Glycopyrrolate
Glycopyrrolate is a synthetic quaternary ammonium **antimuscarinic agent** used primarily as a preanesthetic anticholinergic, to treat bradyarrhythmias, and to reduce hypersialism (excessive salivation). Unlike atropine, its quaternary structure prevents it from crossing the blood-brain barrier appreciably, resulting in **fewer central nervous system (CNS) side effects**. It also has a longer duration of action for controlling salivary secretions compared to atropine. > **Clinical Pearl:** Glycopyrrolate is often preferred over atropine for preanesthetic use when prolonged reduction of salivary and respiratory secretions is desired without the risk of CNS stimulation or depression.
กลไกการออกฤทธิ์: Glycopyrrolate acts as a competitive antagonist of **acetylcholine** at postganglionic **muscarinic receptors** (M1, M2, M3). **Acetylcholine** → Blocked at **Muscarinic Receptors** → Decreased parasympathetic tone. This blockade leads to: - **Heart:** Vagolytic effect → Increased heart rate (tachycardia). - **Secretions:** Antisialagogue effect → Profound reduction in salivary, tracheobronchial, and pharyngeal secretions. - **GI/Urinary:** Decreased smooth muscle motility and tone. - **Eye:** Mydriasis (pupil dilation) and cycloplegia.
ขนาดยาตามชนิดสัตว์
- As an adjunct to anesthesia · 0.011 mg/kg · IM · For maximum effect give 15 minutes prior to anesthetic administration
- For bradyarrhythmias · 0.005-0.01 mg/kg IV or IM, 0.01-0.02 mg/kg SC · IV, IM, SC
- Associated with anesthesia · 0.005-0.01 mg/kg · IV
- As a premed · 0.01 mg/kg · SC or IM
- As a premed · 0.01-0.02 mg/kg · IM or IV
- For treatment of bradyarrhythmias · 0.005-0.01 mg/kg (5-10 micrograms/kg) · IV · Note: ARCI UCGFS Class 3 Drug
- As a bronchodilator · 2-3 mg · IM · two to three times daily · Dose for a 450 kg animal
- To control muscarinic adverse effects associated with imidocarb therapy · 0.0025 mg/kg · IV
- For prevention of bradycardia and to decrease airway and salivary secretions (Rabbits) · 0.01-0.1 mg/kg IM, SC; 0.01 mg/kg IV · IM, SC, IV
- As adjunct to anesthesia (Rabbits) · 0.01-0.02 mg/kg · SC · as needed
วิธีการให้ยา
ข้อห้ามใช้
- Narrow angle glaucoma
- Tachycardias
- Gastrointestinal ileus
- Urinary obstruction
- Hypersensitivity to the drug
- Pregnancy (per some manufacturer labels)
อาการไม่พึงประสงค์
- Dry secretions (xerostomia)
- Initial bradycardia followed by tachycardia
- Decreased gastrointestinal motility (risk of ileus)
- Decreased urinary tract motility
- Mydriasis and cycloplegia
อันตรกิริยาระหว่างยา
- Amantadine · May enhance the activity or toxicity of glycopyrrolate.
- Antihistamines (e.g., diphenhydramine) · May enhance anticholinergic activity or toxicity.
- Meperidine · May enhance anticholinergic activity or toxicity.
- Phenothiazines · May enhance anticholinergic activity or toxicity.
- Tricyclic Antidepressants (e.g., amitriptyline, clomipramine) · May enhance anticholinergic activity or toxicity.
- Amitraz · May aggravate signs seen with amitraz toxicity, leading to hypertension and further inhibition of peristalsis.
- Antacids · May decrease PO absorption; give oral glycopyrrolate at least 1 hour prior to oral antacids.
- Corticosteroids (long-term use) · May increase intraocular pressure when used concurrently.
- Digoxin (slow-dissolving) · May increase serum digoxin levels; use regular digoxin tablets or oral liquid.
- Ketoconazole · Increased gastric pH may decrease GI absorption; administer 2 hours after ketoconazole.
- Metoclopramide · Glycopyrrolate may antagonize the prokinetic actions of metoclopramide.
การติดตาม
- Heart rate and rhythm
- Respiratory rate and effort
- Gastrointestinal motility (auscultation for bowel sounds)
- Salivary and respiratory secretions
การได้รับยาเกินขนาด
In dogs, the LD50 is reported to be 25 mg/kg IV. In cats, the LD50 after IM injection is 283 mg/kg. Because of its quaternary structure, **minimal CNS effects** would be expected after an overdose compared to atropine. Overdose may present with severe anticholinergic signs (extreme tachycardia, mydriasis, dry mucous membranes, ileus). Treatment is generally supportive.
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