Effect of guanfacine on blood pressure and renin activity in hypertensive patients

Does a hot drink provide faster absorption of paracetamol than a tablet? A pharmacoscintigraphic study in healthy male volunteers

PURPOSE

To investigate the hypothesis that paracetamol is absorbed faster from a hot drink than from a standard tablet using simultaneous scintigraphic imaging and pharmacokinetic sampling.

METHODS

Twenty-five healthy male volunteers received both paracetamol formulations in a randomised manner. The formulation administered in the first treatment arm was radiolabelled to allow scintigraphic monitoring. In both treatment arms, blood samples were taken for assessing paracetamol absorption.

RESULTS

Following the hot drink, paracetamol absorption was both significantly faster and greater over the first 60 min post-dose compared with the tablet, as evidenced by the median time to reach t0.25 μg/mL of 4.6 and 23.1 min, respectively, and AUC0-60 of 4668.00 and 1331.17 h*ng/mL, respectively. In addition, tmax was significantly shorter for the hot drink (median time = 1.50 h) compared with the tablet (1.99 h). However, Cmax was significantly greater following the tablet (9,077 ng/mL) compared with the hot drink (8,062 ng/mL). Onset of gastric emptying after the hot drink was significantly faster than after the standard tablet (7.9 versus 54.2 min), as confirmed scintigraphically.

CONCLUSIONS

Compared with a standard tablet, a hot drink provides faster absorption of paracetamol potentially due to more rapid gastric emptying.

Guanfacine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy in the treatment of hypertension

Guanfacine, a phenylacetyl-guanidine derivative, is a centrally acting alpha-adrenoceptor agonist, with a mechanism of antihypertensive action similar to that of clonidine. It reduces blood pressure in patients with essential hypertension at least as effectively as clonidine or methyldopa. Like lower doses of clonidine, guanfacine can be given once daily due to its relatively long elimination half-life. Although dry mouth and sedation occur frequently with higher doses of guanfacine, their incidence is lower than with other centrally acting antihypertensives; in addition, other troublesome side effects such as orthostatic hypotension or sexual dysfunction also occur much less with guanfacine than with other centrally acting antihypertensive agents. While a withdrawal syndrome may occur on abruptly discontinuing guanfacine administration, the symptoms are generally mild, and the incidence of withdrawal symptoms appears lower than occurs with abrupt withdrawal of clonidine. Thus, guanfacine is an effective and well tolerated alternative to other centrally acting antihypertensive drugs. Whether its final place in therapy will be as an alternative 'second-line' drug, or as initial monotherapy in patients with mild to moderate hypertension, remains to be clarified in comparative studies with diuretics, calcium antagonists, and beta-adrenoceptor blocking drugs.

Hemodynamic and endocrine responses to guanfacine in normotensive volunteers and hypertensive patients

The centrally acting alphamimetic antihypertensive drug, guanfacine, was studied in normotensive volunteers and patients with essential and renal hypertension. After acute (0.02 mg/kg, intravenously) and short-term (mean dose: 6.7 mg/day orally for 4 weeks) administration of guanfacine, systolic, diastolic and mean blood pressures (BPs), heart rate, cardiac output and right atrial pressure were measured by standard techniques. Cardiac index, stroke volume and total peripheral vascular resistance were calculated. After medium-term therapy (mean dose: 6 mg/day orally for 12 weeks), antihypertensive efficacy, as well as plasma renin activity and catecholamine levels, was determined. After intravenous administration, guanfacine lowered systolic, diastolic and mean arterial BPs after a brief and transient increase. Guanfacine exerted its antihypertensive action primarily by its effect on total peripheral resistance. Reflex tachycardia was not observed. Heart rate was reduced. Stroke volume increased and right atrial pressure decreased. These effects were maintained or enhanced during the 4 weeks of oral therapy that followed. In the 12-week study, significant reductions in systolic, diastolic and mean BPs were observed. With a constant dose of 3 mg/day for 1 week, BP decreased from 197/115/149 (systolic/diastolic/mean) to 166/97/126 mm Hg. After 4 weeks at varying doses, BP decreased to 157/91/118, and after 12 weeks, to 147/83/109. In the 12 patients treated for 4 weeks with 3 mg/day, a significant decrease from 192/111/145 to 151/87/114 mm Hg was observed, while in the 6 patients treated for 12 weeks with the 3 mg/day dose, the final readings showed a decrease of 50 mm Hg in systolic pressure, 30 mm Hg in diastolic pressure and 38.4 mm Hg in mean arterial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical experience with guanfacine in long-term treatment of hypertension

1 Of 662 hypertensive patients originally selected for long-term treatment, 580 were evaluated after one year and 169 continued for a second year of treatment with guanfacine.

2 There were 257 women (mean age 52.1 yr) and 323 men (mean age 51.7 yr) in the trial: 499 (86%) suffered from essential, 55 (9%) from renal, 22 (4%) from renovascular and 4 (1%) from other forms of hypertension; 200 (34%) were classified as having mild, 275 (47.5%) moderate and 101 (17.5%) severe hypertension. In four patients the degree of severity was not specified. Nearly 40% of all patients had signs of left ventricular hypertrophy, and in 71% a pathological ocular fundus was found; 72% had been pretreated with antihypertensive drugs, 56% suffered from a concomitant disease and 18% had signs of heart failure; 224 patients were classified as having a sedentary mode of life, 316 were moderate and 27 heavy physical workers. In 13 no classification was given.

3 Whenever possible, a wash-out period of 3 weeks with a placebo identical in appearance with the active drug was carried out at the beginning and at the end of the 12-month treatment period to establish the pretreatment blood pressure and the possible withdrawal phenomena after therapy discontinuation. At the beginning, two doses of guanfacine 1 mg were administered daily and the dose was successively increased. A diuretic was added if necessary. To non-responders, a β-adrenoceptor-blocker or a vasodilator was given.

4 In all trial groups a statistically significant decrease in blood pressure was found. The average reduction in mean arterial pressure was 16% at the end of the first year and 17% at the end of the second year. Normalization of blood pressure was achieved in 54% of the patients at the end of the first year and in 66% after the second year of treatment.

5 In patients with hypertension of a higher degree of severity, combined treatment was used more often and higher doses of guanfacine were administered; monotherapy was used predominantly in patients with mild to moderate hypertension.

6 The mean daily dose of guanfacine at the end of the first year was 3.4 mg for monotherapy and 6 mg for combined treatment. After 2 yr, these values were 3.2 mg and 5 mg, respectively.

7 With the once-daily and twice-daily dosage schedules the same antihypertensive effect as with the three times daily dose regimen was observed, with a higher normalization rate and fewer side-effects. Moreover, the normalization rate was higher with doses up to 3 mg than with doses in the range 4-25 mg. This applied to both monotherapy and combined treatment.

8 It is suggested that low doses of guanfacine are more suitable for the treatment of patients with established but uncomplicated hypertension, because of the lack of peripheral α-mimetic effects is the lower dose range. In view of the relatively long half-life of guanfacine, it is recommended that the drug be given only once daily or at the most twice daily.

9 The ECG analysis after one year of treatment revealed signs of regression in left-ventricular size. Ophthalmological examinations showed no deterioration, and there were no pathological changes in laboratory values.

10 No untoward reactions were seen when guanfacine was combined with cardiac glycosides, antidiabetic agents, anticoagulants or psychotropic drugs.