14 CLINICAL STUDIES

Always follow your prescription instructions carefully to reduce the risk of side effects and maximize effectiveness. Use nitrate medications for chest pain or heart problems. Combining sildenafil with nitrates or certain cardiovascular medications can cause a sudden and serious drop in blood pressure. Sudden hearing decrease or ringing in the ears An erection lasting longer than 4 hours (priapism) These may indicate serious side effects requiring urgent medical attention. Alcohol and grapefruit products may increase the likelihood of side effects and should be used cautiously. Viagra is intended for adult men diagnosed with erectile dysfunction.

• The onset of action is usually within 30 minutes.
• Peak effect occurs around 1 hour after ingestion.
• The duration of action can last up to 4-6 hours.

Before starting treatment, discuss your full medical history with your healthcare provider, especially if you have heart disease, high or low blood pressure, liver or kidney conditions, or blood disorders. Because erectile dysfunction can be associated with underlying health conditions, proper medical evaluation is essential. If erectile dysfunction is affecting your quality of life, Viagra (sildenafil) offers a clinically established, on-demand treatment option designed to support natural sexual function. Consult your healthcare provider today to determine whether Viagra is appropriate for you. Regain confidence, improve performance, and take control of your sexual health with a trusted and proven ED treatment. You must be logged in to post a review. Sildenafil citrate is defined as a compound used to treat male erectile dysfunction, belonging to the pyrazolo-pyrimidinyl-methylpiperazine class, and acts as a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5). Sildenafil citrate (250 mg) is dissolved in 50 mL of glacial acetic acid, titrated with 0.1 M perchloric acid, with the end point being detected potentiometrically.

• Sildenafil citrate is used to treat erectile dysfunction.
• It enhances blood flow to the penis for a stronger erection.
• Commonly available in tablet form for oral use.

Each milliliter of 0.1 M perchloric acid VS is equivalent to 66.67 mg of Sildenafil citrate, calculated as C22H30N6O4S • C6H8O7. This method is suitable to assay Sildenafil citrate in its bulk drug form, and in formulated products [3]. In this method, 160 mg of Sildenafil citrate was accurately weighed and dissolved in 50 mL of a 20:80 mixture of methanol / water.

What should I know about storage and disposal of this medication?

A detailed study concerning solid-state structure of this compound is very important for understanding enzyme (PDE5)-inhibitor (sildenafil) interaction. It is also of interest to determine sildenafil’s protonation sites, as they may be responsible for its binding to the phosphodiesterase acidic amino acids. Sildenafil citrate (Viagra) (see Scheme 3, Chapter 3, Part I) and sildenafil base in pure form were characterized by 1H, 13C, 15N NMR spectroscopy in solution, solid-state, and pharmaceutical dosage forms.42 The analysis of chemical shifts showed that: (i) N6-H forms intramolecular hydrogen bonds, (ii) N25 is protonated in the salt, and (iii) intermolecular OH…N hydrogen bonds involving N2 and N4 are present in the solid sildenafil citrate. The 13C CPMAS spectra of the tablets containing different amounts of sildenafil citrate were recorded and showed that chemical shifts of sildenafil citrate in pure form and in pharmaceutical dosage forms are the same. SC is easily detected in the pharmaceutical dosage forms since only two of its carbon resonances (OCH2 and quaternary carbon of the citrate anion) fall into carbohydrate-type region of the excipient.

How should I store sildenafil?

Solid-state 13C and 15N MAS NMR have recently been used to investigate how water interacts with SC.43 When the humidity is altered, the water concentration in the solid compound changes but does not reach a stoichiometric (e.g., 1:1) ratio to form a true hydrate. Only one set of 15N and 13C signals was observed for each humidity level indicating that water incorporated into the crystal lattice of SC is very mobile and exchanges rapidly between various sites. The 13C data showed the formation of a hydrogen bond between water molecule and one carbonyl of the citrate anion. The spectra also show that the water content affects the conformation of the propyl group. Additionally, 15N dipolar dephasing (DD) experiments confirmed that the sildenafil molecule is only protonated in the piperazine ring. Titration against 0.1 N sodium hydroxide was carried out using a Mettler DL-67 potentiometric titrator. Each milliliter of 0.1 N sodium hydroxide VS is equivalent to 22.22 mg of Sildenafil citrate, sildenafil 100g calculated as C22H30N6O4S • C6H8O7[3]. 2.13 Sildenafil citrate (Viagra) – structure and hydrogen bonding Sildenafil citrate (SC) has been widely used for the treatment of erectile disorder. A detailed study concerning solid-state structure of this compound is very important for understanding enzyme (PDE5)-inhibitor (sildenafil) interaction.

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It is also of interest to determine sildenafil’s protonation sites, as they may be responsible for its binding to the phosphodiesterase acidic amino acids. Sildenafil citrate (Viagra) (see Scheme 3, Chapter 3, Part I) and sildenafil base in pure form were characterized by 1H, 13C, 15N NMR spectroscopy in solution, solid-state, and pharmaceutical dosage forms.42 The analysis of chemical shifts showed that: (i) N6-H forms intramolecular hydrogen bonds, (ii) N25 is protonated in the salt, and (iii) intermolecular OH…N hydrogen bonds involving N2 and N4 are present in the solid sildenafil citrate. The 13C CPMAS spectra of the tablets containing different amounts of sildenafil citrate were recorded and showed that chemical shifts of sildenafil citrate in pure form and in pharmaceutical dosage forms are the same. SC is easily detected in the pharmaceutical dosage forms since only two of its carbon resonances (OCH2 and quaternary carbon of the citrate anion) fall into carbohydrate-type region of the excipient.

2.3 Dosage Adjustments in Specific Situations

Rigorous placebo-controlled studies have failed to identify any of these as efficacious in treating this condition. Sildenafil (Viagra, sildenafil citrate, 5.1.8), prescribed today for the treatment of ED (erectile dysfunction), was initially designed to target the cGMP pfizer sildenafil 100 pathway for the treatment of cardiac arrhythmias, especially angina. There are about seven different classes of phosphodiesterases (PDE), among which PDE type 5 is more expressed in corpus cavernosum (smooth muscle), and sildenafil works more selectively against PDE 5 (10 times higher) than other classes of PDE and has no long term adverse effects on ocular functions (caused by the inhibitory action against PDE 6). In further clinical investigations, it has also been found that sildenafil is 4000 folds selective for PDE five than PDE 3 (controls cardiac contractility), which indicates that it has no such interference with cardiac activities at the therapeutic dose. Synthesis of sildenafil and sildenafil citrate has been disclosed in various patents and publications, among which one of the well-mentioned processes is Pfizer's commercial synthetic process.

What does SILDENAFIL CITRATE (Generic for REVATIO) look like?

Precursor molecule 5.1.1, synthesized from diethyl oxalate and 2-pentanone, leads to compound 5.1.2 via one-pot amide conversion from carboxylic derivative in the presence of thionyl chloride. Further, the catalytic reduction of 5.1.2 afforded 5.1.3, which underwent amide bond formation using CDI with 5.1.6 to yield 5.1.7. The compound 5.1.6 was prepared from the precursor 5.1.4; 2-ethoxy benzoic acid via two steps. Finally, 5.1.7 undergoes cyclization in the presence of a base to afford sildenafil (5.1.8) (Scheme 5.1) (Jackson et al., 2005; Pathy & Chakaravathy, n.d.; Roschangar et al., 2015; Terrett et al., 1996). 3.3 DOSY 1H NMR analysis of formulations of genuine Cialis® and a Chinese imitation Nowadays, drugs for the treatment of erectile dysfunction that inhibit the phosphodiesterase type 5 enzyme (PDE-5), sildenafil citrate (Viagra®), tadalafil (Cialis®) or vardenafil hydrochloride (Levitra®, see Figure 2) are among the most counterfeited or imitated. Solid-state 13C and 15N MAS NMR have recently been used to investigate how water interacts with SC.43 When the humidity is altered, the water concentration in the solid compound changes but does not reach a stoichiometric (e.g., 1:1) ratio to form a true hydrate. Only one set of 15N and 13C signals was observed for each humidity level indicating that water incorporated into the crystal lattice of SC is very mobile and exchanges rapidly between various sites. The 13C data showed the formation of a hydrogen bond between water molecule and one carbonyl of the citrate anion. The spectra also show that the water content affects the conformation of the propyl group. Additionally, 15N dipolar dephasing (DD) experiments confirmed that the sildenafil molecule is only protonated in the piperazine ring.

What to avoid

Imitations come generally from Asia (India and China most often) which do not recognize the European and American patent laws so that products manufactured legally in such countries are illegal in Europe, USA and other countries. The original Cialis® tablet from Eli Lilly Laboratories and one copy commercialized in China were analyzed. The DOSY 1H NMR spectra of their solutions are presented in Figure 5. It is obvious that the two formulations do not contain the same active ingredient. Their common excipients are the lubricant magnesium stearate (Mg st, Δ), the tablet binder hypromellose (#) and lactose (□) as a diluent.

How it works

Moreover, the brand formulation is composed of another cellulose derivative with a higher molecular weight known to be hydroxypropylcellulose (▀). Signals of sodium lauryl sulphate (laur; ▴), a wetting agent, and triacetin (♦), a hydrophilic plasticizer, are also present. The intensity of the peaks located in the aromatic region of the 1H NMR spectrum demonstrates that the Chinese fake formulation of Cialis contains a mixture of two active pharmaceutical ingredients. These two compounds were purified by chromatography and then identified by NMR and LC–MS–MS (liquid chromatography–mass spectrometry–mass spectrometry) as vardenafil (V) and homosildenafil (H) (Figure 5). Oral agents are the drugs of choice in the management of erectile dysfunction.

5.8 Effects on Bleeding

Always follow your prescription instructions carefully to reduce the risk of side effects and maximize effectiveness. Use nitrate medications for chest pain or heart problems. Combining sildenafil with nitrates or certain cardiovascular medications can cause a sudden and serious drop in blood pressure. Sudden hearing decrease or ringing in the ears An erection lasting longer than 4 hours (priapism) These may indicate serious side effects requiring urgent medical attention. Alcohol and grapefruit products may increase the likelihood of side effects and should be used cautiously.

Does sildenafil interact with other medicines (drug interactions)?

Viagra is intended for adult men diagnosed with erectile dysfunction. Before starting treatment, discuss your full medical history with your healthcare provider, especially if you have heart disease, high or low blood pressure, liver or kidney conditions, or blood disorders. Because erectile dysfunction can be associated with underlying health conditions, proper medical evaluation is essential. If erectile dysfunction is affecting your quality of life, Viagra (sildenafil) offers a clinically established, on-demand treatment option designed to support natural sexual function. Consult your healthcare provider today to determine whether Viagra is appropriate for you. Sildenafil citrate, a phosphodiesterase (type V) inhibitor, is effective in treating this conditon. Yohimbine, an alpha-2-adrenoceptor antagonist, has been available for some time as a treatment for erectile dysfunction, although its efficacy has remained questionable for many years. Yohimbine has been used in some countries mainly to treat psychogenic impotence. Injection therapy is a second line treatment for erectile dysfunction. The injected agents may be a single agent or a combination of agents, including prostaglandin E1 (PGE1), papaverine, and/or phentolamine.

• Sildenafil is available both by prescription and some online sources.
• Verify authenticity to avoid fake or substandard drugs.
• Consult a healthcare professional before purchasing.

Within minutes after injection directly into the cavernosal body of the penis, a very natural and physiologic erection develops.

Brand names

Oral agents are the drugs of choice in the management of erectile dysfunction. Sildenafil citrate, a phosphodiesterase (type V) inhibitor, is effective in treating this conditon. Yohimbine, an alpha-2-adrenoceptor antagonist, has been available for some time as a treatment for erectile dysfunction, although its efficacy has remained questionable for many years. Yohimbine has been used in some countries mainly to treat psychogenic impotence. Injection therapy is a second line treatment for erectile dysfunction.

Viagra and herbs and supplements

The injected agents may be a single agent or a combination of agents, including prostaglandin E1 (PGE1), papaverine, and/or phentolamine. Within minutes after injection directly into the cavernosal body of the penis, a very natural and physiologic erection develops. The success rate with injection therapy is very high. MUSE (Vivus inc) is a urethral suppository containing PGE1 that is administered 10 to 15 minutes prior to intercourse. It is thought to elevate cavernosal PGE1 drug levels by direct transfer through communicating venules between the urethral spongiosum and cavernosum of the erectile bodies. The success rate with injection therapy is very high. MUSE (Vivus inc) is a urethral suppository containing PGE1 that is administered 10 to 15 minutes prior to intercourse.

Overdose/Missed Dose

Regain confidence, improve performance, and take control of your sexual health with a trusted and proven ED treatment. You must be logged in to post a review. Sildenafil citrate is defined as a compound used to treat male erectile dysfunction, belonging to the pyrazolo-pyrimidinyl-methylpiperazine class, and acts as a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5). Sildenafil citrate (250 mg) is dissolved in 50 mL of glacial acetic acid, titrated with 0.1 M perchloric acid, with the end point being detected potentiometrically. Each milliliter of 0.1 M perchloric acid VS is equivalent to 66.67 mg of Sildenafil citrate, calculated as C22H30N6O4S • C6H8O7.

Sildenafil vs. tadalafil

This method is suitable to assay Sildenafil citrate in its bulk drug form, and in formulated products [3]. In this method, 160 mg of Sildenafil citrate was accurately weighed and dissolved in 50 mL of a 20:80 mixture of methanol / water. Titration against 0.1 N sodium hydroxide was carried out using a Mettler DL-67 potentiometric titrator. Each milliliter of 0.1 N sodium hydroxide VS is equivalent to 22.22 mg of Sildenafil citrate, sildenafil 100g calculated as C22H30N6O4S • C6H8O7[3]. 2.13 Sildenafil citrate (Viagra) – structure and hydrogen bonding Sildenafil citrate (SC) has been widely used for the treatment of erectile disorder. It is thought to elevate cavernosal PGE1 drug levels by direct transfer through communicating venules between the urethral spongiosum and cavernosum of the erectile bodies. It is only effective with mild forms of erectile dysfunction. The vacuum constriction device is a nonpharmacologic, nonsurgical treatment for erectile dysfunction. It consists of a vacuum cylinder that is placed around the penis to allow for venous engorgement of the cavernosal bodies. Once fully erect, a constrictor ring is placed at the base of the penis to maintain rigidity. Although this device can create a functional erection in most men, long-term patient satisfaction is poor. Surgical therapy for the management of erectile dysfunction entails placing two parallel erectile cylinders within the cavernosal bodies. These devices can be either malleable or inflatable. Of all the treatments for erectile dysfunction, surgical implantation has one of the highest patient satisfaction rates. Many over-the-counter herbal supplements are purported to be effective in treating erectile dysfunction. These agents are not FDA-approved for this indication. Rigorous placebo-controlled studies have failed to identify any of these as efficacious in treating this condition. Sildenafil (Viagra, sildenafil citrate, 5.1.8), prescribed today for the treatment of ED (erectile dysfunction), was initially designed to target the cGMP pfizer sildenafil 100 pathway for the treatment of cardiac arrhythmias, especially angina. There are about seven different classes of phosphodiesterases (PDE), among which PDE type 5 is more expressed in corpus cavernosum (smooth muscle), and sildenafil works more selectively against PDE 5 (10 times higher) than other classes of PDE and has no long term adverse effects on ocular functions (caused by the inhibitory action against PDE 6). In further clinical investigations, it has also been found that sildenafil is 4000 folds selective for PDE five than PDE 3 (controls cardiac contractility), which indicates that it has no such interference with cardiac activities at the therapeutic dose. Synthesis of sildenafil and sildenafil citrate has been disclosed in various patents and publications, among which one of the well-mentioned processes is Pfizer's commercial synthetic process.

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Generic Versions	$10 - $30	25 mg, 50 mg, 100 mg	Generic
Super Cheapest Brands	$5 - $15	50 mg	Over-the-counter or online options

Precursor molecule 5.1.1, synthesized from diethyl oxalate and 2-pentanone, leads to compound 5.1.2 via one-pot amide conversion from carboxylic derivative in the presence of thionyl chloride.

Indication	Description	Approved Dose	Additional Notes
Erectile Dysfunction (ED)	Improves erectile response in men	50 mg as needed	Taken 30 min to 1 hour before activity
Pulmonary Arterial Hypertension	Vasodilation of pulmonary vasculature	20 mg TID	Used with other PAH therapies
Raynaud's Phenomenon	Relief from vasospasms	Off-label	Experimental use

Further, the catalytic reduction of 5.1.2 afforded 5.1.3, which underwent amide bond formation using CDI with 5.1.6 to yield 5.1.7. The compound 5.1.6 was prepared from the precursor 5.1.4; 2-ethoxy benzoic acid via two steps. Finally, 5.1.7 undergoes cyclization in the presence of a base to afford sildenafil (5.1.8) (Scheme 5.1) (Jackson et al., 2005; Pathy & Chakaravathy, n.d.; Roschangar et al., 2015; Terrett et al., 1996). 3.3 DOSY 1H NMR analysis of formulations of genuine Cialis® and a Chinese imitation Nowadays, drugs for the treatment of erectile dysfunction that inhibit the phosphodiesterase type 5 enzyme (PDE-5), sildenafil citrate (Viagra®), tadalafil (Cialis®) or vardenafil hydrochloride (Levitra®, see Figure 2) are among the most counterfeited or imitated. Imitations come generally from Asia (India and China most often) which do not recognize the European and American patent laws so that products manufactured legally in such countries are illegal in Europe, USA and other countries. The original Cialis® tablet from Eli Lilly Laboratories and one copy commercialized in China were analyzed. The DOSY 1H NMR spectra of their solutions are presented in Figure 5. It is obvious that the two formulations do not contain the same active ingredient. Their common excipients are the lubricant magnesium stearate (Mg st, Δ), the tablet binder hypromellose (#) and lactose (□) as a diluent. Moreover, the brand formulation is composed of another cellulose derivative with a higher molecular weight known to be hydroxypropylcellulose (▀). Signals of sodium lauryl sulphate (laur; ▴), a wetting agent, and triacetin (♦), a hydrophilic plasticizer, are also present. The intensity of the peaks located in the aromatic region of the 1H NMR spectrum demonstrates that the Chinese fake formulation of Cialis contains a mixture of two active pharmaceutical ingredients. These two compounds were purified by chromatography and then identified by NMR and LC–MS–MS (liquid chromatography–mass spectrometry–mass spectrometry) as vardenafil (V) and homosildenafil (H) (Figure 5).

2.1 Dosage Information

It is only effective with mild forms of erectile dysfunction. The vacuum constriction device is a nonpharmacologic, nonsurgical treatment for erectile dysfunction. It consists of a vacuum cylinder that is placed around the penis to allow for venous engorgement of the cavernosal bodies. Once fully erect, a constrictor ring is placed at the base of the penis to maintain rigidity. Although this device can create a functional erection in most men, long-term patient satisfaction is poor.

Antiretroviral Agents

Surgical therapy for the management of erectile dysfunction entails placing two parallel erectile cylinders within the cavernosal bodies. These devices can be either malleable or inflatable. Of all the treatments for erectile dysfunction, surgical implantation has one of the highest patient satisfaction rates. Many over-the-counter herbal supplements are purported to be effective in treating erectile dysfunction. These agents are not FDA-approved for this indication.