COLISTIMETHATE Drug Interactions: What You Need to Know

Drug Interactions Certain other antibiotics (aminoglycosides and polymyxin) have also been reported to interfere with the nerve transmission at the neuromuscular junction. Based on this reported activity, they should not be given concomitantly with Colistimethate for Injection, USP except with the greatest caution. Curariform muscle relaxants (e.g., tubocurarine) and other drugs, including ether, succinylcholine, gallamine, decamethonium and sodium citrate, potentiate the neuromuscular blocking effect and should be used with extreme caution in patients being treated with Colistimethate for Injection, USP. Sodium cephalothin may enhance the nephrotoxicity of Colistimethate for Injection, USP. The concomitant use of sodium cephalothin and Colistimethate for Injection, USP should be avoided.

CONTRAINDICATIONS The use of Colistimethate for Injection, USP is contraindicated for patients with a history of sensitivity to the drug or any of its components.

WARNINGS Maximum daily dose calculated from colistin base activity should not exceed 5 mg/kg/day with normal renal function. Transient neurological disturbances may occur. These include circumoral paresthesia or numbness, tingling or formication of the extremities, generalized pruritus, vertigo, dizziness, and slurring of speech. For these reasons, patients should be warned not to drive vehicles or use hazardous machinery while on therapy. Reduction of dosage may alleviate symptoms. Therapy need not be discontinued, but such patients should be observed with particular care. Nephrotoxicity can occur and is probably a dose-dependent effect of colistimethate sodium. These manifestations of nephrotoxicity are reversible following discontinuation of the antibiotic. Electrolyte and Acid/Base Abnormalities Postmarketing cases of renal tubulopathy (i.e., Pseudo-Bartter syndrome) have been identified with the use of intravenous colistimethate sodium (see ADVERSE REACTIONS ). All cases reported hypokalemia and metabolic alkalosis. Other common findings included hypocalcemia, hypomagnesemia, increased potassium in the urine, normal serum creatinine, and normal blood pressure. Consider electrolyte monitoring during treatment. Normalization of electrolyte abnormalities may require drug discontinuation. Overdosage can result in renal insufficiency, muscle weakness, and apnea (see OVERDOSAGE section). See PRECAUTIONS, Drug Interactions subsection for use concomitantly with other antibiotics and curariform drugs. Respiratory arrest has been reported following intramuscular administration of colistimethate sodium. Impaired renal function increases the possibility of apnea and neuromuscular blockade following administration of colistimethate sodium. Therefore, it is important to follow recommended dosing guidelines. See DOSAGE AND ADMINISTRATION section for use in renal impairment. Clostridium difficile associated diarrhea (CDAD) has been reported with use of nearly all antibacterial agents, including Colistimethate for Injection, USP, and may range in severity from mild diarrhea to fatal colitis. Treatment with antibacterial agents alters the normal flora of the colon leading to overgrowth of C. difficile . C. difficile produces toxins A and B which contribute to the development of CDAD. Hypertoxin producing strains of C. difficile cause increased morbidity and mortality, as these infections can be refractory to antimicrobial therapy and may require colectomy. CDAD must be considered in all patients who present with diarrhea following antibiotic use. Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents. If CDAD is suspected or confirmed, ongoing antibiotic use not directed against C . difficile may need to be discontinued. Appropriate fluid and electrolyte management, protein supplementation, antibiotic treatment of C. difficile , and surgical evaluation should be instituted as clinically indicated.