Products
Oxybutynin is commercially available in tablet form and as a transdermal patch (Ditropan, Kentera). It has been approved in many countries since 1988, and the transdermal patch has been available since 2007. Extemporaneous formulations are also produced; see Intravesical oxybutynin solution (for use in the urinary bladder). Other dosage forms have been released in the United States that are not available in many countries. These include transdermal gels, which are applied to the skin and release the active ingredient through the skin into the bloodstream.
Structure and properties
Oxybutynin (C22H31NO3, Mr = 357.5 g/mol) is a racemate structurally related to atropine. It is a tertiary amine and is present in drugs either as a base or as oxybutynin hydrochloride. Oxybutynin hydrochloride is a white crystalline powder that is readily soluble in water.
Effects
Oxybutynin (ATC G04BD04) has parasympatholytic (anticholinergic), spasmolytic, and local anesthetic properties. It relaxes bladder smooth muscle, decreases urinary urgency and frequency of bladder emptying. It also reduces the secretion of the sweat glands. The effects are due to competitive antagonism at muscarinic M-acetylcholine receptors.
Indications
- Bedwetting (enuresis nocturna or during the day).
- Unstable bladder with incontinence, frequent urination and urge to urinate.
- Spastic neurogenic bladder
Not all dosage forms are approved for all indications. Oxybutynin can also be used off-label for severe sweating (hyperhidrosis), but is not approved for this purpose by regulatory authorities in many countries.
Dosage
According to the SmPC. Oxybutynin is administered perorally and transdermally; certain extemporaneous formulations are additionally administered intravesically.
Contraindications
Oxybutynin is contraindicated in numerous conditions and diseases because of its anticholinergic properties. For complete precautions, see the drug label.
Interactions
Oxybutynin is biotransformed by CYP3A4 and undergoes high first-pass metabolism when administered orally, reducing bioavailability to low 6%. Corresponding drug interactions are possible. Other anticholinergics may potentiate the anticholinergic side effects of oxybutynin and should be avoided or used with caution. The parasympatholytic properties of the drug may slow intestinal transit and affect the absorption of other drugs. The effectiveness of cholinergic drugs and prokinetics may be abolished. Alcohol may cause increased drowsiness.
Adverse Effects
Potential adverse effects arise mainly as a result of the anticholinergic properties of oxybutynin. The most common possible adverse effects include:
- Dry mouth
- Visual disturbances
- Flush
- Nausea, abdominal discomfort, constipation.
- Micturition disorders
