Doxazosin with Tadalafil Interaction Details

Brand Names Associated with Doxazosin

  • Cardura®
  • Cardura® XL
  • Doxazosin

Brand Names Associated with Tadalafil

  • Adcirca®
  • Cialis®
  • Entadfi® (as a combination product containing Finasteride, Tadalafil)
  • Tadalafil

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Last updated Jan 08, 2024

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Interaction Effect

Increased risk of hypotension

Interaction Summary

Caution should be exercised when doxazosin is coadministered with tadalafil. In drug-drug interaction studies, concomitant use of doxazosin and tadalafil was shown to augment the hypotensive effects of doxazosin . In patients taking doxazosin concomitantly, initiate tadalafil therapy at the lowest dose  and monitor the patient for symptomatic hypotensive effects.

Severity

Moderate

Onset

Rapid

Evidence

Established

How To Manage Interaction

Use doxazosin and tadalafil concomitantly with caution due to the potential for additive hypotensive effects. In patients taking doxazosin concomitantly, initiate tadalafil therapy at the lowest dose  and monitor for symptomatic hypotensive effects.

Mechanism Of Interaction

Additive hypotensive effects

Literature Reports

A) In subjects receiving concomitant tadalafil as a 20-mg single dose and doxazosin 8 mg/day, the blood pressure-lowering effect of doxazosin was augmented by tadalafil. The hypotensive effect was still present at 12 hours following administration and had generally disappeared at 24 hours. The combination resulted in a greater number of subjects with potentially clinically significant hypotension. In an additional study in which subjects were given tadalafil at the same dose and doxazosin 4 and 8 mg/day, augmentation of low blood pressure appeared unrelated to dosing times and resulted in a greater number of outliers for the combination than had been observed in the previous study. In further study in which doxazosin up to 4 mg/day was added to tadalafil 5 mg/day, there was again an augmentation of hypotensive response .

B) The coadministration of tadalafil and doxazosin significantly increased the hypotensive effect of doxazosin, whereas the coadministration of tadalafil and tamsulosin had no such effect. Two randomized, double-blind, placebo-controlled, crossover studies, each conducted in 18 healthy men, evaluated the hemodynamic interaction between tadalafil and 2 alpha-adrenergic antagonists, doxazosin and tamsulosin. In the doxazosin protocol, subjects were given doxazosin 8 mg daily for a minimum of 7 consecutive days to achieve a steady state concentration before administration of a single dose of either tadalafil 20 mg or placebo administered simultaneously with doxazosin. In the tamsulosin protocol, subjects were given tamsulosin 0.4 mg daily for a minimum of 7 consecutive days to achieve a steady state concentration before administration of a single dose of tadalafil 10 mg or 20 mg, or placebo administered 2 hours after the tamsulosin. A washout period of at least 7 days was utilized to separate treatment periods. The mean maximal post-baseline decrease in standing SBP (primary endpoint) was greater for the doxazosin plus tadalafil treatment arm than it was in the doxazosin plus placebo arm, with a mean difference of 9.8 mmHg (95% CI, 4.1 to 15.5 mmHg) between the 2 groups. The mean maximal post-baseline decrease in standing SBP was similar after tamsulosin plus tadalafil 10 mg compared with tamsulosin plus placebo (mean difference, 1.7 mmHg; 95% CI, -4.7 to 8.1 mmHg) and after tamsulosin plus tadalafil 20 mg compared with tamsulosin plus placebo (mean difference, 2.3 mmHg; 95% CI, -4.1 to 8.7 mmHg) .

Doxazosin Overview

  • Doxazosin is used in men to treat the symptoms of an enlarged prostate (benign prostatic hyperplasia or BPH), which include difficulty urinating (hesitation, dribbling, weak stream, and incomplete bladder emptying), painful urination, and urinary frequency and urgency. It is also used alone or in combination with other medications to treat high blood pressure. Doxazosin is in a class of medications called alpha-blockers. It relieves the symptoms of BPH by relaxing the muscles of the bladder and prostate. It lowers blood pressure by relaxing the blood vessels so that blood can flow more easily through the body.

  • High blood pressure is a common condition and when not treated, can cause damage to the brain, heart, blood vessels, kidneys and other parts of the body. Damage to these organs may cause heart disease, a heart attack, heart failure, stroke, kidney failure, loss of vision, and other problems. In addition to taking medication, making lifestyle changes will also help to control your blood pressure. These changes include eating a diet that is low in fat and salt, maintaining a healthy weight, exercising at least 30 minutes most days, not smoking, and using alcohol in moderation.

See More information Regarding Doxazosin

Tadalafil Overview

  • Tadalafil (Cialis) is used to treat erectile dysfunction (ED, impotence; inability to get or keep an erection), and the symptoms of benign prostatic hyperplasia (BPH; an enlarged prostate) which include difficulty urinating (hesitation, dribbling, weak stream, and incomplete bladder emptying), painful urination, and urinary frequency and urgency in adult men. Tadalafil (Adcirca) is used to improve the ability to exercise in people with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the lungs, causing shortness of breath, dizziness, and tiredness). Tadalafil is in a class of medications called phosphodiesterase (PDE) inhibitors. It works to treat erectile dysfunction by increasing blood flow to the penis during sexual stimulation. This increased blood flow can cause an erection. Tadalafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow more easily.

  • If you are taking tadalafil to treat erectile dysfunction, you should know that it does not cure erectile dysfunction or increase sexual desire. Tadalafil does not prevent pregnancy or the spread of sexually transmitted diseases such as human immunodeficiency virus (HIV).

See More information Regarding Tadalafil

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Definitions

Severity Categories

Contraindicated

These drugs, generally, should not be used together simultaneously due to the high risk of severe adverse effects. Combining these medications can lead to dangerous health outcomes and should be strictly avoided unless otherwise instructed by your provider.


Major

This interaction could result in very serious and potentially life-threatening consequences. If you are taking this drug combination, it is very important to be under close medical supervision to minimize severe side effects and ensure your safety. It may be necessary to change a medication or dosage to prevent harm.


Moderate

This interaction has the potential to worsen your medical condition or alter the effectiveness of your treatment. It's important that you are monitored closely and you potentially may need to make adjustments in your treatment plan or drug dosage to maintain optimal health.


Minor

While this interaction is unlikely to cause significant problems, it could intensify side effects or reduce the effectiveness of one or both medications. Monitoring for changes in symptoms and your condition is recommended, and adjustments may be made if needed to manage any increased or more pronounced side effects.

Onset

Rapid: Onset of drug interaction typically occurs within 24 hours of co-administration.

Delayed: Onset of drug interaction typically occurs more than 24 hours after co-administration.

Evidence

Level of documentation of the interaction.

Established: The interaction is documented and substantiated in peer-reviewed medical literature.

Theoretical: This interaction is not fully supported by current medical evidence or well-documented sources, but it is based on known drug mechanisms, drug effects, and other relevant information.

How To Manage The Interaction

Provides a detailed discussion on how patients and clinicians can approach the identified drug interaction as well as offers guidance on what to expect and strategies to potentially mitigate the effects of the interaction. This may include recommendations on adjusting medication dosages, altering the timing of drug administration, or closely monitoring for specific symptoms.

It's important to note that all medical situations are unique, and management approaches should be tailored to individual circumstances. Patients should always consult their healthcare provider for personalized advice and guidance on managing drug interactions effectively.

Mechanism Of Interaction

The theorized or clinically determined reason (i.e., mechanism) why the drug-drug interaction occurs.

Disclaimer: The information provided on this page is for informational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional regarding your specific circumstances and medical conditions.

Where Does Our Information Come From?

Information for our drug interactions is compiled from several drug compendia, including:

The prescribing information for each drug, as published on DailyMED, is also used. 

Individual drug-drug interaction detail pages contain references specific to that interaction. You can click on the reference number within brackets '[]' to see what reference was utilized.

The information posted is fact-checked by HelloPharmacist clinicians and reviewed quarterly.