"The US Food and Drug Administration (FDA) today approved asfotase alfa (Strensiq, Alexion Pharmaceuticals) as the first-ever therapy for patients who develop hypophosphatasia, a rare metabolic bone disorder, in childhood.
RIFATER is a combination of the three drugs, rifampin, isoniazid, and pyrazinamide. Each of these individual drugs has been associated with liver dysfunction.
Rifampin has been shown to produce liver dysfunction. Fatalities associated with jaundice have occurred in patients with liver disease and in patients taking rifampin with other hepatotoxic agents. Because RIFATER contains both rifampin and isoniazid, it should only be given with caution and under strict medical supervision to patients with impaired liver function. In these patients, careful monitoring of liver function, especially serum glutamic pyruvic transaminase (SGPT) and serum glutamic oxaloacetic transaminase (SGOT) should be carried out prior to therapy and then every 2 to 4 weeks during therapy. If signs of hepatocellular damage occur, RIFATER should be withdrawn.
In some cases, hyperbilirubinemia resulting from competition between rifampin and bilirubin for excretory pathways of the liver at the cell level can occur in the early days of treatment. An isolated report showing a moderate rise in bilirubin and/or transaminase level is not in itself an indication for interrupting treatment; rather, the decision should be made after repeating the tests, noting trends in the levels, and considering them in conjunction with the patient's clinical condition.
Rifampin has enzyme-inducing properties, including induction of delta amino levulinic acid synthetase. Isolated reports have associated porphyria exacerbation with rifampin administration.
(See the BOXED WARNING.)
Since RIFATER contains isoniazid, ophthalmologic examinations (including ophthalmoscopy) should be done before treatment is started and periodically thereafter, even without occurrence of visual symptoms.
Since RIFATER contains pyrazinamide, patients started on RIFATER should have baseline serum uric acid and liver function determinations. Patients with preexisting liver disease or those patients at increased risk for drug related hepatitis (e.g., alcohol abusers) should be followed closely.
Because it contains pyrazinamide, RIFATER should be discontinued and not be resumed if signs of hepatocellular damage or hyperuricemia accompanied by an acute gouty arthritis appear. If hyperuricemia accompanied by an acute gouty arthritis occurs without liver dysfunction, the patient should be transferred to a regimen not containing pyrazinamide.
RIFATER should be used with caution in patients with a history of diabetes mellitus, as diabetes management may be more difficult.
For treatment of tuberculosis, rifampin is usually administered on a daily basis. Doses of rifampin ( > 600 mg) given once or twice weekly have resulted in a higher incidence of adverse reactions, including the “flu syndrome” (fever, chills and malaise); hematopoietic reactions (leukopenia, thrombocytopenia, or acute hemolytic anemia); cutaneous, gastrointestinal, and hepatic reactions; shortness of breath; shock, anaphylaxis, and renal failure. Recent studies indicate that regimens using twice-weekly doses of rifampin 600 mg plus isoniazid 15 mg/kg are much better tolerated.
Rifampin is not recommended for intermittent therapy; the patient should be cautioned against intentional or accidental interruption of the daily dosage regimen since rare renal hypersensitivity reactions have been reported when therapy was resumed in such cases.
All drugs should be stopped and an evaluation of the patient should be made at the first sign of a hypersensitivity reaction.
Use of RIFATER, because it contains isoniazid, should be carefully monitored in the following:
- Patients who are receiving phenytoin (diphenylhydantoin) concurrently. Isoniazid may decrease the excretion of phenytoin or may enhance its effects. To avoid phenytoin intoxication, appropriate adjustment of the anticonvulsant dose should be made.
- Daily users of alcohol. Daily ingestion of alcohol may be associated with a higher incidence of isoniazid hepatitis.
- Patients with current chronic liver disease or severe renal dysfunction.
Pyrazinamide inhibits renal excretion of urates, frequently resulting in hyperuricemia which is usually asymptomatic. If hyperuricemia is accompanied by acute gouty arthritis, RIFATER, because it contains pyrazinamide, should be discontinued.
Adults treated for tuberculosis with RIFATER should have baseline measurements of hepatic enzymes, bilirubin, serum creatinine, a complete blood count (CBC) and platelet count (or estimate), and blood uric acid.
Patients should be seen at least monthly during therapy and should be specifically questioned concerning symptoms associated with adverse reactions. All patients with abnormalities should have follow-up, including laboratory testing, if necessary. Routine laboratory monitoring for toxicity in people with normal baseline measurements is generally not necessary.
Carcinogenesis, Mutagenesis, Impairment of Fertility
Increased frequency of chromosomal aberrations was observed in vitro in lymphocytes obtained from patients treated with combinations of rifampin, isoniazid, and pyrazinamide and combinations of streptomycin, rifampin, isoniazid, and pyrazinamide.
A few cases of accelerated growth of lung carcinoma have been reported in man, but a causal relationship with the drug has not been established. Hepatomas were increased in female (C3Hf/DP) mice dosed for 60 weeks with rifampicin followed by an observation period of 46 weeks, at 20 to 120 mg/kg (equivalent to 0.1 to 0.5 times the maximum dosage used clinically, based on body surface area comparisons). There was no evidence of tumorigenicity in male C3Hf/DP mice or, in similar studies in BALB/c mice, or in two year studies in Wistar rats.
There was no evidence of mutagenicity in both prokaryotic (Salmonella typhi, Escherichia coli) and eukaryotic (Saccharomyces cerevisiae) bacteria, Drosophila melanogaster, or ICR/Ha Swiss mice. An increase in chromatid breaks was noted when whole blood cell cultures were treated with rifampin. Increased frequency of chromosomal aberrations was observed in vitro in lymphocytes obtained from patients treated with combinations of rifampin, isoniazid, and pyrazinamide and combinations of streptomycin, rifampin, isoniazid, and pyrazinamide.
Isoniazid has been reported to induce pulmonary tumors in a number of strains of mice.
Pyrazinamide was not carcinogenic in lifetime bioassays in rats (at doses up to 500 mg/kg, about three times the recommended human dose, based on body surface area comparisons) or mice (at doses up to 2000 mg/kg, about five times the recommended human dose, based on body surface area comparisons).
Pyrazinamide was not mutagenic in the Ames bacterial test, but induced chromosomal aberrations in human lymphocyte cell cultures.
Pregnancy – Teratogenic Effects
Category C. Although animal reproduction studies have not been conducted with RIFATER teratogenic effects (including cleft palate and spina bifida) have been observed in rodents treated with rifampin at doses 0.2 to 2 times the maximum recommended human dose, based on body surface area comparisons. There are no adequate and well-controlled studies of RIFATER in pregnant women. RIFATER should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Congenital malformations, primarily spina bifida were increased in the offspring of pregnant rats given rifampin during organogenesis at oral doses of 150 to 250 mg/kg/day (about 1 to 2 times the maximum recommended human dose based on body surface area comparisons). Cleft palate was increased in a dose-dependent fashion in fetuses of pregnant mice treated at oral doses of 50 to 200 mg/kg (about 0.2 to 0.8 times the maximum recommended human dose based on body surface area comparisons). Imperfect osteogenesis and embryotoxicity were also reported in pregnant rabbits given rifampin at oral doses up to 200 mg/kg/day (about 3 times the maximum recommended daily human dose based on body surface area comparisons). Although there are no adequate and well-controlled studies in pregnant women, rifampin has been reported to cross the placental barrier and appear in cord blood.
It has been reported that in both rats and rabbits, isoniazid may exert an embryocidal effect when administered orally during pregnancy, although no isoniazid-related congenital anomalies have been found in reproduction studies in mammalian species (mice, rats, and rabbits).
Animal reproductive studies have not been conducted with pyrazinamide. It is also not known whether pyrazinamide can cause fetal harm when administered to a pregnant woman.
Pregnancy – Non-Teratogenic Effects
When administered during the last few weeks of pregnancy, rifampin can cause post-natal hemorrhages in the mother and infant for which treatment with vitamin K may be indicated.
When administered during the last few weeks of pregnancy, rifampin can cause postnatal hemorrhages in the mother and infant. In this case, treatment with vitamin K may be indicated for postnatal hemorrhage.
Since rifampin, isoniazid, and pyrazinamide are known to pass into maternal breast milk, a decision should be made whether to discontinue nursing or to discontinue RIFATER, taking into account the importance of the drug to the mother.
Clinical studies of RIFATER did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. Caution should therefore be observed in using rifampin and isoniazid in elderly patients. (See WARNINGS)This monograph has been modified to include the generic and brand name in many instances.
Last reviewed on RxList: 3/18/2013
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