Desloratadine

BRAND NAMES:

Brand names for desloratadine include Clarinex (a widely recognized brand in the United States), Aerius, and Neoclarityn. Additional brand names may differ by region and can include Mondeslor, Dazit M, Dezlorid, and Des-OD, among others.

• Clarinex: A well-known brand of desloratadine, also available in an orally disintegrating form known as Clarinex RediTabs.
• Aerius: Another frequently used brand name for desloratadine.
• Neoclarityn: A brand marketed in certain regions.
• Other brands: Depending on the country, desloratadine may also be sold under names such as Mondeslor, Dazit M, Dezlorid, Des-OD, and others.

MECHANISM OF ACTION

Similar to other H₁-blockers, desloratadine works by competing with free histamine for binding to H₁ receptors located in the gastrointestinal tract, uterus, large blood vessels, and bronchial smooth muscle. By blocking the effects of endogenous histamine, it provides temporary relief from allergy-related symptoms such as nasal congestion and watery eyes.

PHARMACOKINETICS:

Absorption            

When 5 mg of desloratadine was administered orally once daily for ten days to healthy volunteers, the drug reached a mean Tmax of about 3 hours, with a steady-state Cmax of 4 mg/mL and an AUC of 56.9 ng·hr/mL. A similar absorption pattern occurred with the oral solution form, and food intake had no effect on its absorption.

Distribution

Desloratadine is widely distributed throughout the body's tissues and is highly bound to plasma proteins. It is primarily metabolized in the liver to its active metabolite, 3-hydroxydesloratadine, and then approximately 87% of the dose is equally eliminated in the urine and feces. 

Metabolism

Desloratadine is extensively metabolized in the liver to 3-hydroxydesloratadine, which is then glucuronidated. Around 6% of individuals are poor metabolizers, leading to higher drug exposure in these cases.

Excreation 

The mean elimination half-life of desloratadine is about 27 hours. Around 87% of the administered doseis excreted in the urine and feces in nearly equal amounts as metabolites, and both desloratadine and its active metabolite are not effectively removed by hemodialysis.

PHARMACODYNAMICS

Desloratadine is a long-acting, second-generation H₁-receptor antagonist that acts selectively on peripheral H₁ receptors. Histamine, a chemical released from mast cells, triggers many allergy symptoms such as tissue swelling by binding to histamine receptors on various cells. This binding activates the cells, leading to the release of other substances responsible for allergic reactions. Desloratadine blocks H₁ receptors, preventing histamine from activating these cells and thereby reducing allergic symptoms. Unlike many older antihistamines, it does not readily cross the blood–brain barrier, so it does not typically cause drowsiness.

ADMINISTRATION

Desloratadine is administered orally, typically once a day, with or without food. The specific form and dosage depend on the patient's age and condition, and should always be used according to a healthcare provider's instructions. 

DOSAGE AND STRENGTHS

Desloratadine is available in oral tablets, orally disintegrating tablets, and oral solution forms, with common strengths of 2.5 mg and 5 mg. The standard adult dosage for allergic rhinitis or chronic hives is typically 5 mg once daily. 

Available Strengths

Desloratadine is available in the following strengths and forms: 

• Oral Tablets (film-coated): 5 mg

• Orally Disintegrating Tablets: 2.5 mg and 5 mg

• Oral Solution (syrup): 0.5 mg/mL (typically a 1.25 mg dose in 2.5 mL, or a 2.5 mg dose in 5 mL) 

DRUG INTERACTIONS

Desloratadine has no severe drug interactions but does have potentially serious or moderate interactions with a variety of medications, primarily involving other central nervous system (CNS) depressants and certain drugs that affect its metabolism. 

Serious Interactions

Desloratadine has serious interactions with a number of drugs, which in many cases require avoiding co-administration or close monitoring due to increased sedation or altered drug levels. 

• CNS Depressants: Co-administration with opioids (e.g., alfentanil, codeine, fentanyl, hydrocodone, morphine, and oxycodone), other antihistamines (e.g., olopatadine intranasal), benzodiazepines, and other sedatives can significantly increase sedation and respiratory depression.

• Monoamine Oxidase (MAO) Inhibitors: Drugs such as isocarboxazid and tranylcypromine can increase the effects of desloratadine by causing additive CNS depression and intensifying anticholinergic effects.

Moderate and Minor Interactions

Desloratadine has numerous moderate interactions with other drugs, many of which can increase the risk of CNS depression or affect heart rhythm (QTc prolongation). 

• Antibiotics: Erythromycin and azithromycin may increase desloratadine levels in the blood, but studies show no clinically relevant changes in the safety profile.

• Antifungals: Ketoconazole may increase desloratadine levels in the blood, with no reported clinically relevant safety issues.

FOOD INTERACTIONS 

Desloratadine has no clinically relevant food interactions, and doses can be taken with or without a meal. 

Specifically:

• Food does not affect the overall absorption or bioavailability of desloratadine.

• Grapefruit juice has been found to have no clinically relevant effect on the disposition (pharmacokinetics) of the drug.

• Alcohol may increase the risk of drowsiness when combined with desloratadine, so caution is advised, but clinically relevant pharmacodynamic interactions have not been observed in studies. 

CONTRAINDICATIONS

Desloratadine is contraindicated in individuals with a known hypersensitivity to desloratadine, loratadine, or any component of the formulation. It should be avoided in patients with severe hepatic impairment, as metabolism may be affected. Caution is advised in renal impairment, where drug clearance can be reduced. The medication is not recommended for use in children below the approved age unless directed by a physician. Additionally, it should be used with caution during pregnancy and lactation, only if the potential benefits outweigh the risks.

SIDE EFFECTS

Common Side effects

• Headache

• Fatigue or unusual tiredness

• Dry mouth

• Sore throat (pharyngitis)

• Nausea, diarrhea, or upset stomach

• Dizziness

• Muscle aches or pain

• Sleepiness or drowsiness

• Painful menstrual cramps (dysmenorrhea)

Serious side effects (rare):

• Symptoms of a severe allergic reaction (anaphylaxis), such as hives, rash, itching, or swelling of the face, lips, tongue, eyes, hands, or throat

• Difficulty breathing or swallowing

• Rapid or irregular heartbeat (tachycardia)

• Wheezing

• Fever or feeling generally unwell

• Liver problems (e.g., yellow skin or eyes)

OVER DOSE

An overdose of desloratadine occurs when the drug is taken in amounts exceeding the recommended dose. Symptoms are usually mild to moderate and may include drowsiness, rapid heartbeat, headache, dry mouth, and gastrointestinal discomfort. Treatment is primarily supportive andsymptomatic, as there is no specific antidote, and hemodialysis is ineffective in removing the drug from the body.

TOXICITY

Desloratadine is generally well-tolerated and exhibits low toxicity at recommended doses. Symptoms of overdose usually resemble its common side effects, though rare cases may involve more serious reactions such as seizures or heart problems, particularly in vulnerable groups like young children.