Inactive Ingredients

Microbiology

Mechanism of Action

Penicillinase-resistant penicillins exert a bactericidal action against penicillin-susceptible microorganisms during the state of active multiplication. All penicillins inhibit the biosynthesis of the bacterial cell wall.

Antibacterial Activity

Dicloxacillin sodium has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section.

Gram-positive Bacteria

Staphylococcus spp.

Susceptibility Test Methods

Susceptibility of staphylococcal isolates to dicloxacillin may be inferred by testing penicillin and either oxacillin or cefoxitin 1. For staphylococcal isolates, penicillin susceptibility implies susceptibility to other β-lactam agents, and penicillin resistance implies resistance to penicillinase-labile penicillins. Resistance to oxacillin (or cefoxitin) implies resistance to all other β-lactam agents, except newer agents with activity against methicillin-resistant Staphylococcus aureus. Routine testing of dicloxacillin is not advised.

Pharmacokinetics

Methicillin sodium is readily destroyed by gastric acidity and must be administered by intramuscular or intravenous injection. The isoxazolyl penicillins (cloxacillin, dicloxacillin and oxacillin) and nafcillin are more acid-resistant and may be administered orally.

Absorption of the isoxazolyl penicillins after oral administration is rapid but incomplete; peak blood levels are achieved in 1 to 1.5 hours. In one study, after ingestion of a single 500 mg oral dose, peak serum concentrations range from 5 to 7 micrograms/milliliter for oxacillin, from 7.5 to 14.4 mcg/mL for cloxacillin and from 10 to 17 mcg/mL for dicloxacillin.

Oral absorption of cloxacillin, dicloxacillin, oxacillin and nafcillin is delayed when the drugs are administered after meals.

Once absorbed, the penicillinase-resistant penicillins bind to serum protein, mainly albumin. The degree of protein binding reported varies with the method of study and the investigator (see TABLE II).

The penicillinase-resistant penicillins vary in the extent to which they are distributed in the body fluids. With normal doses, insignificant concentrations are found in the cerebrospinal fluid and aqueous humor. All the drugs in this class are found in therapeutic concentrations in the pleural, bile and amniotic fluids.

The penicillinase-resistant penicillins are rapidly excreted, primarily as unchanged drug in the urine by glomerular filtration and active tubular secretion. The elimination half-life for dicloxacillin is about 0.7 hour. Nonrenal elimination includes hepatic inactivation and excretion in bile.

General

Prescribing dicloxacillin sodium capsules in the absence of a proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.

Dicloxacillin should generally not be administered to patients with a history of sensitivity to any penicillin.

Penicillin should be used with caution in individuals with histories of significant allergies and/or asthma. Whenever allergic reactions occur, penicillin should be withdrawn unless, in the opinion of the physician, the condition being treated is life-threatening and amenable only to penicillin therapy.

The oral route of administration should not be relied upon in patients with severe illness, or with nausea, vomiting, gastric dilatation, cardiospasm or intestinal hypermotility. Occasionally, patients will not absorb therapeutic amounts of orally administered penicillin.

The use of antibiotics may result in overgrowth of nonsusceptible organisms. If new infections due to bacteria or fungi occur, the drug should be discontinued and appropriate measures taken.

Information for the Patient

Patients should be counselled that antibacterial drugs including dicloxacillin sodium capsules should only be used to treat bacterial infections. They do not treat viral infections (e.g., the common cold). When dicloxacillin sodium capsules are prescribed to treat a bacterial infection, patients should be told that although it is common to feel better early in the course of therapy, the medication should be taken exactly as directed. Skipping doses or not completing the full course of therapy may (1) decrease the effectiveness of the immediate treatment and (2) increase the likelihood that bacteria will develop resistance and will not be treatable by dicloxacillin sodium capsules or other antibacterial drugs in the future.

Patients receiving penicillins should be given the following information and instructions by the physician:

1. Patients should be told that penicillin is an antibacterial agent which will work with the body’s natural defenses to control certain types of infections. They should be told that the drug should not be taken if they have had an allergic reaction to any form of penicillin previously, and to inform the physician of any allergies or previous allergic reactions to any drugs they may have had (see WARNINGS).
2. Patients who have previously experienced an anaphylactic reaction to penicillin should be instructed to wear a medical identification tag or bracelet.
3. Because most antibacterial drugs taken by mouth are best absorbed on an empty stomach, patients should be directed, unless circumstances warrant otherwise, to take penicillin one hour before meals or two hours after eating (see CLINICAL PHARMACOLOGY - Pharmacokinetics).
4. Patients should be told to take the entire course of therapy prescribed, even if fever and other symptoms have stopped (see PRECAUTIONS - General).
5. If any of the following reactions occur, stop taking your prescription and notify the physician: shortness of breath, wheezing, skin rash, mouth irritation, black tongue, sore throat, nausea, vomiting, diarrhea, fever, swollen joints or any unusual bleeding or bruising (see ADVERSE REACTIONS).
6. Do not take any additional medications without physician approval, including nonprescription drugs such as antacids, laxatives or vitamins.
7. Discard any liquid forms of penicillin after seven days if stored at room temperature or after 14 days if refrigerated.

Laboratory Tests

Bacteriologic studies to determine the causative organisms and their susceptibility to the penicillinase-resistant penicillins should be performed (see CLINICAL PHARMACOLOGY - Microbiology). In the treatment of suspected staphylococcal infections, therapy should be changed to another active agent if culture tests fail to demonstrate the presence of staphylococci.

Periodic assessment of organ system function, including renal, hepatic and hematopoietic, should be made during prolonged therapy with the penicillinase-resistant penicillins.

Blood cultures, white blood cell and differential cell counts should be obtained prior to initiation of therapy and at least weekly during therapy with penicillinase-resistant penicillins.

Periodic urinalysis, blood urea nitrogen and creatinine determinations should be performed during therapy with the penicillinase-resistant penicillins and dosage alterations should be considered if these values become elevated. If any impairment of renal function is suspected or known to exist, a reduction in the total dosage should be considered and blood levels monitored to avoid possible neurotoxic reactions (see DOSAGE AND ADMINISTRATION).

SGOT and SGPT values should be obtained periodically during therapy to monitor for possible liver function abnormalities.

Drug Interactions

Tetracycline, a bacteriostatic antibiotic, may antagonize the bactericidal effect of penicillin and concurrent use of these drugs should be avoided.

Carcinogenesis, Mutagenesis, Impairment of Fertility

No long-term animal studies have been conducted with these drugs.

Studies on reproduction (nafcillin) in rats and rabbits reveal no fetal or maternal abnormalities before conception and continuously through weaning (one generation).

Pregnancy Category B

Reproduction studies performed in the mouse, rat and rabbit have revealed no evidence of impaired fertility or harm to the fetus due to the penicillinase-resistant penicillins. Human experience with the penicillins during pregnancy has not shown any positive evidence of adverse effects on the fetus. There are, however, no adequate or well-controlled studies in pregnant women showing conclusively that harmful effects of these drugs on the fetus can be excluded. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.

Nursing Mothers

Penicillins are excreted in breast milk. Caution should be exercised when penicillins are administered to a nursing woman.

Pediatric Use

Because of incompletely developed renal function in newborns, penicillinase-resistant penicillins (especially methicillin) may not be completely excreted, with abnormally high blood levels resulting. Frequent monitoring of blood levels is advisable in this group, with dosage adjustments when necessary. All newborns treated with penicillins should be monitored closely for clinical and laboratory evidence of toxic or adverse effects (see DOSAGE AND ADMINISTRATION).

Body as a Whole

The reported incidence of allergic reactions to penicillin ranges from 0.7% to 10% (see WARNINGS). Sensitization is usually the result of treatment, but some individuals have had immediate reactions to penicillin when first treated. In such cases, it is thought that the patients may have had prior exposure to the drug via trace amounts present in milk and vaccines.

Two types of allergic reactions to penicillin are noted clinically, immediate and delayed.

Immediate reactions usually occur within 20 minutes of administration and range in severity from urticaria and pruritus to angioneurotic edema, laryngospasm, bronchospasm, hypotension, vascular collapse and death. Such immediate anaphylactic reactions are very rare (see WARNINGS) and usually occur after parenteral therapy, but have occurred in patients receiving oral therapy. Another type of immediate reaction, an accelerated reaction, may occur between 20 minutes and 48 hours after administration and may include urticaria, pruritus and fever. Although laryngeal edema, laryngospasm and hypotension occasionally occur, fatality is uncommon.

Delayed allergic reactions to penicillin therapy usually occur after 48 hours and sometimes as late as two to four weeks after initiation of therapy. Manifestations of this type of reaction include serum sickness-like symptoms (i.e., fever, malaise, urticaria, myalgia, arthralgia, abdominal pain) and various skin rashes. Nausea, vomiting, diarrhea, stomatitis, black or hairy tongue and other symptoms of gastrointestinal irritation may occur, especially during oral penicillin therapy.

Nervous System Reactions

Neurotoxic reactions similar to those observed with penicillin G may occur with large intravenous doses of the penicillinase-resistant penicillins, especially with patients with renal insufficiency.

Urogenital Reactions

Renal tubular damage and interstitial nephritis have been associated with the administration of methicillin sodium and, infrequently, with the administration of nafcillin and oxacillin. Manifestations of this reaction may include rash, fever, eosinophilia, hematuria, proteinuria and renal insufficiency. Methicillin-induced nephropathy does not appear to be dose-related and is generally reversible upon prompt discontinuation of therapy.

Metabolic Reactions

Agranulocytosis, neutropenia and bone marrow depression have been associated with the use of methicillin sodium and nafcillin. Hepatotoxicity, characterized by fever, nausea and vomiting associated with abnormal liver function tests, mainly elevated SGOT levels, has been associated with the use of oxacillin.