Scared to re-try AV

[Mackee]

Hi all! I was initially prescribed Valtrex @ 1g., 3x/day for CEBV (currently reactivated). My pharmacy filled it with the generic equivalent by Mylan.
I took 1 dose and felt as if my heart was beating much too hard, if that makes sense...not just fast but pounding in a way that made it uncomfortable (especially while laying down).
Fyi, I have normal-low BP (normally 105-112/70's) & am on the thin side.
I called my specialist and was instructed to lower the dose of Valtrex to 500 mg, 2x a day for appx. 2 weeks & then titrate back up to the original dosage. This time I asked for the Valtrex brand pills only and pharmacy got them in this week for me. Can they be cut safely? I want to try starting on 1/4 pill.
Also, I was rx'ed Zantac @ 300 mg, 2x/day & was told to take 1 before each dose of the Valtrex. The protocol = Take 300 mg/Zantac pill. Eat a FULL MEAL. Afterwards, take 1 dose of Valtrex.
Does Zantac work synergistically with the Valtrex somehow? I thought I saw a mention of that on another thread, perhaps...?
I am afraid to take the Valtrex after my initial reaction even at the new lowered dose.
My specialist has no distinct preference for Valtrex over Famvir, by the way, and uses either to address CEBV.
Suggestions?

 

[whodathunkit]

Below is some info on Valtex.

It seems that cimetidine (Tagamet), which is another acid-reducing drug similar to Zantac (rantidine), works synergistically with Valtrex to increase blood concentrations of it. But my source doesn't say anything about rantidine/Zantac doing the same thing. However, they probably both produce effects in a similar manner because they both end in -ine.

Maybe Zantac is an off-label way to do the same thing as Tagamet (which may cost more or something).

Or maybe the Zantac and full meal recs are to offset the possibility of GI problems (highlighted in red below) because Valtrex bothers the guts of some people. Your doc didn't prescribe Tagamet because s/he didn't necessarily want to increase blood concentration of Valtrex or risk kidney effects.

Wish I could be more helpful. Probably best to ask your doc.


valACYclovir (val-ay-sye-kloe-veer)
Valtrex

Classification
Therapeutic: antivirals

Indications
Treatment of herpes zoster (shingles). Treatment/suppression of genital herpes. Reduction of transmission of genital herpes. Treatment of chickenpox. Treatment of herpes labialis (cold sores).

Action
Rapidly converted to acyclovir. Acyclovir interferes with viral DNA synthesis. Therapeutic Effects: Inhibited viral replication, decreased viral shedding, reduced time to healing of lesions. Reduced transmission of genital herpes.
Pharmacokinetics

Absorption: 54% bioavailable as acyclovir after oral administration of valacyclovir. Distribution: CSF concentrations of acyclovir are 50% of plasma concentrations. Acyclovir crosses placenta; enters breast milk. Metabolism and Excretion: Rapidly converted to acyclovir via intestinal/hepatic metabolism. Half-life: 2.5–3.3 hr; up to 14 hr in renal impairment (acyclovir).

Time-Action Profile
(blood levels†)ROUTE ONSET PEAK DURATION
PO unknown 1.5–2.5 hr 8–24 hr
†Acyclovir

Contraindications and Precautions
Contraindicated in: Hypersensitivity to valacyclovir or acyclovir. Use Cautiously in: Renal impairment (↓ dose/↑ dosing interval recommended if CCr <50 mL/min); Obstetric: Lactation: Pediatric: Pregnancy, lactation, or children <2 yr (safety not established); Geriatric: Dose ↓ may be necessary due to ↑ risk of acute renal failure and CNS side effects.

Adverse Reactions and Side Effects
CNS: headache, agitation, confusion, delirium, dizziness, encephalopathy, hallucinations, seizures, weakness. GI: nausea, abdominal pain, anorexia, constipation, diarrhea. GU: renal failure, crystalluria. Hemat: thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (very high doses in immunosuppressed patients).
Interactions

Drug-Drug: Probenecid and cimetidine↑ blood levels; significant only in renal impairment. Concurrent use of other nephrotoxic drugs↑ risk of adverse renal effects.

Route and Dosage
Herpes Zoster
Oral (Adults): 1 g 3 times daily for 7 days.

Genital Herpes
Oral (Adults): Initial treatment—1 g twice daily for 10 days. Recurrence—500 mg twice daily for 3 days. Suppression of recurrence—1 g once daily or 500 mg once daily in patients experiencing <10 recurrences/yr. Suppression of recurrence in HIV-infected patients—500 mg q 12 hr. Reduction of transmission—500 mg once daily for source partner.

Herpes Labialis
Oral (Adults and Children ≥12 yr): 2 g then 2 g 12 hr later.

Chickenpox
Oral (Children ≥2 yr): 20 mg/kg 3 times daily for 5 days (not to exceed 1 g 3 times daily).
Renal Impairment
Oral (Adults): CCr 30–49 mL/min—1 g q 12 hr for herpes zoster treatment, no ↓ required for treatment of genital herpes; 1 g then 1 g 12 hr later for herpes labialis. CCr 10–29 mL/min—1 g q 24 hr for initial treatment of genital herpes, 500 mg q 24 hr for treatment of recurrent episodes of genital herpes, 500 mg q 48 hr for suppression of genital herpes in patients with 9 or fewer recurrences/yr, 500 mg q 24 hr for suppression of genital herpes in patients with ≥10 recurrences/yr or HIV-infected patients, 1 g q 24 hr for treatment of herpes zoster; 500 mg then 500 mg 12 hr later for herpes labialis. CCr <10 mL/min—500 mg q 24 hr for initial treatment of genital herpes, 500 mg q 24 hr for treatment of recurrent episodes of genital herpes, 500 mg q 48 hr for suppression of genital herpes in patients with 9 or fewer recurrences/yr, 500 mg q 24 hr for suppression of genital herpes in patients with ≥10 recurrences/yr or HIV-infected patients, 500 mg q 24 hr for treatment of herpes zoster; single 500 mg dose for herpes labialis.

Availability (generic available)

Tablets: 500 mgRx, 1 gRx