Stability of nicardipine hydrochloride in intravenous solutions.

The stability of nicardipine hydrochloride in large-volume i.v. solutions was studied. Admixtures of nicardipine hydrochloride 0.05 and 0.5 mg/mL were prepared in 5% dextrose and 0.45% sodium chloride injection, 5% dextrose and 0.9% sodium chloride injection, 0.45% sodium chloride injection, 0.9% sodium chloride injection, 5% dextrose and lactated Ringer's injection, 5% dextrose injection, lactated Ringer's injection, 5% sodium bicarbonate injection, and 5% dextrose injection with potassium chloride 40 meq/L. Two glass and two polyvinyl chloride (PVC) containers of each solution were prepared and stored at ambient room temperature under normal fluorescent light. Samples were removed and tested for nicardipine concentration by stability-indicating high-performance liquid chromatography at 0, 24, 48, and 72 hours and seven days. Testing included visual checking and optical density measurements. The admixtures remained clear and slightly yellow except for nicardipine hydrochloride in sodium bicarbonate injection, which showed immediate precipitation, and nicardipine hydrochloride in lactated Ringer's injection, which increased in optical density at 400 nm over time. There were no significant changes in nicardipine concentrations in nicardipine concentrations in glass containers. Admixtures stored in PVC containers showed a slow, constant decline in nicardipine concentrations, sometimes to less than 85% of the initial drug concentration within 24 hours, except for nicardipine hydrochloride in lactated Ringer's injection or 5% dextrose and lactated Ringer's injection, which showed an immediate and continuing rapid loss. Nicardipine hydrochloride 0.5 and 0.05 mg/mL in eight i.v. solutions was stable in glass containers for up to seven days. Drug concentrations slowly decreased in PVC containers. The drug was not stable in 5% sodium bicarbonate injection or in PVC bags containing lactated Ringer's injection or 5% dextrose and lactated Ringer's injection.

NMR structure of a bacteriophage T4 RNA hairpin involved in translational repression.

A high-resolution structure of a 16-nucleotide bacteriophage T4 RNA hairpin, 5'-GCCU[AAUAACUC]GGGC (loop bases in square brackets), has been determined in solution by proton, phosphorus, and carbon (natural abundance) NMR spectroscopy. This RNA hairpin is known to play a crucial role in the translational repression of bacteriophage T4 DNA polymerase. Ultraviolet absorbance melting curves indicate that the structure formed is unimolecular. The NMR spectra indicate that a single conformation consistent with a hairpin structure is formed. Strong imino-imino NOEs confirm the formation of the G.U base pair at the stem-loop junction. There is no evidence that A5 is protonated (at pH 6.0) and involved in an A+.C pair. However, the NMR data indicate that the stem is extended beyond the G.U pair and that A-form stacking continues for three nucleotides on the 5' side and one nucleotide on the 3' side. Structure calculations using restraints obtained from NMR data give a precisely defined structure with an average root mean square deviation (RMSD) of approximately 1.2 A for the entire molecule. The assignment of all the protons and most of the 31P resonances in the loop yielded a large number of distance and torsion angle restraints for these nucleotides. These helped obtain a well-defined loop with an average RMSD of 1.1 A for the loop nucleotides of 11 converged structures.

A quadruple mutant T4 RNA hairpin with the same structure as the wild-type translational repressor.

The solution structure of a 16-nucleotide RNA hairpin, 5'-GCCUAG[CAAC]CUGGGC (loop bases in square brackets), has been determined by proton, phosphorus, and carbon (natural abundance) nuclear magnetic resonance (NMR) spectroscopy. This RNA tetraloop hairpin varies in four loop nucleotides from the wild-type T4 RNA hairpin (with eight loop nucleotides) involved in the translational repression of bacteriophage T4 DNA polymerase. Despite the differences in their sequence and proposed secondary structures, these two hairpins bind T4 DNA polymerase with equal affinity. The NMR spectra of the mutant hairpin indicate that its stem is extended in comparison to that of the wild-type hairpin by the formation of two additional Watson-Crick base pairs. The NMR data provide a precisely defined structure for the mutant hairpin with an average root mean square deviation of approximately 0.7 A for all 16 residues in the molecule. The structure of the mutant loop is very similar to that determined previously for the wild-type hairpin. The three loop bases that are conserved between the mutant and wild-type hairpins point out in solution with the groups capable of hydrogen bond formation exposed to the solution. This is exactly what was seen for the wild-type hairpin. Also, unusual, long-range NOEs, loop hydrogen bonds, and even the position at which the loop bends are common features between the two loops. This explains how two different hairpins, by adopting similar three-dimensional structures, have the same affinity for the DNA polymerase.