[Furanocoumarins contents and cytochrome P450 3A (CYP3A) inhibitory activities of various processed fruit peel products: outflow of 6',7'-Dihydroxybergamottin during processing treatment of peel].

Furanocoumarins (FCs) such as bergamottin (BG) and 6',7'-dihydroxybergamottin (DHBG) contained in grapefruits are known to be cytochrome P450 3A4 (CYP3A4) inhibitors. These are contained in larger quantity in peel than in pulp, and therefore, processed peel products possibly have strong CYP3A4 inhibitory activity. The CYP3A4 inhibitory potency of these processed peel products, however, remains to be elucidated. The FC content and CYP3A inhibitory activities of various processed fruit peel products were investigated. CYP3A inhibitory activities of crystallized grapefruit peel, grapefruit marmalade, lemon peel and bitter orange slice were close to that of 100% grapefruit juice, while the activities of yuzu slice, pomelo (buntan) marmalade and crystallized iyokan peel were very weak, 1/8-1/20 of 100% grapefruit juice. The maximum BG content was 5.6 µg/g in lemon peel. The maximum DHBG content was 7.2 µg/g in crystallized grapefruit peel, about 1/30 that of raw peel. Grapefruit marmalade and crystallized grapefruit peel contained similar amounts of FCs to 100% grapefruit juice, but FCs were not detected in pomelo (buntan) marmalade or crystallized iyokan peel. Good correlation (r=0.78) was observed between the FC contents of these peel products and those CYP3A inhibitory activities. Preparation of homemade grapefruit marmalade and crystallized peel revealed that considerably lower DHBG content in these products and lower CYP3A inhibitory activity than anticipated were attributable to outflow of DHBG to broth during boiling of the raw peel.

[Possibility of interactions between prescription drugs and OTC drugs (2nd report)--interaction between levodopa preparation and OTC Kampo medicines for upset stomach].

Our series of studies aimed to examine the possibility of interactions between prescription drugs and over-the-counter (OTC) drugs by monitoring plasma drug concentrations in rats. When a levodopa preparation indicated for patients with Parkinson's disease was administered in combination with Takeda Kampo Ichoyaku K-matsu (A), Taisho Kampo Ichoyaku (B), or Kanebo Kampo Ichoyaku H(C), which are OTC kampo medicines for upset stomach, the plasma levodopa concentration-time curves were shifted downward and the AUC for levodopa was significantly lowered. These results indicate that there may be some interactions between the levodopa preparation and these OTC kampo medicines when ingested together, which leads to a reduction in the bioavailability of levodopa. On the other hand, concomitant administration of the levodopa preparation with Takeda Kampo Ichoyaku A-matsu (D) did not alter any of the pharmacokinetic parameters for levodopa. According to the package inserts for the OTC kampo medicines, A, B and C, but not D, contain metallic additives, such as aluminum silicate and magnesium stearate. In addition, combination with a kampo basis of D (Koshaheiisan-ka-shakuyaku) showed no detectable change in levodopa bioavailability. From these results, it was concluded that metallic additives may play an essential role in generating the drug-interaction between levodopa preparation and OTC kampo medicine for upset stomach.

Banana juice reduces bioavailability of levodopa preparation.

This study aimed to examine the effects of banana juice on levodopa bioavailability in rats. When a levodopa preparation (EC-Doparl tablets) was orally administered with banana juice made by mixing with a fresh banana and water, there were significant decreases in C(max) (17.4+/-2.5 vs. 8.6+/-3.1 microg/ml; alpha=0.05) and AUC (1882.8+/-49.2 vs. 933.5+/-286.6 microg.min/ml; alpha=0.05) for levodopa. On the other hand, administration of the levodopa preparation with a commercial beverage containing 10% banana juice resulted in no significant change in C(max) or AUC. These results indicate that concomitant intake of levodopa preparations with banana juice, but not with a commercial banana beverage, may cause a drug-food interaction reducing levodopa bioavailability, and we should pay attention to such interactions during levodopa therapy for patients with Parkinson's disease.

[Simple method for precognition of drug interaction between oral iron and phenolic hydroxyl group-containing drugs].

In the present study, we devised a simple method for detecting the drug interaction between oral iron preparations and phenolic hydroxyl group-containing drugs, using the coloring reaction as indicator, due to the formation of complexes or chelates. In the method, oral iron preparations and test drugs in amounts as much as single dose for adults were added to 10 ml of purified water to make sample suspensions for testing. Thirty minutes after mixing an oral iron suspension and a test drug suspension, the change of color in the mixture was observed macroscopically and graded as 0 to 3, with a marked color change judged as grade 3 and no color change as grade 0. Screening of 14 test drugs commonly used orally was carried out. When using sodium ferrous citrate preparations as oral iron, 5 were classified as grade 3, 2 as grade 2, 4 as grade 1, and 3 as grade 0, respectively. To verify usefulness of the method, the interactions suggested by screening were pharmacokinetically assessed by measuring serum concentrations of the drug in mice. When a levodopa or droxidopa preparation, judged as grade 3 in screening, was concomitantly administered with an iron preparation, a significant reduction in bioavailability of the test drug was observed, indicating possible drug interaction between the test drug and oral iron. Combined administration of an acetaminophen preparation, judged as grade 1, and oral iron preparation showed no influence on the bioavailability of the test drug, implying no detectable interactions between them. In conclusion, the simple method devised in the present study is useful for precognition of drug interactions between oral iron preparations and phenolic hydroxyl group-containing drugs, and the drugs with a higher grade in screening may induce drug interactions with oral iron.