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Generic Name
Doxepin
Brand Names
Prudoxin, Silenor, Zonalon
FDA approval date: May 13, 1986
Classification: Tricyclic Antidepressant
Form: Cream, Tablet, Capsule, Solution
What is Prudoxin (Doxepin)?
PRUDOXIN ® Cream is indicated for the short-term management of moderate pruritus in adult patients with atopic dermatitis or lichen simplex chronicus.
Approved To Treat
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Brand Information
PRUDOXIN (doxepin hydrochloride)
1DESCRIPTION
PRUDOXIN
Doxepin hydrochloride, USP is one of a class of agents known as dibenzoxepin tricyclic antidepressant compounds. It is an isomeric mixture of N,N-dimethyldibenz[
PRUDOXIN
2CLINICAL PHARMACOLOGY
Although doxepin HCl does have H1 and H2 histamine receptor blocking actions, the exact mechanism by which doxepin exerts its antipruritic effect is unknown. PRUDOXIN
Once absorbed into the systemic circulation, doxepin undergoes hepatic metabolism that results in conversion to pharmacologically-active desmethyldoxepin. Further glucuronidation results in urinary excretion of the parent drug and its metabolites. Desmethyldoxepin has a half-life that ranges from 28 to 52 hours and is not affected by multiple dosing. Plasma levels of both doxepin and desmethyldoxepin are highly variable and are poorly correlated with dosage. Wide distribution occurs in body tissues including lungs, heart, brain, and liver. Renal disease, genetic factors, age, and other medications affect the metabolism and subsequent elimination of doxepin. (See
3INDICATIONS AND USAGE
PRUDOXIN
4CONTRAINDICATIONS
Because doxepin HCl has an anticholinergic effect and because significant plasma levels of doxepin are detectable after topical PRUDOXIN
PRUDOXIN
5WARNINGS
Drowsiness occurs in over 20% of patients treated with PRUDOXIN
The sedating effects of alcoholic beverages, antihistamines, and other CNS depressants may be potentiated when PRUDOXIN
If excessive drowsiness occurs it may be necessary to reduce the frequency of applications, the amount of cream applied, and/or the percentage of body surface area treated, or discontinue the drug. However, the efficacy with reduced frequency of applications has not been established.
Keep this product away from the eyes.
6PRECAUTIONS
General Drowsiness: Since drowsiness may occur with the use of PRUDOXIN® Cream, patients should be warned of the possibility and cautioned against driving a car or operating dangerous machinery while using this drug. Patients should also be cautioned that their response to alcohol may be potentiated.
Sedating drugs may cause confusion and oversedation in the elderly; elderly patients generally should be observed closely for confusion and oversedation when started on PRUDOXIN
Use under occlusion: Occlusive dressings may increase the absorption of most topical drugs; therefore, occlusive dressings should not be utilized with PRUDOXIN® Cream.
Contact sensitization: Use of PRUDOXIN® Cream can cause Type IV hypersensitivity reactions (contact sensitization) to doxepin.
6.1Drug Interactions
Studies have not been performed examining drug interactions with PRUDOXIN
Drugs Metabolized by P450 2D6: The biochemical activity of the drug metabolizing isozyme cytochrome P450 2D6 (debrisoquin hydroxylase) is reduced in a subset of the Caucasian population (about 7-10% of Caucasians are so-called "poor metabolizers"); reliable estimates of the prevalence of reduced P450 2D6 isozyme activity among Asian, African and other populations are not yet available.
Poor metabolizers have higher than expected plasma concentrations of tricyclic antidepressants (TCAs) when given usual doses. Depending on the fraction of drug metabolized by P450 2D6, the increase in plasma concentration may be small, or quite large (8-fold increase in plasma AUC of the TCA).
In addition, certain drugs inhibit the activity of this isozyme and make normal metabolizers resemble poor metabolizers. An individual who is stable on a given dosage regimen of a TCA may become abruptly toxic when given one of these inhibiting drugs as concomitant therapy. The drugs that inhibit cytochrome P450 2D6 include some that are not metabolized by the enzyme (quinidine; cimetidine) and many that are substrates for P450 2D6 (many other antidepressants, phenothiazines, and the Type 1C antiarrhythmics propafenone and flecainide). While all the selective serotonin reuptake inhibitors (SSRIs), e.g., fluoxetine, sertraline, and paroxetine, inhibit P450 2D6, they may vary in the extent of inhibition. The extent to which SSRI-TCA interactions may pose clinical problems will depend on the degree of inhibition and the pharmacokinetics of the SSRI involved. Nevertheless, caution is indicated in the co-administration of TCAs with any of the SSRIs. Of particular importance, sufficient time must elapse before initiating TCA treatment in a patient being withdrawn from fluoxetine, given the long half- life of the parent and active metabolite (at least 5 weeks may be necessary).
Concomitant use of tricyclic antidepressants with drugs that can inhibit cytochrome P450 2D6 may require lower doses than usually prescribed for either the tricyclic antidepressant or the other drug. It is desirable to monitor TCA plasma levels whenever a TCA is going to be co-administered with another drug known to be an inhibitor of P450 2D6.
MAO Inhibitors: Serious side effects and even death have been reported following the concomitant use of certain drugs with MAO inhibitors. Therefore, MAO inhibitors should be discontinued at least two weeks prior to the cautious initiation of therapy with PRUDOXIN® Cream. The exact length of time may vary and is dependent upon the particular MAO inhibitor being used, the length of time it has been administered, and the dosage involved.
Cimetidine: Serious anticholinergic symptoms (i.e., severe dry mouth, urinary retention and blurred vision) have been associated with elevations in the serum levels of tricyclic antidepressant when cimetidine therapy is initiated. Additionally, higher than expected tricyclic antidepressant levels have been observed when they are begun in patients already taking cimetidine.
Alcohol: Alcohol ingestion may exacerbate the potential sedative effects of PRUDOXIN® Cream. This is especially important in patients who may use alcohol excessively.
Tolazamide: A case of severe hypoglycemia has been reported in a type II diabetic patient maintained on tolazamide (1 gm/day) 11 days after the addition of oral doxepin (75 mg/day).
6.2Carcinogenesis, Mutagenesis, Impairment of Fertility
Carcinogenesis, mutagenesis, and impairment of fertility studies have not been conducted with doxepin hydrochloride.
6.3Pregnancy
Reproduction studies have been performed in which doxepin was orally administered to rats and rabbits at doses up to 0.6 and 1.2 times, respectively, the estimated exposure to doxepin that results from use of 16 grams of PRUDOXIN
6.4Nursing Mothers
Doxepin is excreted in human milk after oral administration. It is possible that doxepin may also be excreted in human milk following topical application of PRUDOXIN
One case has been reported of apnea and drowsiness in a nursing infant whose mother was taking an oral dosage form of doxepin HCl.
Because of the potential for serious adverse reactions in nursing infants from doxepin, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.
6.5Pediatric Use
The use of PRUDOXIN
6.6Geriatric Use
Clinical studies of PRUDOXIN
The extent of renal excretion of doxepin has not been determined. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selections.
Sedating drugs may cause confusion and oversedation in the elderly; elderly patients generally should be observed closely for confusion and oversedation when started on PRUDOXIN
7ADVERSE REACTIONS
Controlled Clinical Trials
Systemic Adverse Effects: In controlled clinical trials of patients treated with PRUDOXIN® Cream, the most common systemic adverse event reported was drowsiness. Drowsiness occurred in 71 of 330 (22%) of patients treated with PRUDOXIN® Cream compared to 7 of 334 (2%) of patients treated with vehicle cream. Drowsiness resulted in the premature discontinuation of the drug in approximately 5% of patients treated with PRUDOXIN® Cream in controlled clinical trials.
Local Site Adverse Effects: In controlled clinical trials of patients treated with PRUDOXIN® Cream, the most common local site adverse event reported was burning and/or stinging at the site of application.
These occurred in 76 of 330 (23%) of patients treated with PRUDOXIN
The table below presents the adverse events reported at an incidence of ≥ 1 % in either PRUDOXIN
Adverse events occurring in 0.5% to < 1.0% of PRUDOXIN
8Post-Marketing Experience
Twenty-six cases of allergic contact dermatitis have been reported in patients using PRUDOXIN
9OVERDOSAGE
Deaths may occur from overdosage with this class of drugs. As the management is complex and changing, it is recommended that the physician contact a poison control center for current information on treatment. Signs and symptoms of toxicity develop rapidly after tricyclic antidepressant overdose; therefore, hospital monitoring is required as soon as possible.
9.1Manifestations
Should overdosage with topical application of PRUDOXIN
Other signs of overdose may include: confusion, disturbed concentration, transient visual hallucinations, dilated pupils, agitation, hyperactive reflexes, stupor, drowsiness, muscle rigidity, vomiting, hypothermia, hyperpyrexia, or any of the symptoms listed under ADVERSE REACTIONS.
9.2General Recommendations
General: Obtain an ECG and immediately initiate cardiac monitoring. Protect the patient's airway, establish an intravenous line and initiate gastric decontamination. A minimum of six hours of observation with cardiac monitoring and observation for signs of CNS or respiratory depression, hypotension, cardiac dysrhythmias and/or conduction blocks, and seizures is strongly advised. If signs of toxicity occur at any time during this period, extended monitoring is recommended. There are case reports of patients succumbing to fatal dysrhythmias late after overdose; these patients had clinical evidence of significant poisoning prior to death and most received inadequate gastrointestinal decontamination.
Monitoring of plasma drug levels should not guide management of the patient.
Cardiovascular: A maximal limb-lead QRS duration of ≥ 0.10 seconds may be the best indication of the severity of the overdose. Intravenous sodium bicarbonate should be used to maintain the serum pH in the range of 7.45 to 7.55. If the pH response is inadequate, hyperventilation may also be used. Concomitant use of hyperventilation and sodium bicarbonate should be done with extreme caution, with frequent pH monitoring. A pH>7.60 or a pCO2 <20 mm Hg is undesirable. Dysrhythmias unresponsive to sodium bicarbonate therapy/hyperventilation may respond to lidocaine, bretylium or phenytoin. Type 1A and 1C antiarrhythmics are generally contraindicated (e.g., quinidine, disopyramide, and procainamide).
In rare instances, hemoperfusion may be beneficial in acute refractory cardiovascular instability in patients with acute toxicity. However, hemodialysis, peritoneal dialysis, exchange transfusions, and forced diuresis generally have been reported as ineffective in tricyclic antidepressant poisoning.
CNS: In patients with CNS depression, early intubation is advised because of the potential for abrupt deterioration. Seizures should be controlled with benzodiazepines, or if these are ineffective, other anticonvulsants (e.g., phenobarbital, phenytoin). Physostigmine is not recommended except to treat life- threatening symptoms that have been unresponsive to other therapies, and then only in consultation with a poison control center.
Pediatric Management: The principles of management of child and adult overdosages are similar. It is strongly recommended that the physician contact the local poison control center for specific pediatric treatment.
10DOSAGE AND ADMINISTRATION
A thin film of PRUDOXIN
The risk for sedation may increase with greater body surface area application of PRUDOXIN
Occlusive dressings may increase the absorption of most topical drugs; therefore, occlusive dressings should not be utilized with PRUDOXIN
11HOW SUPPLIED
PRUDOXIN
NDC 0378-8130-45
Store below 27° C (80° F).
Manufactured for:
Manufactured by:
PRUDOXIN is a registered trademark of Delcor Asset Corporation, a Mylan Company
©2017 Mylan Pharmaceuticals Inc.
DPT:PRUD:R1
140901-0617
12PRINCIPAL DISPLAY PANEL – 5%
NDC 0378-8130-45
PRUDOXIN
For Topical Dermatologic Use Only
Rx only Net Wt. 45 g
Warnings: For External Use Only. Not For Oral, Intravaginal or Ophthalmic Use. Keep away from eyes.
Keep this and all medication out of the reach of children.
Directions: Apply a thin film of PRUDOXIN four times each day with at least a 3 to 4 hour interval between applications. If excessive drowsiness occurs it may be necessary to do one or more of the following: reduce the body surface area treated, reduce the number of applications per day, reduce the amount of cream applied, or discontinue the drug.
Refer to product insert for prescribing information and inactive ingredient listing.
Store below 27ºC (80ºF).
Warnings: For External Use Only. Not For Oral, Intravaginal or Ophthalmic Use.
Keep away from eyes.
Contains: Doxepin hydrochloride, USP, 5% (equivalent to 4.4% doxepin) in a vehicle of sorbitol, cetyl alcohol, isopropyl myristate, glyceryl stearate, PEG-100 stearate, petrolatum, benzyl alcohol, titanium dioxide and purified water.
Manufactured for:
Manufactured by:
PRUDOXIN is a registered
©2017 Mylan Pharmaceuticals Inc.
DPT:8130:45:1C:R1
Mylan.com
