acyclovir sodium intraven. adverse effects list & discussion more frequent diarrhea inflammation at injection site severe lightheadedness nausea stomach pain vomiting less frequent renal failure severe rare or very rare encephalopathy severe local effects the most frequent adverse effects of parenteral acyclovir are local reactions at the injection site. local reactions, including cutaneous irritation and erythema or inflammation, pain, and phlebitis, may occur at the site of injection. these local effects appear to occur more frequently following inadvertent extravasation of acyclovir solutions containing more than 8 mg/ml. because of the risk of adverse renal effects, diluted solutions of acyclovir should not be infused over a period less than 1 hour. s_bsn