Combating Nitrate Tolerance

Effect of nitrate withdrawal on quality of life and adherence to treatment in patients with stable angina: evidence from a randomized clinical trial

BACKGROUND

Long-term nitrate treatment of stable angina is associated with side effects that can interfere with health-related quality of life (HRQoL) and medication adherence. The aim of the present study was to compare HRQoL and adherence to treatment in patients with stable angina undergoing nitrate withdrawal or maintenance.

METHODS

This study is a randomized clinical trial. Patients were allocated to an intervention group (nitrate withdrawal followed by introduction of placebo) or a control group (nitrate maintenance). The assessments were made at baseline and 30 and 120 days using the Short Form Health Survey and the Seattle Angina Questionnaire. Treatment adherence was measured on the basis of the Morisky scale and pill count.

RESULTS

A total of 105 patients with stable angina were randomized for replacement of nitrate with placebo (n=51) and for maintenance of treatment with nitrate (n=54). After 4 months, Short Form Health Survey scores increased for bodily pain (P=0.005) and general health (P=0.004) in the nitrate maintenance group. Decreased Seattle Angina Questionnaire scores were also noted for physical limitations (P=0.039) and angina frequency (P=0.011) in the nitrate maintenance group. However, the effect size was small (≤0.44) when the intervention and control groups were compared. At the end of the study, adherence was significantly higher in the placebo group (P=0.041), but no difference was detected between the groups with the pill count method.

CONCLUSION

HRQoL was similar in patients with stable angina using nitrate regularly as compared with patients undergoing nitrate withdrawal. However, adherence to treatment was lower in nitrate users according to the Morisky scale.

No evidence of nitrate tolerance caused by nebivolol

BACKGROUND

Continuous long-term treatment with nitrates may cause nitrate tolerance. Nebivolol is a highly selective beta1-adrenergic antagonist with additional nitric oxide (NO)-mediated vasodilatory effects. However, there have been no investigations into whether or not the long-term administration of nebivolol might cause nitrate tolerance.

METHODS

We performed a randomized, double-blind, placebo-controlled, cross-over study in 16 healthy men. Subjects received 5 mg nebivolol or placebo once daily for 8 days in random order divided by a drug-free interval of 2 weeks. Forearm blood flow (FBF) was measured by venous occlusion plethysmography 3 h after oral intake of the first and last doses of nebivolol and placebo, respectively. FBF was measured again following the intravenous administration of 4 μg nitroglycerin/kg body weight/min for 5 min.

RESULTS

Following 8 days of continuous intake of placebo, nitroglycerin increased FBF by 54% (p < 0.05), whereas nitroglycerin increased FBF by 96% (p < 0.01) following 8 days of continuous intake of nebivolol, and the increase after 8 days of nebivolol was significantly (p < 0.05) more pronounced than after 8 days of placebo.

CONCLUSIONS

These findings indicate no evidence of nitrate tolerance caused by long-term administration of nebivolol. On the contrary, long-term intake of nebivolol increases rather than decreases the NO-mediated vasodilating effects.

Coadministration of carvedilol attenuates nitrate tolerance by preventing cytochrome p450 depletion

BACKGROUND

Long-term administration of nitroglycerin (NTG) causes tolerance secondary to increased vascular formation of reactive oxygen species. Carvedilol, which has potent antioxidant activity in addition to functioning as an adrenergic blocker, prevents nitrate tolerance by a still to be elucidated mechanism. The present study investigated how carvedilol attenuates nitrate tolerance, particularly with reference to cytochrome P450 (CYP), an enzyme involved in the development of tolerance.

METHODS AND RESULTS

Male Wistar rats were subjected to 48-h continuous infusion of NTG alone (0.5 mg/h) or NTG with concomitant carvedilol (20 or 100 microg/h), and then compared with vehicle-treated rats (4 groups; n=6 in each group). Following the continuous administration, nitrate tolerance, assessed by bolus NTG injections, was hemodynamically prevented by coadministration of carvedilol. Levels of CYP1A1/1A2, superoxide production, and phosphorylated vasodilator-stimulated phosphoprotein at serine 239 (P-VASP) were examined in the aortic wall and heart tissue. When NTG alone was continuously administered, vascular superoxide was produced, there was a decrease in the cardiac CYP1A1/1A2 level, and depletion of P-VASP. However, each of these changes induced by continuous NTG administration was significantly attenuated by coadministration of carvedilol and the extent of attenuation was more pronounced at the higher dose (100 microg/h).

CONCLUSIONS

Coadministration of carvedilol attenuates nitrate tolerance through maintenance of NO/cGMP pathway activity by preventing free radical generation and CYP depletion.