From the Guidelines
Medical expulsion therapy (MET) is a non-surgical treatment approach that involves the use of medications, primarily alpha-blockers, to facilitate the spontaneous passage of ureteral stones by relaxing the ureter and reducing pain. The most commonly used medications for MET are alpha-blockers such as tamsulosin, silodosin, or alfuzosin, which work by relaxing the smooth muscle of the ureter, particularly at the ureterovesical junction, creating a wider passage for the stone 1. MET is most effective for distal ureteral stones measuring 5-10 mm in size, and patients with uncomplicated ureteral stones ≤10 mm should be offered observation, and those with distal stones of similar size should be offered MET with alpha-blockers 1. Some key points to consider when using MET include:
- The use of alpha-blockers as the preferred agents for MET, with a statistically significant 29% more patients passing their stones with alpha blocker therapy than did control patients 1
- The importance of maintaining adequate hydration and using pain medications as needed during MET
- The contraindications for MET, including severe obstruction, infection, intractable pain, or renal insufficiency, where urgent intervention may be necessary
- The physiological basis for MET, which lies in the presence of alpha-adrenergic receptors in the distal ureter, which when blocked, reduce peristaltic amplitude and frequency, decreasing intraureteral pressure and facilitating stone passage 1. Overall, MET is a viable treatment option for patients with ureteral stones, particularly those with distal stones ≤10 mm in size, and can help reduce the need for surgical intervention and improve patient outcomes.
From the Research
Definition of Medical Expulsive Therapy
Medical expulsive therapy (MET) is a treatment approach aimed at increasing the rate of stone expulsion along the ureter to avoid ureteral obstruction and reduce ureteral colic, thereby avoiding the need for surgical and more invasive interventions 2.
Key Objectives of Medical Expulsive Therapy
The primary goals of MET include:
- Increasing the rate of stone expulsion along the ureter
- Reducing ureteral colic
- Avoiding the need for surgical and more invasive interventions 2
Mechanisms and Agents Used in Medical Expulsive Therapy
MET typically involves the use of certain pharmacological agents, such as:
- Alpha-antagonists (e.g., alpha-blockers)
- Calcium channel blockers
- Phosphodiesterase type 5 enzyme inhibitors
- Beta-adrenoceptors
- 5-HT receptors 2 These agents work by relaxing the ureteral muscles, thereby facilitating the passage of stones.
Efficacy of Medical Expulsive Therapy
Studies have shown that MET can significantly improve stone expulsion rates, reduce the time to stone expulsion, and lower analgesia requirements for ureteral stones 3, 4. Additionally, MET may decrease colic events, narcotic use, and hospital visits, and may also reduce medical costs and prevent unnecessary surgeries and associated risks 5.
Emerging Pharmacological Targets for Medical Expulsive Therapy
Research is ongoing to identify new pharmacological targets for MET, including the use of mirabegron, a beta-3 adrenergic receptor agonist, which has shown promise in facilitating stone expulsion in distal ureteral stones 6.