Pharmacokinetics and tumor disposition of PEGylated, methotrexate conjugated poly-l-lysine dendrimers

Dendrimers have potential for delivering chemotherapeutic drugs to solid tumours via the enhanced permeation and retention (EPR) effect. The impact of conjugation of hydrophobic anticancer drugs to hydrophilic PEGylated dendrimer surfaces, however, has not been fully investigated. The current study has therefore characterised the effect on dendrimer disposition of conjugating α-carboxyl protected methotrexate (MTX) to a series of PEGylated 3H-labelled poly-L-lysine dendrimers ranging in size from generation 3 (G3) to 5 (G5) in rats. Dendrimers contained 50% surface PEG and 50% surface MTX. Conjugation of MTX generally increased plasma clearance when compared to conjugation with PEG alone. Conversely, increasing generation reduced clearance, increased metabolic stability and reduced renal elimination of the administered radiolabel. For constructs with molecular weights >20 kDa increasing the molecular weight of conjugated PEG also reduced clearance and enhanced metabolic stability but had only a minimal effect on renal elimination. Tissue distribution studies revealed retention of MTX conjugated smaller (G3-G4) PEG570 dendrimers (or their metabolic products) in the kidneys. In contrast, the larger G5 dendrimer was concentrated more in the liver and spleen. The G5 PEG1100 dendrimer was also shown to accumulate in solid Walker 256 and HT1080 tumours and comparative disposition data in both rats (1 to 2% dose/g in tumour) and mice (11% dose/g in tumour) are presented. The results of this study further illustrate the potential utility of biodegradable PEGylated poly-L-lysine dendrimers as long circulating vectors for the delivery and tumour-targeting of hydrophobic drugs.

Delivering crushed paracetamol tablets using thickened fluids : does it alter the pharmacokinetics?

Dysphagia, often associated with conditions such as stroke, Parkinson’s disease, multiple sclerosis, and dementia, causes patients to have difficulty with swallowing food and/or liquids. These patients require their fluids to be thickened using gum-based thickening powders in order to facilitate safe swallowing. These thickened fluids are also used as a vehicle for delivery of crushed medicines. Our in vitro measurements suggest that thickened fluids can delay and reduce the dissolution of a number of medications. This study was conducted to assess the impact of the use of thickened fluids on the clinical pharmacokinetics of oral paracetamol. METHODS 20 Healthy volunteers were administered a single oral dose (1g) of paracetamol as either whole tablets, crushed with water, crushed with semi-solid jam, or crushed with thickened fluid according to a randomised, crossover design. Saliva samples were collected periodically over 8 hr and paracetamol concentration analysed by HPLC-UV. Non-compartmental pharmacokinetic analysis was conducted using Winnonlin®. RESULTS The mean peak concentration (Cmax) of paracetamol ranged between 5.62 – 8.00 μg/mL. Comparison between the crushed paracetamol with thickened water (Level 900) and other treatment options (whole, crushed with water, and crushed with jam) showed there was a significant difference in Cmax at 90% CI (p < 0.05). Also, whole tablet had a significant difference in Cmax between crushed with water and crushed with jam. There was no significant difference in AUC irrespective of the treatment. DISCUSSION The use of thickened water resulted in alteration in the absorption kinetics of paracetamol. Given this interaction, co-administration with thickened fluids may have important clinical implications for medications with a narrow therapeutic index.

The lipophilic opioids: Fentanyl, alfentanil, sufentanil and remifentanil

discusses fentanyl, alfentanil, sufentanil, and remifentanil which are synthetic opioid analgesics with high affinity for the mu opioid receptor. They have been widely adopted in anaesthetic practice for various surgical procedures (e.g. in cardiac surgery) and for long-term analgesia and sedation. Important pharmacokinetic differences between these analgesics have been described, and this chapter addresses how the pharmacokinetic profile of each analgesic is affected by many factors, including patient age, plasma protein content, acid–base balance status, cardiopulmonary bypass, changes in hepatic blood flow, and the co-administration of other drugs which compete for plasma protein carriers and metabolic pathways, although their profile is not significantly affected by renal insufficiency or compensated hepatic dysfunction, which has major clinical implications.

Pharmacokinetics, efficacy, and safety of pravastatin in children : Studies in children with heterozygous familial hypercholesterolemia and in pediatric cardiac transplant recipients

Background. Hyperlipidemia is a common concern in patients with heterozygous familial hypercholesterolemia (HeFH) and in cardiac transplant recipients. In both groups, an elevated serum LDL cholesterol level accelerates the development of atherosclerotic vascular disease and increases the rates of cardiovascular morbidity and mortality. The purpose of this study is to assess the pharmacokinetics, efficacy, and safety of cholesterol-lowering pravastatin in children with HeFH and in pediatric cardiac transplant recipients receiving immunosuppressive medication. Patients and Methods. The pharmacokinetics of pravastatin was studied in 20 HeFH children and in 19 pediatric cardiac transplant recipients receiving triple immunosuppression. The patients ingested a single 10-mg dose of pravastatin, and plasma pravastatin concentrations were measured up to 10/24 hours. The efficacy and safety of pravastatin (maximum dose 10 to 60 mg/day and 10 mg/day) up to one to two years were studied in 30 patients with HeFH and in 19 cardiac transplant recipients, respectively. In a subgroup of 16 HeFH children, serum non-cholesterol sterol ratios (102 x mmol/mol of cholesterol), surrogate estimates of cholesterol absorption (cholestanol, campesterol, sitosterol), and synthesis (desmosterol and lathosterol) were studied at study baseline (on plant stanol esters) and during combination with pravastatin and plant stanol esters. In the transplant recipients, the lipoprotein levels and their mass compositions were analyzed before and after one year of pravastatin use, and then compared to values measured from 21 healthy pediatric controls. The transplant recipients were grouped into patients with transplant coronary artery disease (TxCAD) and patients without TxCAD, based on annual angiography evaluations before pravastatin. Results. In the cardiac transplant recipients, the mean area under the plasma concentration-time curve of pravastatin [AUC(0-10)], 264.1 * 192.4 ng.h/mL, was nearly ten-fold higher than in the HeFH children (26.6 * 17.0 ng.h/mL). By 2, 4, 6, 12 and 24 months of treatment, the LDL cholesterol levels in the HeFH children had respectively decreased by 25%, 26%, 29%, 33%, and 32%. In the HeFH group, pravastatin treatment increased the markers of cholesterol absorption and decreased those of synthesis. High ratios of cholestanol to cholesterol were associated with the poor cholesterol-lowering efficacy of pravastatin. In cardiac transplant recipients, pravastatin 10 mg/day lowered the LDL cholesterol by approximately 19%. Compared with the patients without TxCAD, patients with TxCAD had significantly lower HDL cholesterol concentrations and higher apoB-100/apoA-I ratios at baseline (1.0 ± 0.3 mmol/L vs. 1.4 ± 0.3 mmol/L, P = 0.031; and 0.7 ± 0.2 vs. 0.5 ± 0.1, P = 0.034) and after one year of pravastatin use (1.0 ± 0.3 mmol/L vs. 1.4 ± 0.3 mmol/L, P = 0.013; and 0.6 ± 0.2 vs. 0.4 ± 0.1, P = 0.005). Compared with healthy controls, the transplant recipients exhibited elevated serum triglycerides at baseline (median 1.3 [range 0.6-3.2] mmol/L vs. 0.7 [0.3-2.4] mmol/L, P=0.0002), which negatively correlated with their HDL cholesterol concentration (r = -0.523, P = 0.022). Recipients also exhibited higher apoB-100/apoA1 ratios (0.6 ± 0.2 vs. 0.4 ± 0.1, P = 0.005). In addition, elevated triglyceride levels were still observed after one year of pravastatin use (1.3 [0.5-3.5] mmol/L vs. 0.7 [0.3-2.4] mmol/L, P = 0.0004). Clinically significant elevations in alanine aminotransferase, creatine kinase, or creatinine ocurred in neither group. Conclusions. Immunosuppressive medication considerably increased the plasma pravastatin concentrations. In both patient groups, pravastatin treatment was moderately effective, safe, and well tolerated. In the HeFH group, high baseline cholesterol absorption seemed to predispose patients to insufficient cholesterol-lowering efficacy of pravastatin. In the cardiac transplant recipients, low HDL cholesterol and a high apoB-100/apoA-I ratio were associated with development of TxCAD. Even though pravastatin in the transplant recipients effectively lowered serum total and LDL cholesterol concentrations, it failed to normalize their elevated triglyceride levels and, in some patients, to prevent the progression of TxCAD.

Effects of SLCO1B1 polymorphism on the pharmacokinetics of the oral antidiabetic drugs repaglinide, nateglinide, rosiglitazone, and pioglitazone

Organic anion-transporting polypeptide 1B1 (OATP1B1), encoded by the SLCO1B1 gene, is an influx transporter expressed on the sinusoidal membrane of human hepatocytes. The common c.521T>C (p.Val174Ala) single-nucleotide polymorphism (SNP) of the SLCO1B1 gene has been associated with reduced OATP1B1 transport activity in vitro and increased plasma concentrations of several of its substrate drugs in vivo in humans. Another common SNP of the SLCO1B1 gene, c.388A>G (p.Asn130Asp), defining the SLCO1B1*1B (c.388G-c.521T) haplotype, has been associated with increased OATP1B1 transport activity in vitro. The aim of this thesis was to investigate the role of SLCO1B1 polymorphism in the pharmacokinetics of the oral antidiabetic drugs repaglinide, nateglinide, rosiglitazone, and pioglitazone. Furthermore, the effect of the SLCO1B1 c.521T>C SNP on the extent of interaction between gemfibrozil and repaglinide as well as the role of the SLCO1B1 c.521T>C SNP in the potential interaction between atorvastatin and repaglinide were evaluated. Five crossover studies with 2-4 phases were carried out, with 20-32 healthy volunteers in each study. The effects of the SLCO1B1 c.521T>C SNP on single doses of repaglinide, nateglinide, rosiglitazone, and pioglitazone were investigated in Studies I and V. In Study II, the effects of the c.521T>C SNP on repaglinide pharmacokinetics were investigated in a dose-escalation study, with repaglinide doses ranging from 0.25 to 2 mg. The effects of the SLCO1B1*1B/*1B genotype on repaglinide and nateglinide pharmacokinetics were investigated in Study III. In Study IV, the interactions of gemfibrozil and atorvastatin with repaglinide were evaluated in relation to the c.521T>C SNP. Plasma samples were collected for drug concentration determinations. The pharmacodynamics of repaglinide and nateglinide was assessed by measuring blood glucose concentrations. The mean area under the plasma repaglinide concentration-time curve (AUC) was ~70% larger in SLCO1B1 c.521CC participants than in c.521TT participants (P ≤ 0.001), but no differences existed in the pharmacokinetics of nateglinide, rosiglitazone, and pioglitazone between the two genotype groups. In the dose-escalation study, the AUC of repaglinide was 60-110% (P ≤ 0.001) larger in c.521CC participants than in c.521TT participants after different repaglinide doses. Moreover, the AUC of repaglinide increased linearly with repaglinide dose in both genotype groups (r > 0.88, P 0.001). The AUC of repaglinide was ~30% lower in SLCO1B1*1B/*1B participants than in SLCO1B1*1A/*1A (c.388AA-c.521TT) participants (P = 0.007), but no differences existed in the AUC of nateglinide between the two genotype groups. In the drug-drug interaction study, the mean increase in the repaglinide AUC by gemfibrozil was ~50% (P = 0.002) larger in c.521CC participants than in c.521TT participants, but the relative (7-8-fold) increases in the repaglinide AUC did not differ significantly between the genotype groups. In c.521TT participants, atorvastatin increased repaglinide peak plasma concentration and AUC by ~40% (P = 0.001) and ~20% (P = 0.033), respectively. In each study, after repaglinide administration, there was a tendency towards lower blood glucose concentrations in c.521CC participants than in c.521TT participants. In conclusion, the SLCO1B1 c.521CC genotype is associated with increased and the SLCO1B1*1B/*1B genotype with decreased plasma concentrations of repaglinide, consistent with reduced and enhanced hepatic uptake, respectively. Inhibition of OATP1B1 plays a limited role in the interaction between gemfibrozil and repaglinide. Atorvastatin slightly raises plasma repaglinide concentrations, probably by inhibiting OATP1B1. The findings on the effect of SLCO1B1 polymorphism on the pharmacokinetics of the drugs studied suggest that in vivo in humans OATP1B1 significantly contributes to the hepatic uptake of repaglinide, but not to that of nateglinide, rosiglitazone, or pioglitazone. SLCO1B1 polymorphism may be associated with clinically significant differences in blood glucose-lowering response to repaglinide, but probably has no effect on the response to nateglinide, rosiglitazone, or pioglitazone.

Cyclosporine population pharmacokinetics in pediatric renal transplant recipients

Cyclosporine is an immunosuppressant drug with a narrow therapeutic index and large variability in pharmacokinetics. To improve cyclosporine dose individualization in children, we used population pharmacokinetic modeling to study the effects of developmental, clinical, and genetic factors on cyclosporine pharmacokinetics in altogether 176 subjects (age range: 0.36–20.2 years) before and up to 16 years after renal transplantation. Pre-transplantation test doses of cyclosporine were given intravenously (3 mg/kg) and orally (10 mg/kg), on separate occasions, followed by blood sampling for 24 hours (n=175). After transplantation, in a total of 137 patients, cyclosporine concentration was quantified at trough, two hours post-dose, or with dose-interval curves. One-hundred-four of the studied patients were genotyped for 17 putatively functionally significant sequence variations in the ABCB1, SLCO1B1, ABCC2, CYP3A4, CYP3A5, and NR1I2 genes. Pharmacokinetic modeling was performed with the nonlinear mixed effects modeling computer program, NONMEM. A 3-compartment population pharmacokinetic model with first order absorption without lag-time was used to describe the data. The most important covariate affecting systemic clearance and distribution volume was allometrically scaled body weight i.e. body weight**3/4 for clearance and absolute body weight for volume of distribution. The clearance adjusted by absolute body weight declined with age and pre-pubertal children (< 8 years) had an approximately 25% higher clearance/body weight (L/h/kg) than did older children. Adjustment of clearance for allometric body weight removed its relationship to age after the first year of life. This finding is consistent with a gradual reduction in relative liver size towards adult values, and a relatively constant CYP3A content in the liver from about 6–12 months of age to adulthood. The other significant covariates affecting cyclosporine clearance and volume of distribution were hematocrit, plasma cholesterol, and serum creatinine, explaining up to 20%–30% of inter-individual differences before transplantation. After transplantation, their predictive role was smaller, as the variations in hematocrit, plasma cholesterol, and serum creatinine were also smaller. Before transplantation, no clinical or demographic covariates were found to affect oral bioavailability, and no systematic age-related changes in oral bioavailability were observed. After transplantation, older children receiving cyclosporine twice daily as the gelatine capsule microemulsion formulation had an about 1.25–1.3 times higher bioavailability than did the younger children receiving the liquid microemulsion formulation thrice daily. Moreover, cyclosporine oral bioavailability increased over 1.5-fold in the first month after transplantation, returning thereafter gradually to its initial value in 1–1.5 years. The largest cyclosporine doses were administered in the first 3–6 months after transplantation, and thereafter the single doses of cyclosporine were often smaller than 3 mg/kg. Thus, the results suggest that cyclosporine displays dose-dependent, saturable pre-systemic metabolism even at low single doses, whereas complete saturation of CYP3A4 and MDR1 (P-glycoprotein) renders cyclosporine pharmacokinetics dose-linear at higher doses. No significant associations were found between genetic polymorphisms and cyclosporine pharmacokinetics before transplantation in the whole population for which genetic data was available (n=104). However, in children older than eight years (n=22), heterozygous and homozygous carriers of the ABCB1 c.2677T or c.1236T alleles had an about 1.3 times or 1.6 times higher oral bioavailability, respectively, than did non-carriers. After transplantation, none of the ABCB1 SNPs or any other SNPs were found to be associated with cyclosporine clearance or oral bioavailability in the whole population, in the patients older than eight years, or in the patients younger than eight years. In the whole population, in those patients carrying the NR1I2 g.-25385C–g.-24381A–g.-205_-200GAGAAG–g.7635G–g.8055C haplotype, however, the bioavailability of cyclosporine was about one tenth lower, per allele, than in non-carriers. This effect was significant also in a subgroup of patients older than eight years. Furthermore, in patients carrying the NR1I2 g.-25385C–g.-24381A–g.-205_-200GAGAAG–g.7635G–g.8055T haplotype, the bioavailability was almost one fifth higher, per allele, than in non-carriers. It may be possible to improve individualization of cyclosporine dosing in children by accounting for the effects of developmental factors (body weight, liver size), time after transplantation, and cyclosporine dosing frequency/formulation. Further studies are required on the predictive value of genotyping for individualization of cyclosporine dosing in children.

Pharmacokinetics and chemotherapeutic efficacy of adriamycin encapsulated in immunoliposomes against avian myeloblastosis virus infection

Immunoliposomes were prepared using rabbit anti-AMV gp80 IgG for the targeted chemotherapy of avian myeloblastosis virus infection. Adriamycin was encapsulated into immunoliposomes and used for in vivo studies. Comparative pharmacokinetics of free drug, drug encapsulated in free liposomes and of drug encapsulated in immunoliposomes in the virus-infected cells revealed that (i) the drug encapsulated in liposomes was cleared from the plasma slowly, and (ii) the drug encapsulated in immunoliposomes accumulated in the target tissue, the bone marrow, 5- and 8.5-fold more than the drug encapsulated in free liposomes and free drug, respectively. The drug encapsulated in immunoliposomes inactivated the virus and exhibited more chemotherapeutic efficacy as compared to controls when injected up to 24 h post-infection. However, when injected 48 h post-infection the drug encapsulated in immunoliposomes did not offer any protection against the virus infection. There is no detectable antibody response against immunoliposomes in the infected animals.