1. Clinical Overview
Phenolphthalein is a stimulant laxative belonging to the diphenylmethane derivative class. It acts directly on the colonic mucosa to stimulate peristalsis and promote bowel evacuation. Historically used for constipation, its use has drastically declined in India and globally due to concerns about carcinogenic potential and the availability of safer alternatives. The 0.19gm (190 mg) strength is a high dose, typically intended for single-dose bowel cleansing.
| Onset | Duration | Bioavailability |
|---|---|---|
| 6 to 8 hours | 3 to 4 days | Poorly absorbed from the GI tract (<15%) |
2. Mechanism of Action
Phenolphthalein acts locally on the colonic mucosa. It stimulates the myenteric plexus (Auerbach's plexus), increasing intestinal motility and peristalsis. It also inhibits the absorption of water and electrolytes (Na+, K+, Cl-) from the colonic lumen, increasing intraluminal fluid volume and softening the stool.
3. Indications & Uses
- Acute constipation (short-term relief)
- Bowel evacuation prior to diagnostic procedures (e.g., radiology, endoscopy)
4. Dosage & Administration
Adult Dosage: 190 mg (0.19 gm) taken orally once daily, preferably at bedtime. Use for a maximum of 7 days. For bowel prep, a single 190 mg dose may be used as per physician's instruction.
Administration: Take with a full glass of water (240 ml). Can be taken with or without food, but bedtime administration is common to produce effect in the morning. Do not crush or chew if in tablet form. Do not use for more than one week without medical supervision.
5. Side Effects
Common side effects may include:
- Abdominal cramping or discomfort
- Diarrhea
- Nausea
- Perianal irritation
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Diuretics (e.g., Furosemide, Hydrochlorothiazide) | Additive risk of hypokalemia and dehydration. | Major |
| Corticosteroids (e.g., Prednisolone) | Increased risk of hypokalemia. | Moderate |
| Digoxin | Hypokalemia potentiates digoxin toxicity (arrhythmias). | Major |
| Antiarrhythmics (e.g., Amiodarone, Sotalol) | Electrolyte imbalance may increase pro-arrhythmic risk. | Major |
| Oral Contraceptives | Reduced efficacy of OCPs due to decreased absorption from rapid GI transit. | Moderate |
| Warfarin and other Anticoagulants | Potential for decreased absorption of vitamin K, affecting INR. Also, diarrhea can affect vitamin K status. | Moderate |
| Lithium | Diarrhea can reduce lithium levels, decreasing efficacy. | Moderate |
7. Patient Counselling
- DO take with a full glass of water.
- DO use only as directed by your doctor for the shortest duration necessary.
- DO inform your doctor if you are pregnant, planning pregnancy, or breastfeeding.
- DONT use for more than 7 consecutive days.
- DONT take if you have stomach pain, nausea, or vomiting.
- DONT take other laxatives concurrently unless advised by a doctor.
- DONT crush or chew the tablet.
8. Toxicology & Storage
Overdose: Severe, watery diarrhea leading to profound dehydration, electrolyte depletion (hypokalemia, hyponatremia), metabolic acidosis or alkalosis, muscle weakness, cardiac arrhythmias, hypotension, shock, and renal failure.
Storage: Store in a cool, dry place, protected from light and moisture. Keep out of reach of children. Store at room temperature (below 30°C). Do not use after the expiry date printed on the pack.