Mefenamic acid

Analgesic, anti‐inflammatory properties less  effective than aspirin 

Short half‐lives, should not be used for longer  than one week and never in pregnancy and in  children. 

Enhances oral anticoagulants

Used to treat pain, including menstrual pain. It decreases inflammation (swelling) and uterine contractions.

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. 

Calcium Channel Blocking Agents 

• Act on contractile and conductive tissues of the heart and on vascular smooth muscles 
• Prevent movement of extracellular calcium into the cell 
– Coronary and peripheral arteries dilate
– Myocardial contractility decreases 
– Depress conduction system

Therapeutic Actions
• Inhibit movement of calcium ions across the membranes of myocardial and arterial muscle cells. Altering the action potential and blocking muscle cell contraction 
• Depress myocardial contractility 
• Slow cardiac impulse formation in the conductive tissues 
• Cause a fall in BP 
 

Factors affecting onset and duration of action of local anesthetics

pH of tissue

pKa of drug

Time of diffusion from needle tip to nerve

Time of diffusion away from nerve

Nerve morphology

Concentration of drug

Lipid solubility of drug

Azithromycin

Azithromycin is the first macrolide antibiotic belonging to the azalide group. Azithromycin is derived from erythromycin by adding a nitrogen atom into the lactone ring of erythromycin A, thus making lactone ring 15-membered.

Azithromycin has similar antimicrobial spectrum as erythromycin, but is more effective against certain gram-negative bacteria, particularly Hemophilus influenzae.

azithromycin is acid-stable and can therefore be taken orally without being protected from gastric acids.

Main elimination route is through excretion in to the biliary fluid, and some can also be eliminated through urinary excretion

Clarithromycin Used to treat  pharyngitis, tonsillitis, acute maxillary

sinusitis, acute bacterial exacerbation of chronic  bronchitis,  pneumonia (especially atypical pneumonias associated with Chlamydia pneumoniae or TWAR), skin and skin structure infections, and, in HIV and AIDS patients to prevent, and to treat, disseminated Mycobacterium avium complex or MAC.

Unlike erythromycin, clarithromycin is acid-stable and can therefore be taken orally without being protected from gastric acids. It is readily absorbed, and diffused into most tissues and phagocytes.

Clarithromycin has a fairly rapid first-pass hepatic metabolism, i.e it is metabolised by the liver. However, this metabolite, 14-hydroxy clarithromycin is almost twice as active as clarithromycin.

Contraindications Clarithromycin should be used with caution if the patient has liver or kidney disease, certain heart problems (e.g., QTc prolongation or bradycardia), or a mineral imbalance (e.g., low potassium or magnesium levels).