Adverse effects most commonly reported with sildenafil are headache, flushing, and dyspepsia. Also common are visual disturbances such as blurred vision, photophobia, chromatopsia, cyanopsia, eye irritation, pain and redness of the eyes. Retinal haemorrhage has occurred, and non-arteritic anterior ischaemic optic neuropathy (NAION) causing permanent loss of vision has been reported rarely.
Other common adverse effects include dizziness, insomnia, anxiety, vertigo, epistaxis, nasal congestion, pyrexia, and gastrointestinal disturbances such as diarrhoea and vomiting. Priapism can occur.
Other adverse effects include skin rashes, erythema, alopecia, limb and/or back pain, myalgia, facial oederna, fluid retention, paraesthesia, and urinary-tract infection. Dyspnoea, cough, rhinitis, sinusitis, bronchitis, and cellulitis can occur.
Sudden decrease or loss of hearing has been reported. Other reported effects include anaemia, leucopenia, gynaecomastia, urinary frequency or incontinence, haematuria, and seizures, Hypersensitivity reactions have been reported rarely.
Cerebrovascular haemorrhage and transient ischaemic attacks have occurred. There have also been reports of palpitations, syncope, hypertension, hypotension and serious cardiovascular events including myocardial infarction, arrythmias, tachycardia, unstable angina, and sudden cardiac death.
Convulsions: A report of 2 patients who had a first tonic-clonic seizure shortly after taking sildenafil.
Effect on the blood: Thrombocytopenia has been reported in a patient taking sildenafil 25 mg three timed daily. The patient's platelet count increased when sildenafil was stopped and decreased on rechallenged.
Effects on the cardiovascular system: The effect of phosphodiesterase type-5 inhibitors (sildenafil, tadalafil, and vardelafil) on the cardiovascular system, and the potential risk of sexual activity in men with cardiovascular disease, have been reviewed.
There has been considerable uncertainty about the potential cardiovascular risk associated with sildenafil treatment. Minor effects associated with vasodilatation, such as headache and flushing are relatively common, but in patients without preexisting cardiovascular risk factors the risk of serious cardiovascular events associated with the drug appears to be low. However, there have been reports of myocardial infarction in patients who had no apparent risk factors.
Effects on the ears: It had received a total of 29 post marketing reports of sudden hearing loss with phosphodiesterase type-5 inhibitors. The problem was sometimes accompanied by tinnitus, vertigo, oi dizziness. In most of the cases, the hearing loss involved one ear, and it was either a partial or complete loss of hearing. In about one-third of cases, the loss was temporary. While a causal relationship could not be established, patients should be advised that hearing loss may be relate to these drugs, and to seek medical attention if affected.
Effects on the eyes: It had received 65 reports of abnormal vision from a total of 773 adverse reactions associated with use of sildenafil reported over 3 years. A bluish tinge or haze to vision and some increased light sensitivity has been reported by patients taking sildenafil, with the percentage of reports increasing with increasing dose. The visual symptoms usually peak 1 to 2 hours after ingestion and resolve about 3 to 4 hours later. The effects of a single dose of sildenafil 100 mg were studied in 5 healthy subjects. Electroretinogram measurements showed significant changes that correlated well with plasma sildenafil concentrations, peaking at 1 hour after administration and showing complete recovery at the 6- hour measurements. Inhibition of phosphodiesterase type-6 in rod photoreceptor is the most likely mechanism of sildenafil-associated retinal dysfunction.
A review of visual disorders associated with 5-phosphodiesterase inhibitors noted that pooled reports of disturbances of vision with sildenafil suggest an incidence of 2 to 5%; the frequency with vardenafil and tadalafil seems to be lower although the evidence is limited. There is also little evidence of retinal toxicity, but this class of drugs is not recommended for use in patients with hereditary degenerative retinal disorders since they have minor inhibitory effects on 6-phosphodiesterase which has an important role in the visual transduction cascade.
Other visual disturbances reported in patients taking sildenafil have included temporary loss of vision and increased intra-ocular pressure. A 69-year-old man who had permanent loss of vision in one eye a few hours after taking sildenafil 100 mg was found to have an occlusion in a retinal artery. In another similar case of retinal artery occlusion 7 the patient also had uncontrolled hypertension; the authors suggested that embolisation by a "preexisting arteriosclerotic plaque of the carotid artery resulted from elevated blood pressure and cardiac workload during sexual activity, rather than as a direct adverse effect of sildenafil.
Several cases of persistent blurred vision and visual loss caused by nonarteritic anterior ischaemic optic neuropathy (NAION; vascular insufficiency and ischaemia at the optic nerve head) associated with sildenafil use have been reported. Generally, visual defects developed in one eye only within 24 hours of sildenafil ingestion, although many of these men had taken doses of sildenafil on past occasions without adverse effect. A small number of cases have also been reported for tadalafil and vardenafil. However, many of these men bad underlying anatomic or vascular risk factors for NAION, including low cup to disc ratio (crowded disc), age over 50, diabetes, hypertension, ischaemic heart disease, hyperipidaemia, and smoking. A small, retrospective, case-control study suggested that men who use sildenafil or tadalafil and have a history of myocardial· infarction may be at an increased risk of NAION. As of May 2005 the FDA had concluded that it was not possible to determine "Whether NAlON was directly related to the use of phosphodiesterase type-5 inhibitors, the patients' underlying vascular risk factors or anatomical defects, a combination of these factors, or other factors. Later reviews came to similar conclusions, and the estimated incidence of NAION in men receiving sildenafil has been calculated to be similar to estimates for the general population.
Effects on mental function: There have been a few cases reported of transient global amnesia after the use of sildenafil or tadalafil.