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Dicloxacillin (INN) is a narrow-spectrum β-Lactam antibiotic of the penicillin class. It is used to treat infections caused by susceptible Gram-positive bacteria. It is active against beta-lactamase-producing organisms such as Staphylococcus aureus, which would otherwise be resistant to most penicillins. Dicloxacillin is available under a variety of trade names including Diclocil (BMS).

Medical Uses
Dicloxacillin is used to treat mild-to-moderate staphylococcal infections. To decrease the development of resistance, dicloxacillin is recommended to treat infections that are suspected or proven to be caused by beta-lactamase-producing bacteria. However, like methicillin, it is less potent than benzylpenicillin against non-β-lactamase-producing Gram-positive bacteria.

Dicloxacillin has similar pharmacokinetics, antibacterial activity, and indications to flucloxacillin, and the two agents are considered interchangeable. It is believed to have lower incidence of severe hepatic adverse effects than flucloxacillin, but a higher incidence of renal adverse effects.

Dicloxacillin is used for the treatment of infections caused by susceptible bacteria. Specific approved indications include:
 * Staphylococcal skin infections and cellulitis – including impetigo, otitis externa, folliculitis, boils, carbuncles, and mastitis
 * Pneumonia (adjunct)
 * Osteomyelitis, septic arthritis, throat infections, streptococcus
 * Septicaemia
 * Empirical treatment for endocarditis
 * Surgical prophylaxis

Available forms
Dicloxacillin is commercially available as a sodium salt, dicloxacillin sodium, in capsules and as a powder for reconstitution.

Contraindications
Dicloxacillin is contraindicated in those with a previous history of allergy (hypersensitivity/anaphylactic reaction) to any penicillins. It should also not be used in the eye, or those with a history of cholestatic hepatitis associated with the use of dicloxacillin or flucloxacillin.

It should be used with caution in the elderly, particularly with intravenous administration, due to a risk of thrombophlebitis.

Dicloxacillin is Pregnancy Category B-with no conclusive studies about its fetal effects. However, penicillins do show up in breast milk and caution should be taken in nursing women.

Adverse effects
Common adverse drug reactions (ADRs) associated with the use of dicloxacillin include: diarrhea, nausea, rash, urticaria, pain and inflammation at injection site, superinfection (including candidiasis), allergy, and transient increases in liver enzymes and bilirubin.

On rare occasions, cholestatic jaundice (also referred to as cholestatic hepatitis) has been associated with dicloxacillin therapy. The reaction may occur up to several weeks after treatment has stopped, and takes weeks to resolve. The estimated incidence is 1 in 15,000 exposures, and is more frequent in people >55 years, females, and those with treatment longer than 2 weeks.

Interactions
Dicloxacillin has potential interactions with following drugs:
 * Warfarin
 * Methotrexate
 * Tetracyclines

Resistance
Despite dicloxacillin's being insensitive to beta-lactamases, some organisms have developed resistance to it and other narrow-spectrum β-lactam antibiotics including methicillin. Such organisms include methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible Staphylococcus aureus (MSSA).

Mechanism of action
Like other β-Lactam antibiotics, dicloxacillin acts by inhibiting the synthesis of bacterial cell walls. It inhibits cross-linkage between the linear peptidoglycan polymer chains that make up a major component of the cell wall of Gram-positive bacteria.

Medicinal chemistry
Dicloxacillin is insensitive to beta-lactamase (also known as penicillinase) enzymes secreted by many penicillin-resistant bacteria. The presence of the isoxazolyl group on the side chain of the penicillin nucleus facilitates the β-lactamase resistance, since they are relatively intolerant of side-chain steric hindrance. Thus, it is able to bind to penicillin-binding proteins (PBPs) and inhibit peptidoglycan crosslinking, but is not bound by or inactivated by β-lactamases.