PRIMAXIN I.V.(Imipenem and Cilastatin for Injection) is a
sterile formulation of imipenem (a thienamycin antibiotic) and cilastatin
sodium (the inhibitor of the renal dipeptidase, dehydropeptidase I), with
sodium bicarbonate added as a buffer. PRIMAXIN I.V. is a potent broad
spectrum antibacterial agent for intravenous administration.
Imipenem (N-formimidoylthienamycin monohydrate) is a crystalline derivative
of thienamycin, which is produced by Streptomyces cattleya. Its chemical
name is (5R,6S)-3-[[2-(formim idoylamino)ethyl]thio]-6-[(R)-1-hydroxyethyl]-7-oxo1-azabicyclo[3.2.0]hept-2-ene-2-carboxylic
acid monohydrate. It is an off-white, nonhygroscopic crystalline compound
with a molecular weight of 317.37. It is sparingly soluble in water and
slightly soluble in methanol. Its empirical formula is C12H17N3O4SH2O.
Cilastatin sodium is the sodium salt of a derivatized heptenoic acid.
Its chemical name is sodium (Z)-7-[[(R)-2-amino-2 carboxyethyl]thio]-2-[(S)-2,2-dimethylcyclopropanecarboxamido]-2-heptenoate.
It is an off-white to yellowish-white, hygroscopic, amorphous compound
with a molecular weight of 380.43. It is very soluble in water and in
methanol. Its empirical formula is C16H25N2O5S
PRIMAXIN I.V. is buffered to provide solutions in the pH range of 6.5
to 8.5. There is no significant change in pH when solutions are prepared
and used as directed. (See DOSAGE AND ADMINISTRATION: COMPATIBILITY
AND STABILITY.) PRIMAXIN I.V. 250 contains 18.8 mg of sodium (0.8
mEq) and PRIMAXIN I.V. 500 contains 37.5 mg of sodium (1.6 mEq). Solutions
of PRIMAXIN I.V. range from colorless to yellow. Variations of color within
this range do not affect the potency of the product.