Dr Sharon Rees @reesprescribe
Day 1: #sildenafil #Viagra was originally conceived and licensed as a drug for hypertension/angina. During clinical trials, the side effect of enhancing male erectile function was reported, and further trials led to licensing for erectile dysfunction (ED) in US/Europe in 1998. #Viagra was disallowed on NHS, except in special groups, due to concerns that demand for ‘performance enhancement’ could cost >1 billion!. Restrictions were removed in 2014 after generic #sildenafil became available. Now available over the counter in UK.
Dr Sharon Rees @reesprescribe
Day 2: #Viagra dosing for ED is 25–100 mg oral once daily. Typically given as a 50mg single dose 1 hour pre-sexual activity. Maximum 1 dose/day. Unlicensed use for digital ulcers, eg in Raynaud's phenomenon. Used for pulmonary hypertension for all ages, but unlicensed under 1 year old.
Dr Sharon Rees @reesprescribe
Day 3: #Viagra has fast oral absorption (food slows especially if high fat) and a high volume of distribution. Metabolised by CYP3A4 and 2C9 (minor), which release an active metabolite with ~ 50% potency of the parent drug. Primary excretion in faeces, but about 13% is renal. Dose adjustment in severe renal impairment is recommended. T½ 3–5 hrs.
Dr Sharon Rees @reesprescribe
Day 4: MOA: #sildenafil inhibits PDE5, which normally degrades cGMP. More cGMP prolongs smooth muscle relaxation in the corpus cavernosum, increasing penile blood flow. This only works with sexual stimulation, as the process relies upon activation of the nitric oxide/cGMP pathway.
Dr Sharon Rees @reesprescribe
Day 5: Common ADEs #Viagra: headache, dizziness, flushing, nausea, visual disturbances. Cardiovascular (CV) events (eg chest pain/arrhythmias) are uncommon, but more likely if underlying CV issues. Serious/rare: seizure, retinal disorders, allergic reaction, deafness, priapism (not exhaustive).
Dr Sharon Rees @reesprescribe
#Viagra drug-drug interactions: There is an increased effect when given with any drug which lowers BP; #Viagra potentiates effects of nitrates (severe) and should be avoided with any drug linked to QT prolongation, eg lithium. Drugs which lead to liver enzyme inhibition (eg clarithromycin and ritonavir) can increase exposure (use lower dose), as might grapefruit (not exhaustive).
Dr Sharon Rees @reesprescribe
Day 7: Weak evidence only for #Viagra use in women. The FDA have licensed two drugs since 2015 for low libido in pre-menopausal women: flibanserin (oral) and bremelanotide (s.c inj), but there is no equivalent available for women in the UK.
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Complete the further reading suggested below and then answer the ten questions. Please submit the answers to reesprescribe@gmail.com as a numbered list with TRUE/FALSE or the correct A, B, C, D option. If you achieve 8 or more out of ten on the questions, a CPD certifcate will be emailed to you.
Further reading on #sildenafil #viagra
- Sildenafil: https://bnf.nice.org.uk/drugs/sildenafil/
- Sildenafil 50mg film-coated tablets: https://www.medicines.org.uk/emc/product/7141/smpc#PRODUCTINFO
- Sildenafil works for erectile dysfunction in men and women TRUE or FALSE?
- It is important to take the drug around 1 hour before sexual activity TRUE or FALSE?
- Which of the following is TRUE?
- A. The dose should be lowered if also taking an inhibitor of CYP3A4
- B. Sildenafl should only be used where a condition like diabetes has caused erectile dysfunction
- C. Sildenafil is licensed as a cream for topical use
- D. Sildenafil is only licensed for erectile dysfunction
- Sildenafil has a very short half-life TRUE or FALSE?
- Which is a common ADE?
- A. Myocardial infarction
- B. Deafness
- C. Eye disorders
- D. Seizure
- Which of the following is TRUE?
- A. Sildenafil is not available over the counter
- B. There are no severe DDIs for sildenafil
- C. CYP3A4 inhibitors including grapefruit can decrease the effects
- D. If renal impairment is severe, dose adjustment is recommended
- Sildenafil works by activating the sexual stimulation pathways in the brain TRUE or FALSE?
- Sildenafil can reduce the sperm count TRUE or FALSE?
- It is important to check cardiovascular status before using, as pathology can increase risks of adverse drug effects TRUE or FALSE?
- Equivalents to sildenafil are available for women in the UK TRUE or FALSE?