Nursing Pharmacology Chapter 27:  Gastrointestinal Drugs

• Gastrokinetic agents: useful in reducing gastric fluid volume.

  • Rationale: Reduction of gastric fluid volume: important to decrease risk of aspiration pneumonitis

    •  High-risk patients:

      • Acute pain; "full stomach" -- emergency surgery

      • Patient with hiatus hernia

      • Patient with esophageal reflux

  • Aspiration gastric contents may lead to chemical pneumonitis

  • Pulmonary aspiration of gastric content: rare in elective surgery

  • Drinking clear fluid -- up to three hours before surgery: no measurable gastric volume or pH effect in healthy children (age group: 2-12 years){note: healthy patients; clear liquids only}

  •  In adults: possibly, relatively high-risk of pulmonary complications if aspiration volume:

    1. > 25 ml and

    2. pH < 2.5

• Metoclopramide (Reglan)

  • Classification: dopamine agonist

  • Gastrokinetic activity:

    • Stimulates upper gastrointestinal motility

    • Increases gastroesophageal sphincter tone

    • Relaxes the pylorus

    • Relaxes the duodenum

  • Clinical Uses:

    • Reduction of preoperative gastric fluid volume

    • Anti-emesis

      • metoclopramide (Reglan) reduces vomiting incidents in children after tonsillectomy {administered on arrival in post-anesthesia care unit}

    • Symptomatic relief of gastroesophageal reflux

    • Treatment of gastroparesis

    • Metoclopramide (Reglan) speeds gastric emptying; useful:

      • Before anesthesia induction

      • Facilitation of small-bowel intubation

      • Enhanced radiographic small intestine examination

    • Anesthesia induction-cases in which metoclopramide (Reglan)-mediated gastric-emptying may be beneficial:

      • Patients who have recently eaten

      • Trauma patients

      • Patients with diabetes mellitus and symptoms of gastroparesis

        • Oral

      • Parturients (particularly those with a history of esophagitis {"heartburn", indicating lower esophageal sphincter dysfunction and gastric hypomotility}

      • Obese patients

  • Mechanism of Action:

    • Selective cholinergic stimulation of the GI tract (gastrokinetic effect)

      • Affects smooth muscle of the proximal GI tract;requires some basal cholinergic tone

  • Increases of the rate of gastric emptying

    • No known effect on gastric acid secretion or gastric fluid pH

  • Routes of Administration:

    •  Oral: onset within 30-60 minutes

    •  Parenteral:  15-30 minutes before induction

      • IV administration over 3-5 minutes in order to prevens abdominal cramping which may occur with more rapid infusion.

  •  No guarantee of gastric emptying with metoclopramide

    • Significant gastric fluid could still remain

    • Prior administration of other drugs (e.g. opioids) or concurrent atropine administration may offset metoclopramide's effect on the upper gastrointestinal tract.

      • However, gastric stasis due to morphine may be reversed by metoclopramide (Reglan); opioid-mediated nausea/vomiting may be reduced by metoclopramide (Reglan)

      • In parturients undergoing elective cesarean section with epidural anesthesia,metoclopramide (Reglan) {0.15 mg/kg IV} reduces early, postoperative nausea & vomiting

    • Gastric volume will not be reduced further (elective surgery) in the presence of already small gastric volumes

  • May not be effective: following sodium citrate administration

  • Particularly effective in reducing aspiration pneumonia's risk when metoclopramide is combined with a H₂ receptor antagonist (e.g. Ranitidine) before elective surgery

  •  Side effects

    • May include extrapyramidal reactions and stimulation of prolactin secretion due to dopamine receptor antagonist properties

      • Extrapyramidal reactions:-- frequency = < 1% with chronic metoclopramide (Reglan) administration

        • Dystonic:

          • Oculogyric crisis

          • Opisthotonus

          • Trismus

          • Torticollis

        • Akathisia (restlessness, lower extremity)

    • Abdominal cramps following rapid IV administration (less than three minutes)

    • Cardiac arrhythmias: in patients receiving ondansetron (Zofran) + metoclopramide (Reglan) IV

• Cisapride (Propulsid)--REMOVED FROM US MARKET (Cardiac arrhythmias including ventricular tachycardia, ventricular
  fibrillation, torsades de pointes, and QT prolongation have been reported in patients taking cisapride)

• Use of gastrokinetic drugs does not diminish the need for correct, diligent anesthetic techniques to protect the airway during anesthesia:

  • Induction

  • Maintenance

  • Emergence

1. Moyers, J.R., Preoperative Medication, Chapter 21, In: Clinical Anesthesia 3rd edition, (Barash, P.G., Cullen, B.F. and Stoelting, R.K., eds) Lippincott-Ravin, Philadelphia, New York, 1997, pp. 519-529

2. Stoelting, R.K., "Antacids in Gastrointestinal Prokinetics", in Pharmacology and Physiology in Anesthetic Practice, Lippincott-Raven Publishers, 1999, pp 444-451.