Junichi Kawakami

Prediction of brain delivery of ofloxacin, a new quinolone, in the human from animal data

We attempted to predict the delivery of ofloxacin (OFLX), a new quinolone antibacterial agent (NQ), into cerebrospinal fluid (CSF) in the human based on the physiological properties and pharmacokinetic paramters of NQs in various animals. Physiological properties for evaluation of drug delivery into CSF such as volume and the bulk flow rate of CSF and weight of choroid plexus, were compared among the rat, rabbit, cat, dog, and human. Statistically significant correlations with power values of 0.82–0.89 in the linear regression were observed on log-log plots between brain weight and those properties of each species. Delivery of OFLX into CSF from blood was analyzed by “diffusion and flow model” with unidirectional efflux process from CSF to blood. The blood-CSF diffusion clearance and the efflux clearance of OFLX in the human were extrapolated from animal data based on the allometric correlations between brain weight and these parameters in the rat, rabbit, and dog. The apparent volume of distribution and the total body clearance of NQs in the human could also be predicted from animal data based on the classical Adolph-Dedrick approach. To simulate the CSF concentration-time profile of OFLX in the human by using these predicted parameters, it was necessary to consider both the lumbar CSF compartment and the ventricular CSF compartment. Both plasma and CSF concentration-time profiles of OFLX predicted from only animal experimental data were in good agreement with those observed clinically.

Inhibitory Effects of Terpenoids on Multidrug Resistance-Associated Protein 2-and Breast Cancer Resistance Protein-Mediated Transport

The possibility of interactions between natural products/supplements and conventional prescription medicines is one of the most important issues in pharmacotherapeutic safety. Recently, we reported that some terpenoids such as (R)-(+)-citronellal and glycyrrhetic acid, which are present in herbal medicines, can act as inhibitors of P-glycoprotein (MDR1/ABCB1). In the present study, the effects of seven terpenoids on multidrug resistance-associated protein 2 (MRP2/ABCC2) and breast cancer resistance protein (BCRP/ABCG2)-mediated transport were investigated in vitro. Membrane vesicles were prepared from MRP2 cDNA transfected Sf9 cells derived from pupal ovarian tissue of Spodoptera frugiperda, a fall armyworm, and BCRP cDNA transfected LLC-PK1 cells derived from porcine kidney. MRP2- or BCRP-mediated efflux transport was measured as ATP-dependent accumulation of [3H]estradiol 17-β-d-glucuronide (E217βG) into membrane vesicles collected by a rapid filtration technique. The effects of (R)-(+)-citronellal, (S)-(-)-β-citronellol, α-terpinene, terpinolene, (-)-β-pinene, abietic acid, and glycyrrhetic acid on the intravesicular accumulation of [3H]E217βG were examined. Large decreases in the [3H]E217βG accumulation into vesicles from MRP2-overexpressing Sf9 cells were observed in the presence of glycyrrhetic acid and abietic acid, and their IC50 values were about 20 and 51 μM, respectively. [3H]E217βG accumulation into vesicles from BCRP-overexpressing LLC-PK1 cells was suppressed by only glycyrrhetic acid, with an IC50 value of about 39 μM. Other terpenoids used in this study did not alter the ATP-dependent accumulation of [3H]E217βG. These findings suggest that glycyrrhetic acid and abietic acid can potently inhibit MRP2- or BCRP-mediated membrane transport and may interact with their substrates in pharmacokinetic processes.

Selective high-performance liquid chromatographic method for the determination of glycyrrhizin and glycyrrhetic acid-3-O-glucuronide in biological fluids: application of ion-pair extraction and fluorescence labelling agent.

A selective high-performance liquid chromatographic method has been developed for the simultaneous determination of glycyrrhizin and glycyrrhetic acid-3-O-glucuronide in biological fluids of the rat. The procedure is based on the ion-pair formation using tetra-n-amylammonium bromide, extraction with ethyl acetate-n-heptane from the salt-saturated aqueous phase, labelling with 4-bromomethyl-7-methoxycoumarin, followed by chromatographic separation with fluorescence detection. Glycyrrhizin in plasma, bile and urine could be precisely determined in concentrations as low as 1, 1 and 2.5 micrograms/ml, respectively, in a 0.1-ml sample. The equivalent values for the glucuronide were 1, 2.5 and 2.5 micrograms/ml, respectively. The method is applicable in pharmacokinetic studies of glycyrrhizin in small animals.

Effect of acute renal failure on neurotoxicity of cimetidine in rats

AbstractPurpose. We investigated the effect of acute renal failure on the neurotoxicity of cimetidine in rats. Methods. Experimental acute renal failure was produced by bilateral ureteral ligation. Cimetidine was intravenously infused to ureter ligated (UL) and control rats, and cimetidine concentration in plasma, brain and cerebrospinal fluid (CSF) were compared. Results. The cimetidine concentration in plasma was rapidly increased in UL rats as compared to control rats. The cimetidine concentration in CSF at the onset of convulsion did not depend on the infusion rate, suggesting that cimetidine in CSF equilibrates rapidly with the site of action for clonic convulsion. The cimetidine concentration in CSF of UL rats at the onset of clonic convulsion was lower than those of control rats. Conclusions. Increased sensitivity to the drug on the central nervous system may contribute to increased toxicity of cimetidine with renal failure.

Effect of renal or hepatic dysfunction on neurotoxic convulsion induced by ranitidine in mice.

We investigated the effect of acute renal and hepatic dysfunction on the neurotoxicity of ranitidine, a histamine H2 receptor antagonist. Experimental acute hepatic and renal dysfunction in mice were produced by i.p. injection of uranyl nitrate (UN) and carbon tetrachloride (CT), respectively. Ranitidine was then constantly infused into the tail vein until the onset of clonic convulsion. When compared to control mice, UN treated mice had a significantly shorter onset time to clonic convulsion, lower total dose and higher plasma concentration at initiation of clonic convulsion. In contrast, the convulsive threshold concentration in the brain of UN treated mice was not significantly different from that of control mice. In CT treated mice, all pharmacokinetic and pharmacodynamic data described above were not significantly different from those of the control mice. No significant difference in the brain/plasma concentration ratio was observed between both disease models and the corresponding control mice. Finally, the effect of UN and CT treatment on the convulsive potency after intracerebral (i.e.) administration of ranitidine was investigated in mice. Potentiation of the intrinsic neurotoxic sensitivity to ranitidine could not be demonstrated for mice with renal or hepatic dysfunction. From these findings, we conclude that renal dysfunction is a risk factor for ranitidine neurotoxicity, and this increased risk results from increase in the drug concentration in plasma and brain as a result of impaired renal excretion. No apparent effect of acute hepatic dysfunction was observed on both the pharmacokinetic and pharmacodynamic behavior of the drug.

A Validated Fluorometric Method for the Rapid Determination of Pregabalin in Human Plasma Applied to Patients With Pain.

Background: Pregabalin has been used for the treatment of pain. A clinically accepted method applied to patients with pain has not been published for the determination of pregabalin in human plasma. This study developed a fluorometric ultrahigh-performance liquid chromatography (UHPLC) method to measure pregabalin concentration in patients with pain. Methods: After plasma pretreatment involving protein precipitation, pregabalin and gabapentin as an internal standard were derivatized with 4-fluoro-7-nitrobenzofurazan (NBD-F) under the following reaction conditions: 1 minute, pH 10, and 60°C. The UHPLC separation was performed using a 2.3-&mgr;m particle size octadecylsilyl column. The fluorescence detector was set at excitation and emission wavelengths of 470 and 530 nm, respectively. The predose blood samples were collected from 40 patients with pain who have been treated with 75 mg of pregabalin twice daily. Results: The chromatographic run time was 1.25 minutes. No interfering peaks were observed in the blank plasma at the retention times of NBD derivatives. The calibration curve of pregabalin was linear at a range of 0.05–10 mcg/mL (r > 0.999). The lower limit of quantification was 0.05 mcg/mL. The intra-assay accuracy and precision were 98.3%–99.8% and within 4.3%, respectively. The inter-assay accuracy and precision were 103.2%–107.1% and within 4.1%, respectively. The predose plasma concentration of pregabalin in patients with pain ranged from 0.14 to 8.5 mcg/mL. Conclusions: This study provides a validated fluorometric UHPLC method with fast analytical performance for the determination of pregabalin in human plasma. The present method could be applied to patients with pain and be used for the clinical research or therapeutic drug monitoring of pregabalin.

Interindividual variation of pharmacokinetic disposition of and clinical responses to opioid analgesics in cancer pain patients

Use of prescription opioids for cancer pain according to the World Health Organization analgesic ladder has been accepted in Japan. Although oxycodone and fentanyl are commonly used as first-line analgesics, a few clinical reports have been published on interindividual variations in their pharmacokinetics and clinical responses in cancer patients. (1) Some factors relating to CYP2D6, CYP3A, ATP-binding cassette sub-family B member 1 (ABCB1), and opioid receptor mu 1 (OPRM1) involve oxycodone pharmacokinetics and sensitivity in humans. The relations between their genetic variations and clinical responses to oxycodone are being revealed in limited groups. In our study, the impact of genetic variants and pharmacokinetics on clinical responses to oxycodone were evaluated in Japanese populations. (2) Opioid switching improves the opioid tolerance related to the balance between analgesia and adverse effects. Some patients have difficulty in obtaining better opioid tolerance in recommended conversion ratios. The activities of CYP3A, ABCB1, and OPRM1 contribute to the interindividual variations in clinical responses to fentanyl in cancer patients. However, the variations in opioid switching remain to be clarified in clinical settings. In our study, genetic factors related to interindividual variations in clinical responses in opioid switching to fentanyl were revealed in Japanese populations. In this symposium review, the possibility of approaches to personalized palliative care using opioids based on genetic variants of CYP2D6, CYP3A5, ABCB1, and OPRM1 is discussed.

Trends in Non-prescription Drug Recalls in Japan.

Recalls of non-prescription drugs can contribute to preventing harm to human health, however, they also interrupt the supply of medicines to the market. The aim of the present study was to investigate the trends in non-prescription drug recalls in Japan. Class I, II, and III recalls reported from April 2009 to March 2014 were obtained from the websites of the Ministry of Health, Labour and Welfare and the Pharmaceuticals and Medical Devices Agency. Each drug recall was classified according to year, dosage form, therapeutic category, and reasons for the recall. The trends over the 5 year period were assessed for each class. A total of 220 recalls were reported in the 5-year study period. The numbers of drug recalls were 21, 16, 80, 58, and 45 in 2009, 2010, 2011, 2012, and 2013, respectively. The drugs recalled consisted of 177 internal medications, 35 topical agents, and 8 others. Drug recalls were observed in 12 therapeutic categories of drug effects. The largest number of recalls was for Chinese herbal medicines and crude drugs. Of all the drug recalls in 2011, Chinese herbal medicines and crude drugs produced by one manufacturer accounted for 84%. Slightly more than half (54%) of drug recalls were due to a violation of the regulations. One manufacturer recalled many drugs because of non-compliance with the standard regulations for manufacturing drugs after 2011. In conclusion, non-prescription drug recalls can occur for any drug regardless of the dosage form and therapeutic category.

Clinical pharmacology and pharmacoepidemiology for medication safety in clinical settings

In this review, optimization of individualized analgesic therapy in cancer-pain patients (1), pharmacoepidemiological studies using a hospital database (DB) (2), and other clinical and practical research studies (3) were summarized. (1) The aim of the analgesic study was to evaluate individual factors in the effects of pain-relief, and ADR of analgesics from the viewpoints of clinical pharmacokinetics and pharmacodynamics. Oxycodone, fentanyl, and gabapentin were used. For the dose escalation and ADR of oxycodone, the plasma disposition of noroxycodone regulated by CYP3A5 polymorphisms and cancer cachexia were found to be individual factors. The ADR and clinical response of fentanyl were affected by polymorphisms of CYP3A5 and ABCB1. In the pharmacokinetics of gabapentin, concomitant magnesium oxide reduced the intestinal absorption of gabapentin. (2) The aim of the DB study was to demonstrate a pharmacoepidemiological advantage using a hospital DB of a million-scale for post-marketing safety management. We tried to detect fluoroquinolone (FQ)-induced tendon disorders, because its risk ratio in Japan has not been clarified. The risk of a tendon disorder in FQ-prescribed patients was 0.082% (95%CI: 0.049-0.137%), and significantly higher than that in cephalosporin-prescribed patients. The risk ratio in FQ-prescribed patients in relation to cephalosporin-prescribed patients was 6.29 (95%CI: 2.27-17.46). (3) Individual variation of plasma exposure of free linezolid and its ratio to minimum inhibitory concentration in critically ill patients, as well as three other studies, were described. In conclusion, our achievement in accurately assessing these would contribute to medication safety and the appropriate use of medicines in clinical settings.