The penicillins are among the earliest classes of antibacterial drugs. Penicillins are divided into subclasses based on chemical structure (eg, penicillins, monobactams, and carbapenems), spectrum (narrow, broad, or extended), source (natural, semisynthetic, or synthetic), and susceptibility to β-lactamase destruction. Manipulation of some drugs has improved the spectrum, resistance to β-lactamase destruction, or clinical pharmacologic characteristics that enhance efficacy.


Most penicillins in aqueous solution are rapidly absorbed from parenteral sites. Absorption is delayed when the inorganic penicillin salts are suspended in vegetable oil vehicles or when the sparingly soluble repository organic salts (eg, procaine penicillin G and benzathine penicillin G) are administered parenterally. Although prolonged absorption results in longer persistence of plasma and tissue drug concentrations, peak concentrations may not be sufficiently high to be effective against organisms unless MICs are low. The penicillin G repositol salts should never be injected IV. Only selected penicillins are acid stable and can be administered PO at standard doses. Absorption from the upper GI tract differs markedly in amount and rate among the various penicillins. Penicillin V must be given at high oral doses. The aminopenicillins are orally bioavailable, although food impairs the absorption of ampicillin.

Paracellular (as opposed to transcellular) transport may play a major role in oral absorption. The indanyl form of carbenicillin is orally bioavailable, but effective concentrations are likely to be achieved only in the urine. Serum concentrations of penicillins generally peak within 2 hr of PO administration. Penicillins may also be absorbed after intrauterine infusion. There is no information regarding bioavailability of human generic products when used off-label in veterinary patients.

Features of Oral Penicillin For Cattle

The penicillins, particularly the β-lactam ring, are somewhat unstable, being sensitive to heat, light, extremes in pH, heavy metals, and oxidizing and reducing agents. Also, they often deteriorate in aqueous solution and require reconstitution with a diluent just before injection. Penicillins are poorly soluble, weak organic acids administered parenterally either as suspensions in water or oil or as water-soluble salts. For example, sodium or potassium salts of penicillin G are highly water soluble and are absorbed rapidly from injection sites, whereas organic esters in microsuspension such as procaine penicillin G or benzathine penicillin G are gradually absorbed over 1–3 (or even more) days, respectively. The trihydrate forms of the semisynthetic penicillins have greater aqueous solubility than the parent compounds and are usually preferred for both parenteral and oral use.

The β-lactam nucleus that characterizes penicillins, when cleaved by a β-lactamase enzyme (penicillinase), produces penicilloic acid derivatives that are inactive but may act as the antigenic determinants for penicillin hypersensitivity. Modification of the 6-aminopenicillanic acid nucleus, either by biosynthetic or semisynthetic means, has produced the array of penicillins used clinically. These differ in their antibacterial spectra, pharmacokinetic characteristics, and susceptibility to microbial enzymatic degradation

Uses/benefits of Oral Penicillin For Cattle

Antibiotics are given to animals that are sick, in order to help relieve the pain and distress due to the illness, help the animal feel better, and recover.  Antibiotics may also be given to animals that are in danger of becoming sick in order to prevent the illness or infection from happening in the first place.  Just like in people, however, antibiotics do not have any effect on diseases of animals that are caused by viruses or parasites, or other germs besides bacteria.  Some antibiotics, for reasons that aren’t totally understood, help cattle grow faster and get more out of the feed they eat.  These medicines are used at lower concentrations than when they are used to treat illness, and typically are included in the food that cattle eat.  The decision whether to use such products for this use (or any other reason) rests with the individual cattle raiser.  Not all of them choose to use antibiotics in this manner.  

Prices of Oral Penicillin For Cattle

$24.39 – $151.54

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