Naftopidil, an α1-adrenoceptor antagonist also known as an α1-blocker, is widely used to treat lower urinary tract symptoms (LUTS) in people with benign prostatic hyperplasia (BPH). Because prostate volume (PV) may determine the drug’s efficacy, Japanese researchers studied PV impact on the drug’s short-term use to conclude that an increased dose of naftopidil after a maintenance-dose period improved symptoms even in patients with large prostate volumes.

The study, “Does prostate volume affect the efficacy of α1D/A: Adrenoceptor antagonist naftopidil?,” was published in the journal Urology Annals.

Researchers administered 50 mg/day of naftopidil for four weeks to a group of LUTS/BPH patients, a dosage that was increased to 75 mg/day for an additional four weeks. The team then evaluated disease symptoms in patients with large PVs (≥40 mL) and small PVs (<40 mL) using the International Prostate Symptom Score (IPSS), IPSS storage symptoms, and IPSS quality-of-life score.

All patients improved at four and eight weeks after treatment. Importantly, IPSS and IPSS voiding symptoms (IPSS-VS) in those with large PVs were significantly improved at eight weeks compared with four weeks. Although the study did not evaluate whether a longer 50 mg/day maintenance therapy might improve drug’s efficacy in these patients, the authors think the results indicate that a higher naftopidil dose is a better treatment option in patients with large PVs.

“Our present study found that PV is a predictive factor affecting the efficacy of naftopidil 50 mg/day for subjective symptoms, particularly voiding symptoms, and the dose increase to 75 mg/day is effective for IPSS-VS. Therefore, 50 mg/day of naftopidil is the maintenance dose for LUTS/BPH patients with a small PV, and 75 mg/day dose increase therapy should be chosen for patients with a large PV,” the authors wrote.

These results reveal that an increased dose of naftopidil should be considered by clinicians when treating this specific subgroup of LUTS/BPH patients. “We currently have many kinds of treatment strategies, including dose increase in drug administration, switching to another drug or additional therapy with a different mechanism. In general, it is possible to increase the dose of naftopidil to 75 mg/day because the maintenance dose is 50 mg/day,” the authors concluded.