RiteMED Diphenhydramine HCl

Diphenhydramine hydrochloride.

Each capsule contains: Diphenhydramine hydrochloride 50 mg.

Pharmacology: Pharmacodynamics: Diphenhydramine HCl is an ethanolamine antihistamine with anticholinergic (antimuscarinic), antitussive, anti-emetic, anti-vertigo, and sedative and hypnotic properties.
Antihistamine action occurs by blocking the spasmogenic and congestive effects of histamine by competing with histamine for H₁-receptor sites on effector cells, thus preventing but not reversing responses mediated by histamine alone.
The antitussive effect of diphenhydramine is due to a central mechanism involving suppression of the medullary cough center.
The anti-emetic and anti-motion sickness effects of diphenhydramine result from its central anticholinergic and central nervous system (CNS) depressant properties. Likewise, its activity on parkinsonian syndrome and drug-induced extrapyramidal reactions are related to its central anticholinergic effects.
Anti-vertigo action is by central antimuscarinic effect on the vestibular apparatus and the integrative vomiting center and medullary chemoreceptor trigger zone of the mid brain.
The exact mechanism for CNS depressant action is not known, but it is thought to cause indirect reduction of stimuli to the brain stem reticular formation.
Pharmacokinetics: After oral administration, diphenhydramine HCl is well absorbed from the gastrointestinal (GI) tract. The drug appears in plasma within 15 minutes and peak plasma concentrations are attained within 1 to 4 hours.
After single oral doses of 50 and 100 mg in healthy adults, peak plasma concentrations of 37 to 83 ng/mL and 81 to 159 ng/mL, respectively, have been reported. After oral administration of diphenhydramine at dosages of 2.5 mg every 4 hours or 50 mg every 6 hours, peak steady-state plasma concentrations of the drug were 55 to 85 ng/mL, respectively, and minimum steady-state plasma concentrations were 27.5 or 30 ng/mL, respectively.
Diphenhydramine is widely distributed throughout the body, including the CNS. The drug crosses the placenta and has been detected in milk, although the extent of distribution into milk has not been quantified. Diphenhydramine is approximately 80 to 85% bound to plasma proteins in vitro. Less extensive protein binding of the drug has been reported in healthy Asian adults and in adults with liver cirrhosis.
In a study among Caucasian and Asian patients, diphenhydramine 50 mg given orally caused greater peak plasma concentrations among Asians compared with Caucasians. Plasma protein binding was 85.2% in Caucasians and 76% in Asians. Asians had higher mean volumes of distribution and mean clearance values.
Diphenhydramine is rapidly and almost completely metabolized. After oral administration, the drug undergoes substantial first-pass metabolism in the liver and only about 40 to 60% of an oral dose reaches systemic circulation as unchanged diphenhydramine. Diphenhydramine appears to be metabolized principally to diphenylmethoxyacetic acid, which may further undergo conjugation. The drug also undergoes dealkylation to form the N-demethyl N, N-didemethyl derivatives. Diphenhydramine and its metabolites are excreted principally in urine.
Plasma concentrations of diphenhydramine appear to decline in a monophasic manner, although some pharmacokinetic data suggest a polyphasic elimination. The terminal elimination half-life of diphenhydramine has not been fully-explained, but appears to range from 2.4 to 9.3 hours in healthy adults.

Antihistamine: For the relief of symptoms associated with seasonal, perennial vasomotor rhinitis; allergic conjunctivitis due to foods; mild, uncomplicated allergic skin manifestations of urticaria and angioedema; amelioration of allergic reactions lo blood or plasma; dermatographism; as therapy for anaphylactic reactions adjunctive to epinephrine and other standard measures after acute manifestations have been controlled.
Antiparkinsonism: For parkinsonism (including drug-induced) in the elderly unable to tolerate more potent agents; mild cases of parkinsonism (including drug-induced) in other age groups; in other cases of parkinsonism (including drug-induced) in combination with centrally acting anticholinergic agents.
Nighttime Sleep-Aid: For the short-term management of insomnia.
Antitussive: For the relief of cough caused by minor throat and bronchial irritation such as may occur with the common colds, inhaled irritants or allergy.
Antiemetic/Motion Sickness: For the prevention and treatment of nausea, vomiting, and/or dizziness associated with motion sickness.

See table.

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Dosing in Patients with Renal Failure: In patients with renal failure, dosage intervals should be lengthened from 6 hours to 12 hours depending on the degree of renal impairment.

Diphenhydramine HCl overdosage may vary from CNS depression to CNS stimulation. Stimulation is particularly likely in children. Atropine-like signs and symptoms such as dry mouth, fixed and dilated pupils, flushing, and GI symptoms may also occur. Additional symptoms may include mydriasis, fever, flushing, agitation, tremor, dystonic reactions, hallucinations, and electrocardiogram changes. Large overdose may cause rhabdomyolysis, convulsions, delirium, toxic psychosis, arrhythmias, coma, and cardiovascular collapse.
Treatment should be supportive and directed towards specific symptoms. Administration of activated charcoal should be considered. Empty stomach by aspiration and lavage. Emetics may be tried if the patient is alert. Convulsions and marked CNS stimulation should be treated with parenteral diazepam.

Hypersensitivity to diphenhydramine or any ingredient in the product.
Asthma attack; narrow angle glaucoma; prostatic hypertrophy.
Stenosing peptic ulcer and pyloroduodenal obstructions predispose the patient to an increased risk of GI obstruction. Agents with anticholinergic properties such as diphenhydramine reduce the tone and motility of the GI tract and thus increase the risk of worsening/contributing to GI obstruction.
Bladder-neck obstruction; porphyria.
Do not use in premature infants and neonates.
Do not use in breastfeeding women.
Do not use in patients receiving antidepressant therapy.

Diphenhydramine can cause marked drowsiness; it severely impairs driving performance in standard off the road tests. Patients should avoid driving or performing other tasks requiring complete mental alertness within 8 hours of ingestion.
Diphenhydramine should not be taken with other antihistamines, sedatives or tranquilizers except on medical advice.
Patients should be advised to avoid alcoholic beverages while taking this product. Alcohol potentiates the sedative effects of diphenhydramine.
Patients should be advised to avoid using diphenhydramine for self-medication for longer than 7 to 10 nights and to consult a physician if insomnia persists continuously for longer than two weeks because insomnia may be indicative of a serious underlying physical, emotional, or psychological condition requiring medical attention.
Do not use with any other product containing diphenhydramine, including topical formulations.
Caution should be exercised if given to patients with liver disease (the terminal half-life of diphenhydramine may be prolonged in cirrhotic patients), glaucoma, urinary retention, myasthenia gravis, seizure disorders, hyperthyroidism, cardiovascular disease, or hypertension.
Use in Children: As in adults, antihistamines may diminish mental alertness in children. In the young child, particularly, they may produce excitation.
Use in Elderly: Antihistamines are more likely to cause dizziness, sedation and hypotension in elderly patients.

Use in Pregnancy: Pregnancy Category B. There are no adequate and well-controlled studies in pregnant women. Therefore, diphenhydramine should be used in pregnancy only if the potential benefit justifies the potential risk to the fetus.
Use in Lactation: Diphenhydramine is excreted in human milk. Therefore, use of diphenhydramine when breastfeeding is not recommended.

General: Fatigue, hypersensitivity reactions (e.g., bronchospasm, anaphylaxis and angioedema).
Cardiovascular: Tachycardia, palpitations, hypotension.
Gastrointestinal: Dry mouth, GI disturbance including nausea and vomiting, diarrhea.
Hematologic: Blood disorders.
Hepatic: Liver dysfunction.
Musculoskeletal: Muscle twitching, muscular weakness, myalgia.
Nervous System: Sedation, drowsiness, disturbance in attention, unsteadiness, dizziness, convulsions, headache, paresthesia, dyskinesia, confusion, paradoxical excitation (e.g., increased energy, restlessness, nervousness), incoordination, euphoria, extrapyramidal effects, depression, sleep disturbances, tremors.
Renal: Urinary difficulty, urinary retention, dysuria.
Respiratory: Thickening of bronchial secretions, tightness of chest, dyspnea.
Skin and Appendages: Rash, urticaria, photosensitivity reactions, sweating, hair loss.
Special Senses: Blurred vision, tinnitus.

Alcohol and Other CNS Depressants Including Barbiturates, Tranquilizers, Hypnotics, Sedatives, Antianxiety Agents, and Narcotic Analgesics: Have additive effects with antihistamines. Dosage adjustments of CNS depressants may be necessary to avoid profound CNS depression.
Monoamine Oxidase Inhibitors (MAOI) (Phenelzine, Tranylcypromine, Isocarboxazid, Furazolidone, Procarbazine): May prolong and intensify the anticholinergic and CNS depressant effects of diphenhydramine. Diphenhydramine should be used with caution wit MAOIs or within two weeks of stopping a MAOI.
Anticholinergic Drugs (e.g., Atropine): May potentiate diphenhydramine's anticholinergic side effects.
β-Blockers (Metoprolol, Carvedilol, Labetalol, Propranolol, Timolol): Diphenhydramine increases the plasma concentrations and cardiovascular effects of these drugs.
PAS (4-Aminosalicylic Acid): Diphenhydramine administration significantly reduces absorption of the antituberculosis agent PAS from the GI tract.

Store at temperatures not exceeding 30°C.

Antihistamines & Antiallergics

R06AA02 - diphenhydramine ; Belongs to the class of aminoalkyl ethers used as systemic antihistamines.

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