Dose-dependent response to phenylpropanolamine: inhibition of orthostasis

The impact of oral phenylpropanolamine on blood pressure: a meta-analysis and review of the literature

Oral phenylpropanolamine is commonly used to treat congestion and obesity. Clinicians often wonder what effect it has on blood pressure and whether they are safe in hypertensive patients. The purpose of our systematic review was to assess whether these drugs cause clinically meaningful elevations in pulse or blood pressure. English-language, randomized, placebo-controlled trials of oral phenylpropanolamine in adults with extractable data on pulse or blood pressure were studied. MEDLINE (1966-2003), Embase, the Cochrane library and reviewed article references were used as sources. Systolic (SBP) and diastolic blood pressure (DBP) and heart rate data were extracted. Additional extracted data included demographics, year, study design, study duration, drug dose and frequency, duration of washout and country. Study quality was assessed using the methods of Jadad and data were synthesized using a random effects model using weighted mean differences. In all, 33 trials reporting 48 treatment arms with 2165 patients were included. Phenylpropanolamine increased SBP 5.5 mmHg (95% CI: 3.1-8.0) and DBP 4.1 mmHg (95% CI: 2.2-6.0) with no effect on pulse. Patients with controlled hypertension were not at greater risk of blood pressure elevation. Immediate release preparations had greater effects on blood pressure than sustained release ones. Higher doses and shorter duration use also caused greater increases. Eighteen studies contained at least one treated subjects having blood pressure elevations > or =140/90 mmHg, an increase in SBP > or =15 mmHg or an increase in DBP > or =10 mmHg. In conclusion, phenylpropanolamine caused a small, but significant increase in systolic blood pressure. The effect was more pronounced with shorter-term administration, higher doses of medication and immediate release formulations.

Effects of dl-norephedrine and its enantiomers on norepinephrine uptake and release in isolated rat caudal artery

Racemic norephedrine (dl-NOR), is a phenylethylamine derivative that is pharmacologically classified as a mixed-acting sympathomimetic amine. It is the active ingredient in many over-the-counter nasal decongestants and diet aid products. This research project was performed to examine the effects of dl-NOR and constituent enantiomers on the uptake and release of tritiated norepinephrine (3H-NE) in vascular tissue. All three NOR species significantly inhibited the uptake of 3H-NE into the isolated caudal artery of male Sprague-Dawley rats (p < 0.01). There was no significant difference in potency between either d- or l-NOR for this effect. There was, however, no effect of any NOR species on 3H-NE release, not even at concentrations which effectively inhibited uptake. These results indicate that inhibition of NE reuptake may be a component of the mechanism of action of NOR, but that a displacement of NE from neuronal storage sites is not. However, because the vasoactive effects of NOR have been shown to be mediated almost exclusively through the l-enantiomer, the lack of stereoselectivity in the current study indicates that the blockade of NE uptake by NOR is only a minor component of its vasoactive properties.