Laxatives and cathartics Notes

NOTES NOTES LAXATIVES & CATHARTICS GENERALLY, WHAT ARE THEY? Laxatives ▪ Ease fully-formed stool passage from rectum Cathartics ▪ Evacuate colon; produce loose, unformed/ liquid stool BULK-FORMING AGENTS Figure 1.1 Bulk-forming agents: mechanism of action. OSMOSIS.ORG 1

WHAT ARE THEY? Basic information ▪ Composed of indigestible, fibrous compounds derived from plants Mechanism of action ▪ Not absorbed in gastrointestinal (GI) tract; absorb water in lumen → stool bulking → colonic distention → ↑ peristalsis CLINICAL CONCERNS ADVERSE EFFECTS ▪ Fecal impaction, bloating, flatulence ADMINISTRATION ▪ Take with fluids to avoid fecal impaction CONTRAINDICATIONS ▪ Intestinal obstruction TYPES Natural ▪ Methylcellulose (Citrucel): PO ▪ Psyllium (Metamucil): PO PATIENT EDUCATION ▪ Only laxative product that can be used on a daily basis Synthetic ▪ Polycarbophil (FiberCon): PO Common indications ▪ Constipation (long-term); acute diarrhea Figure 1.2 Bulk-forming agents: common drug-drug interactions. 2 OSMOSIS.ORG

Gastrointestinal Laxatives & Cathartics Figure 1.3 Bulk-forming agents: general adult dosing guidelines. *Dose, dosing interval varies depending on individual characteristics STOOL SOFTENERS Figure 1.4 Stool softeners: mechanism of action. WHAT ARE THEY? Basic information ▪ Anionic surfactants used to soften fecal matter Mechanism of action ▪ ↓ surface tension between water outside stool, fat in stool → water penetrates, mixes with fecal matter → softer, formed stool OSMOSIS.ORG 3

TYPES ▪ Docusate (Colace): PO, PR Common indications ▪ Constipation (low efficacy); prevention of constipation, ↓ straining during defecation (in hospitalized patients) CLINICAL CONCERNS ADVERSE EFFECTS ▪ Diarrhea (↑ intestinal fluid, electrolyte secretion) Figure 1.5 Stool softeners: common drug-drug interactions. Figure 1.6 Stool softeners: general adult dosing guidelines. *Dose, dosing interval varies depending on individual characteristics 4 OSMOSIS.ORG

Gastrointestinal Laxatives & Cathartics OSMOTIC LAXATIVES Figure 1.7 Osmotic laxatives: mechanism of action. WHAT ARE THEY? Basic information ▪ Poorly-absorbed salts, sugars stimulate colonic peristalsis ▪ Can be abused by bulimics Mechanism of action ▪ ↑ osmotic pressure → ↑ fluid/electrolytes into bowel lumen → water incorporates into stool → softens stool, ↑ peristalsis → bowel evacuation TYPES Saline laxatives ▪ Magnesium hydroxide (Milk of Magnesia): PO ▪ Magnesium sulfate (Epsom salt): PO ▪ Magnesium citrate: PR (suppository) ▪ Sodium phosphate: PR (Fleet enema) Indigestible alcohols and sugars ▪ Polyethylene glycol 3350 (MiraLax): PO ▪ Polyethylene glycol-electrolyte solution OSMOSIS.ORG 5

(PEG, GoLYTELY): PO ▪ Lactulose (Enulose): PO ▪ Lactulose ▫ Cramping, bloating, flatulence Common indications ▪ Constipation, bowel cleansing before gastrointestinal procedures DISEASE-RELATED CONCERNS Drug-specific indications ▪ Lactulose: hepatic encephalopathy ▫ Metabolized into lactic, formic, acetic acids by colonic bacteria → ↓ colonic pH → ↑ conversion of NH3 to NH4 → ↓ NH3 diffusion into blood CLINICAL CONCERNS ADVERSE EFFECTS ▪ Diarrhea, dehydration Drug-specific adverse effects ▪ Magnesium-containing medications ▫ Hypermagnesemia (e.g. heart block, neuromuscular block, CNS depression) ▪ Phosphate-containing medications ▫ Hyperphosphatemia (e.g. acute renal failure, metabolic acidosis, hypocalcemia, tetany, death) ▪ Renal impairment ▫ Use with caution: magnesium- and phosphate-containing medications (↑ risk of hypermagnesemia, hyperphosphatemia) ADMINISTRATION ▪ Maintain adequate hydration to compensate for fluid fecal loss CONTRAINDICATIONS ▪ Pre-existing electrolyte imbalance, cardiac disease, renal impairment PATIENT EDUCATION ▪ ↑ fluid intake to avoid dehydration ▪ Polyethylene glycol-electrolyte solution: rapid drinking of each portion yields better results than sipping Figure 1.8 Osmotic laxatives: common drug-drug interactions. 6 OSMOSIS.ORG

Gastrointestinal Laxatives & Cathartics Figure 1.9 Osmotic laxatives: general adult dosing guidelines. *Dose, dosing interval varies depending on individual characteristics OSMOSIS.ORG 7

STIMULANT LAXATIVES Figure 1.10 Stimulant laxatives: mechanism of action. WHAT ARE THEY? Basic information ▪ AKA irritant laxatives Mechanism of action ▪ Mild inflammations irritate small and large intestinal walls → ↑ electrolyte and water secretion into intestinal lumen ▫ Direct stimulation of enteric nervous system → ↑ smooth muscle contraction → ↑ peristalsis 8 OSMOSIS.ORG TYPES ▪ Bisacodyl (Dulcolax): PO, PR (suppository, enema) ▪ Senna (Senokot): PO Common indications ▪ Constipation, colonic cleansing

Gastrointestinal Laxatives & Cathartics CLINICAL CONCERNS ADVERSE EFFECTS ▪ Abdominal cramps, nausea, vomiting, diarrhea; fluid, electrolyte imbalance ▫ Bisacodyl: atonic colon ▫ Senna: melanosis coli (benign, reversible, dark discoloration of colon wall) ADMINISTRATION ▪ Bisacodyl: do not use > 10 consecutive days (↑ risk of atonic colon) Figure 1.11 Stimulant laxatives: general adult dosing guidelines. *Dose, dosing interval varies depending on individual characteristics OSMOSIS.ORG 9