A dose in grams  benzathine penicillin will result in penicillinaemia due to over accumulation. International units are well defined in case of penicillin as other antibiotics are given on any particular day during the week after injection, ambulant adult males were injected with 2 400 000 IU of ”all-purpose” penicillin (600 000 IU potassium penicillin G, 600 000 IU procaine penicillin G and 1 200 000 IU of benzathine penicillin. benzathine penicillin is a long lasting component  has an extremely low solubility and the drug is slowly released from IM injection sites (blood levels persist from 4 to 14 days depending on dose). T max is 4 h (procaine IM). Penicillin G–sensitive is highly sensitive to microorganisms that are susceptible to the low and very prolonged serum levels common to this dose form in man. All penicillins are ineffective toward cell wall-deficient microorganisms such as Mycoplasma or Chlamydia spp. International unit of penicillin is the specific penicillin activity  0.6 microgram of sodium salt. of penicillin G. Thus  1 mg pure penicillin G  sodium equals 1667 units, 1 mg pure penicillin G potassium equals  1595 units. its 400, 000 units are equal to (250 mg),  The dosage of synthetic penicillin is expressed in terms of weight given in mg/body weight, while natural prescription is always provided in internation units.

A dose in grams  benzathine penicillin will result in penicillinaemia due to over accumulation. International units are well defined in case of penicillin as other antibiotics are given on any particular day during the week after injection, ambulant adult males were injected with 2 400 000 IU of ”all-purpose” penicillin (600 000 IU potassium penicillin G, 600 000 IU procaine penicillin G and 1 200 000 IU of benzathine penicillin. benzathine penicillin is a long lasting component  has an extremely low solubility and the drug is slowly released from IM injection sites (blood levels persist from 4 to 14 days depending on dose). T max is 4 h (procaine IM). Penicillin G–sensitive is highly sensitive to microorganisms that are susceptible to the low and very prolonged serum levels common to this dose form in man. All penicillins are ineffective toward cell wall-deficient microorganisms such as Mycoplasma or Chlamydia spp. International unit of penicillin is the specific penicillin activity  0.6 microgram of sodium salt. of penicillin G. Thus  1 mg pure penicillin G  sodium equals 1667 units, 1 mg pure penicillin G potassium equals  1595 units. its 400, 000 units are equal to (250 mg),  The dosage of synthetic penicillin is expressed in terms of weight given in mg/body weight, while natural prescription is always provided in internation units.

Thank you sir for your kind explanation. 

Thank you too

• Thanks so much

Thanks So MUcH

The use of penicillin units dates to the 1940's. The original penicillin produced in fermentations broths of Streptomyces chrysogenum was a natural mixture of 7 penicillins: penicillin D, F, G, K, U1, U6 and X. Each penicillin has a different potency (penicillin K being the least potent and penicillin X being the most potent) and the proportion of each constituent penicillin varied greatly from batch to batch.

Because of this batch to batch variation, each batch had to be "standardised" against a single standard batch of penicillin, based on its ability to kill Staphylococcus aureus. So, for example: the second international unit of penicillin was equivalent to 0.0005988 mg of a single large batch of penicillin (or approx 0.60 units per gram). So if 1.2g of the new batch had the same killing power (potency) as 1.0g of the international standard, then 1.2g of the new batch was said to contain 0.60 units of penicillin. Ampoules were filled with a fixed number of "units" of penicillin (the weight of which, in milligrams, would therefore vary from batch to batch).

It later became possible to purify penicillin to produce pure preparations of penicillin G. With pure crystallised penicillins, there is no need to specify the number of units, and dose can instead be specified by weight in grams or milligrams.

The information is really useful. Thanks!

I was taught that each mg of penicillin is 1667 IU. We generally dose animals with penicillin at 10,000 IU/Kg body weight which is approximately 6 mg/kg body weight up to 60-80,000 IU/kg body weight or 36-48mg/kg body weight once, twice or more times daily depending upon the severity of the infection in the animal.

In the USA, the standard is 300,000 IU/mL in procaine penicillin G, 150,000 IU Procaine Pen G/150,000 IU/mL Benzithine penicillin G in BP48 or combicillin. Or with potassium/sodium penicillin, concentration dependent upon rehydration volume.

In the USA, the label dose (legally allowed doses provided on the label) is generally 1mL/100 lbs body weight (1 mL/45.45 kg) which is low. Using the higher doses by routes not on label is a reason for violative residues in animals going to harvest. Mainly subcutaneous route but certain by other routes when the dosing interval is decreased or providing treatment past that on the drug label. So giving more frequently than once a day or administering by subcutaneous route commonly results in milk or meat residues when label withdrawal time is observed.

I was not around in 1940 so I can only refer to Dr. Ravi Kant Upadhyay knowledge about purity of preparations. It seems to reflect what we were taught in Veterinary School (1980's).

very nice explanations