Telmisartan (Micardis, Boehringer Ingelheim), a nonpeptide AT-II-receptor antagonist, gained FDA approval for use in the treatment of hypertension in 1998. After oral administration, peak concentrations are reached in 0.5-1 hour. The absolute bioavailability of telmisartan is dose dependent.[70,71] A dose of 40 mg achieves 40% bioavailability, whereas 160 mg is 58% bioavailable. The bioavailability of oral telmisartan is reduced slightly, but not significantly, by food. The half-life is 24 hours, which allows for once-daily administration. About 97% of a telmisartan dose is eliminated unchanged in the feces via biliary excretion. Renal excretion does not contribute to telmisartan's elimination.
Given that CYP isoenzymes are not involved in telmisartan's metabolism, no interactions with drugs that inhibit or are metabolized by CYP isoenzymes would be expected, with the possible exception of interference with the metabolism of drugs metabolized by CYP2C19. When telmisartan is administered with digoxin, peak and trough plasma concentrations of digoxin are increased 49% and 20%, respectively. When telmisartan is given with warfarin there is no evidence of any change in the International Normalized Ratio.[c]
The antihypertensive effects of telmisartan 20-160 mg were assessed in clinical trials in patients with mild to moderate hypertension. Reductions in systolic and diastolic blood pressure were on the order of 6-8 and 6 mm Hg, respectively, with 20 mg/ day; 9-13 and 6-8 mm Hg with 40 mg/day; and 12-13 and 7-8 mm Hg with 80 mg/day.[70,72] A further decrease in blood pressure was not seen with a larger dosage (120-160 mg/ day). It is recommended that telmisartan be initiated at 40 mg/day with or without food; the dosage may be increased to up to 80 mg/day if further blood pressure reduction is needed. In situations in which even further blood pressure reduction is needed (beyond that achieved with 80 mg/day), the addition of hydrochlorothiazide has been found to produce incremental reductions. Antihypertensive activity begins within 3 hours and is maintained for 24 hours. A maximum reduction in blood pressure is evident in approximately four weeks. No reduction in the starting dosage is necessary in patients with mild to moderate renal impairment or the elderly. Caution should be used when administering telmisartan to patients with biliary obstructive disorders or hepatic insufficiency, since this agent is eliminated primarily by biliary excretion.
The overall frequency of adverse events with telmisartan 20-160 mg/ day was reported to be similar to that with placebo. Rates of upper-respiratory-tract infection (7%), dizziness (5%), back pain (3%), sinusitis (3%), and diarrhea (3%) were similar to the rates for placebo (6%, 6%, 1%, 3%, and 2%, respectively). The rate of cough with telmisartan (15.6%) was comparable to that with placebo (9.6%) and significantly less than with lisinopril (60%).[76,77]
Am J Health Syst Pharm. 2000;57(13) © 2000 American Society of Health-System Pharmacists
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