Professional Information — Ditropan

Indications and Usage

DITROPAN XL^® (oxybutynin chloride) is a once-daily controlled-release tablet indicated for the treatment of overactive bladder with symptoms of urge urinary incontinence, urgency, and frequency.

DITROPAN XL^® is also indicated in the treatment of pediatric patients aged 6 years and older with symptoms of detrusor overactivity associated with a neurological condition (e.g., spina bifida).

Dosage and Administration

DITROPAN XL^® (oxybutynin chloride) must be swallowed whole with the aid of liquids, and must not be chewed, divided, or crushed.

DITROPAN XL^® may be administered with or without food.

Adults

The recommended starting dose of DITROPAN XL^® is 5 or 10 mg once daily at approximately the same time each day. Dosage may be adjusted in 5-mg increments to achieve a balance of efficacy and tolerability (up to a maximum of 30 mg/day). In general, dosage adjustment may proceed at approximately weekly intervals.

Pediatric Patients Aged 6 Years of Age and Older

The recommended starting dose of DITROPAN XL^® is 5 mg once daily at approximately the same time each day. Dosage may be adjusted in 5-mg increments to achieve a balance of efficacy and tolerability (up to a maximum of 20 mg/day).

Contraindications

DITROPAN XL^® (oxybutynin chloride) is contraindicated in patients with urinary retention, gastric retention and other severe decreased gastrointestinal motility conditions, uncontrolled narrow-angle glaucoma and in patients who are at risk for these conditions.

DITROPAN XL^® is also contraindicated in patients who have demonstrated hypersensitivity to the drug substance or other components of the product.

Adverse Reactions

Adverse Events with DITROPAN XL^®

The safety and efficacy of DITROPAN XL^® (oxybutynin chloride) were evaluated in a total of 580 participants who received DITROPAN XL^® in 4 clinical trials (429 patients) and four pharmacokinetic studies (151 healthy volunteers). The 429 patients were treated with 5–30 mg/day for up to 4.5 months. Three of the 4 clinical trials allowed dose adjustments based on efficacy and adverse events and one was a fixed-dose escalation design. Safety information is provided for 429 patients from these three controlled clinical studies and one open-label study in the first column of Table 3 below.

Adverse events from two additional fixed-dose, active-controlled, 12-week treatment duration, postmarketing studies, in which 576 patients were treated with DITROPAN XL^® 10 mg/day, are also listed in Table 3 (second column). The adverse events are reported regardless of causality.

The most common adverse events reported by the 429 patients receiving 5–30 mg/day DITROPAN XL^® were the expected side effects of anticholinergic agents. The incidence of dry mouth was dose-related.

The discontinuation rate for all adverse events was 6.8% in the 429 patients from the 4 studies of efficacy and safety who received 5–30 mg/day. The most frequent adverse event causing early discontinuation of study medication was nausea (1.9%), while discontinuation due to dry mouth was 1.2%.

In addition, the following adverse events were reported by ≥ 1 to < 5% of all patients who received DITROPAN XL^® in the 6 adjustable and fixed-dose efficacy and safety studies. Infections and infestations: nasopharyngitis, upper respiratory tract infection, sinusitis, bronchitis, cystitis; Psychiatric disorders: insomnia, depression, nervousness, confusional state; Nervous System Disorders: dysgeusia; Cardiac disorders: palpitations; Vascular disorders: hypertension; Respiratory, thoracic and mediastinal disorders: nasal dryness, cough, pharyngolaryngeal pain, dry throat; Gastrointestinal Disorders: gastroesophageal reflux disease, abdominal pain, loose stools, flatulence, vomiting; Skin and subcutaneous tissue disorders: dry skin, pruritis; Musculoskeletal and connective tissue disorders: back pain, arthralgia, pain in extremity; Renal and urinary disorders: urinary retention, urinary hesitation, dysuria; General disorders and administration site conditions: fatigue, edema peripheral, asthenia, chest pain; Investigations: blood pressure increased.

Postmarketing Surveillance

Because postmarketing reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. The following additional adverse drug reactions have been reported from worldwide postmarketing experience with DITROPAN XL^®: Psychiatric Disorders: psychotic disorder, agitation, hallucinations, memory impairment; Nervous System Disorders: convulsions; Eye Disorders: glaucoma; Cardiac Disorders: arrhythmia, tachycardia, QT interval prolongation; Vascular Disorders: flushing; Skin and Subcutaneous Tissue Disorders: rash; Renal and Urinary Disorders: impotence; General Disorders and Administration Site Conditions: hypersensitivity reactions, including angioedema with airway obstruction, urticaria, and face edema; rare anaphylactic reactions requiring hospitalization for emergency treatment; Injury, poisoning and procedural complications: fall.

Additional adverse events reported with some other oxybutynin chloride formulations include: cycloplegia, mydriasis, and suppression of lactation.

Drug Interactions

The concomitant use of oxybutynin with other anticholinergic drugs or with other agents which produce dry mouth, constipation, somnolence (drowsiness), and/or other anticholinergic-like effects may increase the frequency and/or severity of such effects.

Anticholinergic agents may potentially alter the absorption of some concomitantly administered drugs due to anticholinergic effects on gastrointestinal motility. This may be of concern for drugs with a narrow therapeutic index.

Mean oxybutynin chloride plasma concentrations were approximately 2 fold higher when DITROPAN XL^® was administered with ketoconazole, a potent CYP3A4 inhibitor. Other inhibitors of the cytochrome P450 3A4 enzyme system, such as antimycotic agents (e.g., itraconazole and miconazole) or macrolide antibiotics (e.g., erythromycin and clarithromycin), may alter oxybutynin mean pharmacokinetic parameters (i.e., C_max and AUC). The clinical relevance of such potential interactions is not known. Caution should be used when such drugs are co-administered.

Overdosage

The continuous release of oxybutynin from DITROPAN XL^® (oxybutynin chloride) should be considered in the treatment of overdosage. Patients should be monitored for at least 24 hours. Treatment should be symptomatic and supportive. Activated charcoal as well as a cathartic may be administered.

Overdosage with oxybutynin chloride has been associated with anticholinergic effects including central nervous system excitation, flushing, fever, dehydration, cardiac arrhythmia, vomiting, and urinary retention.

Ingestion of 100 mg oxybutynin chloride in association with alcohol has been reported in a 13-year-old boy who experienced memory loss, and a 34-year-old woman who developed stupor, followed by disorientation and agitation on awakening, dilated pupils, dry skin, cardiac arrhythmia, and retention of urine. Both patients fully recovered with symptomatic treatment.

Description

DITROPAN XL^® (oxybutynin chloride) is an antispasmodic, anticholinergic agent. Each DITROPAN XL^® Extended Release Tablet contains 5 mg, 10 mg, or 15 mg of oxybutynin chloride USP, formulated as a once-a-day controlled-release tablet for oral administration. Oxybutynin chloride is administered as a racemate of R- and S-enantiomers.

Chemically, oxybutynin chloride is d,l (racemic) 4-diethylamino-2-butynyl phenylcyclohexylglycolate hydrochloride. The empirical formula of oxybutynin chloride is C₂₂H₃₁NO₃•HCl.

Its structural formula is:

Oxybutynin chloride is a white crystalline solid with a molecular weight of 393.9. It is readily soluble in water and acids, but relatively insoluble in alkalis.

DITROPAN XL^® also contains the following inert ingredients: cellulose acetate, hypromellose, lactose, magnesium stearate, polyethylene glycol, polyethylene oxide, synthetic iron oxides, titanium dioxide, polysorbate 80, sodium chloride, and butylated hydroxytoluene.

System Components and Performance

DITROPAN XL^® uses osmotic pressure to deliver oxybutynin chloride at a controlled rate over approximately 24 hours. The system, which resembles a conventional tablet in appearance, comprises an osmotically active bilayer core surrounded by a semipermeable membrane. The bilayer core is composed of a drug layer containing the drug and excipients, and a push layer containing osmotically active components. There is a precision-laser drilled orifice in the semipermeable membrane on the drug-layer side of the tablet. In an aqueous environment, such as the gastrointestinal tract, water permeates through the membrane into the tablet core, causing the drug to go into suspension and the push layer to expand. This expansion pushes the suspended drug out through the orifice. The semipermeable membrane controls the rate at which water permeates into the tablet core, which in turn controls the rate of drug delivery. The controlled rate of drug delivery into the gastrointestinal lumen is thus independent of pH or gastrointestinal motility. The function of DITROPAN XL^® depends on the existence of an osmotic gradient between the contents of the bilayer core and the fluid in the gastrointestinal tract. Since the osmotic gradient remains constant, drug delivery remains essentially constant. The biologically inert components of the tablet remain intact during gastrointestinal transit and are eliminated in the feces as an insoluble shell.

Clinical Pharmacology

Oxybutynin chloride exerts a direct antispasmodic effect on smooth muscle and inhibits the muscarinic action of acetylcholine on smooth muscle. Oxybutynin chloride exhibits only one-fifth of the anticholinergic activity of atropine on the rabbit detrusor muscle, but four to ten times the antispasmodic activity. No blocking effects occur at skeletal neuromuscular junctions or autonomic ganglia (antinicotinic effects).

Oxybutynin chloride relaxes bladder smooth muscle. In patients with conditions characterized by involuntary bladder contractions, cystometric studies have demonstrated that oxybutynin increases bladder (vesical) capacity, diminishes the frequency of uninhibited contractions of the detrusor muscle, and delays the initial desire to void. Oxybutynin thus decreases urgency and the frequency of both incontinent episodes and voluntary urination.

Antimuscarinic activity resides predominantly in the R-isomer. A metabolite, desethyloxybutynin, has pharmacological activity similar to that of oxybutynin in in vitro studies.

Pharmacokinetics

Absorption

Following the first dose of DITROPAN XL^® (oxybutynin chloride), oxybutynin plasma concentrations rise for 4 to 6 hours; thereafter steady concentrations are maintained for up to 24 hours, minimizing fluctuations between peak and trough concentrations associated with oxybutynin.

The relative bioavailabilities of R- and S-oxybutynin from DITROPAN XL^® are 156% and 187%, respectively, compared with oxybutynin. The mean pharmacokinetic parameters for R- and S-oxybutynin are summarized in Table 1. The plasma concentration-time profiles for R- and S-oxybutynin are similar in shape; Figure 1 shows the profile for R-oxybutynin.

Figure 1. Mean R-oxybutynin plasma concentrations following a single dose of DITROPAN XL^® 10 mg and oxybutynin 5 mg administered every 8 hours (n=23 for each treatment).

Steady state oxybutynin plasma concentrations are achieved by Day 3 of repeated DITROPAN XL^® dosing, with no observed drug accumulation or change in oxybutynin and desethyloxybutynin pharmacokinetic parameters.

DITROPAN XL^® steady state pharmacokinetics were studied in 19 children aged 5–15 years with detrusor overactivity associated with a neurological condition (e.g., spina bifida). The children were on DITROPAN XL^® total daily dose ranging from 5 to 20 mg (0.10 to 0.77 mg/kg). Sparse sampling technique was used to obtain serum samples. When all available data are normalized to an equivalent of 5 mg per day DITROPAN XL^®, the mean pharmacokinetic parameters derived for R- and S-oxybutynin and R- and S-desethyloxybutynin are summarized in Table 2. The plasma-time concentration profiles for R- and S-oxybutynin are similar in shape; Figure 2 shows the profile for R-oxybutynin when all available data are normalized to an equivalent of 5 mg per day.

Figure 2. Mean steady state (± SD) R-oxybutynin plasma concentrations following administration of 5 to 20 mg DITROPAN XL^® once daily in children aged 5–15. Plot represents all available data normalized to an equivalent of DITROPAN XL^® 5 mg once daily.

Food Effects

The rate and extent of absorption and metabolism of oxybutynin are similar under fed and fasted conditions.

Distribution

Oxybutynin is widely distributed in body tissues following systemic absorption. The volume of distribution is 193 L after intravenous administration of 5 mg oxybutynin chloride. Both enantiomers of oxybutynin are highly bound (>99%) to plasma proteins. Both enantiomers of N-desethyloxybutynin are also highly bound (>97%) to plasma proteins. The major binding protein is alpha-1 acid glycoprotein.

Metabolism

Oxybutynin is metabolized primarily by the cytochrome P450 enzyme systems, particularly CYP3A4 found mostly in the liver and gut wall. Its metabolic products include phenylcyclohexylglycolic acid, which is pharmacologically inactive, and desethyloxybutynin, which is pharmacologically active. Following DITROPAN XL^® administration, plasma concentrations of R- and S-desethyloxybutynin are 73% and 92%, respectively, of concentrations observed with oxybutynin.

Excretion

Oxybutynin is extensively metabolized by the liver, with less than 0.1% of the administered dose excreted unchanged in the urine. Also, less than 0.1% of the administered dose is excreted as the metabolite desethyloxybutynin.

Dose Proportionality

Pharmacokinetic parameters of oxybutynin and desethyloxybutynin (C_max and AUC) following administration of 5–20 mg of DITROPAN XL^® are dose proportional.

Special Populations

Geriatric

The pharmacokinetics of DITROPAN XL^® were similar in all patients studied (up to 78 years of age).

Pediatric

The pharmacokinetics of DITROPAN XL^® were evaluated in 19 children aged 5–15 years with detrusor overactivity associated with a neurological condition (e.g., spina bifida). The pharmacokinetics of DITROPAN XL^® in these pediatric patients were consistent with those reported for adults (see Tables 1 and 2, and Figures 1 and 2 above).

Gender

There are no significant differences in the pharmacokinetics of oxybutynin in healthy male and female volunteers following administration of DITROPAN XL^®.

Race

Available data suggest that there are no significant differences in the pharmacokinetics of oxybutynin based on race in healthy volunteers following administration of DITROPAN XL^®.

Renal Insufficiency

There is no experience with the use of DITROPAN XL^® in patients with renal insufficiency.

Hepatic Insufficiency

There is no experience with the use of DITROPAN XL^® in patients with hepatic insufficiency.

Drug-Drug Interactions

See PRECAUTIONS: Drug Interactions .

Clinical Studies

DITROPAN XL^® (oxybutynin chloride) was evaluated for the treatment of patients with overactive bladder with symptoms of urge urinary incontinence, urgency, and frequency in three controlled studies and one open-label study. The majority of patients were Caucasian (89.0%) and female (91.9%) with a mean age of 59 years (range, 18 to 98 years). Entry criteria required that patients have urge or mixed incontinence (with a predominance of urge) as evidenced by ≥ 6 urge incontinence episodes per week and ≥ 10 micturitions per day. Study 1 was a fixed-dose escalation design, whereas the other studies used a dose-adjustment design in which each patient's final dose was adjusted to a balance between improvement of incontinence symptoms and tolerability of side effects. Controlled studies included patients known to be responsive to oxybutynin or other anticholinergic medications, and these patients were maintained on a final dose for up to 2 weeks.

The efficacy results for the three controlled trials are presented in the following tables and figures.

How Supplied / Storage and Handling

DITROPAN XL^® (oxybutynin chloride) Extended Release Tablets are available in three dosage strengths, 10 mg (pink), and 15 mg (gray) and are imprinted with "10 XL", or "15 XL". DITROPAN XL^® Extended Release Tablets are supplied in

Storage

Store at 25°C (77°F); excursions permitted to 15–30°C (59–86°F) [see USP Controlled Room Temperature]. Protect from moisture and humidity.

Patient Counseling Information

Patients should be informed that oxybutynin may produce angioedema that could result in life-threatening airway obstruction. Patients should be advised to promptly discontinue oxybutynin therapy and seek immediate medical attention if they experience edema of the tongue, edema of the laryngopharynx, or difficulty breathing.

Patients should be informed that heat prostration (fever and heat stroke due to decreased sweating) can occur when anticholinergics such as oxybutynin chloride are administered in the presence of high environmental temperature.

Because anticholinergic agents such as oxybutynin may produce drowsiness (somnolence) or blurred vision, patients should be advised to exercise caution.

Patients should be informed that alcohol may enhance the drowsiness caused by anticholinergic agents such as oxybutynin.

Patients should be informed that DITROPAN XL^® should be swallowed whole with the aid of liquids. Patients should not chew, divide, or crush tablets. The medication is contained within a nonabsorbable shell designed to release the drug at a controlled rate. The tablet shell is eliminated from the body; patients should not be concerned if they occasionally notice in their stool something that looks like a tablet.

DITROPAN XL^® should be taken at approximately the same time each day.