Erythromycin

used for people who have an allergy to penicillins. For respiratory tract infections, it has better coverage of atypical organisms, including  mycoplasma. It is also used to treat outbreaks of chlamydia, syphilis, and gonorrhea.

Erythromycin is produced from a strain of the actinomyces Saccaropolyspora erythraea, formerly known as Streptomyces erythraeus.

Mechanism of action Erythromycin prevents bacteria from growing, by interfering with their protein synthesis. Erythromycin binds to the subunit 50S of the bacterial ribosome, and thus inhibits the translocation of peptides.

Erythromycin is easily inactivated by gastric acids, therefore all orally administered formulations are given as either enteric coated or as more stable salts or  esters. Erythromycin is very rapidly absorbed, and diffused into most tissues and  phagocytes. Due to the high concentration in phagocytes, erythromycin is actively transported to the site of infection, where during active phagocytosis, large concentrations of erythromycin are released.

Most of erythromycin is metabolised by demethylation in the liver. Its main route elimination route is in the bile, and a small portion in the urine.

Erythromycin's half-life is 1.5 hours.

Side-effects. More serious side-effects, such as reversible deafness are rare. Cholestatic jaundice, Stevens-Johnson syndrome and toxic epidermal necrosis are some other rare side effects that may occur.

Contraindications Earlier case reports on sudden death prompted a study on a large cohort that confirmed a link between erythromycin, ventricular tachycardia and sudden cardiac death in patients also taking drugs that prolong the metabolism of erythromycin (like verapamil or diltiazem)

erythromycin should not be administered in patients using these drugs, or drugs that also prolong the QT time.

Local Anesthetics

1. Procaine (Novocaine)

a) Classic Ester type agent, first synthetic injectable local anesthetic.

 b) Slow onset and short duration of action

 2. Tetracaine (Pontocaine)

a) Ester type agent--ten times as potent and toxic as procaine.

 b) Slow onset but long duration of action.

 c) Available in injectable and topical applications.

 3. Propoxycaine (Ravocaine)

a) Ester type agent–five times as potent and toxic as procaine.

 b) Often combined with procaine to increase duration of action.

 4. Lidocaine (Xylocaine)

a) Versatile widely used amide type agent.

 b) Two - three times as potent and toxic as procaine.

 c) Rapid onset and relatively long duration of action.

 d) Good agent for topical application.

 5. Mepivacaine (Carbocaine)

a) Amide type agent similar to lidocaine.

 b) Without vasoconstrictor has only short duration of action.

6. Prilocaine (Citanest)

a) Amide type agent — less potent than lidocaine.

 b) Without vasoconstrictor has only short duration of action.

 c) Metabolized to o-toluidine which can cause methemoglobinemia — significant only with large doses of prilocaine.

 d) Higher incidences of paresthesia reported with 4 % preparation

7. Bupivacaine (Marcaine)

a) Amide type agent of high potency and toxicity.

 b) Rapid onset and very long duration of action even without vasoconstrictor.

 8. Articaine (Septocaine)

a) Amide type agent

 b) Only amide-type local anesthetic that contains an ester group, therefore metabolized both in the liver and plasma.

 c) Approved by the FDA in 2000

 d) Evidence points to improved diffusion through hard and soft tissues as compared to other local anesthetics.

 e) Reports of a higher incidence of paresthesia, presumably due to the 4% concentration

 f) Not recommended for use in children under 4 years of age

Oxytetracycline

Treats Oxytetracycline is a medicine used for treating a wide range of infections including infections of the lungs, urinary system, skin and eyes. It may also be used to treat sexually transmitted infections, infections caused by lice, rickettsial infections, cholera and plague. It is very occasionally used to treat leptospirosis, gas gangrene, and tetanus.

Pharmacodynamic Effects of NSAIDs

A. Positive

analgesic - refers to the relief of pain by a mechanism other than the reduction of inflammation (for example, headache);

- produce a mild degree of analgesia which is much less than the analgesia produced by opioid analgesics such as morphine

anti-inflammatory - these drugs are used to treat inflammatory diseases and injuries, and with larger doses - rheumatoid disorders

antipyretic - reduce fever; lower elevated body temperature by their action on the hypothalamus; normal body temperature is not reduced

Anti-platelet - inhibit platelet aggregation, prolong bleeding time; have anticoagulant effects

B. Negative

Gastric irritant

Decreased renal perfusion

Bleeding

(CNS effects)

Adverse effects

The two main adverse drug reactions (ADRs) associated with NSAIDs relate to gastrointestinal (GI) effects and renal effects of the agents.

Gastrointestinal ADRs

The main ADRs associated with use of NSAIDs relate to direct and indirect irritation of the gastrointestinal tract (GIT). NSAIDs cause a dual insult on the GIT - the acidic molecules directly irritate the gastric mucosa; and inhibition of COX-1 reduces the levels of protective prostaglandins.

Common gastrointestinal ADRs include:

Nausea, dyspepsia, ulceration/bleeding, diarrhoea

Risk of ulceration increases with duration of therapy, and with higher doses. In attempting to minimise GI ADRs, it is prudent to use the lowest effective dose for the shortest period of time..

 Ketoprofen and piroxicam appear to have the highest prevalence of gastric ADRs, while ibuprofen (lower doses) and diclofenac appear to have lower rates.

Commonly, gastrointestinal adverse effects can be reduced through suppressing acid production, by concomitant use of a proton pump inhibitor, e.g. omeprazole

Renal ADRs

NSAIDs are also associated with a relatively high incidence of renal ADRs. The mechanism of these renal ADRs is probably due to changes in renal haemodynamics (bloodflow), ordinarily mediated by prostaglandins, which are affected by NSAIDs.

Common ADRs associated with altered renal function include:

salt and fluid retention,hypertension

These agents may also cause renal impairment, especially in combination with other nephrotoxic agents. Renal failure is especially a risk if the patient is also concomitantly taking an ACE inhibitor and a diuretic - the so-called "triple whammy" effect.

In rarer instances NSAIDs may also cause more severe renal conditions.

interstitial nephritis, nephrotic syndrome, acute renal failure

Photosensitivity

Photosensitivity is a commonly overlooked adverse effect of many of the NSAIDs. These antiinflammatory agents may themselves produce inflammation in combination with exposure to sunlight. The 2-arylpropionic acids have proven to be the most likely to produce photosensitivity reactions, but other NSAIDs have also been implicated including piroxicam, diclofenac and benzydamine.

ibuprofen having weak absorption, it has been reported to be a weak photosensitising agent.

Other ADRs

Common ADRs, other than listed above, include: raised liver enzymes, headache, dizziness.

Uncommon ADRs include: heart failure, hyperkalaemia, confusion, bronchospasm, rash.

The COX-2 paradigm

It was thought that selective inhibition of COX-2 would result in anti-inflammatory action without disrupting gastroprotective prostaglandins.

The relatively selective COX-2 oxicam, meloxicam, was the first step towards developing a true COX-2 selective inhibitor. Coxibs, the newest class of NSAIDs, can be considered as true COX-2 selective inhibitors and include celecoxib, rofecoxib, valdecoxib, parecoxib and etoricoxib.

Aquaretics
An aquaretic is a class of drug that is used to promote aquaresis, the excretion of water without electrolyte loss.

Lithium, demeclocycline

Mechanism of Action

1.    Block ADH action on distal tubule and collecting duct. Blocking ADH decreases H2O permeability. H2O is not recovered (distal tubule) using osmotic draw of counter-current multiplier so aquaretics reduce water reabsorption (tubule to blood stream). 
2.    Net effect is an increase in free water clearance
 

DIURETICS

The basis for the use of diuretics is to promote sodium depletion (and thereby water) which leads to a decrease in extracellular fluid volume.
An important aspect of diuretic therapy is to prevent the development of tolerance to other antihypertensive drugs.

TYPES OF DIURETICS
A. Thiazide Diuretics examples include     chlorothiazide 
hydrochlorothiazide 
a concern with these drugs is the loss of potassium as well as sodium

B. Loop Diuretics (High Ceiling Diuretics) examples include 
furosemide (Lasix)
bumetanide
these compounds produce a powerful diuresis and are capable of producing severe derangements of electrolyte balance

C. Potassium Sparing Diuretics examples include
triamterene
amiloride 
spironolactone 
unlike the other diuretics, these agents do not cause loss of potassium

Mechanism of Action

Initial effects: through reduction of plasma volume and cardiac output.
Long term effect: through decrease in total peripheral vascular resistance.

Advantages

Documented reduction in cardiovascular morbidity and mortality.
Least expensive antihypertensive drugs.
Best drug for treatment of systolic hypertension and for hypertension in theelderly.
Can be combined with all other antihypertensive drugs to produce synergetic effect.

Side Effects
Metabolic effects (uncommon with small doses): hypokalemia,hypomagnesemia, hyponatremia, hyperuricemia, dyslipidemia (increased total
and LDL cholesterol), impaired glucose tolerance, and hypercalcemia (with thiazides).
Postural hypotension.
Impotence in up to 22% of patients.  

 Considerations
- Moderate salt restriction is the key for effective antihypertensive effect of diuretics and for protection from diuretic - induced hypokalaemia. 
- Thiazides are not effective in patients with renal failure (serum creatinine > 2mg /dl) because of reduced glomerular filtration rate.
- Frusemide needs frequent doses ( 2-3 /day ).Thiazides can be given once daily or every other day.
- Potassium supplements should not be routinely combined with thiazide or loop diuretics. They are indicated with hypokalemia (serum potassium < 3.5 mEq/L) especially with concomitant digitalis therapy or left ventricular hypertrophy.
- Nonsteroidal antiinflammatory drugs can antagonize diuretics effectiveness.

Special Indications

Diuretics should be the primary choice in all hypertensives.

They are indicated in:
- Volume dependent forms of hypertension: blacks, elderly, diabetic, renal and obese hypertensives.
- Hypertension complicated with heart failure.
- Resistant hypertension: loop diuretics in large doses are recommended.
- Renal impairment: loop diuretics