What is oxybutynin hydrochloride used for?

Oxybutynin hydrochloride selectively acts on the cholinergic M1 and M3 receptors and is mainly used for treating overactive bladder syndrome. However, the oral formulation of oxybutynin can directly inhibit the cholinergic receptors in the salivary glands, leading to the production of N-desethyloxybutynin, which has a higher likelihood of causing dry mouth due to its high concentration after gastrointestinal absorption and liver metabolism. This side effect often leads many patients to discontinue the oral formulation. The transdermal patch avoids direct action on oral M receptors and first-pass metabolism, thereby reducing the incidence of dry mouth. Additionally, the patch is convenient to use and offers sustained release through skin absorption, making it suitable for elderly patients. According to the 2012 American Urological Association (AUA) guidelines for the management of incontinence, oxybutynin transdermal patch can be used if the patient cannot tolerate the dry mouth caused by oral anticholinergic medications.

Indications

FDA Approved Indications

Oxybutynin is an anticholinergic medication approved by the U.S. Food and Drug Administration (FDA) for the treatment of overactive bladder or detrusor overactivity symptoms (such as frequent urination and urgency). Animal studies indicate that its antispasmodic effect is 4 to 10 times stronger than atropine. Oxybutynin is also used for patients with detrusor instability associated with neurogenic bladder disorders (e.g., spina bifida). The medication has been thoroughly studied and is approved for use in patients aged 5 years and older.

Off-Label Indications

In certain cases, oxybutynin may be used to control bladder spasms caused by indwelling ureteral stents or Foley catheters. However, this particular use has not been approved by the FDA. Oxybutynin, when used in conjunction with desmopressin, can treat refractory nocturnal enuresis. Additionally, this medication is used to treat primary focal hyperhidrosis.

Oxybutynin Hydrochloride for hyperhidrosis

According to a case report, oxybutynin seems to be effective in treating hyperhidrosis induced by methadone. Another case report describes successful treatment of hyperhidrosis associated with buprenorphine or naloxone in opioid withdrawal. Research is ongoing on topical formulations of oxybutynin for hyperhidrosis, aiming to minimize systemic adverse effects.

What is oxybutynin hydrochloride used for？

In a 2023 report by Vanden Eynde J J and colleagues, a search using "oxybutynin" in the National Library of Medicine database revealed 69 registered clinical trials. Most of these (50 trials) studied the safety and/or efficacy of oxybutynin for treating bladder dysfunction, with one anecdotal study (NCT03877289) investigating its safety and/or efficacy for treating pediatric cystitis. A Phase II trial analyzed the effect of combining oxybutynin with desloratadine for seasonal allergic rhinitis (NCT00816972; started in 2005), while another Phase II trial examined the effect of combining oxybutynin with clonidine for excessive salivation in Parkinson's disease (NCT01370811; started in 2011).

The remaining trials explored the repositioning of oxybutynin for treating hyperhidrosis (nine trials, though one NCT02099695 was withdrawn) and hot flashes (four trials). The first registered clinical trial specifically investigating the efficacy of oxybutynin for axillary hyperhidrosis began in Brazil in 2007 (NCT01118429). Positive results were published in 2011, with authors claiming that "over 80% of patients experienced improvement in axillary hyperhidrosis with minimal side effects, the most common being dry mouth (73.5%)". Notable other trials include a Phase III trial started in 2013 (NCT01855256) and a Phase IV trial started in 2010 (NCT01310712). Nowadays, physicians might prescribe oxybutynin for treating hyperhidrosis.

Recently, there has been growing interest in using oxybutynin as a therapeutic option for obstructive sleep apnea (four trials).

Oxybutynin Hydrochloride dosage

Approved formulations of oxybutynin hydrochloride are used as follows:

Specific Patient Population Dosing:

• Elderly Patients: According to the American Geriatrics Society (Beers Criteria), oxybutynin may be inappropriate for elderly patients due to its anticholinergic side effects. It should only be used when the potential benefits outweigh the risks, with a recommendation to start treatment at a lower dose.
• Pediatric Patients: For children aged 5 years and older, the recommended starting or maximum dose is 5 mg tablets taken 2 to 3 times daily for immediate release. For children aged 6 years and older, the recommended starting dose is 5 mg extended-release oxybutynin, taken once daily. The maximum daily dose for these children should not exceed 20 mg. Extended-release oxybutynin is not recommended for children under 6 years or those unable to swallow whole tablets.
• Pregnancy Considerations: An observational study indicated that oxybutynin use in pregnant women with spinal cord injuries does not adversely affect pregnancy outcomes. However, further research is needed to thoroughly assess the safety of oxybutynin during pregnancy. Oxybutynin is classified as a Pregnancy Category B drug. Although animal studies have not shown definitive harm to the fetus during pregnancy, concrete safety data during this period is lacking. Oxybutynin should only be prescribed during pregnancy when the clinical benefits to the mother outweigh the potential risks to the fetus.
• Breastfeeding Considerations: There is currently no evidence regarding the use of oxybutynin by breastfeeding mothers. In some cases, if a breastfeeding woman is on long-term oxybutynin, monitoring for any signs of reduced milk supply in the infant, such as slow weight gain or insufficient satiety, is advised.

Oxybutynin Hydrochloride side effects

Oxybutynin is one of the most popular anticholinergic agents and has been widely used for overactive bladder syndrome for decades. However, anticholinergic receptors are present in many parts of the body, including the salivary glands, gastrointestinal smooth muscles, eyes, heart, and brain. This explains the range of side effects observed, including the most common dry mouth, reduced sweating, constipation, blurred vision, tachycardia, and nausea. Cognitive impairment has also been reported, likely due to the drug's ability to cross the blood-brain barrier, as it is lipophilic. This adverse effect is particularly noted in elderly patients, as MRI studies show increased permeability of the blood-brain barrier with age. Factors contributing to blood-brain barrier disruption include endothelial cell narrowing and degradation, changes in tight junction proteins, and transport mechanism dysregulation. The clinical adverse reactions and incidence rates of oxybutynin's formulations are as follows:

Warnings

Oxybutynin is primarily used to alleviate symptoms such as frequent urination, urgency, and incontinence caused by overactive bladder syndrome. However, as each patient's condition and needs vary, it is essential to consult a healthcare provider before using oxybutynin to obtain personalized treatment advice and ensure the safety and effectiveness of the medication.

References:

1. Vanden Eynde J J. Repositioning Oxybutynin Hydrochloride: State of the Art in Synthesis, Mode of Action, Metabolism, and Formulations. Drugs and Drug Candidates, 2023, 2(4): 865-882.
2. Zeng Qian, Xie Xueyuan, Tang Huihui. Preparation and Quality Evaluation of Oxybutynin Hydrochloride Transdermal Patch. Journal of PLA Medical College, 2015, 31 (02): 130-132.
3. Wang Xue, Zhou Bin, Wang Hao, et al. Development of Oxybutynin Hydrochloride Formulations. World Clinical Drugs, 2014, 35 (01): 54-59.
4. Dwyer J, Tafuri S M, LaGrange C A. Oxybutynin. StatPearls [Internet]. StatPearls Publishing, 2023.
5. https://baike.baidu.com/item/%E7%9B%90%E9%85%B8%E5%A5%A5%E6%98%94%E5%B8%83%E5%AE%81