Anesthesia Pharmacology:  Gastrointestinal Drugs

• Antacids as Preoperative Medication

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

    1. > 25 ml and

    2. pH < 2.5

  • Antacids neutralize gastric acid content

    • Single dose: 15-30 minutes before induction: about 100% effective in increasing gastric fluid pH above 2.5

    • Sodium citrate (0.3M) --nonparticulate antacid:  commonly given before the procedure when an increase in gastric fluid pH is required

    • Nonparticulate antacids:

      • Do not themselves produce pulmonary damage if aspiration of gastric fluid containing these antacids occur.

      • Colloid antacid suspensions: more effective than nonparticulate agents in increasing gastric acid pH

        •  Aspiration of gastric fluid containing particulate antacids produce significant/persistent damage even if gastric pH has been increased:

          •  Damage:

            •   Pulmonary edema

            •   Arterial hypoxemia

  • Onset: no "lag time" as seen with H₂ receptor antagonists

    • Effective on fluid already present in the stomach

    • Good choice in emergency situations (assuming patients can take oral medication)

  • Other issues:

    • Antacids increase gastric fluid volume (unlike H₂ receptor antagonists)

      • Most evident following repeated dosing -- e.g., during labor {concurrent opioid administration may promote gastric emptying delay}

    • Do not withhold antacids because of possible increases in gastric volume --increasing the pH is more important

• Other drugs

  • Omeprazole: gastric acid suppression by inhibition of parietal cell proton pump.

    • Parietal cells H ion secretion depends on a H+,K+-ATPase pump-- promoting H K exchange

    • H⁺,K⁺-ATPase located in apical membrane to and tubulovesicular apparatus of parietal cells

    • Luminal surface of the membrane enzyme: exposed to gastric luminal acid

    • Omeprazole and lansoprazole inhibit the proton pump, effectively irreversibly -- requiring synthesis of new enzyme protein

    • Omeprazole and lansoprazole approved for treatment of:

      • Duodenal ulcer

        •   May be used in conjunction with triple therapy

      • Erosive esophagitis

      • Gastric acid hypersecretory states, including Zollinger-Ellison syndrome

    Friedman, L. S. and Peterson, W.L. Peptic Ulcer and Related Disorders In Harrison's Principles of Internal Medicine 14th edition, (Isselbacher, K.J., and Braunwald, E., Wilson, J.D., Martin, J.B., Fauci, A.S. and Kasper, D.L., eds) McGraw-Hill, Inc (Health Professions Division), 1998, pp. 1597-1616.

  • IV 30 minutes prior to induction has been employed

  • Oral 2-4 hours before surgery is required

  • Duration of action of effects on gastric pH: about 24 hours

  • pH increases; variable effects on gastric volume with omeprazole and H₂ receptor antagonists

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

This Web-based pharmacology and disease-based integrated teaching site is based on reference materials, that are believed reliable and consistent with standards accepted at the time of development. Possibility of human error and on-going research and development in medical sciences do not allow assurance that the information contained herein is in every respect accurate or complete. Users should confirm the information contained herein with other sources. This site should only be considered as a teaching aid for undergraduate and graduate biomedical education and is intended only as a teaching site. Information contained here should not be used for patient management and should not be used as a substitute for consultation with practicing medical professionals. Users of this website should check the product information sheet included in the package of any drug they plan to administer to be certain that the information contained in this site is accurate and that changes have not been made in the recommended dose or in the contraindications for administration.  Advertisements that appear on this site are not reviewed for content accuracy and it is the responsibility of users of this website to make individual assessments concerning this information.  Medical or other information  thus obtained should not be used as a substitute for consultation with practicing medical or scientific or other professionals.