OXYBUTYNIN CHLORIDE

Chemistry - A synthetic tertiary amine, oxybutynin chloride occurs as white to off-white crystals.
It is freely soluble in water.

Storage, Stability, Compatibility

Tablets and oral solution should be stored at room temperature in tight containers. Protect oral solution from light. Tablets have an expiration date of 4 yearsafter manufacture.

Pharmacology - OXYBUTYNIN CHLORIDE

Considered a urinary antispasmodic, oxybutynin has direct antimuscarinic(atropine-like) and spasmolytic (papaverine-like) effects on smooth muscle. Spasmolytic effectsappear to be most predominant on the detrusor muscle of the bladder and small and large intestine.
It does not have appreciable effects on vascular smooth muscle. Studies done in patients withneurogenic bladders showed that oxybutynin increased bladder capacity, reduced the frequency ofuninhibited contractions of the detrusor muscle and delayed initial desire to void. Effects were morepronounced in patients with uninhibited neurogenic bladders than in patients with reflex neurogenicbladders. Other effects noted in lab animal studies include moderate antihistaminic, local anesthetic, mild analgesic, very low mydriatic and antisialagogue effects.
Uses, Indications - Oxybutynin may be useful for the adjunctive therapy of detrusor hyperreflexiain dogs and in cats with FeLV-associated detrusor instability.

Pharmacokinetics - OXYBUTYNIN CHLORIDE

Oxybutynin is apparently rapidly and well absorbed from the GI tract.
Studies done in rats show the drug distributed into the brain, lungs, kidneys, and liver. Whileelimination characteristics have not been well documented, oxybutynin apparently is metabolized inthe liver and also excreted in the urine. In humans, the duration of action is from 6-10 hours after adose.

Contraindications, Precautions, Reproductive Safety

Because of the drug's pharmacologicactions, oxybutynin should be used when its benefits outweigh its risks when the following conditions are present: obstructive GI tract disease or intestinal atony/paralytic ileus, angle closureglaucoma, hiatal hernia, cardiac disease (particularly associated with mitral stenosis, associatedarrhythmias, tachycardia, CHF, etc.), myasthenia gravis, hyperthyroidism, prostatic hypertrophy, severe ulcerative colitis, urinary retention or other obstructive uropathies.
While safety during pregnancy has not been firmly established, studies in a variety of lab animalshave demonstrated no teratogenic effect associated with the drug. While oxybutynin may inhibitlactation, no documented problems associated with its use in nursing offspring have been noted.

Adverse Effects, Warnings

While use in small animals is limited, diarrhea and sedation havebeen reported. Other adverse effects reported in humans, and potentially seen in animals are primarily as a result of the drug's pharmacologic effects. These can include dry mouth or eyes, urinary retention or hesitancy, constipation, tachycardia, anorexia, vomiting, weakness, or mydriasis.

Overdosage, Acute Toxicity

Overdosage may cause CNS effects (e.g., restlessness, excitement, seizures), cardiovascular effects (e.g., hyper or hypotension, tachycardia, circulatory failure), fever, nausea or vomiting may also be present. Massive overdoses may lead to paralysis, coma, respiratoryfailure and death. Treatment of overdoses should consist of general techniques to limit absorptionof the drug from the GI tract and supportive care as required. Intravenous physostigmine may beuseful. See the atropine monograph for more information on the use of physostigmine.

Drug Interactions

Other drugs with anticholinergic effects (e.g., atropine, propantheline, scopolamine, isopropamide, glycopyrrolate, hyoscyamine, tricyclic antidepressants, disopyramide, procainamide, antihistamines, etc.) may intensify oxybutynin's anticholinergic effects. Othersedating drugs may exacerbate the sedating effects of oxybutynin.