Chemical formula: C₂₅H₃₂F₃N₃O₄ Molecular mass: 495.535 g/mol PubChem compound: 5312125
Silodosin interacts in the following cases:
Minimal pharmacodynamic interactions have been observed between silodosin and maximum doses of sildenafil or tadalafil. In a placebo-controlled study in 24 subjects 45-78 years of age receiving silodosin, the co-administration of sildenafil 100 mg or tadalafil 20 mg induced no clinically meaningful mean decreases in systolic or diastolic blood pressure, as assessed by orthostatic tests (standing versus supine).
In the subjects over 65 years, the mean decreases at the various time points were between 5 and 15 mmHg (systolic) and 0 and 10 mmHg (diastolic). Positive orthostatic tests were only slightly more common during co-administration; however, no symptomatic orthostasis or dizziness occurred. Patients taking PDE-5 inhibitors concomitantly with silodosin should be monitored for possible adverse reactions.
There is inadequate information about the safe use of silodosin in association with other α-adrenoreceptor antagonists. Consequently, the concomitant use of other α-adrenoreceptor antagonists is not recommended.
In an interaction study, a 3.7-fold increase in maximum silodosin plasma concentrations and a 3.1-fold increase in silodosin exposure (i.e. AUC) were observed with concurrent administration of a potent CYP3A4 inhibitor (ketoconazole 400 mg). Concomitant use with potent CYP3A4 inhibitors (such as ketoconazole, itraconazole, ritonavir or cyclosporine) is not recommended.
When silodosin was co-administered with a CYP3A4 inhibitor of moderate potency such as diltiazem, an increase in silodosin AUC of approximately 30% was observed, but Cmax and half-life were not affected. This change is clinically not relevant and no dose adjustment is required.
A starting dose of 4 mg once daily is recommended in patients with moderate renal impairment (CLCR ≥30 to <50 ml/min), which may be increased to 8 mg once daily after one week of treatment, depending on the individual patient’s response.
The use of silodosin in patients with severe renal impairment (CLCR <30 ml/min) is not recommended.
As no data are available, the use in patients with severe hepatic impairment is not recommended.
In the clinical study program, many patients were on concomitant antihypertensive therapy (mostly agents acting on the renin-angiotensin system, beta-blockers, calcium antagonists and diuretics) without experiencing an increase in the incidence of orthostatic hypotension. Nevertheless, caution should be exercised when starting concomitant use with antihypertensives and patients should be monitored for possible adverse reactions.
In clinical studies, the occurrence of ejaculation with reduced or no semen has been observed during treatment with silodosin, due to the pharmacodynamic properties of silodosin. Before starting treatment, the patient should be informed that this effect may occur, temporarily affecting male fertility.
The incidence of orthostatic effects with silodosin is very low. However, a reduction in blood pressure can occur in individual patients, leading in rare cases to syncope. At the first signs of orthostatic hypotension (such as postural dizziness), the patient should sit or lie down until the symptoms have disappeared. In patients with orthostatic hypotension, treatment with silodosin is not recommended.
IFIS (a variant of small pupil syndrome) has been observed during cataract surgery in some patients on α1-blockers or previously treated with α1-blockers. This may lead to increased procedural complications during the operation.
The initiation of therapy with silodosin is not recommended in patients for whom cataract surgery is scheduled. Discontinuing treatment with an α1-blocker 1-2 weeks prior to cataract surgery has been recommended, but the benefit and duration of stopping the therapy prior to cataract surgery has not yet been established.
During pre-operative assessment, eye surgeons and ophthalmic teams should consider whether patients scheduled for cataract surgery are being or have been treated with silodosin, in order to ensure that appropriate measures will be in place to manage IFIS during surgery.
Not applicable as silodosin is intended for male patients only.
Not applicable as silodosin is intended for male patients only.
In clinical studies, the occurrence of ejaculation with reduced or no semen has been observed during treatment with silodosin, due to the pharmacodynamic properties of silodosin. Before starting treatment, the patient should be informed that this effect may occur, temporarily affecting male fertility.
Silodosin has minor or moderate influence on the ability to drive and use machines. Patients should be informed about the possible occurrence of symptoms related to postural hypotension (such as dizziness) and should be cautioned about driving or operating machines until they know how silodosin will affect them.
The safety of silodosin has been evaluated in four Phase II-III double-blind controlled clinical studies (with 931 patients receiving silodosin 8 mg once daily and 733 patients receiving placebo) and in two long-term open-label extension phase studies. In total, 1,581 patients have received silodosin at a dose of 8 mg once daily, including 961 patients exposed for at least 6 months and 384 patients exposed for 1 year.
The most frequent adverse reactions reported with silodosin in placebo controlled clinical studies and during long-term use were ejaculatory disorders such as retrograde ejaculation and anejaculation (ejaculatory volume reduced or absent), with a frequency of 23%. This may temporarily affect male fertility. It is reversible within a few days upon discontinuation of treatment.
In the list below, adverse reactions reported in all clinical studies and in the worldwide post-marketing experience for which a reasonable causal relationship exists are listed by MedDRA system organ class and frequency: very common (≥1/10); common (≥1/100 to <1/10); uncommon (≥1/1,000 to <1/100); rare (≥1/10,000 to <1/1,000); very rare (<1/10,000), not known (cannot be estimated from available data). Within each frequency grouping the observed adverse reactions are presented in order of decreasing seriousness.
Very rare: Allergic-type reactions including facial swelling, swollen tongue and pharyngeal oedema1
Uncommon: Libido decreased
Common: Dizziness
Rare: Syncope, Loss of consciousness1
Uncommon: Tachycardia1
Rare: Palpitations1
Common: Orthostatic hypotension
Uncommon: Hypotension1
Common: Nasal congestion
Common: Diarrhoea
Uncommon: Nausea Dry mouth
Uncommon: Abnormal liver function tests1
Uncommon: Skin rash1, Pruritus1, Urticaria1, Drug eruption1
Very common: Ejaculatory disorders, including retrograde ejaculation, anejaculation
Uncommon: Erectile dysfunction
Not known: Intraoperative, Floppy Iris Syndrome
1 adverse reactions from spontaneous reporting in the worldwide post-marketing experience (frequencies calculated from events reported in Phase I-IV clinical trials and non-interventional studies).
The incidence of orthostatic hypotension in placebo-controlled clinical studies was 1.2% with silodosin and 1.0% with placebo. Orthostatic hypotension may occasionally lead to syncope.
IFIS has been reported during cataract surgery.
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