Metirosine is an antihypertensive drug. Metyrosine inhibits tyrosine hydroxylase, which catalyzes the first transformation in catecholamine biosynthesis, i.e., the conversion of tyrosine to dihydroxyphenylalanine (DOPA). Because the first step is also the rate-limiting step, blockade of tyrosine hydroxylase activity results in decreased endogenous levels of catecholamines and their synthesis. This consequently, depletes the levels of the catecholamines dopamine, adrenaline and noradrenaline in the body,usually measured as decreased urinary excretion of catecholamines and their metabolites. One main end result of the catecholamine depletion is a decrease in blood presure. Metirosine is used for the treatment of patients with pheochromocytoma, for preoperative preparation of patients for surgery, management of patients when surgery is contraindicated, and chronic treatment of patients with malignant pheochromocytoma.

Tamoxifen (brand name Nolvadex), is selective estrogen receptor modulators (SERM) with tissue-specific activities for the treatment and prevention of estrogen receptor positive breast cancer. Tamoxifen itself is a prodrug, having relatively little affinity for its target protein, the estrogen receptor (ER). It is metabolized in the liver by the cytochrome P450 isoform CYP2D6 and CYP3A4 into active metabolites such as 4-hydroxytamoxifen (4-OHT) (afimoxifene) and N-desmethyl-4-hydroxytamoxifen (endoxifen) which have 30–100 times more affinity with the ER than tamoxifen itself. These active metabolites compete with estrogen in the body for binding to the ER. In breast tissue, 4-OHT acts as an ER antagonist so that transcription of estrogen-responsive genes is inhibited. Tamoxifen has 7% and 6% of the affinity of estradiol for the ERα and ERβ, respectively, whereas 4-OHT has 178% and 338% of the affinity of estradiol for the ERα and ERβ. The prolonged binding of tamoxifen to the nuclear chromatin of these results in reduced DNA polymerase activity, impaired thymidine utilization, blockade of estradiol uptake, and decreased estrogen response. It is likely that tamoxifen interacts with other coactivators or corepressors in the tissue and binds with different estrogen receptors, ER-alpha or ER-beta, producing both estrogenic and antiestrogenic effects. Tamoxifen is currently used for the treatment of both early and advanced estrogen receptor (ER)-positive (ER+) breast cancer in pre- and post-menopausal women. Additionally, it is the most common hormone treatment for male breast cancer. Patients with variant forms of the gene CYP2D6 (also called simply 2D6) may not receive full benefit from tamoxifen because of too slow metabolism of the tamoxifen prodrug into its active metabolites. Tamoxifen is used as a research tool to trigger tissue-specific gene expression in many conditional expression constructs in genetically modified animals including a version of the Cre-Lox recombination technique. Tamoxifen has been shown to be effective in the treatment of mania in patients with bipolar disorder by blocking protein kinase C (PKC), an enzyme that regulates neuron activity in the brain. Researchers believe PKC is over-active during the mania in bipolar patients.

Vidarabine or 9-β-D-arabinofuranosyladenine (ara-A, trade name Vira-A) is a synthetic purine nucleoside analog with in vitro and in vivo inhibitory activity against herpes simplex virus types 1 (HSV-1), 2 (HSV-2), and varicella-zoster virus (VZV). The inhibitory activity of Vidarabine is highly selective due to its affinity for the enzyme thymidine kinase (TK) encoded by HSV and VZV. This viral enzyme converts Vidarabine into Vidarabine monophosphate, a nucleotide analog. The monophosphate is further converted into diphosphate by cellular guanylate kinase and into triphosphate by a number of cellular enzymes. in vitro, Vidarabine triphosphate stops replication of herpes viral DNA. When used as a substrate for viral DNA polymerase, Vidarabine triphosphate competitively inhibits dATP leading to the formation of 'faulty' DNA. This is where Vidarabine triphosphate is incorporated into the DNA strand replacing many of the adenosine bases. This results in the prevention of DNA synthesis, as phosphodiester bridges can longer to be built, destabilizing the strand.

Rifampin is an antibiotic that inhibits DNA-dependent RNA polymerase activity in susceptible cells. Specifically, it interacts with bacterial RNA polymerase but does not inhibit the mammalian enzyme. It is bactericidal and has a very broad spectrum of activity against most gram-positive and gram-negative organisms (including Pseudomonas aeruginosa) and specifically Mycobacterium tuberculosis. It is FDA approved for the treatment of tuberculosis, meningococcal carrier state. Healthy subjects who received rifampin 600 mg once daily concomitantly with saquinavir 1000 mg/ritonavir 100 mg twice daily (ritonavir-boosted saquinavir) developed severe hepatocellular toxicity. Rifampin has been reported to substantially decrease the plasma concentrations of the following antiviral drugs: atazanavir, darunavir, fosamprenavir, saquinavir, and tipranavir. These antiviral drugs must not be co-administered with rifampin. Common adverse reactions include heartburn, epigastric distress, anorexia, nausea, vomiting, jaundice, flatulence, cramps.

Hydroxyurea is an oral antimetabolite; inhibits ribonucleotide reductase and DNA synthesis. It is used for resistant chronic myeloid leukemia, locally advanced squamous cell carcinomas of the head and neck (excluding lip) in combination with concurrent chemoradiation, and to reduce the frequency of painful crises and the need for blood transfusions in patients with sickle cell anemia with recurrent moderate to severe painful crises. Hydroxyurea, a myelosuppressive agent, is the only effective drug proven to reduce the frequency of painful episodes. It raises the level of HbF and the haemoglobin level. It usually decreases the rate of painful episodes by 50%. It was first tested in sickle cell disease in 1984. It also decreases the rate of ACS episodes and blood transfusions by ~50 % in adults. It was developed as an anticancer drug and has been used to treat myeloproliferative syndromes-leukemia, melanoma, and ovarian cancer. It was approved for use by FDA in adults. Side effects includes neutropenia, bone marrow suppression, elevation of hepatic enzymes, anorexia, nausea, vomiting and infertility.

Allopurinol is a xanthine oxidase inhibitor used to decrease high blood uric acid levels. Allopurinol is specifically used to prevent gout, prevent specific types of kidney stones, and for the high uric acid levels that can occur with chemotherapy. Allopurinol acts on purine catabolism, without disrupting the biosynthesis of purines. It reduces the production of uric acid by inhibiting the biochemical reactions immediately preceding its formation. Allopurinol is a structural analog of the natural purine base, hypoxanthine. It is an inhibitor of xanthine oxidase, the enzyme responsible for the conversion of hypoxanthine to xanthine and of xanthine to uric acid, the end product of purine metabolism in man. Allopurinol is metabolized to the corresponding xanthine analog, oxypurinol (Allopurinol), which also is an inhibitor of xanthine oxidase. Allopurinol is taken by mouth or injected into a vein. Common side effects, when used by mouth, include itchiness and rash. Common side effects when used by injection include vomiting and kidney problems.

Tegafur (INN, BAN, USAN) is a chemotherapeutic fluorouracil prodrug used in the treatment of cancers. It is a component of the combination drugs tegafur/uracil and tegafur/gimeracil/oteracil. UFT is an anticancer medication composed of a fixed molar ration (1:4) of tegafur and uracil. This drug is commonly used in the treatment of head and neck cancer, gastric cancer, colorectal cancer, hepatic cancer, gallbladder cancer, bile-duct cancer, pancreatic cancer, lung cancer, breast cancer, bladder cancer, prostatic cancer, or uterine cervical cancer. In the body, tegafur is converted into 5-fluorouracil (5-FU), the active antineoplastic metabolite. The mechanism of cytotoxicity of 5-FU is thought to be derived from the fact that 5-fluoro-deoxyuridine-monophosphate (FdUMP), the active metabolite of 5-FU, competes with deoxyuridine-monophosphate (dUMP), thereby inhibiting thymidylate synthase and subsequently DNA synthesis. Another active metabolite of 5-FU, 5-fluorouridine-triphosphate (FUTP) is integrated into cellular RNA, inhibiting RNA function. Uracil, when combined with tegafur, enhances the antitumor activity of 5-FU due to higher 5-FU concentrations in the tumor tissue versus normal surrounding tissue compared with tegafur alone. Uracil inhibits degradation of the released 5-FU. The combination of these two drugs enhances the antitumor activity of Tegafur.

Dipyridamole, a non-nitrate coronary vasodilator that also inhibits platelet aggregation, is combined with other anticoagulant drugs, such as warfarin, to prevent thrombosis in patients with valvular or vascular disorders. Dipyridamole is also used in myocardial perfusion imaging, as an antiplatelet agent, and in combination with aspirin for stroke prophylaxis. Dipyridamole likely inhibits both adenosine deaminase and phosphodiesterase, preventing the degradation of cAMP, an inhibitor of platelet function. This elevation in cAMP blocks the release of arachidonic acid from membrane phospholipids and reduces thromboxane A2 activity. Dipyridamole also directly stimulates the release of prostacyclin, which induces adenylate cyclase activity, thereby raising the intraplatelet concentration of cAMP and further inhibiting platelet aggregation. Used for as an adjunct to coumarin anticoagulants in the prevention of postoperative thromboembolic complications of cardiac valve replacement and also used in prevention of angina.

Phenelzine is an irreversible non-selective inhibitor of monoamine oxidase. Although the exact mechanism of action has not been determined, it appears that the irreversible, nonselective inhibition of MAO by phenelzine relieves depressive symptoms by causing an increase in the levels of serotonin, norepinephrine, and dopamine in the neuron. Phenelzine is used for the treatment of major depressive disorder. Has also been used with some success in the management of bulimia nervosa.

Tranylcypromine is a non-hydrazine monoamine oxidase inhibitor with a rapid onset of activity. Tranylcypromine has being marketed under original trade name Parnate, indicated for the treatment of major depressive episode without melancholia. Tranylcypromine irreversibly and nonselectively inhibits monoamine oxidase (MAO). Within neurons, MAO appears to regulate the levels of monoamines released upon synaptic firing. Since depression is associated with low levels of monoamines, the inhibition of MAO serves to ease depressive symptoms, as this results in an increase in the concentrations of these amines within the CNS.