Side Effects of Flomax (tamsulosin)

Flomax (tamsulosin) is an alpha-blocker used to treat men who are having difficulty urinating because of enlarged prostates from benign prostatic hyperplasia (BPH).

Common side effects of Flomax include

• anemia (decreased red blood cells),
• decreased white blood cells,
• nausea,
• vomiting,
• abnormal taste,
• increased triglycerides,
• weakness,
• low blood pressure,
• dizziness,
• fainting,
• headache,
• abdominal pain,
• weight loss,
• muscle pain,
• abnormal ejaculation,
• upper respiratory tract infections, and
• rash.

Serious side effects of Flomax include

• low blood pressure when standing (orthostatic hypotension),
• prolonged erection (priapism), and
• an eye problem called intraoperative floppy iris syndrome (IFIS).

Drug interactions of Flomax include erythromycin, ketoconazole, paroxetine, cimetidine, ritonavir, lopinavir, and other drugs that reduce the elimination of drugs by liver enzymes because the elimination of Flomax from the body may be reduced by these drugs. 

Reduced elimination may lead to increased side effects of Flomax. PDE-5 inhibitors (for example, vardenafil, sildenafil, tadalafil) add to the blood pressure lowering effects of Flomax and may result in severe blood pressure reduction. 

Flomax is used only in men. Flomax is not prescribed for women and is not intended for use during pregnancy or while breastfeeding. 

The most common adverse effects of Flomax are

• anemia (decreased red blood cells),
• decreased white blood cells,
• nausea,
• vomiting,
• abnormal taste,
• increased triglycerides, and
• weakness.

Other side effects include

• low blood pressure,
• dizziness,
• fainting,
• headache,
• abdominal pain,
• weight loss,
• muscle pain,
• abnormal ejaculation,
• upper respiratory tract infections, and
• rash.

More serious side effects of Flomax

The following have been observed in male patients during Flomax treatment:

• orthostatic hypotension (low blood pressure when rising from sitting or lying down position),
• priapism (prolonged erection), and an eye problem called intraoperative floppy iris syndrome (IFIS).

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reactions rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. The incidence of treatment-emergent adverse events has been ascertained from six short-term U.S. and European placebo-controlled clinical trials in which daily doses of 0.1 to 0.8 mg Flomax capsules were used.

These studies evaluated safety in 1783 patients treated with Flomax capsules and 798 patients administered placebo. Table 1 summarizes the treatment-emergent adverse events that occurred in ≥2% of patients receiving either Flomax capsules 0.4 mg or 0.8 mg and at an incidence numerically higher than that in the placebo group during two 13-week U.S. trials (US92-03A and US93-01) conducted in 1487 men.

Table 1: Treatment-Emergent* Adverse Events Occurring in ≥2% of Flomax Capsules or Placebo Patients in Two U.S. Short-Term Placebo-Controlled Clinical Studies

Signs And Symptoms Of Orthostasis

• In the two U.S. studies, symptomatic postural hypotension was reported by 0.2% of patients (1 of 502) in the 0.4 mg group, 0.4% of patients (2 of 492) in the 0.8 mg group, and by no patients in the placebo group.
• Syncope was reported by 0.2% of patients (1 of 502) in the 0.4 mg group, 0.4% of patients (2 of 492) in the 0.8 mg group, and 0.6% of patients (3 of 493) in the placebo group.
• Dizziness was reported by 15% of patients (75 of 502) in the 0.4 mg group, 17% of patients (84 of 492) in the 0.8 mg group, and 10% of patients (50 of 493) in the placebo group. Vertigo was reported by 0.6% of patients (3 of 502) in the 0.4 mg group, 1% of patients (5 of 492) in the 0.8 mg group, and by 0.6% of patients (3 of 493) in the placebo group.
• Multiple testing for orthostatic hypotension was conducted in a number of studies. Such a test was considered positive if it met one or more of the following criteria:
  • (1) a decrease in systolic blood pressure of ≥20 mmHg upon standing from the supine position during the orthostatic tests;
  • (2) a decrease in diastolic blood pressure ≥10 mmHg upon standing, with the standing diastolic blood pressure <65 mmHg during the orthostatic test;
  • (3) an increase in pulse rate of ≥20 bpm upon standing with a standing pulse rate ≥100 bpm during the orthostatic test; and
  • (4) the presence of clinical symptoms (faintness, lightheadedness/lightheaded, dizziness, spinning sensation, vertigo, or postural hypotension) upon standing during the orthostatic test.
• Following the first dose of double-blind medication in Study 1, a positive orthostatic test result at 4 hours post-dose was observed in 7% of patients (37 of 498) who received Flomax capsules 0.4 mg once daily and in 3% of the patients (8 of 253) who received placebo.
• At 8 hours post-dose, a positive orthostatic test result was observed for 6% of the patients (31 of 498) who received Flomax capsules 0.4 mg once daily and 4% (9 of 250) who received placebo (Note: patients in the 0.8 mg group received 0.4 mg once daily for the first week of Study 1).
• In Studies 1 and 2, at least one positive orthostatic test result was observed during the course of these studies for 81 of the 502 patients (16%) in the Flomax capsules 0.4 mg once-daily group, 92 of the 491 patients (19%) in the Flomax capsules 0.8 mg once-daily group, and 54 of the 493 patients (11%) in the placebo group.
• Because orthostasis was detected more frequently in Flomax capsule-treated patients than in placebo recipients, there is a potential risk of syncope.

Abnormal Ejaculation

• Abnormal ejaculation includes ejaculation failure, ejaculation disorder, retrograde ejaculation, and ejaculation decrease.
• As shown in Table 1, abnormal ejaculation was associated with Flomax capsules administration and was dose-related in the U.S. studies.
• Withdrawal from these clinical studies of Flomax capsules because of abnormal ejaculation was also dose-dependent, with 8 of 492 patients (1.6%) in the 0.8 mg group and no patients in the 0.4 mg or placebo groups discontinuing treatment due to abnormal ejaculation.

Laboratory Tests

• No laboratory test interactions with Flomax capsules are known. Treatment with Flomax capsules for up to 12 months had no significant effect on prostate-specific antigen (PSA).

Postmarketing Experience

The following adverse reactions have been identified during post-approval use of Flomax capsules. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. Decisions to include these reactions in labeling are typically based on one or more of the following factors:

• (1) seriousness of the reaction,
• (2) frequency of reporting, or
• (3) strength of causal connection to Flomax capsules.

Allergic-type reactions such as skin rash, urticaria, pruritus, angioedema, and respiratory symptoms have been reported with positive rechallenge in some cases. Priapism has been reported rarely.

 Infrequent reports of dyspnea, palpitations, hypotension, atrial fibrillation, arrhythmia, tachycardia, skin desquamation including reports of Stevens-Johnson syndrome, erythema multiforme, dermatitis exfoliative, constipation, vomiting, dry mouth, visual impairment, and epistaxis have been received during the postmarketing period.

During cataract and glaucoma surgery, a variant of small pupil syndrome known as Intraoperative Floppy Iris Syndrome (IFIS) has been reported in association with alpha₁ blocker therapy.

Cytochrome P450 Inhibition

Strong And Moderate Inhibitors Of CYP3A4 Or CYP2D6

• Tamsulosin is extensively metabolized, mainly by CYP3A4 and CYP2D6.
• Concomitant treatment with ketoconazole (a strong inhibitor of CYP3A4) resulted in an increase in the Cmax and AUC of tamsulosin by a factor of 2.2 and 2.8, respectively. The effects of concomitant administration of a moderate CYP3A4 inhibitor (e.g., erythromycin) on the pharmacokinetics of Flomax have not been evaluated.
• Concomitant treatment with paroxetine (a strong inhibitor of CYP2D6) resulted in an increase in the Cmax and AUC of tamsulosin by a factor of 1.3 and 1.6, respectively. A similar increase in exposure is expected in CYP2D6 poor metabolizers (PM) as compared to extensive metabolizers (EM).
• Since CYP2D6 PMs cannot be readily identified and the potential for significant increase in tamsulosin exposure exists when Flomax 0.4 mg is co-administered with strong CYP3A4 inhibitors in CYP2D6 PMs, Flomax 0.4 mg capsules should not be used in combination with strong inhibitors of CYP3A4 (e.g., ketoconazole).
• The effects of concomitant administration of a moderate CYP2D6 inhibitor (e.g., terbinafine) on the pharmacokinetics of Flomax have not been evaluated.
• The effects of co-administration of both a CYP3A4 and a CYP2D6 inhibitor with Flomax capsules have not been evaluated. However, there is a potential for significant increase in tamsulosin exposure when Flomax 0.4 mg is co-administered with a combination of both CYP3A4 and CYP2D6 inhibitors.

Cimetidine

• Treatment with cimetidine resulted in a significant decrease (26%) in the clearance of tamsulosin hydrochloride, which resulted in a moderate increase in tamsulosin hydrochloride AUC (44%).

Other Alpha Adrenergic Blocking Agents

• The pharmacokinetic and pharmacodynamic interactions between Flomax capsules and other alpha adrenergic blocking agents have not been determined; however, interactions between Flomax capsules and other alpha adrenergic blocking agents may be expected.

PDE5 Inhibitors

• Caution is advised when alpha adrenergic blocking agents including Flomax are co-administered with PDE5 inhibitors. Alpha-adrenergic blockers and PDE5 inhibitors are both vasodilators that can lower blood pressure. Concomitant use of these two drug classes can potentially cause symptomatic hypotension.

Warfarin

• A definitive drug-drug interaction study between tamsulosin hydrochloride and warfarin was not conducted. Results from limited in vitro and in vivo studies are inconclusive. Caution should be exercised with concomitant administration of warfarin and Flomax capsules.

Nifedipine, Atenolol, Enalapril

• Dosage adjustments are not necessary when Flomax capsules are administered concomitantly with nifedipine, atenolol, or enalapril.

Digoxin And Theophylline

• Dosage adjustments are not necessary when a Flomax capsule is administered concomitantly with digoxin or theophylline.

Furosemide

• Flomax capsules had no effect on the pharmacodynamics (excretion of electrolytes) of furosemide. While furosemide produced an 11% to 12% reduction in tamsulosin hydrochloride Cmax and AUC, these changes are expected to be clinically insignificant and do not require adjustment of the Flomax capsules dosage.