工藤 敏之

Creatinine is a common biomarker of renal function and is secreted in the renal tubular cells via drug transporters such as organic cation transporter 2 and multidrug and toxin extrusion (MATE) 1/2-K. To differentiate between drug-induced acute kidney injury (AKI) and drug interactions through the renal transporter, it has been examined whether these transporter inhibitions quantitatively explained increases in serum creatinine (SCr) at their clinically relevant concentrations using drugs without any changes in renal function. For such renal transporter inhibitors and recently approved tyrosine kinase inhibitors (TKIs), this mini-review describes clinical increases in SCr and inhibitory potentials against the renal transporters. Most cases of SCr elevations can be explained by considering the renal transporter inhibitions based on unbound maximum plasma concentrations, except for drugs associated with obvious changes in renal function. SCr increases for cobicistat, dolutegravir, and dronedarone, and some TKIs were significantly underestimated, and these underestimations were suggested to be associated with low plasma unbound fractions. Sensitivity analysis of SCr elevations regarding inhibitory potentials of MATE1/2-K demonstrated that typical inhibitors such as cimetidine, DX-619, pyrimethamine, and trimethoprim could give false interpretations of AKI according to the criteria based on relative or absolute levels of SCr elevations. Recent progress and current challenges of physiologically-based pharmacokinetics modeling for creatinine disposition were also summarized. Although it should be noted for the potential impact of in vitro assay designs on clinical translatability of transporter inhibitions data, mechanistic approaches could support decision-making in clinical development to differentiate between AKI and creatinine-drug interactions. Significance Statement Serum creatinine (SCr) is widely used as an indicator of kidney function, but it increases due to inhibitions of renal transporters such as multidrug and toxin extrusion protein ½-K despite no functional changes in the kidney. Such SCr elevations were quantitatively explained by renal transporter inhibitions except for some drugs with high protein binding. The present analysis demonstrated that clinically relevant inhibitors of the renal transporters could cause SCr elevations above levels corresponding to acute kidney injury criteria.

BACKGROUND: Caffeine consumption is a risk factor for chronic daily headache but few studies have addressed relationships between pediatric patient caffeine levels and headache severity. We examined associations between serum and urine caffeine levels and headache severity in childhood and adolescent migraine cases. METHODS: Levels of caffeine and caffeine metabolites in serum and urine samples were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The Wilcoxon rank-sum test was used for comparisons of age, sleep time, headache severity, caffeine consumption, and caffeine detection. Spearman's rank correlation coefficient (ρ) was calculated for associations. Correlations where ρ ≥ 0.3 and differences where p < 0.05 were considered statistically significant. RESULTS: Of the 40 patients studied, 34 declared caffeine consumption and six declared no caffeine consumption. These two groups did not differ significantly in any of the above clinical parameters. Liquid chromatography-tandem mass spectrometry analysis of both serum and urine samples revealed nine caffeine-negative (level <0.0625 μM) and 31 caffeine-positive cases. The Headache Impact Test-6 (HIT-6) score was higher (p = 0.033) for the caffeine-positive group versus the caffeine-negative group. Caffeine was detected by LC-MS/MS in the serum and/or urine of three of the six patients who declared no caffeine consumption. No significant correlations were observed among age, sleep times, headache severity score, or levels of caffeine and caffeine metabolites. CONCLUSION: Thirty one of 40 (77.5%) cases of childhood/ adolescence migraine showed serum and urine caffeine positivity based on LC-MS/MS. The HIT-6 score, a measure of headache severity, was significantly higher for caffeine-positive versus caffeine-negative cases. Symptoms of childhood/adolescence migraine were exacerbated by caffeine consumption.

Rilpivirine is a non-nucleoside reverse transcriptase inhibitor, used for the treatment of human immunodeficiency virus type-1 infection. An open label study was conducted to investigate the pharmacokinetics (PK) and safety of a single oral dose of rilpivirine 25 mg in Japanese healthy adult subjects. No adverse events were reported. The mean Cmax (144.3 ng/mL) and AUCinf (4542 ng h/mL) in Japanese subjects were approximately 30 % higher than those reported from a similar study in Caucasian healthy subjects, whereas the median tmax and mean t1/2 values were comparable between studies. A simple physiologically based PK model was developed to characterize the rilpivirine PK profile. The model adequately described rilpivirine PK profiles, and well-predicted drug-drug interactions. With exploration using the model, body size and CYP3A4 abundance were identified as factors which explained the observed inter-ethnic difference in rilpivirine exposure. The inter-ethnic difference in rilpivirine exposure was however considered not clinically relevant, since inter-individual variabilities of those intrinsic factors are larger than inter-ethnic ones; and the observed AUCinf in Japanese subjects was within the range of AUCtau associated with efficacy and safety in Phase 3 studies. This study results support the use of rilpivirine without dose modification specific to Japanese patients.

We have previously shown that two enteral nutrition formulas suppressed gastric lesions induced by the oral administration of indomethacin (IND) in mice. However, the mechanism of their protective effect is unknown. In this study, the effect of the two enteral nutrition formulas on gastric lesions induced by subcutaneous IND injection was investigated, with the objective of exploring the possibility that they may interact directly with IND in the gastrointestinal tract. Ten-week-old, male, ICR mice were fasted, then orally given either purified water, Mermed® One, or 2-fold diluted Terumeal® 2.0α as enteral nutrition formula (25 mL/kg). IND was injected subcutaneously at 20 mg/kg after 30 min, and the stomach was removed 6 h later and fixed in formalin. The number and area of lesions in the stomachs of mice given enteral nutrition formula was reduced to 56-89% and 34-61%, respectively, compared with the mice given purified water. The time courses of plasma IND concentrations were comparable among the three groups. These results suggested that the effect of these enteral nutrition formulas on gastric lesions did not originate from their direct interaction with IND in the gastrointestinal tract or their effect on the disposition of IND.

PURPOSE: Menkes disease is a rare hereditary disease in which systemic deficiency of copper due to mutation of the ATP7A gene causes severe neurodegenerative disorders. The present parenteral drugs have limited efficacy, so there is a need for an efficacious drug that can be administered orally. This study focused on glyoxal-bis (N(4)-methylthiosemicarbazonato)-copper(II (CuGTSM), which has shown efficacy in macular mice, a murine model of Menkes disease, and examined its pharmacokinetics. In addition, nanosized CuGTSM (nCuGTSM) was prepared, and the effects of nanosizing on CuGTSM pharmacokinetics were investigated. METHODS: CuGTSM or nCuGTSM (10 mg/kg) was administered orally to male macular mice or C3H/HeNCrl mice (control), and plasma was obtained by serial blood sampling. Plasma concentrations of CuGTSM and GTSM were measured by LC-MS/MS and pharmacokinetic parameters were calculated. RESULTS: When CuGTSM was administered orally, CuGTSM and GTSM were both detected in the plasma of both mouse strains. When nCuGTSM was administered, the Cmax was markedly higher, and the mean residence time was longer than when CuGTSM was administered for both CuGTSM and GTSM in both mouse strains. With macular mice, the AUC ratio (GTSM/CuGTSM) was markedly higher and the plasma CuGTSM concentration was lower than with C3H/HeNCrl mice when either CuGTSM or nCuGTSM was administered. CONCLUSION: Absorption of orally administered CuGTSM was confirmed in macular mice, and the nano-formulation improved the absorption and retention of CuGTSM in the body. However, the plasma concentration of CuGTSM was lower in macular mice than in control mice, suggesting easier dissociation of CuGTSM.

In vitro-in vivo extrapolation (IVIVE) using human liver microsomes has been widely used to predict metabolic clearance, but some of the factors used in the process of prediction show variability for the same compound: notably, microsomal intrinsic clearance values corrected by the unbound fraction (CLint, u), physiological parameters used for scale-up, and the source of in vivo clearance data.The purpose of this study was to assess the correlation between in vitro and in vivo CLint with a focus on factors showing variability using four cytochrome P450 (CYP)3A substrates.We surveyed in vivo clearance values in literature and also determined the microsomal CLint, u values. A scaling factor (SFdirect) was defined as in vivo CLint divided by the microsomal CLint, u, which ranged from 1190 to 2310 (mg protein per kg body weight). The application of a mean SFdirect of 1600 (mg protein per kg body weight) and further normalization by the microsomal CLint, u values of midazolam, the most commonly used substrate, resulted in improved prediction accuracy for CLint, u values from various microsomal batches.The results suggest the normalization of variability might be useful for predicting the in vivo CLint.

Ceftriaxone (CTRX) is a third-generation cephalosporin commonly used to treat infections such as community-acquired pneumonia and urinary tract infections caused by mainly Gram-negative bacteria and some Gram-positive bacteria. Here, we report a case of a patient on hemodialysis who had chorea-like symptoms with high blood concentration of CTRX. A 74-year-old Japanese woman receiving hemodialysis was admitted with obstructive cholangitis and was started on CTRX therapy at a dose of 2 g every 24 hours. On the 6th day after starting administration of CTRX, chorea-like symptoms appeared. We suspected that her symptoms were caused by a high blood concentration of CTRX. We performed a series of blood sampling to determine the concentration of CTRX at different time points before and after discontinuing CTRX administration. CTRX concentrations were higher than those expected in healthy adults, and her chorea-like symptoms had disappeared from the second day of discontinuation of CTRX. The association between CTRX blood concentration and chorea-like symptoms is unclear. However, measuring a series of plasma or serum concentrations from symptom onset to disappearance suggested that chorea-like symptoms appeared when the concentration exceeded approximately 450 μg/mL. Care should be taken when administering CTRX to patients with cholestasis undergoing hemodialysis, as blood CTRX levels may rise unexpectedly and result in complications.

We investigated the effects of enteral nutrition formula on non-steroidal anti-inflammatory drug (NSAID)-induced gastric lesions in mice. Male ICR mice aged 7-9 weeks old were fasted, then orally given either purified water, Mermed® One, or 2-fold diluted Terumeal® 2.0α as enteral nutrition (25 or 50 mL/kg each). Indomethacin (IND) was orally administered at 20 mg/kg after 30 min, and the stomach was removed 6 h later and fixed in formalin. The number and area of lesions in the stomachs of the mice given enteral nutrition showed a significant, dose-dependent decrease compared to the purified water-treated group, and no significant difference was seen between the two enteral nutrition-treated groups. Comparable time courses of plasma IND concentrations suggest that enteral nutrition does not inhibit gastrointestinal absorption of IND. Our findings indicate that administering enteral nutrition could inhibit the onset of NSAID-induced gastric ulcers.

Creatinine is excreted into urine by glomerular filtration and renal tubular secretion through drug transporters such as organic anion transporter 2 (OAT2), organic cation transporter 2 (OCT2), OCT3, multidrug and toxin extrusion protein 1 (MATE1), and MATE2-K. We aimed to investigate whether our method for estimating percentage changes in serum creatinine concentration (SCr) and creatinine clearance (CLcre) from the baseline is applicable for studying renal transporter inhibitors. We tested 14 compounds (cimetidine, cobicistat, dolutegravir, dronedarone, DX-619, famotidine, INCB039110, nizatidine, ondansetron, pyrimethamine, rabeprazole, ranolazine, trimethoprim, and vandetanib), which were reported to cause reversible changes in SCr and/or CLcre in healthy subjects excluding elderly. Percentage changes were estimated from the relative contributions of the forementioned transporters to CLcre and competitive inhibition by these compounds at their maximum plasma unbound concentrations. For 7 and 9 out of these compounds, changes in SCr and/or CLcre were estimated within 2- and 3-fold of observed values, respectively. Less than 10% changes in SCr and/or CLcre caused by cobicistat, dolutegravir, and rabeprazole were reproduced as such by our method. These findings suggest that our method can be used to estimate changes in SCr and CLcre caused by competitive inhibitions of renal drug transporters.

AIMS: Vonoprazan, a new class of potassium-competitive proton pump inhibitors has been found to attenuate the antiplatelet function of clopidogrel in a recent clinical study, despite weak in vitro activity against CYP2C19. To elucidate the mechanism of this interaction, the present study investigated the effects of esomeprazole and vonoprazan on the pharmacokinetics of proguanil, a CYP2C19 substrate. METHODS: Seven healthy male volunteers (CYP2C19 extensive metabolizers) received a single oral administration of 100 mg proguanil/250 mg atovaquone (control phase), oral esomeprazole (20 mg) for 5 days followed by proguanil/atovaquone (esomeprazole phase) and oral vonoprazan (20 mg) for 5 days followed by proguanil/atovaquone (vonoprazan phase). Concentrations of proguanil and its metabolite, cycloguanil, in plasma and urine in each phase were determined using liquid chromatography-tandem mass spectrometry. RESULTS: Coadministration with proton pump inhibitors resulted in increase and decrease in the area under the plasma concentration-time curve (AUC) of proguanil and cycloguanil, respectively, significantly reducing their AUC ratio (cycloguanil/proguanil) to 0.317-fold (95% confidence interval [CI] 0.256-0.379) and 0.507-fold (95% CI 0.409-0.605) in esomeprazole phase and vonoprazan phase, respectively. Esomeprazole and vonoprazan also significantly reduced the apparent formation clearance (cumulative amount of cycloguanil in urine divided by AUC of proguanil) to 0.324-fold (95% CI 0.212-0.436) and 0.433-fold (95% CI 0.355-0.511), respectively, without significant changes in renal clearance of proguanil and cycloguanil. CONCLUSIONS: Although further studies are needed, both esomeprazole and vonoprazan potentially inhibit CYP2C19 at clinical doses, suggesting caution in the coadministration of these drugs with CYP2C19 substrates.

薬物代謝酵素と薬物トランスポーターについて概説した。

SPFマウスを用いて、抗生物質投与がCyp3a11の発現に及ぼす影響をreal-time RT-PCRを用いてmRNAレベルで検討し、Cyp3aの特異的な基質であるトリアゾラムを用いてその活性変化についても検討した。さらに、Cyp3a11の変化が、投与した薬物の直接的な影響ではないことを確認するために、GFマウスに抗生物質を投与し、Cyp3a11の発現変化を定量した。SPFマウスにおけるCyp3a11のmRNA発現量は、コントロール群と比較してABPC、CPX、LVX及びVCM+IPM投与群のいずれにおいても有意に低い値を示した。一方、GFマウスは、ABPC及びVCM+IPM投与群で増加傾向を示したもののいずれの投与群でも有意な変化はみられなかった。肝臓におけるTLCA量は、コントロール群と比較してCPXあるいはVCM+IPM投与群で有意に低い値を示した。LCA及びGLCAは、いずれの群においても検出限界以下であった。