Laxatives and cathartics (purgatives)

Constipation is a common problem in older adults and laxatives are often used or overused. Non drug measures to prevent constipation (e.g. increasing intake of fluid and high–fiber foods, exercise) are much preferred to laxatives.

Laxatives and cathartics are drugs used orally to evacuate the bowels or to promote bowel elimination (defecation). Both terms are used interchangeably because it is the dose that determines the effects rather than a particular drug. For example, Castor oil laxative effect = 4ml while Cathartic effect = 15-60ml

The term laxative implies mild effects, and eliminative of soft formed stool. The term cathartic implies strong effects and elimination of liquid or semi liquid stool. 

 Laxatives are randomly classified depending on mode of action as:
 
1. Bulk-forming laxatives: are substances that are largely unabsorbed from the intestine.
They include psyllium, bran, methylcellulose, etc. When water is added, the substances swell and become gel-like which increases the bulk of the faecal mass that stimulates peristalsis and defecation.

2. Osmotic laxatives such as magnesium sulphate, magnesium hydroxide, sodium phosphate, etc. These substances are not efficiently absorbed and cause water retention in the colon. The latter causes increase in volume and pressure which stimulates peristalsis and defecation.

Lactulose is a semisynthetic disaccharide sugar that also acts as an osmotic laxative. 
Electrolyte solutions containing polyethylene glycol(PEG) are used as colonic lavage solutions to prepare the gut for radiologic or endoscopic procedures

3. Stimulant (irritant) laxatives: these are irritant that stimulate elimination of large bowel contents. Individual drugs are castor oil, bisacodyl, phenolphthalein, cascara sagrada, glycerine, etc. The faeces are moved too rapidly and watery stool is eliminated. Glycerine can be administered rectally as suppositories.

4. Faecal softeners: they decrease the surface tension of the faecal mass to allow water to penetrate into the stool. They have detergent– like property e.g. docusate(docusate sodium, docusate calcium, and docusate spotassium. )

5. Lubricant laxatives e.g. liquid paraffin (mineral oil). It lubricates the intestine and is thought to soften stool by preventing colonic absorption of faecal water. They are used as retention enema. 

6. Chloride channel activators

Lubiprostone works by activating chloride channels to increase fluid secretion in the intestinal lumen. This eases the passage of stools and causes little change in electrolyte balances. Nausea is a relatively common side effect with lubiprostone.

Clinical indications of laxatives

1. To relieve constipation.
2. To prevent straining.
3. To empty the bowel in preparation for bowel surgery or diagnostic procedures.
4. To accelerate elimination of potentially toxic substances from the GI tract.
5. To accelerate excretion of parasite after anti-helmintic drugs have been administered. 

Procoagulant Drugs:

Desmospressin Acetate

• Is a synthetic analogue of the pituitary antidiuretic hormone (ADH).

• Stimulates the activity of Coagulation Factor VIII

• Use for treatment of hemophilia A with factor VIII levels less than or equal to 5%, treatment of hemophilia B or in clients who have factor VIII antibodies. Treatment of severe classic von Willebrand's disease (type I) and when an abnormal molecular form of factor VIII antigen is present. Use for type IIB von Willebrand's disease.

Different Systems of the CNS & their functions

These systems are pathways formed of specific parts of the brain and the neurons connecting them. 

They include:
1.The pyramidal system 
2.The extrapyramidal system 
3.The limbic system 
4.The reticular formation 
5.The tuberohypophyseal system

The pyramidal system: 

It originates from the motor area of the cerebral cortex and passes through the spinal cord, therefore it is also known as the “corticospinaltract”. 
It is responsible for the regulation of the fine voluntary movements.

The extrapyramidal system: 

It also controls the motor functionbut involves areas other than the corticospinal tract. 
It is involved in the regulation of gross voluntary movements, thus it complements the function of the pyramidal system. 

The “basal ganglia” constitute an essential part of this system. 

Degenerative changes in the pathway running from the “substantianigra”to the “corpus striatum”(or nigrostriatal pathway) may cause tremors and muscle rigidity characteristic of “Parkinson’s disease”.

The limbic system: 

The major parts of this system are: the hypothalamus, the basal ganglia, the hippocampus(responsible for short term memory), and some cortical areas. 

The limbic system is involved in the control of “behavior”& “emotions”.

The reticular formation:

It is composed of interlacing fibers and nerve cells that run in all directions beginning from the upper part of the spinal cord and extending upwards. 
It is important in the control of “consciousness” and “wakefulness”.

The tuberohypophyseal system: 

It is a group of short neurons running from the hypothalamusto the hypophysis(pituitary gland) regulating its secretions.
 

Ether (diethylether)

Ether (diethylether) MAC 2.0%, Blood/gas solubility ratio 15
- Ether is generally mixed with 3% ethanol to retard oxidation. Peroxides form on exposure to air and can enhance the danger of an explosion.
- Slow rate of induction and recovery due to its high blood/gas solubility ratio.
- Produces profound muscular relaxation.
- Both the rate and the minute volume of ventilation tend to be elevated during the inhalation of ether.
- Ether maintains good circulatory stability and does not sensitize the heart to the arrhythmogenic action of catecholamines.
- More than 90% of the absorbed ether can be recovered unchanged in the expired air. Metabolism is not extensive and the metabolites are not hepatotoxic.
- Ether is a versatile anesthetic of unexcelled safety, but it is flammable and irritating to breathe. Secretions can be blocked with anticholinergics.

PLASMA FRACTIONS:

a) Fresh frozen plasma.

b) Platelets.

c) Plasma concentrates.

d) Non-plasma recombinant factor concentrates.

Doxycycline

Commonly prescribed for infections and to treat acne. treat urinary tract infections, gum disease, and other bacterial infections such as gonorrhea and chlamydia., as a prophylactic treatment for infection by Bacillus anthracis (anthrax). It is also effective against Yersinia pestis and malaria.