Sildenafil Concentrations Research Articles

Determination of mirodenafil and sildenafil in the plasma and corpus cavernous of SD male rats

The purpose of the present study was to determine sildenafil and a novel PDE-5 inhibitor, mirodenafil in the plasma and corpus cavernosum tissue of rats to compare their pharmacokinetic properties. The concentrations of mirodenafil and sildenafil in the rat plasma and corpus cavernosum tissue samples were analyzed using LC–MS/MS after a single oral administration at a dose of 40 mg/kg to rats. Although the T max, Tλ 1/2 and MRT were not different between mirodenafil and sildenafil, the C max and AUC of mirodenafil were significantly higher than those of sildenafil in the plasma and corpus cavernosum tissue. Consequently mirodenafil remained longer than sildenafil in the plasma and tissue. This may provide pharmacokinetic evidence for assessment of the in vivo efficacy of mirodenafil and sildenafil.

Relaxant Effects of Sildenafil on the Human Isolated Bladder Neck

To evaluate potential in vitro relaxant actions of sildenafil on human isolated bladder neck smooth muscle. Bladder neck strips were sampled from patients (aged 55-77 years) submitted to prostatic surgery (6 adenomectomies and 1 radical prostatectomy). These were carefully dissected into 1-2 x 0.5-cm pieces and suspended in an organ bath containing 30 mL of a modified Krebs Henseleit solution, bubbled with 95% O(2)/5% CO(2). After tissue stabilization and viability test with KCl, the tissue was precontracted with phenylephrine, and a concentration-response relaxant curve to sildenafil was constructed. The effect of sildenafil was also assessed in tissues treated with N(omega)-nitro-L-arginine methyl ester (L-NAME) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ) (inhibitors of nitric oxide synthase and guanylyl cyclase, respectively). Sildenafil induced significant bladder neck relaxation at all concentrations tested. The maximum relaxation was 86.97% +/- 6.69%, obtained with a high concentration of sildenafil (5.1 x 10(-4) M). Both L-NAME and ODQ significantly reduced sildenafil-induced relaxation. Sildenafil was effective in inducing bladder neck smooth muscle relaxation in vitro. This effect was almost abolished by L-NAME and ODQ, clearly demonstrating a dependence of the nitric oxide-cyclic guanosine monophosphate pathway. Our in-vitro results suggest that sildenafil might be useful in improving lower urinary tract symptoms due to benign prostatic hyperplasia.

Hypercontractility and impaired sildenafil relaxations in the BKCachannel deletion model of erectile dysfunction

Erectile dysfunction (ED) can be elicited by a variety of pathogenic factors, particularly impaired formation of and responsiveness to nitric oxide (NO) and the downstream effectors soluble guanylate cyclase (sGC) and cGMP-dependent protein kinase I (PKGI). One important target of PKGI in smooth muscle is the large-conductance, Ca2+ -activated potassium (BKCa) channel. In our previous report (42), we demonstrated that deletion of the BKCa channel in mice induced force oscillations and led to reduced nerve-evoked relaxations and ED. In the current study, we used this ED model to explore the role of the BKCa channel in the NO/sGC/PKGI pathway. Electrical field stimulation (EFS)-induced contractions of corpus cavernosum smooth muscle strips were significantly enhanced in the absence of BKCa channel function. In strips precontracted with phenylephrine, EFS-induced relaxations were converted to contractions by inhibition of sGC, and this was further enhanced by loss of BK channel function. Sildenafil-induced relaxations were decreased to a similar extent by inhibition of sGC or BKCa channels. At concentrations >1 microM, sildenafil caused relaxations independent of inhibition of sGC or BKCa channels. Sildenafil did not affect the enhanced force oscillations that were induced by the loss of BKCa channel function. Yet, these oscillations could be completely eliminated by blocking L-type voltage-dependent Ca2+ channels (VDCCs). These results suggest that therapeutically relevant concentrations of sildenafil act through cGMP and BKCa channels, and loss of BKCa channel function leads to hypercontractility, which depends on VDCCs and cannot be modified by the cGMP pathway.

Role of K + and Ca 2+ fluxes in the cerebroarterial vasoactive effects of sildenafil

The aim of this study was to assess the role of K + and Ca 2+ fluxes in the cerebroarterial vasoactive effects of the phosphodiesterase-5 inhibitor sildenafil. We used isolated rabbit basilar arteries to assess the effects of extracellular K + raising on sildenafil-induced vasodilatation, and studied the pharmacological interaction of sildenafil with selective modulators of membrane K + and Ca 2+ channels. Expression of Kv1 subunits of K + channels was assessed at messenger and protein levels. Parallel experiments were carried out with zaprinast for comparison. Sildenafil (10 nM–0.1 mM) induced concentration-dependent relaxation of endothelin-1 (10 nM)-precontracted arteries, which was partially inhibited by depolarization with KCl (50 mM), 3 mM tetraethylammonium (non-selective K + channel blocker) or 1 mM aminopyridine (inhibitor of K v channels), but not by 1 μM glibenclamide (inhibitor of K ATP channels) or 50 nM iberiotoxin (inhibitor of K Ca channels). Arterial smooth muscle expressed messengers for Kv1.2, Kv1.3, Kv1.4, Kv1.5 and Kv1.6, and proteins of Kv1.1, Kv1.2 and Kv1.4. CaCl 2 (10 μM- 10 mM) induced concentration-dependent contraction in Ca 2+-free, depolarizing (50 mM KCl) medium. Sildenafil (0.1–100 μM) produced reversible concentration-dependent inhibition of the response to CaCl 2, which was completely abolished by the highest sildenafil concentration. By contrast, only 100 μM zaprinast inhibited the response to CaCl 2. The L-type Ca 2+ channel activator Bay K 8644 (0.1 nM–1 μM) induced concentration-dependent potentiation of the response to CaCl 2 inhibited by 100 μM sildenafil. Moreover, Bay K 8644 (0.1 nM–1 μM) induced concentration-dependent contraction in slightly depolarizing (15 mM) medium, which was inhibited to the same extent and in a concentration-dependent way by sildenafil (0.1–100 μM) and zaprinast (1 or 100 μM). These results show that sildenafil relaxes the rabbit basilar artery by increasing K + efflux through K v channels, which in turn may affect Ca 2+ signalling. Expression of Kv1 subunits involved in this pharmacological effect occurs at the messenger and, in some cases, at the protein level. In addition to this phosphodiesterase-5-related effect, sildenafil and zaprinast inhibit cerebroarterial vasoconstriction at least in part by directly blocking L-type Ca 2+ channels, although a decrease in the sensitivity of the contractile apparatus to Ca 2+ can not be discarded.

Mutual pharmacokinetic interactions between steady-state bosentan and sildenafil

The aim of this study was to systematically investigate the mutual pharmacokinetic interactions in healthy volunteers between sildenafil, a phosphodiesterase-5 inhibitor, and bosentan, a dual endothelin receptor antagonist, both approved for treating pulmonary arterial hypertension (PAH). A randomised, double-blind, placebo-controlled, parallel-group study with three treatment arms (sildenafil plus placebo, bosentan plus placebo and sildenafil plus bosentan) was conducted in 55 healthy male volunteers (51 completers). Study duration was 18 days per treatment group. Sildenafil was administered three times daily on Days 1-6 and 11-16 (20 mg initially, increased to 80 mg after 3 days), and bosentan (125 mg) was administered twice daily on Days 7-17. On Day 16, bosentan decreased the maximum plasma concentration of sildenafil (c)(max)) by 55.4% [90% confidence interval (CI) 40.3-66.6%] and the area under the plasma concentration versus time curve over a dosing interval (AUC(tau)) by 62.6% (90% CI 56.8-67.7%). Sildenafil increased bosentan C(max) by 42.0% (90% CI 15.4-74.8%) and (AUC(tau)) by 49.8% (90% CI 28.7-74.5%). Bosentan and sildenafil in combination were well tolerated, with no serious adverse events reported. All adverse events were of mild or moderate intensity. In healthy volunteers, there is a mutual pharmacokinetic interaction between bosentan and sildenafil that may influence the dosage of each drug in a combination treatment. The clinical implications of combination therapy with bosentan and sildenafil are as yet unknown, and further trials in patients with PAH are needed.

Sildenafil Inhibits the Proliferation of Cultured Human Endothelial Cells

The proliferation of endothelial cells plays a crucial role in the development of intraplaque angiogenesis (IPA). IPA is a major source of intraplaque hemorrhage and therefore contributes to the destabilization of atherosclerotic plaques. Therefore, the aim of the present study was to examine, whether sildenafil inhibits endothelial cell growth. The proliferation of human endothelial cells derived from umbilical cord veins (HUVEC) was examined on DNA level by measurements of (3H)-thymidine incorporation. Cell viability was analyzed using trypan blue staining. The proliferation of cultured human endothelial cells was significantly decreased by 1 μmol/l (-48.4%) and 10 μmol/l (-89.6%) sildenafil (n=10, p<0.05). This was not a cytotoxic effect, because cell viability was only reduced at sildenafil concentrations of 50 μmol/l or greater. In addition sildenafil significantly reduced endothelial proliferation induced by bFGF (n=10, p<0.05). The presented results demonstrate an antiangiogenic effect of sildenafil that might be useful in the prevention of atherosclerotic plaque vascularization.

The effects of the phosphodiesterase type V inhibitor sildenafil on human and bovine retinal function in vitro

After the ingestion of sildenafil (Viagra), visual adverse events have been reported, possibly caused by an inhibition of the phototransduction cascade by sildenafil via phosphodiesterase (PDE 6). Therefore, we investigated the effects of sildenafil on photoreceptors and postsynaptic neurons of human and bovine retinas using the isolated superfused vertebrate retina technique. Human and bovine retina preparations were perfused with an oxygen preequilibrated standard solution. The electroretinogram (ERG) was recorded using Ag/AgCl electrodes. After recording stable ERG amplitudes, sildenafil was added to the solution for 45 min. Thereupon, the preparations were reperfused with standard solution for 240 min. Following the application of sildenafil (3 microMol/l), the b-wave amplitude of bovine and human preparations was reduced continuously and disappeared completely. After reperfusion with the standard solution for 4 h, the b-wave amplitude did not recover completely. Using the same sildenafil concentration (3 microMol/l), the a-wave amplitude of the human retina was not totally abolished, but reduced to 21% of the initial amplitude and remained reduced at washout. For all retinal preparations, the implicit time of the ERG amplitudes remained significantly extended at the end of the washout. Strong similarities were detected in the drug-induced changes of the ERG when comparing human and bovine retinas. The results suggest that sildenafil impairs retinal function at not only the level of the photoreceptors, but it also affects the neuronal network of the inner retina at concentrations of approximately 30-fold higher than at therapeutic plasma concentrations.

Sildenafil citrate ingestion and prolonged priapism and tachycardia in a pediatric patient

Introduction. Little is known about the toxicity of sildenafil overdose in the pediatric population. We present a case of prolonged priapism and tachycardia due to unintentional sildenafil overdose in a child. Case report. A 19-month-old male ingested up to six 50 mg Viagra tablets 45 minutes prior to presentation at the emergency department. Initial vital signs included temperature 98.2°F, blood pressure 90/58 mmHg, heart rate 140, respirations 20, and oxygen saturation of 100% on room air. The child weighed 10.4 kg. Physical exam revealed a happy, smiling, laughing toddler who was cooperative with all aspects of his exam. He had mild facial flushing and an erect penis which was normal in color and had a capillary refill of two seconds. Precordial palpation did not show evidence of increase dynamic force, his heart sounds were regular, and no ectopy was noted. His peripheral pulses were strong and regular in all four extremities. No gastrointestinal decontamination was performed. The patient was started on maintenance IV fluids and admitted to the pediatric floor for observation. The patient had a non-painful tumescent penis and mild tachycardia for about 24 hours post-ingestion. The child never had pain from the constant erection. Sildenafil concentration drawn approximately seven hours after ingestion was 3900 ng/ml (reporting limit 24 ng/ml) and N-desmethylsildenafil level was 1700 ng/ml (reporting limit 24 ng/ml). Conclusion. This case of pediatric sildenafil ingestion (up to 30mg/kg) initially resulted in facial flushing and priapism. The child had asymptomatic tachycardia and prolonged priapism that persisted until hospital discharge approximately 24 hours after ingestion. The erection was non-painful and required no urologic intervention, most likely representing a high flow state. In this ingestion, only supportive care was required.

Mechanisms of direct relaxant effect of sildenafil, tadalafil and vardenafil on corpus cavernosum

Sildenafil, tadalafil, vardenafil and verapamil induced concentration-dependent relaxation of the rabbit corpus cavernosum muscle precontracted with noradrenaline. The maximal relaxation (%) at 20 μM was 61.4 ± 6.9, 32.4 ± 5.4, 100.0 ± 5.5 and 86.6 ± 5.1 ( n = 5 each) respectively. Pre-incubation of cavernosal muscle strips with N ω-nitro- l-arginine or guanylate cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) but not adenylate cyclase inhibitor, cis- N-[2-phenylcyclopentyl]-azacyclotridec-1-en-2-amine] (MDL12330A) culminated in only a 20–30% reduction in muscle relaxant action of the 3 phosphodiesterase inhibitors. This suggests that another mechanism of relaxation independent of nitric oxide–cGMP or cAMP pathway was involved. Higher concentrations of sildenafil (100 μM) and vardenafil (10 and 100 μM) produced non-competitive antagonism of noradrenaline-induced contraction characterized by reduced maximal effect. In contrast, tadalafil was devoid of significant effect on noradrenaline. On K +-depolarized tissues, sildenafil was as potent as vardenafil whereas tadalafil was the least effective in relaxing K +-induced tone. The maximal relaxation (% of K +-induced tone) at 20 μM sildenafil, tadalafil and vardenafil was respectively 84.1 ± 6.5, 9.0 ± 19.9, and 88.9 ± 6.2 ( n = 5 each). In addition, verapamil, sildenafil and vardenafil were more efficacious than tadalafil in reversing tonic contractions by Ca 2+ channel activator, 1,4,dihydro-2,6-dimethyl-5-nitro-4-[2(triflouromethyl)phenyl]pyridine-3-carboxylic acid methyl ester (BAY K-8644). These results indicate that vardenafil and sildenafil possess direct muscle relaxant potential possibly via inhibiting Ca 2+ influx through both receptor-operated and voltage-dependent Ca 2+ channels whereas tadalafil appears capable of inhibiting receptor-operated transmembrane Ca 2+ entry only.

Phosphodiesterase 5 in the female pig and human urethra: morphological and functional aspects

To characterize the distribution of phosphodiesterase 5 (PDE-5), cGMP and cGMP-dependent protein kinase I (PKG1), and to evaluate the effect of pharmacological inhibition of PDE-5 in isolated preparations of pig and human urethra, as the nitric oxide (NO)/cGMP pathway generates the main inhibitory signals to reduce resistance in the bladder outlet and urethra during emptying of the bladder. After obtaining ethics committee approval, urethral specimens were obtained from three female patients during cystectomy, and from young female pigs. The specimens were prepared for immunohistochemical investigations and for functional studies in organ baths. Effects of sildenafil, vardenafil and tadalafil (1 nm to 30 microm) were studied in l-noradrenaline (1 microm)-activated or spontaneously contracted preparations, and on relaxations induced by electrical-field stimulation (EFS). Levels of cGMP were determined by radioimmunoassay. After stimulation with the NO donor, DETA NONO-ate (1 mm), there was greater cGMP-immunoreactivity (IR) in urethral and vascular smooth muscles. There was a wide distribution of cGMP- and vimentin-positive interstitial cells between pig urethral smooth muscle bundles. There was also cGMP-IR within NO-synthase-IR endothelium. There was PDE-5 IR within the urethral and vascular smooth muscle cells, but also in vascular endothelial cells that expressed cGMP-IR. In pig and human sections, there was strong PKG1-IR in alpha-actin-IR urethral smooth muscle cells that also contained IR for cGMP. Sildenafil, vardenafil and tadalafil caused mean (sem) concentration-dependent relaxations of the pig urethra which, at 30 microm, were 80 (3)% (11 samples), 81 (5)% (12 samples) and 64 (4)% (10 samples) of the spontaneous tone. The relaxation of L-noradrenaline-contracted female human urethra was 100% in response to 10 microm sildenafil, and 85 (15)% and 47 (13)% for 30 microm of vardenafil and tadalafil, respectively (three samples). Vardenafil or sildenafil (30 microm) doubled cGMP levels in pig specimens. There were no effects on cGMP levels with tadalafil. EFS (1-32 Hz) caused l-NG-nitroarginine-sensitive relaxations of pig urethral muscle that were increased in amplitude and duration by PDE-5 inhibition. At 0.1 microm, sildenafil, vardenafil or tadalafil significantly prolonged the mean (sem) duration of the relaxation at 4 Hz by 55 (19)%, 45 (14)% and 51 (12)%, respectively. PDE-5-, cGMP- and PKG1-IR is widely distributed in human and pig urethral tissues. Nerve-induced relaxations of urethral preparations were enhanced at low concentrations of sildenafil, vardenafil and tadalafil, whereas there were direct smooth muscle-relaxant actions of the PDE-5 inhibitors at high concentrations. Inhibition of PDE-5 might be an interesting option to facilitate cGMP-mediated relaxation of the outflow region.

Photoimmunoprotection by UVA (320–400 nm) Radiation Is Determined by UVA Dose and Is Associated with Cutaneous Cyclic Guanosine Monophosphate

The immunomodulating properties of UVA radiation remain controversial. Here, we demonstrate in female inbred Skh:hr-1 mice that single subinflammatory UVA exposures between 1.61 and 580.5 kJ/m(2) are not immunosuppressive. Furthermore, UVA exposures between 16.13 and 580.5 kJ/m(2) provided dose-related immunoprotection against UVB-induced immunosuppression. Higher UVA exposures (870.8-1,161 kJ/m(2)) became inflammatory and immunosuppressive alone, and lost the photoimmunoprotective capacity. We previously reported that UVA photoimmunoprotection depends on the induction of cutaneous heme oxygenase-1, particularly its enzymatic product, carbon monoxide (CO). CO was suggested to activate cutaneous guanylyl cyclase (GC), as the specific GC inhibitor, 1H-(1,2,4)oxadiazolo-(4,3-a)quinoxalin-1-one (ODQ), abrogated CO photoimmunoprotection in the mouse. This study shows that cutaneous cyclic guanosine monophosphate (cGMP) concentration increased only following immunoprotective UVA doses, or immunoprotective topical CO treatment, and cGMP production was inhibited by ODQ. Conversely, cGMP concentration was increased by inhibition of its degradative phosphodiesterase (PDE) with topical sildenafil. The PDE-5 isoform was identified in normal mouse skin. Subsequently, a moderate concentration of sildenafil was shown to simulate the effect of UVA in protecting against photoimmunosuppression by solar-simulated UV radiation or its mediator cis-urocanic acid. Thus, cutaneous cGMP, controlled by its synthesis via CO-activated GC and its degradation by PDE-5, is strongly associated with UVA photoimmunoprotection.

Intestinal absorption and presystemic disposition of sildenafil citrate in the rabbit: evidence for site-dependent absorptive clearance

Sildenafil citrate is the first oral treatment for erectile dysfunction. Its oral bioavailability is about 40%. This research investigated the intestinal transport parameters of sildenafil citrate in rabbit using an in situ intestinal perfusion technique. This was studied in four different anatomical sites, namely duodenum, jejunoileum, ascending colon and rectum. The results revealed the highest absorptive clearance in the jejunoileum. The values of the permeability area product normalized to segment length (ml/min.cm) were 0.0101, 0.0063, 0.0059 and 0.0023 and those of the percentage absorbed were 68.0, 32.3, 23.0 and 5.0 in jejunoileum, duodenum, ascending colon and rectum, respectively. The values of the length (cm) required for complete absorption were 87.6, 137, 153 and 384 for each anatomical site in the same order. The absorptive clearance did not correlate with the net water flux in the four anatomical regions studied, indicating a mainly passive diffusion mechanism through a transcellular pathway. The plasma sildenafil concentrations achieved during intestinal perfusion experiments and sildenafil total body clearance in the rabbit were used to calculate the fraction of sildenafil that reached the systemic circulation relative to the amount that disappeared from the intestinal segment. Only 34% of sildenafil that disappeared from the intestinal segment appeared in the systemic circulation indicating that the presystemic elimination of sildenafil is 66%. These results confirm that the incomplete bioavailability of sildenafil is mainly due presystemic elimination.

INTESTINAL ABSORPTION AND PRESYSTEMIC DISPOSITION OF SILDENAFIL CITRATE IN THE RABBIT: EVIDENCE FOR SITEDEPENDENT ABSORPTIVE CLEARANCE

Sildenafil citrate is the first oral treatment of erectile dysfunction. Its oral bioavailability is about 40%. This research characterized the intestinal transport parameters of sildenafil citrate in rabbit using in situ intestinal perfusion technique. This was studied in four different anatomical sites, namely duodenum, jejunoileum, ascending-colon, and rectum. The results revealed the highest absorptive clearance in the jejunoileum. The values of permeability area product normalized to segment length (ml/min cm) were 0.0101, 0.0063, 0.0059 and 0.0023 and those of percentage absorbed were 67.95, 32.27, 23 and 5.03 in jejunoileum, duodenum, ascending colon, and rectum respectively. The values of the length (cm) required for complete absorption were 87.58, 137.23, 153.27, and 384.09 for each segment in the same order. The absorptive clearance did not correlate with the net water flux in the four anatomical regions studied, indicating mainly passive diffusion mechanism through transcellular pathway. The plasma sildenafil concentrations achieved during intestinal perfusion experiments and sildenafil total body clearance in rabbit were used to calculate the fraction of sildenafil that reached the systemic circulation relative to the amount disappeared from the intestinal segment. Only 34% of sildenafil disappeared from the intestinal segment appeared in the systemic circulation indicating that the presystemic elimination of slidenafil is 66%. These results confirm that the incomplete bioavailability of sildenafil is mainly due presystemic elimination.

Dapoxetine, a novel treatment for premature ejaculation, does not have pharmacokinetic interactions with phosphodiesterase-5 inhibitors

Potential pharmacokinetic interactions between dapoxetine, a serotonin transporter inhibitor developed for the treatment of premature ejaculation (PE), and the phosphodiesterase-5 inhibitors tadalafil and sildenafil, agents used in the treatment of erectile dysfunction (ED), were investigated in an open-label, randomized, crossover study (n=24 men) comparing dapoxetine 60 mg, dapoxetine 60 mg+tadalafil 20 mg, and dapoxetine 60 mg+sildenafil 100 mg. Plasma concentrations of dapoxetine, tadalafil, and sildenafil were determined by liquid chromatography-tandem mass spectrometry. Tadalafil did not affect the pharmacokinetics of dapoxetine, whereas sildenafil increased the dapoxetine AUCinf by 22%; these effects were deemed not clinically important. Dapoxetine did not appear to affect the pharmacokinetics of tadalafil or sildenafil. Most adverse events were mild in nature. Thus, dapoxetine has no clinically important pharmacokinetic interactions with tadalafil or sildenafil, and the combinations are well tolerated.

Effects of Phosphodiesterase Type 5 Inhibitor Sildenafil on Retinal Function in Isolated Superfused Retina

After the oral ingestion of sildenafil, visual abnormalities have been reported constantly. The mechanism of these adverse events has been presumed to be a result of the interaction of sildenafil with the retinal phosphodiesterase (PDE) type 6. To investigate the physiological basis of the effects of sildenafil on retinal function, bovine retinas were isolated and perfused with an oxygen pre-equilibrated standard solution. The electroretinogram (ERG) was recorded as a transretinal potential using silver/silver-chloride electrodes. After reaching stable ERG amplitudes, sildenafil was added to the nurient solution at different concentrations, and its effect on the a- and b-wave amplitude was studied separately. The 0.1 microM and higher concentrations of sildenafil reduced the b-wave amplitude, while a reduction of the a-wave amplitude was observed at an elevated threshold of 0.3 microM. The changes of the ERG amplitudes were fully reversible for the b-wave at a concentration of 0.1 microM and for the a-wave at 0.3 microM sildenafil. At higher concentrations, sildenafil was found to be only partially reversible within recovery time. In conclusion, besides an inhibitory influence on photoreceptors, sildenafil performs additional effects on the postsynaptic neuronal network. Higher concentrations of sildenafil were found to have a potential for retinal degeneration, suggesting that further trials should be designed to evaluate the long-term effects of sildenafil. The physiological consequences of an abuse or long-term, daily use of sildenafil are not clear.

Bosentan decreases sildenafil concentration in patients with PAH

Bosentan decreases sildenafil concentration in patients with PAH

Bosentan decreases the plasma concentration of sildenafil when coprescribed in pulmonary hypertension

To determine whether bosentan decreases the plasma concentration of sildenafil in patients with pulmonary arterial hypertension. Ten patients (aged 39-77 years) with pulmonary arterial hypertension in WHO functional class III received bosentan 62.5 mg twice daily for 1 month, then 125 mg twice daily for a second month. Sildenafil 100 mg was given as a single dose before starting bosentan (visit 1) and at the end of each month of bosentan treatment (visits 2 and 3). Sildenafil and its primary metabolite, desmethylsildenafil, were measured in plasma at 0 h and 0.25, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10, 12, 18 and 24 h using liquid chromatography-tandem mass spectrometry. Statistical analysis was by repeated measures anova, using log transformed data where appropriate. Treatment with bosentan 62.5 mg twice daily for 4 weeks was associated with a two-fold increase in sildenafil clearance/F and a 50% decrease in the AUC (P < 0.001). Increasing the dose of bosentan to 125 mg twice daily led to a further increase in sildenafil oral clearance and decrease in the AUC (P < 0.001 vs. 62.5 mg bosentan). The ratio of AUC on bosentan treatment relative to that of visit 1 was 0.47 [95% confidence interval (CI) 0.36, 0.61] for visit 2 and 0.31 (95% CI 0.23, 0.41) for visit 3 (P < 0.001). Sildenafil C(max) fell from 759 ng ml(-1) on visit 1 to 333 ng ml(-1) on visit 3 (P < 0.01) and there was a significant decrease in the plasma half-life of sildenafil on the higher bosentan dose (P < 0.05). The AUC and plasma half-life of desmethylsildenafil was also decreased by bosentan in a dose-dependent manner (P < 0.01). Bosentan significantly decreases the plasma concentration of sildenafil when coadministered to patients with pulmonary hypertension.

Dose-dependency and Time-course of Electrophysiologic Short-term Effects of VIAGRA®: A Case Study

The dose-dependency and time-course of the short-term visual effects of sildenafil citrate (VIAGRA) were tested in two subjects. Blood pressure was measured and samples of blood taken at 30 min intervals before and after drug administration. In the first experiment, prolongations of the implicit times of the scotopic maximum a-wave, cone a- and b-wave, 33 Hz flicker, ON-response a- and b-wave and 3.3 Hz a- and b-wave electroretinogram (ERG) recordings and of the oscillatory potentials OP1, OP2, and OP3 were observed for both eyes of both subjects, following 100 or 200 mg dosings. Interestingly, no prolongation was found for OP4, to which the OFF-bipolar cell pathway significantly contributes. In the second experiment, in which visual function was repeatedly assessed following a 200 mg dose, similar prolongations were found in both eyes of one subject for the implicit times of the oscillatory potential OP2, the cone b-wave response and the 3.3 Hz a-wave. Moreover, the steady-state (A0) and immediate extinction (B0) blue target thresholds of transient tritanopia were raised relative to the pre-drug administration baseline effects. While the maximum lowering of both systolic and diastolic blood pressure approximately correlated with the peak plasma concentration of sildenafil (c. 30-60 min after administration), the peak magnitudes of most visual effects were found at c. 110 min, consistent with a second compartment kinetic.

Effect of Sildenafil on Reperfusion Function, Infarct Size, and Cyclic Nucleotide Levels in the Isolated Rat Heart Model

We have previously shown that NO-donor induced elevation in myocardial cGMP levels is associated with improved reperfusion function of the isolated rat heart. The phosphodiesterase 5 (PDE 5) inhibitor, sildenafil could potentially increase myocardial cGMP levels and thus protect the heart against ischaemic/reperfusion injury. To test our hypothesis we treated the isolated working rat heart with vehicle, OR sildenafil (10, 20, 50, 100, 200 nM), OR sildenafil (50 nM) plus a sarcolemmal (HMR 1098) or a mitochondrial (5-Hydroxydecanoate (5-HD)) K(ATP) channel blocker. Hearts were then subjected to 20 min global, or 35 min regional ischaemia at 37( composite function)C before reperfusion function (aortic output, coronary flow and aortic pressure) and infarct size were documented. Pre-ischaemic, ischaemic and reperfusion myocardial cAMP and cGMP concentrations were determined. Low concentrations of sildenafil (10, 20 and 50 nM) improved reperfusion aortic output (AO) recovery (61.4+/- 4.5%, 64.8 +/- 5.2% and 62.3 +/- 5.0% vs. 45.4 +/- 3.8% for controls (p < 0.05)) and infarct size, while high concentrations (200 nM) worsened AO recovery (24.9 +/- 4.9.0%, p < 0.05). Myocardial cGMP levels of ischaemic tissue were elevated (34.7 +/- 2.4 vs. 27.3 +/- 2.2 pmol/g ww) and cAMP levels were suppressed (0.59 +/- 0.03 vs. 0.87 +/- 0.06 nmol/g ww) in the sildenafil (50 nM) treated hearts. Co-perfusion with sildenafil plus HMR 1098 decreased AO recovery (21.7 +/- 7.6% vs. 62.3 +/- 5.0% for sildenafil alone, p < 0.05) and increased infarct size (29.7 +/- 2.04% vs. 8.6 +/- 2.39% for sildenafil alone, p < 0.05).Similarly, sildenafil plus 5-HD decreased reperfusion AO recovery (44.4 +/- 6.0% vs. 62.3 +/- 5.0% for sildenafil alone, p < 0.05) and increased infarct size (33.8 +/- 1.62% vs. 8.6 +/- 2.39% for sildenafil alone, p < 0.05). (1) Pretreatment with low concentrations of sildenafil (20-50 nM) improves, while higher concentrations (200 nM) worsen reperfusion function in this model. (2) Low concentrations of sildenafil (20-50 nM) decrease infarct size while the higher concentrations had no effect. (3) These protective properties of low concentrations of sildenafil may be related to its cGMP elevating and cAMP suppressing effects in the ischaemic heart. (4) Possible end-effectors for sildenafil in the ischaemic heart include the mitochondrial and sarcolemmal K(ATP) channel.

The effect of Sildenafil on human platelet secretory function is controlled by a complex interplay between phosphodiesterases 2, 3 and 5

Human platelets contain the cyclic nucleotide-hydrolyzing phosphodiesterases (PDEs) 2, 3 and 5. The cGMP-PDE5 inhibitors Sildenafil and Zaprinast have been demonstrated to potentiate the anti-platelet aggregatory effect of NO donors like sodium nitroprusside (SNP) in vitro but the mechanisms of Sildenafil's action on the secretory function of human platelets have not been analysed in detail. In the present paper, we show (1) that both compounds potentiate the SNP-induced increase in cGMP in human platelets concentration-dependently. (2) However, whereas Sildenafil plus SNP treatment only partially inhibits thrombin-induced release of serotonin, the less selective Zaprinast plus SNP cause a complete inhibition. (3) The inhibition mediated by Sildenafil plus SNP is limited to low compound concentrations at which cAMP levels are increased, probably due to cGMP-mediated inhibition of PDE3. (4) High concentrations of Sildenafil (plus SNP) neither affect cAMP levels, likely due to the activation of PDE2, nor inhibits the release of serotonin. Thus, increases in both cyclic nucleotides seem to control platelet function. (5) Accordingly, treatment with increasing concentrations of Sildenafil plus SNP and a selective PDE2 inhibitor, which by its own has no effect, induced a concentration-dependent increase in cAMP and complete inhibition of platelet activation. In summary, our data indicate that Sildenafil inhibits secretory function of human platelets at least in part due to the cGMP-mediated effects on intracellular cAMP and that entire inhibition of serotonin release from thrombin-activated platelets is controlled by both cyclic nucleotides.