Acyclovir Interactions
- Aminoglycosides
- Entecavir
- Ethotoin
- Fosphenytoin
- Mycophenolate
- Pemetrexed
- Phenytoin
- Probenecid
- Tenofovir, PMPA
- Zidovudine, ZDV
Acyclovir Interactions
In a single case report, the addition of acyclovir to a regimen of phenytoin and valproate led to a clinically significant decrease in phenytoin serum concentrations and loss of seizure control. Adjustments to the phenytoin dose were necessary when acyclovir was added and discontinued. Acyclovir did not appear to affect valproate concentrations in this report. Based on these data, until more information is known, clinicians should be prepared to make adjustments in ethotoin, phenytoin or fosphenytoin dosing if acyclovir or valacyclovir therapy is added or discontinued.
Probenecid decreases the renal tubular secretion of acyclovir and can increase serum and CSF concentrations of acyclovir, increasing the potential for toxicity. This interaction would appear to be more significant for parenteral acyclovir.
Coadministration of mycophenolate mofetil and acyclovir to healthy volunteers resulted in no significant change in mycophenolic acid concentrations or AUC. However, the glucuronide metabolite of mycophenolate (MPAG) and acyclovir AUCs were increased 10.6% and 21.9%, respectively. Because MPAG and acyclovir concentrations are increased in the presence of renal impairment, the potential exists for the two drugs to compete for tubular secretion, further increasing the concentration of both drugs in patients renal dysfunction.
Acyclovir has been reported to enhance the in vitro activity of zidovudine, ZDV. Acyclovir and zidovudine have been administered together in an effort to enhance the activity of zidovudine against HIV. No additional benefit was seen with combination therapy over zidovudine alone and combination treatment was associated with severe somnolence and lethargy in some patients.
Since tenofovir, PMPA is primarily eliminated by the kidneys, concurrent administration of tenofovir disoproxil with acyclovir may increase the serum concentrations of tenofovir via competition for renal tubular secretion.
Because entecavir is primarily eliminated by the kidneys and acyclovir can affect renal function, concurrent administration with acyclovir may increase the serum concentrations of entecavir and adverse events. The manufacturer of entecavir recommends monitoring for adverse effects when these drugs are coadministered.
Additive nephrotoxicity is possible if systemic aminoglycosides are used with acyclovir. Carefully monitor renal function during concomitant therapy.
Patients with reduced renal function may have significant impairment of pemetrexed elimination, as most of the drug is eliminated unchanged in the urine. Acyclovir can adversely affect renal function. Therefore, recent exposure to acyclovir, in the absence of overt renal impairment, may adversely affect pemetrexed excretion and increase risk of toxicity from pemetrexed. Assessing renal function in patients who have received acyclovir may be prudent, so appropriate pemetrexed dose modifications, if necessary, can be made.
[ Last revised: 5/18/2005 4:59:00 PM ]
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