Cysteine effects on the pharmacokinetics of etoposide in protein-calorie malnutrition rats: increased gastrointestinal absorption by cysteine.

Protein-calorie malnutrition (PCM) occurs frequently in advanced cancer patients and has a profound impact on the toxicity of many drugs. Thus, the pharmacokinetics of etoposide were evaluated in control, control with cysteine (CC), PCM, and PCM with cysteine (PCMC) rats. Etoposide was administered intravenously (2 mg/kg) or orally (10 mg/kg). Changes in hepatic and intestinal cytochrome P450s (CYPs) and effects of cysteine on intestinal P-glycoprotein (P-gp)-mediated efflux were also measured. In PCM rats, the CL(NR) (AUC(0-∞)) of intravenous etoposide was significantly slower (greater) than that in controls, because of the significant decrease in the hepatic CYP3A subfamily and P-gp. In PCMC rats, the slowed CL(NR) of etoposide in PCM rats was restored to the control level by cysteine treatment. PCMC rats showed a significantly greater AUC(0-6 h) of oral etoposide than PCM rats, primarily because of the increased gastrointestinal absorption of etoposide as a result of the inhibition of intestinal P-gp by cysteine. The gastrointestinal absorption of an oral anticancer drug, which is a substrate of P-gp, may be improved by co-administration of cysteine in advanced cancer patients if the present rat data can be extrapolated to patients.

Pharmacokinetics of sildenafil and its metabolite, N-desmethylsildenafil, in rats with liver cirrhosis and diabetes mellitus, alone and in combination.

Pharmacokinetics of sildenafil and its metabolite, N-desmethylsildenafil, in humans and rats with liver cirrhosis (LC) and diabetes mellitus (DM), alone and in combination (LCD) did not seem to be reported. Sildenafil was administered intravenously (10 mg/kg) and orally (20 mg/kg) to control, LC, DM, and LCD rats. Expression of intestinal CYP isozymes in those rats was also measured. In LC, DM, and LCD rats, the areas under the curve (AUCs) of intravenous sildenafil were significantly greater (by 195%, 54.2%, and 127%, respectively) than controls. In LC and LCD rats, AUCs of oral sildenafil were significantly greater (3010% and 2030%, respectively) than controls. In LC, DM, and LCD rats, significantly greater AUCs of intravenous sildenafil were due to the slower hepatic extraction of sildenafil (because of decrease in the protein expression of hepatic CYP2C11 and 3A subfamily in LC and LCD rats, and CYP2C11 in DM rats). In LC and LCD rats, greater magnitude of increase in AUCs of oral sildenafil than those after the intravenous administration could be mainly due to the decrease in the intestinal extraction of sildenafil (because of decrease in the protein expression of intestinal CYP2C11 in LC and LCD rats).

Pharmacokinetics of liquiritigenin and its two glucuronides, M1 and M2, in rats with acute hepatitis induced by d-galactosamine/lipopolysaccharide or CCl(4).

Cytoprotective effects of liquiritigenin (LQ) against liver injuries have been reported, but its pharmacokinetics has not been studied in acute hepatitis. Thus, pharmacokinetics of LQ and its two conjugated glucuronide metabolites: 4'-O-glucuronide (M1) and 7-O-glucuronide (M2), in rats with acute hepatitis induced by d-galactosamine/lipopolysaccharide (GalN/LPS) rats or carbon tetrachloride-treated (CCl(4)-treated) rats were evaluated. LQ was administered intravenously (20 mg kg(-1)) and orally (50 mg kg(-1)) to control GalN/LPS and CCl(4)-treated rats. Expression of uridine 5'-diphospho-glucuronosyltransferases 1A (UGT1A) and in vitro metabolism of LQ in hepatic and intestinal microsomes were also measured. After intravenous administration of LQ, area under the plasma concentration-time curve (AUC) of LQ in GalN/LPS rats was significantly smaller than that in controls due to faster non-renal clearance, as a result of its greater free fraction in plasma and faster hepatic blood flow rate than the controls. In CCl(4)-treated rats, the AUC(M1, 0-8 h)/AUC(LQ) and AUC(M2, 0-8 h)/AUC(LQ) ratios were significantly greater than the controls due to decrease in biliary excretion of M1 and M2. However, no significant pharmacokinetic changes were observed in both acute hepatitis rats after oral administration due to comparable intestinal metabolism of LQ. Modification of oral dosage regimen of LQ may not be necessary in patients with acute hepatitis; but human studies are required.

Pharmacokinetic interaction between telithromycin and metformin in diabetes mellitus rats.

Telithromycin and metformin have been reported to be commonly metabolized via hepatic CYP3A1/2 in rats. Community-acquired respiratory tract infection was reported to be frequent in patients with diabetes mellitus. Compared with controls, hepatic CYP3A1/2 was reported to be increased in male rats with diabetes mellitus induced by streptozotocin (DMIS rats). After the intravenous administration of both drugs together to male DMIS rats, the time-averaged non-renal clearance (CL(NR)) of metformin was significantly slower (by 33.1%; 10.3 versus 15.4 ml min(-1) kg(-1)) than metformin alone due to the inhibition of hepatic metabolism of metformin by telithromycin via CYP3A1/2. After the oral administration of both drugs together, the total area under the plasma concentration-time curve (AUC) of metformin was comparable possibly due to the increased intestinal metabolism of metformin by telithromycin.

Pharmacokinetics and first-pass effects of liquiritigenin in rats: low bioavailability is primarily due to extensive gastrointestinal first-pass effect.

Pharmacokinetics of liquiritigenin, a candidate for inflammatory liver disease, and its two glucuronide conjugates, M1 and M2, were evaluated in rats. The hepatic and gastrointestinal first-pass effects of liquiritigenin were also evaluated in rats. After oral administration of liquiritigenin at a dose of 20 mg kg(-1), 1.07% of the dose was not absorbed from the gastrointestinal tract up to 24 h, and the F-value was only 6.68%. In vitro metabolism of liquiritigenin in S9 fractions of rat tissues showed that the liver and intestine were major tissues responsible for glucuronidation of liquiritigenin. The hepatic and gastrointestinal first-pass effects of liquiritigenin were approximately 3.67% and 92.5% of the oral dose, respectively. Although the hepatic first-pass effect of liquiritigenin after absorption into the portal vein was 57.1%, the value was only 3.67% of the oral dose due to extensive gastrointestinal first-pass effect in rats. Therefore, the low F-value of liquiritigenin in rats was primarily attributable to an extensive gastrointestinal first-pass effect although liquiritigenin was well absorbed. Compared with rats, the higher F-value of liquiritigenin could be expected in humans.

Interaction between udenafil and tamsulosin in rats: non-competitive inhibition of tamsulosin metabolism by udenafil via hepatic CYP3A1/2.

BACKGROUND AND PURPOSE: Orthostatic hypotension has been observed when PDE 5 (cGMP-specific phosphodiesterase type 5) inhibitors are co-administered with alpha-adrenoceptor antagonists. Here we assessed the pharmacokinetic and haemodynamic interactions between udenafil and tamsulosin in rats, as both drugs are metabolized via rat hepatic cytochrome P450 3A1/2. EXPERIMENTAL APPROACH: Interactions between the two drugs were evaluated in rats after simultaneous 1 or 15 min i.v. infusion or after p.o. administration of udenafil (30 mg x kg(-1)) and/or tamsulosin (1 mg x kg(-1)). In vitro metabolism of tamsulosin with udenafil was measured to obtain the inhibition constant (K(i)) and [I]/K(i) ratio of udenafil. KEY RESULTS: The total area under the plasma concentration-time curve from time zero to time infinity (AUC)s (or AUC(0-4 h)) of tamsulosin were significantly greater after 15 min of i.v. infusion or after oral administration with udenafil, compared with tamsulosin alone. The hepatic first-pass metabolism of tamsulosin was inhibited by udenafil, and the inhibition in vitro was in a non-competitive mode. The arterial systolic blood pressure was significantly lower at 5, 10 and 60 min after oral co-administration of the drugs. CONCLUSIONS AND IMPLICATIONS: The significantly greater AUC of tamsulosin after i.v. and p.o. administration of both drugs may be attributable to non-competitive inhibition of cytochrome P450 3A1/2-mediated hepatic tamsulosin metabolism by udenafil. The inhibition was also observed in human liver S9 fractions, suggesting that a reassessment of the oral dosage of tamsulosin is necessary when udenafil and tamsulosin are co-administered to patients with benign prostatic hyperplasia.