Altered Pharmacokinetics of Paclitaxel in Experimental Hepatic or Renal Failure

Rutin and Hesperidin Revoke the Hepatotoxicity Induced by Paclitaxel in Male Wistar Rats via Their Antioxidant, Anti-Inflammatory, and Antiapoptotic Activities

Paclitaxel, one of the most effective chemotherapeutic drugs, is used to treat various cancers but it is exceedingly toxic when used long-term and can harm the liver. This study aimed to see if rutin, hesperidin, and their combination could protect male Wistar rats against paclitaxel (Taxol)-induced hepatotoxicity. Adult male Wistar rats were subdivided into 5 groups (each of six rats). The normal group was orally given the equivalent volume of vehicles for 6 weeks. The paclitaxel-administered control group received intraperitoneal injection of paclitaxel at a dose of 2 mg/Kg body weight twice a week for 6 weeks. Treated paclitaxel-administered groups were given paclitaxel similar to the paclitaxel-administered control group together with oral supplementation of rutin, hesperidin, and their combination at a dose of 10 mg/Kg body weight every other day for 6 weeks. The treatment of paclitaxel-administered rats with rutin and hesperidin significantly reduced paclitaxel-induced increases in serum alanine transaminase, aspartate transaminase, lactate dehydrogenase, alkaline phosphatase, and gamma-glutamyl transferase activities as well as total bilirubin level and liver lipid peroxidation. However, the levels of serum albumin, liver glutathione content, and the activities of liver superoxide dismutase and glutathione peroxidase increased. Furthermore, paclitaxel-induced harmful hepatic histological changes (central vein and portal area blood vessel congestion, fatty changes, and moderate necrotic changes with focal nuclear pyknosis, focal mononuclear infiltration, and Kupffer cell proliferation) were remarkably enhanced by rutin and hesperidin treatments. Moreover, the elevated hepatic proapoptotic mediator (caspase-3) and pro-inflammatory cytokine (tumor necrosis factor-α) expressions were decreased by the three treatments in paclitaxel-administered rats. The cotreatment with rutin and hesperidin was the most effective in restoring the majority of liver function and histological integrity. Therefore, rutin, hesperidin, and their combination may exert hepatic protective effects in paclitaxel-administered rats by improving antioxidant defenses and inhibiting inflammation and apoptosis.

Differential effect of liver cirrhosis on the pregnane X receptor-mediated induction of CYP3A1 and 3A2 in the rat

Conflicting results have been obtained by clinical studies investigating the effect of liver cirrhosis on enzyme induction. Because ethical concerns do not give consent for methodologically rigorous studies in humans, we addressed this question by examining the effect of the prototypical inducer dexamethasone (DEX) on the pregnane X receptor (PXR)-mediated induction of CYP3A1 and 3A2 in a validated animal model of liver cirrhosis obtained by exposure of rats to carbon tetrachloride. For this purpose, we assessed mRNA levels, protein expressions, and enzymatic activities of both CYP3A enzymes, as well as mRNA and protein expressions of PXR in rat populations rigorously stratified according to the severity of liver insufficiency. Constitutive mRNA and protein expressions of CYP3A1 and CYP3A2 and their basal enzyme activities were not affected by liver dysfunction. DEX treatment markedly increased steady-state mRNA level, protein content, and enzymatic activity of CYP3A1 in healthy and cirrhotic rats, irrespective of the degree of liver dysfunction. On the contrary, the inducing effect of DEX on gene and protein expressions and enzyme activity of CYP3A2 was preserved in moderate liver insufficiency, whereas it was greatly curtailed when liver insufficiency became severe. mRNA and protein expressions of PXR were neither reduced by liver dysfunction nor increased by DEX treatment. These results indicate that even the inducibility of cytochrome P450 isoforms under the transcriptional control of the same nuclear receptor may be differentially affected by cirrhosis and may partly explain why conflicting results were obtained by human studies.

A model based analysis of IPEC dosing of paclitaxel in rats

PURPOSE

A strong pharmacokinetic rational exists for the use of (Hyperthermic) Intraperitoneal Perioperative Chemotherapy in peritoneal carcinomatosis. However, controversy remains regarding the optimal treatment strategies. Paclitaxel is believed to be a good compound for IPEC treatment because of its favourable pharmacokinetic properties.

METHODS

Rat experiments were set up to gain insight in PTX's pharmacokinetics and pharmacodynamics after IPEC treatment with Taxol®. Afterwards a Pharmacokinetic-Pharmacodynamic model was developed, that concurrently describes plasma and tumour exposure post IPEC dosing. Moreover, the developed model adequately describes the time-course of tumour apoptosis as well as the treatment effect on tumour volume.

RESULTS

We show that the complex absorption processes underlying PTX absorption from the peritoneal cavity post IPEC dosing, give rise to a markedly non-linear dose response relationship. Furthermore, we show that, in order to optimize treatment efficiency whilst concurrently minimizing the possibility of systemic toxicities, lowering the dose and extending exposure to the cytotoxic solution is the way forward.

CONCLUSIONS

Based on the close resemblance between tumour exposure in our animal model and tumour exposure in patients treated under similar conditions, we hypothesise that, according to our findings in the rat, in the treatment of PC using IPEC administration of PTX, less is truly more.

Increased elimination of paclitaxel by magnesium isoglycyrrhizinate in epithelial ovarian cancer patients treated with paclitaxel plus cisplatin: a pilot clinical study

Magnesium isoglycyrrhizinate (MI) has been complementarily used for restoring the hepatic impairments caused by taxol plus platinum based chemotherapies in China. Due to the hepatic dependence of paclitaxel elimination, this pilot clinical study aimed to investigate the influence of MI on the pharmacokinetics of paclitaxel in epithelial ovarian cancer patients. During the standard chemotherapy of intravenous paclitaxel (125 mg/m(2) infused over a 3-h period) and intraperitoneal cisplatin (60 mg/m(2)) for patients with FIGO stage II epithelial ovarian cancer, 9 each of total 18 patients were respectively treated with intravenous MI (100 mg) or vehicle control for 4 days. Plasma paclitaxel was analyzed by HPLC and the pharmacokinetic parameters were calculated with non-compartmental analysis. The hematological, hepatic and renal status was monitored before and 3 days after paclitaxel administration. It was observed the terminal t 1/2 and MRT of paclitaxel were significantly (p = 0.002 and 0.001) reduced by MI, respectively, from 11.0 ± 2.2 and 5.6 ± 1.0 h to 7.7 ± 1.7 and 4.0 ± 0.3 h. Hematological toxicity indicated by platelet count and hepatic events marked with ALT, AST and γ-GT were significant in both groups. In spite of the insignificance of decreased system exposure of paclitaxel and recovered hepatic function by MI, they did correlate with each other. It was therefore deduced that the liver toxicities of paclitaxel plus cisplatin chemotherapy potentially decrease hepatic elimination and increase system exposure of paclitaxel, and the recovery of liver function by MI helps to restore hepatic clearance of paclitaxel. The clinical significance of this pharmacokinetic interaction requires further studies with larger population size.

Impact of obesity on drug metabolism and elimination in adults and children

The prevalence of obesity in adults and children is rapidly increasing across the world. Several general (patho)physiological alterations associated with obesity have been described, but the specific impact of these alterations on drug metabolism and elimination and its consequences for drug dosing remains largely unknown. In order to broaden our knowledge of this area, we have reviewed and summarized clinical studies that reported clearance values of drugs in both obese and non-obese patients. Studies were classified according to their most important metabolic or elimination pathway. This resulted in a structured review of the impact of obesity on metabolic and elimination processes, including phase I metabolism, phase II metabolism, liver blood flow, glomerular filtration and tubular processes. This literature study shows that the influence of obesity on drug metabolism and elimination greatly differs per specific metabolic or elimination pathway. Clearance of cytochrome P450 (CYP) 3A4 substrates is lower in obese as compared with non-obese patients. In contrast, clearance of drugs primarily metabolized by uridine diphosphate glucuronosyltransferase (UGT), glomerular filtration and/or tubular-mediated mechanisms, xanthine oxidase, N-acetyltransferase or CYP2E1 appears higher in obese versus non-obese patients. Additionally, in obese patients, trends indicating higher clearance values were seen for drugs metabolized via CYP1A2, CYP2C9, CYP2C19 and CYP2D6, while studies on high-extraction-ratio drugs showed somewhat inconclusive results. Very limited information is available in obese children, which prevents a direct comparison between data obtained in obese children and obese adults. Future clinical studies, especially in children, adolescents and morbidly obese individuals, are needed to extend our knowledge in this clinically important area of adult and paediatric clinical pharmacology.

Altered pharmacokinetics of enrofloxacin in experimental models of hepatic and renal impairment

We investigated the effects of hepatic and renal impairment on the pharmacokinetics of enrofloxacin in Sprague-Dawley rats. Experimental hepatic and renal failure were induced by carbon tetrachloride (CCL(4)) and 5/6 nephrectomy, respectively. After intravenous dosing of enrofloxacin (10 mg/kg), plasma concentrations of enrofloxacin were measured using liquid chromatograph/mass spectrometry. There was no significant effect of hepatic impairment on enrofloxacin pharmacokinetics. However, renal impairment markedly prolonged elimination half life (t(1/2lambdaz)) of enrofloxacin (P < 0.05), comparing with respective control. Total body clearance (Cl(b)) and volume of distribution at steady state (V(ss)) were significantly decreased (P < 0.05) by renal impairment. In conclusion, these results suggested that renal impairment could affect the pharmacokinetics of enrofloxacin.

Pharmacology, pharmacokinetics and pharmacogenomics of paclitaxel

Paclitaxel is widely used in many cancers including ovarian, breast, lung, head and neck and primary unknown. Paclitaxel is extensively metabolized by cytochrome P450s and excreted in bile. The cytochromes involved include 2C8 and 3A4. This is a review of the pharmacokinetics, pharmacodynamics, drug interactions, metabolism and pharmacogenomics of paclitaxel.

Pharmacokinetics and pharmacodynamics of paclitaxel with carboplatin or gemcitabine, and effects of CYP3A5 and MDR1 polymorphisms in patients with urogenital cancers

BACKGROUND

We investigated the pharmacokinetics and pharmacodynamics of paclitaxel with carboplatin or gemcitabine in patients with urogenital cancer to clarify the significance of monitoring of the serum concentration of paclitaxel.

METHODS

Paclitaxel was administered at 175 mg/m(2) or 150 mg/m(2) to patients with hormone-refractory prostate cancer (n = 10) or advanced transitional cell carcinoma (n = 6) along with carboplatin or gemcitabine, respectively. The relationships between pharmacokinetic parameters and hematological adverse effects, as well as pharmacological effects, were examined. The effects of patient characteristics, including single-nucleotide polymorphisms of MDR1(ABCB1), CYP2C8, CYP3A4, and CYP3A5, on the total body clearance of paclitaxel were evaluated.

RESULTS

Total body clearance and volume of distribution at a steady-state after the intravenous infusion of paclitaxel were not significantly different between patients with carboplatin or gemcitabine. The percent decreases in neutrophils and platelets for the regimen with gemcitabine were significantly greater than those with carboplatin, and showed a significant positive relationship with the observed concentration at the end of infusion or time above 0.1-microM concentration of paclitaxel. Post-therapy decreases in prostate-specific antigen were not positively correlated with the extent of paclitaxel exposure in the prostate cancer patients. Neither the polymorphisms at exon 26 (C3435T) and at exon 21 (G2677A/T) in MDR1 nor the CYP3A5*1 allele significantly affected the total body clearance of paclitaxel.

CONCLUSION

The hematological side effects of paclitaxel were intensified by gemcitabine, and were correlated with paclitaxel pharmacokinetics. Monitoring of the serum concentration of paclitaxel will facilitate the therapy, with less myelosuppression and without any loss of therapeutic efficacy.

Cancer chemotherapy I: hepatocellular injury

Although hepatotoxicity is a frequent concern with all medications, chemotherapeutic agents are more often implicated in causing liver damage than most other drug classes. In many instances, these reactions are considered dose related because cytotoxic therapy directed at rapidly growing cancer cells may readily impact hepatocytes even though they are dividing more slowly. Because the stakes (remission of cancer) are high, so are the risks that the oncologist and the patient are willing to assume. The dose of many chemotherapeutic agents is limited by the toxic effects on the lungs, bone marrow, kidneys, and gastrointestinal system, including the liver. An awareness of the toxic potential of each chemotherapeutic agent is necessary before initiation of new oncologic treatments.

Feasibility study and pharmacokinetics of low-dose paclitaxel in cancer patients with severe hepatic dysfunction

The aim of this study is to investigate the feasibility and determine the pharmacokinetics of low-dose paclitaxel in cancer patients with severe hepatic dysfunction. This was a prospective study. Patients with liver metastases who had either transaminase serum levels higher than 10 times the upper normal limit or bilirubin serum levels higher than 5 times the upper normal limit were eligible. All patients underwent pharmacokinetic evaluation during the first course of treatment. Pharmacokinetics in severe hepatic dysfunction patients were compared with data from a reference group of patients with normal hepatic function who participated in a phase I study. Nine severe hepatic dysfunction patients were treated with paclitaxel 70 mg/m administered as a 1-h infusion every 2 weeks. They received a median three treatment courses (range 1-9) without clinically relevant toxicity. The area under the concentration-time curve of paclitaxel was markedly higher in severe hepatic dysfunction patients when compared with the normal hepatic function control group treated with the same dose (98% increase, P<0.001). Area under the concentration-time curve and the time above 0.1 micromol/l (T>0.1) concentration threshold in the severe hepatic dysfunction patients who received paclitaxel 70 mg/m approximated pharmacokinetics of paclitaxel in patients with normal liver function who received 130 mg/m. Maximum plasma concentration (Cmax) did not differ between the two groups. In conclusion, paclitaxel 70 mg/m was safely delivered every 2 weeks in patients with severe hepatic dysfunction and resulted in adequate plasma concentrations. Paclitaxel at this dosage can be taken as an option for severe hepatic dysfunction patients who are expected to get clinical benefits from taxanes.

International Society of Geriatric Oncology (SIOG) recommendations for the adjustment of dosing in elderly cancer patients with renal insufficiency

A SIOG taskforce was formed to discuss best clinical practice for elderly cancer patients with renal insufficiency. This manuscript outlines recommended dosing adjustments for cancer drugs in this population according to renal function. Dosing adjustments have been made for drugs in current use which have recommendations in renal insufficiency and the elderly, focusing on drugs which are renally eliminated or are known to be nephrotoxic. Recommendations are based on pharmacokinetic and/or pharmacodynamic data where available. The taskforce recommend that before initiating therapy, some form of geriatric assessment should be conducted that includes evaluation of comorbidities and polypharmacy, hydration status and renal function (using available formulae). Within each drug class, it is sensible to use agents which are less likely to be influenced by renal clearance. Pharmacokinetic and pharmacodynamic data of anticancer agents in the elderly are needed in order to maximise efficacy whilst avoiding unacceptable toxicity.

Pharmacogenetics of paclitaxel metabolism

Paclitaxel is one of the most widely used and effective anticancer drugs. Paclitaxel's clinical utility spans many tumor sites, including treatment of ovarian, breast, lung, head and neck, and unknown primary cancers. As is the case with most chemotherapy drugs, paclitaxel is administered empirically with little individualization of dose other than adjustment for body surface area. Metabolism of the drug is predominantly by the liver by cytochromes P450 2C8 and 3A4. Recent evidence points to the presence of polymorphisms in these enzymes. The clinical relevance of these polymorphisms is not yet fully explored, though they are expected to be key in fulfilling the ultimate goal of individualized dosing of paclitaxel. Here we review the pharmacology of paclitaxel and consider the possible effects pharmacogenetics may have on paclitaxel therapy.

Intravenous administration of paclitaxel in Sprague-Dawley rats: what is a safe dose?

Few studies describe the administration of Taxol to rats; however, rats are typically used to study the toxicity of new drugs or novel formulations. A dose finding study was conducted to determine a safe dose of Taxol following intravenous administration in rats. Male Sprague-Dawley rats received a bolus of paclitaxel 5-20 mg/kg i.v. Blood was drawn before administration and at the following times after administration: 0.5, 1, 2, 3, 4, 6, 8, 12, 16, 20 and 24 h. Plasma concentrations were determined using high performance liquid chromatography. Two rats received paclitaxel 20 mg/kg and died immediately. Nine rats received paclitaxel 10 mg/kg; seven of these rats died within 12 h and two rats were killed due to moribund conditions. Ten rats received paclitaxel 5 mg/kg with no morbidity. The following pharmacokinetics for paclitaxel in the plasma were estimated: C0, 8977 ng/ml; AUC(0 --> infinity), 7477 ng*h/ml; CL(s), 668 ml/h*kg; V(ss), 1559 ml/kg; V(z) 2557 ml/kg and t(1/2), 2.6 h. It is concluded that further pharmacokinetic studies that are rationally designed to include appropriate measures of preclinical toxicity associated with paclitaxel are needed to identify formally the safest dose in rats following intravenous administration; however, these data indicate that male Sprague-Dawley rats can safely receive Taxol in a 5 mg/kg i.v. bolus.