This medication has been discontinued due to safety concerns, particularly the risk of cardiac arrhythmias associated with Terfenadine. Fexofenadine is a safer alternative antihistamine that is often used in combination with Pseudoephedrine. This document will discuss this discontinued combination, but it is crucial to understand that it should not be prescribed.
Usage
Pseudoephedrine + Terfenadine was previously used to treat symptoms associated with allergic rhinitis and the common cold, such as nasal congestion, runny nose, sneezing, and itchy or watery eyes.
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Pharmacological Classification: This combination belongs to the class of Upper Respiratory Combination products containing a decongestant (Pseudoephedrine) and an antihistamine (Terfenadine).
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Mechanism of Action: Pseudoephedrine acts as a decongestant by stimulating alpha-adrenergic receptors in the nasal mucosa, causing vasoconstriction and reducing nasal swelling. Terfenadine is a histamine H1-receptor antagonist, blocking the effects of histamine and relieving allergy symptoms.
Alternate Names
- Brand Name: Seldane-D (discontinued)
How It Works
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Pharmacodynamics: Pseudoephedrine acts on alpha-adrenergic receptors, primarily in the respiratory tract, leading to vasoconstriction. Terfenadine selectively blocks peripheral H1 receptors, reducing histamine-mediated responses.
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Pharmacokinetics: Both drugs are absorbed orally. Terfenadine is extensively metabolized in the liver, primarily by CYP3A4, to its active metabolite, fexofenadine. Pseudoephedrine is partially metabolized in the liver and excreted primarily by the kidneys.
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Elimination: Terfenadine’s active metabolite, fexofenadine, is excreted in the feces and urine. Pseudoephedrine is primarily eliminated renally.
Dosage
(This dosage information is historical and should not be used for current practice as the drug has been withdrawn from market.)
Standard Dosage
Adults: 1 tablet (60mg terfenadine/120mg pseudoephedrine) twice daily.
Children: Use in children was not recommended.
Special Cases:
- Elderly Patients and Patients with Hepatic Impairment: 1 tablet (60 mg terfenadine/120 mg pseudoephedrine) once daily was recommended due to potential pharmacokinetic changes.
- Patients with Renal Impairment: Dose adjustments were needed as pseudoephedrine is eliminated renally.
Clinical Use Cases
This combination is no longer used in any clinical setting.
Side Effects
Common Side Effects
- Headache
- Dizziness
- Insomnia
- Nervousness
- Dry mouth
- Nausea
Rare but Serious Side Effects
- Cardiac arrhythmias (including Torsades de Pointes), especially with higher doses or in patients with liver disease or those taking interacting medications. This was the primary reason for the drug’s withdrawal.
Contraindications
- Hypersensitivity to terfenadine or pseudoephedrine
- Severe hypertension or coronary artery disease
- Narrow-angle glaucoma
- Urinary retention
- Concomitant use of MAO inhibitors or within 14 days of discontinuing MAOIs
- Patients with hypersensitivity to adrenergic agents
Drug Interactions
- CYP3A4 Inhibitors: Drugs that inhibit CYP3A4 (e.g., ketoconazole, erythromycin, grapefruit juice) can significantly increase terfenadine levels, increasing the risk of cardiac arrhythmias.
- MAO Inhibitors: Co-administration with MAO inhibitors can cause hypertensive crises.
- Antihypertensive Drugs: Pseudoephedrine can counteract the effects of antihypertensive medications.
- Other Sympathomimetics: Additive effects on blood pressure and heart rate can occur.
Pregnancy and Breastfeeding
Terfenadine is classified as Pregnancy Category C. Due to potential risks, use during pregnancy was not recommended unless the benefit clearly outweighed the risk. Pseudoephedrine is also not generally recommended during pregnancy, especially in the first trimester, due to concerns about possible birth defects. Neither drug is recommended during breastfeeding.
Drug Profile Summary
(Historical information only)
- Mechanism of Action: Decongestant (pseudoephedrine) and antihistamine (terfenadine).
- Side Effects: Headache, dizziness, insomnia, nervousness, dry mouth, nausea, serious cardiac arrhythmias.
- Contraindications: Hypersensitivity, severe cardiovascular disease, glaucoma, urinary retention, MAOI use.
- Drug Interactions: CYP3A4 inhibitors, MAO inhibitors, antihypertensives.
- Pregnancy & Breastfeeding: Not recommended.
Popular Combinations
This drug is no longer in use and therefore has no popular combinations. Fexofenadine combined with pseudoephedrine is a more current combination.
Precautions
This drug should no longer be used, therefore precautions are not relevant.
FAQs
Q1: What is the recommended dosage for Pseudoephedrine + Terfenadine?
A: This drug is no longer used. Historically, the adult dose was one tablet (60mg terfenadine/120mg pseudoephedrine) twice a day.
Q2: Why was Terfenadine + Pseudoephedrine discontinued?
A: It was discontinued due to the risk of serious cardiac arrhythmias, particularly Torsades de Pointes, associated with terfenadine, especially when interacting with certain drugs or in patients with liver disease.
Q3: What is a safer alternative to Terfenadine?
A: Fexofenadine, the active metabolite of Terfenadine, does not carry the same risk of cardiac arrhythmias and is considered a safer alternative. It is also available in combination with pseudoephedrine.
Q4: What are the symptoms of a Terfenadine overdose?
A: Symptoms may include cardiac arrhythmias, palpitations, dizziness, syncope, and potentially cardiac arrest.
Q5: Can pregnant women take Pseudoephedrine + Terfenadine?
A: No. This drug is contraindicated during pregnancy.
Q6: What are the potential drug interactions with Terfenadine?
A: Significant interactions can occur with drugs that inhibit CYP3A4 (e.g., ketoconazole, erythromycin), MAO inhibitors, and antihypertensives.
Q7: What should patients do if they experience side effects while taking this medication?
A: As this medication is no longer used, patients should not be taking it. If anyone is still using this medication, they should stop immediately and contact their doctor for an alternative treatment.
Q8: Can Pseudoephedrine + Terfenadine be used in children?
A: No. This medication is not recommended for children.
Q9: How does Pseudoephedrine affect blood pressure?
A: Pseudoephedrine can elevate blood pressure. It should be used cautiously in patients with hypertension.
