For general information on the penicillins, including adverse effects, contraindications, overdosage, drug interactions and monitoring parameters, refer to the monograph: Penicillins, General Information.
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.
For susceptible infections:
a) For respiratory infections: 20 - 30 mg/kg PO q6h (Beech 1987b)
b) Amoxicillin trihydrate: 20 mg/kg q12h IM. (Upson 1988)
a) 11 mg/kg IM q 24 h (Schmidt, 1978).
a) Schmidt,M.J. 1978. Penicillin and amoxicillin in elephants: A study comparing dose regimens administered with serum levels achieved in healthy elephants. Journal of Zoo Animal Medicine 9:(4):127-136 Abstract: Several dose regimens of an aqueous suspension of benzathine penicillin G combined with procaine penicillin G, and an aqueous suspension of amoxicillin were administered to five healthy adult female Asian elephants. Blood samples were drawn and serum levels of the drugs were measured after each dose was administered. Based upon serum levels, suggestions are made for therapeutic dose regimens for clinical use of both penicillin and amoxicillin in elephants, based on comparable data available for other large domestic animals.
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.
Dosage Forms/Preparations/FDA Approval Status/Withholding Times -
Amoxicillin Oral Tablets 50 mg, 100 mg, 150 mg, 200 mg, , 400 mg; Amoxi-Tabs® (Pfizer), (Rx) Approved for use in dogs and cats. Robamox-V® (Fort Dodge); (Rx) Approved for use in dogs only.
Amoxicillin Powder for Oral Suspension 50 mg/ml (after reconstitution) in 15 ml or 30 ml bottles; Amoxi-Drop® (Pfizer); (Rx); Approved for use in dogs and cats.Robamox-V® (Fort Dodge) (Rx); Approved for use in dogs.
Amoxicillin Oral Bolus 400 mg; Amoxi-Bol® (Pfizer); (Rx) Approved for use in non-ruminating calves, including veal calves. Slaughter withdrawal = 20 days.
Amoxicillin Powder for Suspension (Injection): 3 gram vial (Dogs, Cats) and 25 g vial (non-lactating cattle); Amoxi-Inject® (Pfizer); (Rx) Approved for use in dogs and cats (3 g vial), Slaughter withdrawal (cattle) = 25 days. Milk withdrawal = 96 hours.
Amoxicillin Intramammary Infusion 62.5 mg/syringe in 10 ml syringes; Amoxi-Mast® (Pfizer); (Rx) Approved for use in lactating dairy cattle. Slaughter withdrawal = 12 days; Milk withdrawal = 60 hours.
Amoxicillin Tablets (chewable) 125 mg (As trihydrate) & 250 mg (as trihydrate);Amoxil ®(SK Beecham); generic, (Rx)
Amoxicillin Capsules (as trihydrate) 250 mg, 500 mg; Polymox® (Apothecon); Wymox® (Wyeth-Ayerst); generic (Rx)
Amoxicillin (as the trihydrate) Powder for Oral Suspension 50 mg/ml (as trihydrate) (in 15 and 30 ml bottles), 125 mg/5 ml (as trihydrate) and 250 mg/5 ml (as trihydrate) 80 ml, 100 ml, 150 ml, and 200 ml bottles. (Rx)
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