 N/A/N/A/2086.3/N/A 34 165/300 day 21 14.0/11789.0/4874.4/199749.0 72 Single dose N-87 tumor bearing mice 200 mg/kg 4.8/21841.0/N/A/135779.8 N/A * Hsp70 induction (ng/ mg of total protein) Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A218.

EVA copolymer matrix for intra-oral delivery of antimicrobial and antiviral agents

Biocompatible ethylene vinyl acetate copolymer (EVA) was utilized to study the release of an antiviral drug (acyclovir (ACY)) and an antimicrobial drug (doxycycline hyclate (DOH)). Release of both drugs from EVA was measured individually and in combination. The effect of drug combination of DOH and ACY is presented. Additionally, the release rate of DOH after coating of the matrix with a different copolymer, in drug-loading with increasing loads of DOH, and with increases in temperature are also presented. The drugs incorporated in EVA films were prepared from the dry sheet obtained by solvent evaporation of polymer casting solutions with drugs. Drug release from the films was examined for about 12 days in distilled water at 37 degrees C. Changes in optical density were followed spectrophotometrically. The combination of ACY and DOH resulted in an increased release of ACY by about three times (P < 0.001) while DOH showed a decrease in rate of about two times compared to the individual release rates (P = 0.008). Increases in drug levels of DOH resulted in increases in drug release rates (P = 0.001). The release rate of DOH increased with temperature (P = .001; 27, 32, 37 and 42 degrees C were studied) and the energy of activation (DeltaE ( not equal) = 56.69 kJ/mol) was calculated using the Arrhenius equation for the diffusion of DOH molecules. Thus, the release rates of drugs were influenced by many factors: drug combination, coating the device, drug-loading, and temperature variation. Therefore it is proposed that controlling these variables should make it possible to obtain therapeutic levels of drugs released from drug loaded polymer, which may be beneficial in treating oral infections.

Ocular Tolerability and In Vivo Bioavailability of Poly(ethylene glycol) (PEG)‐Coated Polyethyl‐2‐Cyanoacrylate Nanosphere‐Encapsulated Acyclovir

Acyclovir‐loaded polyethyl‐2‐cyanoacrylate (PECA) nanospheres were prepared by an emulsion polymerization process in the micellar phase and characterized. The influence of the presence of nonionic surfactant as well as other substances [i.e., 2‐hydroxypropyl‐β‐cyclodextrin (HP‐β‐CyD) and poly(ethylene glycol) (PEG)], on formulation parameters and loading capacity was investigated. In particular, the presence of PEG resulted in an increase of mean size and size distribution. To obtain PEG‐coated PECA nanospheres with a mean size of < 200 nm, Pluronic F68 at concentrations > 1.5% (w/v) should be used during preparation. The presence of PEG also resulted in a change in zeta potential, from −25.9 mV for uncoated nanospheres to −12.2 mV for PEG‐coated PECA nanospheres. The presence of HP‐β‐CyD elicited an increase of nanosphere size and size distribution, but zeta potential was not influenced. In vitro drug release from nanospheres was determined in both phosphate buffer (pH 7.4) and plasma. The presence of HP‐β‐CyD and PEG did not influence the acyclovir release rate in plasma. In the case of release in phosphate buffer, PEG‐coated nanospheres showed a slower release. Ocular tolerability of PEG‐coated PECA nanospheres was evaluated by the in vivo Draize test. This colloidal carrier was well tolerated, eliciting no particular inflammation at the level of the various ocular structures. In vivo ocular bioavailability was evaluated by instilling 50 μL of the acyclovir‐loaded nanospheres only once in the conjunctival sac of rabbit eyes. At various time intervals, aqueous humour acyclovir content was determined by high‐performance liquid chromatography. Acyclovir‐loaded PEG‐coated PECA nanospheres were compared with an aqueous solution of the drug and a physical mixture of acyclovir nanospheres. The acyclovir‐loaded PEG‐coated PECA nanospheres showed a significant (p < 0.001) increase of drug levels (25‐fold) in aqueous humor compared with the free drug or the physical mixture. This finding is probably due to an improved ocular mucoadhesion of PEG‐coated PECA nanospheres. © 2001 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:288–297, 2001

Doxorubicin encapsulated in sterically stabilized liposomes for the treatment of a brain tumor model: biodistribution and therapeutic efficacy.

Anthracyclines entrapped in small-sized, sterically stabilized liposomes have the advantage of long circulation time, reduced systemic toxicity, increased uptake into systemic tumors, and gradual release of their payload. To date, there is no information on the behavior of these liposomes in brain tumors. The objective of this study was to compare the biodistribution and clinical efficacy of free doxorubicin (F-DOX) and stealth liposome-encapsulated DOX (SL-DOX) in a secondary brain tumor model. Nine days after tumor inoculation Fischer rats with a right parietal malignant sarcoma received an intravenous dose of 6 mg/kg of either F-DOX or SL-DOX for evaluation of drug biodistribution. For therapeutic trials a single dose of 8 mg/kg was given 6 or 11 days after tumor induction, or alternatively, weekly doses (5 mg/kg) were given on Days 6, 13, and 20. Liposome-encapsulated DOX was slowly cleared from plasma with a t1/2 of 35 hours. Free-DOX maximum tumor drug levels reached a mean value of 0.8 microgram/g and were identical in the adjacent brain and contralateral hemisphere. In contrast, SL-DOX tumor levels were 14-fold higher at their peak levels at 48 hours, declining to ninefold increased levels at 120 hours. A gradual increase in drug levels in the brain adjacent to tumor was noted between 72 and 120 hours (up to 4 micrograms/g). High-performance liquid chromatography analysis identified a small amount of aglycone metabolites within the tumor mass from 96 hours and beyond, after SL-DOX injection. Cerebrospinal fluid levels were barely detectable in tumor-bearing rats treated with F-DOX up to 120 hours after drug injection (< or = 0.05 microgram/ml), whereas the levels found after SL-DOX were 10- to 30-fold higher. An F-DOX single-dose treatment given 6 days after tumor inoculation increased the rats' life span (ILS) by 135% over controls (p < 0.05) but was not effective if given on Day 11. In contrast, SL-DOX treatment resulted in an ILS of 168% (p < 0.0003) with no difference when given after 6 or 11 days. Treatment with three weekly doses of SL-DOX produced an ILS of 189% compared to 126% by F-DOX (p < 0.0002). The authors conclude that the use of long-circulating liposomes as cytotoxic drug carriers in brain tumor results in enhanced drug exposure and improved therapeutic activity, with equal effectiveness against early small- and large-sized brain tumors.

Drug-resistance transfer among rodent plasmodia

A study on transfer of drug resistance between species of malaria parasites was carried out in mixed infections ofP. bergheiandP. vinckei. The biological characters which served as contrasting markers for separation of the two species were the inability of the ‘old’ blood-passaged strain ofP. vinckeito develop in suitable mosquito vectors and its failure to produce parasitaemia in the adult golden hamster. Facility of sporogonic development and cyclical transmission and a pronounced virulence for the adult hamster marked the N.K. 65 strain ofP. berghei.Development of a maximal and stable resistance to 200 mg/kg pyrimethamine in theP. vinckeistrain was achieved by a gradual increase in drug level in successive blood transfers.Mixed, simultaneous infections of pyrimethamine-resistantP. vinckeiand sensitiveP. bergheiwere experimentally induced in white mice. Subinoculations of the mixed infection at the height of parasitaemia was carried out in adult hamsters. Suppression of theP. vinckeiinfection in the hamster by innate resistance and the reappearance ofP. bergheiin the blood was noted. Tests with the maximal concentration of pyrimethamine (200 mg/kg) showed the acquisition of drug resistance in some of theP. bergheiinfected hamsters. Persistence of the acquired resistance was demonstrated following fifteen successive blood transfers in the absence of drug pressure and after five cyclical transmissions.Parallel control experiments with pyrimethamine-sensitiveP. vinckeiandP. bergheiin mixed infections failed to reveal any enhancement in drug resistance. No spontaneous drug-resistant mutant was found in the sensitiveP. bergheiafter exposure to a single course of treatment with the drug, and persistence of parasites in some treated animals was considered as individual variations in host reactions to the drug. This resistance never persisted after blood transfer or cyclical transmission. No loss in drug resistance had been found following transfer of the resistant R strain from mouse to hamster. A marked difference in the course of the plasmodial infection and in the length of survival of mice inoculated with the drug-resistantP. bergheiwas noted following treatment with pyrimethamine in various concentrations. It is suggested that these differences represent a selective action of the drug on a heterogenicP. bergheipopulation, consisting of drug-resistant and drug-sensitive parasites in the blood of the host.Injection of sonified material from pyrimethamine-resistantP. vinckeiandP. bergheiinto mice inoculated with a drug-sensitiveP. bergheifailed to induce enhancement of resistance to the drug.The phenomenon of drug-resistance transfer observed under experimental conditions in rodent malaria is viewed in the light of similar phenomena in micro-organisms.We gratefully acknowledge the assistance rendered by Mr Jerold Sklarsh.This paper is Contribution no. N 408 from the Army Research Programme on Malaria. The work was carried out under the sponsorship of the Commission on Malaria, Armed Forces Epidemiological Board, and supported in part by the United States Office of the Surgeon General, Department of the Army.