3116-76-5

Chemically this is 3(2,6-dichlorophenyl)-5-methyl-4-isoxazolyl penicillin. It differs from cloxacillin by having two chloride ions attached to the phenyl group. It comes as oral capsules of 250 and 500 mg, and in an injectable formulation of 500 mg and 1 g.

Dynapen,Bristol,US,1968

Antibacterial.

ChEBI: A penicillin that is 6-aminopenicillanic acid in which one of the amino hydrogens is replaced by a 3-(2,6-dichlorophenyl)-5-methyl-1,2-oxazol-4-yl]formyl group.

A suspension of 6-aminopenicillanic acid (216 grams) in water (2 liters) was adjusted to pH 6.8 by the addition of N aqueous sodium hydroxide (approximately 1 liter) and the resulting solution was stirred vigorously while a solution of 3-(2',6'-dichlorophenyl)-5-methylisoxazole-4-carbonyl chloride (290 grams) in acetone (1.5 liters) was added in one portion.
The temperature rose to 26°C and as reaction proceeded the free acid form of the penicillin separated as a white solid. After 30 minutes the suspension was cooled to 10°C and stirring was continued at this temperature for 1 hour more. The mixture was then cooled to 0°C, centrifuged, and the solid product washed with aqueous acetone (250 ml) and finally dried in an air oven at 30°C. The product (440 grams, 94%) had [α]D20 +106.3° (c 1 in EtOH) and was shown by alkalimetric assay to be 97.5% pure.
The salt was prepared by dissolving the free acid form of the penicillin in the equivalent amount of aqueous sodium bicarbonate and freeze drying the resulting solution. The hydrated salt so obtained was shown by alkalimetric assay to be 94% pure and to contain 6% water.

Antibacterial

It is very highly bound to serum protein, and its activity in the presence of human serum in vitro is depressed to a greater extent than that of other isoxazolylpenicillins.

Oral absorption: c. 50%
C_max , 250 mg oral: 9 mg/L after 1 h
500 mg intramuscular: 14–16 mg/L after 0.5–1 h
Plasma half-life: 0.5 h
Plasma protein binding: 95–97%
Absorption
Absorption in the very young is poor and unpredictable.
Metabolism and excretion
Dicloxacillin is partly metabolized in the liver and about 10% of the circulating drug is in the form of metabolites. Some 50–70% of a dose is excreted in the urine, about 20% as metabolites. It is eliminated both in the glomerular filtrate and by tubular secretion, and plasma concentrations are raised by probenecid. Parent drug and increased proportions of metabolites accumulate in renal failure. Elimination is increased through enhanced tubular secretion in patients with cystic fibrosis.

In terms of mechanism of action, antibacterial spectrum, and indications for use, it is essentially no different than oxacillin and cloxacillin. Synonyms of this drug are diclocil, novapen, diclex, and others.
The following type of semisynthetic penicillins that should be considered are those in which amino acids, mainly α-aminophenylacetic or p-oxy-α-amino-phenylacetic acids, act as the acyl radical (ampicillin, amoxacillin).
The antimicrobial spectrum of aminopenicillins is similar to penicillin G, with the exception that they also act on a number of Gram-negative microorganisms. Both aminopenicillins are destroyed by staphylococcus penicillinase.

Phlebitis is common after intravenous injection. Its toxicity is otherwise similar to that of other penicillins. Clinical uses are those of the group 3 penicillins.