Clinical evaluation of propofol as sedative for endotracheal intubation in neonates.

AIM: To determine the effects of propofol for endotracheal intubation in neonates in daily clinical practice. METHODS: We prospectively studied the pharmacodynamic effects of intravenous propofol administration in neonates who needed endotracheal intubation at the neonatal intensive care unit. RESULTS: Propofol was used for 62 intubations in neonates with postmenstrual ages ranging from 24 + 3 weeks to 44 + 5 weeks and bodyweights ranging from 520 to 4380 g. A 2 mg/kg bodyweight propofol starting dose was sufficient in 37% of patients; additional propofol was needed less often on the first postnatal day. The mean amount of propofol used was 3.3 (±1.2) mg/kg. The success rate of intubation depended on the experience of the physician and was related to the total administered amount of propofol. Hypotension occurred in 39% of patients and occurred more often at the first postnatal day. In 15% of procedures, propofol mono therapy was insufficient. CONCLUSION: This study shows that high doses of propofol are needed to reach effective sedation in neonates for intubation, with hypotension as a side effect in a considerable percentage of patients. Further research in newborn patients needs to identify optimal propofol doses and risk factors for hypotension.

Comparison of the time courses and potencies of the vasodilator effects of nifedipine and felodipine in the human forearm.

In a previous study we investigated the differential time courses of the vasodilator effect of various calcium antagonists (CA) in small isolated rat mesenteric arteries (van der Lee et al., Fundam Clin Pharmacol, 1998: 12: 607-12). We concluded that the differences observed could be due to differences in lipophilicity between the CA studied. A measure for lipophilicity is the logarithm of the membrane-partition coefficient (log P). The log P values of nifedipine and felodipine are 2.50 and 4.46, respectively. It was the aim of the present study to compare the time courses of nifedipine and felodipine effects by means of forearm venous occlusion plethysmography in healthy subjects. Healthy male non-smoking volunteers (age 31 +/- 7 years, n = 14) were studied. Informed consent was obtained prior to each experiment from all subjects. The study commenced with the vehicle of either CA (NaCl 0.9% or a PEG400-solution for nifedipine and felodipine, respectively). In four subsequent runs, increasing concentrations of CA were studied for 20 min each, at an infusion rate of 0.3 ml/min. During experiments both hands were excluded from the circulation using small wrist cuffs, inflated to at least 40 mmHg over systolic blood pressure. Mean arterial pressure remained stable in all subjects (88 +/- 3 and 83 +/- 3 mmHg for nifedipine and felodipine, respectively), thus a systemic effect of the CA was not likely. Log IC50 values were -7.46 +/- 0.17 and -8.47 +/- 0.14 for nifedipine and felodipine, respectively (p < 0.01). Averaged KD values were 4.3 +/- 0.6 and 4.6 +/- 0.6 for nifedipine and felodipine, respectively (n.s.). In this model, felodipine appears to be a more potent vasodilator than nifedipine. The 100-fold difference in lipophilicity between the two CA tested is apparently not sufficient to cause major differences in K(D) values in the plethysmography experimental set-up.

The differential time courses of the vasodilator effects of various 1,4-dihydropyridines in isolated human small arteries are correlated to their lipophilicity.

OBJECTIVES: To investigate a possible relationship between the time courses of action of various calcium antagonists and their lipophilicity, characterized as log P-values. METHODS: The functional experiments were performed in vitro in human small subcutaneous arteries (internal diameter 591 +/- 51 microm, n = 7 for each concentration), obtained from cosmetic surgery (mamma reduction and abdominoplasty). The vessels were investigated in an isometric wire myograph. The vasodilator effect of the calcium antagonists was quantified by means of log IC50-values, and the onset of the vasodilator effect for each concentration studied was expressed as time to Eeq90-values (time to reach 90% of the maximal effect). RESULTS: Log IC50-values were -8.46 +/- 0.09, -8.33 +/- 0.25 and -8.72 +/- 0.16 for nifedipine, felodipine and (S)-lercanidipine, respectively (not significant). On average, nifedipine reached time to Eeq90 in 11 +/- 1 min. For felodipine and (S)-lercanidipine the corresponding values were 60 +/- 11 min and 99 +/- 9 min, respectively. The differences between these values were statistically significant (P< 0.01). In spite of these differences in the in-vitro human vascular model, the three calcium antagonists are equipotent with regard to their vasodilator effects. Linear regression analysis of the correlation between the logarithm of the membrane partition coefficient (log P-values) of the calcium antagonists tested [2.50, 4.46 and 6.88 for nifedipine, felodipine and (S)-lercanidipine, respectively] and their respective values found for time to Eeq90 was highly significant. CONCLUSIONS: It appears that a higher log P-value is correlated with a slower onset of action.

Evidence for a sympatholytic effect of mibefradil in the pithed rat preparation.

OBJECTIVE: The T-type prevalent calcium channel blocker mibefradil (MIB) was shown to possess N-type calcium channel blocking properties. As this particular type of calcium channel is known to be crucially involved in the neuronal release of noradrenaline, we have investigated whether MIB could be a sympatholytic drug. METHODS: To evaluate the sympathoinhibitory action, the effects of 3 and 10 micromol/kg MIB on the tachycardic effect of electrical stimulation of the preganglionic cardioaccelerator nerves in the pithed rat were investigated. The effect of MIB on the dose-response curve of externally applied noradrenaline was also studied. To compare the results with a classic L-type calcium channel blocker, the experiments were repeated with 3 and 10 micromol/kg verapamil (VER). RESULTS: The maximal increase in heart rate in response to electrical nerve stimulation was 96 +/- 7 bpm (control, n = 6), 70 +/- 6 bpm (3 micromol/kg MIB, n = 8), 57 +/- 6 bpm (10 micromol/kg MIB, n = 5), 93 +/- 5 bpm (3 micromol/kg VER, n = 6) and 46 +/- 7 bpm (10 micromol/kg VER, n = 5). The tachycardic response to electrical stimulation at 1, 5 and 10 Hz was completely blocked by 5 mg/kg intravenous guanethidine. The maximal increase in heart rate in response to noradrenaline was 96 +/- 4 bpm (control, n = 6), 103 +/- 6 (3 micromol/kg MIB, n = 6), 42 +/- 9 bpm (10 micromol/kg MIB, n = 5), 73 +/- 5 bpm (3 micromol/kg VER, n = 5) and 40 +/- 7 bpm (10 micromol/kg VER, n = 6). Under control conditions and in the presence of 3 micromol/kg MIB and VER the maximal effect of noradrenaline was reached at 0.1 micromol/kg whereas in the presence of 10 micromol/kg MIB and VER it was reached at a dose of 1 micromol/kg. MIB at a dose of 3 micromol/kg was significantly more effective in reducing the chronotropic response to electrical stimulation compared with externally applied noradrenaline. For VER the opposite holds true. These differences were not observed with doses of 10 micromol/kg MIB and VER. CONCLUSION: Mibefradil, besides its direct effect on cardiac T- and L-type calcium channels, reduces the release of noradrenaline from sympathetic nerve endings, most probably by inhibition of presynaptic N-type calcium channels. In the model used this effect is only observable at relatively low concentrations, most probably because of the direct cardiodepressant action of MIB provoked by L-type channel blockade.

Inhibitory effect of mibefradil on contractions induced by sympathetic neurotransmitter release in the rat tail artery.

This study tested whether mibefradil exerts a stronger inhibitory effect than verapamil on sympathetic neurotransmitter release provoked by electrical field stimulation. Tail arteries (diameter 620+/-9 microm) were obtained from male Wistar rats. Ring segments of 2 mm length were mounted in an isometric wire myograph. After an appropriate period of equilibration and a priming procedure the vessels were either subjected to electrical field stimulation (EFS; frequency 0.25-4 Hz for 30 s) or a concentration-response curve was generated with either noradrenaline (concentration range 0.03-3 microM) or ATP (concentration 0.3 mM) which served as baseline parameters. EFS-induced contractions were stable and reproducible and were blocked by tetrodotoxin (1 microM), guanethidine (3 microM), and the combination of suramin (0.5 mM) and prazosin (3 microM). EFS-induced contractions (1 Hz) were almost completely inhibited by 10 microM mibefradil (97%) but only partly by 10 microM verapamil (73%). Log IC50 values were -5.6 for mibefradil and -6.6 for verapamil. Calcium antagonists were equipotent in inhibiting noradrenaline (maximum inhibition by mibefradil and verapamil by 70% and 75%, respectively; log IC50: -6.5 and -6.7, respectively) and ATP-mediated contractions (maximum inhibition by mibefradil and verapamil by 92% and 97%, respectively; log IC50: -6.5 and -7.0, respectively). Consequently mibefradil displays an additional effect on contractions provoked by EFS-induced sympathetic noradrenaline release which cannot be explained by L-type calcium channel blockade. Probably this effect of mibefradil is mediated by the blockade of prejunctional N-type calcium channels, thereby inhibiting sympathetic noradrenaline release. Since activation of the sympathetic nervous system in hypertension is both common and undesirable, a calcium antagonist displaying both L- and N-type calcium channel blocking activities, would have major advantages over calcium antagonists lacking N-type calcium channel blocking activities.

Comparative effects of mibefradil and other calcium antagonists on resistance arteries of different end organs.

The biphasic contractile responses of rat isolated mesenteric, renal, coronary and basilar small arteries to potassium-induced depolarization were investigated. The tonic phase is assumed to be exclusively the result of L-type calcium channel (LCC) activation, whereas in the generation of the phasic phase T-type calcium channels (TCC) may be involved. In order to evaluate whether TCC blockade has any influence on depolarization-induced contractions the effects of the LCC antagonists nifedipine, diltiazem and verapamil were compared with those of the combined L- and TCC antagonist mibefradil. Small arteries (size 393.6 +/- 4.8 microns, n = 104) were dissected from the respective organs of male Wistar rats (300-350 g) and studied in an isometric wire myograph. The effects of increasing concentrations of the calcium antagonists on repetitive potassium-induced contractions were quantified by means of cumulative concentration-response curves. A comparison was made with mesenteric vessels of SHR and WKY for nifedipine and mibefradil. Nifedipine was the most potent compound in blocking both the phasic phase (reduction 66-77%) and the tonic phase (IC50 = 1.1-5.4 nM). The effect of mibefradil on the phasic response was comparable to that of verapamil and diltiazem. With respect to the tonic response mibefradil was comparable to verapamil (IC50 = 19.6-178.9 nM). These findings indicate that the TCC blockade does not contribute to the vasodilator effect of mibefradil under the conditions investigated.

Differential time course of the vasodilator action of various calcium antagonists.

It is rather the rate of the vasodilator effect than its magnitude which determines the triggering of reflex tachycardia associated with dihydropyridine calcium antagonists (DHP-CA). We therefore compared the rate of the vasodilator effects of a series of CA (both DHP and non-DHP) in rat isolated mesenteric artery preparations (size 256 +/- 3 microns, length 2 mm) from male Wistar rats (weighing 300-350 g) in an isolated wire myograph according to Mulvany and Halpern [12]. The mean force of the KCl-induced contraction amounted to 2.3 +/- 0.1 mN/mm. Potency (given as IC50-values), differential time course of action and recovery of the contractile response of the vessels after wash-out were established. These three parameters adhere to the following sequences: (1. potency) barnidipine [corrected] > (S)-lercanidipine > barnidipine racemate [corrected]> amlodipine > nifedipine, lacidipine > (R)-lercanidipine > verapamil, mibefradil; (2. differential time course) lacidipine, amlodipine > (S)- and (R)-lercanidipine, barnidipine [corrected], barnidipine racemate [corrected] > mibefradil, verapamil, nifedipine; (3. recovery) nifedipine > verapamil, barnidipine [corrected], amlodipine > barnidipine, lacidipine > mibefradil, (R)-lercanidipine > (S)-lercanidipine. In conclusion, barnidipine [corrected] proved to be the most potent vasodilator agent; interestingly, barnidipine was 20 times less potent when applied as a racemic mixture. A slow onset of action in DHP is a very important mechanism in preventing reflex tachycardia. For non-DHP (verapamil, mibefradil) reflex tachycardia probably is prevented by a direct effect on the conductive tissue in the myocardium.

Industrial manufacture of parenteral products in The Netherlands. A survey of eight years of media fills and sterility testing.

Sterility testing and media fills are essential requirements in the pharmaceutical industry. With the results obtained the manufacturer must ensure that the aseptic filling process is under control. In an eight year (1988-1995) retrospective survey of three major Dutch pharmaceutical companies the performance of the sterility test, of media fills and their relationship have been statistically evaluated. The products included human and veterinary pharmaceuticals and biologicals, and were divided into six different groups according to their production process and primary containers. A distinction was made between the results from the period 1985-1991 and the period 1992-1995, because this made the statistical analyses of a number of types of products possible, and because some significant changes in the production process were made in 1991 at some of the production sites. The results of the evaluation of the sterility test show that the frequency of false positives has not changed significantly. The overall rate of false positives of 0.17% is a factor ten better than considered acceptable by USP XXIII. For all product groups the frequency of positive sterility tests has decreased during the period of investigation. During the period 1992-1995 there was no significant difference between the results of product sterility tests and the negative controls for any of the product groups. This indicates that given the present state-of-the-art production the sterility test offers little or no additional security. The overall contamination of the media fills done in the more recent period is a factor twenty better than the limit given in the PDA Technical Monograph No. 2. In the more recent period there is a good agreement between the observed positive rate of the sterility tests and the positive rate that had been estimated from the results of the media fills. This indicates that despite some shortcomings, media fills are an adequate simulation of the production process and can be used to give an estimate of the rejection rate for the various product groups. The overall conclusion is that the production conditions of the participating Dutch pharmaceutical companies comply with the current international guidelines for aseptic production and sterility testing.

Protein digestion and intestinal amino acids in dairy cows fed fresh Lolium perenne with different nitrogen contents.

An experiment was carried out to study digestion and intestinal AA in three ruminally and duodenally cannulated, lactating cows fed freshly cut grass (Lolium perenne) fertilized with 500 and 275 kg of N/ha per yr, respectively. High N grass was fed in June and October, and low N grass was offered in July and September. Composite samples of the grass fed in each period also were tested for in situ degradation of OM, CP, and NDF. When low N grass was fed, the digestibilities of OM and CP were lower than when high N grass was fed. On low N grass, the duodenal N flow expressed per unit of N intake was higher, although the flow of AA N on low N grass was reduced in September, mainly because of reduced microbial protein synthesis from slower OM degradation of low N grass. Duodenal N flow per unit of N intake was related negatively to the N:OM ratio of the diet. The rate of N fertilization had no effect on ruminal OM and NDF turnover rates. Turnover and passage rates in this experiment were not different from reported data on cows on winter rations with similar DMI.