Mode of action
Non-absorbable salts retain fluid in the colon by osmotic effect and stimulate peristalsis.
Indications
Bowel preparation, for GI endoscopic or surgical procedures; Chronic constipation.
Contraindications
Intestinal obstruction, partial or complete, Severe colitis, especially toxic megacolon, Phenylketonuria, Heart failure (products containing sodium phosphate), Renal impairment (products containing sodium phosphate; leads to hyperphosphataemia).
Specific considerations
Cardiovascular disease (e.g. heart failure) avoid use of sodium salts; use with caution as fluid and electrolyte disturbances can occur. Electrolyte disturbance may be worsened, avoid use.
Renal impairment: Avoid use of magnesium or sodium salts; significant fluid and electrolyte disturbance may occur, Elderly: Use with caution; risk of electrolyte disturbance and dehydration.
Children: Use of sodium phosphate in children <2 years may cause hypocalcaemia.
Small volume preparations may cause dehydration and electrolyte disturbance if not used with adequate hydration.
Pregnancy: Other sodium/magnesium laxatives: limited data available; safe to use short term if other agents ineffective.
Breastfeeding: Safe to use.
Adverse effect
Small volume products that contain sodium phosphate used for bowel preparation can cause serious fluid and electrolyte disturbance, including hypocalcaemia, hyperphosphataemia and hyperkalaemia. Acute renal failure has also been reported. All sodium or magnesium laxatives may cause nausea, bloating, fluid and electrolyte depletion and rectal irritation.
Rectal gangrene has been associated with the use of phosphate enemas in elderly patients and was believed to be due to a direct necrotizing effect of the phosphate on the rectum.
Dosage
See directions on label.
Patient counselling
Bowel preparation, do not eat from 1–2 hours before starting preparation until after procedure performed; clear fluids are permitted; expect diarrhoea usually after about 1 hour and a clear water-like discharge by 4 hours.
Practice points
onset of action is 30 minutes – 3 hours
oral medication taken during or within the hour before sodium or magnesium laxative may be flushed from the GIT without absorption
avoid laxatives containing sodium phosphate in renal impairment
sodium or magnesium laxatives may be given orally or rectally; they are poorly and slowly absorbed.
Products
PHOSPHATE ENEMA (SODIUM ACID PHOSPHATE+SODIUM PHOSPHATE) 125-133 ML BOTTLE
(PHOSPHATE ENEMA B®, FLETCHERS PHOSPHATE ENEMA®, JO-ENEMA®,, KLYSMOL®)