Cefalexin Chemische Eigenschaften,Einsatz,Produktion Methoden
R-Sätze Betriebsanweisung:
R42/43:Sensibilisierung durch Einatmen und Hautkontakt möglich.
S-Sätze Betriebsanweisung:
S22:Staub nicht einatmen.
S36/37:Bei der Arbeit geeignete Schutzhandschuhe und Schutzkleidung tragen.
S45:Bei Unfall oder Unwohlsein sofort Arzt zuziehen (wenn möglich, dieses Etikett vorzeigen).
Beschreibung
Use of the ampicillin-type side chain conveys oral activity to cephalexin. Whereas it no longer has an
activating side chain at C-3 and, as a consequence, is somewhat less potent, it does not undergo metabolic
deactivation and, thus, maintains potency. It is rapidly and completely absorbed from the GI tract and has
become quite popular. Somewhat puzzling is the fact that the use of the ampicillin side chain in the
cephalosporins does not result in a comparable shift in antimicrobial spectrum. Cephalexin, like the other
first-generation cephalosporins is active against many Gram-positive aerobic cocci but is limited against
Gram-negative bacteria. It is a widely used drug, particularly against Gram-negative bacteria causing urinary
tract infections, Gram-positive infections (Staphyl ococcus aureus, Streptococcus pneumoni ae and
Streptococcus pyogenes) of soft tissues, pharyngitis, and minor wounds.
Chemische Eigenschaften
White cryst. powder
Verwenden
Antibacterial.
Definition
ChEBI: A semisynthetic first-generation cephalosporin antibiotic having methyl and beta-(2R)-2-amino-2-phenylacetamido groups at the 3- and 7- of the cephem skeleton, respectively. It is effective against both Gram-negative and G
am-positive organisms, and is used for treatment of infections of the skin, respiratory tract and urinary tract.
Antimicrobial activity
It is resistant to staphylococcal β-lactamase. Gram-positive
rods and fastidious Gram-negative bacilli, such as Bordetella
spp. and H. influenzae, are relatively resistant. It is active
against a range of enterobacteria, but it is degraded by
many enterobacterial β-lactamases. Citrobacter, Edwardsiella,
Enterobacter, Hafnia, Providencia and Serratia spp. are all
resistant. Gram-negative anaerobes other than B. fragilis are
susceptible. Because of its mode of action it is only
slowly bactericidal to Gram-negative bacilli.
Pharmakokinetik
Oral absorption: >90%
C
max 500 mg oral: c. 10–20 mg/L after 1 h
Plasma half-life: 0.5–1 h
Volume of distribution: 15 L
Plasma protein binding: 10–15%
Absorption and distribution
It is almost completely absorbed when given by mouth, the
peak concentration being delayed by food. Intramuscular
preparations are not available: injection is painful and produces
delayed peak plasma concentrations considerably lower
than those obtained by oral administration.
In synovial fluid, levels of 6–38 mg/L have been described
after a 4 g oral dose, but penetration into the CSF is poor.
Useful levels are achieved in bone (9–44 mg/kg after 1 g orally)
and in purulent sputum. Concentrations of 10–20 mg/L have
been found in breast milk. Concentrations in cord blood
following a maternal oral dose of 0.25 g were minimal.
Metabolism and excretion
It is not metabolized. Almost all the dose is recoverable from
the urine within the first 6 h, producing urinary concentrations
exceeding 1 g/L. The involvement of tubular secretion
is indicated by the increased plasma peak concentration and
reduced urinary excretion produced by probenecid. Renal
clearance is around 200 mL/min and is depressed in renal
failure, although a therapeutic concentration is still obtained
in the urine. It is removed by peritoneal and hemodialysis.
Some is excreted in the bile, in which therapeutic concentrations
may be achieved.
Clinical Use
Cephalexin, 7α-(D-amino-α-phenylacetamido)-3-methylcephemcarboxylicacid (Keflex, Keforal), was designed purposelyas an orally active, semisynthetic cephalosporin. Theoral inactivation of cephalosporins has been attributed to twocauses: instability of the β-lactam ring to acid hydrolysis(cephalothin and cephaloridine) and solvolysis or microbialtransformation of the 3-methylacetoxy group (cephalothin,cephaloglycin). The α-amino group of cephalexin renders itacid stable, and reduction of the 3-acetoxymethyl to a methylgroup circumvents reaction at that site.
Cephalexin occurs as a white crystalline monohydrate. Itis freely soluble in water, resistant to acid, and absorbed wellorally. Food does not interfere with its absorption. Becauseof minimal protein binding and nearly exclusive renal excretion,cephalexin is recommended particularly for the treatmentof urinary tract infections. It is also sometimes used forupper respiratory tract infections. Its spectrum of activity isvery similar to those of cephalothin and cephaloridine.Cephalexin is somewhat less potent than these two agentsafter parenteral administration and, therefore, is inferior tothem for the treatment of serious systemic infections.
Nebenwirkungen
Nausea, vomiting and abdominal discomfort are relatively
common. Pseudomembranous colitis has been described and
overgrowth of Candida with vaginitis may be troublesome.
Otherwise, mild hypersensitivity reactions and biochemical
changes common to cephalosporins occur. Very rare neurological
disturbances have been described, particularly in patients
in whom very high plasma levels have been achieved. There
are rare reports of Stevens–Johnson syndrome and toxic epidermal
necrolysis.
Sicherheitsprofil
Poison by intraperitoneal route.Moderately toxic by ingestion and other routes. An experimental teratogen. Other experimental reproductiveeffects. Human systemic effects by ingestion: nausea,vomiting, and diarrhea. When heated to decomposition itemits
Cefalexin Upstream-Materialien And Downstream Produkte
Upstream-Materialien
Downstream Produkte
