PHARMACOLOGY 

UNIT TWO (2)

 

   ANTI-DIARRHEAL AGENT

Diarrhea is an increased frequency and decreased consistency of fecal discharge as compared with an individual's normal bowel pattern

Frequency and consistency of diarrhea are variable within and between individuals

CAUSE 

Diarrhea is a symptom of an underlying cause Therefore, you must treat the underlying cause while treating the diarrhea.

Systemic infection is most common cause of diarrhea

ANTI-DIARRHEAL AGENT

Antidiarrheal drugs used to treat 

acute diarrhea and should not be used for longer than 2 days and should not be used if a fever is present 

Class of antidiarrheal agents

1. Antimotility like Diphenoxylate, loperamide , Opium tincture and Difenoxin

2. Adsorbents like Kaolin-pectin mixture and polycarbophil

3. Antisecretary agents like Bismuth subsalicylate 

Antimotility

Mechanism of action (MOA)

decrease the hypermotility then decreases peristalsis

Example

Loperamide: Is anti-peristaltic anti-diarrhea agent

Dose; Initially 4 mg, then 2 mg after each loose stool; do not exceed 16 

mg/day

Diphenoxylate

the most effective agents for relief of diarrhea. 

Dose: 5 mg tablet or 5mg/5ml four times daily

side effect of Antimotility 

drowsiness, abdominal cramps, Constipation

Contraindication (CI )

they should not be used in young children or in patients

with severe colitis.

Adsorbents

Moa

•these agents act by adsorbing intestinal toxins or microorganisms

and/or by coating or protecting the intestinal mucosa

•They are much less effective than  antimotility a gents and they can interfere with the absorption of other drugs.

Example 

Kaolin-pectin mixture

Dosage; 120 mL after each loose stool

Polycarbophil

Dosage; Chew 1g tablets four times daily or after each loose stool; do not exceed 12 

tablets/day

Antisecretary agents

Moa 

decreases fluid secretion in the Its action may be due to its 

decreases fluid secretion in the bowel, 

bowel, 

salicylate component as well as its coating action.

Example 

Bismuth subsalicylate

Dose; 524mg or 30ml every 30 min to 1 h as needed up to 8 doses/day

Side effects-dark tongue, constipation, anxiety, drowsiness

CONSTIPATION AND LAXATIVES

Constipation - accumulation of hard fecal material in the large intestine - 

a major problem of the elderly Causes 

• "poor H2O intake & poor dietary habits, lack of exercise "
• bowel obstruction, chronic laxative use Drugs like (anticholinergics, narcotics & certain antacids) 

LAXATIVES 

Laxatives are commonly used for constipation to accelerate the movement of food through the gastrointestinal tract 

These drugs can be classified on the basis of their mechanism of action

 Class of laxatives 

Stimulants like Bisacodyl, Castor oil and Senna 

Bulk laxatives like Methylcellulose and Psyllium 

Osmotic laxatives like Magnesium citrate and Lactulose Stool softeners like Docusate

Stimulants 

Moa 

Increase peristalsis and Increase secretion of water into large and small intestine 

Example 

✓ Bisacodyl 

Dose; 

Orally-5-15 mg (≥ 12 yr) or 5-10mg(3-11yr) daily given as a single dose

 Rectal- 10mg(≥12 yr) or 5-10 mg(2-11 yr) or 5mg(2 yr) daily as a single dose 

Evacuation 6-12 hours after oral and 15-60 mins suppossitory 

Side effecs; 

abd cramp, 

irritation, 

fluid and electrolyte depletion, 

N and vomiting 

✓ Bulk laxatives 

Moa 

Are Natural fibrous substances that promote large soft stools by absorbing water into the intestine - increase fecal bulk & peristalsis 

Examples 

Methylcellulose 

Dose: 6 g daily given in divided dose(≥12) 3 g daily given in divided doses(6-11 

Side effects: 

abdominal fullness, allergic reaction, rectal bleeding, stomach pain 

✓ Osmotic laxatives 

Moa 

draws water into the intestine, inc. 

H 20 causes fecal mass to soften and swell stretches intestine & stimulate peristalses 

Example 

Lactulose

 dose; -15ml po once a day 

Side effects:

 flatulence, diarrhea, abd. cramping, N & V

Stool softeners 

Moa 

Surface-active agents that become emulsified with the stool produce softer feces and ease passage They may take days to become effective and are often used for prophylaxis rather than acute treatment Rugby 

Example 

Docusate

ANTIEMETIC AGENTS

Vomiting Vomiting (emesis) is the expulsion of gastric contents of the stomach through the esophagus and out the oral cavity

 cause

• motion sickness 
• viral and bacterial infections 
• food intolerance 
• surgery, pregnancy, pain, And drugs etc 

ANTIEMETIC

Antiemetics are drugs or agents used to prevent and treat symptoms of nausea and vomiting 

antiemetics represent a variety of classes and offer a range of efficacies 

►H1-receptor antagonists eg. dimenhydrinate, meclizine, and cyclizine ➤ dopamine antagonists eg. Metoclopramide 

➤ Serotonin inhibitors eg Ondansetron ➤Anticholinergic drugs eg. scopolamine or Hyocine H1-receptor antagonists 

H1-receptor antagonists

Moa

Blocks H1 receptor on GI smooth muscles and prevent GI muscle spasm 

Dimenhydrinate is used principally in the prevention and treatment of nausea, vomiting, and/or 

vertigo associated with motion sickness

Dose; 25-100 mg PO QID or TID, 

before 30min of the exposure of motion

Dimenhydrinate 

S/E 

Headache, dizziness, dry mouth and blurred vision 

Who should not take 

Glaucoma, HTN, blocked urinary bladder

dopamine antagonists 

MOA 

block D2-receptor in CTZ-antinausea and antiemetic action block gastrointestinal D2-receptor promote vermiculation Metoclopramide prevention of vomitting caused by postoperation and cancer chemotherapy

Dosage: 

IV infusion or oral; 2 mg/kg is given initially 30 minutes(IV inf, diluted with 5% dextrose, 0.9% sodium chloride) or 1hr(oral) before administration of a highly emetogenic drug 

IM/IV injection; 10 mg administered slowly over 1-2 minutes at the end of the surgical procedure and repeated every 4-6 hrs

Adverse reaction: 

Feeling restless, headache, confusion and insomnia 

Contraindications 

GI hemorrhage, epilepsy, Parkinson's disease Pregnancy category is B

Serotonin inhibitors 

MOa

Blocks serotonin receptor then prevent serotonin vomiting triggering effect in brain 

Ondansetron 

Prevent nausea and vomiting associated with emetogenic cancer chemotherapy eg cisplatin 

Prevention and treatment of postoperative nausea and vomiting Dosage 

Ondansetron 4mg, 8mg PO OD Ondansetron 32mg/50ml IV 

S/E 

Headache, fatigue, constipation 

Contraindications

Hypotensive patient

ANTI-CHOLINERGIC DRUGS

MOA 

Blocks the cholinergic receptor in GI that triggers secretion and intestinal motility 

Scopolamine or HYOCINE Is used to prevent nausea and vomiting caused by motion sickness, abdominal pain, GI spasm 

Also used at preoperative procedure 

Dosage 5mg, 10mg PO OD or BID • 

Dermal patch 0.3 to 0.6mg SC, IM or IV 

S/E 

Flushing, tachycardia, dryness, urinary retention, constipation, 

CI 

Glaucoma, Paralytic ileus, myasthenia gravis