Pharmacokinetic and pharmacodynamic consequences of inhibition of terazosin metabolism via CYP3A1 and/or 3A2 by DA-8159, an erectogenic, in rats

Drug interactions between antiretrovirals and drugs used to treat benign prostatic hyperplasia/lower urinary tract symptoms

INTRODUCTION

Significant advances in antiretroviral (ARV) therapy have transformed HIV into a chronic manageable disease. Co-morbidities associated with aging, such as benign prostatic hyperplasia (BPH), are becoming increasingly prevalent in the HIV-infected population. The pharmacological treatment of BPH involves medications mainly metabolized by CYP 450 enzymes, while many ARVs have inducing or inhibiting effects on the CYP 450 system. Consequently, there is potential for significant pharmacokinetic (PK) interactions between these two classes of medications.

AREAS COVERED

This article reviews the pharmacology and metabolism of selected BPH drug therapies and ARVs, in addition to highlighting potential interactions between these two drug categories. The authors also present PK evidence of interactions from available clinical trials, product monographs and international conference abstracts. Potentially significant drug interactions are summarized and strategies for management are discussed.

EXPERT OPINION

Drugs most likely to interact with BPH medications include protease inhibitors, the non-nucleoside reverse transcriptase inhibitors efavirenz, nevirapine, etravirine, and the cobicistat-boosted integrase inhibitor elvitegravir. Clinically significant PK interactions with BPH medications and dolutegravir, raltegravir, rilpivirine, or the investigational agent doravirine do not appear to exist. Clinicians working with HIV-infected individuals need to recognize the potential for interactions involving BPH and ARV treatments to ensure effective and safe drug therapy use.

Preliminary safety evaluation of a taurocholate-conjugated low-molecular-weight heparin derivative (LHT7): a potent angiogenesis inhibitor

In our previous studies, taurocholic acid (TA)-conjugated low-molecular-weight heparin derivative (LHT7) has been proven to be a potent anti-angiogenic agent by demonstrated successful blockage capability of vascular endothelial growth factors (VEGF). Preliminary safety evaluations were conducted based on its mechanism of action and chemical behavior. For this purpose, acute toxicity study, and hematological and serological evaluations were carried out. Additionally, in order to evaluate mechanism-related side effects, both blood pressure and the occurrence of proteinuria were measured using a treatment regime of multiple high doses of LHT7 in a biodistribution study. LD50 values for LHT7 in female and male mice were 56.9 and 64.7 mg kg(-1) doses, respectively. There were no vital fluctuations in the serological and hematological parameters, except for the elevated levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) at 100 and 200 mg kg(-1) doses of LHT7, representing vital changes in the liver function. Moreover, the results of mechanism-related studies showed that blood pressure at 50 mg kg(-1) did not change but showed elevated levels of protein in urine. In the biodistribution study, a slight accumulation of LHT7 in the kidney and the liver were observed at the 50 mg kg(-1) repeated dose owing to the presence of bile acid. No fatal damage was observed in this study; most observations were related to the chemical composition or the mechanism of action of the material.

Effects of cytochrome P450 (CYP) inducers and inhibitors on ondansetron pharmacokinetics in rats: involvement of hepatic CYP2D subfamily and 3A1/2 in ondansetron metabolism

The types of hepatic microsomal cytochrome P450 (CYP) isozymes responsible for the in-vivo metabolism of ondansetron in rats have not been reported. In this study, ondansetron at a dose of 8 mg kg−1 was administered intravenously to rats pretreated with various inducers of CYP isozymes, such as 3-methylcholanthrene, orphenadrine citrate, isoniazid and dexamethasone phosphate (the main inducers of CYP1A1/2, 2B1/2, 2E1 and 3A1/2 in rats, respectively), and inhibitors, such as SKF-525A (a non-specific inhibitor of CYP isozymes), sulfaphenazole, quinine hydrochloride and troleandomycin (the main inhibitors of CYP2C6, 2D subfamily and 3A1/2 in rats, respectively). In rats pretreated with quinine hydrochloride and troleandomycin, the time-averaged non-renal clearance of ondansetron was significantly slower (48.9 and 13.2% decrease, respectively) than that in control rats. In rats pretreated with dexamethasone phosphate, the time-averaged non-renal clearance was significantly faster (18.2% increase) than that in control rats. The results suggest that ondansetron is primarily metabolized via the CYP2D subfamily and 3A1/2 in rats.

Effect of hepatic CYP inhibitors on the metabolism of sildenafil and formation of its metabolite, N-desmethylsildenafil, in rats in vitro and in vivo

Objectives

It has been reported that hepatic cytochrome P450 (CYP)2C9 and CYP3A4 are responsible for the metabolism of sildenafil and formation of its metabolite, N-desmethylsildenafil, in humans. However, in-vivo studies in rats have not been reported.

Methods

Sildenafil (20 mg/kg) was administered intravenously to rats pretreated with sulfaphenazole, cimetidine, quinine hydrochloride or troleandomycin, inhibitors of CYP2C6, CYP2C11, CYP2D subfamily and CYP3A1/2, respectively. In-vitro studies using rat liver microsomes were also performed.

Key findings

The area under the plasma-concentration time curve (AUC) was increased and clearance of sildenafil decreased in rats pretreated with cimetidine or troleandomycin. The AUC ratio for N-desmethylsildenafil (0–4 h): sildenafil (0–∞) was significantly decreased only in rats pretreated with cimetidine. Similar results were obtained in the in-vitro study using rat liver microsomes.

Conclusions

Sildenafil is metabolised via hepatic CYP2C11 and 3A1/2, and N-desmethylsildenafil is mainly formed via hepatic CYP2C11 in rats. Thus, rats could be a good model for pharmacokinetic studies of sildenafil and N-desmethylsildenafil in humans.

Pharmacogenetics and pharmacogenomics of sexual dysfunction: current status, gaps and potential applications

Although treatment of different types of sexual dysfunction has improved in the past decade with the introduction of phosphodiesterase type 5 inhibitors and selective serotonin reuptake inhibitors, response rates to these targeted therapies are variable. There are a number of studies in the published literature that provide proof-of-concept that genetic variation contributes to the variable response. Pharmacogenomics will most likely be one part of our therapeutic armamentarium in the future and will provide a stronger scientific basis for optimizing drug therapy on the basis of each patient’s genetic constitution. This article will review English language medical literature on the state-of-the-art genetic polymorphisms of drug targets, transporters and signaling molecules as well as pharmacogenetic studies of sexual dysfunction and suggested possible applications. Collectively, the data demonstrate that pharmacogenomics in the field of sexual medicine is still in its infancy. More research will provide further intriguing new discoveries in years to come.

Pharmacokinetic interaction between tamoxifen and ondansetron in rats: non-competitive (hepatic) and competitive (intestinal) inhibition of tamoxifen metabolism by ondansetron via CYP2D subfamily and 3A1/2

PURPOSE

Tamoxifen and ondansetron were commonly metabolized via rat hepatic CYP2D subfamily and 3A1/2, and ondansetron is used to treat chemotherapy-induced nausea. The purpose of this study was to report the pharmacokinetic interaction between tamoxifen and ondansetron in rats.

METHODS

The pharmacokinetics of tamoxifen and ondansetron were evaluated after the intravenous and oral administration of tamoxifen, ondansetron, and both drugs together to rats. The Vmax (maximum velocity), Km (apparent Michaelis-Menten constant), CLint (intrinsic clearance), Ki (inhibition constant), and [I] (concentration of inhibitor in the liver and intestine)/Ki ratio of ondansetron were also measured.

RESULTS

The AUC0-infinitys of tamoxifen were significantly greater after both intravenous and oral administration with ondansetron compared to those of tamoxifen alone. The significantly slower hepatic and intestinal CLints for the disappearance of tamoxifen with both drugs together were due to inhibition of metabolism of tamoxifen by ondansetron via CYP2D subfamily and 3A1/2.

CONCLUSIONS

The significantly greater AUC0-infinity of tamoxifen after the intravenous administration of both drugs together could have possibly been attributable to a non-competitive (hepatic) inhibition of CYP2D subfamily- and 3A1/2-mediated tamoxifen metabolism by ondansetron. The significantly greater AUC0-infinity of tamoxifen after the oral administration of both drugs together could have been attributable to a competitive (intestinal) inhibition of CYP2D subfamily- and 3A1/2-mediated tamoxifen metabolism by ondansetron in addition to non-competitive inhibition in the liver.

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.