Flomax dosage, forms, and strengths

Flomax is the brand name for the prescription drug tamsulosin hydrochloride. Flomax is FDA-approved to treat the signs and symptoms of an enlarged prostate, which is known as benign prostatic hyperplasia (BPH). BPH is an enlargement of the prostate that is not prostate cancer. Flomax can also be prescribed to aid in the passage of large kidney stones in adults. It may be used in children when the benefits of Flomax outweigh the risks. For both indications, Flomax is typically dosed at 0.4 mg once per day in capsule form, which is taken by mouth. 

RELATED: Get Flomax discounts | What is Flomax?

Flomax forms and strengths 

Flomax is only available in one dosage form:

• Capsule: 0.4 mg 

Flomax dosage for adults

Flomax is dosed at 0.4 mg once per day for the treatment of symptoms associated with benign prostatic hyperplasia and nephrolithiasis in adults. 

Flomax dosage for benign prostatic hyperplasia

Benign prostatic hyperplasia is a condition where the prostate is enlarged in men. The prostate gland surrounds the urethra, the tube that releases urine from the bladder. When the prostate gland is enlarged, the urethra becomes compressed, making it difficult and sometimes painful to urinate. Flomax does not shrink the prostate, but it does help alleviate the symptoms of benign prostatic hyperplasia. 

Flomax is in a class of drugs called alpha-blockers. Alpha-blockers, or alpha adrenoreceptor antagonists, are drugs that bind to the arteries in smooth muscle and cause the muscles to relax. By binding to the arteries in the smooth muscle of the bladder and prostate, Flomax relaxes the muscles, making it easier to urinate and improving urine flow. 

Flomax is taken as a 0.4 mg dose once per day for the treatment of urinary symptoms associated with BPH. The dose may be increased to 0.8 mg after two to four weeks if symptom improvement has not been reached. 

Flomax for nephrolithiasis 

Kidney stones (nephrolithiasis) are hard deposits of minerals and acidic salts that form in the kidney when the urine is too concentrated. These stones are usually passed in the urine and can sometimes cause severe pain in the abdomen, back, or urethra when they are being passed in the urine. 

Flomax is routinely used off-label in the treatment of symptomatic or painful kidney stones. By relaxing smooth muscles around the structures in the urinary system including the ureter and neck of the bladder, Flomax is used to facilitate the spontaneous (without medical intervention) expulsion of the stone.

Flomax is taken as a 0.4 mg dose once per day to facilitate kidney stone passage in symptomatic individuals. 

Flomax dosage for children

The FDA Pediatric Advisory Committee granted Flomax “pediatric exclusivity” in 2009. Flomax is not FDA-approved for use in children, however pediatric exclusivity allows a healthcare provider to safely prescribe or administer Flomax to children if the benefit of use outweighs any potential risks there may be associated with taking the drug. Ask your healthcare provider about the benefits and risks associated with Flomax if you are considering this drug for your child. 

In pediatric patients, Flomax is used to treat kidney stones or certain bladder problems like voiding dysfunction caused by neurogenic or anatomical abnormalities. In an article published in Nature Reviews Urology, Flomax has been shown to improve incontinence (lack of control of urination) and decrease the frequency of urination when used in children with neurologic or anatomic abnormalities.

* Dosage from Epocrates

** Dosage from Lexicomp and other references

Flomax dosage restrictions 

There are no defined dosage restrictions for Flomax in adults or children. Individuals with renal or liver impairment do not require dose adjustments. 

Flomax dosage for pets 

While Flomax is approved for use in humans, tamsulosin is commonly prescribed by veterinarians to treat the symptoms of BPH in companion animals like dogs and cats. Flomax can relax the muscles of the bladder and prostate, relieving pain and allowing urine to flow more easily. It can also be used to treat urethrospasm associated with inflammation or stones in the ureter. 

For veterinary use, Flomax is administered in a capsule by mouth. Capsules can be placed in food during feeding times or at the back of your pet’s tongue to aid in swallowing. Flomax is generally very well tolerated in animals, however, notify your veterinarian if your pet seems unwell while taking this medication. 

Flomax prescribed for veterinary use should not be taken by humans. If you accidentally take Flomax that was intended for animal use, contact the Poison Control Centers at 1-800-222-1222 or go to your local emergency room.

The typical veterinary dosages of Flomax are different for dogs and cats.

• Dogs: 0.1 - 0.2 mg/10 kg up to 0.4 mg maximum 

• Cats: 0.004 - 0.0006 mg/kg

How to take Flomax

Flomax should be taken by mouth, once per day, approximately 30 minutes after a meal. Flomax should be taken with food to ensure that the maximum concentration of the medication circulating in the bloodstream isn’t reached too quickly. It is recommended that Flomax be taken after the same meal each day. For example, if you wanted to take Flomax during your lunchtime, and you eat lunch at 12:30 pm most days, Flomax should be taken at 1:00 pm, after eating lunch each day. 

• Take your medicine as directed. Your dose may need to be changed to find what works best for you.

• Take this medicine 30 minutes after the same meal each day. Swallow the capsule whole. Do not crush, chew, or open it.

• Read and follow the patient instructions that come with this medicine. Talk to your healthcare provider if you have any questions.

• If you have missed a dose, take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose. If you forget to take this medicine for several days in a row, talk to your doctor before you start taking it again.

• Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light.

Flomax dosage FAQ

How long does it take Flomax to work?

Flomax usually begins to work rapidly, but in some individuals, improvement may take two to four weeks. In clinical studies, most Flomax users have been shown to have symptom improvement for at least five years while taking the medication. 

Flomax is not dosed by weight in adult or pediatric patients, although clinical studies suggest that weight-based dosing in pediatric patients may be worth consideration. 

How long does Flomax stay in your system?

Flomax has a half-life (the time it takes a drug to lose half of its biological activity) of approximately nine to 13 hours in healthy individuals and 14 to 15 hours for most people who actively take the drug. Most drugs are completely eliminated from the body in four to five half-lives, so traces of Flomax could be found in the body for up to three days after discontinuing use.

What happens if I miss a dose of Flomax?

If you miss a dose of Flomax, you should take the missed dose as soon as you remember. If it is close to the time for the next dose, skip the missed dose and take the next scheduled dose. After that, you can go back to your regular dosing schedule. Do not take double the dose or an extra dose to make up for a missed dose. 

How long can you take Flomax?

Long-term treatment with Flomax is considered safe and well-tolerated in most people with lower urinary tract symptoms and BPH. There is no set period of time after which Flomax must be discontinued. As long as symptom relief is adequate and there are no severe drug-related side effects, Flomax usage may be continued for as long as the patient and provider as a team feel is appropriate. 

How do I stop taking Flomax?

Pilot studies suggest that continuous use of Flomax may not be necessary for long-term symptom relief. However, Flomax should not be discontinued without seeking medical advice. If you discontinue the use of Flomax, you may experience a recurrence of symptoms. If for some reason you stop taking Flomax for several days, talk to your healthcare provider before you start taking it again. 

If Flomax needs to be discontinued due to unpleasant side effects, your healthcare provider may prescribe an alternative alpha-1 blocker such as Hytrin (terazosin), Uroxatral (alfuzosin), Rapaflo (silodosin), Minipress (prazosin), or Cardura (doxazosin). Another class of medications that are commonly used for BPH is 5-alpha-reductase inhibitors (finasteride and dutasteride). Talk to your healthcare provider about whether alternative options to Flomax may be right for you. 

Can you overdose on Flomax?

It is possible to overdose on Flomax. Too much Flomax can lead to low blood pressure. Signs of overdose include dizziness, headaches, lightheadedness, fainting, chest pain, or rapid heartbeat. You should contact the Poison Control Centers at 1-800-222-1222 or go to your local emergency room if you accidentally take too much medication.

What interacts with Flomax?

Certain foods, like grapefruit products and alcohol, may actually increase the action of Flomax and increase the chance that negative side effects may occur. Notify your healthcare provider if you feel unwell when eating certain foods or if you experience an allergic reaction while taking Flomax. 

There are also several important drug interactions to be aware of before taking Flomax. 

Flomax should not be taken with other medications that can cause hypotension, with other alpha-adrenergic blocking agents, or with medications that are strong inhibitors of CYP3A4 (e.g, ketoconazole). 

Flomax should be used with caution in combination with drugs that are moderate inhibitors of CYP3A4 (e.g., erythromycin), strong (e.g., paroxetine) or moderate (e.g., terbinafine) inhibitors of CYP2D6, in individuals who are CYP2D6 poor metabolizers, in combination with other cytochrome P450 inhibitors (e.g., cimetidine), or with warfarin. 

It is important to inform your healthcare provider if you are taking any of the medications above as well as to review your entire health history and any medical conditions you may have before starting Flomax.

What are the side effects of Flomax?

Flomax is routinely recommended to be taken with food as it is known to be “food sensitive,” which means the serum concentration is affected by a fed compared to fasted state. When taken with food, the serum concentration of Flomax is lower, reducing the probability that any potential negative side effects may occur.

Users of Flomax may experience a number of common reactions including:

• Orthostatic hypotension (reduced blood pressure with suddenly standing upright)

• Syncope (passing out)

• Severe skin rashes

• Hives

• Dizziness

• Rhinitis or a runny nose

• Infection

• Back pain

• Cough

• Sinusitis 

• Asthenia (abnormal weakness or lack of energy)

• Pharyngitis (sore throat)

• Somnolence (tiredness)

• Decreased libido (lowered sex drive)

Other Flomax warnings include:

• Priapism: A rare but serious side effect when the penis stays erect for longer than four hours without sexual stimulation. This occurs more frequently in men who take Flomax with PDE5 inhibitors like Viagra (sildenafil) or Cialis (tadalafil).

• Abnormal ejaculation: Some men taking Flomax may experience erectile dysfunction, ejaculatory dysfunction, or abnormal ejaculation. Types of ejaculatory problems may include decreased frequency, delay, dryness, decreased strength/force, decreased volume, decreased pleasure, or pain with ejaculation.

• Intraoperative floppy iris syndrome (IFIS): Some patients taking Flomax can experience iris billowing, pupil constriction, and iris prolapse during cataract and glaucoma surgery, even when they had discontinued Flomax prior to surgery. If you plan on having cataract surgery, tell your ophthalmologist that you have taken Flomax and inform your primary healthcare provider prior to having the surgery.

• Prostate cancer: BPH and prostate cancer usually co-exist. Flomax can alleviate the symptoms of BPH, potentially masking the evidence of prostate cancer. All men should be screened for the presence of prostate cancer prior to treatment with Flomax and at regular intervals afterward. 

• Sulfa allergy: Allergic reactions to Flomax in individuals with sulfa allergy have been reported. Therefore, caution should be used when administering Flomax to any individual with a history of a serious or life-threatening sulfa allergy.

What happens when you mix Flomax and alcohol?

Alcohol does not directly affect Flomax. However, it is possible that alcohol can lower your blood pressure making you feel faint or dizzy while taking Flomax. 

Is it safe to take Flomax during pregnancy and breastfeeding?

Flomax is not approved for use in women. The use of Flomax as expulsive therapy for kidney stones in women is controversial, however may provide relief when compared to placebo. Retrospective studies have shown no difference in fetal outcomes for women taking Flomax compared to those who were not. While there is no published clinical trial data on the effects of tamsulosin HCl use during human pregnancy or while breastfeeding, according to the FDA, animal studies revealed no evidence of harm to the developing fetus. If you are pregnant or nursing, talk with your healthcare provider about the benefits and risks of taking Flomax. 

Related resources for Flomax dosages:

• Flomax drug information

• Pediatric dysfunctional voiding treated with tamsulosin

• Adult dosing for Flomax

• Pediatric dosing for Flomax

• Tamsulosin: current clinical experience

• Drugs used to manage urinary incontinence in dogs and cats

• Grapefruit-medication interactions

• IFIS: Know the risks and manage the signs

• Long-term efficacy and safety of tamsulosin for BPH

• Population pharmacokinetics of tamsulosin hydrochloride in pediatric patients with neuropathic and non-neuropathic bladder

• Long-term use of tamsulosin to treat lower urinary tract symptoms/BPH

• Discontinuation of tamsulosin treatment in men with lower urinary tract symptoms: a pilot study

• Flomax adverse reactions

• Tamsulosin for treatment of lower urinary tract symptoms in women

• Safety and efficacy of Tamsulosin as medical expulsive therapy in pregnancy