Sorted By Test Name - Mayo Medical Laboratories

RIBAV
60536
VITB2
61637
Ribavirin, Serum
Clinical Information: Ribavirin is a nucleoside analog with antiviral activity against a number of
RNA and DNA viruses, including hepatitis C virus (HCV). In combination with interferon, ribavirin is a
treatment of choice for chronic HCV infection. In this setting, higher serum concentrations of ribavirin
appear to correlate with the likelihood of achieving virological response; however, the drug dose is
limited by concentration-dependent hemolytic anemia. Although no consensus therapeutic targets or toxic
thresholds have been established, ribavirin concentrations between 2,500 and 4,000 ng/mL have been
suggested to improve virological response and minimize toxicity. The half-life of ribavirin is very long,
typically 5 days or more. For this reason, steady-state concentrations are not achieved until several weeks
into therapy; most studies have performed initial therapeutic monitoring after at least 28 days of ribavirin
treatment. Specimens should be drawn immediately prior to the next scheduled dose, or at minimum >12
hours after the last dose. Elimination of ribavirin is also very slow, and due to incorporation of the drug
into red blood cells, may take up to 6 months after the cessation of therapy. Ribavirin has shown
teratogenic activity in animal models, thus patients are recommended to practice stringent birth control
until at least 6 months after the end of treatment.
Useful For: Assessing adequacy of ribavirin therapy or potential drug-related toxicity
Interpretation: Ribavirin concentrations >2,500 ng/mL appear to correlate with greater likelihood of
virological response in patients with chronic hepatitis C virus infection. Elevated concentrations in the
setting of hemolytic anemia are consistent with ribavirin toxicity.
Reference Values:
2,500-4,000 ng/mL
Clinical References: 1. Jen JF, Glue P, Gupta S, et al: Population pharmacokinetic and
pharmacodynamic analysis of ribavirin in patients with chronic hepatitis C. Ther Drug Monit
2000;22(5):555-65 2. Marquet P, Sauvage FL, Loustaud-Ratti V, et al: Stability of ribavirin
concentrations depending on the type of blood collection tube and preanalytical conditions. Ther Drug
Monit 2010;32:237-241 3. Pedersen C, Alsio A, Lagging M, et al: Ribavirin plasma concentration is a
predictor of sustained virological response in patients treated for chronic hepatitis C virus genotype 2/3
infection. J Viral Hepatitis 2011;18(4):245-51
Riboflavin (Vitamin B2), Plasma
Clinical Information: There are 3 principle vitamin B2-active flavins found in nature-riboflavin,
riboflavin 5-phosphate (flavin mononucleotide [FMN]), and riboflavin-5'-adenosyl-diphosphate (flavin
adenosine dinucleotide [FAD]). In biological tissues, FMN and FAD serve as prosthetic units for a large
variety of flavoproteins, which are hydrogen carriers in oxidation-reduction processes. Dietary deficiency
of riboflavin (ariboflavinosis) is characterized by sore throat, cheilosis (lesions on the lips), angular
stomatitis (lesions on the angles of the mouth), glossitis (fissured and magenta-colored tongue), corneal
vascularization, dyssebacia (red, scaly, greasy patches on the nose, eyelids, scrotum, and labia), and
normocytic, normochromic anemia. Severe riboflavin deficiency may affect the conversion of vitamin B6
to its coenzyme, as well as conversion of tryptophan to niacin. Riboflavin has a low level of toxicity and
no case of riboflavin toxicity in humans has been reported. The limited absorptivity of riboflavin and its
ready excretion in the urine normally preclude a health problem due to increased intake of riboflavin.
Useful For: Evaluation of persons who present the signs of ariboflavinosis
Interpretation: Low concentrations in the blood plasma are indicative of nutritional deficiency.
Concentrations