Oseltamivir phosphate is an ethyl ester prodrug requiring ester hydrolysis for conversion to the active form, oseltamivir carboxylate. Oseltamivir carboxylate is an inhibitor of influenza virus neuraminidase affecting release of viral particles. Oseltamivir is a well tolerated orally active neuraminidase inhibitor which significantly reduces the duration of symptomatic illness and hastens the return to normal levels of activity when initiated promptly in patients with naturally acquired influenza.

Rizatriptan (trade name Maxalt) is a 5-HT1 receptor agonist of the triptan class of drugs developed by Merck & Co. for the treatment of migraine headaches. Rizatriptan (trade name Maxalt) is a 5-HT1 receptor agonist of the triptan class of drugs developed by Merck & Co. for the treatment of migraine headaches. Rizatriptan acts as an agonist at serotonin 5-HT1B and 5-HT1D receptors. Rizatriptan binds with high affinity to human cloned 5-HT1B/1D receptors. Rizatriptan benzoate presumably exerts its therapeutic effects in the treatment of a migraine headache by binding to 5-HT1B/1D receptors located on intracranial blood vessels and sensory nerves of the trigeminal system. Rizatriptan is completely absorbed following oral administration. The mean oral absolute bioavailability of the rizatriptan benzoate tablet is about 45%, and mean peak plasma concentrations are reached in approximately 1-1.5 hours. The presence of a migraine headache did not appear to affect the absorption or pharmacokinetics of rizatriptan. Food has no significant effect on the bioavailability of rizatriptan but delays the time to reach peak concentration by an hour. The primary route of rizatriptan metabolism is via oxidative deamination by monoamine oxidase-A (MAO-A) to the indole acetic acid metabolite, which is not active at the 5-HT1B/1D receptor. N-mono-desmethyl-rizatriptan, a metabolite with activity similar to that of parent compound at the 5-HT1B/1D receptor, is formed to a minor degree. Plasma concentrations of N-mono-desmethyl-rizatriptan are approximately 14% of those of parent compound, and it is eliminated at a similar rate. Other minor metabolites, the N-oxide, the 6-hydroxy compound, and the sulfate conjugate of the 6-hydroxy metabolite are not active at the 5-HT1B/1D receptor.

Candesartan is classified as an angiotensin II receptor type 1 antagonist. Candesartan is an orally active lipophilic drug and possesses rapid oral absorption. It causes a reduction in blood pressure and is used in the treatment of hypertension. It is also used in the treatment of congestive heart failure and given as prophylaxis to reduce the severity and duration of migraine. Candesartan cilexetil, a prodrug of Candesartan, is available in the market under the trade names Atacand, Amias. Candesartan cilexetil is rapidly converted to candesartan, its active metabolite, during absorption from the gastrointestinal tract. Candesartan confers blood pressure lowering effects by antagonizing the hypertensive effects of angiotensin II via the RAAS (renin–angiotensin–aldosterone system). RAAS is a homeostatic mechanism for regulating hemodynamics, water, and electrolyte balance. During sympathetic stimulation or when renal blood pressure or blood flow is reduced, renin is released from granular cells of the juxtaglomerular apparatus in the kidneys. Renin cleaves circulating angiotensinogen to angiotensin I, which is cleaved by angiotensin converting enzyme (ACE) to angiotensin II. Angiotensin II increases blood pressure by increasing total peripheral resistance, increasing sodium and water reabsorption in the kidneys via aldosterone secretion, and altering the cardiovascular structure. Angiotensin II binds to two receptors: type-1 angiotensin II receptor (AT1) and type-2 angiotensin II receptor (AT2). Candesartan selectively blocks the binding of angiotensin II to AT1 in many tissues including vascular smooth muscle and the adrenal glands. This inhibits the AT1-mediated vasoconstrictive and aldosterone-secreting effects of angiotensin II and results in an overall decrease in blood pressure. Candesartan is greater than 10,000 times more selective for AT1 than AT2.

Rizatriptan (trade name Maxalt) is a 5-HT1 receptor agonist of the triptan class of drugs developed by Merck & Co. for the treatment of migraine headaches. Rizatriptan (trade name Maxalt) is a 5-HT1 receptor agonist of the triptan class of drugs developed by Merck & Co. for the treatment of migraine headaches. Rizatriptan acts as an agonist at serotonin 5-HT1B and 5-HT1D receptors. Rizatriptan binds with high affinity to human cloned 5-HT1B/1D receptors. Rizatriptan benzoate presumably exerts its therapeutic effects in the treatment of a migraine headache by binding to 5-HT1B/1D receptors located on intracranial blood vessels and sensory nerves of the trigeminal system. Rizatriptan is completely absorbed following oral administration. The mean oral absolute bioavailability of the rizatriptan benzoate tablet is about 45%, and mean peak plasma concentrations are reached in approximately 1-1.5 hours. The presence of a migraine headache did not appear to affect the absorption or pharmacokinetics of rizatriptan. Food has no significant effect on the bioavailability of rizatriptan but delays the time to reach peak concentration by an hour. The primary route of rizatriptan metabolism is via oxidative deamination by monoamine oxidase-A (MAO-A) to the indole acetic acid metabolite, which is not active at the 5-HT1B/1D receptor. N-mono-desmethyl-rizatriptan, a metabolite with activity similar to that of parent compound at the 5-HT1B/1D receptor, is formed to a minor degree. Plasma concentrations of N-mono-desmethyl-rizatriptan are approximately 14% of those of parent compound, and it is eliminated at a similar rate. Other minor metabolites, the N-oxide, the 6-hydroxy compound, and the sulfate conjugate of the 6-hydroxy metabolite are not active at the 5-HT1B/1D receptor.

Tolterodine is competitive muscarinic receptors M3 and M2 antagonist. It was sold under trade names detrol for the treatment of overactive bladder with symptoms of urge urinary incontinence. Both urinary bladder contraction and salivation are mediated via cholinergic muscarinic receptors. After oral administration, tolterodine is metabolized in the liver, resulting in the formation of the 5-hydroxymethyl derivative, a major pharmacologically active metabolite. The 5-hydroxymethyl metabolite, which exhibits an antimuscarinic activity similar to that of tolterodine, contributes significantly to the therapeutic effect. Both tolterodine and the 5-hydroxymethyl metabolite exhibit a high specificity for muscarinic receptors, since both show negligible activity and affinity for other neurotransmitter receptors and other potential cellular targets, such as calcium channels. Tolterodine has a pronounced effect on bladder function. The main effects of tolterodine at 1 and 5 hours were an increase in residual urine, reflecting an incomplete emptying of the bladder, and a decrease in detrusor pressure. These findings are consistent with an antimuscarinic action on the lower urinary tract.

Tazarotene is a prodrug and a member of the acetylenic class of retinoids. Following topical application, tazarotene undergoes esterase hydrolysis to form its active metabolite, tazarotenic acid. When treating acne tazarotene may be taken in conjunction with an oral antibiotic. Tazarotene has been shown in peer-reviewed double blinded studies to reduce: mottling and hyperpigmentation, sallowness, fine wrinkling and coarse wrinkling in sun damaged skin. Histological studies have shown that long term (greater than 1 year) use of Tazarotene is associated with a significant reduction in atypical melanocytes and keratocytes - cells considered to be precursors of skin cancer. Some studies have shown long term use of Tazarotene to be associated with increased collagen production and better organization of skin collagen bundles. Although the exact mechanism of tazarotene action is not known, studies have shown that the active form of the drug (tazarotenic acid) binds to all three members of the retinoic acid receptor (RAR) family: RARa, RARb, and RARg, but shows relative selectivity for RARb, and RARg and may modify gene expression. It also has affinity for RXR receptors. Tazarotene is used to treat psoriasis, acne and sun damaged skin (photodamage). Tazarotene is marketed as Tazorac, Avage, Zorac, and Fabior.

Tamsulosin, a sulfamoylphenethylamine-derivative alpha-adrenoceptor blocker with enhanced specificity for the alpha-adrenoceptors of the prostate, is commonly used to treat benign prostatic hyperplasia (BPH). The drug is commercially available in a racemic mixture of 2 isomers, and is pharmacologically related to doxazocin, prazosin, and terazosin. However, unlike these drugs, tamsulosin has a higher affinity for the alpha-1A- adrenergic receptors, which are located in vascular smooth muscle. Studies show that tamsulosin has about 12 times greater affinity for alpha-1 adrenergic receptors in the prostate than those in the aorta, which may result in a reduced incidence of adverse cardiovascular effects. Tamsulosin is sold under the trade name Flomax.

Ropinirole (INN; trade names Requip, Repreve, Ronirol, Adartrel) is a dopamine agonist of the non-ergoline class of medications, used in the treatment of Parkinson's disease and restless legs syndrome. Although the precise mechanism of action of ropinirole as a treatment for Parkinson's disease is unknown, it is believed to be related to its ability to stimulate dopamine receptors in the striatum. This conclusion is supported by electrophysiologic studies in animals that have demonstrated that ropinirole influences striatal neuronal firing rates via activation of dopamine receptors in the striatum and the substantia nigra, the site of neurons that send projections to the striatum. Ropinirole is a nonergot dopamine agonist with high relative in vitro specificity and full intrinsic activity at the D2 subfamily of dopamine receptors, binding with higher affinity to D3 than to D2 or D4 receptor subtypes. The relevance of D3 receptor binding in Parkinson's disease is unknown. The mechanism of ropinirole-induced postural hypotension is presumed to be due to a D2 -mediated blunting of the noradrenergic response to standing and subsequent decrease in peripheral vascular resistance. Ropinirole can cause nausea, dizziness, hallucinations, orthostatic hypotension, and sudden sleep attacks during the daytime. Unusual side effects specific to D3 agonists such as ropinirole and pramipexole can include hypersexuality, punding, and compulsive gambling, even in patients without a history of these behaviors.

Topotecan, a semi-synthetic derivative of camptothecin (a plant alkaloid obtained from the Camptotheca acuminata tree), is an anti-tumor drug with topoisomerase I-inhibitory activity similar to irinotecan. DNA topoisomerases are enzymes in the cell nucleus that regulate DNA topology (3-dimensional conformation) and facilitate nuclear processes such as DNA replication, recombination, and repair. During these processes, DNA topoisomerase I creates reversible single-stranded breaks in double-stranded DNA, allowing intact single DNA strands to pass through the break and relieve the topologic constraints inherent in supercoiled DNA. The 3'-DNA terminus of the broken DNA strand binds covalently with the topoisomerase enzyme to form a catalytic intermediate called a cleavable complex. After DNA is sufficiently relaxed and the strand passage reaction is complete, DNA topoisomerase reattaches the broken DNA strands to form the unaltered topoisomers that allow transcription to proceed. Topotecan interferes with the growth of cancer cells, which are eventually destroyed. Since the growth of normal cells can be affected by the medicine, other effects may also occur. Unlike irinotecan, topotecan is found predominantly in the inactive carboxylate form at neutral pH and it is not a prodrug. Topotecan has the same mechanism of action as irinotecan and is believed to exert its cytotoxic effects during the S-phase of DNA synthesis. Topoisomerase I relieves torsional strain in DNA by inducing reversible single strand breaks. Topotecan binds to the topoisomerase I-DNA complex and prevents religation of these single strand breaks. This ternary complex interferes with the moving replication fork, which leads to the induction of replication arrest and lethal double-stranded breaks in DNA. As mammalian cells cannot efficiently repair these double strand breaks, the formation of this ternary complex eventually leads to apoptosis (programmed cell death). Topotecan mimics a DNA base pair and binds at the site of DNA cleavage by intercalating between the upstream (−1) and downstream (+1) base pairs. Intercalation displaces the downstream DNA, thus preventing religation of the cleaved strand. By specifically binding to the enzyme–substrate complex, Topotecan acts as an uncompetitive inhibitor. Topotecan is used for the treatment of advanced ovarian cancer in patients with disease that has recurred or progressed following therapy with platinum-based regimens. Also used as a second-line therapy for treatment-sensitive small cell lung cancer, as well as in combination with cisplatin for the treatment of stage IV-B, recurrent, or persistent cervical cancer not amenable to curative treatment with surgery and/or radiation therapy. Topotecan is sold under the trade name Hycamtin.

Irinotecan is an antineoplastic enzyme inhibitor primarily used in the treatment of colorectal cancer. Irinotecan is sold under the brand name Camptosar among others. CAMPTOSAR is a topoisomerase inhibitor indicated for: • First-line therapy in combination with 5-fluorouracil and leucovorin for patients with metastatic carcinoma of the colon or rectum. • Patients with metastatic carcinoma of the colon or rectum whose disease has recurred or progressed following initial fluorouracil-based therapy. Irinotecan is a derivative of camptothecin. Camptothecins interact specifically with the enzyme topoisomerase I, which relieves torsional strain in DNA by inducing reversible single-strand breaks. Irinotecan and its active metabolite SN-38 bind to the topoisomerase I-DNA complex and prevent religation of these single-strand breaks. Current research suggests that the cytotoxicity of irinotecan is due to double-strand DNA damage produced during DNA synthesis when replication enzymes interact with the ternary complex formed by topoisomerase I, DNA, and either irinotecan or SN-38. Mammalian cells cannot efficiently repair these double-strand breaks.