The nucleoside analog 2',3'-dideoxycytidine (ddCyd), also known as Zalcitabine is a nucleoside analog reverse transcriptase inhibitor (NRTI) sold under the trade name Hivid. HIVID is indicated in combination with antiretroviral agents for the treatment of HIV infection. It is used as part of a combination regimen with antiretroviral agents. But it was discontinued by Roche Pharmaceuticals on December 31, 2006 due to the availability of newer HIV medicines. Within cells, zalcitabine is converted to the active metabolite, dideoxycytidine 5'-triphosphate (ddCTP), by the sequential action of cellular enzymes. Dideoxycytidine 5'-triphosphate inhibits the activity of the HIV-reverse transcriptase both by competing for utilization of the natural substrate, deoxycytidine 5'-triphosphate (dCTP), and by its incorporation into viral DNA. The lack of a 3'- OH group in the incorporated nucleoside analogue prevents the formation of the 5' to 3' phosphodiester linkage essential for DNA chain elongation and, therefore, the viral DNA growth is terminated. The active metabolite, ddCTP, is also an inhibitor of cellular DNA polymerasebeta and mitochondrial DNA polymerase-gamma and has been reported to be incorporated into the DNA of cells in culture.

Tocainide is a primary amine analog of lidocaine with antiarrhythmic properties useful in the treatment of ventricular arrhythmias. Tocainide, like lidocaine, produces dose-dependent decreases in sodium and potassium conductance, thereby decreasing the excitability of myocardial cells. In experimental animal models, the dose-related depression of sodium current is more pronounced in ischemic tissue than in normal tissue. Tocainide is a Class I antiarrhythmic compound with electrophysiologic properties in man similar to those of lidocaine, but dissimilar from quinidine, procainamide, and disopyramide. The recommended initial dosage is 400 mg every 8 hours. The usual adult dosage is between 1200 and 1800 mg/day in a three-dose daily divided regimen. Doses beyond 2400 mg per day have been administered infrequently. Patients who tolerate the t.i.d. the regimen may be tried on a twice-daily regimen with careful monitoring. Tocainide commonly produces minor, transient, nervous system and gastrointestinal adverse reactions, but is otherwise generally well tolerated.

Aminoglutethimide, marketing as Cytadren has been used in the treatment of advanced breast and prostate cancer. It was formerly used for its weak anticonvulsant properties. Cytadren is indicated for the suppression of adrenal function in selected patients with Cushing’s syndrome. Morning levels of plasma cortisol in patients with adrenal carcinoma and ectopic ACTH producing tumors were reduced on the average to about one half of the pretreatment levels, and in patients with adrenal hyperplasia to about two thirds of the pretreatment levels, during 1-3 months of therapy with Cytadren. Data available from the few patients with adrenal adenoma suggest similar reductions in plasma cortisol levels. Measurements of plasma cortisol showed reductions to at least 50% of baseline or to normal levels in one third or more of the patients studied, depending on diagnostic groups and time of measurement. Because Cytadren does not affect the underlying disease process, it is used primarily as an interim measure until more definitive therapy such as surgery can be undertaken or in cases where such therapy is not appropriate. Only small numbers of patients have been treated for longer than 3 months. A decreased effect or “escape phenomenon” seems to occur more frequently in patients with pituitary dependent Cushing’s syndrome, probably because of increasing ACTH levels in response to decreasing glucocorticoid levels. Cytadren blocks several other steps in steroid synthesis, including the C-11, C-18, and C-21 hydroxylations and the hydroxylations required for the aromatization of androgens to estrogens, mediated through the binding of Cytadren to cytochrome P-450 complexes. A decrease in adrenal secretion of cortisol is followed by an increased secretion of pituitary adrenocorticotropic hormone (ACTH), which will overcome the blockade of adrenocortical steroid synthesis by Cytadren. The compensatory increase in ACTH secretion can be suppressed by the simultaneous administration of hydrocortisone. Since Cytadren increases the rate of metabolism of dexamethasone but not that of hydrocortisone, the latter is preferred as the adrenal glucocorticoid replacement. Although Cytadren inhibits the synthesis of thyroxine by the thyroid gland, the compensatory increase in thyroid-stimulating hormone (TSH) is frequently of sufficient magnitude to overcome the inhibition of thyroid synthesis due to Cytadren. In spite of an increase in TSH, Cytadren has not been associated with increased prolactin secretion. At low doses, aminogluthethimide is only an effective inhibitor of aromatase (Cytochrome P450 11A1), but at higher doses, it effectively blocks Cytochrome P450 11A1 (P450scc) as well. Citadel was marketed previously as an anticonvulsant but was withdrawn from marketing for that indication in 1966 because of the effects on the adrenal gland.

Viomycin is a basic peptide antibiotic, which is among the most effective agents against multidrug-resistant tuberculosis. The tuberactinomycins, such as Viomycin, target bacterial ribosomes, binding RNA and disrupting bacterial protein biosynthesis. Specifically, viomycin binds to a site on the ribosome which lies at the interface between helix 44 of the small ribosomal subunit and helix 69 of the large ribosomal subunit. The structures of this complexes suggest that the viomycin inhibits translocation by stabilizing the tRNA in the A site in the pretranslocation state.

Procaine is an anesthetic agent indicated for production of local or regional anesthesia, particularly for oral surgery. Procaine (like cocaine) has the advantage of constricting blood vessels which reduces bleeding, unlike other local anesthetics like lidocaine. Procaine is an ester anesthetic. It is metabolized in the plasma by the enzyme pseudocholinesterase through hydrolysis into para-aminobenzoic acid (PABA), which is then excreted by the kidneys into the urine. Procaine acts mainly by inhibiting sodium influx through voltage gated sodium channels in the neuronal cell membrane of peripheral nerves. When the influx of sodium is interrupted, an action potential cannot arise and signal conduction is thus inhibited. The receptor site is thought to be located at the cytoplasmic (inner) portion of the sodium channel. Procaine has also been shown to bind or antagonize the function of N-methyl-D-aspartate (NMDA) receptors as well as nicotinic acetylcholine receptors and the serotonin receptor-ion channel complex.

Betaxolol is a competitive, beta(1)-selective (cardioselective) adrenergic antagonist. Betaxolol is used to treat hypertension, arrhythmias, coronary heart disease, glaucoma, and is also used to reduce non-fatal cardiac events in patients with heart failure. (R)-Betaxolol (Dextrobetaxolol) is the R-isomer of Betaxolol (B328000), a cardioselective β1-adrenergic blocker. It is also an antihypertensive and antiglaucoma agent. Dextrobetaxolol had a much weaker affinity at both b1 and b2 receptors than levobetaxolol. Levobetaxolol (Kb=6 nM at b1 and Kb=39 nM at b2 receptors) more potently inhibited functional activities in cells expressing human recombinant b1 and b2 receptors than dextrobetaxolol (Kb=350 and 278 nM, respectively). Likewise, levobetaxolol was a more potent antagonist in isolated tissues than dextrobetaxolol. In functional assays in cultured human NPE cells levobetaxolol (Ki =16.4 nM) was a potent antagonist of isoproterenol-induced cAMP production with dextrobetaxolol (Ki =2.9 uM) being considerably weaker than the latter antagonist. In ocular hypertensive cynomolgus monkeys, levobetaxolol was more effective at reducing IOP than dextrobetaxolol. The results of the study of the pharmacokinetic behavior of the R and S enantiomers of betaxolol following iv and oral administration of the racemate to healthy male subjects failed to reveal any important difference between the pharmacokinetics of the R and S enantiomer of betaxolol. Thus, the pharmacokinetic behavior of racemic betaxolol accurately reflects the behavior of betaxolol enantiomers in this subject group.

Alaproclate is a selective 5-HT uptake inhibitor. Alaproclate enantiomers block potassium and NMDA receptor currents in a stereoselective manner. Alaproclate was practically devoid of action on a number of receptors as examined in binding studies in vitro: 5-HT, histamine-H1, alpha 1, -alpha 2-adrenergic and dopamine D2 receptors. Alaproclate was investigated in trials for the treatment of depression and dementia.

Cathine, known as D-norpseudoephedrine, is a psychoactive drug of amphetamine class, found naturally in Catha edulis (khat). It is a norepinephrine and dopamine releasing agent, and has thermogenic and anorectic effect. In the United States, cathine is classified as a Schedule IV controlled substance. Cathine hydrochloride is used as an appetite suppressant during the first few weeks of dieting to help establish new eating habits.

Apramycin is a broad-spectrum aminocyclitol antibiotic produced by a strain of Streptomyces tenebrarius. It has a bactericidal action against many gram-negative bacteria. Apramycin is a structurally unique antibiotic that contains a bicyclic sugar moiety and a monosubstituted deoxystreptamine. It is not approved for use in humans. Apramycin is registered for use in more than twenty countries in cattle, pigs and chickens. The drug exerts its antibacterial effect by inhibiting protein synthesis at the level of peptidyl translocation. It is mostly used for treating gastrointestinal infections. Apramycin is available in soluble powder and feed premix formulations.

Esatenolol is the (S) enantiomer of atenolol, a beta1-adrenergic receptor antagonist. Only (S)-atenolol, but not (R)-atenolol, contributes to the beta-blocking effect of currently used racemic atenolol since the same effect can be elicited with the (S)-enantiomer alone. Pure (S)-atenolol has been launched in India for the treatment of hypertension and angina pectoris.