The administration of drugs like piperacillin, may disrupt the elimination of flucloxacillin since they would be excreted via renal tubular secretion. Moreover, flucloxacillin may decrease sugammadex response. This is a drug which helps to reverse the neuromuscular blockade induced during general anesthesia.
Drug-Drug Interactions with regards to Flucloxacillin only
Co-administration of allopurinol with amoxicillin can increase the tendency of allergic skin reactions. However, this is not the case with flucloxacillin.
Drug-Drug Interactions with regards to Amoxicillin only
Tetracycline is a type of bacteriostatic drug, meaning it inhibits the growth or reproduction of bacteria, and it may disrupt the bactericidal effects of both amoxicillin and flucloxacillin.
Even though there are no reported occurrences of oral anticoagulant and penicillin interaction, literature has shown that there are certain cases of changes in international normalized ratios (INR). Therefore, if the co-administration of amoxicillin or flucloxacillin with an oral anticoagulant, such as warfarin, is necessary, prothrombin time and INR should be closely monitored on a regular basis, especially when adding or withdrawing amoxicillin and flucloxacillin doses. Consequently, adjustments in the dose of oral anticoagulants may be necessary.
Penicillins such as amoxicillin and flucloxacillin may inhibit methotrexate renal tubular secretion thus causing a potential increase in methotrexate plasma levels which can ultimately lead to methotrexate toxicity. Studies have shown drastic methotrexate clearance reductions when methotrexate was taken with penicillin. If the two drugs must be used concurrently, close monitoring of methotrexate plasma concentrations is required.
The oral typhoid vaccine is inactivated by both amoxicillin and flucloxacillin.
Oral Typhoid Vaccine
Probenecid decreases renal tubular secretion of both amoxicillin and flucloxacillin thus the overall elimination of the drug decreases. Therefore, concomitant use of these drugs is generally avoided to prevent the accumulation of amoxicillin and flucloxacillin in blood plasma.
DRUG-DRUG INTERACTIONS (Interactions with other medicinal products and other forms of interaction)
PLASMA CONCENTRATION – TIME CURVES
DOSE TO BE TAKEN BY AN INDIVIDUAL WEIGHING 40KG OR MORE
500mg every 8 hours
250mg every 6 hours
Both amoxicillin and flucloxacillin are to be swallowed with water. The amoxicillin dose for an adult, elderly patient and a child weighing 40kg or more is 500mg every 8 hours. However, this dose is increased to 1g every 8 hours if necessary in the case of severe infections. On the other hand, the flucloxacillin dose for an adult, elderly patient or a child weighing 40kg or more is 250mg every 6 hours i.e. 4 times a day.
MEAN ELIMINATION HALF LIFE (min)
PERCENTAGE DRUG EXCRETEDUNCHANGED (%)
After the administration of a single 250mg – 500mg dose of amoxicillin, around 60-70% of this dose is excreted unaltered in urine during the first 6 hours. Moreover, studies have shown that over a period of 24 hours urinary excretion percentage for amoxicillin is equal to 50-85%. On the other hand, approximately 65.5% of a flucloxacillin dose is recovered in its unchanged active form in urine within the first 8 hours. Additionally, a small proportion of an administered dose of flucloxacillin is also excreted in bile.
Both amoxicillin and flucloxacillin are mainly excreted by the kidneys via urine. The mean elimination half-life for amoxicillin is one hour while that of flucloxacillin is 53 minutes, with regards to healthy subjects.
The metabolite formed by both amoxicillin and flucloxacillin during biotransformation is penicilloic acid. Between 10-25% of the initial administered amoxicillin dose is excreted as inactive penicilloic acid in urine. On the other hand. Only approximately 10% of flucloxacillin is metabolized to penicilloic acid.
Studies have shown that both amoxicillin and flucloxacillin can be detected, in small quantities, in mothers’ milk. Moreover, amoxicillin does not distribute in the cerebrospinal fluid as required but flucloxacillin diffuses adequately, in small quantities, into the cerebrospinal fluid of subjects whose meninges are not inflamed.
PERCENTAGE PROTEIN BINDING (%)
VOLUME OF DISTRIBUTION (l/kg)
Around 82% of amoxicillin is free to cause an effect on a particular part of the body, as only approximately 18% of the total plasma amoxicillin is bound to protein and therefore unable to bring about an effect by binding to other receptors. The serum protein binding rate of flucloxacillin is approximately 95%, therefore only 5% of the administered doe is able to bring about an effect. The distribution volume for amoxicillin in around 0.3-0.4 l/kg whereas that of flucloxacillin is approximately 8.9mg/l.
The time taken for both amoxicillin and flucloxacillin plasma concentrations to peak is approximately 1 hour.
Both amoxicillin and flucloxacillin are well and rapidly absorbed, by the gastrointestinal tract, when administered orally. However, amoxicillin is 70% bioavailable whereas flucloxacillin is approximately 79% bioavailable. This refers to the fraction of a drug that has an active effect once introduced into the body circulation. Additionally, it is important to take flucloxacillin on an empty stomach, due to food-drug interactions. However, amoxicillin can be both taken on a full and empty stomach since its extent of absorption is not influenced by the simultaneous intake of food.
ABSORPTION PHARMACOKINETIC PARAMETERS
Amoxicillin exhibits a two compartment model which means that the drug slowly equilibrates with peripheral tissues. On the other hand, flucloxacillin exhibits a one compartment model therefore, it exhibits an initial central compartment distributions before distribution into the peripheral tissues.
Both amoxicillin and flucloxacillin are antibiotics, classified as penicillins, which treat infections that are caused by bacteria in various parts of the body. In general, penicillins exert both a bactericidal and a bacteriostatic effect on bacteria which are still in their final stages of synthesizing their peptidoglycan layer. Penicillins can be administered orally, intramuscularly, topically as ointments and in liquid or tablet form. Discussed below will be the oral administration of amoxicillin and flucloxacillin in adults.