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Skeletal Muscle Relaxants

Skeletal muscle relaxants (SMRs) are used in urology to relax three different anatomic targets: the external urethral sphincter (in detrusor sphincter dyssynergia), the pelvic floor musculature (in high-tone pelvic floor dysfunction and myofascial pelvic pain), and indirectly the detrusor (via spinal-cord-acting agents). Botulinum toxin A is covered separately: evidence and licensing differ between intradetrusor treatment and off-label sphincter or pelvic-floor injection. This page addresses systemic SMRs (baclofen, tizanidine, dantrolene, diazepam, cyclobenzaprine) and compounded vaginal diazepam, whose urologic evidence is generally limited.[1][2]

For agents covered separately:

Anatomic targets​

TargetMuscle typeAgent classes
External urethral sphincterStriatedBaclofen (oral, intrathecal); tizanidine; dantrolene; intrasphincteric BoNT-A
Pelvic floor (levator ani, obturator internus)StriatedDiazepam (oral, vaginal); cyclobenzaprine (off-label); BoNT-A injection
Detrusor (indirectly)SmoothIntrathecal baclofen (spinal-cord effect on EUS motoneurons and detrusor reflexes); intradetrusor BoNT-A
Bladder neck / prostate / ureterSmoothAlpha-blockers (covered separately)

Baclofen — for DSD and neurogenic spasticity​

A GABA-B receptor agonist used principally for limb spasticity in spinal-cord pathology, with possible secondary effects on detrusor sphincter dyssynergia (DSD) and bladder reflexes.[3]

Mechanism in urology​

  • Oral: central GABA-B agonism depresses pudendal-to-pudendal nerve reflex via spinal cord presynaptic hyperpolarization leading to reduced external urethral sphincter resistance[4]
  • Intrathecal (ITB): in a 10-patient study of severe spasticity from spinal-cord pathology, ITB abolished DSD in 40%.[5] In spinal-cord-transected rats, baclofen applied at L6–S1 relaxed the urethra during isovolumetric bladder contractions at doses below those inhibiting bladder contractions; suppression of EUS motoneurons and C-fiber bladder afferents were proposed mechanisms.[6]

Oral baclofen evidence​

In a 1980 uncontrolled series of 25 men with SCI and DSD (100 urodynamic profiles), lower residual urine was reported in 73% of cases after a mean 4.98 weeks.[4] A 2025 scoping review records baclofen doses of 80–160 mg/day for that series, compared with the current US oral solution label maximum of 80 mg/day.[32][7] Separately, EAU 2026 gives a weak recommendation to offer oral baclofen to women with functional bladder outlet obstruction, particularly with increased sphincter EMG activity and sustained detrusor contraction during voiding.[29] A 60-woman crossover trial tested 10 mg three times daily for 4 weeks and found fewer voids per day and an improved EMG index versus placebo; patient-reported symptom and quality-of-life scales and long-term follow-up were not assessed.[28][29] The principal limitation is poor blood–brain barrier penetration: tolerable oral doses often produce sedation and weakness without reaching effective spinal cord concentrations for DSD.[3]

Intrathecal baclofen for genitourinary effects​

In a prospective study of 10 patients with severe spasticity from spinal-cord pathology, acute bolus testing was blinded against placebo; chronic infusion was compared with pretreatment values:[5]

  • Eliminated uninhibited bladder contractions in all patients with irritative voiding and urge incontinence
  • Abolished DSD in 40%[5]
  • Achieved 72% increase in bladder capacity and 16% improvement in compliance (in non-cervical SCI patients)[5]
  • 1 of 3 patients with an indwelling catheter converted to clean intermittent self-catheterization

Mean capacity, compliance, sensation and voiding pressures were not significantly different across the whole small cohort. The capacity and compliance percentages above apply to a subgroup. Reassess PVR and bladder storage after ITB changes: a 2025 retrospective cohort of patients with severe supraspinal spasticity had an overall PVR increase, and a small subgroup had serious increases in reflex and residual volumes that pretreatment urodynamics did not predict; pump selection should remain grounded in the primary spasticity indication.[3][5][33]

Oral dosing[7]​

The label titration starts at 5 mg three times daily, increasing by 5 mg per dose every 3 days as tolerated, to a maximum of 80 mg daily (20 mg four times daily).[7] In spinal cord injury, use the lowest effective dose and taper slowly. Baclofen should be used with caution in patients with a history of autonomic dysreflexia, since nociceptive stimuli or abrupt withdrawal can precipitate an episode.

Adverse effects relevant to LUT[7]​

Sedation, weakness, dizziness, headache; LUT-specific: urinary frequency (2–6%) and other label-listed effects including enuresis, urinary retention, dysuria, impotence, ejaculatory failure, nocturia.[7] Baclofen is primarily excreted unchanged by the kidneys; because excess exposure can cause marked drowsiness and respiratory depression, use caution in renal impairment and consider dose reduction.[7] Abrupt withdrawal of oral or especially intrathecal treatment can cause seizures, hyperthermia, severe spasticity and multiorgan failure. Avoid abrupt discontinuation; pump interruption requires urgent specialist management.

Tizanidine — central alpha-2 agonist for spasticity​

A centrally acting alpha-2 adrenergic agonist used for spasticity from multiple sclerosis and spinal cord injury. Tizanidine is a common alternative for spasticity when baclofen is not tolerated; no controlled trial establishes benefit for DSD or dysfunctional voiding.[26][30] A 2026 retrospective series of 114 adults with dysfunctional voiding or poor external-sphincter relaxation reported patient-perceived symptom improvement in 69.3% after adding tizanidine to alpha-blockade and pelvic-floor relaxation (median 6 mg/day; median follow-up 12 months); 25% had dose-limiting sedation.[26][30]

  • Dosing (label): 2 mg every 6–8 hours as needed, up to three doses in 24 hours; titrate by 2–4 mg per dose every 1–4 days to a maximum of 36 mg daily.[26] Use lower individual doses if creatinine clearance is below 25 mL/min or in hepatic impairment.[26]
  • Liver injury: hepatocellular injury occurs; the label advises aminotransferases at baseline and 1 month after reaching the maximum dose, or if injury is suspected.
  • CYP1A2 interactions: strong CYP1A2 inhibitors (fluvoxamine, ciprofloxacin) are contraindicated because of marked hypotension, sedation and psychomotor impairment. Avoid moderate or weak inhibitors where possible. Ciprofloxacin is relevant in urologic practice, for example when treating a UTI in a spinal cord injury patient already taking tizanidine.
  • Other: hypotension, sedation and dry mouth are common; taper rather than stop abruptly after prolonged high-dose use. Alpha-2 agonism can compound hypotension in patients also taking alpha-blockers or antihypertensives.

Dantrolene — for external sphincter hypertonicity (largely historical)​

A peripherally acting oral SMR; it interferes with calcium release from the sarcoplasmic reticulum to reduce excitation–contraction coupling in skeletal muscle.[8][9][12]

Selectivity matters​

Dantrolene primarily relaxes striated muscle. Isolated canine and human detrusor preparations showed no significant inhibition at tested concentrations, supporting interest in EUS hypertonicity.[10][18]

Evidence​

  • In a 15-patient SCI series with PVR > 150 mL and urethral closure pressure > 100 cm H₂O, 8/15 (53%) reached PVR < 100 mL and continued external condom drainage; their mean urethral pressure fell by 77 cm H₂O (49%).[8] Five of the 8 responders required doses up to 600 mg/day; 600 mg/day exceeds the current 400 mg/day oral label ceiling.[8][12]
  • A 1976 uncontrolled report described apparent benefit in selected patients with neurologic or non-neurologic external-sphincter spasm identified by sphincter EMG, cystometrography and voiding cystourethrography.[9]
  • In one woman with cerebral palsy, overactive-bladder symptoms improved after dantrolene was started for spasticity while she was taking oxybutynin and mirabegron.[11]

Limitations​

  • Fatal and nonfatal hepatitis is a boxed-warning risk; the current oral label ceiling is 100 mg four times daily, with baseline and ongoing liver assessment, lowest effective dosing and discontinuation if no benefit within 45 days[12]
  • Generalized muscle weakness limits functional utility, particularly in incomplete SCI where ambulation is preserved
  • Intrasphincteric BoNT-A is an off-label alternative in selected DSD, with transient effects and limited evidence; systemic toxin effects remain possible[23]
  • In the 15-patient SCI series, detrusor hyporeflexia was proposed as a possible contributor to treatment failure.[8]

Current role​

Urologic sphincter use is historical and off-label. Active hepatic disease, or spasticity needed for posture or function, contraindicates oral use.[11][12]

Diazepam — for high-tone pelvic floor dysfunction​

The most-studied SMR for myofascial pelvic pain and high-tone pelvic floor disorders, available as oral tablets and as compounded vaginal suppositories (10 mg in several small studies; no FDA-approved vaginal formulation).[1][13]

Pharmacokinetics — vaginal vs oral​

Compounded 10 mg vaginal diazepam has a distinctive PK profile: peak concentration 31.0 ng/mL at about 3.1 h, bioavailability 70.5%, and a terminal half-life of 82 hours in eight healthy volunteers. Three reported fatigue.[14] The long half-life predicts accumulation with repeated daily dosing.[14]

Evidence — mixed at best​

StudyDesignResult
Stone systematic review[13]5 studies (2 observational, 3 RCTs)Observational studies report 71–96% subjective improvement in sexual function; one RCT found no significant between-group difference in FSFI or VAS pain scores, a second found no VAS pain difference, and the third (diazepam + TENS) improved dyspareunia but not VAS pain
Crisp triple-blinded RCT (n = 21)[15]10 mg vaginal diazepam nightly × 4 wk vs placeboNo improvement in resting pelvic-floor EMG or subjective outcomes
Murina RCT — vestibulodynia[16]Vaginal diazepam + TENS vs placebo + TENSImproved dyspareunia and relaxation measures, but no significant between-group VAS pain improvement
Rogalski retrospective (26 complete charts from 72 reviewed)[17]Vaginal diazepam + PT + trigger-point injectionsPelvic-floor muscle tone improved from baseline at rest, squeeze, and relaxation after a mean 6.21 months of treatment

The small studies provide insufficient evidence for routine or adjunctive benefit. NICE NG210 recommends against vaginal diazepam for pelvic-floor dysfunction, including women with high tone.[24] Separately, a 2024 expert Delphi algorithm for high-tone pelvic-floor dysfunction lists vaginal muscle relaxants, including diazepam, as second-line options with or after pelvic-floor physical therapy.[31] Discuss the uncertainty if considering specialist off-label use; pelvic-floor physical therapy remains central.[24][1][13][15] For men with pelvic-floor or abdominopelvic myalgia, AUA 2025 permits individualized internal and external manual physical therapy .[27]

Oral diazepam​

Pelvic-floor use is off-label. Oral and systemically absorbed vaginal diazepam carry sedation, cognitive, dependence and withdrawal risks. Opioids, alcohol and other CNS depressants increase respiratory-depression or overdose risk; an established course should be tapered rather than abruptly stopped.[25] At the concentrations tested, diazepam had no direct effect on human bladder smooth-muscle contractility in vitro.[18]

Cyclobenzaprine and Other Centrally Acting Antispasmodics​

A tricyclic-related agent prescribed off-label for myofascial pelvic pain and CP/CPPS, with very limited supporting evidence.[1][19][20]

  • No high-quality studies demonstrate improvement in pelvic-pain scales with cyclobenzaprine specifically
  • Anticholinergic effects can worsen urinary retention; dry mouth and sedation also occur. The cited extended-release label limits use to short-term acute musculoskeletal spasm (up to 2–3 weeks) and does not recommend use in older adults or patients with hepatic impairment. It contraindicates MAOI use or use within 14 days after MAOI discontinuation, acute myocardial-infarction recovery, arrhythmias or conduction disorders, heart failure and hyperthyroidism. Serotonergic combinations can cause serotonin syndrome.[19]
  • Other centrally acting agents (methocarbamol, metaxalone, carisoprodol) have no established urologic role
  • The ACOG Chronic Pelvic Pain Practice Bulletin cites a Cochrane review that found insufficient evidence, from only two studies, to recommend muscle relaxants for myofascial pain[2]

For the broader pelvic-pain pharmacotherapy framework, see Antispasmodics.

SMRs for Postoperative Urinary Retention​

Methocarbamol, meprobamate, chlormezanone, and carisoprodol were discussed as possible approaches to postoperative urinary retention (POUR) based on proposed relaxation of reflex pelvic-floor and EUS contracture or anxiety-related voiding inhibition, but were not tested in the cited Cochrane review. Its included sedative arms used diazepam with carbachol or midazolam alone or with bethanechol.[21] The Cochrane review found insufficient evidence to support routine use of any drug, including SMRs, for the treatment of POUR. That 2010 review included only seven studies and 494 participants.[21] Drugs must not delay decompression of a significantly distended bladder.[21]

Evidence Summary​

AgentSettingEvidenceBottom line
Oral baclofenDSD in SCI25 men, 100 urodynamic profiles; lower PVR in 73% of reported cases after mean 4.98 weeks[4]Uncontrolled historical evidence; renal/CNS toxicity limits use
Intrathecal baclofenDSD + detrusor hyperreflexia in SCI10-patient study: DSD abolished in 40%; capacity improvement confined to a subgroup[5]Reassess bladder effects
TizanidineSpasticity in MS/SCI; dysfunctional voiding or poor EUS relaxation in adultsIn a 114-adult retrospective adjunct series, 69.3% reported symptom improvement (median follow-up 12 months)[30]; label-based dosing and interaction warnings[26]Alternative to baclofen for spasticity; check CYP1A2 inhibitors and LFTs
DantroleneEUS hypertonicity in SCI8/15 benefited in an old series; some received doses above today’s label ceiling[8]Historical/off-label; hepatotoxicity and weakness are limiting
Vaginal diazepamHigh-tone pelvic floor dysfunctionTwo small RCTs found no significant between-group difference in pain measures; a third found less dyspareunia with diazepam plus TENS than placebo plus TENS, without a VAS pain difference[13][15][16]No established routine benefit; NICE recommends against use[24]
CyclobenzaprineMyofascial CPPNo high-quality urologic data[1]Off-label; consider only as multimodal adjunct
POUR (any SMR)Postoperative urinary retentionCochrane: insufficient evidence[21]Not recommended as primary therapy
Functional BOO in NLUTD (surgical approaches)Sphincterotomy, urethral stent or EUS BoNT-ACochrane: five trials (199 adults), with no robust evidence favoring a surgical option[22]Multimodal, individualized strategy

Clinical Positioning​

  • Intradetrusor BoNT-A has established OAB or NDO indications; intrasphincteric DSD treatment is off-label with limited evidence. These are separate clinical decisions; see Botulinum toxin.[23]
  • Baclofen may affect bladder function when treating neurologic spasticity; monitor emptying and storage.
  • Dantrolene is historical and off-label for urinary sphincter dysfunction.
  • Vaginal diazepam has substantial systemic absorption and no established routine efficacy; NICE recommends against its use for pelvic-floor dysfunction.[24]
  • Cyclobenzaprine and other antispasmodics lack high-quality urologic evidence, and their anticholinergic burden can worsen voiding dysfunction
  • No SMR is routinely indicated for postoperative urinary retention[21]
  • The urologic adverse effects of systemically administered SMRs (urinary retention with baclofen and dantrolene; anticholinergic effects with cyclobenzaprine) must be considered when these agents are prescribed for non-urologic indications in patients with pre-existing LUTS[7][12][19]

See Also​

References​

1. Flatow V, Uy-Kroh J, Carey ET, Ascher-Walsh C, Khalil S. "Skeletal muscle relaxants for the treatment of myofascial pelvic pain and high tone pelvic floor disorders." Curr Opin Obstet Gynecol. 2023;35(4):311–315. doi:10.1097/GCO.0000000000000894

2. American College of Obstetricians and Gynecologists. "Chronic pelvic pain: ACOG Practice Bulletin, Number 218." Obstet Gynecol. 2020;135(3):e98–e109. doi:10.1097/AOG.0000000000003716

3. Verduzco-Gutierrez M, Raghavan P, Pruente J, et al. "AAPM&R consensus guidance on spasticity assessment and management." PM R. 2024;16(8):864–887. doi:10.1002/pmrj.13211

4. Leyson JF, Martin BF, Sporer A. "Baclofen in the treatment of detrusor-sphincter dyssynergia in spinal cord injury patients." J Urol. 1980;124(1):82–84. doi:10.1016/s0022-5347(17)55307-0

5. Steers WD, Meythaler JM, Haworth C, Herrell D, Park TS. "Effects of acute bolus and chronic continuous intrathecal baclofen on genitourinary dysfunction due to spinal cord pathology." J Urol. 1992;148(6):1849–1855. doi:10.1016/s0022-5347(17)37048-9

6. Miyazato M, Sasatomi K, Hiragata S, et al. "Suppression of detrusor-sphincter dyssynergia by GABA-receptor activation in the lumbosacral spinal cord in spinal cord-injured rats." Am J Physiol Regul Integr Comp Physiol. 2008;295(1):R336–R342. doi:10.1152/ajpregu.90315.2008

7. Baclofen oral solution prescribing information. DailyMed. Accessed September 12, 2026.

8. Hackler RH, Broecker BH, Klein FA, Brady SM. "A clinical experience with dantrolene sodium for external urinary sphincter hypertonicity in spinal cord injured patients." J Urol. 1980;124(1):78–81. doi:10.1016/s0022-5347(17)55305-7

9. Murdock MM, Sax D, Krane RJ. "Use of dantrolene sodium in external sphincter spasm." Urology. 1976;8(2):133–137. doi:10.1016/0090-4295(76)90340-x

10. Harris JD, Benson GS. "Effect of dantrolene sodium on canine bladder contractility." Urology. 1980;16(2):229–231. doi:10.1016/0090-4295(80)90095-3

11. Bulchandani S, Toozs-Hobson P, Kennedy A, Sturman S. "Dantrolene an unusual option for detrusor overactivity: observations of a patient with cerebral palsy." Eur J Obstet Gynecol Reprod Biol. 2015;194:255–256. doi:10.1016/j.ejogrb.2015.08.012

12. Dantrium oral capsules prescribing information. DailyMed. Accessed September 12, 2026.

13. Stone RH, Abousaud M, Abousaud A, Kobak W. "A systematic review of intravaginal diazepam for the treatment of pelvic floor hypertonic disorder." J Clin Pharmacol. 2020;60(Suppl 2):S110–S120. doi:10.1002/jcph.1775

14. Larish AM, Dickson RR, Kudgus RA, et al. "Vaginal diazepam for nonrelaxing pelvic floor dysfunction: the pharmacokinetic profile." J Sex Med. 2019;16(6):763–766. doi:10.1016/j.jsxm.2019.03.003

15. Crisp CC, Vaccaro CM, Estanol MV, et al. "Intra-vaginal diazepam for high-tone pelvic floor dysfunction: a randomized placebo-controlled trial." Int Urogynecol J. 2013;24(11):1915–1923. doi:10.1007/s00192-013-2108-9

16. Murina F, Felice R, Di Francesco S, Oneda S. "Vaginal diazepam plus transcutaneous electrical nerve stimulation to treat vestibulodynia: a randomized controlled trial." Eur J Obstet Gynecol Reprod Biol. 2018;228:148–153. doi:10.1016/j.ejogrb.2018.06.026

17. Rogalski MJ, Kellogg-Spadt S, Hoffmann AR, Fariello JY, Whitmore KE. "Retrospective chart review of vaginal diazepam suppository use in high-tone pelvic floor dysfunction." Int Urogynecol J. 2010;21(7):895–899. doi:10.1007/s00192-009-1075-7

18. Ayyat FM, Lloyd LK, Kuhlemeier KV. "Effect of skeletal muscle relaxants on bladder smooth muscle." J Urol. 1984;132(2):372–375. doi:10.1016/s0022-5347(17)49630-3

19. Cyclobenzaprine hydrochloride extended-release prescribing information. DailyMed. Accessed September 12, 2026.

20. Pena VN, Engel N, Gabrielson AT, Rabinowitz MJ, Herati AS. "Diagnostic and management strategies for patients with chronic prostatitis and chronic pelvic pain syndrome." Drugs Aging. 2021;38(10):845–886. doi:10.1007/s40266-021-00890-2

21. Buckley BS, Lapitan MC. "Drugs for treatment of urinary retention after surgery in adults." Cochrane Database Syst Rev. 2010;(10):CD008023. doi:10.1002/14651858.CD008023.pub2

22. Utomo E, Groen J, Blok BF. "Surgical management of functional bladder outlet obstruction in adults with neurogenic bladder dysfunction." Cochrane Database Syst Rev. 2014;(5):CD004927. doi:10.1002/14651858.CD004927.pub4

23. EAU. Neuro-urology Guidelines. 2026; botulinum toxin and bladder-outlet sections. Guideline.

24. NICE. Pelvic floor dysfunction: prevention and non-surgical management. NG210, recommendation 1.6.33. Recommendations.

25. FDA. Boxed warning updated to improve safe use of benzodiazepines. September 23, 2020. Safety communication.

26. Tizanidine tablets prescribing information. DailyMed. Accessed September 24, 2026.

27. Lai HH, Pontari MA, Argoff CE, et al. Male Chronic Pelvic Pain: AUA Guideline: Part II Treatment of Chronic Prostatitis/Chronic Pelvic Pain Syndrome. J Urol. 2025;214(2):127-137. doi:10.1097/JU.0000000000004565 Full 2025 guideline

28. Xu D, Qu C, Meng H, et al. "Dysfunctional voiding confirmed by transdermal perineal electromyography, and its effective treatment with baclofen in women with lower urinary tract symptoms: a randomized double-blind placebo-controlled crossover trial." BJU Int. 2007;100(3):588–592. doi:10.1111/j.1464-410X.2007.06987.x

29. European Association of Urology. EAU Guidelines on Non-neurogenic Female LUTS. 2026, section 4.5.4.b.2.b. Guideline.

30. Agarwal MM, Bhaskar V, Gupta SK, et al. "Tizanidine as an adjunct to alpha-blockers in adults with dysfunctional voiding/poor relaxation of the external sphincter: a retrospective review." Low Urin Tract Symptoms. 2026;18(4):e70077. doi:10.1111/luts.70077

31. Torosis M, Carey E, Christensen K, et al. "A treatment algorithm for high-tone pelvic floor dysfunction." Obstet Gynecol. 2024;143(4):595–602. doi:10.1097/AOG.0000000000005536

32. Tousignant A, Blais MA, Tu LM, Morin M, Ismail S. "A scoping review of the oral treatment options for the management of detrusor sphincter dyssynergia." Neurourol Urodyn. 2025;44(4):743-753. doi:10.1002/nau.25642

33. Kofler M, Halbmayer LM, Kiss G, et al. "Effect of intrathecal baclofen on bladder function in patients with severe supraspinal spasticity." Neurourol Urodyn. 2025;44(2):276-286. doi:10.1002/nau.25666