Efficacy of sildenafil citrate at 12 hours after dosing: re-exploring the therapeutic window

Clinical Trial

. 2004 Sep;46(3):357-60; discussion 360-1.

doi: 10.1016/j.eururo.2004.04.025.

Ignacio Moncada 
¹
, José Jara, David Subirá, Irene Castaño, Carlos Hernández

Affiliations

Affiliation

• ¹ Urology Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain. [email protected]

• PMID:

  15306108

• DOI:

  10.1016/j.eururo.2004.04.025

Clinical Trial

Ignacio Moncada et al.

Eur Urol.

2004 Sep.

. 2004 Sep;46(3):357-60; discussion 360-1.

doi: 10.1016/j.eururo.2004.04.025.

Authors

Ignacio Moncada 
¹
, José Jara, David Subirá, Irene Castaño, Carlos Hernández

Affiliation

• ¹ Urology Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain. [email protected]

• PMID:

  15306108

• DOI:

  10.1016/j.eururo.2004.04.025

Abstract

Objective:

This open-label study investigated the efficacy of sildenafil citrate at 12 hours postdose among prior treatment responders.

Patients and methods:

Eight 100-mg doses of sildenafil were provided to 40 eligible patients with erectile dysfunction (ED), who were to record the results of each sexual attempt in a patient diary. Each patient was instructed to make a sexual attempt at 1 and 12 hours postdose on 4 occasions (part 1) and only at 12 hours postdose on 4 subsequent occasions (part 2).

Results:

Of 40 enrolled patients, 34 (85%) completed the study. In these evaluable patients, 97% and 74% of patients achieved erections that resulted in successful intercourse at 1 hour and 12 hours postdose, respectively. There was a nonsignificant reduction in the percentage of responders at 12 hours during part 1 versus part 2 of this study (71% versus 78%).

Conclusions:

This study demonstrates that, in the majority of these patients with ED, sildenafil remains clinically active 12 hours after administration. Larger studies may be necessary to confirm and clarify the therapeutic window of sildenafil.

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Sildenafil Dosage: How Much Sildenafil is Too Much?

1. Sildenafil side effects
2. How much sildenafil is too much?
3. Sildenafil alternatives

Sildenafil (brand name Viagra; see Important Safety Information), is an effective treatment for erectile dysfunction. But sildenafil doesn’t give you an immediate erection. The medication requires sexual arousal to work properly. So if you’re expecting fireworks and left disappointed, it’s understandable that you may consider doubling or increasing your sildenafil dosage—but don’t do this.

Sildenafil, like all medications, comes with a risk of side effects and contraindications. If you’re wondering how much sildenafil is too much, make an appointment with a healthcare provider to discuss your concerns and potentially increase your dosage instead of taking matters into your own hands.

With any medication, it’s common for healthcare providers to prescribe the minimum effective dose—the smallest dose that will work for you. That’s because the higher the dose of a medication, the higher the risk of side effects. Sildenafil is no exception.

Some sildenafil side effects include headache, redness in the face, changes in vision, stuffy nose, muscle aches, back pain, nausea, dizziness, and rash. The frequency of these side effects may increase dramatically with a higher dose. For example, 16% of people who take 25 mg of sildenafil experience headaches. At a higher dose of 100 mg, 28% of people experience headaches (DailyMed, 2017).

There have been numerous reports of people who have taken more than the recommended amount of Viagra. While we still don’t know all the risks associated with taking too much ED medication, one potential complication is an eye problem called retinal toxicity. This can cause blurred vision, changes in color vision, and light sensitivity. Fortunately, these symptoms usually go away after you stop taking the medication, but some people suffer permanent damage (DailyMed, 2017; Kim, 2017; Kolomeyer, 2018).

Ensuring that you can tolerate the medication is one reason healthcare providers typically start with a smaller dose and increase the dose according to your needs. Following your healthcare provider’s instructions minimizes your risk of adverse effects.

As with all medication, you should take the recommended dose of sildenafil prescribed to you by your healthcare provider, and no more. You also shouldn’t take sildenafil more than once every 24 hours. Your healthcare provider will likely start you on a 50 mg dose of the medication to test how well you respond to it. Your healthcare provider may increase your dose to 100 mg or decrease it to 25 mg, depending on whether you achieve the desired results and/or experience side effects.

You should take sildenafil at least 30 minutes before sex, but you can take it up to four hours in advance. Talk to your healthcare provider if your prescription isn’t helping you get and maintain erections firm enough for satisfying sex. Do not take an extra dose of sildenafil if the first one didn’t work. If you took sildenafil less than 30 minutes before sex, give it a little more time, as its effects may strengthen.

As you adjust your sildenafil dosage (with the guidance of a healthcare provider) for the best results, other options exist to help you get and maintain erections. Penis pumps and cock rings help draw blood into the penis for a firmer erection (with a penis pump) and prevent the blood from draining (with a cock ring). 

A 25 mg sildenafil dosage is considered a low dose, and low-dose sildenafil is only used in certain circumstances. If you’re over the age of 65 or if you’ve ever experienced side effects when taking the standard starting dose (50 mg), you may be prescribed low-dose sildenafil. Your healthcare provider also may prescribe low-dose sildenafil if you have kidney or liver medical conditions or are taking certain medications (DailyMed, 2017).

Researchers have used doses as high as 200 mg to treat severe erectile dysfunction, but more research is needed on the safety of high dosages. One small study of 54 participants with erectile dysfunction showed that high-dose sildenafil improved erectile dysfunction in just 13 of the 54 participants (24.1%). At the highest dose, 63% of the participants reported experiencing side effects like headaches and facial flushing, which was also true in patients who didn’t notice improvements in their erectile dysfunction symptoms (McMahon, 2002).  

Even among the participants who saw improvements in their erectile dysfunction symptoms, the side effects were so severe that many decided it wasn’t worth it. Of the 13 participants who had success with the high-dose treatment, 31% refused to continue because of the adverse effects. (McMahon, 2002).

Your healthcare provider will weigh the pros and cons of various sildenafil doses to help you make the right decision.

If sildenafil doesn’t work for you, there are plenty of other safe and effective options to treat erectile dysfunction. Sildenafil is a member of a class of drugs known as PDE-5 inhibitors, which include alternative medications like tadalafil (Cialis; see Important Safety Information), vardenafil (Levitra), and avanafil (Strendra).

Depending on your lifestyle, one of these medications may work better for you than sildenafil: 

• Tadalafil takes 1–2 hours to work, but its effects can last up to 36 hours off and on. Tadalafil is available in a daily tablet, while other PDE-5 inhibitors are taken just before having sex.  
• Vardenafil may be the best option if you plan to take your medication with food. High-fat meals can slow down other PDE-5 inhibitors, but vardenafil works at the same speed even when taken with a moderate-fat meal (Zucchi, 2019). 
• Avanafil works within 15 minutes for many people, making it the fastest-acting PDE-5 inhibitor currently available (DailyMed, 2021). 

As with any medication, a good rule of thumb is to take sildenafil as prescribed by your healthcare provider. The symptoms of erectile dysfunction are frustrating, but your healthcare provider is there to help you develop a treatment plan that’s right for you. 

If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

1. Coombs, P. G., Heck, M., Guhring, P., et al. (2012). A review of outcomes of an intracavernosal injection therapy programme. BJU International 110(11), 1787-1791. doi:10.1111/j.1464-410X.2012.11080.x. Retrieved from https://pubmed.ncbi.nlm.nih.gov/22564343/
2. Food and Drug Administration (FDA). (2014). Label: VIAGRA (sildenafil citrate) tablets. Retrieved from https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/20895s039s042lbl.pdf
3. DailyMed. (2021). STENDRA- avanafil tablet. Retrieved from https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=a8726f90-9329-46ca-9379-2b50c78fe0e2
4. DailyMed. (2017). VIAGRA- sildenafil citrate tablet, film coated. Retrieved from https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=a2a9f459-e692-4e85-83b0-a35fbf35e91b
5. Dhaliwal, A. & Gupta, M. (2022). PDE5 inhibitor. StatPearls. Retrieved on Oct. 12, 2022 from https://www.ncbi.nlm.nih.gov/books/NBK549843/
6. Galiè, N., Ghofrani, H.A., Torbicki, A. , et al. (2005). Sildenafil citrate therapy for pulmonary arterial hypertension. New England Journal of Medicine, 353(20), 2148-2157. doi:10.1056/NEJMoa050010. Retrieved from https://pubmed.ncbi.nlm.nih.gov/16291984/
7. Karaarslan, C. (2020). Ocular side effects of sildenafil that persist beyond 24 h—A case series. Frontiers in Neurology, 11(67). doi:10.3389/fneur.2020.00067. Retrieved from https://www.frontiersin.org/articles/10.3389/fneur.2020.00067/full
8. Kim, H. D., Chang, J. H., Kim, Y. K., & Ohn, Y. (2017). Electrophysiologic effects of very high-dose sildenafil. JAMA Ophthalmology, 135(2), 165. doi:10.1001/jamaophthalmol.2016.4017. Retrieved from https://jamanetwork.com/journals/jamaophthalmology/article-abstract/2595044
9. Kolomeyer, A. M. & Kim, B. J. (2018). High-dose sildenafil-associated acute macular neuroretinopathy variant. Ophthalmology Retina, 2(7), 711. doi:10.1016/j.oret.2017.08.024. Retrieved from https://www. ophthalmologyretina.org/article/S2468-6530(17)30382-2/pdf
10. McMahon, C. G. (2002). High dose sildenafil citrate as a salvage therapy for severe erectile dysfunction. International Journal of Impotence Research, 14(6), 533-538. doi:10.1038/sj.ijir.3900936. Retrieved from https://pubmed.ncbi.nlm.nih.gov/12494291/
11. Rajagopalan, P., Mazzu, A., Xia, C., et al. (2003). Effect of high-fat breakfast and moderate-fat evening meal on the pharmacokinetics of vardenafil, an oral phosphodiesterase-5 inhibitor for the treatment of erectile dysfunction. Journal of Clinical Pharmacology, 43(3), 260-267. doi:10.1177/0091270002250604. Retrieved from https://pubmed.ncbi.nlm.nih.gov/12638394/
12. Seidman, S. N., Pesce, V. C., & Roose, S. P. (2003). High-dose sildenafil citrate for selective serotonin reuptake inhibitor-associated ejaculatory delay: open clinical trial. Journal of Clinical Psychiatry, 64(6), 721-725. doi:10.4088/jcp.v64n0616. Retrieved from https://pubmed. ncbi.nlm.nih.gov/12823089/
13. Sun, L., Peng, F., Yu, Z., et al. (2014). Combined sildenafil with vacuum erection device therapy in the management of diabetic men with erectile dysfunction after failure of first-line sildenafil monotherapy. International Journal of Urology, 21(12), 1263-1267. doi:10.1111/iju.12564. Retrieved from https://onlinelibrary.wiley.com/doi/abs/10.1111/iju.12564
14. Yanoga F., Gentile, R. C., Chui, T. Y. P, et al. (2018). Sildenafil citrate induced retinal toxicity – ERG, OCT, and adaptive optics findings. Retinal Cases and Brief Reports, 12(Suppl 1), S33-S40. doi:10.1097/ICB.0000000000000708. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6110976/ 
15. Zucchi, A., Costantini, E., Scroppo, F. I., et al. (2019). The first-generation phosphodiesterase 5 inhibitors and their pharmacokinetic issue. Andrology, 7(6), 804–817. doi:10.1111/andr.12683. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6790582/

Dr. Chimene Richa is a board-certified Ophthalmologist and Senior Medical Writer/Reviewer at Ro.

How Viagra works for men and women, instructions for use, composition

THERE ARE CONTRAINDICATIONS. POSSIBLE SIDE EFFECTS. A SPECIALIST’S CONSULTATION IS REQUIRED. For men

The author of the article

Ershov Grigory Vasilievich,

Urologist

All authors

The content of the article

• How VIA works gra
• Viagra for men
• Viagra: how to take and how much it works
• Viagra for women
• Viagra and alcohol
• Viagra or Cialis — what is better

Do you know the history of Viagra discovery?

During clinical trials of a new heart drug, scientists noticed a “side effect” in male patients. This observation marked the beginning of a new era in the treatment of erectile dysfunction (ED). The drug Viagra appeared in 1998 and “blew up” the global pharmaceutical market.

All products Viagra

20 reviews

How Viagra works

The famous Viagra contains the active ingredient Sildenafil. The drug is produced in tablets of three dosages – 25 mg, 50 mg and 100 mg.

Viagra acts in the body through a complex chain of biochemical reactions. As a result, they lead to relaxation of the muscular walls of the vessels of the cavernous bodies in the penis and filling them with blood. This ensures a natural response to sexual arousal.

It is important to understand that Viagra does not treat the cause of erectile dysfunction (ED), it simply helps to cope with the consequences. Viagra does not increase sexual desire. If there is no attraction to a partner, then the medicine is useless.

Viagra for men

The drug was created for men and has the only indication for use:

• treatment of erectile dysfunction.

The clinical efficacy of Viagra has been confirmed by numerous world studies.

Here is an example of one of the clinical trials: 12 weeks after the start of taking the drug, an improvement in erection was noted by 76% of patients who received Viagra, and 22% of those who received placebo (that is, “pacifiers”).

The advent of Viagra has changed the lives of millions of men in the world. Patients with erectile dysfunction thanks to her return to a normal sexual life.

Despite the high efficiency, in a number of patients taking the drug does not lead to an improvement in erection. This is due to the wrong medication or the fact that ED is simply a consequence of another disease. In such cases, consultation and examination with a doctor is required.

Viagra: how to take and how much it works

How to take Viagra pills correctly:

• oral, on an empty stomach – coated tablets
• with or without water – orodispersible tablets
• recommended daily dose of 50 mg
• 60 minutes before sexual activity
• multiplicity – no more than 1 time per day
• maximum daily dose 100 mg

the recommended dose may be reduced to 25 mg or increased to 100 mg depending on the efficacy, tolerability of the drug and diseases in the patient

Data from the study of the drug showed that increasing the dose to 200 mg did not lead to an increase in the effect, but side effects (headache, “hot flashes”, dizziness, stomach problems, nasal congestion, visual disturbances) became more frequent.

The drug begins to act 30 minutes after ingestion. Active for 2-4 hours.

Viagra is contraindicated in patients:

• receiving nitrate therapy for heart disease
• in severe liver disease
• for severe heart failure, heart attack, stroke, arrhythmias
• for too high and low blood pressure
• for diseases of the optic nerve
• in case of hypersensitivity to sildenafil and drug components
• under 18

It is safe to take the drug if you follow the instructions and consult your doctor first. All medications taken on a regular basis must be reported. A number of drugs are incompatible with Viagra.

Viagra for Women

Viagra is not intended for use in women for its registered indication. The drug does not affect the sexual arousal of a woman in any way.

Viagra and alcohol

There are no instructions on the incompatibility of alcoholic beverages and Viagra in the instructions.

The drug at a dose of 50 mg did not enhance the hypotensive effect of ethanol at low blood concentrations in healthy volunteers.

But the general recommendation – do not take alcohol in combination with drugs – also applies to Viagra.

Ethanol depresses the central nervous system, increases heart rate, burdens the liver and kidneys.

Viagra has serious restrictions and contraindications.

Therefore, it is better to refrain from taking alcoholic beverages while taking the drug. Then you can not be afraid of imposing the negative effects of drugs and alcohol on the body.

Viagra or Cialis — what is better

Viagra is the first drug, branded and still popular. A little later, his main competitor Cialis appeared. The cardinal differences between drugs are the chemical formula and duration of action. Tadalafil in Cialis “supports” a man for 36 hours. For this reason, the drug quickly became widespread in all countries. Other differences are shown in the table:

Viagra and Cialis are prescription drugs. The selection of therapy should be carried out by a doctor, taking into account the patient’s age, condition, concomitant diseases, and medications already taken.

If the physician recommends both, the patient’s preference and personal experience will help decide which is better.

Viagra was the first effective and safe drug for the treatment of erectile dysfunction. She made a breakthrough in the history of sexual medicine. Analogues and generics, which appeared later, will long remain second in people’s minds. This does not detract from their importance – the choice allows you to expand the circle of users, choose the best remedy for individual indications.

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A side effect that has changed the lives of millions of men

One of the main conditions for a harmonious and long relationship between a man and a woman is the physical and sexual health of the partner. However, daily troubles, conflicts at work, stressful situations, the desire to succeed in life sometimes affect both the physical and sexual well-being of the stronger sex. And now, to unpleasant situations at work and daily stresses, problems in the intimate sphere gradually begin to be added, which sometimes fall on the heads of men with a diagnosis of “erectile dysfunction”. In this context, it should be remembered that the problem of erectile dysfunction can be eliminated with the help of modern effective drugs with a favorable safety profile.

The term “erectile dysfunction” was proposed in 1988 by the US National Institutes of Health (National Institutes of Health) and replaced the outdated concept of “impotence”. Erectile dysfunction is defined as the inability to achieve and/or maintain an erection sufficient for sexual intercourse. In the structure of sexual disorders, this pathology occupies a leading place in terms of frequency of occurrence and social significance [1, 2].

A NEW ERA IN THE TREATMENT OF ERECTILE DYSFUNCTION

A revolutionary event in the treatment of erectile dysfunction was the appearance in 1998 of the drug sildenafil citrate, known under the trade name Viagra ^® [3].

Interesting facts:

• Viagra® is known worldwide for its side effects. The results of clinical studies of sildenafil conducted in 1992 with the participation of several thousand patients with coronary heart disease disappointed the developers of the drug Viagra P. Dunn and A. Wood, however, its side effect, which was reported by many participants in the study, namely: a pronounced effect on blood flow in the area of ​​the pelvic organs (including the penis), prompted the idea of ​​using this drug for the treatment of erectile dysfunction [4];
• later, sildenafil also showed efficacy in the treatment of pulmonary hypertension [5];
• in 1998. Viagra ^® was mentioned in connection with the award of the Nobel Prize in Physiology and Medicine [6];
• Viagra ^® was awarded the Galen Prize in 1999 in the Netherlands, in 2000 in France and Great Britain, and in 2001 in Canada [7].
• in 2001, Pfizer was awarded the Queens Award for Enterprise (UK) for the discovery and development of Viagra ^® [8];
• in 2003, Viagra ^® won the nomination “The brightest brand of the Ukrainian pharmaceutical market” [9].

Sildenafil is a selective inhibitor of cyclic guanosine monophosphate specific phosphodiesterase type 5 (PDE5), in cavernous bodies, where PDE5 is responsible for the breakdown of cyclic guanosine monophosphate (cGMP). Blockade of this enzyme leads to the accumulation of cGMP, which causes relaxation of smooth myocytes, providing an erection.

Sildenafil is the gold standard in the treatment of erectile dysfunction today. This is primarily due to its high efficiency, as well as to the oral non-invasive form of sildenafil [10].

It should be noted that the effect of the drug, that is, the onset of an erection, begins 14-20 minutes after taking it [11], and the duration of action of Viagra® 100 mg in most men is 12 hours [12]. Viagra® remains effective even 4 years after the start of regular intake, so, more than 94% of patients who participated in the clinical study of the effectiveness of Viagra®, after 4 years of regular use, noted that they were satisfied with the result of treatment and significantly increased the level of sexual activity [13 ]. With Viagra®, men can have sex more often and longer. Viagra® 100 mg increases the duration of erection in men with erectile dysfunction without changing the characteristics of sperm, and has a positive effect on the resumption of erection after ejaculation in the presence of continuous sexual arousal [14]. It should be noted that Viagra ^® has a favorable safety profile. Thus, the incidence of acute cardiovascular diseases in patients with erectile dysfunction who took Viagra ^® does not exceed that in the general population [2].

Viagra ^® — do not forget about physical pleasure!

Representative office of Pfizer has developed an educational website for Ukrainian consumers, which is dedicated to the problem of erectile dysfunction — top-result.com.ua . On the site you can get information on possible problems with erection and ways to solve it.

REFERENCES

1. Pushkar D.Yu., Rasner P. I. Drug treatment of erectile dysfunction: a preliminary comparison of existing methods//Farmateka. – 2004. – 3.4 (82): 31–35. Available at http://medi.ru/doc/260122.htm dated 09/01/2014.

2. Gorilovsky L.M., Lakhno D.A. Erectile dysfunction//Russian medical journal. 2005; 10:653–656. Available at http://rmj.ru/articles_3734.htm from 01.09.2014.

3. FDA Home Drug Databases Orange Book. Available at http://www.accessdata.fda.gov/scripts/cder/ob/docs/obdetail.cfm?Appl_No=020895& TABLE1=OB_Rx on 08/28/2014.

4. Katzenstein L. Viagra: The Remarkable Story of the Discovery and Launch. New York, NY: Medical Information Press. 2001.

5. Avdeev S.N. Pulmonary hypertension in chronic respiratory diseases. Atmosphere. Pulmonology and Allergology. 2010; 2:2–10.

6. Robert F. Furchgott, Louis J. Ignarro, Ferid Murad. The Nobel Prize in Physiology or Medicine 1998. Press release. Available at http://www.nobelprize.org/nobel_prizes/medicine/laureates/1998/press. html dated 07/30/2014.

7. Prix Galien – winners. Available at http://www.prixgalien.com/en/05/02/winners-sorted-by-medical-field.htm on 29/08/2014.

8. T. Harding Royal birthday award for makers of Viagra. Available at http://www.telegraph.co.uk/news/uknews/1316876/Royal-birthday-award-for-makers-of-Viagra.html on 28/08/2014.

9. Brands of the Ukrainian pharmaceutical market. Weekly PHARMACY. Available at http://www.apteka.ua/online/19779 dated 07/31/2014.

10. Mazo E.B., Dmitriev D.G., Gamidov S.I. et al. Pharmacotherapy of erectile dysfunction // Russian Medical Journal. 2001.9:1077–78. Available at http://rmj.ru/articles_1461.htm from 09/01/2014.

11. Padma-Nathan H., Stecher V., Sweeney M., et al. Minamal time to successful intercourse after sildenafil citrate: results of a randomized, double-blind, placebo-controlled trial//Urology. 2003. 62(3): 400–403.

12. Moncada I., Jara J., Subira D., et al. Efficacy of sildenafil citrate at 12 hours after dosing: Reexploring the therapeutic window//Eur Urol. 2004; 46(3): 357–61.

13. McMurray J.G., Feldman R.A., Auerbach S.M., et al., for the Multicenter Study Group. Long-term safety and effectiveness of sildenafil citrate in men with erectile dysfunction. Ther Clean Risk Management. 2007; 3(6): 975–981.

14. A. Aversa, F. Mazzilli, T. Rossi, et al.; Effects of sildenafil (Viagra) administration on seminal parameters and post-ejaculatory refractory time in normal males; Hyman reproduction. 2000; 15(1): 131–134.

Svetlana Shelepko

Information for the professional activities of medical and pharmaceutical workers.

Viagra® (sildenafil), film-coated tablets, 50 mg and 100 mg; 1 or 4 tablets per pack. Brief instructions for the medical use of Viagra®. Indications. Treatment of erectile dysfunction, which is defined as the inability to achieve and maintain a penile erection necessary for successful intercourse. Method of application and dose. The drug is used orally. The recommended dose of Viagra® is 50 mg and is used, if necessary, approximately 1 hour before sexual intercourse. The maximum recommended dose is 100 mg. The maximum recommended frequency of use of the drug is 1 time per day. Contraindications. Hypersensitivity to the active substance or any of the auxiliary components of the drug; simultaneous use with nitric oxide donors (such as amyl nitrite) or nitrates in any form is contraindicated. Sildenafil is contraindicated in men who are not recommended for sexual activity. Side effects. The most commonly reported adverse reactions were headache, flushing, dyspepsia, visual disturbances, nasal congestion, loss of consciousness, and impaired color perception. Application features. Since sexual activity is associated with a certain risk on the part of the heart, before starting any treatment for erectile dysfunction, the doctor should assess the patient’s cardiovascular status. Methods for the treatment of erectile dysfunction, including sildenafil, should be administered with caution to patients with anatomical deformities of the penis (such as angulation, cavernous fibrosis, or Peyronie’s disease), or patients with conditions that cause priapism.