What is the role of active medical expulsive therapy (MET) in the emergency treatment of nephrolithiasis?

Updated: Jan 13, 2020
  • Author: Chirag N Dave, MD; Chief Editor: Bradley Fields Schwartz, DO, FACS  more...
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The traditional outpatient treatment approach detailed above has recently been improved with the application of a more aggressive treatment approach known as active medical expulsive therapy (MET). Many randomized trials have confirmed the efficacy of MET in reducing the pain of stone passage, increasing the frequency of stone passage, and reducing the need for surgery. [55, 56, 57, 58, 59, 60, 61, 62]

MET should be considered in any patient with a reasonable probability of stone passage. Given that stones smaller than 3 mm are already associated with an 85% chance of spontaneous passage, MET is probably most useful for stones 3-10 mm in size, though many urologists would argue for the addition of MET with alpha-blockers even with smaller or proximal stones due to the relative in-expense and few side effects for patients undergoing trial of passage if it can potentially avoid need for operative intervention. Overall, MET is associated with a 65% greater likelihood of stone passage with greatest benefits seen with > 5 mm distal stones. [63, 1, 64]

The original rationale for MET was based on the possible causes of failure to spontaneously pass a stone, including ureteral stricture, muscle spasm, local edema, inflammation, and infection. Various common drugs were considered that would potentially benefit these problems, improve spontaneous stone passage, and alleviate renal colic discomfort.

Although NSAIDs have ureteral-relaxing effects and, as such, can be considered a form of MET, they are not generally considered MET. Corticosteroids have also been considered and tested for MET, though they are not used in current practices due to concerns about unwanted potential side effects.breakthrough pain

The calcium channel blocker nifedipine is indicated for angina, migraine headaches, Raynaud disease, and hypertension, but it can also reduce muscle spasms in the ureter, which helps reduce pain and facilitate stone passage. Ureteral smooth muscle uses an active calcium pump to produce contractions, so a calcium channel blocker such as nifedipine would be expected to relax ureteral muscle spasms.

The alpha-blockers, such as terazosin, and the alpha-1 selective blockers, such as tamsulosin, also relax the musculature of the ureter and lower urinary tract, markedly facilitating passage of ureteral stones. Some literature suggests that the alpha-blockers are more effective in this setting than the calcium channel blockers, and most practitioners currently use alpha-blockers preferentially over calcium channel blockers and current guidelines suggest alpha-blockers as the medication of choice for MET.

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