Design and in vivo evaluation of entecavir-3-palmitate microcrystals for subcutaneous sustained delivery.

The objectives of this study were to formulate microcrystals of entecavir-3-palmiate (EV-P), a palmitic acid ester of entecavir (EV), and evaluate the influence of particle size on its pharmacokinetic behavior following subcutaneous (SC) injection. Systemic toxicity and local tolerability of the hepatitis B anti-viral suspension were further evaluated in normal rats. EV-P microcrystals possessing median diameters of 2.1, 6.3, and 12.7 µm were fabricated using anti-solvent crystallization technique with polysorbate 20 and polyethylene glycol 4000 as steric stabilizer. Dissolution rate of EV-P microcrystals was controlled by adjusting the particle size, under sink condition. Pharmacokinetic profiles of 2.1 µm-sized and 6.3 µm-sized EV-P microcrystals were quite comparable (1.44 mg/kg as EV), over 46 days in rats. The absorption rate and extent of EV after SC injection of 12.7 µm-sized microcrystals were significantly retarded, due to its slower dissolution rate in aqueous media. No single-dose systemic toxicity was observed after SC injection of high dose of EV-P microcrystal suspension (30-300 mg/kg as EV). The microcrystals were tolerable in the injected site, showing mild inflammatory responses at a dose of 30 mg/kg. Therefore, the novel microcrystal system with median particle size of below 6.3 µm is expected to be a unique long-acting system of the anti-viral agent, improving patient's compliance with chronic disease.

Microsuspension of fatty acid esters of entecavir for parenteral sustained delivery.

Entecavir (EV), an anti-viral agent for hepatitis B infection, should be administered under fasted state, as intestinal absorption of this hydrophilic compound is markedly decreased under post-prandial conditions. Herein, in order to improve therapeutic adherence, a parenteral sustained delivery system was constructed, by synthesizing water-insoluble ester prodrugs of the nucleotide analogous with fatty acids. EV-3-palmitate (named EV-P), exhibited the lowest solubility in phosphate buffered saline (pH 7.4, 1.1 µg/ml), with extended release profile compared with EV, EV-3-myristate, and EV-3-stearate, was selected as a candidate to formulate drug suspension. The crystalline suspension was fabricated using anti-solvent crystallization technique, with a mean particle size of 7.7 µm. After subcutaneous (SC) injection in beagle dogs (0.43 mg/kg as EV), the plasma concentrations of EV were markedly protracted with lowered maximum plasma concentration (Cmax, 4.7 ng/ml), extended time required to reach Cmax (Tmax, 9.0 days), and lengthened elimination half-life (T1/2, 129.3 h) compared with those after oral administration (0.0154 mg/kg, Cmax, 15.4 ng/ml; Tmax, 0.01 days; T1/2, 4.1 h). The systemic exposure of the lipidic prodrug was below 0.1% compared with that of EV following SC injection, denoting that EV-P was rapidly converted into the parent compound in blood. Therefore, SC delivery of EV-P microsuspension can be an alternative to oral EV therapy, offering prolonged pharmacokinetic profile after single injection.

Candidate molecule for premature ejaculation, DA-8031: in vivo and in vitro characterization of DA-8031.

OBJECTIVES: To evaluate the efficacy of DA-8031 against premature ejaculation, we performed in vitro and in vivo pharmacologic studies. METHODS: We used a monoamine transporter binding affinity assay, receptor binding affinity assay, monoamine reuptake inhibition assay, and serotonin uptake inhibition assay in platelets and chemically induced ejaculation models in rats. RESULTS: The present study reports on the pharmacologic profile of the putative antipremature ejaculation drug, DA-8031. DA-8031 exhibits high affinity and selectivity to the serotonin transporter (Ki value 1.94 nM for 5-hydroxytryptamine transporter, 22 020 nM for norepinephrine transporter, and 77 679 nM for dopamine transporter) and potency to inhibit serotonin reuptake into the rat brain synaptosome in vitro (half maximal inhibitory concentration 6.52 nM for 5-hydroxytryptamine, 30.2 µM for norepinephrine, and 136.9 µM for dopamine). In the platelet serotonin uptake study, DA-8031 exhibited significant inhibition at oral doses of 10 and 30 mg/kg in a dose-dependent manner. In the sexual response studies, after oral and intravenous administration of DA-8031, ejaculation was significantly inhibited in both para-chloroamphetamine- and meta-chlorophenylpiperazine-mediated ejaculation models in rats. CONCLUSIONS: The pharmacologic profiles observed in the present study suggest the potential for DA-8031 as a therapeutic agent useful in the treatment of premature ejaculation.

Drug synergism of antihypertensive action in combination of telmisartan with lercanidipine in spontaneous hypertensive rats.

To examine drug synergism between angiotensin II AT1-receptor blocker and Ca(2+) channel blocker for lowering blood pressure (BP), telmisartan and lercanidipine were orally injected into to telemetered-spontaneous hypertensive rats and BP was monitored. The highest doses of both drugs (7.66 mg/kg of telmisartan and 1.92 mg/kg of lercanidipine) were clinically relevant at 80 and 20 mg human equivalent doses, respectively, and denoted as dose 1. After constructing the dose-response curve using 0 (vehicle-treated control), 1/16, 1/8, 1/4, 1/2 and 1 doses, all possible combinations of both drugs were tested. Drug synergism in combination therapy of telmisartan with lercanidipine was assessed by calculating the interaction index (γ) as evaluated by γ < 1. We found statistically significant drug synergism in the investigated (telmisartan: lercandipine) combinations of (1/8:1/4), (1/4:1) and (1/8:1). Our results suggest that the combination therapy of telmisartan and lercanidipine at lower doses are effective in lowering BP, and also reduce side effects caused by maximal doses of each drug. Therefore, drug combination of AT1-receptor blocker with Ca(2+) channel blocker is a clinically important tool for the management of hypertension and hypertension-related cardiovascular risks.

Enhanced effect of losartan and rosuvastatin on neointima hyperplasia.

The beneficial effects of losartan and rosuvastatin on neointimal formation have been well characterized, but little is known about the combined treatment benefit of these two drugs. This study was designed to investigate the synergistic effect of losartan combined with rosuvastatin on the magnitude of protective action in vascular injury mediated by cuff-induced neointimal formation model in vivo. Losartan at 20 mg/kg or rosuvastatin at 40 mg/kg significantly decreased both the neointimal formation and BrdU-positive cells in neointima, indicating the inhibition of cell proliferation including a progress of DNA synthesis. The combination treatment used lower doses of losartan with rosuvastatin (10 + 20 & 5 + 10 mg/kg, respectively) that proved to be significant in decreasing the neointimal formation and BrdU incorporation. These results were comparable to the diminution attained with monotherapy of either drug in higher doses. Interaction index measured by isobolar method indicated drug synergism in these two combinations of both drugs at lower doses. Therefore, the administration of losartan and rosuvastatin in combination with low doses synergistically decreased in cuff-induced neointimal formation by reducing cell proliferation, suggesting that this drug synergism may be fully effective with, lower adverse effects, for the treatment of vascular remodeling such as restenosis.

Synergistic decrease in blood pressure by captopril combined with losartan in spontaneous hypertensive rats.

This study was designed to examine the anti-hypertensive effect of the combination therapy of captopril with losartan by oral administration using both independent and cross-over experimental protocols. In independent experimental protocols, four different groups of spontaneous hypertensive rats (SHR) were treated for 1 or 2 weeks: control, captopril (20 mg/kg/day), losartan (20 mg/kg/day), and combination captopril (10 mg/kg/day) with losartan (10 mg/kg/day). In cross-over protocols, each SHR received all four treatments for 1 or 3 days with an interval of several days between each injection for washing-out and return to high blood pressure (BP) levels. BP and heart rate (HR) were measured in conscious telemetered SHR. According to the results from the independent protocol, regardless of a 1- or 2-week administration period, combination therapy with low doses of captopril and losartan had a greater anti-hypertensive effect than individual high-dose monotherapy. Similarly, results from the cross-over protocol showed that regardless of 1-day or 3-day administration, the decrease in BP in the 11(th) and 12(th) hour after administration was greatest with the combination of low-dose captopril and losartan. Therefore, combination therapy with low doses of captopril with losartan lowered BP to a greater extent than a high dose of either individual monotherapy.