Valtrex: Uses, Dosage & Side Effects

The EC50 values for acyclovir against most laboratory strains and clinical isolates of VZV range from 0.53 to 48 microM (0.12 to 10.8 mcg/mL). Acyclovir also demonstrates activity against the Oka vaccine strain of VZV with a mean EC50 value of 6 microM (1.35 mcg/mL). The plasma elimination half-life of acyclovir typically averaged 2.5 to 3.3 synthroid shakiness hours in all trials of VALTREX in subjects with normal renal function. There is no accumulation of acyclovir after the administration of valacyclovir at the recommended dosage regimens in adults with normal renal function. Valacyclovir was noncarcinogenic in lifetime carcinogenicity bioassays at single daily doses (gavage) of valacyclovir giving plasma acyclovir concentrations equivalent to human levels in the mouse bioassay and 1.4 to 2.3 times human levels in the rat bioassay.

Pharmacokinetics

There are no data on the safety or effectiveness of chronic suppressive therapy of more than 6 months’ duration in HIV-1-infected patients. Zovirax treats viral infections caused by genital herpes, cold sores, shingles, and chicken pox … Dopamine used in critical illness and the dopamine agonist bromocryptine used for disorders like hyperprolactinemia can suppress serum TSH.

Acute Renal Failure

Valtrex showed no effects on the fetus in animal studies; however, there has been no adequate evaluation of Valtrex or (acyclovir) in pregnant women. Valtrex should only be used during pregnancy when the benefits to the mother outweigh risks to the fetus. The safety of Valtrex in breastfeeding infants has not been established. Methods other than breastfeeding should be considered if Valtrex must be taken while nursing. Add your drug list to My Med List to view medical information in a simple, easy-to-read, personalized format.

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In addition, absorption of levothyroxine may be decreased and/or delayed by foods such as soybean flour, cotton seed meal, walnuts, dietary fiber, calcium, calcium fortified juices and grapefruit or grapefruit juice. These foods should be avoided within several hours of dosing if possible. It is important to tell your doctor about all other medications you use, including vitamins and herbs.

Elderly patients are also more likely to have renal or CNS adverse events see DOSAGE AND ADMINISTRATION, WARNINGS AND PRECAUTIONS, CLINICAL PHARMACOLOGY. The recommended dosage of VALTREX for treatment of initial genital herpes is 1 gram twice daily for 10 days. Therapy was most effective when administered within 48 hours of the onset of signs and symptoms. Dopamine exerts its effect on the hypothalamic-pituitary-thyroid axis through the activation of dopamine D2 receptors (D2R), but appears to have opposite effects on the hypothalamus and the pituitary thyrotrope. Dopamine infusions in healthy volunteers reduces TSH pulse amplitude without significantly altering TSH pulse frequency (12;13).

Subjects self-initiated therapy within 24 hours of the first sign or symptom of a recurrent genital herpes episode. After single-dose administration of 1 gram of VALTREX in healthy geriatric subjects, the half-life of acyclovir was 3.11 ± 0.51 hours compared with 2.91 ± 0.63 hours in healthy younger adult subjects. The pharmacokinetics of acyclovir following single- and multiple-dose oral administration of VALTREX in geriatric subjects varied with renal function.

TTP/HUS, in some cases resulting in death, has occurred in patients with advanced HIV-1 disease and also in allogeneic bone marrow transplant and renal transplant recipients participating in clinical trials of VALTREX at doses of 8 grams per day. Treatment with VALTREX should be stopped immediately if clinical signs, symptoms, and laboratory abnormalities consistent with TTP/HUS occur. The recommended dosage of VALTREX for treatment of recurrent genital herpes is 500 mg twice daily for 3 days. The recommended dosage of VALTREX for treatment of cold sores is 2 grams twice daily for 1 day taken 12 hours apart. Therapy should be initiated at the earliest symptom of a cold sore (e.g., tingling, itching, or burning). Valacyclovir is converted to acyclovir and L-valine by first-pass intestinal and/or hepatic metabolism.

Most of these drugs act at the level of the thyroid in patients with normal thyroid function, or at the level of thyroid hormone absorption or metabolism in patients requiring exogenous levothyroxine. A small subset of medications including glucocorticoids, dopamine agonists, somatostatin analogs and rexinoids affect thyroid function through suppression of TSH in the thyrotrope or hypothalamus. Fortunately, most of these medications do not cause clinically evident central hypothyroidism. A newer class of nuclear hormone receptors agonists, called rexinoids, cause clinically significant central hypothyroidism in most patients and dopamine agonists may exacerbate ‘hypothyroidism’ in patients with nonthyroidal illness. In this review, we explore mechanisms governing TSH suppression of these drugs and the clinical relevance of these effects. The recommended dosage of VALTREX for treatment of chickenpox in immunocompetent pediatric patients aged 2 to less than 18 years is 20 mg/kg administered 3 times daily for 5 days.

• The removal of acyclovir after CAPD and CAVHD is less pronounced than with hemodialysis, and the pharmacokinetic parameters closely resemble those observed in patients with end-stage renal disease (ESRD) not receiving hemodialysis.
• Subjects self-initiated therapy within 24 hours of the first sign or symptom of a recurrent genital herpes episode.
• Acyclovir pharmacokinetic parameter estimates following administration of VALTREX to healthy adult volunteers are presented in Table 3.

Bromocryptine appears to have the same effect on TSH pulse amplitude and is likely occurring through the same D2R mechanism (14). Prolonged treatment with bromocryptine does not appear to cause central hypothyroidism since many patients treated with bromocryptine for macroprolactinomas actually have resolution of central hypothyroidism caused by the adenoma (16). Studies using dopamine infusions in critically ill adults and neonates with the nonthyroidal illness (NTI) syndrome suggest that dopamine and NTI have and additive effect of HPT axis suppression. This may lead to iatrogenic central hypothyroidism in these patients (17;18). It is not clear whether treatment with levothyroxine is indicated in patients with NTI who are receiving dopamine infusions.

Bexarotene rapidly and significantly suppressed serum TSH, but had no effect on prolactin or cortisol levels, suggesting this was a specific effect on thyrotropes. Our group and others have also shown that rexinoids likely affect thyroid hormone metabolism as well through deiodination, sulfation and possibly glucuronidation (39). Figure 1 is a summary of the proposed mechanisms by which rexinoids cause clinically significant central hypothyroidism.