Polymyxins



Polymyxins
Polymyxin B & E (Colistin) are two clinically important polypeptide antibiotics obtained from Bacillus polymyxa and Bacillus colistinus respectively.
Both are narrow spectrum, rapidly bactericidal antibiotics.
Highly active against G -ve orgs. Such as E. Coli, Salmonella spp. And P. Aeruginosa.
They are ineffective against G +ve orgs.
These have detergent like action on the Bac.’s cell membrane.
They bind with bac. Cell membrane phospholipids with high affinity, distort it. As a result ions, aminoacids, etc leak out and bac. Cells die.
They are neither absorbed topically nor orally and do not penetrate BBB.
For systemic they are administered parenterally.
Systemically rarely used due to serious toxicity (nephrotoxicity, neurotoxicity and neuromuscular blockade) and only used in life threatening infections caused by G –ve bacilli or Pseudomonas.
Orally it is used in G – ve enteritis in calves and pigs, topically in skin infections (along with neomycin / bacitracin), otitis externa (with OTC), in bovine mastitis (with OTC for Klebsiella spp.) and as semen additive (in bull semen containing Pseudomonas org.)
Dose:
Oral: 20000 units/kg, bid.
IM: 5000 units/kg, bid.
Intramammary: 50000 – 1L units.
Intrauterine: 1L units.

Comments

Post a Comment

Popular posts from this blog

Pharmacokinetics - Drug absorption and Transport of drugs across biological membranes

Transport of drugs across biological membranes All pharmacokinetic processes involved transport of the drug across biological membranes. Biological Membrane Biological membranes may be viewed as mosaics of functional units composed of lipoprotein complex. Most membranes are composed of a fundamental structure called the unit membrane or plasma membrane. This boundary, which is 80 to 100 A° thick, surrounds single cell and nuclei. More complex barriers such as the intestinal epithelia and the skin are composed of multiples of this functional structure. The plasma membrane consists of a bilayer of amphipathic lipids with their hydrocarbon chains oriented inward to form a continuous hydrophobic phase and their hydrophilic heads oriented outward. Individual lipid molecules in the bilayer can move laterally, endowing the membrane with fluidity, flexibility, high electrical resistance and relative impermeability to highly polar molecules. The known fluidity of the phospholipids i
Read more

Skeletal muscle relaxants

Image
Skeletal muscle relaxants Physiology of SKM Contraction 1. Motor nerve impulse à 2. Release of ACh à 3. Binds with N M receptors at NMJ à 4. Depolarization & development of EPP at motor end plate (Mainly due to influx of Na + ) à 5. Muscle action potential (MAP) – contraction of SKM à 6. ACh is rapidly inactivated by ChE leading to repolarization à 7. Muscle is ready for a fresh nerve impulse. MECHANISM OF ACTION OF MUSCLE RELAXANTS Centrally acting muscle relaxants -           Reduce SKM tone by a selective action in the cerebrospinal axis, without altering consciousness. -           They selectively depress spinal and supraspinal polysynaptic reflexes involved in the regulation of muscle tone without significantly affecting monosynaptically mediated stretch reflex. -           Polysynaptic pathways in ascending reticular formation also depressed, though to a lesser extent. -           All centrally acting muscle relaxants have some sedative property
Read more

PHARMACOGNOSY - SOURCES AND COMPOSITION OF DRUGS

PHARMACOGNOSY - SOURCES AND COMPOSITION OF DRUGS             A large number of drugs are used in the clinics for the cure of various ailments. These drugs are diverse in chemical structure and are obtained from a wide variety of sources. In earlier days, simple chemical substances and different parts of plants were employed as medicinal agents, but most drugs currently used in therapeutics are synthetic in nature. However, natural sources are still used for obtaining some drugs mainly because their synthesis is difficult and uneconomical. Drugs are mainly obtained from following sources. I. NATURAL SOURCE A. Organic drugs . Organic drugs are mainly obtained from 1. Vegetable source 2. Animal source 3. Microorganisms. B. Inorganic drugs . These are mainly obtained from 1.   Metallic source 2.   Non-metallic source. II. SYNTHETIC SOURCE (I) NATURAL SOURCES OF DRUGS Active principles of drugs are mainly present in crude form in minute amounts. T
Read more