{"ok":true,"entry":{"slug":"sildenafil","kind":"medication","name":"sildenafil","aliases":["Viagra"],"brands_sg":["Viagra","Revatio","Sildegra","Olvion","Maxigra"],"class":"PDE5 inhibitor","tags":["other"],"use_for":"erectile dysfunction; also pulmonary arterial hypertension","use_after":"as-needed, about 1 hour before sex; once a day at most","use_duration":null,"take_with":"water · with or without food; a fatty meal slows onset","pros":["healthhub: works within 1 hour, lasts up to 4 hours","healthhub: may be taken with or without food","sg label: 25, 50 and 100 mg strengths registered here"],"cons":["healthhub: flushing, headache, blue-tinged vision","sg label: nitrates are contraindicated with it","healthhub: an erection over 4 hours is an emergency"],"dose_note":"the singapore label for viagra states 'For most patients, the recommended dose is 50 mg taken, as needed approximately 1 hour before sexual activity' and 'The maximum recommended daily dose is 100 mg. The maximum recommended dosing frequency is once per day.' the same label lowers that to a 25 mg starting dose in severe renal impairment, hepatic impairment and elderly men, and states 'it is recommended not to exceed a maximum single dose of 25 mg of sildenafil in a 48-hour period' with ritonavir. registered strengths in singapore are 25, 50 and 100 mg tablets (plus revatio 20 mg for pulmonary arterial hypertension). the prescriber sets the dose.","dosage":null,"ul_status":null,"sg_class":"prescription-only","cautions":["nitrates for chest pain — contraindicated (sg label)","alpha-1 blockers such as tamsulosin — bp may fall (healthhub)","recent stroke or heart attack, low or uncontrolled bp (healthhub)","severe heart, liver or kidney problems, or retinitis pigmentosa (healthhub)"],"clashes":[{"src":["ndf_viagra_contra","hh_sil_precautions"],"note":"sg label: contraindicated; healthhub says nitrates are withheld at least 24 hours after the last dose","with":"nitrates (gtn, isosorbide mono/dinitrate)"},{"src":["hh_sil_precautions"],"note":"healthhub: the combination may further lower blood pressure","with":"alpha-1 blockers (tamsulosin, terazosin, prazosin, alfuzosin)"},{"src":["ndf_viagra_ritonavir"],"note":"sg label: not more than a 25 mg single dose in 48 hours","with":"ritonavir"},{"src":["hh_sil_avoid"],"food":true,"note":"healthhub: may interact and increase the risk of side-effects","with":"grapefruit or grapefruit juice"}],"sources":[{"id":"hsa_register","url":"https://data.gov.sg/datasets/d_767279312753558cbf19d48344577084/view","label":"HSA — Listing of Registered Therapeutic Products (data.gov.sg open dataset, 5,511 rows, cached in full and filtered locally)","quote":"All 23 registered sildenafil products carry Forensicclassification 'Prescription Only' — SIN10804P VIAGRA TABLET 25 mg · SIN10805P VIAGRA TABLET 50 mg · SIN10806P VIAGRA TABLET 100 mg · SIN13244P Revatio Film-Coated Tablets 20mg · SIN14188P Sildegra Tablet 100mg","accessed":"2026-08-27"},{"id":"ndf_viagra_ind","url":"https://www.ndf.gov.sg/about-drugs/product-information/sin10806p/","label":"Singapore National Drug Formulary — VIAGRA TABLET 100 MG [SIN10806P], section 4.1 therapeutic indications","quote":"Sildenafil is indicated for the treatment of erectile dysfunction, which is the inability to achieve or maintain a penile erection sufficient for satisfactory sexual performance. In order for sildenafil to be effective, sexual stimulation is required.","accessed":"2026-08-27"},{"id":"ndf_viagra_dose","url":"https://www.ndf.gov.sg/about-drugs/product-information/sin10806p/","label":"Singapore National Drug Formulary — VIAGRA TABLET 100 MG [SIN10806P], section 4.2 posology","quote":"For most patients, the recommended dose is 50 mg taken, as needed approximately 1 hour before sexual activity … The maximum recommended daily dose is 100 mg. The maximum recommended dosing frequency is once per day.","accessed":"2026-08-27"},{"id":"ndf_viagra_ritonavir","url":"https://www.ndf.gov.sg/about-drugs/product-information/sin10806p/","label":"Singapore National Drug Formulary — VIAGRA TABLET 100 MG [SIN10806P], use with other medications","quote":"If ritonavir is co-administered with sildenafil, it is recommended not to exceed a maximum single dose of 25 mg of sildenafil in a 48-hour period.","accessed":"2026-08-27"},{"id":"ndf_viagra_contra","url":"https://www.ndf.gov.sg/about-drugs/product-information/sin10806p/","label":"Singapore National Drug Formulary — VIAGRA TABLET 100 MG [SIN10806P], section 4.3 contraindications","quote":"administration to patients who are concurrently using nitric oxide donors, organic nitrates or organic nitrites in any form either regularly or intermittently is therefore contraindicated","accessed":"2026-08-27"},{"id":"hh_sil_uses","url":"https://www.healthhub.sg/medication-devices-and-treatment/medications/sildenafil","label":"HealthHub (National Medication Information workgroup, SG) — Sildenafil: what is this medication for","quote":"Sildenafil is used to treat erectile dysfunction, a condition where you are unable to get or keep an erection firm enough to have sexual intercourse … Therefore it is taken on an as-needed basis.","accessed":"2026-08-27"},{"id":"hh_sil_howto","url":"https://www.healthhub.sg/medication-devices-and-treatment/medications/sildenafil","label":"HealthHub — Sildenafil: how should I take this medication","quote":"It starts to work within 1 hour and is effective up to 4 hours before sexual activity … takes longer to start working if you take it with a high-fat meal","accessed":"2026-08-27"},{"id":"hh_sil_food","url":"https://www.healthhub.sg/medication-devices-and-treatment/medications/sildenafil","label":"HealthHub — Sildenafil: taking it with food","quote":"This medication may be taken with or without food.","accessed":"2026-08-27"},{"id":"hh_sil_side","url":"https://www.healthhub.sg/medication-devices-and-treatment/medications/sildenafil","label":"HealthHub — Sildenafil: common side effects","quote":"Facial flushing where the skin on your face feels hot · Headache · Giddiness due to lowered blood pressure · Visual disturbances (including blurring of vision, blue tinge in vision) · Indigestion or stomach pain · Nosebleed","accessed":"2026-08-27"},{"id":"hh_sil_rare","url":"https://www.healthhub.sg/medication-devices-and-treatment/medications/sildenafil","label":"HealthHub — Sildenafil: rare but serious side effects","quote":"Priapism (an erection that will not go away) - If you have an erection that lasts more than 4 hours, get medical attention immediately at the emergency department … Sudden vision loss in one or both eyes","accessed":"2026-08-27"},{"id":"hh_sil_precautions","url":"https://www.healthhub.sg/medication-devices-and-treatment/medications/sildenafil","label":"HealthHub — Sildenafil: what precautions should I take","quote":"The combination of nitrates with sildenafil may lead to a dangerous fall in your blood pressure. Nitrates must be withheld at least 24 hours after the last dose of Sildenafil … Alpha-1 Blockers (such as Tamsulosin, Terazosin, Prazosin, Alfuzosin)","accessed":"2026-08-27"},{"id":"hh_sil_avoid","url":"https://www.healthhub.sg/medication-devices-and-treatment/medications/sildenafil","label":"HealthHub — Sildenafil: what food or medication should I avoid","quote":"Avoid taking grapefruit, or grapefruit juice as they may interact with your medication and increase the risk of side-effects.","accessed":"2026-08-27"}],"brand_certs":null,"updated_at":"2026-08-29T16:16:31.341231+08:00"},"disclaimer":"kozen-x is not a medical device and does not give medical advice. it lists what published sources have written down. absence of a record is not the same as safe."}