Amoxicillin (Page 4 of 7)

8.6 Dosing in Renal Impairment

Amoxicillin is primarily eliminated by the kidney and dosage adjustment is usually required in patients with severe renal impairment (GFR < 30 mL/min). See Dosing in Renal Impairment ( 2.4) for specific recommendations in patients with renal impairment.

10 OVERDOSAGE

In case of overdosage, discontinue medication, treat symptomatically, and institute supportive measures as required. A prospective study of 51 pediatric patients at a poison-control center suggested that overdosages of less than 250 mg/kg of amoxicillin are not associated with significant clinical symptoms.

Interstitial nephritis resulting in oliguric renal failure has been reported in a small number of patients after overdosage with amoxicillin ¹.

Crystalluria, in some cases leading to renal failure, has also been reported after amoxicillin overdosage in adult and pediatric patients. In case of overdosage, adequate fluid intake and diuresis should be maintained to reduce the risk of amoxicillin crystalluria.

Renal impairment appears to be reversible with cessation of drug administration. High blood levels may occur more readily in patients with impaired renal function because of decreased renal clearance of amoxicillin. Amoxicillin may be removed from circulation by hemodialysis.

11 DESCRIPTION

Amoxicillin, USP is a semisynthetic antibiotic, an analog of ampicillin, with a broad spectrum of bactericidal activity against many gram-positive and gram-negative microorganisms. Chemically, it is (2 S ,5 R ,6 R)-6-[( R)-(-)-2-amino-2-( p -hydroxyphenyl)acetamido]-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid trihydrate. The structural formula is:

C ₁₆ H ₁₉ N ₃ O ₅ S•3H ₂ O M.W. 419.45

Amoxicillin Capsules USP

Each capsule, for oral administration, contains 250 mg or 500 mg amoxicillin, USP as the trihydrate.

Inactive Ingredients: CAPSULES-DRUG PRODUCT: magnesium stearate, talc.

CAPSULE SHELL AND PRINT CONSTITUENTS: black iron oxide, D&C Yellow #10, D&C Yellow #10 Aluminum Lake, FD&C Blue #1 Aluminum Lake, FD&C Blue #2 Aluminum Lake, FD&C Red #40, FD&C Red #40 Aluminum Lake, gelatin, propylene glycol, shellac, titanium dioxide. In addition, the 500 mg capsule shell may also contain methylparaben, potassium hydroxide, propylparaben, and sodium lauryl sulfate; and the 250 mg capsule shell contains D&C Red #28 and FD&C Blue #1.

Amoxicillin for Oral Suspension USP

Each 5 mL of reconstituted suspension contains 125 mg or 250 mg of amoxicillin, USP as the trihydrate.

Inactive Ingredients: SUSPENSION: FD&C Red #40, mixed berry flavoring, silicon dioxide, sodium benzoate, sodium citrate, sucrose, and xanthan gum.

Amoxicillin Tablets USP (Chewable)

Each chewable tablet, for oral administration, contains 125 mg or 250 mg of amoxicillin, USP as the trihydrate.

Inactive Ingredients: CHEWABLE TABLETS: cherry flavor, lactose anhydrous, magnesium stearate, mannitol, microcrystalline cellulose, sodium citrate, and sucrose.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Amoxicillin is an antibacterial drug [ see Microbiology ( 12.4) ].

12.3 Pharmacokinetics

Absorption

Amoxicillin is stable in the presence of gastric acid and is rapidly absorbed after oral administration. The effect of food on the absorption of amoxicillin from the tablets and suspension of amoxicillin has been partially investigated; 400 mg and 875 mg formulations have been studied only when administered at the start of a light meal.

Orally administered doses of 250 mg and 500 mg amoxicillin capsules result in average peak blood levels 1 to 2 hours after administration in the range of 3.5 mcg/mL to 5 mcg/mL and 5.5 mcg/mL to 7.5 mcg/mL, respectively.

Mean amoxicillin pharmacokinetic parameters from an open, two-part, single-dose crossover bioequivalence study in 27 adults comparing 875 mg of amoxicillin with 875 mg of amoxicillin/clavulanate potassium showed that the 875 mg of amoxicillin tablet produces an AUC _{0 to ∞} of 35.4 ± 8.1 mcg•hr/mL and a C _max of 13.8 ± 4.1 mcg/mL. Dosing was at the start of a light meal following an overnight fast.

Orally administered doses of amoxicillin suspension, 125 mg/5 mL and 250 mg/5 mL, result in average peak blood levels 1 to 2 hours after administration in the range of 1.5 mcg/mL to 3 mcg/mL and 3.5 mcg/mL to 5 mcg/mL, respectively.

Oral administration of single doses of 400 mg chewable tablets and 400 mg/5 mL suspension of amoxicillin to 24 adult volunteers yielded comparable pharmacokinetic data:

Table 3: Mean Pharmacokinetic Parameters of Amoxicillin (400 mg chewable tablets and 400 mg/5 mL suspension) in Healthy Adults

* Administered at the start of a light meal. † Mean values of 24 normal volunteers. Peak concentrations occurred approximately 1 hour after the dose.
Dose *	AUC 0 to ∞ (mcg • hr/mL)	C max (mcg/mL) †
Amoxicillin	Amoxicillin (± S.D.)	Amoxicillin (± S.D.)
400 mg (5 mL of suspension)	17.1 (3.1)	5.92 (1.62)
400 mg (1 chewable tablet)	17.9 (2.4)	5.18 (1.64)

Distribution

Amoxicillin diffuses readily into most body tissues and fluids, with the exception of brain and spinal fluid, except when meninges are inflamed. In blood serum, amoxicillin is approximately 20% protein-bound. Following a 1 gram dose and utilizing a special skin window technique to determine levels of the antibiotic, it was noted that therapeutic levels were found in the interstitial fluid.

Metabolism and Excretion

The half-life of amoxicillin is 61.3 minutes. Approximately 60% of an orally administered dose of amoxicillin is excreted in the urine within 6 to 8 hours. Detectable serum levels are observed up to 8 hours after an orally administered dose of amoxicillin. Since most of the amoxicillin is excreted unchanged in the urine, its excretion can be delayed by concurrent administration of probenecid [ see DRUG INTERACTIONS ( 7.1) ].