Laxatives Pps

8/6/2019 Laxatives Pps

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Drugs for costipation

These are the drugs that promote evacuationof bowels.

Distinction is made according to theintensity of action.

Laxatives :milder action .used for theelimination of soft and formed stools

Purgatives or cathartics: strong action.

results in more fluid evacuation. Many drugs in low doses act as laxatives

and in large doses as purgatives.


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LAXATIVES

Miscoception about bowel habit

leads to excessive use of laxatives

Ingested water and fluids are excreted byvarious g.i.t.glands and are largely

reabsorbed

Only little is excreted through faeces.

The reabsorption takes place in (a) smallintestine and (b) colon

Laxatives which act mainly in intestine

produce loss of fluid,electrolytes,nutrients.

Those which act on colon produce lessfluid loss


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Excessive use of laxatives should be

avoided except in the following conditions.

Angina, Hemorrhoidbleeding.(straining deteriotes theexisting disease.)

To clear the bowel before surgeryand for x-ray.

Drug-induced constipation.example verapamil.

Expulsion of intestinalparasites,specially with the use ofsome anthelminthics. examplepiperazine preps.


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Abuse of laxatives may lead to

Hypokalemia

Atonic non-functional colon


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Classification

1) Bulk forming (eg;dietary

fibre, bran, psyllium, isphagula, methylcellose)

2) Stool softeners (eg; Docusates,liq.paraffin)

3) Stimulant purgatives

(A) Diphenylmethanes

(phenophthaleine,Bisacodyl,sodim picosulfate)

(B) Anthraquinones(senna,cascara,)

(C) 5HT4 agonist (tegaserod)

(D) fixed oil (eg; castor oil)

4) Osmotic purgatives (eg; mg.salts. sod.salts and

lactulose)


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MOA

All purgatives increase the water

content of faeces i) by hydrophilic or osmotic action,

retaining water n electrolytes in thelumen- increase volume of colonic

content n make it propelled easily. ii) by acting on ints. Mucosa, decrease

net absorption of water n electrolyte.ints.transit is increased indirectly by the

fluid bulk. iii) by increasing propulsive activity asprimary action n allowing less time forabsorption of salt n water as secondaryeffect.


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Certain purgatives increase motility viamyenteric plexus.

Laxtives modify the fluid dynamics ofmucosal cell n cause fluid accumulation ingut lumen by one or more of the followingmechanisms.

a) inhibiting sodiumpotasium ATPase ofvillaous cells impairing electrolite n waterabsorption.

b) stimulating adenylcyclase in cryptcells,increasing h2o n electr.secretion.

C ) enhancing PG synthesis in mucosa wchincreases secretion.

d) structural injury to the absorbingintestinal mucosal cells.


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Bulk purgatives

Dietary fibre (bran)

Most appropriate method and first line approach for

prevention and treatment of functional constipation .

Consists of unabsorbable cell wall and other constitutes

of vegetables food (polysaccharides). Bran consists of40% dietary fibre

Some dietry fibers like gums. lignins. pectins bind with

bile acids promotes excretion in faeces.reduces

plasma LDL cholestrol.

Should not be used in patients with Gastric

ulceration,Adhesion,Stenosis.

Commonly used are :isphaghula (isogel), husk in granular

form.MethylcelluloseSemisynthetic,colloidal,hydrophilic

derivative of cellulose.

Generous use of water must be taken with all bulk

forming agents.


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Stool softener

Docusate

Mild laxative

Specially indicated when straining at hard stool must be

avoided Bitter liquid ,may produce nausea,cramps and abdominal

pain.

Prolonged use may cause hepototoxicity.

It should not be given along with liquid paraffin. because

due its detergent action, it can disrupt the mucosal

barrier and enhance the absorption of non-absorbable

drug like paraffin.


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Lubricant laxative

Emollient laxative Example:Liquid Paraffin

Mineral oil.Viscous.Mixture of hydrocarbons

obtained from petroleum.

Pharmacologically inert.

Lubricated hard Scybali by coating them

Straining avoided due to lubricant action.

Disadvantages

Bland but unpleasant to swallow(oily). Embracing due to leakage of oil from postanal

sphincter.

While swallowing it may trickle into lungs and may

cause lipid pneumonia(rare).

Used mainly in post-operative conditions or wherestrain has to be avoided.


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Osmotic (saline) purgatives

Certain salts, when given

orally, are not much

absorbed and are

retained in g.i.t. They exert osmotic

pressure and thus

retain considerable

amount of water .

Thus increases the bulk

and distends theintestine.

Magnesium salts also

stimulate intestinal

secretion.

Magnesi

um

sulphat

e

Epsom

salts

Bitter in

taste

5-15g

Magnesi

umhydroxi

de

Milk of

magnesia

Bland in

taste.used as

antacid

also.

15-30ml

Sodium

sulphat

e

Glabers

salts

Bad in

taste

10-15g

sodium

potassi

um

tartrate

Rochell

e salts

Relative

ly

pleasan

t taste

8-15g


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These salts have to be dissolved in 150-200ml water

and then taken.

1-2 fluid evacuation within 1 hour.

Hence they are taken early in the morning before

breakfast.

In the doses mentioned above causes complete

evacuation of bowel.

Smaller doses may have a milder laxatives action.

They are preferred purgatives for preparation of bowel

before surgery and colonoscopy.

Food and drug poisoning

After purge in the treatment of tapeworm infestation.

Mg salts are C/I in renal insufficiency. Sodium salt in C.H.F and other sodium-retaining states.


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lactulose

Neither digested nor absorbed in small intestine.retains water.

4-19g TID, with plenty of water

Produces soft formed stool

Not a favored purgative because flatulence is common.

but lactulose can reduce blood NH3 by 25-40% inpatients wit Hepatic encephalopathy

it is broken down into acid( e.g. lactic acid) andreduces the pH of the stool.

NH3 produced by bacteria in colon or due to heptatic

dysfunction is

For this purpose ,20g TID or more is needed.

Other drugs used to NH3 in hepatic coma are sodiumbenzote and sodium phenyl acetate.

These combine with ammonia in blood to form

hippuric acid or phenyl acetic glutamine which arerapidly excreted in urine.


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stimulants Powerful purgatives and often produce griping pain.

Large doses of these can cause

excess purgation, n produce fluid and electrolyteimbalance.

Hypokalaemia on regular use.

Long term use must be discourged.It produces colonicatony.

C\ I in subacute and chronic intestinal obstruction.

Reflexly stimulates gravid uterus.C\I during pregnancy.

But often used at the time of labour to help induction

of labor.Phenophthalein

o Used as indicator and purgative.

o It turns urine pink if alkaline.


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It was added later but is used more popularly.

They are partly absorbed and re-excreted in bile.

The entero-hepatic circulation is more important for

phenophthalein because it produces protracted action.

BISACODYL

Bisacodyl is activated in the intestine bydeacetylation.

The action of both these are in the colon.

Thus action is 6-8 hours.

Therefore to be taken at bedtime

Bisacodyl is active as suppository also.

Suppository acts by irritating the anal and rectal

mucosa and reflexy increases Motility.

Action with in 20-40 minutes.

Regular use by this route may cause inflammation and

mucosal damage.


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Anthraquinones Senna and cascara sagrada. Active constituent present as precursor glycoside

On oral administration --->anthraquinone,mainlyOxymethyl anthraquinones are liberated in intestinewhere they are partly absorbed because the release ofactive principle is very slow.

Unabsorbed in sufficient quantity are passed to largeintestine.

In colan the active anthrol form is liberated.

It acts locally or is absorbed into the circulation andgoes for entero-hepatic circulation.

It takes 6-8 hour to produce action. Amount excreted in milk is sufficient to cause

purgation.

Regular use for4-12 months causes colonic atony andrarely mucosal pigmentation.

Pulverised Senna Pod ------->Glaxenna*

Ca salt of sennosida---------->Persennid*


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Choice n use of purgatives

Functional constipation. Ch.bed ridden patients

To avoid straining at stools

(hernia ,cardio vasularafflictions ,piles, fissures n analsurgery)

Food/drug poisoning

After certain antihelmenthics

Preparation of bowel for surgerycolonoscopy n abd .x-ray.


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TEGASEROD New selective 5HT4 partial agonist wch has no

action on other receptors

It acts n activates prejunctional 5HT4 receptors on

intrinsic enteric afferents.

It increases CGRP ( calcitonine gene related

peptide ) and also increases excitatory transmitter

Ach wch inturn helps peristalitic reflex n colonic

secretions by increasing cAMPmediated cl- efflux.

The propulsive movement is more prominent in

colon n less in stomach n ileum.

DOSE: 2mg or6mg.BD before meals.

PK: Small fraction is absorbed. unchanged is

excreted in faeces.t1/2 is 11 hrs.

Indications: 1) IBS; relieves abd pain, bloatinf and

increses frequency of stools. 2) ch. Constipation.

S/Es: Flautulance, loose motions, headche.


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Constipation may be spastic or atonic.

SPASTICCONSTIPATION

It also named as irritable bowel. stools arehard, round, stone like and difficult topass.

Dietary fibre is the first choice or bulkforming agent may be taken for

wks/months. Stimulants are C/I ted in this ATONICCONSTIPATION ( sluggish bowel )

Commonly seen in advanced age, debilityin laxative abuse.

Plenty of fluids, exercise are measures areto be taken.

In resistant cases bulk forming may betried ( isphagula, methyl cellulose )


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Functional constipation

It is corrected by Increase in fibre content of regular diet.

Increase in daily fluid intake.

Increase in physcical activity.

Not neglecting the natures call Adjusting the daily routine

Selecting alternativr drugs ( wch cause

costipation shud be avoided like

antihistaminics,anticholinergics andmorphine etc.)

Correcting the underlying pathology like

vit.B1

defficiency,hypothyroidism,parkinsonsdise

ase DM etc.


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LUBRICANT LAXATIVE

Liquid paraffin is the eg of this type

it acts luminally and pharmacologically it is an inertmineral oil.

It is a foecal lubricant and stool softener as it retardswater absorption from the stools.

It is given as 15-30 ml syrup at bed time.

Latency period is 1-3 days.

SURFACTANT LAXATIVE

DOCUSATE AND GLYCERINE SUPPOSITORIES ARE

EGS OF THIS TYPE.They act luminally. acts by decreasing the surfacetension offluids in the bowel and also act as wettingagent for the bowel,because by emulsifying thecolonic contents facilitate the penetration of water

into faeces.


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Laxatives Pps