Pharmacology is the study of drugs and the way they interact with living systems.  Clinical pharmacology is the study of drugs in humans.

A drug is any chemical that can effect living processes.

Therapeutics: the medical use of drugs.

An ideal drug has several important properties.  Three of these properties are of utmost importance: effectiveness, safety and selectivity. 

Effectiveness: This is the most important quality that a drug can have.  Effectiveness refers to the drug's ability to do what it is supposed to do.

Safety:  Although no drug can be totally safe, proper usage can lessen the risks of adverse effects.

Selectivity:  A truly selective drug would have no side effects, and would effect only the body process' for which it is designed and given.  Therefore, there is no such thing as a selective drug.

Pharmacokinetics: The way the body deals with a drug.  Pharmacokinetics is concerned with the processes of absorption, distribution, metabolism and excretion.

Pharmacodynamics:  What a drug does to the body.

Pharmacokinetics and pharmacodynamics are two of the processes that determine how a person will respond to a drug.  Other factors include how a drug is administered (dose, route, and timing of administration), interactions with other drugs, and individual physiological variables (weight, age, function of body systems).

NSAIDs: Classification by Plasma Elimination Half Lives

Short Half Life (< 6 hours):

more rapid effect and clearance

• Aspirin (0.25-0.33 hrs),

• Diclofenac (1.1 ± 0.2 hrs)

• Ketoprofen (1.8± 0.4 hrs),

• Ibuprofen (2.1 ± 0.3 hrs)

• Indomethacin (4.6 ± 0.7 hrs)

Long Half Life (> 10 hours):

slower onset of effect and slower clearance

• Naproxen (14 ± 2 hrs)

• Sulindac (14 ± 8 hrs),

• Piroxicam (57 ± 22 hrs)

Antiemetics

 Antiemetic drugs are generally more effective in prophylaxis than treatment. Most antiemetic agents relieve nausea and vomiting by acting on the vomiting centre, dopamine receptors, chemoreceptors trigger zone (CTZ), cerebral cortex, vestibular apparatus, or a combination of these.
 
 Drugs used in the treatment of nausea and vomiting belong to several different groups. These include:
 
1. Phenothiazines, such as chlorpromazine, act on CTZ and vomiting centre, block dopamine receptors, are effective in preventing or treating nausea and vomiting induced by drugs, radiation therapy, surgery and most other stimuli (e.g. pregnancy).
They are generally ineffective in motion sickness.
Droperidol had been used most often for sedation in endoscopy and surgery, usually in combination with opioids or benzodiazepines

2. Antihistamines such as promethazine and Dimenhyrinate are especially effective in prevention and treatment of motion.

3. Metoclopramide has both central and peripheral antiemetic effects. Centrally, it antagonizes the action of dopamine. Peripherally metoclopramide stimulates the release of acetylcholine, which in turn, increases the rate of gastric. It has similar indications to those of chlorpromazine.

4. Scopolamine, an anticholinergic drug, is very effective in reliving nausea & vomiting associated with motion sickness.

5. Ondansetron, a serotonin antagonist, is effective in controlling chemical-induced vomiting and nausea such those induced by anticancer drugs. 

6. Benzodiazepines: The antiemetic potency of lorazepam and alprazolam is low. Their beneficial effects may be due to their sedative, anxiolytic, and amnesic properties

CNS acting drugs are of major therapeutic and clinical importance. 

They can produce diverse physiologicaland psychologicaleffects such as:

•Induction of Anesthesia 
•Relief of Pain 
•Prevention of Epileptic seizures 
•Reduction of Anxiety 
•Treatment of Parkinsonism 
•Treatment of Alzheimer's disease 
•Treatment of Depression 
•Centrally acting drugs also include drugs that are administered without medical intervention like tea, coffee, nicotine, and opiates.
 

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. 

Example calculations of maximum local anesthetic doses for a 15-kg child

Articaine

5 mg/kg maximum dose × 15 kg = 75 mg

4% articaine = 40 mg/mL

75 mg/(40 mg/mL) = 1.88 mL

1 cartridge = 1.8 mL

Therefore, 1 cartridge is the maximum

Lidocaine

7 mg/kg × 15 kg = 105 mg

2% lidocaine = 20 mg/mL

105 mg/(20 mg/mL) = 5.25 mL

1 cartridge = 1.8 mL

Therefore, 2.9 cartridges is the maximum

Mepivacaine

6.6 mg/kg × 15 kg = 99 mg

3% mepivacaine = 30 mg/mL

99 mg/(30 mg/mL) = 3.3 mL

1 cartridge = 1.8 mL

Therefore, 1.8 cartridges is the maximum.

Prilocaine

8 mg/kg × 15 kg = 120 mg

4% prilocaine = 40 mg/mL

120 mg/(40 mg/mL) = 3 mL

1 cartridge = 1.8 mL

Therefore, 1.67 cartridges is the maximum