Medihist

Uses

Medihist provides faster relief from the symptoms of hay fever, allergic rhinitis such as sneezing, nasal discharge, itching, ocular itching and burning, nasal and ocular sign and symptoms are relieved rapidly after oral administration.

Medihist is also effective in idiopathic chronic urticaria. In children over 2 years, Medihist is used for the symptomatic relief of seasonal allergic rhinitis and allergic skin conditions such as urticaria nettle rash.

Medihist is also used to associated treatment for these conditions: Allergic Dermatologic Disorders, Allergic Rhinitis (AR), Allergies, Chronic Urticaria, Common Cold, Eye pruritus, Fever, Nasal Congestion, Nasal Itching, Pain, Perennial Allergic Rhinitis (PAR), Perennial Rhinitis, Pollen Allergy, Pruritus, Rhinorrhoea, Seasonal Allergic Rhinitis, Sneezing, Sensation of burning in the eyes, Watery eyes, Watery itchy eyes

How Medihist works

Histamine release is a key mediator in allergic rhinitis and urticaria. As a result, loratadine exerts it's effect by targeting H1 histamine receptors.

Medihist binds to H1 histamine receptors found on the surface of epithelial cells, endothelial cells, eosinophils, neutrophils, airway cells, and vascular smooth muscle cells among others. H1 histamine receptors fall under the wider umbrella of G-protein coupled receptors, and exist in a state of equilibrium between the active and inactive forms. Histamine binding to the H1-receptor facilitates cross linking between transmembrane domains III and V, stabilizing the active form of the receptor. On the other hand, antihistamines bind to a different site on the H1 receptor favouring the inactive form.

Hence, loratadine can more accurately be classified as an "inverse agonist" as opposed to a "histamine antagonist", and can prevent or reduce the severity of histamine mediated symptoms.

Dosage

Medihist dosage

Adult & children over 12 years of age: One Medihist 10 mg tablet once daily (usually in the morning).

Children:

• 2-12 years (body weight more than 30 Kg): 10 mg Medihist once daily.
• 2-12 years (body weight less than 30 Kg): 5 mg Medihist once daily.
• Below 2 years of age: Safety and efficacy of Medihist have not been established.

Liver & renal impairment: Patients with liver impairment and renal insufficiency (GFR <30 ml/min) should be given a lower initial dose (10 mg every other day).

Side Effects

Fatigue, nausea and headache were reported rarely. Scientific studies showed that Medihist does not cause drowsiness. It does not affect performance and ability to drive or tasks requiring concentration.

Toxicity

Second generation antihistamines such as loratadine have very few adverse effects; however, insomnia, headache, fatigue, drowsiness and rash have been reported. Symptoms of loratadine overdose include gastrointestinal side effects, agitation, drowsiness, tachycardia, and headache. It is advised to obtain an ECG in the event of loratadine overdose.

Precaution

Patients with liver impairment and renal insufficiency (GFR <30 ml/min) should be given a lower initial dose (10 mg every other day).

Interaction

When administered concurrently with alcohol, Medihist has no potentiating effect as measured by psychomotor performance studies. Interactions with other drugs have not been reported.

Food Interaction

[Minor] Theoretically, grapefruit juice may increase the plasma concentrations of loratadine as it does other drugs that are substrates of the CYP450 3A4 enzymatic pathway.

The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits.

The clinical significance of this potential interaction is unknown.

Reported interactions with potent CYP450 3A4 inhibitors like clarithromycin, erythromycin and ketoconazole have produced substantial increases in the area under the plasma concentration-time curve (AUC) of loratadine and its active metabolite, descarboethoxyloratadine, without associated changes in the overall safety profile of the drug.

Medihist Drug Interaction

Unknown: fluticasone / salmeterol, aspirin, aspirin, diphenhydramine, ubiquinone, duloxetine, omega-3 polyunsaturated fatty acids, fluticasone nasal, pregabalin, metoprolol, metoprolol, polyethylene glycol 3350, albuterol, montelukast, budesonide / formoterol, levothyroxine, acetaminophen, cyanocobalamin, ascorbic acid, cholecalciferol

Medihist Disease Interaction

Moderate: renal/liver disease

Volume of Distribution

The volume of distribution of loratadine is 120 L/Kg.

Elimination Route

Medihist is rapidly absorbed and achieves peak plasma concentration in 1-2 hours, while it's main metabolite achieves peak plasma concentration in 3-4 hours.

In the rapid dissolve formulation, the pharmacokinetic parameters of loratadine are as follows: Cmax = 2.56 ng/ml, Tmax = 1.14 hrs, AUC = 6.14 ng x hr/ml.

In the rapid dissolve formulation, the pharmacokinetic parameters of descarboethoxyloratadine are as follows: Cmax = 3.72 ng/ml, Tmax = 1.97 hr, AUC = 49.1 ng x hr/ml.

In the conventional formulation, the pharmacokinetic parameters of loratadine are as follows: Cmax = 2.11 ng/ml, Tmax = 1.00 hr, AUC = 4.64 ng x hr/ml

In the conventional formulation, the pharmacokinetic parameters of descarboethoxyloratadine are as follows: Cmax = 3.66 ng/ml, Tmax = 1.97 hr, AUC = 48.4 ng x hr/ml

Half Life

The elimination half life is approximately 10 hours for loratadine and 20 hours for descarboethoxyloratadine.

Clearance

The clearance of loratadine after single oral doses of 20 mg and 40 mg are 12 L/h/kg and 9 L/h/kg respectively. P-glycoprotein is involved in the clearance of many 2nd generation antihistamines, including loratadine, from the central nervous system. 1st generation antihistamines are not cleared by P-glycoprotein, which may help explain why they have a different central nervous system adverse effect profile compared to their 2nd generation counterparts. It appears that an antihistamine with higher affinity for p-glycoprotein will have a lower incidence of CNS adverse effects.

Elimination Route

Over a 10 day period, 40% of loratadine is excreted in the urine, and 42% is eliminated in the faeces.

Pregnancy & Breastfeeding use

Use in pregnancy: There is no experience of the use of Medihist in human pregnancy, hence it should not be used during pregnancy.

Use in lactation: Medihist is excreted in breast milk, so it should not be administered to lactating mother.

Contraindication

Medihist is contraindicated in patients who have shown hypersensitivity or idiosyncracy to their components.

Acute Overdose

Symptoms: Somnolence, tachycardia headache, drowsiness, extrapyramidal manifestations and palpitations.

Management: Symptomatic and supportive treatment. Immediately empty stomach by inducing emesis with ipecac syrup. Admin of activated charcoal after emesis may be useful. If induction of vomiting is unsuccessful or contraindicated (e.g. patient is comatose, having seizures or lacks gag reflex), gastric lavage with NaCl 0.9% soln may be performed to prevent aspiration of gastric contents. Saline cathartics may be useful to rapidly dilute bowel contents.

Storage Condition

Store between 20-25° C.

Innovators Monograph

You find simplified version here Medihist