Pregnancy, since cimetidine is known to cross the placental barrierĭrink a glass of H 2O before dining: H2 blockers need to be taken before dinner.Nearly everyone has spent at least one night lying in bed wishing for sleep.Gastroesophageal reflux disease ( GERD).Symptomatic treatment of peptic ulcers: reduce the production of hydrochloric acid (less effective than PPIs ).Anaphylactic shock(together with H1 antihistamines).Reduces renal creatinine excretion (along with ranitidine).Can cross the placenta (but is considered safe).Headaches, dizziness, confusion due to its ability to cross the blood-brain barrier.Inhibition of cytochrome P450 ( CYP2C19) → various drugs interactions, e.g., clopidogrel.Antiandrogenic effect (via release of prolactin) → erectile dysfunction, gynecomastia, low libido in men.Almost all side effects are caused by cimetidine side effects in other H2 blockers are rare.Smooth muscle relaxation leading to vasodilatationĬompetitive, reversible antagonism of histamine H2 receptors ( G s protein-coupled receptor ) on parietal cells → ↓ adenylyl cyclase activity → ↓ cAMP levels → ↓ protein kinase A activity → ↓ phosphorylation and activation of H +/K + ATPase → ↓ gastric acid (H +) secretion Side effects.Positive inotropism and enhanced automaticity.Gastric parietal cells ( oxyntic cells ).Second-generation antihistamines: childhood and pregnancy.Allergies : used as antiallergic agent (e.g., in cases of rhinitis, conjunctivitis, hypersensitivity to drugs, urticaria )Īntihistamines are ineffective in acute hereditary angioedema attacks.Nausea: used as antiemetic agents (e.g., diphenhydramine in hyperemesis during pregnancy) because of their central effects.Insomnia: used as sedatives (sleep aid).Anaphylactic shock (e.g., clemastine, dimetindene ).Anti- α-adrenergic effects, e.g, postural hypotension (can lead to falls), weight gain.Anticholinergic effects, e.g., dry mouth and eyes, mydriasis, urinary retention, tachycardia, dizziness, tinnitus ( mostly with first-generation antihistamines).Sedation (significantly less pronounced in second-generation antihistamines due to their limited CNS activity).Central action: sedation (especially first-generation antihistamines due to crossing of blood-brain barrier).Inhibition of allergic bronchial constriction.Inhibition of increased vascular permeability.Competitive, reversible antagonism or inverse agonism of histamine H1 receptors ( G q protein-coupled receptor).↑ Activation of peripheral nociceptive receptors → ↑ pain and pruritus.↑ Bronchiolar smooth muscle contraction (via IP3 and DAG release) → bronchoconstriction.↑ Capillary dilation and permeability → hypotension and edema.Smooth muscles (especially bronchial and nasopharyngeal lining).Usually used as second-line treatment or in combination with proton pump inhibitors ( PPIs).Ranitidine (no longer available in the US).Adjuvant treatment for anaphylactic shock.Hay fever, urticaria, angioedema, and rhinorrhea.First-generation H1 antihistamines are specifically contraindicated in angle-closure glaucoma and pyloric stenosis. Most H1 and H2 antihistamines are contraindicated during pregnancy and childhood. H2 antihistamines are indicated primarily for gastric reflux disease because they reduce the production of stomach acid by reversibly blocking the H2 histamine receptors in the parietal cells of the gastric mucosa. While first-generation H1 antihistamines have a central effect and, thus, are also used as sedatives, second-generation H1 antihistamines have less central effects and are primarily used as antiallergic drugs. This subtype is further divided into two generations. H1 antihistamines are mostly used to treat allergic reactions and mast cell-mediated disorders. They are categorized as either H1 or H2 according to the type of H receptor targeted.
Antihistamines are drugs that antagonize these effects by blocking or inhibiting histamine receptors ( H receptors). Histamine is a biologically active substance that potentiates the inflammatory and immune responses of the body, regulates physiological function in the gut, and acts as a neurotransmitter.
0 kommentar(er)
