Determination of quinapril and quinaprilat in human plasma by ultraperformance liquid chromatography-electrospray ionization mass spectrometry.

A novel, specific and sensitive ultraperformance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was developed for the simultaneous determination of quinapril and its active metabolite quinaprilat in human plasma. The method involves a simple, one-step extraction procedure coupled with an Acquity UPLC BEH C(18 )column (100 x 2.1 mm, i.d., 1.7 microm) with isocratic elution at a flow-rate of 0.2 mL/min and lisinopril as the internal standard. Detection was performed on a triple-quadrupole tandem mass spectrometer in multiple reaction monitoring mode via electrospray ionization. Using 250 microL plasma, the methods were validated over the concentration range 5.010-500.374 ng/mL for quinapril and 10.012-1000 ng/mL for quinaprilat, with a lower limit of quantification of 5.010 ng/mL for quinapril and 10.012 ng/mL for quinaprilat. The intra- and inter-day precision and accuracy were within 10.0%. The recovery was 85.8, 62.6 and 61.3% for quinapril, quinaprilat and lisinopril, respectively. Total run time was 3.0 min only.

The practical assessment of compliance with ACE-inhibitor therapy--a novel approach.

Poor compliance may be responsible for symptomatic decompensation or neurohormonal "escape" in patients with heart failure treated over the long term with angiotensin-converting enzyme-1 (ACEI) drugs. Serum ACE activity is a poor index of neurohormonal suppression or haemodynamic effect after ACE-inhibitor treatment. Serum ACE activity may, however, be a useful index of compliance with treatment, as serum ACE is sensitive to the presence of an ACE inhibitor in the blood. Sixteen normotensive male volunteers of known ACE genotype received 7 days of randomised, double-blind therapy on four occasions 2 weeks apart with lisinopril 20 mg (L) or matched placebo (P) to simulate (A) noncompliance (all P), (B) full compliance (all L), (C) partial compliance (L days, 1, 3, 6; P days, 2, 4, 5, 7), or (D) single dose (L day 7; P, 1-6). Supine (30 min) blood pressure (BP)/heart rate (HR), ACE, and angiotensins were measured on d7 before dose and 4-6 h after dose. Results are mean +/- 1 SD. BP showed the expected small decrease with active treatment on d7 (B or D) but not with placebo (A) or partial compliance (C). Prestudy serum ACE, despite a wide range (16-124 U/L), was reproducible within subjects [coefficient of variation (CV), 1.7%]. Serum ACE activity, before (41.9 +/- 30) and after (41 +/- 30) angiotensin (A) I or II, were unaffected by treatment (placebo A). Active treatment (B) resulted in very low serum ACE activity and d7 and a small further suppression after dosing (before, 3.9 +/- 4; after, 1.8 +/- 4). AI was elevated in this group with further elevation after dosing (before, 234 +/- 116; after, 551 +/- 250). AII was only modestly reduced from baseline and showed little further suppression after dosing (before, 7.8 +/- 4; after, 6.3 +/- 5). Partial compliance (C) showed low ACE but no reduction after treatment (before, 7 +/- 3; after, 7 +/- 4), an elevated AI but no dosing effect (before, 187 +/- 198; after, 200 +/- 151) and reduced AII but with no further dose suppression (before, 6.4 +/- 3.4; after, 7 +/- 4) induced increase in peptide (compared with B). Single-dose treatment (D) showed ACE inhibition as expected (before, 47 +/- 30; after, 2.2 +/- 3). There was a dosing-related increase of AI but to a lesser extent than seen with chronic active dosing (B) (before, 39 +/- 10; after, 240 +/- 200). In contrast to long-term dosing, there was marked ANG II suppression (before, 8.8 +/- 4; after, 2.9 +/- 3). With this long-acting ACEI in a dose relevant to congestive heart failure management, we suggest that 4-6 h after-dosing serum ACE (< 5 EU/L) and elevated ANG I (> 300 pg/ml) can be used to confirm compliance with treatment. These absolute values may be altered in patients treated concomitant with loop diuretics. In principle, however, this may be a useful tool in clinical trials or in clinical practice after further work has been done to assess the limits in patients across the doses and across the range of available drugs used.