[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.

A selective alpha1A-adrenoceptor antagonist inhibits detrusor overactivity in a rat model of benign prostatic hyperplasia.

PURPOSE: Alpha(1)-adrenoceptor antagonists relax the obstructed prostatic urethra and suppress the irritative symptoms frequently observed in patients with benign prostatic hyperplasia. We investigated the effects of 3 alpha(1)-adrenoceptor antagonists on urodynamics in rats with hormone induced benign prostatic hyperplasia to determine which alpha(1)-adrenoceptor subtype selective antagonists would suppress irritative symptoms. MATERIALS AND METHODS: Rats were treated with testosterone and 17beta-estradiol by weekly intramuscular injections. After 4 weeks a pressure flow study was done and the effects of the alpha(1)-adrenoceptor antagonists KMD-3213 silodosin, tamsulosin and prazosin on urodynamics were compared. We especially investigated the involvement of the bladder and prostatic urethra to clarify the mechanism of detrusor overactivity expression. RESULTS: Hormone treatment induced benign prostatic hyperplasia and resulted in detrusor overactivity, as determined by cystometry. Baseline perfusion urethral pressure and the phenylephrine induced increase in it were significantly higher in rats with vs without benign prostatic hyperplasia. Cystometry in hormone treated female rats did not show detrusor overactivity. KMD-3213 decreased detrusor overactivity, similar to other alpha(1)-adrenoceptor antagonists. CONCLUSIONS: These results suggest that an excessive response to sympathetic nerve stimulation, which is mainly mediated via alpha(1A)-adrenoceptor, in the hypertrophied prostate gives rise to detrusor overactivity. Furthermore, the alpha(1A)-adrenoceptor selective antagonist KMD-3213 would be suitable for improving irritative symptoms in patients with benign prostatic hyperplasia.

Cardiovascular effects of the selective alphalA-adrenoceptor antagonist silodosin (KMD-3213), a drug for the treatment of voiding dysfunction.

The aim of this study was to assess the cardiovascular effects of silodosin (CAS 160970-54-7, (-)-1-(3-hydroxypropyl)-5-[(2R)-2-({2-[2-(2,2,2-trifluoroethoxy) phenoxy]ethyllamino)propyll-2,3-dihy-dro-1H-indole-7-carboxamide, KMD-3213), a potent selective alpha1A-adrenoceptor (AR) antagonist used for the treatment of dysuria. In conscious dogs, orally administered silodosin, at doses (0.2, 2 and 20 mg/kg) considerably higher than the pharmacologically effective dose, decreased blood pressure. These doses, however, had no effects on heart rate or on the electrocardiogram (PR interval, QRS interval, QT interval or QTc). In addition, the cardiac effects of silodosin were evaluated in an in vitro electrophysiological study. Silodosin inhibited the human ether-a-go-go-related gene (HERG) tail current, leaving a residual tail current of 45 % control at 10 micromol/L. However, the concentration that inhibited the HERG tail current was considerably higher than its affinity for alphal-ARs. These results suggest that while the alpha1B-AR subtype is mainly involved in the regulation of blood pressure, the alphalA-AR subtype is not. There seems to exist no evidence of a correlation between the function of alphal-AR and ECG changes reflecting inhibition of the HERG current. The cardiovascular profile of silodosin suggests therefore that it is a safe and well-tolerated drug.

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.