Understanding the Medications: Finasteride vs. Terazosin
To determine the safety and effectiveness of combining these drugs, it's crucial to understand their distinct mechanisms of action. Finasteride and terazosin address benign prostatic hyperplasia (BPH) through different pharmacological pathways.
How Finasteride Works
Finasteride is a 5-alpha reductase inhibitor (5-ARI). The enzyme 5-alpha reductase is responsible for converting testosterone into dihydrotestosterone (DHT), a hormone that plays a key role in the growth of the prostate. By inhibiting this enzyme, finasteride reduces DHT levels, which in turn leads to a gradual shrinking of the enlarged prostate gland.
This process is slow and can take several months—sometimes up to six months—for patients to experience a noticeable improvement in symptoms. Because it targets the underlying cause of prostate enlargement, it can be effective in preventing long-term complications like acute urinary retention or the need for surgery.
How Terazosin Works
Terazosin is an alpha-1 adrenergic receptor blocker, or alpha-blocker. It works by relaxing the smooth muscles in the prostate, bladder neck, and blood vessels. This relaxation increases urine flow and provides rapid relief from the urinary symptoms of BPH, such as hesitancy, weak stream, and incomplete emptying. The effects of terazosin are typically felt much faster than finasteride, often within a few weeks of starting treatment.
Terazosin is also used to treat high blood pressure, and patients taking it should be aware of potential side effects like dizziness and orthostatic hypotension (a drop in blood pressure when standing up).
The Clinical Evidence on Co-Administration
Several clinical trials have investigated the safety and efficacy of combining finasteride and terazosin. The results, particularly regarding efficacy, are mixed and depend on the patient population.
A significant randomized, placebo-controlled study published in The New England Journal of Medicine in 1996 followed 1,229 men with BPH for one year. The study compared groups receiving placebo, finasteride alone, terazosin alone, and the combination of both. The primary findings were notable:
- Terazosin alone was effective in reducing symptoms and increasing urinary flow rates.
- Finasteride alone was not significantly more effective than placebo for the overall study population.
- Combination therapy was no more effective than terazosin alone.
A secondary analysis of this study, however, suggested a more pronounced benefit from the combination in men with larger prostate volumes. This highlights the importance of individual patient characteristics in determining the most appropriate treatment. Furthermore, other studies, like the MTOPS trial (using a different alpha-blocker, doxazosin), have shown an additive benefit from combination therapy.
Pharmacokinetic Interaction
One study involving 90 healthy men reported a statistically significant pharmacokinetic interaction between finasteride and terazosin. In this study, co-administration with terazosin led to significantly higher Cmax and AUC (measures of drug concentration in the body) for finasteride compared to finasteride alone. The clinical significance of this specific interaction, however, remains to be definitively determined. Other, smaller studies found no statistically significant alterations. Based on the available data, drug information resources generally conclude that no special precautions are recommended at this time, though monitoring is always advised.
Comparison of Finasteride and Terazosin
| Feature | Finasteride | Terazosin |
|---|---|---|
| Drug Class | 5-alpha reductase inhibitor (5-ARI) | Alpha-1 adrenergic receptor blocker |
| Mechanism | Inhibits conversion of testosterone to DHT, which shrinks the prostate gland over time. | Relaxes smooth muscles in the prostate and bladder neck for rapid symptom relief. |
| Onset of Action | Slow; can take up to 6 months for noticeable effect. | Rapid; provides symptom relief within weeks. |
| Primary Use | Treatment of BPH and male pattern baldness. | Treatment of BPH and high blood pressure. |
| Primary Goal | Reduce prostate size and prevent long-term complications. | Improve urinary flow and relieve bothersome urinary symptoms. |
| Common Side Effects | Sexual side effects (erectile dysfunction, decreased libido, reduced ejaculate). | Dizziness, weakness, headache, and orthostatic hypotension. |
| Combination Effect | Can increase finasteride exposure, but clinical significance is uncertain. | Can potentially increase side effects, such as dizziness, compared to monotherapy. |
Important Safety Considerations
Before starting a combination of finasteride and terazosin, patients must discuss their full medical history with a doctor. This includes existing conditions like hypertension and any history of depression or suicidal thoughts.
Finasteride-Specific Precautions
- Women and Children: Finasteride is not for use in women or pediatric patients. Pregnant women or those who may become pregnant should not handle crushed or broken tablets due to the risk of birth defects in male babies.
- PSA Testing: Finasteride can affect prostate-specific antigen (PSA) test results, which are used to screen for prostate cancer. It is crucial to inform your doctor that you are taking finasteride if undergoing a PSA test.
- Mental Health: Monitor for psychiatric side effects, including depression and suicidal thoughts. Some sexual side effects, like decreased libido and erectile dysfunction, have been reported to persist even after stopping treatment.
Terazosin-Specific Precautions
- Dizziness and Hypotension: Due to the risk of orthostatic hypotension, terazosin is often started at a low dose and taken at bedtime. This helps minimize the risk of dizziness and fainting, especially when standing up quickly.
- Alcohol Interaction: Concomitant use of alcohol can increase the hypotensive effects of alpha-blockers like terazosin and should be avoided or limited.
Conclusion
Yes, finasteride and terazosin can be taken together under a doctor's supervision for the treatment of BPH. Their different mechanisms of action—finasteride shrinking the prostate over time and terazosin providing rapid symptomatic relief—are complementary. However, it is important to be aware of the pharmacokinetic interaction, mixed clinical efficacy results (especially for certain patient populations), and the unique side effect profile of each drug. Patients should have a thorough discussion with their healthcare provider about their specific condition, potential risks, and the expected benefits of combination therapy. For some individuals, one medication may be more appropriate or effective than the combination.
Potential benefits of combination therapy
While early studies showed no added benefit for the combination in some populations, other research suggests that for patients with larger prostates or those who don't respond adequately to monotherapy, the combined approach might be beneficial. The decision to use combination therapy is highly individualized and should be made in consultation with a urologist or other medical professional, weighing the potential benefits against the risks and side effects.
Authoritative resource
For more detailed information on finasteride and its prescribing guidelines, refer to the FDA-approved labeling available on Drugs.com.
