Oxybutynin: uses, dosing, side effects & brands

OXYTROL (oxybutynin transdermal system) is designed to deliver oxybutynin over a 3- to 4-day interval after application to intact skin. OXYTROL is available as a 39 cm 2 transdermal system containing 36 mg of oxybutynin. OXYTROL has a nominal in vivo delivery rate of 3.9 mg oxybutynin per day through skin of average permeability (inter-individual variation in skin permeability is approximately 20%). Oxybutynin is an antispasmodic, anticholinergic agent. Oxybutynin is administered as a racemate of R- and S-isomers.

The FDA classifies oxybutynin as a cholinergic muscarinic antagonist. These drugs block muscarinic receptors, the docking sites for the nerve signal acetylcholine. By preventing acetylcholine from acting, they calm the 'rest-and-digest' nervous system, which can dry secretions, relax airway and bladder muscles, and speed up the heart, depending on the drug. If you are checking whether it is safe to combine with something else, the class is what matters — two drugs from the same class usually should not be stacked.

The elimination half-life of oxybutynin is about 2 to 3 hours — that is how long the body takes to clear half of a dose. This is the immediate-release oral figure: the label states oxybutynin is rapidly absorbed, reaching peak levels within an hour, after which plasma levels fall with an effective half-life of about 2 to 3 hours. The same label notes that in the frail elderly the elimination half-life is prolonged to about 5 hours and a lower starting dose is recommended — the group most often prescribed this drug clears it more slowly. Extended-release tablets do not clear faster or slower: the apparent half-life after a single 10 mg ER dose is about 12 to 13 hours, which reflects slow release, not slower elimination. The active metabolite N-desethyloxybutynin outlasts the parent and reaches far higher levels after a swallowed dose (metabolite-to-parent AUC ratio 11.9 to 1 after a single 5 mg oral dose, versus 1.3 to 1 with the transdermal patch, which skips first-pass metabolism). Oxybutynin is cleared almost entirely by liver CYP3A4 (under 0.1% of the dose leaves unchanged in urine), so CYP3A4 inhibitors can raise exposure. No studies were conducted in kidney or liver impairment. Half-life is not the same as how long a drug test can detect the drug, and it varies with age, kidney and liver function.

It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run oxybutynin against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.

We track 2 oxybutynin-containing products in the U.S.: Oxytrol and Oxytrol for Women. They are the same active ingredient; they differ in form, manufacturer, price and FDA recall record.

Across the brands we track, oxybutynin is currently marketed as patch, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.

We do not currently list a generic-labelled oxybutynin product. That does not always mean none exists — it means none appears under a generic name in the FDA data we track. Ask your pharmacist.

Dry mouth, by a wide margin. In five controlled trials, dry mouth occurred in 34.9% of patients on the extended-release tablets versus 72.4% on immediate-release oxybutynin. The other reactions at 5% or more with the extended-release form were constipation 8.7%, diarrhea 7.9%, headache 7.5%, drowsiness 5.6%, and dizziness 5.0%; blurred vision came in at 4.3%. The same trials show the immediate-release form was worse on nearly every count — constipation 15.1%, drowsiness 14.1%, dizziness 16.6%, blurred vision 9.6%, nausea 11.6%. If dry mouth or grogginess is what is bothering you, the extended-release form is the label-supported answer to raise with your prescriber.

No, oxybutynin has no FDA boxed warning. The most urgent labeled risk is angioedema — swelling of the face, lips, tongue, or voice box — which has occurred after the first dose in some cases and can be life-threatening if it involves the tongue, throat, or larynx. If that happens, stop the drug and get emergency care immediately to protect your airway. The label also flags anticholinergic CNS effects: hallucinations, agitation, confusion, and drowsiness, which should be watched for particularly in the first few months of treatment and after any dose increase.

Four groups must not take it. Do not take oxybutynin if you have urinary retention, if you have gastric retention or another condition causing severely decreased movement of the digestive tract, if you have uncontrolled narrow-angle glaucoma, or if you are allergic to oxybutynin or any component of the product. Beyond those absolute bans, the label says use caution — not avoid entirely — if you have pre-existing dementia and take a cholinesterase inhibitor, Parkinson's disease, myasthenia gravis, autonomic neuropathy with slowed gut motility, clinically significant bladder outflow obstruction, gastroesophageal reflux, or you take other drugs that can worsen esophagitis.

It requires real caution. Oxybutynin causes anticholinergic effects on the brain — hallucinations, agitation, confusion, and drowsiness are all in the label — and you should be monitored for these especially during the first few months and after any dose increase. If they appear, the label's direction is to lower the dose or stop the drug. It should be used with caution if you have pre-existing dementia and take a cholinesterase inhibitor, because it can worsen your symptoms, and the same caution applies in Parkinson's disease. Do not drive or use machinery until you know how the drug affects you, and know that alcohol adds to the drowsiness.

Oxybutynin reduces sweating, which can cause heat prostration when you are in a hot environment — that is a labeled anticholinergic effect, not your imagination. Be careful with heat waves, hot workplaces, saunas, and hard exercise in the heat. On the tablet: do not chew, divide, or crush the extended-release form. Swallow it whole with liquid. The drug sits inside a nonabsorbable shell built to release it at a controlled rate, and crushing that shell defeats the design. The empty shell passes through and is eliminated in your stool, so seeing something tablet-shaped in the toilet is expected and does not mean the medicine failed to work.