AMOXICILLIN

AMOXICILLIN

Chemistry - An aminopenicillin, amoxicillin is commercially available as the trihydrate. It occurs as a practically odorless, white, crystalline powder that is sparingly soluble in water. Amoxicillin differs structurally from ampicillin only by having an additional hydroxyl group on the phenyl ring.

Amoxicillin may also be known as amoxycillin, p-hydroxyampicillin, or BRL 2333.

Storage/Stability/Compatibility - Amoxicillin capsules, tablets, and powder for oral suspension should be stored at room temperature (15-30¡C) in tight containers. After reconstitution, the oral suspension should preferably be refrigerated (refrigeration not absolutely necessary) and any unused product discarded after 14 days. After reconstitution, the injectable veterinary suspension is stable for 3 months at room temperature and 12 months when refrigerated.

Pharmacology/Uses/Indications - Although there may be some slight differences in activity against certain organisms, amoxicillin generally shares the same spectrum of activity and uses as ampicillin. Because it is better absorbed orally (in non-ruminants), higher serum levels may be attained than with ampicillin. Refer to the ampicillin monograph or the general penicillin statement for more information.

Pharmacokinetics (specific) - Amoxicillin trihydrate is relatively stable in the presence of gastric acid. After oral administration, it is about 74-92% absorbed in humans and animals (monogastric). Food will decrease the rate, but not the extent of oral absorption and many clinicians suggest giving the drug with food, particularly if there is concomitant associated GI distress. Amoxicillin serum levels will generally be 1.5-3 times greater than those of ampicillin after equivalent oral doses. After absorption the volume of distribution for amoxicillin is approximately 0.3 L/kg in humans and 0.2 L/kg in dogs. The drug is widely distributed to many tissues, including liver, lungs, prostate (human), muscle, bile, and ascitic, pleural and synovial fluids. Amoxicillin will cross into the CSF when meninges are inflamed in concentrations that may range from 10-60% of those found in serum. Very low levels of the drug are found in the aqueous humor, and low levels found in tears, sweat and saliva. Amoxicillin crosses the placenta, but it is thought to be relatively safe to use during pregnancy. It is approximately 17-20% bound to human plasma proteins, primarily albumin. Protein binding in dogs is approximately 13%. Milk levels of amoxicillin are considered to be low. Amoxicillin is eliminated primarily through renal mechanisms, principally by tubular secretion, but some of the drug is metabolized by hydrolysis to penicilloic acids (inactive) and then excreted in the urine. Elimination half-lives of amoxicillin have been reported as 45-90 minutes in dogs and cats, and 90 minutes in cattle. Clearance is reportedly 1.9 ml/kg/min in dogs.

Doses

Dogs:

For susceptible infections:

a) 10 - 22 mg/kg PO or SubQ q8h

b) Trihydrate injectable: 5.5 - 11 mg/kg IM or SQ q8h

Oral Forms: 11 - 22 mg/kg PO q8-12h

c) For routine infections: 10 mg/kg PO, SQ bid

For chlolangiohepatitis: 20 mg/kg PO, SQ bid

d) 22 mg/kg PO q12h

e) 10 - 55 mg/kg q6-12h PO; 5 - 11 mg/kg IV, IM, or SQ q6-12h

f) For Lyme Disease: 22 mg/kg PO q12h for 21-28 days

Cats:

For susceptible infections:

a) 10 - 22 mg/kg PO or SubQ q8h

b) Trihydrate injectable: 5.5 - 11 mg/kg IM or SQ q8h

Oral Forms: 11 - 22 mg/kg PO q8-12h

c) 11 - 22 mg/kg PO q8-12h

d) For bacterial respiratory infections: 10 mg/kg PO or parenterally q12-24h

e) 22 mg/kg PO q12h

Cattle:

For susceptible infections:

a) 6 -10 mg/kg SQ or IM q24h (Withdrawal time = 30 days)

b) For respiratory infections: 11 mg/kg IM or SQ q12h.

c) For respiratory infections: 11 mg/kg IM or SQ q12h

d) Calves: Amoxicillin trihydrate: 7 mg/kg PO q8-12h

e) 13.2 - 15.4 mg/kg IM or SQ once daily

Horses:

For susceptible infections:

a) For respiratory infections: 20 - 30 mg/kg PO q6h

b) Amoxicillin trihydrate: 20 mg/kg q12h IM.

Birds:

For susceptible infections:

a) For most species: 150 - 175 mg/kg PO once to twice daily (using 50 mg/ml suspension)

b) 100 mg/kg q8h PO

c) 100mg/kg q8h, IM, SubQ, PO

Reptiles:

For susceptible infections:

a) For all species: 22 mg/kg PO q12-24h; not very useful unless used in combination with aminoglycosides.

Client Information - The oral suspension should preferably be refrigerated, but refrigeration is not absolutely necessary; any unused oral suspension should be discarded after 14 days. Amoxicillin may be administered orally without regard to feeding status. If the animal develops gastrointestinal symptoms (e.g., vomiting, anorexia), giving with food may be of benefit.