Urinary stone disease affects 5 to 10% of the world's population, and it is one of the most common reasons for patients to visit a urologic clinic [1]. Furthermore, several studies have shown a worldwide trend toward an increasing prevalence of stone disease [2]; a trend that is also observed in Korea [3].

The goal of treating ureter stones is to achieve complete stone clearance with minimal patient morbidity. The standard treatment of ureter stones today is observation, medical therapy, shockwave lithotripsy (SWL), and ureteroscopic ureterolithotomy [4]. Medical expulsive therapy (MET) for ureter stones has especially gained increasing attention in the past decade, and there is growing evidence that MET can be efficacious to facilitate stone passage [5,6]. Various medications, such as calcium channel blockers (nifedipine and verapamil), α-blockers (tamsulosin, alfuzosin, doxazosin, and terazosin), and corticosteroids have been investigated [5,6]. Among these drugs, tamsulosin seems to be the most effective in facilitating stone clearance, both in patients undergoing expectant management and in those undergoing SWL. Several reports based on meta-analyses of randomized controlled trials (RCTs) support this fact [4-7].

However, the effectiveness of tamsulosin in Korean patients remains controversial. Although there are several RCTs on this subject, the majority of them were small, single-center studies [8-12]. Thus, even if the study showed a trend favoring tamsulosin, the results would be statistically insignificant or partly significant by subgroup analysis. There is currently no conclusive evidence that tamsulosin augments stone clearance in the Korean population.

The aim of this study was to conduct a meta-analysis of evidence from RCTs to assess the efficacy of tamsulosin in the treatment of ureter stones with or without SWL in Korean patients. Such evidence can aid physicians in making decisions in their clinical practice for the Korean population.

The initial search strategy identified 191 possible articles. Of these retrieved publications, 10 studies were conducted with Korean patients. Finally, a total of 6 articles were identified by our search strategy that met the eligible criteria (Fig. 1). There were no placebo-controlled studies. Two studies were for expectant treatment [8,10], three studies were for concomitant use with SWL [9,11,12], and one multicenter study was for both situations [14]. All studies used 0.2 mg tamsulosin per day. The characteristics and the Jadad scale scores of the 6 included studies are summarized in Table 1.

Funnel plot analysis demonstrated a mild publication bias (Fig. 2). No significant heterogeneity of the studies was detected (χ²=0.52, p=0.991). The forest plot represented in Fig. 3 shows that tamsulosin had an overall benefit for ureteral stone clearance over the control (RR, 1.43; 95% CI, 1.24 to 1.65). Subgroup analyses also demonstrated this significant effect in all situations (Figs. 4, 5). Tamsulosin treatment for lower ureter stones (RR, 1.50; 95% CI, 1.20 to 1.88) showed a relatively higher RR than for upper ureter stones (RR, 1.31; 95% CI, 1.02 to 1.68).

Tamsulosin is a combined α_1A- and α_1D-selective adrenergic antagonist. The adrenoceptors of these subtypes exist in the smooth muscle cells of the human ureter [15,16]. α₁-Blockers decrease tension, release the spasm of smooth muscles, lessen obstructions, and, consequently, enhance stone elimination in the ureter [17]. The distal ureter has the highest density of adrenoceptors, and the α_1D-receptor is the most common receptor present in all portions of the ureter [16,18]. Thus, tamsulosin, which is more selective for the α_1D-subtype, can be considered the most effective drug for MET among the α-blockers. Distal ureter stones in particular may be more affected by tamsulosin, because the highest density of α_1D-receptors can be found in the distal ureter. In this study, the RR for lower ureter stones (RR, 1.50; 95% CI, 1.20 to 1.88) was higher than that for upper ureter stones (RR, 1.31; 95% CI, 1.02 to 1.68) in the subgroup meta-analysis.

Several systematic reviews and meta-analyses have already demonstrated the effectiveness of tamsulosin in facilitating stone clearance in both patients being managed by watchful waiting and patients after SWL. Seitz et al. [5] reported a higher rate of stone expulsion in watchful waiting patients treated with either 0.2 mg (RR, 1.56; 95% CI, 1.21 to 2.03) or 0.4 mg (RR, 0.40; 95% CI, 1.28 to 1.54) of tamsulosin. They also demonstrated that SWL plus tamsulosin (0.4 mg) was more effective than SWL alone (RR, 1.38; 95% CI, 1.22 to 1.56) by meta-analysis [5]. In the meta-analysis performed by Zheng et al. [19], a 24% (RR, 1.24; 95% CI, 1.12 to 1.37) improvement was demonstrated in stone clearance by tamsulosin after SWL for renal and ureter stones. The tamsulosin group had a shorter expulsion time, lower analgesic requirements, and fewer colic episodes and adverse effects. A meta-analysis performed by Zhu et al. [7] showed a 16% RD of stone clearance after SWL, favoring the tamsulosin group over the control group. In addition, the expulsion time was shortened by 8 days in the tamsulosin group. However, no conclusive evidence exists of the effectiveness of tamsulosin for stone clearance in Korean patients.

The results of the present meta-analysis showed that a 0.2-mg dose of tamsulosin is effective in enhancing stone expulsion in Korean patients. The pooled analysis showed a 43% higher expulsion rate in the tamsulosin group than in the control group. Furthermore, similar results were obtained regardless of stone location or concomitant SWL. The RCTs included were mostly small, single-center studies; therefore, the results were inconclusive or partly significant. However, more conclusive evidence can be generated by a meta-analysis of these RCTs.

Similar to Korea, low-dose tamsulosin of 0.2 mg is the usual accepted dose in Japan. Two RCTs have evaluated the efficacy of a 0.2-mg tamsulosin dose in MET for ureteral stones in a Japanese population [20,21]. The low dose of tamsulosin shortened the stone expulsion time (15.66±6.14 days vs. 35.47±53.70 days, p=0.0424) in Japanese men with ureteral stones after SWL [20]. However, the stone expulsion rates were not significantly different (84.21% vs. 88.24%, p=0.34). Concerning the watchful waiting setting, 0.2 mg of tamsulosin significantly facilitates ureteral stone clearance (77% vs. 50%, p=0.002) in Japanese men [21]. These data further support our results, because all studies were conducted with the 0.2-mg dose of tamsulosin in a Far East Asian population.

Nevertheless, this meta-analysis could have possible limitations. Most studies were predominantly small, single-center trials that did not present the power calculations needed. Again, only one report described the randomization method used, and none of the reports presented dropouts. Owing to the qualities of the included studies, the pooled analysis could be affected. The other limitation was the publication bias. As the funnel plot suggested, studies with a negative result seemed to be unpublished.

We could not compare the duration of stone expulsion or the degree of colic pain. Only one study described the expulsion duration, and there was no standardized reporting protocol for pain. Furthermore, a study that evaluates pain and adverse events should be placebo-controlled and double-blinded. All included studies used an open-label protocol. We could not evaluate the dose-response relationship of tamsulosin in stone clearance that was suggested by other articles [7,19]. There is some evidence that a combination of tamsulosin and other agents, such as corticosteroids, might be more effective than α-blockers alone [22,23]. Future studies should focus on the dose-response relationship of tamsulosin and its combination with other drugs.

Despite the abovementioned potential limitations, this study provides the highest level of evidence to date from RCTs conducted with Korean patients. To the best of our knowledge, this is the first well-performed meta-analysis that has incorporated RCTs conducted with only Korean patients in a urologic field. These results support the use of tamsulosin for the ureteral stone patients who are commonly encountered in the urologic clinic.

The results of the present meta-analysis suggest that treatment with tamsulosin facilitates the stone expulsion rate for ureter stones with or without SWL in the Korean population. Despite the high level of evidence provided by this meta-analysis of RCTs, there was a lack of well-designed, high-quality prospective studies. More information should be assessed, and large-scale, multicenter, placebo-controlled RCTs should be performed in the future.